GEO-HEAT CENTER QUARTERLY BULLETINA Quarterly Progress and Development Reporton the Direct Utilization of Geothermal Resources
ISSN 0276-1084
CONTENTS
Geothermal Heat Pumps -An Overview
John W. Lund
Page
1
PUBLISHED BY
GEO-HEAT CENTEROregon Institute of Technology
3201 Campus DriveKlamath Falls, OR 97601Phone: 541-885-1750Email: geoheat@oit.edu
All articles for the Bulletin are solicited. If you wish tocontribute a paper, please contact the editor at the aboveaddress.
Feasibility Study on the
Utilization of Geothermal HeatPump (GHP) Systems in Japan
3
Shinji Takasugi, Tsukashi Akazawa, Takashi Okumura and Mineyuki Hanano
Hot Water Supply Test Using
Geothermal Heat Pump systems atPetroPavlovsk-Kamchatsky, theCapital of Kamchatka, Russia
Ken Ikeuchi, Shinji Takasugi and Shin-ichi Miyazaki
9
EDITOR
John W. Lund
Typesetting/Layout - Donna GibsonGraphics - Tonya Toni Boyd
WEBSITE http://www.oit.edu/~geoheat13
FUNDING
The Bulletin is provided compliments of the Geo-HeatCenter. This material was prepared with the support ofthe U.S. Department of Energy (DOE Grant No. FG01-99-EE35098). However, any opinions, findings,
conclusions, or recommendations expressed herein arethose of the author(s) and do not necessarily reflect theview of USDOE.
Current Status and FutureDirections of Geothermal HeatPumps in Turkey
A. Hepbasli, M. Eltez and H. Duran
Design Aspects of CommercialOpen-Loop Heat Pump Systems
Kevin Rafferty
16
Specificationof Water Wells
Kevin Rafferty
2531
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A Guide to On-Line GeologicalInformation and Publications forUse in GSHP Site Characterization
Kevin Rafferty
Dual-Set Point Control of Open-Loop Heat Pump Systems
Kevin Rafferty
38
Cover: GHP/GSHP in the heating mode. Modified from adrawing by IGSHPA, Oklahoma State University.
GEOTHERMAL HEAT PUMPS - AN OVERVIEW
John W. LundGeo-Heat Center
Geothermal heat pumps (ground-source heat pumps)
(GHP or GSHP) are used in two basic modes: ground coupled(vertical and horizontal)--closed loop, or groundwater types -open loop (Figures 1 and 2). These have been describedextensively in a previous Geo-Heat Center Bulletin (Vol 18,No. 2 - April 1997) and in more detail in “An InformationSurvival Kit for the Prospective Geothermal Heat PumpOwner” by Kevin Rafferty--both of which are available on ourwebsite: The installation and use of geothermal heat pumps worldwide have had a large increase over the past ten yearswith almost a 10% annual increase during this time. Most ofthis growth has occurred in the United States and Europe,though interest is developing in other countries such as Japanand Turkey. The present worldwide installed capacity is 6,875 MWt and the annual energy use is 23,287 TJ/yr (22,088billion Btu/yr or 6,453 GWh/yr) at the beginning of 2000 in 27countries (Table 1). The actual number of installed units isaround 500,000, but the data are incomplete. The equivalentnumber of 12 kW units installed is slightly over 570,000. The12 kW (3.4 tons) equivalent is used as typical of homes in theUnited States and some western European countries. The sizeof individual units, however, range from 5.5 kW (Poland andSweden) for residential use to large units of over 150 kW(Germany and the United States) for commercial andinstitutional installations. In the United States, most units are sized for the peak cooling load and are oversized for heating (except in thenorthern states) and, thus, are estimated to average only 1,000full-load heating hours per year (capacity factor of 0.11). In Table 1.Worldwide Geothermal Heat Pump Installations in 2000 Country AustraliaAustriaBulgariaCanada Czech RepublicDenmarkFinlandFranceGermanyGreeceHungaryIcelandItalyJapanLithuaniaNetherlandsNorwayRussiaPolandSerbia Slovak RepublicSloveniaSwedenSwitzerlandTurkeyUKUSATOTALMWt2422813.33608.0380.5483440.43.841.23.92110.861.226.261.42.63775000.50.64,8006,875.4TJ/yr57.61,09416289138.220.84842551,1493.120.2206.464598.857.431.911.5108.34012.146.84,1281,9804.02.712,00023,286.9GWh/yr16.0303.945.0247.510.65.8134.570.8319.20.95.65.61.817.8166.315.98.93.230.111.13.413.01,146.8550.01.10.83,333.66,453.1Actual #2,00019,0001630,00039025010,00012018,00033173100323139005001004,00050086355,00021,0002349350,000512,678Equiv. # (12 kW) 2,000 19,0001,10830,0006632506,7084,00028,667333173331003231,7509005001002,18350011721731,41741,6674353400,000572,949GHC BULLETIN, MARCH 2001 1 Europe, most units are sized for the heating load and are oftendesigned to provide just the base load with peaking by fossilfuel. As a result, these units may operate from 2,000 to 6,000full-load hours per years (capacity factor of 0.23 to 0.68).Unless the actual number of full-load hours were known, avalue of 2,200 hours was used for energy output (TJ/yr) basedon data for several of the European countries. As an example,Finland has approximately 10,000 units installed, 70%horizontal installation, where the ground temperature isaround 10oC (50oF). Since performance of heat pumps is described in the papers in this Bulletin, several definitions are appropriate.Heating performance is defined by the index called COP(Coefficient of Performance), which is the heating affectproduced by the unit (in Btu/hr) divided by the energyequivalent of the electrical input (in Btu/hr) resulting in adimensionless number. Cooling performance is defined by anindex called EER (Energy Efficiency Ratio), which (in theU.S.) is the cooling affect produced by the unit (in Btu/hr)divided by the electrical input (in watts) resulting in units ofBtu/watt@hr. The energy reported for heat pumps should be reduced from the installed capacity based on a COP(coefficient of performance) of 3.0, which allows for one unitof energy input (usually electricity) to three units of energyoutput. Thus, the geothermal component is 67% of the energyoutput. Newer units have COPs in the 4 to 5 range whichincreases the geothermal use to 75% to 80% of rated capacity. In the United States, geothermal heat pump installations have steadily increased over the past 10 yearswith an annual growth rate of about 12%, mostly in the mid-western and eastern states from North Dakota to Florida. At the end of 1999, there are an estimated 400,000 units installed,with 45,000 installed annually. Today these figures are450,000 and 50,000 respectively. Of these, 46% are verticalclosed loop, 38% horizontal closed loop and 15% open loopsystems. Projections for the future are that the growth ratewill increase about 12% annually, so that by 2010 anestimated 140,000 new units would be installed in that year, thus, adding almost one million units for a total of about 1.5million units. Over 600 schools have installed these units forheating and cooling, especially in Texas. Using a COP of 3.0and 1,000 full-load hours per year in the heating mode, the450,000 equivalent 12 kW (3.4 ton) units removeapproximately 12,900 TJ/yr (12,250 billion Btu/yr) from theground. The cooling mode energy is not consideredgeothermal, since this rejects heat to the ground; however, thecooling mode does replace other forms of energy and is, thus,considered in fossil fuel and greenhouse gases emissionsavings. It should be noted at this point, that in the UnitedStates, heat pumps are rated on tonnage (i.e., one ton ofcooling power--produced by a ton of ice) is equal to 12,000Btu/hr or 3.51 kW. One of the recent converts to this form of energy savings is President George W. Bush, who recently installeda geothermal heat pump on his Texas ranch during the electioncampaign. Howard Newton, a consultant on the job,overheard the then President-elect explaining to VicePresident-elect Dick Cheney and General Colin Powell thatgeothermal heat is “environmentally hip” (Julie V. Iovine,The New York Times, January 4, 2001). The unit total is 14tons (49 kW) broken into five separate systems withdesuperheater. The vertical closed loop installation cuts hisheating and cooling cost by 40%. Figure 1. Ground-coupled (closed-loop) types. Figure 2. Groundwater (open-loop) types. 2 GHC BULLETIN, MARCH 2001 FEASIBILITY STUDY ON THE UTILIZATION OFGEOTHERMAL HEAT PUMP (GHP) SYSTEMS IN JAPAN Shinji Takasugi*1, Tsukashi Akazawa*1, Takashi Okumura*1 and Mineyuki Hanano*2 *1: JMC Geothermal Engineering Co., Ltd., 8-4, Koami-cho, Nihonbashi Chuo-ku, Tokyo. 103-0016, Japan*2: Japan Metals and Chemicals Co., Ltd., 8-4, Koami-cho, Nihonbashi Chuo-ku, Tokyo. 103-0016, Japan ABSTRACT Low-enthalpy geothermal resources have not been utilized to their potential in the past. However, since vasttracts of low-enthalpy geothermal resources exist as energy inthe form of differential temperatures, the reserves areestimated to be enormous. As a result, there is growinginterest in using this untapped energy in order to reducecarbon dioxide emissions which are the main cause for globalwarming, one of today’s most serious issues as addressed bythe U.S. Department of Energy and Environmental ProtectionAgency documents (e.g., EPA, 1993). The purpose of this feasibility study is to investigate the different aspects of the problem with respect to cost,technology and measures affecting the introduction andwidespread acceptance of geothermal heat pump (GHP)systems. Specifically, the study was conducted by collectinginformation from relevant literature, random surveys,discussion forums and expert groups. STATUS OF THE GHP (GEOTHERMAL HEAT PUMP)SYSTEM The GHP system is grouped under the following three systems on the basis of the objective or the manner inwhich heat is extracted (Kavanaugh, 1991; Oklahoma StateUniversity, 1997; GeoExchange, 1998).• Earth heat exchanger (earth-coupled heat exchanger)type heat pump system. This type of heat exchangercan be placed vertically in boreholes or in shallowtrenches, approximately 2 meters deep. •Heat pump system using ground water directly. • Heat pump system using surface (lake, marsh orriver) water directly, or using it as the heat source.This system requires a series of coiled tubing to beplaced into the appropriate lake, marsh or river. The system to be examined in this survey is “one using a vertical ground heat exchanger type heat pump system(Figure 1).” It could be of the horizontal installation type(horizontal ground heat exchanger type) or the verticalinstallation type (vertical ground heat exchanger type)depending on the arrangement of the heat exchanger. Many space heating and cooling systems utilizing the GHP system are being used worldwide, especially in the USA,Switzerland and northern Europe. The approximate(minimum) number of installed facilities includes 300,000 setsin the USA, 20,000 in Switzerland and 30,000 in northernEurope. While most of the systems are for single-familyhousing in Switzerland and northern Europe, many have beenGHC BULLETIN, MARCH 2001 installed in large buildings in the USA. Since one heat pumpmight be sufficient for a house or large building, the numberof installations does not necessarily correspond to the numberof users, particularly in the USA (Rybach et al., 1992; Rybachand Eugster, 1997). Figure 1. General layout of a GHP system using aborehole heat exchanger. COST PERFORMANCE EVALUATION AND THEEFFECT OF AN INCREASED USE OF GHP SYSTEMSCost Performance Evaluation The status of the research, development and utilization of GHP systems in Japan has been described byNEDO (New Energy Industrial Comprehensive DevelopmentOrganization)(1999). The cost of these systems wascompared with that of other space heating and cooling systemsin Switzerland. A comparison with conventional systems inJapan has also been made. These studies indicate that if the use of GHP systems becomes more popular, it will reduce the cost of drillingboreholes for the vertical ground heat exchangers, which is themain cause of the high initial cost. If also a 50% subsidy isobtained from the government to promote the introduction ofthese systems, the installation investment for the geothermalheat pump can be recovered in about two years. In addition ifa 30% subsidy is assumed, the increased cost (i.e., the costdifference with respect to a conventional system) can berecovered in less than 10 years. If the cost over the life cycleof the system (i.e., 24 years) is considered, a savings of2,050,000-3,490,000 yen (approx. a US$ 19,000 to 32,000)can be achieved assuming a 30% subsidy. 3 Table 1. Initial and operating costs of existing heating, cooling and hot water supply systems, compared withthose of GHP systems installed an elderly peoples’ home. Investment cost for facilities to lower carbondioxide emissions. Carbon dioxide reductions associated with the installation of GHP systems in 10,000homes for elderly people (1 US$ = 110 Yen–approx.). Table 2. Comparison of life-cycle costs (LCC) of existing and GHP systems described in Table 1 (for a 50-yearevaluation period)(1 US$ = 110 Yen). If a GHP system is installed in the home of the elderly where many people are living, the amount added to theinitial cost can be recovered in 9.5 years, by applying theexisting government subsidy for this type of homes (i.e.,2/3 of the home construction costs). If a 7% subsidy topromote the introduction of GHP systems is assumed, theadditional can be recovered in 5 years (Table 1). A costreduction of 0.45 million yen (US$ 4,000) can be achievedover the life cycle of the home (50 years) if no subsidy isapplicable (Table 2). Benefits of Using GHP Systems The benefits resulting from the installation of large numbers of GHP systems are:••• Reduction in carbon dioxide emissions,Lower heat radiation from urban areas, andDecrease in peak power demands. respect to the 1990 emissions in Japan; Table 1). Since almostno waste heat is discharged to the atmosphere, the use of thesesystems is expected to contribute to a reduction of the heatisland effect. It would also lower the demand for peak power.TECHNICAL ADVANCES NEEDED FOR FUTUREGHP SYSTEMS The following technical advances were considered to make GHP systems more effective and attractive in the future:••••• Improvement of the performance of heat pumps,particularly for single-family housing. Selection of a heating and cooling system that ismost suitable for GHP systems. Development of a highly efficient vertical groundheat exchanger. Implementation of new tools and techniques toreduce drilling costs. Preparation of drilling manuals. Regarding the first benefit, if all households in Japan would use the GHP system, the annual CO2 emissions wouldbe lowered by 52 million tonnes (a 4.3% reduction with4 GHC BULLETIN, MARCH 2001 Although there are no serious technical problems associated with the GHP systems, the most important projectsto be considered to reduce their costs are the development ofsmall-sized, highly mobile drilling rigs designed primarily forheat- exchanger holes, and the preparation of drilling manuals(items d. and e. in the list above). TASKS TO ASSIST IN THE INTRODUCTION,PROMOTION AND WIDESPREAD ACCEPTANCE OFGHP To promote the widespread introduction of GHP systems, the establishment of a support system is veryimportant. This system should be primarily directed toward: • Basic Research New developments to improve the thermal efficiencyof vertical ground heat exchanger are expected in thefuture. While the basic studies on this subject havebeen mostly completed in Europe and the USA,presently in Japan the lack of the subsurface dataneeded to install vertical ground heat exchangersmay slow down the introduction of GHP systems.The collection of such information is urgentlyneeded. • Applied Research Applied research on the use of GHP systems has alsobeen mostly done in Europe and the USA, where themain efforts have been directed toward theirintroduction in different regions. On the other hand,in Japan the most urgent tasks to be undertaken arethe standardization of systems, preparation oftechnical manuals, and testing the reliability of thesystems by conducting demonstrations. • Promotion Activities GHP promotion centers should be created. Theiractivities should include solving the variousproblems associated with the installation and use ofGHP systems and for the preparation of subsidiarysystems. Basic Research – Development of SubsurfaceTemperature, Groundwater level and Geologic Maps foran Optimal Design of Borehole Heat Exchangers A characteristic of the GHP system is that its heat exchanger is installed in boreholes. The installations above theground surface are similar to those of conventional heatingand cooling systems. Therefore, it is important to obtain theinformation necessary for designing and estimating the cost ofthe vertical ground heat exchanger. It must be made clear thatall associated studies should consider the prevailing conditions(climate, topography, geology) of Japan, as well as thedistribution of a) subsurface temperatures, b) geothermalgradients, c) soil thermal conductivities and d) groundwaterflow conditions. GHC BULLETIN, MARCH 2001Besides the need to obtain the thermal gradient down to 100 m depth (Figure 2), data on the groundwater levels and,if possible, the groundwater flow direction and rate are veryimportant. The design of vertical ground heat exchanged canbe made easy if maps with the required information areavailable. Sometimes, the lack of adequate information resultsin an unnecessarily conservative design. Figure 2. An example of downhole temperaturelogs. Appropriate geological information about the area where the vertical ground heat exchanger is going to beinstalled (less than the 100 m deep) allows the preparation ofadequate drilling cost estimates. The data should includeinformation on the presence of conglomerate layers, faults orbedrock (Marui, 1997; Uchida, 1998). Applied Research - Standardization of the GHP Systemand Preparation of Manuals To promote the installation of GHP systems, all the parties involved, including designers and system builders,must share common recognition and understanding of thesystem. This requires standardization of the system andpreparation of manuals. By designing and installing GHPsystems in accordance to the manuals the quality can beproperly controlled and a high level of reliability assured. The standardization of GHP systems and the preparation of manuals should be made as soon as possiblealso in Japan. In the USA, these activities are being promotedprimarily by IGSHPA (International Ground-Source HeatPump Association at Oklahoma State University) with thecooperation of universities, scientific societies and nationallaboratories. 