Han, Linjun

Li, Xianting

Shi, Wenxing

Wang, Baolong

English

Purdue E-Pubs

Purdue UniversityPurdue e-PubsInternational Refrigeration and Air ConditioningConference School of Mechanical Engineering2010A Novel Capacity Modulation Technology forHeat Pump System with Scroll CompressorBaolong WangTsinghua UniversityLinjun HanTsinghua UniversityWenxing ShiTsinghua UniversityXianting LiTsinghua UniversityFollow this and additional works at: http://docs.lib.purdue.edu/iraccThis document has been made available through Purdue e-Pubs, a service of the Purdue University Libraries. Please contact epubs@purdue.edu foradditional information.Complete proceedings may be acquired in print and on CD-ROM directly from the Ray W. Herrick Laboratories at https://engineering.purdue.edu/Herrick/Events/orderlit.htmlWang, Baolong; Han, Linjun; Shi, Wenxing; and Li, Xianting, "A Novel Capacity Modulation Technology for Heat Pump System withScroll Compressor" (2010). International Refrigeration and Air Conditioning Conference. Paper 1074.http://docs.lib.purdue.edu/iracc/10742267, Page 1International Refrigeration and Air Conditioning Conference at Purdue, July 12-15, 2010A Novel Capacity Modulation Technology for Heat Pump Systemwith Scroll CompressorBaolong Wang1*, Linjun Han2, Wenxing Shi3, Xianting Li41Department of Building Science, Tsinghua University, Beijing, 100084, P.R. ChinaPhone: +86-10-62786571, Fax: +86-10-62773461, E-mail: wangbl@tsinghua.edu.cn2Department of Building Science, Tsinghua University, Beijing, 100084, P.R. ChinaPhone: +86-10-62786571, Fax: +86-10-62773461, E-mail: hanlinjun@gmail.com3Department of Building Science, Tsinghua University, Beijing, 100084, P.R. ChinaPhone: +86-10-62796114, Fax: +86-10-62773461, E-mail: wxshi@mail.tsinghua.edu.cn4Department of Building Science, Tsinghua University, Beijing, 100084, P.R. ChinaPhone: +86-10-62775860, Fax: +86-10-62773461, E-mail: xtingli@tsinghua.edu.cn* Corresponding AuthorABSTRACTHeat pump technology has been rapidly developed recently as a clean and efficient heating method. Continuouscapacity modulation of heat pumps is necessary for enhancing room thermal comfort and reducing start-stop losses.A novel capacity modulation method for the scroll compressor heat pump system based on refrigerant injection andrefrigerant release is proposed. The experiments indicate the refrigerant injection increases the heating/coolingcapacity by 21.9%/21.4% and enhances the heating COP/cooling EER by 5.6%/9.0% when the glycol inlettemperature of condenser and evaporator is fixed at 40 and 0 , respectively. The tests also show the refrigerantrelease decreases the heating/cooling capacity by 26.6%/31.4% and enhances the heating COP/cooling EER by16.0%/8.4% when the condensing and evaporating temperature fix at 40 and 1.7 , respectively. To sum up, thetechnology combining refrigerant injection and refrigerant release is a remarkable capacity modulation method forheat pump systems with scroll compressors, which can modulate the capacity continuously within a wide range aswell as increase its energy efficiency ratio.1. INTRODUCTIONBecause of possible energy savings and emission reduction, heat pump technology has been rapidly developedrecently as a clean and efficient heating method. For space heating, the heating requirement varies in a large rangedue to the change of indoor and outdoor situations, so the ability of continuous capacity modulation is necessary forenhancing room thermal comfort and reducing start-stop losses. Moreover, increasing the energy efficiency of heatpump system under off-design conditions is the main way to increase the seasonal performance of the systembecause field surveys show that the system is operated under off-design conditions for most of the operating time.So continuous capacity modulation method considering the energy efficiency under off-design conditions willlargely accelerate the development and promote the application of heat pump systems.Much research has been done for capacity control of the heat pump and different methods are proposed, such as hotgas bypass, suction pressure modulation, suction valve control, and so on. For heat pump systems with scrollcompressors, frequency conversion and digital scroll technology are often utilized. However, these methods aboveeither achieve the capacity reduction only or sacrifice the system efficiency.2267, Page 2International Refrigeration and Air Conditioning Conference at Purdue, July 12-15, 2010Actually, refrigerant injection and refrigerant release technologies are remarkable capacity modulation methods forheat pump systems with scroll compressors, which can modulate the capacity as well as increase the energyefficiency under off-design conditions.2. REFRIGERANT INJECTION TECHNOLOGYFor upward capacity modulation, refrigerant injection technology is an effective method. Figure 1 shows the heatpump system of scroll compressor with refrigerant injection technology. This system is constituted by the maincircuit and the injection circuit. The main circuit is made up of a scroll compressor, a condenser, an expansion valveand an evaporator orderly, which is just a conventional heat pump. The injection circuit includes an expansion valve,a heat exchanger, an adjust valve and a check valve. One end of the injection circuit locates on two injection ports ofthe fixed scroll plate of the scroll compressor and the other connects with the outlet of the condenser.(a) Configuration schematics (b) Schematic p-h diagramFigure 1. Scroll compressor refrigeration system with refrigerant injectionWhen the capacity of the heat pump matches the requirement, the adjust valve in the injection circuit turns off andthe injection circuit is out of work. In this case, the system just operates as an ordinary heat pump. Once the capacitysupplied by the heat pump is not enough for the requirement, the adjust valve turns on and adjusts with theexpansion valve for injection according to the capacity needed. In this case, part of the refrigerant at the outlet ofcondenser will be throttled by the expansion valve of the injection circuit, then be heated by the refrigerant of maincircuit in the heat exchanger and inject into the compressor chamber finally.As a result, the refrigerant mass flow through the condenser is increased, which raises the heating capacity of theheat pump. The cooling capacity is also increased because the enthalpy