1、160 2016 U.S. GovernmentABSTRACTThis paper summarizes a case study of an innovativeground-source heat pump (GSHP) system that uses floodedmines as a heat source and heat sink. This GSHP systemprovidesspaceconditioningtoanexisting56,000ft2(5203m2)research facility, in conjunction with existing space
2、heatingand space cooling systems. Heat transfer performance andoverallefficiencyoftheGSHPsystemwereanalyzedusingtheavailablemeasureddatafromJanuarythroughJuly2014.Theperformance analysis identified some issues with using minewater for cooling and the integration of the GSHP system withthe existing s
3、team heating system. Recommendations weremade to improve the control and operation of the GSHPsystem.Theserecommendations,inconjunctionwiththeavail-ablemeasureddata,wereusedtopredicttheannualenergyuseof the system. Finally, the energy and cost savings and CO2emission reduction potential of the GSHP
4、system were esti-mated by comparing them with a baseline scenario. This casestudy provides insights into the performance of and potentialissues with the mine-water-source heat pump system, which isrelatively underexplored compared to other GSHP systemdesigns and configurations.INTRODUCTIONDevelopmen
5、t and deployment of clean energy technologieshas become one of the forefront agenda items in both developedand developing countries to strengthen the economy, protect theenvironment, and reduce dependence on foreign oil (NSF 2014;EERE 2015a, b; Gallagher 2014; CEM 2014). Geothermal tech-nologies are
6、 among the potential clean energy technologiesdevelopedforvariousapplicationsrangingfromgeneratingelec-tricity using high-grade heat from deep subsurface sources toprovide space heating, cooling, and hot water using the nearlyconstant temperature of the earths crust as both heat sink andsource (ASHR
7、AE 2011). For the latter, heat transfer between thebuilding and the ground is made possible using a heat pump anda system of pipes buried in the shallow ground, hence the nameground-source heat pump (GSHP) system. Through innovativedesign and configuration of the ground heat exchanger, a varietyofhe
8、atsink/sourceshavebeenexplored,dependingonthehydro-geological features of the site such as standing column wells,lakes/ponds,municipalwastewater,sewageeffluent,foundation/pilings,undergroundmines,andacombinationofvariousgroundand water sources (Goetzler et al. 2012; Sachs et al. 1998). Onesuch innov
9、ative design of the GSHP system using flooded-minewater as a heat sink and source is implemented at a 56,000 ft2(5203 m2) newly constructed research facility in Butte, MT.The use of mines is a promising option for geothermalenergy recovery (Ghomshei and Meech 2003; Wazlaf andAckman 2006) as a heat s
10、ource, a heat sink, or both. Its poten-tial lies in the use of otherwise unexploited resourcesaban-doned and flooded mines. However, such application has notbeen extensively studied as for other conventional GSHPsystems (Hall et al. 2011). An investigation of about1600 abandoned mines in the United
11、States for prospects forongoing discharge of useful quantities of warm water resultedin a detailed look at 80 sites (Lawson and Sonderegger 1978).This project is one of the 26 GSHP projects, which werecompetitively selected under the 2009 American Recovery andReinvestment Act (ARRA) to demonstrate t
12、he benefits of inno-vative technologies for reducing the cost and/or improving theperformance of GSHP systems. The installed mine-waterGSHP system uses two abandoned and flooded undergroundmineslocatedapproximately900ft(274m)westofthebuildingPerformance Analysis of aGround-Source Heat Pump SystemUsi
13、ng Mine Water as Heat Sink and SourceXiaobing Liu, PhD Mini Malhotra, PhD Adam WalburgerMember ASHRAE Associate Member ASHRAE Member ASHRAEJack L. Skinner, PhD, PE Donald M. Blackketter, PhD, PEXiaobingLiuandMiniMalhotraareresearchstaffatOakRidgeNationalLaboratory,OakRidge,TN.Adam Walburgerisgeneral
14、managerat CDH Energy Corp., Cazenovia, NY. Jack L. Skinner is an assistant professor and Donald M. Blackketter is a professor at Montana Tech,Butte, MT.ST-16-017Published in ASHRAE Transactions, Volume 122, Part 2 ASHRAE Transactions 161that is being heated or cooled. These two mines are connectedun
15、derwater, as indicated by the same water levels in both mineshafts, and considered as a single underground reservoir. Thewater level in the mines is 110120 ft (33.536.6 m) below theground surface. The mine-water temperature is about 78F(25C). Nearly 20 years of continuous pumping at a nearbymine has
16、 demonstrated that mine-water temperatures are stableand ample heat is available for long-term use (Thornton et al.2013).A set of 6 in. (0.152 m) supply and return pipes wasinstalled from the building to the mine. These pipes werebranched out with 3 in. (0.076 m) high-density polyethylenepipe (HDPE)