5 The introduction of manuals already completed in Europe and the USA is considered very helpful to promote thesystems in Japan. Therefore for the time being, we shouldintroduce the overseas technologies and determine which areadequate for Japan and where to make additions and changes.Promotion Activities - Demonstrations, Promotion Centersand Subsidy Program • Demonstration of GHP Systems Demonstrations are extremely effective forrecognizing the advantages and points of excellenceof the GHP system. It is important to summarize theresults of the demonstrations in case studies reportsand to be used in promotion activities. At this time and for this study, a number of elderlypeoples' homes will be selected as the demonstrationtargets. The selected types of homes shall be suchthat:SA substantial number of units are expectedto be built. SEmphasis is placed on low-maintenancecost rather than low-investment cost units.S They are operational 24 hours a day forheating and cooling with a fairly largethermal capacity, including hot watersupply. SThey are public facilities requiring comfortand tranquility. STheir limited operation budget does notallow employing engineers for maintainingthe heating and cooling facilities. S Elderly peoples’ homes that fulfill theseconditions are considered to be prospectivetargets for the installation of demonstrationGHP systems. Subsidizing the cost ofinstalling vertical ground heat exchangers isconsidered to be an effective promotionactivity since it provides the incentive andmotivation to introduce the GHP systems inelderly peoples’ homes. Such homesshould be utilized for demonstration andmonitoring purposes. The results should besummarized and published in case studyreports. •Creating Promotion Centers The widespread installation of GHP systems will beenvironmentally effective and be helpful in levelingpower consumption rates and lowering the heatisland phenomenon. From this viewpoint, theEnvironmental Protection Agency, the Department ofEnergy, and power companies in the USA arepromoting the installation of these systems and 6created the GHPC (Geothermal Heat PumpConsortium) as a part of joint government/privatesector effort.. The GHP system is applicable to almost all areas ofJapan. The fast growth in the number of installedunits in Europe and the USA is an excellentencouragement for Japan. A rapid adoption of thesystem, even faster than in Europe and the USA, canalso be expected in Japan by creating adequate GHPpromotion centers. For 1996, the number of installed GHP systems inthe USA was reported to be 50,000. The subsequentyearly growth rate is about 20%. Although the rateis below the target proposed by GHPC, it is stillfairly high. However, in Japan the system is not wellknown by parties that could benefit from it, includingconsumers, architects, engineers, builders andmanufacturers (HPTC, 1998). Considering that presently Japan is still in the initialstate of GHP system application, it is essential thatNEDO should lead promotion and demonstrationefforts by creating centers to assist in theintroduction of systems suitable for the Japan’sconditions. It is essential to study the systems in theUSA and Europe very closely, and to determinewhich is the optimal system for Japan and settarget(s) before starting the promotion activities. • Subsidy Program When promoting the use of the GHP system, oneshould stress its economic merits, along with itsbeneficial effects like energy peak demand reductionand global environmental preservation. The mostimportant point on its economic merits should be thatthe higher installation costs can be reduced. In thisconnection, the application of subsidies is consideredvery important for increasing the system’s economicadvantages. In view of the present situation of lownumber of installations in Japan, the application of asubsidy program is expected to have an immediateeffect on promoting the introduction of GHP systemsand creating an initial demand. To help in the creation and design of a subsidyprogram for the introduction of GHP systems, onecould learn from those for solar and wind energy.These types of energies seem to have becomeeconomical partly because of the existence ofsubsidies. A possible subsidy program for introducing andincreasing the use of GHP systems should includesubsidies for: GHC BULLETIN, MARCH 2001 •Private persons who desire to install thesystems in their house, •Manufacturers, builders and/or dealers whoproduce, install and sell the systems, and • Organizations that promote the use of thesystems. The funds might be used to coveroperational costs, provide infrastructure,prepare manuals, and perform preliminaryinvestigations, including planning. The subsidy program for private persons would payfor a certain percent of the GHP system installationcosts. This would be similar to the programencouraging the introduction of solar energygeneration units; it covers the cost difference withrespect to a conventional space heating andcooling system. In addition, the financial or taxincentive program used to promote wind powerprojects would also be important. The subsidy program for manufacturers, buildersand/or dealers is expected to be funded by the powercompanies. It would be similar to the one payingmanufacturers 20,000-50,000 yen (US$ 180 - 450)for each kW of the peak shift achievable by the ice-energy storage-type air-conditioning system called\"Eco-Ice.\" The subsidies to manufacturers andbuilders was offered so that the new technologywould be commercially feasible, allowing the repairof the facilities as they become old. Further energy savings could be realized if theelectricity for the GHP system compressor could begenerated using solar or wind energy, and the Eco-Ice. In this way, the impact of the subsidy programwould be further enhanced. If the economy and performance of the GHP systemin Japan could be demonstrated, its use could also bepromoted in neighboring Asian countries, as part ofthe environmental yen loan program being conductedunder the Kyoto Protocol adopted at the ThirdConference of Parties to the UN Convention onClimate Change (COP3). CONCLUSIONS The results of the GHP feasibility study in Japan can be summarized as follows:• Present Situation Currently the number of GHP systems installed inthe USA is about 400,000, and is expected toincrease by approximately 50,000 units per year (i.e.,about 12% annual growth). In Switzerland, there areabout 50,000 systems and the number is growing atan annual rate of 20 % (L. Rybach, pers. comm.).With the more favorable subsurface temperature GHC BULLETIN, MARCH 2001 conditions prevailing in Japan, the introduction ofthese systems has been found to be feasible.Geothermal heat pump systems (with vertical andhorizontal ground heat exchanger, lake loops,etc.) are considered to suit the requirements of Japanfrom both the topographical and environmentalpoints of view. • Costs and Widespread Acceptance of GHPSystems Studies have shown that if drilling costs for thesubsurface heat exchanger can be reduced by anincreased number of installed systems, the additionalinstallation costs of a GHP system for an averageresidential building can be recovered in two yearsassuming a cost subsidy of 50%, and in 10 years fora 30% subsidy (assuming that the subsidies areavailable during the initial stages of GHPinstallation). When the costs are considered over theoperating life of the system (typically 24 years), asaving of 2,050,000 - 3,490,000 yen (approx. US$19,000 - 32,000) can be achieved with a 30%subsidy. When the installation of a GHP system in an elderlypeoples’ home is evaluated, the additional initialcosts of the GHP system is recoverable in 9.5 yearsby applying subsidies currently available (a subsidyof 2/3 of the home construction cost), andrecoverable in five years (Table 1) when the subsidyis increased by an additional 7%. When theoperating life is extended to 50 years, it can beshown that a project lifetime savings of 0.45 millionyen (US$ 4,000) is possible even without subsidies(Table 2). It can be shown that if all residential buildings inJapan would install a GHP system, a reduction of 52million tonnes in carbon dioxide emissions could beachieved (a reduction of 4.3 % compared to 1990’semissions; Table 1). In addition, as almost no wasteheat is released into the air, these systems areexpected to lower heat island effects and reduce peakelectric power demands. •Technical Tasks Although there are no specific technologicalproblems, several aspects of the GHP systems couldbe improved, including the development of small-scale drilling rigs specially designed for installingGHPs and for drilling into soft and hard rockformations. Also drilling manuals should beprepared, including sections showing the distributionof geologic formation and faults that might affectdrilling performance. 7 • Tasks to Assist in the Introduction, Promotionand Widespread Acceptance of GHP Systems These tasks include the gathering of geological data,the standardization of systems, the preparation ofmanuals, the demonstration and monitoringactivities, the establishment of a GHP systemdistribution network, and the creation of a subsidyprogram. Proposals, relating to GHP systems inJapan, have been based upon examples from Europeand the United States. ACKNOWLEDGMENTS This study was performed by JMC Geothermal Engineering Co. Ltd., with support from the New EnergyIndustrial Comprehensive Development Organization(NEDO). We express our gratitude to the NEDO personnelwho gave us the opportunity to present this paper. The authors are grateful to Michael E. Albertson, Global Logic, Oklahoma City, Oklahoma, USA, and Phil E.Albertson, Ditch Witch, Perry, Oklahoma, USA for theirgeneral comments and review. The authors also thank Drs. L.Rybach, Y. Niibori and M. J. Lippmann for their helpful andcritical comments on the manuscript. “This paper was published with kind permission of the International Geothermal Association. The original paperwas presented at the World Geothermal Congress 2000, heldin Japan in May-June 2000.” REFERENCES EPA, 1993. “Space Conditioning: The Next Frontier - The Potential of Advanced Residential Space HeatingTechnologies for Reduction Pollution and SavingCustomers Money,” U.S. Environmental ProtectionAgency, 103 p.GeoExchange, 1998. Materials and Publications Catalogand Reference Guide, Geothermal Heat PumpConsortium (GHPC). 8HPTC, 1998. “Report HPTC-185,” Heatpump and Thermal Storage Technology Center, 114 p.Kavanaugh, S., 1991. “ Ground and Water Source Heat Pumps - A Manual for the Design and Installation ofGround-Coupled, Groundwater and Lake WaterHeating and Cooling Systems in Southern Climates,”University of Alabama in cooperation with theAlabama Power Company, 154 p.Marui, A., 1997. “The Outline of Japanese Well and Hydrology Database,” 1997 Fall Meeting ofAmerican Geophysical Union (AGU), EOSTransactions, 78(46) F304, San Francisco, CA.NEDO, 1999. “Feasibility Study on Utilization of Geothermal Heat Pump (GHP) System for SpaceHeating/Cooling, Warm-Water Supply and RoadHeating in Japan (in Japanese),” 133 p. Oklahoma State University, 1997. “Geothermal Heat Pumps Introductory Guidance,” International GroundSource Heat Pump Association (IGSHPA), 99 p.Rybach, L.; Eugster, W. J.; Hopkirk, R. J. and B. Kaelin, 1992. “Borehole Heat Exchangers: LongtermOperational Characteristics of a DecentralGeothermal Heating System,” Geothermics, 21, 5/6,861-867Rybach, L. and W. J. Eugster, 1997. “Borehole Heat Exchangers to Tap Shallow Geothermal Resource:The Swiss Success Story,” Proc. 19th NZGeothermal Workshop, pp. 63-68Uchida, Y., 1998. “Effects of Pumping on Subsurface Thermal Regime in the No 0bi Plain,” Journal ofJapanese Association of Hydrological Sciences, 28,2, 45h-60. GHC BULLETIN, MARCH 2001 HOT WATER SUPPLY TEST USING GEOTHERMAL HEATPUMP SYSTEMS AT PETROPAVLOVSK-KAMCHATSKY, THE CAPITAL OF KAMCHATKA, RUSSIA Ken Ikeuchi1, Shinji Takasugi1 and Shin-ichi Miyazaki2 1 JMC Geothermal Engineering Co., Ltd., 8-4, Koami-cho, Nihonbashi Chuo-ku, Tokyo. 103-0016, Japan2 Japan Metals and Chemicals Co., Ltd., 8-4, Koami-cho, Nihonbashi Chuo-ku, Tokyo. 103-0016, Japan ABSTRACT “Fundamental investigation of the promotion of a joint implementation for the fiscal year 1998 - Thefundamental investigation related to local heating utilizinggeothermal in Kamchatka, Russia” was carried out with thesupport of the New Energy and Industrial TechnologyDevelopment Organization (NEDO). It was carried out as afeasibility study and to implement the “joint implementation.” As the results, it was verified that heating by geothermal heat pump (GHP) can be used instead of theexisting boiler heating in the severe climate condition inKamchatka. In this report, the results of the GHP test as a partof this feasibility study is summarized. INTRODUCTION The third conference (COP3) of the parties for the United Nations Framework Convention on Climate Changewas held in Kyoto in December, 1997. In order to prevent theglobal warming by the effects of greenhouse gases such ascarbon dioxide, the protocol in Kyoto adopted reduced targetsfor the quantity of greenhouse gas exhausted in developedcountries. Further, in the protocol in Kyoto, the methods ofachieving the targets were made flexible, such as by “jointimplementation,” among developed countries. With this background, “The fundamental investigation related to local heating utilizing geothermal inKamchatka, Russia” was carried out. The region selected forthis project was Petropavlovsk-Kamchatsky, the capital ofKamchatka (hereinafter called \"P-K city\") and its environs(Figure 1). P-K city faces the Bay of Avanchiskaya located alittle to the south of the center of the east Pacific coast. Threehundred thousand of the state’s total population of about350,000 live in the city and it is the center of administrationand industry of the Peninsula. It is located 30 km from theErizoho airport, the gateway to Kamchatka. There is a district heating system using hot water in P-K city. This includes two systems for the supply of hotwater from exhaust heat of the power plant and the supply ofhot water furnished by heavy oil combustion. Sixty fivepercent of local heating in P-K city is supplied by hot waterfrom heavy oil combustion through a pipeline. The purpose of this test was to verify that the heating can be carried out adequately by GHP instead of theboiler heating in Kamchatka, a severe cold district. GHC BULLETIN, MARCH 2001Figure 1. Southern part of Kamchatka peninsula.GEOTHERMAL HEAT PUMP TEST PROGRAM Selection of Test Site The GHP test began by selecting the test site. As the conditions of the test site, the vertical ground heatexchanger type heat pump system was adopted. Because thesite area was comparatively unrestricted for the location of theheat pump test, it was possible to drill boreholes.Accordingly, as the result of the proposal by Russia and thepreliminary discussion, four locations were selected as theproposed test sites. Then the on–site investigation of theseproposed test sites were carried out, taking the following intoconsideration: 9 1. 2. 3. 4. 5. 6.Geographical position,Geological conditions,Existing heating system, Social importance of installation site, Reliability of electric power supply to theinstallations, and Issue of ownership and the of approval of the test. As the result of the comparison and investigation of the four proposed sites, the sanatorium of KamchatkaEnergo Company (electric power company) in Aginuk regionwas selected as the test site. This sanatorium is located in theParatunsky hot spring area 60 km from P-K city. This sanatorium is the property of Kamchatka Energo Company, used as a children training camp in summerand as the lodging facility for the employees and their familiesof Kamchatka Energo Company in winter. The facilityconsists of two hotel-type residential buildings, anadministration building, a pool and auxiliary buildings. Thearea was most suitable for the GHP test site as a well can bedrilled anywhere. Electricity is supplied by independentpower generation for twenty-four hours. The heating of allbuildings is centralized in a heavy oil boiler system. Thetemperature is controlled by the outdoor temperature and isoperated manually. There were no problem in use or thatcould occur in the drilling and approval. The room selectedfor the test has the advantage in being easily compared withthe adjacent room in which the existing equipment is used.Further, there is no problem in opening to the public or foradvertisement because it is a public building and the facility issuitable for PR, such as observation. It was expected that the underground water level existed at a depth of about 3 m. The static formation tempera-ture is 7-8oC at a depth of approximate 90 m, measured in anexisting borehole. This potential test facility consisted of the administration building in the sanatorium and the lodgingbuilding. The administration building was under constructionand thus, the piping work and the observation of the heatingconditions was made easy. Further, a half of theadministration building was not scheduled for use. Fromthese points of view, the administration building was adoptedas the test house. The plan also considered setting the GHPsystem in a separate house and putting it on the side of theadministration building. Trial Design of Heat Pump Test Since the sanatorium of Kamchatka Energo Company in Aginuk region was selected as the test facility,the project was designed to take the site conditions intoconsideration. Half of the rooms of the administrationbuilding were assigned to be observation rooms in which thetest was carried out; that is, five rooms were to be heated byGHP. The observation rooms were selected by locating theheating pipes coming into the administration building so thatthe supplied hot water only entered approximately half of theheating pipes. To heat the half of the administration buildingof double windows with walls made of concrete, 5.7 kW ormore of GHP capacity was enough. Therefore, the capacityof GHP was set to 6.7 kW using a ready-made article,providing a margin of safety. In Switzerland, the peak heatoutput to be recovered from the heat exchanging well in the Figure 2. GHP piping system diagram. 10 GHC BULLETIN, MARCH 2001 GHP system is 45 W/m (Rybach and Eugster, 1997), so thepeak output of 4.5 kW can be obtained in the case of the wellof 100 m depth. The formation temperature is low in thesevere cold district such as Kamchatka; thus, the COP wouldbe poorer than in a warmer district and the heat output fromthe well was thought to be less. Since the capacity of theGHP used in this test was 6.7 kW, 2.2 wells of depth 100 mwere required. It was estimated that 3 kW could be obtainedfrom a well of depth 100 m. Therefore, three wells of depth100 m were drilled in this test. The system diagram is shownin Figure 2. GEOTHERMAL HEAT PUMP TEST Purpose of Investigation When we visited the Kamchatka Energo Company’s sanatorium in the Aginuk region, the existing heating wascontrolled by a supply temperature of 50oC (0.4 MPag) fromthe supplied hot water and 40oC (0.16 MPag) returntemperature. This facility is also utilized as a sanatorium inwinter by using this heating system. Therefore, the purpose ofthis test using this sanatorium was to prepare the hot water forheating of at least 50oC or more by GHP and to verify that theheating can be carried out sufficiently by GHP instead of theboiler heating in Kamchatka, a severe cold district.Result of Investigation Temperature Measurement of Heat Exchange BoreholeThe temperature in the well measured on April 17, 1999 is shown in Table 1. These values were measured inWell-2 (standing time was one month or more) which wasfinished first with water level at a depth of 20 m. Thesevalues were measured separately by using a maximum tem-perature thermometer (max.100oC). The maximum tempera-ture in Well-2 was 13oC at a depth of 100 m and it was a littlehigher than the estimated value (7 to 8oC at a depth of 90 m).Table 1.Results of Well-2 Temperature Measurement (measured on April 17, 1999). DepthTemperature 20 m10oC50 m10oC100 m 13oC Conditions of GHP InstallationThe drilling was carried out using a truck mounted rig. The polyethylene U-shape tubes, with outside diameter of33.4 mm, were inserted just after completion of drilling to beused as the heat exchanger (Oklahoma State University,1997), and a casing was set for the reason of timing problemsin the installation. The space between the casing and the U-shape tubes were back-filled with pure bentonite. After that,glass wool insulation was wound around the surface piping.The house for the heat pump system was installed in the spacebetween the administration building and the wells. The heatpump and the observation unit were placed in this building.GHC BULLETIN, MARCH 2001 Result of GHP TestThe piping system diagram of the GHP test is shown in Figure 2 and the results of the observations areshown in Table 2. The test was started at the end of April andthe observation period of the test was 18 days. Half of therooms in the administration building were scheduled to beheated by GHP according to the initial plan, but as shown inFigure 2, a system to heat the whole administration buildingwas adopted because of a problem in welding the piping at thesite. Therefore, the head of the circulating pump of the initialplan was not adequate and a sufficient quantity of hot watercould not be circulated in the entire administration building.The positions of the respective measurement channels (ch.) inTable 2 are shown in Figure 2. Since May 2-4, during themeasurement period, was a public holiday in Russia, data