ASHRAE ST-16-017-2016 Performance Analysis of a Ground-Source Heat Pump System Using Mine Water as Heat Sink and Source.pdf
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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
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