17、 pipes to the 100 ft (30.5 m) underground level,where they were connected with 20 in. (19 mm) 600 ft(183 m)longHDPEparallelloops.Theseloopswereinstalledthrough the airway of a mine shaft and down an abandonedhoistway, then immersed into the mine water, which is 200 ft(61m)belowthemineentrance,asshow
18、ninFigure1.Suchaninstallationwasinventedforthisprojectandhadnotbeendonebefore. The closed-loop piping system was selected instead ofaprobablycheaperopen-loopsystembecausethegranteedoesnothavethewaterrightsandwas,understatelaw,notallowedto pump water out and back into the mine shaft. Even if thegrant
19、eeisallowedtopipethewateroutandthenturnaroundand pump it back in the same holethe grantee would have totreat the water to meet clean water standards.Tworedundantparallel7.5hpconstant-speedpumpsareused alternatively in a lead and lag fashion to circulate waterin the closed loop immersed in the mine w
20、ater (referred asmine-water loop). The pumps shut down with the heat pumpwhen the outside air temperature is above freezing. Freezingmay occur as the pipe enters the airway before it goes downinto the mine, where it is warm. For freeze protection, thepump may run continuously even when the heat pump
21、 wasturned off.TheGSHPsystemworksinconjunctionwithanexisting6200 kBtu/h (1817 kW) heating system, which uses steamproduced at a central plant to make hot water at the building,and a 170 ton (595 kW) air-cooled chiller to provide spaceheating and cooling to the building. As Figure 2 shows, a50 ton (1
22、75 kW) water-to-water heat pump, which has two25 ton (87.5 kW) scroll compressors, is connected with theexisting hot-water and chilled-water piping in the building.The heat pump can operate in heating or cooling mode basedon the outdoor air temperature, as described below:It operates in heating mode
23、 when the outdoor air (OA)temperature is equal to or below 60F (15.6C). In thiscase, the valves modulate to divert part of the return waterof the existing building hot-water loop to the load side ofthe heat pump and isolate the connection to the existingbuilding chilled-water loop. When a substantia
24、l flow rateis detected, the heat pump starts to heat up the returnwater and the heated water then goes back to the buildinghot-water loop before entering the steam heat exchanger(HX). The steam HX then adds the remainder of the heat,if it is needed, to maintain the return temperature from thebuildin
25、g heating water loop at a setpoint according to areset schedule135F at 10F (57.2C at 23C) OAtemperature, 100F at 60F (37.8C at 15.6C) OA tem-Figure 1 An illustration of the abandoned mine shaft and the heat exchanger in it.Published in ASHRAE Transactions, Volume 122, Part 2 162 ASHRAE Transactionsp
26、erature. The remainder of the building hot-water distri-bution system and the heating terminals operate asoriginally designed during GSHP system operation.It operates in cooling mode when the OA temperature isabove 60F (15.6C). In this case, the valves modulate todivert part of the return water from
27、 the building chilled-water loop to the load side of the heat pump and isolate theconnection to the building hot-water loop. When a substan-tial flow rate is detected, the heat pump starts and interceptsthe chilled water back to the building chilled-water loopbefore it returns to the chiller. The ch
28、iller then provides theremainder of the cooling, if it is needed, to maintain thechilled-water supply temperature setting of 45F to 65F(7.2C to 18.3C). The remainder of the building chilled-water distribution system and the air-handling units operateas originally designed during the GSHP system oper
29、ation.Also shown in Figure 2 is the location and name of datacollection points available from the demonstration site,including the supply- and return-water temperatures in themine-water loop (temperature in mine-water supply TMWSandtemperatureinmine-waterreturnTMWR,respectively),the flow rate in the
30、 mine-water loop (FMW), heat pump load-side supply- and return-water temperatures (temperature ofheat pump supply THPS and temperature of heat pumpreturn THPR, respectively), building hot-water loop supply-and return-water temperatures (temperature of building hot-water supply TBHS and temperature o
31、f building hot-waterreturn TBHR, respectively) and flow rate (FBH), and OAtemperature (temperature of outdoor air TOA). A descrip-tion of the collected data points is given in Table 1.Figure 2 GSHP system schematic and available data collection points.Table 1. Description of the Collected Data Point
32、sData Point Description UnitTMWS Mine-water loop supply temperature F (C)TMWR Mine-water loop return temperature F (C)FMW Mine-water loop flow rate gpm (L/s)THPS Heat pump loop supply temperature F (C)THPR Heat pump loop return temperature F (C)TBHS Building hot-water loop supply temperature F (C)TB
33、HR Building hot-water loop return temperature F (C)FBH Building hot-water loop flow rate gpm (L/s)TOA Ambient air temperature F (C)Published in ASHRAE Transactions, Volume 122, Part 2 ASHRAE Transactions 163Analysis was conducted to characterize the performanceof the demonstrated mine-water GSHP sys