werenot obtained. Further, channel 11 which measured thetemperature of the face of the heating pipe, did not measurethe temperature from May 5 to May 10 because of a faultysensor. After May 11, since air entered into the heater, the hotwater could not be circulated around the temperature sensorand thus, heating was insufficient. Therefore, channel 11values are small. As shown in Table 2, the outdoor temperature wasabout 5o C and the room temperature was kept at 18-20oC.This temperature was sufficient in the heating condition of theperiphery of P-K city. Further, in this GHP test, as shown inFigure 2, the system with the buffer tank (called the masstank) was provided to store the hot water created by the GHP.The stored hot water in the tank was then circulated. Asshown in Table 2, the temperature of the hot water deliveredfrom the mass tank was about 44oC to 46oC and the returntemperature was about 41oC to 43oC, resulting in the supply ofheat equivalent to about 3oC. The temperature difference between the delivered hot water and the return hot water was maintained about 3oC.The room temperatures of channels 9, 10 and 12 were kept at18-20oC; while, the output temperature of the hot water onchannel 6 decreased daily. This means that the capacity of theGHP is not enough for all rooms of the administrationbuilding. On the other hand, the reason that the hot water could not be circulated around channel 11 temperature sensorwas that the circulated pump capacity was not enough due toheating twice of the number of test rooms as planned. Because of the above-mentioned reasons, we could not circulate enough hot water. However, the test room couldbe heated adequately in the environment where the outdoortemperature was close to 0oC (sometimes, below-zero atnight). From these tests, it was verified that heating by GHP can be used instead of the existing equipment in thesevere climate condition in Kamchatka. Moreover, it ispossible to decrease the discharge of carbon dioxide with thelocal GHP heating system. CONCLUSIONS Summarizing the GHP test: the proposed test sites were selected first, the final test site was then decided between 11 Table 2. Result of GHP Test Observation. No. 11 channel could not obtain the data because of a faulty sensor, from May 5th to 10th. Further, the sensor operated after May 18th, but due to air entering the inside of the pipe, the channel could not be heated. ____________________________________________________________________________________________________________________________ them, three wells for the ground-coupled heat exchanger weredrilled at that site, and then the on-site actual test was carriedout. The test was started at the end of April and the observation period was 18 days. The test rooms could beheated adequately in the environment which the outdoortemperature was close to zero (sometimes, below-zero atnight). Therefore, it was shown that the heating equipment bythe GHP can be used instead of the existing equipment in thesevere climate condition in Kamchatka. This will alsodecrease the discharge of carbon dioxide using the local GHPheating system in Kamchatka. ACKNOWLEDGMENT This investigation was carried out by Japan Metals and Chemicals Co., Ltd. (JMC) promoted by the New EnergyIndustrial Comprehensive Development Organization (NEDO)as a part of “Fundamental Investigation of promotion of jointimplementation for the fiscal year 1998.” We express our gratitude to NEDO and JMC persons concerned who encouraged the publication of thispaper. The authors also thank Drs L. Rybach, and Y.Nibori fortheir helpful and critical comments on the manuscript. “This paper is published with the kind permission of the International Geothermal Association. The originalpaper was presented at the World Geothermal Congress 2000,held in Japan in May-June 2000.” REFERENCES Rybach, L. and W. J. Eugster, 1997. “Borehole Heat Exchangers to Tap Shallow Geothermal Resource:The Swiss Success Story. Proc. 19th NZGeothermal Workshop 1997. 63-68Oklahoma State University, 1997. Geothermal Heat Pumps Introductory Guidance. International GroundSource Heat Pump Association (IGSHPA), 99pp. 12 GHC BULLETIN, MARCH 2001 CURRENT STATUS AND FUTURE DIRECTIONSOF GEOTHERMAL HEAT PUMPS IN TURKEY A. Hepbasli1, M. Eltez2 and H. Duran2 1 Ege University, Mechanical Engineering Department, Engineering Faculty, 35100 Bornova, Izmir, Turkey2 Dogan Geothermal Co. Inc., Ceyhun Atif Kansu Avenue 9. Street No. 3, 06520, Balgat, Ankara, TurkeyABSTRACT Ground-source or geothermal heat pumps (GHPs) are attractive alternative to conventional heating and coolingsystems owing to their higher energy utilization efficiency. Inthis regard, GHPs have had the largest growth since 1995,almost 59% or 9.7 annually in the United States and Europe.The installed capacity is 6,850 MWt and annual energy use is23,214 TJ/yr in 26 countries. The actual number of installedunits is around 500,000. The utilization of GHPs inresidential buildings is new in Turkey, although they havebeen in use for years in developed countries. In other words,GHPs have been put on the Turkish market for about threeyears. There are no Turkish GHPs’ manufacturers yet. It isestimated that 43 units are presently installed in Turkey,representing a total capacity of 527 kW. Considering theongoing installations, the total installed capacity will reach3,763 kW in this year, with a total of 282 units. The majorityof the installations are in the Marmara region of Turkey (inIstanbul). High-income earners also prefer these systems.The current status of GHPs in Turkey is discussed and twocase studies are described, of which the first one relates to theUniversity of Ege, Izmir, Turkey while the second oneincludes a commercial application, which replaced a furnace. GHPS APPLICATIONS IN TURKEY In Turkey, the concept of the ground-source (or geothermal) heat pumps (GSHPs), in general heat pumps, isnot new. However, the utilization of GSHPs in residentialbuildings is new in Turkey, although they have been in use foryears in developed countries and the performance of the com-ponents is well documented. The first residential geothermalheat pump system in the country was installed in a villa witha floor area of 276 m2 in Istanbul, in 1998; while, the firstexperimental study was carried out in the MechanicalEngineering Department, METU (Middle East TechnicalUniversity) in Ankara, in 1986 (for more detail see Babur,1986; Hepbasli and Gunerhan, 2000). The residential systemconsisted of a heating-only heat pump with a scroll com-pressor (15.6 kW heating) coupled to a 160-m (525-ft) vertical1 ¼ inch U-bend ground coupling. The representative firm ofSwedish GSHPs’ manufacturer imported the heat pump itselfand its relevant ground coupling materials and this system hasbeen successfully operated since its installation. In this context, the studies carried out on GHPs in Turkey can be divided into three groups (for more detail, seeHepbasli and Gunerhan, 2000); a) university studies, b) casestudies (heat pump industry), and c) standardization studies. GHC BULLETIN, MARCH 2001University Studies University studies on GSHPs can be classified into two categories: theoretical and experimental. Up to date, onlythree experimental studies were carried out by Babur (1986),Kara (1999) or Kara and Yuksel (2000) and Hepbasli (2000).Table 1 shows the main characteristics of GHP systemsinstalled at the three different universities. The theoreticalstudies performed were described elsewhere (Hepbasli andGunerhan, 2000).Table 1. Main characteristics of GHPs installedat the Turkish Universities as ofJanuary 2001 (Babur, 1986; Kara, 1999,2000; Hepbasli, 2000) HPName of University YearSystem type cap.built kW A single pipe-horizontal heat pumpMiddle Eastsystem for the heatingTechnical only with R-12; 10 mUniversity1986of ground coil at 1.5 m0.95 (Ankara) depth with a spacing of0.6 m; COP: 1.1 to 1.3.A water-to-watergeothermal heat pumpsystem for the heatingAtaturk Universityonly with R-22; an(Erzurum) 1999actual COP value of7.02 2.8; Geothermal waterinlet/outlet temp. 35/30o C at a flow rate of1,100 L/h A GSHP system forboth heating andEge Universitycooling with a vertical-(Izmir) 2000single U-bend heat5.2 exchanger; 4 ½ inch ofa bore diameter with aboring depth of 50 mHeat Pump Industry (Market) GSHP systems installed so far in Turkey are few in numbers. There are not any Turkish GSHPs’ manufacturersyet. Currently, there are three companies, of which one is thepioneer of GSHPs in Turkey (Firm D) and has installed manysystems. The remainder deals with water-loop heat pumpsystems imported from the USA (Firm A; Firm C), excludingone (Firm B). Besides these, the others are trying to intro-duce GSHPs into the Turkish market nowadays. In order to 13 determine the number of GSHPs installed, information from16 case studies was collected on residential and commercialsystems from Turkish GSHP sellers (and also contractors)throughout Turkey. “Firm A” installed in 1998 a water-loopheat pump system (WLHPS) at Kaya Building consisting of12 storeys in 1998 which was the biggest one in Turkey andis still active. Based on the data given by the “Firm B,” sixprojects have been implemented for building heating rangingfrom an air-conditioned floor area of 650 m2 to 24,900 m2 bymeans of GSHPs. Two of them were completed in 1999 andthe remaining is in progress. In fact, no reliable data wereobtained from “Firm B” and it is heard that this firm wentbankrupt. Besides these, no data was obtained from “Firm C.”Therefore, only data given by the “Firm D,” which is atpresent the single one in the installation of GSHPs in Turkey,were taken into account. The distribution of GHP systemsinstalled by “Firm D” so far amounts to 16 vertical and 5 hori-zontal closed-loop systems, with 275 vertical ones in prog-ress. In 1998 when the first installation was began, two GHPsystems with a total capacity of 26 kW were completed,representing a total floor area of 596 m2. These systems havehad the largest growth since the beginning of the year 2000.Today, the installed capacity is 527 kW while the number ofinstalled units is 23, totaling 43 units with the equivalentnumber of 12 kW. The 12 kW equivalent is used as typical ofhomes in the United States and some western Europeancountries (Lund and Freeston, 2000). The size of individualunits is in the range 9 to 46 kW and 38 to 46 for residentialand commercial uses, respectively. Considering the ongoinginstallations, the total installed capacity will be 3,763 kW,with a total of 282 units ranging from 7.3 to 46.2 kW for bothresidential and commercial uses. In addition, by taking intoaccount the new works, which are at the design stage, with atotal 130 villas ranging from 120 to 310 m2 of floor areas, it isestimated that the installed capacity will reach about 5 MW.Of the GHP systems installed up to date, 80% were verticalground-coupled GHP systems while about half was designedfor both heating and cooling. The diameter of U-bend tubeswas 1 ¼ inches for the both applications. The heating andcooling loads were approximately 80 and 95 W/m2, respec-tively. The majority of the installations are in the Marmararegion (in the province of Istanbul). Standardization Studies Turkish standards relating to heat pumps are few in numbers. Up to date, 14 standards were issued on heat pumpsby TSI (Turkish Standards Institution), of which only twocontained the water to water type heat pumps (Hepbasli andGunerhan, 2000). This means that standardization studies arealso new in Turkey. CASE STUDIES In the following, the two case studies will be described. Of these, the first one relates to the University ofEge, Izmir, Turkey while the second one includes acommercial application, which replaced a furnace. 14Case Study 1: Ege University The water (ground)-to-water type heat pump (GSHP) system was connected to a 64-m2 classroom of the SolarEnergy Institute Building (SEIB) at the University of Ege,Izmir, Turkey. The building constructed in 1986 uses passivesolar techniques and hence it was well insulated. It has threefloors and a total floor area of 3,000 m2. The GSHP systemmainly consisted of three separate circuits, which are calledthe ground coupling circuit (brine circuit or water-antifreezesolution circuit), the refrigerant circuit (or a reversible vaporcompression cycle) and fan-coil circuit (water circuit). Thesystem was commissioned in July 2000. Performance tests stillcontinue. From the measurements, the specific heat extractionrate was found to be 84.4 W per meter of borehole length,while the COP for cooling was about 3.1. Case Study 2: Office Building The building, located in Izmir, has 49 offices. The heating and cooling loads of the structure are 259 and 294kW, respectively. The building was formerly designed for theheating only and hence heated by a 406-kW oil-fired hot watergenerator through fan-coils. The GSHP system replaced thishot water generator in June 2000 and has operated since thattime. It was designed for both heating and cooling. Noperformance data were obtained from the installer. Themeasurement devices were missing in order to monitor theperformance of the system. CONCLUSIONS The importance of energy as an essential ingredient in economic growth as well as in any strategy for improvingthe quality of life human beings is well established. In thiscontext, energy, which can be defined as money and even cashfrom the viewpoint of energy efficiency, is the mainstay of themodern society. So, GHPs are attractive alternative toconventional heating and cooling systems. GSHPs arereceiving increasing interest in Turkey. The technology iswell established with over 500,000 units installed worldwide.The soil type and moisture content on the performance ofGSHP have recently been reported by some investigators(Morino and Oka, 1994; Leong et al., 1998; Allan, 2000).However, in Turkey, this cost reduction factor, which can beachieved by decreasing the necessary ground loop length withthe optimal selection of the backfill material, is not taken intoaccount in the design. Besides these, for the successfuldevelopment of GHPs in Turkey, the other issues givenelsewhere (Hepbasli and Gunerhan, 2000) should be takeninto account. ACKNOWLEDGMENTS This is a condensed version of the paper presented atthe 26th Workshop on Geothermal Reservoir Engineering,Stanford University, CA, January 2001. GHC BULLETIN, MARCH 2001 GHPs Installations with Conventional Horizontal Ground Loop in Turkey as of January 2001 TotalEquiv.Number of12 kWUnits Situation ofApplicationCity ofRegionIstanbul/Marmara BuildingType/No. ofBuildingsVilla / 2Villa / 1 Total FloorArea (m3)1,400 + 400 = 1,800 525 No. of HPUnits (type)2 / (HC)1 / (H) Total PipeLength (m)1,690 + 600= 2,290 850 HPCapacity(kW)38 and 1546.2 Total HPCapacity(kW)53.046.2 C o m p l e t e d Ankara/CentralAnatolianBolu/Black SeaMersin/Mediterrean TOTAL Bungalow / 1Villa / 1 5 240435 1 / (H)1 / (H) 420600 9.015.0 9.015.0 10 3,000(2HC 3 H)4,160123.2 REFERENCES Allan, M. L., 2000. “Materials Characterization of Super-Plasticized Cement-Sand Grout,” Cement andConcrete Research, 30, 937-942.Babur, N., 1986. Design and Construction of an Earth Source Heat Pump. M.Sc. Thesis in MechanicalEngineering, Middle East Technical University, 119pp. Firm A, Form Inc.Firm B, Ente Avrasya Inc.Firm C, TEBA Inc.Firm D, Yesil Cizgi Inc. Hepbasli, A. and H. Gunerhan, 2000. “A Study on the Utilization of Geothermal Heat Pumps in Turkey,”Proceedings of the World Geothermal Congress2000, Kyushu-Tokyo, Japan, May 28-June 10, 2000,pp. 3433-3438. Hepbasli, A., 2000. Both Heating and Cooling a Room by using a Vertical Ground-Coupled GSHP (inTurkish), Research Fund Project of Ege University(not published).Kara, Y. and B. Yuksel, 2000. “Evaluation of Low-Temperature Geothermal Energy through the Use ofHeat Pump,” Energy Conservation andManagement, 42, 773-781.Leong, W. H.; Tarnawski, V. R. and A. Aittomaki, 1998. “Effect of Soil Type and Moisture content onGround Heat pump Performance,” Int. J. Refrig.,21(8), 595-606.Lund, J. W. and D. H. Freeston, 2000. “World-Wide Direct Uses of Geothermal Energy 2000,” ProceedingsWorld Geothermal Congress 2000, Kyushu-Tohoku,Japan, May 28-June 10, 1-21, 2000.Morino, K. and T. Oka, 1994. “Study on Heat Exchanged in Soil by Circulating Water in a Steel Pile,” Energyand Buildings, 21, 65-78. GHC BULLETIN, MARCH 2001 15 DESIGN ASPECTS OF COMMERCIALOPEN-LOOP HEAT PUMP SYSTEMS Kevin RaffertyGeo-Heat Center ABSTRACT Open loop (or groundwater heat pump systems are the oldest of the ground-source systems. Common designvariations include direct (groundwater used directly in the heatpump units), indirect (building loop isolated with a plate heatexchanger), and standing column (water produced andreturned to the same well). Direct systems are typicallylimited to the smallest applications. Standing column systemsare employed in hard rock geology sites where it is notpossible to produce sufficient water for a conventional system.Due to its greater potential application, this paper reviews keydesign aspects of the indirect approach. The general designprocedure is reviewed, identification of optimum groundwaterflow, heat exchanger selection guidelines, well pump control,disposal options, well spacing, piping connections and relatedissues. INTRODUCTION Open-loop or Groundwater Heat Pump (GWHP) systems are the oldest and most well established of theground-source heat pump systems. Despite this, little formaldesign information has been available for them until recently.Although seemingly simple in nature, these systems requirecareful consideration of well design, groundwater flow, heatexchanger selection and disposal in order that an efficient andreliable system results. Several variations on the open loop system are in use. The most common of these are illustrated in Figure 1. Thedirect use of the groundwater in the heat pump units is largely Figure 1. Open-loop systems. 