地源热泵外文翻译英

1、1Energy Efficiency Technologies -Air Source Heat Pump vs. Ground SourceHeat PumpAbstract. Heat pump deserves the name of eco-innovation. It usesfreeenergywarmthcollected in the soil or in the air to provide heating and cooling. There are two main types of heatpumps-air source heat pump and ground so

2、urce heat pump. How do they work? What are thebenefits of each system? How do they compare? First of all, questions like“whatis heat pump,how does it work, what are ASHPs and GSHP”s will be answered. Then a detailed comparisonbetween ASHPs and GSHPs will be carried out, from technological parameters

3、 to social,practical, economical parameters. Finally, the conclusions are drawn from these parameters asto decide which kind of heat pump is better off under different conditions.Keywords: Heat pump, Efficiency, Air Source Heat Pump, Ground Source Heat PumpNomenclatureQe: condensation heat rate, kJ

4、s-1Qc: evaporation heat rate, kJ s-1W: compressor input energy, kWCOP: coefficient of performancem: mass flow rate, kgh: enthalpy, kJ kg-1Q: the rate of heat transfer, kJIsUc/e Ac/e: overall heat transfer coefficient of condenser / evaporator, kW oC-1K: constant, equals Ue Ae / Uc Ac.Tc: temperature

5、 in cold region(heat source), oCTh: temperature of warm region (heat sink), oCTre: temperature of refrigerant in evaporator, oC Trc: temperature of refrigerant in condenser, oCTeout: temperature of outlet fluid in evaporator, oC Tcout: temperature of outlet fluid incondenser, oC1. IntroductionThe ph

6、ysical law tells us that heat normally flows from a warmer medium to a colder one. But canwe move heat from our cooler house and dump it to a higher outside environment in summer?And can we extract heat from a lower temperature outside, to our warmer rooms in winter? Theanswer is yes if we use a hea

7、t pump. The heatpump does so by essentially“pumping ” heat up the temperature scale, transferring itfrom a cold material to a warmer one by adding energy, usually in the form of electricity. The most2com mon type of heat pump is the air-source heat pump, which tran sfers heat betwee n in doorand the

8、 outside air. Ground Source heat pumps (GSHPs) have bee n in use since late 1940s,they use the con sta nt temperature of the earth as the excha nge medium in stead of the outsideair temperature.2. Backgro und2.1 Heat PumpsHeat pumps (vapor compressi on heat pumps) tran sfer heat by circulat ing a ph

9、ase changingsubstanee called a refrigerant through a cycle of evaporation and conden sati on (Figure 1).A compressor pumps the refrigera nt betwee n two heat excha nger coils. In one coil, the refrigerant is evaporated at low pressure and absorbs heat from heat source, the refrigerant is thencompres

10、sed en route to the other coil, where it condenses at high pressure, at this point, itreleases the heat it absorbed earlier in the cycle to the heat sin k(NRCOEE,2004,p.4).CondtnserHqh-Pruturo,HiQhTBTpflfB?jrQ L iquidLOsvPr CM谢札iQwdampvotur* LiquidCompiEssurHigh-Tompc-fipcratura VopaurFigure 1. Basi

11、c Vapor Compressi on CycleSource: NRCOEE (Natural Resources Ca nada Office of En ergy Efficie ncy), 2004, p.42.2 En ergy Bala nee and Efficie ncy of Heat PumpsFrom the laws of thermodynamic, the Energy Balance of a heat pump system is:Qc=Qe+WWhere Qe is the heat absorption rate by the evaporator and

12、 Qc is the heat given off atthe conden ser (Figure 1).3The operating temperatures of the vapor-compression refrigeration cycle are established by thetemperature Tc to be main tai ned in the cold regi on and the temperature Th of the warm regionto which heat is discharged; the refrigerant temperature

13、 in the evaporator must be less tha n Tcand the refrigera nt temperature in the conden ser must be greater tha n Th to allow heat transferri ng (Figure 2).Figure 2a. Vapor-compressio n refrigerati on cycle: T-S diagramSource: Refrig. Lab of Queen s University,2007, p.9Ejcpansk*nVulvcFigure 2b. Vapor

14、-compressio n refrigerati on cycle: In (p)-h diagramSource:Rademacher,2005, p.70As fluids pass through evaporator and conden ser, which are two heat excha ngers thatexcha nge heat betwee n refrigera ntand surrounding fluids. The rate of heat transfer from refrigerant to the surrounding fluidin conde

15、n ser and the rate ofheat tran sfer from surro unding fluid to the refrigera nt in evaporator can be expressedTemperature t/t*arm region.45by-Q:Q=m*Ah=UAOLMTHerem is the mass flow rate of refrigerant,Ah is the enthalpy change of refrigerant,U is termed the overall heat transfer coefficient, A is the

16、 area of the surface separating the fluids throughwhich the heat transfer occurs andLMT is the mean differencesbetwee n the temperatures of the two fluids. The classic parameter that has bee n used to describe theperforma nee of a heat pump is the coefficie nt of performa nce(COP), which is the rati

17、o of the qua ntityof heat tran sferred to the heat si nk (useful en ergy output) to the quantity of work driving thecompressor (total energy input)(ReynoIds1977, pp. 287-289).COP =Qc/W=Qc/(Qc-Qe)=1/(1-Qe / Qc)3. Air Source Heat PumpsAir Source Heat Pumps are the most widely used heat pump no wadays,

18、 ambie nt air is free and widelyavailable, and it is the most com mon heat source for heat pumps.In an air-to-air heat pump system, heat is removed from in door air and rejected to the outside of a building duri ng the cooli ng cycle, while the reverse happe ns duri ng the heati ng cycle (Figure 3).