34、tem; identifyperformance issues, if any; recommend potential improve-ments;andevaluatetheenergysavingsandemissionreductionbenefits compared with a baseline scenario.METHODSTheanalysiswasperformedintwosteps:first,theavailablemeasured data was analyzed to characterize the performance ofthe major compo
35、nents and the entire system; second, the fullyear energy consumption of both the demonstrated and acomparable baseline system was predicted to determine energysavings and environmental benefits from the GSHP system.Measured Performance CharacterizationMeasurementsofthedatapointsindicatedinFigure2wer
36、ecollected through a direct digital control (DDC) system at thefacility. The grantee did not install any submeter for measuringthe power consumption at the pump and the heat pump due toconstraints in the budget. The DDC system polls the sensorsonce per second and provides 15 minute totals or average
37、s ofeach sensor depending on the sensor type. Performance datafromJanuary1throughJuly31,2014havebeenanalyzedinthisstudy. The measured data were analyzed to (1) assess the heattransfer performance of the mine-water loop, (2) determine theoperational efficiency of the heat pump and the overall GSHPsys
38、tem, (3) assess the operation of the pump, and (4) identifyfaults/abnormalities in GSHP system operation and determinepotential improvements to the GSHP system.The coefficient of performance (COPhsys) and energy effi-ciency ratio (EERcsys) of the GSHP system were determinedfollowing the approach sho
39、wn in Figure 3a. From the measuredtemperatures andflow ratein themine-water loop,heat transferrate at the mine-water loop (QGLhand QGLc) was calculated.The operating efficiency of the heat pump (COPheqpandEERceqp), which does not include any pumping power, wasdetermined as a function of the measured
40、 source-side and load-sideleavingwatertemperatures(TMWRandTHPS).Thenheatpump power consumption (WHPhand WHPc) was calculatedbydividingtheheattransferrateatthemine-waterloopwiththeheat pump efficiency. Then, the output of the heat pump (QHPhandQHPc)wascalculatedwiththeheattransferrateatthemine-water
41、loop and the calculated heat pump power consumption.Finally,theoverallGSHPsystemefficiencieswerecalculatedasthe ratio of the total output of the heat pump to the sum of theheat pump power consumption and the mine-water loop pump-ing power consumption.Annual Energy AnalysisAnnualenergyanalysisofthein
42、stalledGSHPsystemwasperformed to (a) predict its full-year performance and (b) esti-matetheenergysavings,operatingcostsavings,andemissionsreduction benefits compared to a baseline system.As discussed in the section “Analysis and Results,” it wasfound that the mine water stayed warmer than the OA tem
43、pera-tureinthesummerandevenwarmerwhenminewaterwasusedasaheatsink,suggestingthatusingtheGSHPsystemtoprovidecoolingwouldbelessefficientthanusingtheexistingair-cooledchiller. Therefore, the annual energy analysis performed wasbasedonthepremisethattheGSHPsystemwouldprovideonlyheating.Figure 3b shows the
44、 methodology to predict full-yearGSHP system performance. First, the building heating loads(QBH) were predicted as a function of TOA based on a curvefit derived from the January through April measured data oftheheatingoutputofthebuildinghot-waterloop.AssuminganOA temperature reset schedule for the h
45、eat pump supplytemperature (THPS, which is the heat pump load-side leavingwater temperature) and a constant mine-water supplytemperature (TMWS) as observed during the monitored timeperiod,theheatpumpheatingcapacityandheatingcoefficientof performance (COP) were determined by using the heatingperforma
46、nce data provided in the product data catalog. Theheat pump heat output (QHPh) was calculated on the basis ofthe assumption that the heat pump operates to satisfy the QBHuntil reaching its full capacity. Then the existing heatingsystem will fill the gap between the building heating load andthe heat
47、pump capacity. The heat pump power consumption(WHPh) was calculated by using the heat pump heat outputandheatingCOP.Themine-waterlooppumppowerconsump-tion(WLP)waspredictedfromthepumpingpowerratiodeter-mined from the curve-fit for the daily mine-water loop pumpenergy use versus heat pump daily heat o
48、utput (QHPH)derived from the January throughApril measured data. TMY3weather data (WBT 2014) for Butte-Bert Mooney Airport,which is 6.5 miles (10.5 km) southeast of the site, is used forthe annual energy analysis.Withthecalculatedheatpumppowerconsumption(WHPH)and WLP, the total power consumption of
49、the GSHP system wascalculated and the overall system COP was determined.ANALYSIS AND RESULTSKey results from the data analysis are presented below.More detailed data analysis and results can be found in anaccompanying technical report (Malhotra and Liu 2014).Measured Performance AnalysisMine-Water Loop