16 an extension of residential design and is sometimes used invery small commercial applications. It is very susceptible towater quality induced problems, the most common of whichis scaling of the refrigerant-to-water heat exchangers. Thisdesign is recommended in only the smallest applications inwhich practicality or economics precludes the use of anisolation heat exchanger and/or groundwater quality isexcellent (the determination of which requires extensivetesting). The standing column system has been installed inmany locations in the northeast portion of the U.S. Like thedirect groundwater system, it too is subject to water qualityinduced problems. In general, water quality in the area wheremost of the installations have been made (New England) isextremely good with low pH and hardness (little scalingpotential). Standing column systems are used in locationsunderlain by hard rock geology; where, wells do not producesufficient water for conventional open loop systems and wherewater quality is excellent. Well depths are often in the 1000to 1500 ft range and the systems operate at temperaturesbetween those of open and closed loop systems. In colderclimates, this sometimes precludes the use of a heat exchangerto isolate the groundwater. Indirect open loop systems employ a heat exchanger between the building loop and the ground water. Thiseliminates exposure of any building components to the groundwater and allows the building loop and ground water loops tobe operated at different flows for optimum systemperformance. Water can be disposed of in an injection well orto a surface body if one is available. These systems offerenergy efficiency comparable to closed loop systems atsubstantially reduced capital cost. Due to the elimination ofwater quality and geology limitations this system type is themost widely applicable of the three and will be the focus ofthe balance of this paper The design of an open loop system is one in which the performance of the system is optimized based on thepower requirements of the well pump, loop pump and heatpumps. In a system of this configuration, it is apparent that thegreater the ground water flow, the more favorable will be thetemperatures at which the heat pumps will operate. As theground water flow is increased, the improvement in heat pumpperformance is increasingly compromised by rising well pumppower. At some point, increasing well pump powerovershadows the improvement in heat pump performance andthe total system performance begins to decline. The task inopen loop design is to gather enough information about thewell pump, loop pump and heat pumps to permit theidentification of these trends and to select the optimum systemperformance point. It is the SYSTEM EER or COP that is the GHC BULLETIN, MARCH 2001 are included in the well completion reports submitted by thedriller upon completion of the well. They are normally kepton file (in some cases available on the internet) by the statewater resources regulatory agency and are public information. It is important that the well be completed in such a way as to minimize the production of sand. This is especiallytrue if an injection well is to be used for disposal of the water.A well producing just 10 ppm of sand, operating a total of1000 hr per year at 19 l/s (300 gpm) will produce 680 kg(1500 lbs) of sand. Sand production is best controlled by thecareful specification of the well completion. Water well con-struction specifications are available from several sources(Roscoe Moss Co, 1985; EPA, 1975; Rafferty, 1999) andshould be incorporated into the construction documents for theproject. Key portions of the specifications related to sand arethe screen slot size and gravel pack gradation. Both should bebased upon a sieve analysis of the cuttings from theproduction zone. Allowable sand content is normallyincorporated into the development portion of the specification. If it is not possible to complete the well in such a way as to limit sand production, some form of surface separatorwill be necessary. Open tanks are not acceptable for thispurpose. These tanks allow oxygen to enter the water andCO2 to evolve from the water. If ferrous iron is present in thewater, the addition of oxygen will alter it to a ferric statehaving much lower solubility. The result will be fouling ofthe heat exchanger. Evolution of CO2 will raise the water pHthus making calcium carbonate scale more likely. The mosteffective surface sand removal device is a strainer. Strainersassure that effective removal will be accomplished at any flowrate or condition. Centrifugal devices are generally notdesigned to achieve the very low sand contents required forthis type of application and they are subject to poorperformance at pump start up and shut down. WELL PUMPS Open loop systems typically use submersible type pumps equipped for the most part with nominal 3,600 rpmmotors. As a result, they are able to produce a higher flow perunit diameter than line shaft pumps which typically operate atspeeds of 1800 rpm or less. The higher speed of thesubmersible also results in a greater susceptibility to erosionif significant sand is produced from the well. Submersiblesare somewhat more sensitive to voltage variation than surfacemotors and adequate voltage (allowing for any drop in wiringto the well and down well) should be verified. Calculating the head for a well pump involves some different issues than a similar calculation for a circulatingpump. There are three main components to the total head: lift,surface losses and injection head. Lift is composed off thestatic water level plus the drawdown at the design rate. Itsname derives from the fact that this is the vertical distance thewater must be “lifted” by the pump to get it to the surface.Data to determine these values comes from the flow test of thewell serving the system (preferred) or from information onnearby wells. Also included in the lift is the friction loss inthe pump column (between the pump and the ground surface) 18which is usually on the order of 0.3 to 0.9 m (1 to 3 ft).Surface losses are those associated with the piping from thewell to the building, mechanical room piping and equipment(heat exchanger, etc.) and piping from the building to thedisposal point. Unless there are significant elevationconsiderations or distances involved, surface losses normallyamount to less than 15 m (40 ft) assuming a 35 kPa (5 psi) lossin the heat exchanger. The type of disposal can have animpact on the total pump head. In surface dischargeapplications, often a pressure sustaining valve is used tomaintain a small (less than 35 kPa [5 psi]) back pressure onthe system to keep it full of water. For injection, the impactmay result in added pump head (if a positive pressure isrequired at the surface) or reduced pump head (if the waterlevel in the well remains below ground surface). A shortdiscussion of injection well head considerations is presentedin Kavanaugh and Rafferty, 1997. Table 1 provides an idea ofthe variation of pump head with flow for a system. Table 1. Well Pump Head Example _____________________________________________________ Flow(L/s) Lift(m) Surface Losses(m) Injection(m) Total(m) 7.9 36.6 10.7 -7.0 40.3 9.5 39.0 12.8 -3.8 48.0 11.0 42.4 14.4 -0.6 56.2 12.6 43.6 7.9 2.5 54.0 14.2 46.1 8.2 5.7 60.0 15.8 48.8 8.5 8.9 66.2 17.4 51.9 9.2 12.1 73.2 18.9 54.3 9.5 15.3 79.1 _____________________________________________________ This example is based upon a confined aquifer with a 23 m (75 ft) static level, specific capacity of 0.62 L/s@m (3.0gpm/ft) a heat exchanger head loss of 70 kPa (10 psi) and 240m (800 ft) total equivalent length of pipe and fittings. It isapparent that the lift is the most significant single component.The drop in the surface losses is due to a pipe size change.Most unusual is the injection head which changes from anegative value (water level in the injection well below theground surface) to a positive value as the pressure builds withgreater injection flow rate. Overall, the total headapproximately linear with flow rate in this case. This ischaracteristic of well pumping applications and results fromthe heavy influence of the lift component. Key components in the connection of the production well to the system are illustrated in Figure 3. Not shown inthis diagram is a pump column check valve which would belocated at the base of the column near the bowl assembly. Thecheck valve maintains the column full of water and in doingso prevents damaging reverse thrust on start up. Submersiblemotors are equipped with a thrust bearing to resist the downthrust developed in normal operation. When starting with anempty column, a pump can exert a temporary up thrust on themotor which if encountered often enough can result inpremature failure of the motor. To prevent this submersiblesshould be equipped with a column check valve. GHC BULLETIN, MARCH 2001 Figure 3. Key connection components for a production well. Control of the well pump can be accomplished by numerous means. In the smallest systems (typically thosewithout an isolation heat exchanger), the water is pumped toa number of pressure tanks arranged in parallel and the wateradmitted to the system from the tanks. Due to the extensivetankage required to accommodate this approach it is notnormally employed in large systems. In these systems,typically one of three methods is employed: dual set-point,multiple-well (staged pumps), and variable-speed. The dual set-point approach is fairly common in systems with a single production well and is reminiscent of thecontrol used in water loop heat pump systems. Well pumpoperation is initiated above a given building loop returntemperature in the cooling mode and below a giventemperature in the heating mode. Between these twotemperatures, the loop “floats.” In actuality, the loop operatesnot between two temperatures but between two temperatureranges in order to adequately control cycling of the pump. For example, if the design indicated an optimum loop returntemperature of 26.7 oC (80oF) in the cooling mode, the pumpmight actually start at a loop temperature of 28.3oC (83oF) andstop at 25oC (77oF). A similar, though smaller, range wouldexist around the heating mode temperature. The size of therange required around the control temperatures is heavilyinfluenced by cycling limitations on the submersible motor(typically 15 min between starts) and the thermal mass of thebuilding loop. Table 2 presents some guidelines for selectionof the ranges based on the building loop thermal mass of thesystem as measured in gallons of water per peak block ton.This table is based on applications in which the cooling loadis the dominant load on the system. This method can result invery large controller range requirements when system thermalmass is less than 8 - 10 l/kW (7 - 9 gal/ton). For suchconditions, an alternate control method should be selected orsome mass added to the loop. Additional detail on this topicis presented in Rafferty, 2000, and in this Bulletin. Table 2. Controller Temperature Range for Dual Set Point Control oC (oF) ____________________________________________________________________________________________________ Motor kW (hp) System Thermal Mass - l/kW (gal/block ton) 2 4 6 8 10 12 14 COOLING MODE - oC (oF) RANGE <3.7kW(5hp) 16(28) 8(14) 5(9) 4(7) 3.3(6) 3(5) 2(4)>3.7kW(5hp) 31(56) 16(28) 11(19) 8(14) 6(11) 5(9) 4(8) HEATING MODE - oC (oF) RANGE <3.7kW(5hp) 9(16) 4(8) 3(5) 2(4) 2(3) 2(3) 1(1)>3.7kW(5hp) 18(32) 9(16) 6(11) 4(8) 3(6) 3(5) 3(5) ____________________________________________________________________________________________________ GHC BULLETIN, MARCH 2001 19 In systems in which multiple wells are required due to aquifer hydrology or redundancy, it is possible to employ astaged ground water pumping arrangement. This approachoffers somewhat greater control than the single well approachabove, but shares the same general approach. Since the pumpsare staged, the required controller ranges can be reduced andthe issue of system thermal mass is less influential. Variable-speed control of well pumps is the least common of the three strategies. One of the reasons for this isthat the primary purpose for using variable speed control,energy savings, is largely absent in well pump applications.Since a large portion of the well pump head is static head(“lift” described earlier) the nature of the relationship betweenflow and head is such that savings arising from the use of thedrive are substantially less than they would be in a frictionhead application. Variable-speed control does offer moreaccurate control, allows optimization of the groundwater flowat any load and eliminates any considerations of systemthermal mass. When using variable-speed, it is important torequire confirmation from the contractor that the motormanufacturer is aware that his product will be used in avariable-speed application. Issues of conductor length (driveto motor) drive switching frequency, critical speeds and motorcooling must be carefully coordinated with and approved bythe motor manufacturer to avoid operational problems. HEAT EXCHANGERS Open loop systems employ plate and frame type heat exchangers almost exclusively. These exchangers are key tothe reliability of the system since they protect the buildingloop from exposure to the groundwater. In most cases, thecost of the exchanger is on the order of $7 to $8.50 per kW($25 to $30 per ton)--a small price for the protection provided.Presence of the exchanger essentially eliminates water qualitylimitations to the use of open loop. The only common waterquality problem which should trigger consideration ofalternate design is iron bacteria. Issues of importance to thedesigner with respect to heat exchangers include pressuredrop, approach temperature, materials, and installation issues. In most commercial applications, the optimum design dictates a flow of 0.045 - 0.054 L/s@kW(2.5 to 3.0 gpm/ton) onthe building loop side of the exchanger and 0.018 - 0.045 L/s@kW(1 to 2.5 gpm/ton) on the groundwater side. As a result ofthis, the approach or minimum temperature difference betweenthe two flows occurs at the building loop return (heat pumpleaving water) and groundwater leaving end of the exchanger.Selecting the approach value is a trade off between operatingcosts (lower at low approach temperature) and heat exchangercapital cost (higher at lower approach). Dropping from an4.4oC (8oF) to a 1.6oC (3oF) approach will normally gainapproximately one full point in system EER. Due to the muchflatter performance in the heating mode relative to EWT, thegain in heating mode performance for the added heatexchanger are amounts to approximately 1/3 of this value. Asa result, the selection of heat exchanger approach is largely afunction of annual system operating hours. The greater theoperating time of the system, the easier it is to justify added 20exchanger area to achieve lower operating cost. For normaloccupancy offices and schools, a 2.2oC to 3.3oC (4 to 6oF)approach is often the most economical. Pressure drop selection is also a trade-of between operating cost and capital cost. Higher pressure drop in aplate exchanger results in higher overall heat transfercoefficient (“U”) and lower transfer area (cost) for the sameduty. The higher pressure drop however translates into pumphead and operating cost. In open loop systems, the higherpressure drop is normally on the building loop side due to thehigher flow rate. For systems involving a constant speedpump on the building side, a pressure drop of no greater than35 kPa (5 psi) on the building side, should be specified. Forsystems using variable-speed on the building side, a pressuredrop of no greater than 70 kPa (10 psi) should be used. Materials considerations for plate heat exchangers are rarely a major issue. Most manufacturers offer 304 or 316stainless steel as the base material for the plates and Buna-N(medium nitrile rubber) as the gasket material all of which aregenerally suitable for groundwater applications. Inapplications in which the groundwater contains more than 150ppm chloride, 316 plates should be used in place of 304. Forchloride concentrations greater than 375 ppm (a very rareoccurrence), titanium plates should be specified. Pipingconnections and placement of plate exchangers should beconfigured in such a way as to allow easy access fordisassembly and cleaning. If piping connections are requiredon the movable end plate, the piping should be of flanged orgrooved end material to permit easy disassembly. It isgenerally not necessary to specify a two heat exchangerinstallation. Exchangers can normally be disassembled,cleaned and reassembled in a single shift. Contractors shouldbe required to furnish at least one spare plate for each type ofplate in the exchanger (usually at least two types of plates).Gaskets for the plates should be provided as well and glued inplace (if of the “glue in” type). DISPOSAL There are two basic options for water disposal from an open loop system: surface and injection. Both options aresubject to regulatory oversight and permitting. Surfacedisposal the most common method used in the past is lessexpensive, but requires that the receiving body be capable ofaccepting the water over a long period. Injection is morecomplex and costly but offers the certainty that thegroundwater aquifer will not be adversely affected (aquiferdecline) by the operation of the system over the long termsince the water is “recycled.” For surface disposal, it may be advisable to place a pressure sustaining valve on the end of the system to maintainthe piping full when the pump is not operating. Somedesigners prefer to simply place a motorized valve at this pointin the system and interlock it with the pump (through an endswitch). Distance from the building has some influence on thestrategy used as the motorized valve requires a control signaland power source and the pilot-operated valve does not. GHC BULLETIN, MARCH 2001 Spacing Requirement - m250 200 150 100 50 0 0 5 10 15 20 25 30 System Average Flow Rate - L/s Aquifer Thickness -612243035 notes: plotbased on aquiferporosity of 20%.For 10%multiply spacingFigure 4. Well spacing requirements - minimum (from Kazmann and Whitehead data). Injection is a more mysterious strategy to most mechanical engineers. Key issues are well design and wellspacing. In theory, the only difference between an productionand an injection well is the direction of flow. In practice,there are some differences in the design depending upon thetype of aquifer penetrated. For wells completed inunconsolidated materials, and equipped with a screen, thescreen area should be twice that used in the production well.The rule of thumb for injection wells is that the entrancevelocity of the water through the screen openings (slots)should be limited to 0.015 m/s (0.05 ft/sec); whereas,production wells are normally based upon 0.030 m/s (0.1ft/sec). This does not mean that a larger diameter well isrequired in all cases. The reduced velocity could also beaccomplished by screening more of the aquifer, particularlyin the case of wells penetrating water table aquifers. For wellscompleted in fractured rock and completed “open hole,” thereis often no difference between the injection and productionwell design. Sealing is an important issue in injection wells.Because it is likely that the water level in the well will behigher than the static water level when in operation, it isimportant that the seal (grout placed between the borehole andthe outside of the casing) be carefully placed and that itextends from the top of the aquifer to the ground surface.This prevents the injected water from finding a path up aroundthe outside of the casing to the surface. Well spacing, or the distance required between the production and injection wells is an important consideration.It is not necessary that the injection well be sited in such a wayas to prevent any flow from the injection to the productionwell, just that any inter-well flow be sufficiently low that itarrives at the production well at a temperature close to theGHC BULLETIN, MARCH 2001 aquifer temperature. For unconsolidated aquifers, the methoddeveloped by Kazmann and Whitehead provides a guidelinefor minimum spacing. In order to use the method, it isnecessary to know the aquifer thickness, porosity, systemaverage flow rate and the period of duration (days) of thedominant load. The method is covered in detail in Kavanaughand Rafferty, 1997. A summary of spacing informationappears in Figure 4. Connection of the system piping to the injection well is illustrated in Figure 5. Of particular importance is theinjection “dip tube” in the well. Injected fluid should alwaysbe released below the static water level in the well so as tominimize the formation of air bubbles. Bubbles entering theinjection zone can impede water flow just as an accumulationof particulate would. The air release valve also helps tominimize the air in the injection well. This component isespecially important in systems which cycle the well pump. Ameans of diverting the water flow in the event that the wellmust be removed from service allows the system to continueoperation with temporary surface disposal. Finally, theprovision for pressure (or water level) monitoring is importantin injection wells as a means of monitoring the performanceof the well and any accumulation of particulate in the injectioninterval. There is a perception that injection wells often fail. This is false. In fact, the failure is normally that of thedesigner not the well. Poor production well performance interms of sand content coupled with the lack of a surfaceremoval system inevitably means that this material will bedeposited in the injection well. Successful injection requiresclean, particle free fluid. The system must be designed withthis as the goal. 21 DESIGN PROCEDURE Figure 6 provides a summary of a spreadsheet developed to design open loop systems. This spreadsheet wasdeveloped in English units and no SI version is available.The spreadsheet illustrates the information necessary toaccurately design an open loop system. Unshaded values areinput and shaded values are output. In general, all of