19、Figure 3. ASHP - Split systemSource: EERE(E nergy Efficie ncy and Ren ewable En ergy),2008aFor application, ASHP is typically roof top units either completely packaged or split packaged systems.Split package heat pumps are desig ned with an air han dli ng unit located in side the con diti onedspace

20、while the conden ser and compressor are packaged for outdoor in stallatio n on the roof.Packaged systems usually have both coils and the fan outdoors. Heated or cooled air is delivered to theinterior from ductwork that protrudes through a wall or roof (EERE,2008).In reality, the capacity and perform

21、a nee of air-source heat pumps decreaserapidly with decreasingambient temperature during heating season,and with increasing ambient temperature during coolingseason. Especially over extended periods of sub-freezing temperatures, as the air source temperaturedrops below 4o C there is potential for th

22、e evaporators to suffer performance degradation due to iceformation(Lu Aye,2003).LtimpresiorLDirwderseiF -uIndoorEklra.oIH.UIjOurdwrEpriWilVisvffu Liquiddri :于髦何 IE r m 谕脚i| ridei “町Outdo cr_，P 3hGa$ uconrifriiwrvtQdliiavjid6Nonetheless, compared with conventional heating methods, an ASHP has follow

23、ing benefits:- Typically draws approximately 1/3 to 1/4 of the electricity of a standard electrical heating for the sameamount of heating, reducing utility bills and greenhouse gas emissions accordingly (HyperPhysics2005).- Typical COP of an ASHP is about 200%-400% compares to 100% for a resistance

24、heater and 70-95%for a fuel-powered boiler (HyperPhysics 2005).- As an electric system, no flammable or potentially asphyxiating fuel is used at the point of heating,reducing the potential danger to users, and removing the need to obtain gas or fuel supplies except forelectricity (HyperPhysics 2005)

25、.4.Ground Source Heat PumpsLike any heat pumps, ground source heat pumps are able to heat, cool the house. Although publicawareness of this beneficial technology is low, GSHPs in fact have been in commercial use for over 50years. The first successful demonstration of GHPs occurred back in 1946, at t

26、he CommonwealthBuilding in Portland, Oregon(Stuebi 2000).4.1 Components of GSHP Systems-The Earth Connection:The earth connection transfers heat into or out of the ground or water body. It often takes the form of anoutdoor heat exchanger. This is a coil or pipe carrying water, an antifreeze mixture,

27、 or another heattransfer fluid. It may be buried in the ground, in which case it is called a ground-coupled system, orsubmerged in a lake or pond, in which case it is called a surface water system(NRC(Natural ResourcesCanada),2008).-A Heat Pump:This is the heart of a GSHP Systems, they operates acco

28、rding to the same principle as conventionalheat pumps. All the components of the heat pump are typically housed in a single enclosure whichincludes the earth connection-to-refrigerant heat exchanger, the compressor, controls, the fan, an airfilter, an air handler, and refrigerant-to-air heat exchang

29、er(NRC,2008).-The Interior Heating or Cooling Distribution System:The distribution system is needed for distributing heating and cooling inside the building. GSHPsystems typically use conventional ductwork to distribute hot or cold air and to provide humiditycontrol(NRC,2008).4.2 Types of Ground Sou

30、rce Heat Pump SystemsThere are different ways to categorize GSHPs. Depending on the When it uses earth as heatsource/sink, the earth connection could be either horizontal or vertical, and they are both closed-loop.When it uses water as heat source/sink, it could be closed-loop or open-loop (Fig 4).7

31、-Horizontal (Closed-Loop)This type of installation is generally most cost-effective for residential installations, particularly for newconstruction where sufficient land is available(EERE,2008b). It requires trenches at least four feetdeep(EERE,2008b).-Vertical (Closed-Loop)Vertical systems are used

32、 when land area required for horizontal loops would be prohibitive or the soil istoo rocky for trenching, they are widely used for large buildings(NRC,2008). Although it requires lesssurface area, it requires much deeper trenches than horizontal loops(NRC,2008).-Pond/Lake (Closed-Loop)A closed pond

33、loop is not as common, it uses water as heat source/sink(NRC,2008).If the site has an adequate water body, this may be the lowest cost option (EERE,2008b).-Open-Loop System (Open-Loop)An open loop system pulls water directly from a well, lake, or pond. Water is pumped from one of thesesources into t