theinformation concerning the well or wells would be availablefrom the driller’s completion report and/or the flow testresults. With the exception of the groundwater temperature,all of the values are used primarily for the calculation of wellpump power. Such items as the static water level, specificcapacity (entered only for confined aquifers), flow anddrawdown (entered only for unconfined aquifers) and aquiferthickness (used in the determination of well spacing) are allcharacteristics of the aquifer itself and although necessary asinputs, they are not “adjustable” by the designer. The finaltwo well related inputs indicate whether or not an injectionwell will be used and if so, what the injection efficiency isexpected to be. Injection efficiency is a value used to adjustthe drawdown (from the flow test) to calculate the expectedpressure buildup at the injection well for the same flow. It isused in the calculation of the well pump head. Building loop related inputs include the building block cooling and heating loads (expressed as space loads),the pressure drop for which the heat exchanger will beselected, surface head losses for the groundwater loop (piping,heat exchanger, fittings etc), heat exchanger approach(between groundwater leaving and building loop entering),building loop flow rate and head loss, heat pump brand (tocalculate COP, EER), and system water volume (to calculateloop thermal mass and well pump control set points). The table in the lower portion of the figure indicates the calculations for the cooling mode. The spreadsheetcalculates heat pump performance at a series of entering watertemperatures (EWT’s), and using the performance and EWT,calculates a series of LWT’s. Using the LWT value (assumedto be equal to the building loop heat exchanger entering EWT LWT35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65 temperature), and the specified heat exchanger approach aground water heat exchanger LWT is calculated. Using theload information and the groundwater temperature rise, thegroundwater flow is calculated. With the input data on thewell performance, the head on the well pump at each of theflows is calculated and from this, pump horsepower and kWare determined. Combining the well pump power, loop pumppower and heat pump power, the final calculation is thesystem EER. A similar calculation is made for the heatingmode (Figure 7). The spreadsheet is configured to look at the cooling load as the primary load and it selects the peak EER valuefrom the table and displays it along with the groundwater flowin the output section. This is the flow rate for which the wellpump would be selected. Well pump design information islocated just below the cooling mode output. Shown are theflow rate and head for which the pump would be selectedalong with the setting depth for the bowl assembly (depth atwhich the pump suction should be located). Heat exchangerdata includes the cooling mode entering and leavingtemperatures at the peak condition along with calculatedsurface area requirements in the heating and cooling modes.These surface area values are not intended to be specified tothe vendor but are used to give the designer an indication ofwhich mode (heating or cooling) is dominant in the systemdesign. If an injection well was specified in the input, thespreadsheet, using the aquifer thickness and flow rate,calculates a separation distance requirement for the productionand injection wells. Based on the flow test drawdown orspecific capacity and the injection well efficiency specified,the spreadsheet calculates the injection well pressure (at theground surface) at peak flow. Peak heating mode performance values are displayed in the next column. All values shown are based on anassumed heat exchanger approach as specified in the input. Inmost cases, the heat exchanger area required for coolingexceeds that for heating. As a result, the system will operateat more favorable temperature than that which is indicated in GW headGW kWSYS COP 136.1 2.20 3.35 138.2 2.42 3.40 140.6 2.69 3.44 143.4 3.02 3.48 146.8 3.42 3.51 151.0 3.94 3.54 156.2 4.62 3.56 162.9 5.56 3.56 172.0 6.91 3.55 184.8 9.01 3.49 204.3 12.64 3.37 237.7 20.03 3.12 308.2 40.53 2.53 262.0 77.55 0.00 -1718.8 2108.74 0.00 -187.8 37.74 0.00 h/p COPLWT GWGW Flo 28.8 3.68 32.8 48.3 30.8 3.75 34.8 52.4 32.8 3.81 36.8 57.1 34.7 3.88 38.7 62.8 36.7 3.94 40.7 69.6 38.7 4.01 42.7 77.9 40.6 4.08 44.6 88.3 42.6 4.14 46.6 101.8 44.6 4.21 48.6 119.9 46.5 4.27 50.5 145.5 48.5 4.34 52.5 184.6 50.5 4.41 54.5 251.5 52.4 4.47 56.4 392.4 54.4 4.54 58.4 883.4 56.4 4.60 60.4 -3661.6 58.4 4.67 62.4 -599.7 Figure 7. Calculations for the heating mode (from Figure 6). GHC BULLETIN, MARCH 2001 23 this column. The spreadsheet includes a heat exchangeranalysis module to make this evaluation. For convenience, the performance of a vertical closed loop system using the same heat pumps and designed for 11o C (20 oF) above the undisturbed soil temperature is displayedin the output to provide the designer with a comparisonsystem. Finally, set point temperature for the well pump in the heating and cooling modes are displayed based on thesystem volume specified in the input. These temperatureassume the use of a single production well with a single speedpump. 4 3.9 hP3.8 OC -3.7 ecn3.6 amro3.5 freP3.4 me3.3 tsyS3.2 3.1 3 3 4 5 6 7 8 Ground Water Flow - L/sFigure 8. Heating performance. Graphs of the heating and cooling mode performance are shown in Figures 8 and 9. These provide a clearerindication of the systems performance in the different modesand permits the designer to evaluate the impact at operation atother than the peak performance selected by the spreadsheet.CONCLUSION Open loop systems can offer the owner performance comparable or in some cases better than that of closed loopsystems. Despite their long history of use and perceivedsimplicity, care is required in the design and installation inorder that the ful potential of the systems be achieved. Someimportant guidelines along with a useful design tool areillustrated in this paper. The following “10 Commandments”of open loop design will help to keep the designer on track toa reliable and efficient system: THINK SYSTEM - well pump, heat pumps, loop pumps PUMP LESS WATER - reasonable loop and groundwater flowsKNOW THE LOAD - design for block load not installed capacityKNOW THE AQUIFER - static level, specific capacity, drawdown,flow test KNOW THE RULES - verify groundwater regulatory issues DO YOUR HOMEWORK - previous groundwater experience inthe area, other wells KNOW THE GROUND WATER - complete chemistry test if useddirectly KEEP THE AIR OUT - no open tanks ISOLATE THE GROUND WATER - use a plate heat exchangerKNOW YOUR LIMITATIONS - in complex settings use ahydrogeologist 244 3.8 cPO3.6 C metsy3.4 S3.2 3 7.5 10 12.5 15 17.5 Ground Water Flow - L/sFigure 9. Cooling performance. REFERENCES EPA, 1975. Manual of Water Well Construction Practices(EPA570/9–75-001), U.S. Environmental ProtectionAgency, Office of Water Supply. Rafferty, K., 1999. “Outline Specifications for Direct-Use Wells and Equipment.” Geo-Heat Center, KlamathFalls, OR.Rafferty, K., 2000. “Dual Set Point Control for Open Loop GSHP Systems.” Draft ASHRAE Transactions, Vol107, Part 1, ASHRAE, Atlanta GA .Kavanaugh, S. and K. Rafferty, 1997. “Ground-Source Heat Pumps: Design of Geothermal Systems forCommercial and Institutional Buildings.” ASHRAE,Atlanta ,GA.Roscoe Moss Company, 1985. The Engineers Manual forWater Well Design, Roscoe Moss Company, LosAngeles, CA. GHC BULLETIN, MARCH 2001 SPECIFICATION OF WATER WELLS Kevin RaffertyGeo-Heat Center ABSTRACT The water well or wells serving a Ground-Water Heat Pump (GWHP) system are as pivotal part of the mechanicaldesign as the boiler and cooling tower would be in a waterloop system. As such they should warrant the same degree ofattention with respect to specification as the moreconventional components would receive. Unfortunately, thisis rarely the case and the HVAC design engineers lack offamiliarity with the topic is sometimes at fault. This paper isintended to identify the key sections of water wellspecifications and briefly discuss their contents. INTRODUCTION Design and construction of water wells is a topic unfamiliar to many, if not most mechanical engineers. As aresult, the task is often poorly handled or worse, ignored. Thisrarely results in a well completed in the best interests of theowner. Although the HVAC engineer may not always bedirectly responsible for the design of the well, it’sspecification or construction management, it is, in the contextof a ground-source heat pump system, a critical part of themechanical design. Consequently, it is in the interest of theHVAC design engineer to become familiar with theterminology of water wells and the key specification issuesrelating to their construction. The goal of this paper is not toprovide suggested specification text but to briefly discuss thekey sections found in a well specification document andcomment on the contents of each. WATER WELL TYPES The design of a water well and the preparation of the construction documents related to it is a function of severalissues including the purpose (domestic, municipal, irrigation,injection, etc.), capacity (low <10 gpm [0.6 L/s], medium 10 -100 gpm [0.6 - 6.0 L/s], high >100 gpm [>6.0 L/s]), geologypenetrated (consolidated, unconsolidated, combination) andconstruction method (mud rotary, air rotary, reversecirculation, cable tool) (NWWA, 1975). Since this paper islimited to wells serving commercial GWHP systems (normallymedium to high capacity, rotary constructed), the primaryinfluence on design and specification is the nature of thegeology penetrated in the process of construction. Although, there are an infinite number of well construction designs for a substantial part of the country, thealternatives can be reduced to some variation on one of thetwo basic designs as shown in Figures 1 and 2. Specialmodifications to these basic designs can be made toaccommodate conditions such as artesian aquifers, injectionrather than production, corrosive water etc. The simplest wellis one completed in rock formations in which the water isproduced from fractures in the rock. In these wells,sometimes called open-hole completions due to the nature ofGHC BULLETIN, MARCH 2001 the geology, no casing or screen is necessary to stabilize andfilter the aquifer materials adjacent to the well bore. Casingis normally placed in the upper portion of the well for a shortdistance to accommodate the installation of a surface seal. Figure 1. Open-hole well completion. Surface Casing Grout Surface Seal CasingShoePump Housing Gravel Envelope Casing Packer Production Zone(unconsolidated materialsScreen Figure 2. Gravel envelope well. 25 For a well completed in a consolidated formation (rock), the sections on screen, gravel and sometimesdevelopment can be eliminated. SCOPE OF WORK This is the section in which a general description of the work is provided. The scope at a minimum, includes thetype of drilling rig to be used, approximate depth and numberof wells along with the expected yield for production wells.When available, the scope may also provide additional detailon the general construction of the well in terms of casing size,depth, screen type diameter, location and developmentmethod. If a performance guarantee with respect to yield, orspecific capacity is required, this is also included in the scopesection (Roscoe Moss, 1985). NON-TECHNICAL WELL ISSUES Non-technical well issues (a phrase used in this paper and not in the specification document) include items notdirectly related to the technical details of construction.Contractor qualifications, site description, noise control,archeological discovery and facilities provided by owner arenormally covered as individual sections, but are groupedtogether here for simplicity. The contractor qualifications paragraph normally includes a minimum experience requirement (number of wellssimilar to the current project, and years in business) and alicensing requirement. Details for a list of reference projectsmay also be spelled out. The site description is especiallyimportant, particularly if potential drillers are from outside thearea. A physical description of the site is provided along withbackground on the geology/hydrogeology. If available, wellcompletion reports from nearby wells are a key part of thisinformation. Noise is normally addressed through thespecification of acceptable operating hours for drillingoperations. Facilities provided by the owner is one of the fewspecification issues actually requested bycontractors–particularly in the case of site access and wateravailability. Sufficient water supply for the drilling operationis a critical issue. EQUIPMENT REQUIREMENTS In this section, either a specification is made with respect to the drilling rig capabilities required and/or a form isprovided on which the contractor must submit a descriptionthe equipment to be used in the construction of the well. Incases of shallow wells, such issues as mast, hook and draw-works load limits are not often approached even for small rigs.As a result, it is possible to omit this section in some smallprojects. DRILLING FLUID This is a section that relates primarily to conventional (direct) rotary drilling operations. In this section, anacceptable value (or range of values) for key drilling fluid(sometimes called “mud”) parameters is provided. Thedrilling fluid or mud is circulated down the rotating drill pipe,out the bit and back up the annular space between the boreholeGHC BULLETIN, MARCH 2001 wall and the drill pipe. It serves to lubricate and cool the bit,carry away the cuttings and form a “cake” stabilizing theborehole walls. Included are such characteristics as weight(11 lbs/gal maximum), marsh funnel viscosity (32-38 secondsmaximum), 30-minute water loss (15 cc maximum), filter cakeformation (2/32\" [1.6 mm] maximum) and sand content (2%maximum). It should be understood that fluid parameters areregularly adjusted in the course of drilling to accommodatesituations encountered in the construction process. In somefluid specifications, reference is made to a requirement for adrilling mud engineer’s involvement in the project. On smallprojects, these services are usually available to the drillingcontractor from the mud vendor and the specification of a mudengineer’s availability to the contractor rather than his on sitepresence is appropriate. DRILLING PROGRAM SUBMITTAL This section provides the requirements for submission, by the contractor, of a schedule of tasks to becompleted in the process of completing the well. Included arepersonnel, schedule of tasks (drilling, casing, screen gravelinstallation, development), and details of the drilling fluidmake-up (additives) (Roscoe Moss Company, 1985)FORMATION SAMPLING Formation sampling, described in this section is a pivotal part of the well drilling process. It is the samplesfrom the production zone of the well from which decisions aremade as to the screen slot size and gravel pack gradationnecessary for completion. In rotary drilled wells, if a pilotbore is used, the samples are taken as the pilot holeprogresses. If the approximate depth of the producing zoneis known, it is normal practice to specify a regular intervalover which samples will be taken, the handling, appropriatecontainers and labeling of the samples along with theindividual (or organization) to whom they should be delivered.Sieve analysis of these samples provides the data upon whichscreen slot size and gravel pack size distribution are based.This consists of passing the samples through a set ofprogressively finer sieves or screens to determine the sizedistribution of the sampled material. LOGS/RECORDS Depending on the depth, drilling method and purpose for the well, a variety of logs and reports may be specified inthis section. For wells of the type used for GSHP systems, itis normally sufficient to specify that the driller report on thedepth and physical description of strata penetrated, depth ofwater producing intervals, and associated static water levelsand penetration rates accomplished. If well completionreports are required by regulatory agencies, copies should beprovided to the owner/engineer as well. Reporting require-ments for flow testing, development and plumbness/alignmentare covered in those respective sections. PLUMBNESS/ALIGNMENT Plumbness (deviation from the vertical) and alignment (“straightness”) of the well are issues of importance 27 with respect to the installation of a pump in the well. Inparticular, lineshaft type pumps are much more sensitive to thealignment issue than are submersible pumps. With a rotatingshaft extending from the surface to the pump (sometimeshundreds of feet down in the well), wells in which lineshaftpumps are to be installed must be held to tighter tolerancesthan submersible installations. Two approaches can be takento this specification. For small projects using a submersiblepump, the required test often involves a 40 ft (12 m) sectionof pipe ½\"(12 mm) smaller in diameter than the inside of thecasing, which must be capable of passing freely through to thebottom of the pump housing casing. For larger wells or thoseusing lineshaft pumps, a more sophisticated test involving adevice for measuring deviation of the bore is necessary.CASING Casing is a term that refers to tubular material extending from the surface to some depth in the well. It isinstalled to accommodate the sealing of the well, to stabilizethe walls of the borehole or to allow the installation of screenor liner (tubular products not extending to the surface). Inshallow wells of the type serving GWHP systems, at least twotypes of casing are often found. Surface casing is installed ashort distance (to the first impermeable strata or minimum of18 ft [6 m] by many codes) from the surface to a depthsufficient to allow the installation of the surface seal (usuallycement grout) between the surface casing and the wellbore.The surface casing also helps to support near surfaceunconsolidated materials during the drilling operation.Sometimes, this surface casing is removed as the grout isplaced. The second casing type is the pump housing casing which as the name implies is the casing in which the pump isinstalled. This casing is installed inside the surface casing,from the surface to the top of the screen in gravel pack wellsor to the top of the producing interval in shallow open holewells. If used, the screen would be attached to the bottom ofthe pump housing casing. In the casing portion of the specification, information is provided on the size, wall thickness, material, andinstallation method of the casing along with the location(depth), in some cases. Surface casing is normally at least twoinches larger than the pump housing casing in order toaccommodate the placement of the grout to an adequatethickness. Diameter of the pump housing casing is a functionof the pump to be paced in the well. Generally, it is desirableto have a pump housing casing of two nominal sizes largerthan the pump to be installed. Pump bowl (impeller housing)diameter is related to pump type and flow rate. Submersiblepumps, which typically operate at 3600 rpm, produce moreflow per unit diameter than lineshaft pumps which operate at1800 rpm or less. In most commercial applications, aminimum of 6\"(150 mm) casing would be used with 8\" (200mm) for flows >100 gpm (6 L/s) and 10\"(250 mm) for flows>300 gpm (18 L/s)(Kavanaugh and Rafferty, 1997). Casingwall thickness is normally specified in this section. Wallthickness requirements vary with drilling method, depth, 28diameter and seal placement. In general for sizes up to 14\"(350 mm) and depths to 600 ft (180 m), 0.250\"(6 mm) wallthickness is acceptable (AWWA, 1997). Most wells servingcommercial applications use carbon steel well casing. Plasticmaterials can be used in very shallow applications permit.Detailed specifications are available on the placement of thecasing; however, drilling method (rig type) largely determinesthe techniques used and in many cases, this issue simply addsneedless detail to the well specification. SCREEN The screen plays a critical role in the performance of the well since it provides the filtering of the water entering thewell. In this section, the type of screen, aperture size,diameter, length, entrance velocity, and material of the screenis described along with the installation method. Thedetermination of aperture (slot) size is made based on theresults of a sieve analysis of the drill cutting samples from theproduction interval of the well. On occasion, when sufficientinformation is available, the screen can be specified based onthe performance of existing wells in the same aquifer. For thisto be an effective strategy, detailed knowledge of the geologymust be available. In applications where no gravel pack willbe used, the screen slot size is specified as that which willretain 30 to 50% of the aquifer materials depending on thecorrosiveness of the water and the uniformity coefficient ofthe aquifer materials. In applications where a gravel pack willbe used, the slot size is selected for retainage of 70 to 100% ofthe gravel pack materials (AWWA, 1997). All slot sizeselections are based on the aquifer materials sieve analysisdistribution curve. The specification can allow the contractorto have a lab do the analysis with the results delivered to theowner/engineer for approval or the samples can be delivereddirectly to the owner/engineer for analysis. There are several types of screens available and two of the most common are wire wound and louvered. Wirewound screens (continuous slot) provide a higher degree ofopen area, through which the water can pass (a critical issuein fine sand aquifers), are generally more expensive than othertypes and in larger diameters are lower in collapse strength.Louvered screens are generally less expensive, have highercollapse strength, lower open area and provide for moreeffective development using swabbing. Entrance velocityspecification influences the type of screen. In manyreferences (some written by a major manufacturer of wirewound screen), an entrance velocity limit of 0.1 ft/sec (0.03m/s) is cited. This low velocity tends to require the use ofscreens with high open area ratios (wire wound). Otherresearch suggests that entrance velocities of as much as anorder of magnitude greater than this do not significantlyreduce well performance in many applications. Wire woundscreens are normally constructed of 304 stainless steel toreduce corrosion problems. Louvered screens can be ofcarbon steel in many applications due to their higher strength. Placement of the screen, like the placement of the casing is best left to the contractor; since, it is determined toa large extent by drilling method. GHC BULLETIN, MARCH 2001 GRAVEL Gravel is sometimes placed outside the screen to support the aquifer materials (called formation stabilizer) or toincrease near bore permeability and to assist in filteringaquifer materials (called artificial filter). Regardless offunction, the common term for the practice is gravel pack.The importance of the selection of the size distribution of thegravel material is much greater when it is intended to serve asan artificial filter. Issues to be addressed are size, gradation(uniformity coefficient), geology, thickness and placement. As in the case of the screen slot size selection, the determination of the gravel pack parameters is based on thecuttings sieve analysis results. One common criteria for thegravel pack specifies that it have a 70% retained grain size of4 to 6 times the 70% grain size of the cuttings sample and auniformity coefficient (40% size divided by 90% size) of notgreater than 2.5 (NWWA, 1975). Gravel material should beclean and well rounded with a maximum of 10% flat surfacesand should be a minimum of 95% siliceous in content (toavoid dissolution in low pH water). The thickness of the gravel pack should be between 3 and 8\" (75 and 200 mm) thickness. Placement of the gravelis generally accomplished by either pouring from the surface(in shallow wells) or by placement through a tremie (in wellsof greater than 1000 ft depth [300 m])(Roscoe MossCompany, 1985). In most shallow wells of the type servingGWHP systems, the pack material will be poured from thesurface. This is done while circulating drilling fluid down thedrill pipe and up the annular space (between the casing and thebore wall). A key part of the specification is the requirementto maintain drill fluid density below a specific density limit(9.1 lb/gal). The fluid tends to pick up drilling mud from thewalls of the borehole as the gravel is placed. The viscositylimit requires this material to be continuously removed duringthe process. The gravel placement should be completed in onecontinuous operation. DEVELOPMENT The process of development is one in which the fines in the aquifer material or gravel pack and any remainingdrilling fluids in the near bore area are removed by a varietyof methods. The development process is divided into twophases--initial development using the drilling rig and finaldevelopment by pumping after the rig has been removed. Tosome extent, the type of development is influenced by thegeology and well type. Specifications describe the type ofdevelopment, when it should be terminated and mostimportantly in the final development, what the acceptable sandproduction for the well is. In gravel pack wells, preliminary development is often by the so called “flushing” method using a tool knownas a “double swab” which can be accomplished with the rotaryrig. A more effective method known as line swabbingrequires the use of a cable tool rig. Both of these methods arebest applied with louver type screens. Jetting is a develop-ment technique often used most effectively with wire woundscreens and it involves directing high velocity water jets at the GHC BULLETIN, MARCH 2001screen/gravel pack. Air lift pumping and sand pumping (usedin naturally developed wells) are other methods ofdevelopment. Preliminary development is carried on until all of the fines and sediment have been removed from the gravel packand the pack ceases to settle. Final development is carried onuntil the specified sand content of the production water isreached. This limit is typically expressed as a sand content inppm after some period of pumping. Water samples forchemical analysis can be taken toward the end of thepreliminary development or during final developmentpumping. WATER SAMPLES Water samples for the purpose of analysis for system design (corrosion and scaling) should be taken during thedevelopment pumping. The specification describes the size ofthe sample and the type of container in which it will be stored(normally a container supplied by the lab doing the analysis)and when the sample should be taken (after 1 hr of pumpoperation). Finally, the chemical constituents to be tested forare listed. All major anions and cations along with alkalinity,total hardness, carbon dioxide, hydrogen sulphide and oxygenshould be included. FLOW TESTING Flow testing of the well provides important data for the design of the heat pump system, since the groundwaterflow rate chosen is based on pumping power (flow anddrawdown). There are several types of flow tests which can bedone on a production well. In many cases, a step drawdowntest is done for wells serving GWHP systems. In this test, thewell is pumped at three rates until water level has stabilized.The specification describes the flow rates, instrumentation (forwater level and flow data), frequency of readings, length oftest and facilities for disposal of the water. This so-calledsingle well test provides information primarily on the wellitself (yield, drawdown, and specific capacity). A moresophisticated test in which nearby wells are monitored,provides information on the aquifer. These tests are rarelydone for GWHP systems. Generally, the flows chosen approximate 1/3, 2/3 and full design flow anticipated for the system served. Startingwith the lowest flow the pump is operated at constant rateuntil the water level in the well has stabilized at which timethe flow is increased to the next rate. Water level is typicallymeasured with an electric continuity device on the end of acalibrated spool of wire. Flow is measured with an orificeplate discharging to atmosphere and pressure across the platemonitored with a manometer. Flow tests are often sub-contracted to a well pump contracting firm. Some jurisdictions require that any well penetrating a potential drinking water aquifer be sterilized. The paragraphrelating to sterilization describes methods, chemical concen-tration and length of the sterilization procedure whichnormally consists of chlorine treatment. 29 ABANDONMENT In the event that the well is unsuccessful and cannot be used for the intended purpose, it must be abandonedaccording to the requirements of the regulatory agencyresponsible for water wells. Most states have very specificregulations covering abandonment which typically requirefilling the well with an impermeable material--often cementgrout. It is not necessary to cover these procedures in detail.Referencing the appropriate state administrative rule willsuffice. INJECTION WELL ISSUES Injection wells, used for disposal of the water after passing through the heat pump system, differ from productionwells in several ways. Two of the more important are screendesign and seal placement. Most references recommend awater velocity through the screen of one half that used in theproduction well. It appears that this guideline is primarilyrelated to the allowance for plugging of the injection screenwith particulate carried into the well with the water. From thiscomes the widely held perception that the injection wellshould be a larger diameter than the production well. This isnot the case. The reduced screen velocity can be achieved byscreening more of the aquifer since production wells in watertable aquifers normally screen only the lower ½ to 1/3 of theaquifer. Beyond this, the need for the additional screen areaassumes the presence of particulate in the injected fluid. If theproduction well is sand-free or if a surface strainer is used tominimize sand, the additional screen may not be necessary. Sealing of an injection well should be done in much the same way as a production well penetrating an artesianaquifer. The reason for this is that in the course of the opera-tion of the well, the pressure exerted on it is greater than thenatural pressure of the aquifer it penetrates. As a result, thereis a tendency for water to migrate up around the casing towardthe surface. If the well is exposed to a positive pressure at theground surface, the potential exists for water to leak outaround the casing at the surface. To prevent this, injectionwells should be sealed from just above the injection zone, con-tinuously to the surface with a minimum 2\" (50 mm) annular(between the casing and the wellbore wall) cement seal. 30The injection stream should be introduced into the well using an injection tube terminating below the watersurface. This prevents the injected water from cascadingdown from the well head and generating air bubbles in theprocess. Bubbles driven out into the aquifer can act as anobstruction to water flow in much the same fashion asparticulate matter. SPECIFICATION TEXT The goal of this paper has been to identify the key sections necessary in the specification document for a waterwell and to comment on the general contents. Actual guidespecification text has been published by many others (RoscoeMoss Company, 1985; AWWA, 1997; EPA, 1975, MontanaWater Well Drillers Assoc, 1970). In many cases, thesereferences are published in the form of guidelines for thespecification of water wells in which explanatory paragraphsare included ahead of actual specification sections. Editingis normally required to use these sources in constructiondocuments. REFERENCES American Water Works Association, 1997. ANSI/AWWA A 100-97 Standard for Water Wells, American WaterWorks Association, Denver, CO.Environmental Protection Agency, 1975. Manual of WaterWell Construction Practices EPA 570/9-75-001, U.S.Environmental Protection Agency, Water SupplyDivision, Washington, DC.Montana Water Well Drillers Association, 1970. Recom-mended Standards for Preparation of WaterWell Construction Specifications, Montana WaterWell Drillers Association, Helena, MT.Kavanaugh, S and K. Rafferty, 1997. Ground-Source HeatPumps: Design of Geothermal Systems for Com-mercial Buildings, American Society of Heating,Refrigeration and Air Conditioning Engineers.Roscoe Moss Company, 1985. The Engineers Manual forWater Well Design, Roscoe Moss Company, LosAngeles, CA. GHC BULLETIN, MARCH 2001 A GUIDE TO ON-LINE GEOLOGICAL INFORMATION AND PUBLICATIONS FOR USE IN GSHP SITE CHARACTERIZATION Kevin RaffertyGeo-Heat Center ABSTRACT The ground-source heat pump industry has historically failed to take full advantage of the publicinformation sources available for site characterization.Virtually every state and province in North America maintainsa website (or sites) dedicated to either groundwater or geologyor both. These sites vary greatly in terms of the informationavailable, but in many cases, offer a wealth of data useful inthe characterization of site geology and hydrology. Sites aretypically maintained by federal and state geological surveysand water resources agencies. Information may include various types of geological maps, publications, databases, water well completion reports,comprehensive reports on water and geology, and monitoringwell water level data. From these sources, it is possible todetermine site geology, depth to bed rock, water levels aquiferpresence or absence, aquifer type, well yields, ground andgroundwater temperatures, well design data, drilling rig typeswhich have worked successfully in the area, and a host ofother useful information. This paper outlines the types of dataavailable, provides a tutorial on reading water well completionreports, and lists websites URLs for sites in the 12 most activeGSHP states. INTRODUCTION One of the first steps in the consideration of a GSHP system is a characterization of the site in terms of geology andgroundwater availability. Information concerning aquifer (oraquifers) available at the site, their ability to produce water,depth to water, geology, depth to bedrock and the nature of thesoil and rock (hydraulic and thermal properties) are key issues.This information guides the designer in the selection of thetype of GSHP system to be used and in the design of thesystem. The ground-source industry has not taken full advantage of available geological information resources in thepast. This document is an effort to introduce GSHP designersto some of these information sources and the nature of the datathat is available. A special emphasis has been placed onInternet based resources operated by government agencies--primarily the USGS and state geological surveys. Thefollowing section provides some background information onthe maps and other information sources in general. This isfollowed by summaries of information available for the mostactive GSHP states. GHC BULLETIN, MARCH 2001GEOLOGICAL TERMINOLOGY One of the hurdles engineers encounter in the process of consulting references such as those referenced below is theterminology used in the field of geology. Contributing to theconfusion is the fact that geology is something of a mixbetween science and history. Publications and maps oftenrefer to materials not by their physical characteristics (theissue we as GSHP professionals are interested in) but by theperiod in the earth’s history in which the material wasdeposited. For geologists, with a background in the scienceand a familiarity with the geographical area, the age of thematerial carries with it a rough idea of the physicalcharacteristics. For engineers or those lacking thisbackground, more information is required. To a large extent,there is no simple solution to this other than experience inreading and interpreting geological maps and data, but thereare some useful references on the Internet to assistus in translating geology-speak into something we canunderstand. The Kentucky Geology Survey’s web site(http://www.ky.edu/KGS/home.htm) has a comprehensiveglossary of geological terms. The Indiana GeologicalSurvey’s website (http://adamite.igs.indiana.edu/index.htm)has a good summary of geological time with a chart anda brief explanation. It is useful to have these sitesbook marked for future reference. An extensive glossaryof aquifer and hydrology terms is available on theKansas State Geological Survey’s site at:http://www.kgs.ukans.edu/highplains/atlas/glossary/htm.KEY REFERENCES USGS Groundwater Atlas of the United Stateshttp://sr6capp.er.usgs.gov/gwa/gwa.html This document may be the best regional scale (many figures readable to +/- 1 mile), groundwater and geologicalreference available. It is published in 13 volumes eachcovering a multi-state region of the country. It providesdetailed descriptions of aquifer locations and physicalcharacteristics, water quality, geology, physiography, crosssections and a host of data useful for both open loop andclosed loop site characterization. All 13 volumes areaccessible through the web site with full text and colorillustrations and maps. They are also available as a hard copypublication. This is a document that answers the questions:Is there an aquifer accessible at the site suitable for an openloop system? What is the general geology of the site? 31 Water Well Completion Reports The single best source of information for any site are water well completion reports from wells on or near the site.These are reports filed (with the state agency responsible forwater well regulation) by the well driller upon completion ofthe construction of the well. There is a host of information(water level, well construction, pump test results, lithology.etc.) on these documents that is of use for both open andclosed loop system site characterization. The availability ofwell completion reports varies from state to state. Anincreasing number of states, as detailed in the state summariesbelow, have these reports available on the Internet.Anatomy of a Water Well Report Figures 1 and 2 are examples of water well reports from the state of Oregon. This form is typical of manywestern states. The level of detail is somewhat less for statesin the east and mid-west. The report contains information on the owner in Section 1 and the nature of the work that was done (new well,deepening, repair etc) in Section 2. The drilling method(Section 3) is of interest since it indicates what type of rig hasworked successfully in the area before. As you can see, well1 was completed in a hard rock formation with an air rotary rigand well 2 in unconsolidated materials with a cable tool rig. Section 3 details the hole diameter or diameters used and this information along with the casing description(Section6) and screen (Section 7) provide a very clear picture of thewell construction. The screen information is very useful fordesign of new wells. If the screen/gravel pack described hasbeen successful in terms of minimizing sand production, it isan effective guide for future wells in the same area. As youcan see, well 1 was completed in a rock formation with noscreen or casing in the lower portion of the well (called openhole completion). Well 2 was completed with a stainless steel“V slot” screen with 0.50 slot size (openings) between 167and 182 ft. The lower portion of the well drilled to 246 ft wasbackfilled and plugged to 202 ft due to the lack of waterproduction in that zone. The 8\" casing was cemented from 2ft to 152 ft . Section 8 is especially important for open loop design. As it presents information concerning the well’sability to produce water is presented along with the watertemperature. The temperature is also important for closedloop design since it’s temperature is the same as the“undisturbed soil/rock temperature” in the same area. Of thetwo examples, well 1's data is less useful than well 2. For well1, the driller indicates that the well produced 100 gpm butdoes not show the drawdown information. Instead he showsthat the drill stem was at 145 ft. This does not tell us what thewater level was in the well at this flow (although it is clear thatit was above 145 ft). Well 2's data indicates both the flow rateand the drawdown. This allows us to calculate a specificcapacity for this well of approximately 2.4 gpm/ft ofdrawdown (200 gpm/85 ft)--a useful value in making wellpump head and system design calculations. 