34、he heat pump, where heat is either extracted or added and the water is then pumped backinto the ground or source body of water(SEW(Shanky Engineering Works),2008). This type was the firstto appear on the market, is the simplest to install, and has been used successfully fordecades(NRC,2008). However

35、, environmental regulations and insufficient water availability may limit itsuse in some areas(NRC,2008).8Source: EERE 2008b5.Comparis ons5.1 Efficie ncyFrom equation,Qe/Qc =(Ue AeLMT)/(c AcLM)For simplification,LMT can be substituted by (Tin+Tout)/2, whereTin is thin let temperature differe nee and

36、Tout is the outlet temperature differe nee (Figure 5 andFigure 6).IBMOalM.Figure 5. Heat exchange in CondenserFigure 6. Heat exchange inClos&d Loop SystevmClosedl Loop Systems沪阳诵3扈Opn Loop SystemsFigure 4. Types of Ground Source Heat Pump Systems910EvaporatorAssuming that refrigerant temperature

37、 in condenser and evaporator are constant, the inletfluid temperature in evaporator is Tc and that in condenser is Th.Qe/Qc = UeAe(Tein+TeOUtCAc(Tcin+Tcout)= Ue Ae (Tc-Tre+Teout-Tre)/Uc Ac(Trc-Th+Trc-Tcout )= K(Tc-Tre+Teout-Tre)/(Trc-Th+Trc-Tcout )Where Tc is the temperature in cold region(heat sour

38、ce), Th is the temperature of warmregion (heat sink); Tre is the refrigerant temperature in evaporator, Trc is the refrigeranttemperature in condenser; Teout is the fluid outlet temperature in evaporator and Tcout isthe fluid outlet temperature in condenser; K is a constant, equals Ue Ae / Uc Ac.To

39、compare between ASHP and GSHP in winter, it is assumed that except Tc, all otherparameters are the same for the ASHP and the GSHP.GSHP has higher Tc than ASHP because ground has dampening effect on temperaturevariation (see Appendix 1), then by using equation, we can see that Qe/Qc of GSHP ishigher

40、than that of ASHP. Also by equation, we see that COP is directly proportional toQe/Qc, thus, GSHP has higher efficiency than ASHP.Furthermore, in the vertical configuration of GSHP, the heat exchanger is buried deeper inthe ground, where, as we can see, temperature is more stable year-round. In cont

41、rast, theheat exchanger of the horizontal configuration is near the surface ground and is thereforeinfluenced by atmospheric temperature. As a result, the vertical exchanger permits theheat pump to operate most efficiently.5.2 Design Criteria- Pre-construction study (feasibility study)ASHPs do not i

42、ncur any civil ground works for the installation and lying of pipe.GSHPs need investigation of the soil or groundwater conditions and it is an important partof a feasibility study. For ground coupled systems, soil conditions will influence not onlythe feasibility of drilling and trenching, but also

43、the performance of the earth connection.Similarly, ground water availability, and regulations concerning its use, will determine thefeasibility of a groundwater earth connection.But for GSHPs, building designers have much greater flexibility. Architects are not facedwith the prospect of unattractive

44、 HVAC equipment on rooftops, and can consequentlyemploy a wider variety of roof types (such as sloped roofs)(Stuebi 2000).- Construction Difficulty Index11For ASHPs, it is very simple to install but for GSHPs, since earth connections in a GSHPsystem are usually very difficult to reach after installa

45、tion, the materials and workmanshipmust be of the highest quality, which in some cases, may block the application of GSHPs.5.3 Cost- Installation costASHPs has a much lower installation cost than GSHPs (see Appendix 2).And cost fordifferent GSHP types also varies (see Appendix 2).- Operation CostDue

46、 to high efficiency and high heating/cooling capacity of GSHP, GSHPs can saveownersoperational cost by reducing energy cost significantly (seepeAnpdix 3).- Maintenance CostGSHPs have a stable geology environment, not affected by such climate disasters likesnows, hailstorm, Typhoon etc, while ASHPs a

47、re vulnerable to the external environmentand thus require more maintenance cost.- Life Cycle CostOverall, GSHPs has a much lower LCC than ASHPs (see Appendix 4).5.4 EnvironmentEnvironmentally, GSHP represent a superior alternative in many aspects. Lowerrefrigerant charges and reduced leakage when co

48、mpared to air-source systems are twoadvantages they share over these systems(Phetteplace 2007). And since they use lessenergy, they produce less CO2, SO2, NOx emissions indirectly (see Appendix 4). ButGSHPs can cause land disturbance when ground-coupled system is implemented andwater contamination p

49、roblems if water source/sink is used.5.5 ReliabilityThe expected lifespan of an ASHP is 15 years(EERE (2001) p.3). Dr. Gordon Bloomquistof Washington State University observes that GSHP installations dating back from themid-1950s“arestill providing a high level of service to building owners”a,ndsuggeststhat“systemreliability of 25-30 years is easily attainable if routine maintenanceprocedures are followed”(Stuebi 2000).In conclusion, the comparison between ASHPs and different types of GSHPs are listedbelow:Table 1. Comparison between ASHPs and different types of GSHPsASHPsGSHPsVenicalHorizont