32Sections 10 and 11 information permits additional conclusions to be drawn as to the type of aquifer in which thewell is completed. The static water level has an impact onpumping for open loop systems and may influence the type ofrig used for drilling (wells or boreholes). Beyond that, thestatic water level when considered in the context of the depthat which water was encountered, suggests the type of aquiferpresent. This is most clear in the well 2 report. This well wasconstructed in such a way that all the water bearing zoneswere cased off except the one between 167 and 182 ft. Thestatic water level in this well is at 11 ft. It is clear that this isan artesian (confined) aquifer since the water bearing zonestarts at 167 ft but the water level is 156 ft higher. This 156ft difference represents the pressure in that aquifer. Section 12, the well log is valuable information for closed loop systems since it indicates the type of materialsencountered in the subsurface. From this information, someidea of the heat transfer characteristics of the material can bedetermined. For well 1, most of the hole is rock (the blackrock indicated is the reference this driller uses for basalt) andwould likely have a fairly high thermal conductivity. Inaddition, the time to complete the well may offer someinformation concerning the drilling difficulty encountered.Well number 1 was completed in a single day in rock. On theother hand, well 2 required a month and a half to complete insoft drilling conditions. It is likely, however, that thedifference in construction period is related more to the rig typesince well 2 was constructed with a cable tool machine--a veryslow process relative to a rotary rig. Useful Maps One very good source of information on the geology of an area is a “geological quadrangle” map. These maps, ofwhich there are over 1700, show bedrock, surficial orengineering geology of selected 7.5 and 15 minutequadrangles of the U.S. Each map is accompanied by anexplanatory text printed on the map margin or sometimes as aseparate pamphlet. Some maps include cross sections andcolumnar sections illustrating stratigraphy. These maps aretypically published in 1:24,000 scale and use the topographicalmap (a map which shows surface elevations) of the same areaas the base. As a result, they bear the same name as the topomap for the area. These names are often related not to a townor city but to a local geological feature making the process ofidentifying the correct map difficult. Most of the map lists onthe sites described below are indexed by the name of the map.Unless the name is known, it is not possible to easily locatethe map you need. The USGS maintains a site to simplify thesearch process. At: http://maping.usgs.gov/mac/findmaps.html, click on the Map Finder (throughGLIS) link. The next page allows you to locate the correctmap by entering the zip code for the area or by clicking on aninteractive map of the U.S. In either case, a map of thegeneral area will come up showing the quadrangles for thatarea. GHC BULLETIN, MARCH 2001 Figure 2.Figure 1.Other maps that may be of interest for GSHP site characterization include bedrock topography maps, surficialgeology maps and Quaternary geology maps. BedrockTopography maps indicate the depth to the top of the localbedrock or stating it another way, the thickness of theoverburden materials. This information is useful indetermining the drilling conditions and in making decisions asto the depth of the boreholes at the site. Surficial Geology maps, in areas in which there is a thick sequence of unconsolidated material above the bedrock,may be the only maps necessary for characterization of sitematerials. For sites with less than 100 ft of unconsolidatedmaterials, these maps would be used in conjunction withbedrock geology maps. As the name implies, these mapsfocus on the materials close to the surface, normally theunconsolidated materials deposited in recent geological time(what geologists refer to as Quaternary (the last 2 millionyears) or Tertiary (from 65 million to 2 million years ago). SUMMARIES OF INFORMATION AVAILABLE INSELECTED STATES The following section presents summaries of information available for the states with the most activecommercial GSHP markets. Similar information for otherstates can be accessed through two very useful sites. TheAmerican Association of State Geologists sitehttp://www.kgs.ukans. edu:80/AASG/AASG.html#STATESincludes an interactive map of the U.S. Clicking on any statebrings up the website for that particular states GeologicalSurvey (or equivalent state agency). The USGS sitehttp://search.usgs.gov/ contains a similar interactive map ofthe U.S. (click on the USGS by state link to access it).Clicking on a state brings up the USGS information resourcesfor that state including groundwater, surface water andgeology. These two websites provided the starting point forall of the information presented below.TEXAS Texas Bureau of Economic Geology (http://www.utexas.edu/research/beg/) no online maps, list ofgeological quadrangle maps (but no online index map), list ofhydro-geological reports, recommended publications (click onPublications, Best Sellers): The Geology of Texas, Vol 1,Stratigraphy, by Sellards, Adkins and Plummer, 1007 pages,$18 #BL3232, Geologic Atlas of Texas, published asindividual sheets (listed on the web site), color, scale1:250,000, $6 ea. Texas Water Research Institute (http://twri.tamu.edu/index.html) appears to be primarily asurface water group but has a good general report indownloadable format Groundwater in the Great Basin(click on icon on first page) also a good links page includinglinks to many Water Research institutes in other states. Texas Water Development Board (http://www.twdb.state.tx.us/). Online publication Aquifersof Texas (click on Publications on first page) has maps ofnine major and 20 minor aquifers in the state along withdescriptions of typical well yields and aquifer geology.34 Online water well completion reports database is accessible by clicking on the Well Information icon on thefirst page (at the bottom of the page). This database takes alittle time to get into and it appears to be well construction andwater quality focused. No driller’s logs (lithology log). USGS Texas information Site (http://usgs.tx.gov/) online data for water levels at about 25 locations in Texas.Data is in real time. Access by clicking on Groundwater underthe Online Data heading. PENNSYLVANIA Pennsylvania Topographic and Geologic Survey (Dept of Conservation and Natural Resources)(http://www.dcnr.state.pa.us/topogeo/indexbig.htm). A mapand listing of libraries which serve as repositories forGeological Survey maps and Publications can be accessed onthe Publications page. Geological quadrangle maps in blackand white online and downloadable. These maps are oflimited value for GSHP applications since they typically donot contain cross sections. They can be accessed by clickingon Publications on the first page and then Atlas ofPreliminary Geological Quadrangle Maps ofPennsylvania. A useful feature of this online publication isthat clicking on the List of Quadrangles link brings up aalphabetical listing of the Quadrangle maps with a summaryof other publications available in that same quadrangle.Recommended Publications: PA Ground Water Information System CD - this is a database of water well completion reports for the entirestate $35. Information about the database is available on thesite. Click on the Pub title on the first page of the site. The Geology of Pennsylvania - 888 pages, $24, description can be found under Publications. Map #7 - Geology of Pennsylvania (Free upon request)Map #15 - Limestone and Dolomite (Free upon request)Map #64 - Surficial Materials (Free upon request)Map #59 - Glacial Deposits (Free upon request) USGS PA Water Information Site (http://pa.water.usgs.gov/). Online, real time depth to waterfor approximately 25 sites in PA. Click on StatewideGroundwater Conditions on the first page of the site.NEW YORK New York State Geological Survey (http://www.nysm.nysed.gov/geology.html). Online maps ofboth bedrock and surficial geology accessible by clicking onMaps and Digital Data on the first page of the site. Usermust have ArcView/ArcInfo software to access the maps. Listof geological quadrangle maps (but no online index map) byclicking on Publications and then Geology. Recommended Publications: Geology of New York: A simplified Account, Isachsen and others, 1991, $18.95 GHC BULLETIN, MARCH 2001 Geology of New York: A Short Account, $5 USGS New York Groundwater Information Site (http://ny.water.usgs.gov). Online, realtime depth-to-waterinformation for 15 sites in the state. Also historicalinformation on another 40 sites which are now discontinued.For access, click on the Groundwater under the Dataheading on the first page. Water table Altitudes in Kings and Queens Counties NY in PDF format under News and Features. Ithas map of water levels. Evidently, water well driller registration and the filing of water well completion reports was not required inNew York state (except in a few counties on Long Island)until 1 Jan 2000. As a result there is no database of thisinformation as there is in other states. Water well regulatoryfunctions are the responsibility of the Department ofEnvironmental Conservation, Division of Water. TENNESSEE Department of Environment and Conservation, Geology Division (http://www.state.tn.us/environment/tdg/index.html). Good generalized geologic mapof the entire state (no cross sections) online. Click on the BigMap link for the best scale. List of geologic quadrangle maps. Click on Publications on first page then click on GeologicQuadrangle Maps on menu on left of page. $3 ea Recommended Publications: State Geologic Map - in 4 sheets (West, W Central. E Central and East). 1:250,000 scale (1\" = 4 miles), color,formation descriptions. $4 per sheet. Department of Environment and Conservation, Division of Water Supply (http://www. state.tn.us/environment/dws/index.html). List of Licensed Water WellDrillers in TN - click on Water Well Drillers List link onfirst page of site. Lists drillers by name, Lic. number andphone number. USGS TN Water Information Site (http://tn.water.usgs.gov/). It appears that USGS, as of 1995,was monitoring water level in 48 wells in the state. Onlineinformation is not available for these wells as it is in otherstates. However, this information would be available bycontacting the state USGS office (email link on site). Online publication Public Water Supply Systems and Associated Water Use in TN, 1995 contains goodinformation about production from public water system wellsthroughout the state. This data is attached as appendices tothe report in table form. Access report by clicking onPublications and Product Information on the first age ofthe site and then Selected Tennessee Publications and thenthe report title. KENTUCKY Kentucky Geological Survey (Univ of Kentucky) (http://www.ky.edu/KGS/home.htm). This is the only statefor which there is 100 % coverage in geological quadranglemaps. List available on siteGHC BULLETIN, MARCH 2001 Hydrologic atlas maps list. These maps include information about water wells, aquifers, availability,chemistry, depth to water etc. Click on Mapping icon at topof first page, then Maps for sale by Commodity. Mapsavailable by county, groups of counties and in some cases byquadrangle (1:24,000 scale). $4.50 to $12. Simplified map of Geology of Kentucky online. Click on the Geology of Kentucky icon at the top of the first page.Includes cross section and explanatory text. Good summaryof geological time scale. A detailed treatment of the geology on a county by county basis is ongoing. Only Fayette County is currentlyonline. Possibly the most useful information for GSHP would be searches of the Kentucky Hydrologic Data Baseand The KGS Oil and Gas Data Base. The hydrologicinformation includes results from 39,000 water wells and18,000 water chemistry analyses. Information on water wellconstruction, yields, depth, static level and water quality data,etc. Database is not searchable online. Contact is BartDavidson (bdavidson@kgs.mm.uky.edu) or 606-257-5500. Oil and gas data includes driller logs, wireline logs(geophysical data) etc. Contact is Brandon Nuttall at KGS(bnuttall@kgs.mm.uky.edu) or 606-257-5500. Minimum feesfor these services appear to be $30 to $40. Downloadable geologic and hydrologic GIS maps available on the site. ArcView/ArcInfo software required forviewing. Click on Mapping icon at top of first page then, GISCoverages. Under State Hydrology Series, the Water Wellsmap appears to be the most useful (data on depth, depth towater, date, use, depth to bedrock, etc.). Using the sameapproach but clicking on Geology Series, the Oil and Gaswells and Generalized Geology maps should provide goodinformation on the subsurface. Kentucky Groundwater Development Commission (http://dlgnt1.state.ky.us/wrdc/). This organization is workingon a Digital Atlas of Groundwater in Kentucky in conjunctionwith the KY Geological Survey. Based on the hydrologicatlas series published in the 1960's, new information will beadded and corrections made. Water well, groundwateravailability and quality and aquifer descriptions will beincluded. Data not yet available. VIRGINIA Virginia Department of Mines, Minerals and Energy, Div of Mineral Resources (http://www.mme.state.va.us/dmr/home.dmr.html). General Geology ofVirginia (access by clicking on the phrase at the top of thefirst page) explains the general geology and physiographicprovinces of the state. Text describes the rock types andfaulting etc. Geological quadrangle maps listed. Click on maps and publications, geological and then geological quadranglemaps. Oil and Gas Database--includes well location, status and stratigraphy. Not available online. Contact Dave Spears804-951-6361 35 The state is working on the digitizing of both 1:100,000 and 1:24,000 geological maps but this work is inprogress. Some maps may soon be available on CD-ROM.Inquire. Recommended Publications: Geologic Map of Virginia and expanded explanation (1993). 1:500,000, 80 pages, $9.50 . Geological map and generalized cross sections of the Coastal Plain and adjacent parts of the Piedmont, VA, RB Mixon, 1:250,000 1989, $6.75. USGS VA Water Information Site (http://va.water.us.gov). Online water level information for 11sites in VA. Click on Groundwater Levels under VADrought Conditions. INDIANA Indiana Geological Survey (http://adamite.igs.indiana.edu/index.htm). This is one of themost comprehensive and useful state geological sites. Excellent glossary of geological terms. Click on Reference Library on the first page and then Glossary ofGeological Terms. Glossary and descriptions of stratigraphic units in inches. Click on Reference Library and the Compendiumof Paleozoic Rocks. Detailed descriptions on rock units. Online maps of both bedrock and surficial geology for the entire state. Click on Reference Library then Mapsand Charts. Bedrock geology shows the types of bedrockunits and their location along with a brief explanation of thematerial (point to the material on map and description isdisplayed). Surficial Materials shows the type and depth ofthese materials on a state map. This allows the determinationof the depth of the “overburden” materials and the type. Databases of core and well samples are “Coming Soon.” Recommended Publications: Regional geological maps 1ox2o. These maps show both bedrock and unconsolidated deposits. Scale 1:250,000.$2.50 ea. To access list, use publications search engine andselect “regional geological maps.” IN Dept of Natural Resources, Division of Water (http://www.state.in.us/dnr/water). Online water wellcompletion reports. Click on databases then search waterwell records. Full well report info available–depth, flow test,construction details, lith log, etc. Several excellent publications on groundwater availability on river basin (regional) and county by countybasis. See publications list. MARYLAND Maryland Geological Survey (http://mgs.dnr.md.gov). Online publication A BriefDescription of Maryland Geology. Click on Earth ScienceInformation Center on the first page, then the document title.Contains a map of the Physiographic provinces of the state 36and a general geological map with formation descriptions andexplanatory text. Publication also includes a downloadablefile of the geological map. Recommended Publications: Most useful appear to be the county geological maps (some of which are out of print). Click on CountyTopographical and Geological Maps $7.50 ea. Alsopublication #69-02-1 Groundwater Aquifers and MineralCommodities of Maryland (also out of print but should beavailable at MGS repositories a list of which is on thewebsites). USGS Maryland Water Information Site (http://md.water.usgs.gov/groundwater/county). Site has historic water level data for at least one well in eachcounty in both MD and DE. Includes a graph of past levelsand a description of well construction and location.MISSOURI Missouri Department of Natural Resources -Division of Geology and Land Survey(http://wwwdnr.state.mo.us/dgls/homedgls.htm). Nothing ofhelp for the GSHP designer on this web site. Thisorganization is also responsible for administering the stateswater well industry but no online data is available. Email address for questions regarding geology, stratigraphy and surficial materials:gspgdam@mail.dnr.state.mo.usOHIO Ohio Geological Survey (http://www.dnr.state.oh.us/odnr/geo_survey/). Online mapsof bedrock, surficial geology and Physiographic provinces inthe state. Click on Geology of Ohio on the first page, thenmap title. Online “Geo Facts” publications - #1 Bedrock Topography of OH. Explains the topic and includes mapordering info. #20 Geology of OH - The Cambrian Useful maps available from the Survey: Bedrock Topography Maps, bycounty. Shows the depth to bedrock as contours. Scale is1:24,000 and cost is $4 ea; Geologic Map of Ohio 1:500,000,$5, order #M1; Quaternary Geologic Map of OH, 1:500,000,$10, order #M2 Department of Natural Resources - Division of Water (http://www.dnr.state.oh.us/odnr/water/). Online searching ofwater well completion reports. Click on Online searching ofwater well logs under New Items on the first page. Canlocate wells by county and road or well number. Informationon water level, production, construction, lithology etc. Online map of generalized water well production (in gpm)for entire state. Click on Publications, thenGroundwater Publications, Maps, Generalized StateGroundwater Map of Well Yields. Online index map to individual county groundwater availability maps. Navigate to same location describedimmediately above for well yield map. Click on Ground- GHC BULLETIN, MARCH 2001 water Resources Map Availability. Includes state mapindicating status of individual county maps and orderinginformation. NEW JERSEY New Jersey Geological Survey (Dept of Environmental Protection) (http://www.state.nj.us/dep/njgs/index.html). Online map Geology of NewJersey on first page of site. Link at bottom of map fordownload of Adobe file with map and text providing adescription of the geology in each of the major physiographicprovinces of the state. Also a link to ordering info for thenewest three map set on New Jersey Geology. Online map of major aquifers in the state with well yields indicated. Click on GEODATA, Groundwater icon,Aquifers of NJ (1:250,000). Map and data are downloadablebut requires ARC/INFO software. Click on image for onlinedisplay of map. Publications search engine online. Best strategy is to use the county name as a key word to locate publication forthe site you are interested in. USGS NJ Water Information Site (http://nj.water.usgs.gov/). Online geologic map of NJ clickon Groundwater, Geologic Map. Also at same location,Aquifers of NJ with maps, text and tables describing aquifersof the state. Groundwater levels for 172 wells in the stateincluding both current and past water level data. MINNESOTA Minnesota Geological Survey (http://www.geo.umn.edu/mgs/index.html). Online map ofbedrock geology of MN with descriptions. Click on moreinformation on MN geology on the first page of the site,state maps then map title. Same location also has map ofQuaternary geology and cross section of the state. GHC BULLETIN, MARCH 2001More detailed information on both the bedrock and Quaternary geology of the state are available in two online(and downloadable publications). Click on more informationon MN geology on the first page and then Minnesota at aglance and then the title of the publication (in AdobeAcrobat). Documents have maps and descriptions of thegeology of the entire state. Geology of central MN presented in some detail in the online document of the same name including text mapsand formation descriptions. Click on more information onMN geology, regional information then the title of thedocument. Water well information is contained in the County Well Index (CWI). Not available online. Database isavailable on disks (typically 1 disk per county) for $5 ea. Usermanual available for $6. Ordering and general information byclicking on the CWI link on the first page of the site.Database contains well construction, production, lithology,static water level information, etc. Recommended Map Publications: County Geologic Atlases. Order numbers C-1 thru C-12 Regional Hydrologic Assesments Order numbers RHA-2thru RHA-5 Geologic and Surficial maps, typically 1:24,000scale. Most recent are available online. Order numbers M-1thru M102. M-83 thru M102 are online. 37 DUAL-SET POINT CONTROL OFOPEN-LOOP HEAT PUMP SYSTEMS Kevin RaffertyGeo-Heat Center ABSTRACT Control of well pumps in open-loop heat pump systems is a topic which has been largely overlooked in theliterature. Three primary methods are in use: dual-set point,variable speed and multiple well (normally employed whenmultiple wells are required for hydrologic or redundancy).This paper explores the issues involved in the dual-set pointmethod. Establishing the system operating set points requiresconsideration of peak loop loads, loop thermal mass, wellpump motor cycling limitations and heat exchangerperformance. Guidelines for pump controller operating rangeare presented along with the method of establishing theoptimum loop temperatures at peak load conditions.INTRODUCTION The design of open-loop heat pump systems and the procedure for identifying the optimum groundwater flow formaximum system performance (EER or COP) is discussed indetail in existing references (Kavanaugh and Rafferty, 1997;ASHRAE, 1999). Basically, this procedure consists ofcalculating the power requirements of both the well pump and the heat pumps over a series of groundwater flows todetermine the system optimum groundwater flow at thedominant peak load (normally the cooling mode in largecommercial buildings). Above this flow, system performancedegrades due to increasing well pump power consumption.Below this flow, system performance degrades due toincreasing heat pump power consumption. The issue leftlargely undefined in the existing literature is the control of thewell pump at conditions other than peak load. A variety ofstrategies have been used and the three most common aredual-set point, multiple well and variable-speed. Multiplewell control is normally a strategy chosen when more than oneproduction well is required for hydrologic or redundancypurposes. The dual-set point method is somewhat similar to the temperature control scheme used in water-loop heat pumpsystems. The well pump is enabled above a given temperaturein the cooling mode and below a given temperature in theheating mode. The multiple well approach is similar in termsof the temperature initiated response of the well pumps;however, the use of multiple wells provides the ability to stage Figure 1. 38 GHC BULLETIN, MARCH 2001 the groundwater flow and sometimes, better match thedifferent heating and cooling mode flow requirements.Variable-speed control of well pumps permits an infinitelyvariable groundwater flow for any system load or modeprovided sophisticated enough controls are available. There is no “best” among the methods listed above. The strategy is selected based on the system size, well designparameters specific to the site and the capabilities of theowners operating personnel. Discussion of well pump controlfrom this point will focus on the dual-set point approach andassume a system configured as indicated in Figure 1.DUAL-SET POINT CONTROL As indicated above, dual-set point control is similar to the cooling tower/boiler control employed on water-loopheat pump systems--in which the cooling tower is employedabove a specific loop temperature in the cooling mode and aboiler is used below a specific temperature in the heatingmode with the loop “floating” between these two set points.In this case, it is the well pump that is used to temper the loopin both cases. Ideally, at the peak condition, the pump runscontinuously. At less than peak loads, the well pump is cycledin response to the size of the load. In fact, there are fourrather than two set points as the name implies: pump on tem-perature and pump off temperature in the cooling mode, andpump on and pump off temperatures in the heating mode.Each of these pairs of set points are normally arranged sym-metrically about the optimum building loop return temperaturefor that mode. Properly done, the design process for an open-loop system identifies a groundwater flow rate, which results in thehighest system performance (system EER or COP) at peakload. Once this flow has been determined and the heatexchanger selected, the operating temperatures at the peakconditions are fixed. Based on the thermal mass of the systemand the loop thermal load, the well pump operating rangearound the optimum temperature in the dominant mode(usually cooling) is established. System performance isdetermined in the peak secondary load (usually heating) andthe operating range around the loop return temperature at thesecondary load peak is established based on the loop thermalload and the system thermal mass. This general procedureestablishes an optimum relationship between the well pumppower, heat pump power and building load. Maintaining thisoptimum relationship at off peak conditions is accomplishedby cycling the well pump. Consider the following example system: peak cool-ing block load 85 tons (299 kW), groundwater temperature60oF (15.6oC), production well static water level 75 ft (23 m),aquifer specific capacity 2 gpm/ft (0.04 L/s-m), building loopflow 213 gpm (13.4 l/s), surface groundwater head losses of37 ft (11.3 m) and a heat exchanger selected for a 4oF (2.2oC)approach temperature (between the building loop return [to theheat exchanger] temperature and the groundwater leavingtemperature). Under these conditions, the optimum ground-water flow would be approximately 1.75 gpm per ton (0.031l/s-kW) or 150 gpm (9.5 l/s). System performance in the peakcooling mode vs. groundwater flow is illustrated in Figure 2.GHC BULLETIN, MARCH 2001 Figure 2. Example system performance. At the design load and the flow of 150 gpm (9.5 l/s), the groundwater would enter the exchanger at 60oF (15.6oC)and leave at 76.6oF (24.8oC). The building loop side wouldenter at 80.6oF (27oC) and leave at 69oF (20.6oC). The build-ing loop return temperature is most commonly used for controlof the well pump. In this case, since the return temperatureunder optimum conditions is approximately 81oF (27.2oC), thiswould be the value around which the well pump would becontrolled. In order to limit the cycling of the well pump,some range around this temperature must be established suchthat pump operation is initiated at a temperature above theoptimum value (pump on temperature) and operation termin-ated at a temperature below the optimum (pump off tempera-ture). The size of the range between these two values is afunction of the thermal mass of the system (gallons of waterper peak block ton [liters of water per peak block kW])and theallowable time between starts for the well pump motor.SUBMERSIBLE PUMP MOTOR CYCLING Submersible motors, like any other motors, are limit-ed in terms of the starts to which they can be subjected over agiven interval of time. Due to the thermal spike imposed onthe motor windings at start up, sufficient time must be permit-ted to dissipate this heat between starts to avoid damage to theinsulation and other thermal cycling damage to the motor. Therecommended limitations are a function of the motor size andelectrical characteristics (primarily whether it is single or 3phase). This information is summarized in Table 1Table 1. Recommended Limitations for Numberof Starts per Day for SubmersibleMotors (Franklin, 1999) ________________________________________________ Motor hp Single Phase3-Phase <5100 300 7 ½ to 30 50 100 >30 – 100 _______________________________________________Most larger commercial open loop system pumps will fall into the 100 starts per day imitation category. In thecontext of the heat pump system, a more useful unit would be15 minutes between starts. 39 BUILDING LOOP THERMAL MASS The nature of the dual-set point approach is such that the building loop is drafted over some temperature interval(difference between the pump on temperature and the pumpoff temperature). The range between these two temperaturesmust be sufficient, given the thermal mass of the loop and theload imposed on it to accommodate the 15-minute limitationbetween starts. In the example system above, the pump mightbe started when the loop reaches 84oF (28.9oC) and operateduntil the loop is reduced to 78oF (25.6oC), a 6oF (3.3oC) range.The time required for the loop to be reduced from 84oF (28.9o C) to 78oF (25.6oC) (while the pump is running), combinedwith the time required for the loop to rise from 78oF (25.6oC)to 84oF (28.9oC)(pump off), is the time between starts andmust be no less than 15 minutes. Obviously, the thermal mass of the building loop is constant as is the capacity of the groundwater (via the heatexchanger) to remove heat from the loop. As a result, theprimary variable in terms of the time between pump starts isthe building thermal load imposed on the loop. Figure 3expresses the relationship between this parameter (in units ofgallons of water per ton of peak block load) and the number ofminutes between pump starts per oF of difference betweenpump on and pump off temperature. This plot is based onspace load (1 ton = 12,000 Btu/hr [3.52kW]) and incorporatesan assumed heat pump unit EER of 14.6, resulting in a loopload of 14,800 Btu/hr (4.34 kW) per ton. Figure 4 provides the same information for the heating mode of operation. The heating mode plot is alsobased on space load (1 ton = 12,000 Btu/h [3.52 kW]) andincorporates a heat pump unit COP of 3.5 which results in aloop load of 8,600 Btu/hr (2.52 kW) per ton. Due to theimpact of compressor heat, the thermal mass/controller rangerequirements needed to avoid short cycling in cooling loaddominant applications are substantially larger than in heatingdominant applications. Although the phenomenon of short cycling in system components is normally considered to be a problem at mini-mum load, it is apparent that in open loop systems, the wellpump cycling issue is of most concern at 50 % load. Thisarises from the fact that it is the time between starts (the timefor one off-cycle plus one on-cycle) that is of interest. Athigh-loop thermal load, the pump on-cycle will be long. Atlow-loop load, the pump off-cycle will be long. Either ofthese two situations lengthens the time between starts. Thus,it is at the mid point that the time between starts for the wellpump is minimized. It is at this 50% load point that the rangefor the pump control is established. For the example systemin the cooling mode, assuming a loop thermal mass of 8gal/ton (1.1 min/oF from Fig 3)(106 l/kW(1.98 min/oC), arange of 15/1.1 or 13.6 oF (7.6 oC) would be required. Thiswould result, in the cooling mode of a pump-on temperatureof 81 + (13.6/2) = 87.8oF (31oC) and a pump-off temperatureof 81 - (13.6/2) = 74.2 oF (23.4 oC). At a loop thermal massof 14 gal/ton (186 l/kW), the necessary range would bereduced to 15/1.9 = 7.9o F (4.3 oC). 40 Time Between Pump Starts - Minutesper F of diff from cut in to cut out5 4 1 F = 0.56 C se3 tuniM2 1 0 10 20 30 40 50 60 70 80 90 Percent of Peak Block Loadthermal mass gal/peak block ton (x 13.3 = 1/kW)468101214Figure 3. Time Between Pump Starts - Minutesper F of diff from cut in to cut out5 4 1 oF = 0.55 oC se3 tuniM2 1 0 10 20 30 40 50 60 70 80 90 Percent of Peak Block Load Thermal mass gal/peak block ton (x 13.3 = l/kW)468101214Figure 4. Values for building loop thermal mass of between 4 and 14 gal per peak block ton (53.2 to 186 l/kW) are consider-ed in the plot; since, these represent the extremes which theauthor has witnessed in these systems. Generally, small multi-story office type buildings with a small foot print tend towardthe lower end of the spectrum and large single story largefootprint (schools) tend toward the upper end of the range. GUIDELINES FOR WELL PUMP CONTROLLERTEMPERATURE RANGE To simplify the process of range selection, Table 2 was developed. The table offers guidelines for minimum wellpump controller range in oF (oC) with examples for large (>5hp [3.7 kW]) and small (5hp [3.7 kW] and less, 3 phase)pumps and both cooling load and heating load dominantapplications. The values in the table are the minimumtemperature ranges necessary to assure adequate time betweenstarts for the system well pump in a single production wellapplication. GHC BULLETIN, MARCH 2001 Table 2. Minimum Controller Range Requirements oF(oC) ____________________________________________________________________________________________________ Motor hp(kW) System Thermal Mass - gal/block ton (l/kW) 2(27) 4(53) 6(80) 8(106) 10(133) 12(160) 14(213) COOLING MODE - oF (oC) RANGE <5hp(3.7kW) 28(16) 14(8) 9(5) 7(4) 6(3.3) 5(3) 4(2)>5hp(3.7kW) 56(31) 28(16) 19(11) 14(8) 11(6) 9(5) 8(4) HEATING MODE - oF (oC) RANGE <5hp(3.7kW) 16(9) 8(4) 5(3) 4(2) 3(2) 3(2) 2(1)>5hp(3.7kW) 32(18) 16(9) 11(6) 8(4) 6(3) 5(3) 5(3) ____________________________________________________________________________________________________It is apparent that at system thermal mass values of less than 8 gal/ton (106 l/kW)(cooling mode dominant), therequired range on the well pump controller becomes verylarge. Although it is reasonable to assume that a systemoperating over a small temperature range about an optimumpoint will, on average achieve the optimum performance, asthe range becomes larger system performance suffers. As aresult for systems with very low mass, it may be worthconsidering an alternate method of well pump control or theaddition of some mass to the system. For small systems, theaddition of sufficient storage to reach the 10 gal/ton(133 l/kW)threshold is achievable for reasonable capital cost. Otherwise,use of the variable-speed or multiple well approach should beconsidered. SECONDARY LOAD SET POINTS The discussion, to this point, has focused on the dominant system load using the cooling load as the examplesince this is normally the dominant load in most large buildingapplications. A similar approach is used for establishing thewell pump controller range at the secondary load peakcondition. The difference is that since the groundwater flowrate and the heat exchanger are sized for the dominant loadpeak, some calculation is necessary to determine the buildingloop operating temperatures in the secondary load peakcondition. Once this value is determined, the appropriateminimum range can be selected from Table 2 to arrive at thepump-on and pump-off temperatures. To determine the operating temperatures at the secondary load peak, it is necessary to evaluate the perform-ance of the heat exchanger at the reduced thermal loadimposed by the secondary peak. This can be done by manualcalculation or with analysis provided by the heat exchangervendor. Using the example 85 ton (299 kW) systemestablished above and assuming a peak heating load of900,000 Btu/hr (264 kW), it can be calculated that the buildingloop return temperature at peak heating conditions would be49oF (9.4oC). From the previous calculations, it wasestablished that the system has a building loop thermal massof 8 gal/ton (106 l/kW) based on the cooling load. As a result,for the heating mode, the value would be (85 tons * 8 gal/ ton)/(900,000/12,000) = 9.1 gal/ton (121 l/kW). FromTable 2, this would result in the selection of a minimum wellpump controller range of approximately 4oF (2.2oC). As aresult, in the heating mode, the well pump for this systemwould be started at 49 - (4/2) = 47oF (8.3 oC) and stopped at49 + (4/2) = 51oF (10.6oC). ADDITIONAL CONSIDERATIONS The issue of thermal mass is an important one in the context of range size determinations. Since the critical pointfor pump cycle time occurs at 50% load, a more useful termmight be effective thermal mass for systems with variable-speed. In systems with variable-speed control of the buildingloop pump, at 50% load by definition, 50% of the heat pumpcapacity will be idle. The water in the branch piping to theidle heat pumps is not available to contribute to the thermalmass of the system as far as calculations for well pumpcycling are concerned. This influence is a complicated oneand more amenable to adjustment after the system is inoperation rather than calculation at the design stage. Again,this is an issue more in small compact buildings thanextensive, large footprint buildings. The system thermal mass used in the development of the guidelines sited in this paper considers only the watervolume. No credit has been taken for the heat pumprefrigerant-to-water heat exchangers or the building looppiping itself. The building loop piping increases the loopthermal mass by approximately 25% for steel and 10% forcopper and PVC materials relative to the water only thermalmass. As a result of this impact, the temperature ranges sitedin Table 2 can be decreased accordingly. The exact impact isinfluenced by the pipe sizes involved. In smaller diameterpipe, the relative contribution of the pipe material to the totalthermal mass (pipe plus water) on a per foot basis, is muchhigher than it is in larger diameter pipe. For example, in 1-1/4\" (32mm) schedule 40 steel pipe, the pipe material consti-tutes 28% of the total thermal mass on a per foot basis and atthe 6\"(152mm) size the pipe material constitutes only 15%.The variation with pipe size is less for copper and PVCmaterials. GHC BULLETIN, MARCH 2001 41 CONCLUSIONS The dual-set point method of well pump control for open loop heat pump systems is a simple, efficient and widelyused strategy. To properly apply it, it is necessary to fullyconsider the issues of dominant and secondary loads, buildingloop thermal mass, submersible motor cycling limitations, andheat exchanger performance. For cooling load dominatedbuildings, it may be necessary to consider another method ofcontrol or the addition of volume to the building loop inapplications with less than approximately 8 gal/ton (106 l/kW)thermal mass. REFERENCES ASHRAE, 1999. Handbook of Applications, Chapter 31 -Geothermal Energy, ASHRAE. Franklin Electric, 1999. Submersible Motor Application,Installation and Maintenance Manual, FranklinElectric Company Inc., Bluffton, IN.Kavanaugh, S. and K. Rafferty, 1997. Ground-Source HeatPumps: Design of Geothermal Systems for Com-mercial and Institutional Buildings, ASHRAE. 因篇幅问题不能全部显示，请点此查看更多更全内容