at the inlet of evaporator is reduced throughthe heat transfer with the injection refrigerant in the internal heat exchanger. Furthermore, because extra refrigerantis injected into compression chamber and compressed, the pressure at the end of compression process is increased,which decreases the under-compression loss thereby improving the efficiency of compressor. In addition, therefrigerant injection can decrease the discharge temperature and thereby ensure the safety of the compressor.A lot of research (Beeton et al., 2003; Ma et al., 2003; Park et al.,2002; Winandy et al., 2002; Yang et al., 2009 )has been conducted on the refrigerant injection system. Some experiments (Wang, 2006;Wang et al., 2009) arecarried out to prove the effect of refrigerant injection and the results are showed in Figure 2. The glycol inlettemperatures of the evaporator and the condenser are 5 and 30 respectively for case 1. For case 2, thecorresponding temperatures are 0 and 40 respectively. In the experiment, the adjust valve turns on fully, and theexpansion valve for injection is adjusted from 90 steps to 140 steps.It can be seen from Figure 2 that the refrigerant injection not only increases the heating and cooling capacityeffectively but also enhances the energy efficiency ratio of the heat pump system with a scroll compressor. Thelargest enhancements of heating and cooling capacity are 21.9% and 21.4% and the largest enhancements of heatingphCondenserScroll compressorCheck valveAdjust valveExpansion valveEvaporatorHeat exchangerExpansion valve for injection2267, Page 3International Refrigeration and Air Conditioning Conference at Purdue, July 12-15, 2010COP and cooling EER are 5.6% and 9.0%, respectively. The increases of heating capacity and COP for case 2 arelarger than case 1, which indicates that refrigerant injection has a better effect on heating under bigger pressure ratiocondition.1.101.121.141.161.181.201.2290 100 110 120 130 140Opening degree of expansion valve (step)Relativecapacityheating capacity of case1heating capacity of case2cooling capacity of case1cooling capacity of case2 0.960.981.001.021.041.061.081.1090 100 110 120 130 140Opening degree of expansion valve (step)Relativeenergyefficiencyheating COP of case1heating COP of case2cooling EER of case1cooling EER of case2(a) Heating and cooling capacity (b) EER/COPFigure 2. Effect of refrigerant injection on the performance of a heat pump system with a scroll compressorGenerally, the refrigerant injection technology is proved to be a practical and effective method for increasingcapacity and enhancing efficiency of heat pumps with scroll compressors under large compression ratio conditions.3. REFRIGERANT RELEASE TECHNOLOGYIn order to decrease the capacity and enhance the efficiency of the scroll compressor refrigeration system undersmall compression ratio conditions, a refrigerant release technology is proposed (Wang et al., 2007). As shown inFigure 3, the system with refrigerant release is constituted by the main circuit and the release circuit. The maincircuit includes a scroll compressor, a condenser, an expansion valve and an evaporator as a conventional heat pump.The release circuit is a bypass channel for refrigerant release with one end connecting with the release port on fixedscroll plate and the other connecting with the suction pipe. A check valve and a adjust valve are settled on therelease circuit for stopping the reverse flow and adjusting the release flow rate.When the capacity of heat pump matches the requirement, the adjust valve in the release circuit turns off and therelease circuit is out of work. In this case, the system just operates as an ordinary heat pump. Once the capacitysupplied by heat pump exceeds the requirement, the adjust valve opens and adjusts according to the capacity needed.(a) Configuration schematics (b) Schematic p-h diagramFigure 3. Scroll compressor refrigeration system with refrigerant releasehpCondenserEvaporatorScroll compressorCheck valveAdjust valveExpansion valve2267, Page 4International Refrigeration and Air Conditioning Conference at Purdue, July 12-15, 2010In this case, part of the refrigerant in the compression chamber will release through the release channel back to theinlet of the compressor driven by the pressure difference. As a result, the refrigerant mass flow through thecondenser and evaporator is decreased, which cuts down the heating/cooling capacity of the heat pump. Furthermore,the effective compression length of scroll compressor is shortened because of the refrigerant release, and the innercompression ratio is reduced, which decreases the over-compression loss. The check valve can prevent the reverseflow of the refrigerant from inlet of the compressor into the compression chamber.Experiment is carried out to prove the effect of refrigerant release. In the experiment, the condensing temperature isfixed at 40 , the evaporating temperature is set at 1.7 , 6.1 and 11.0 respectively, and the adjust valve keepsopen fully. The results are showed in Figure 4. For comparison, the results are expressed in relative value, and thebenchmark is the point at evaporating temperature 6.1 without refrigerant release.Figure 4(a) represents the effect of refrigerant release on the heating and cooling capacity of the system. It can befound that the refrigerant release decreases the heating and cooling capacity effectively. Under different evaporatingtemperature, the heating capacity decreases by 18.2%~31.4% and the cooling capacity decreases by 20.2%~26.6%compared with the capacity without refrigerant release. Because the adjust valve opens fully in the experiment, thedecreases of the capacity here reach their maximum. Therefore, based on the experiment data, the capacity of theheat pump can be modulated within 68.4%~100% continuously with the regulation of the adjust valve.In the experiment, the resistance of the bypass channel is quite large due to the adjust valve and the check valve,which limits the release refrigerant mass flow and weakens the capacity modulation. Once the resistance of thebypass channel gets smaller by optimization, the modulating range of the heat pump will enlarge greatly.Figure 4(b) illustrates the effect of refrigerant release on the energy efficiency ratio of the system. It can be foundthat the refrigerant release enhances the efficiency level largely, and the higher the evaporating temperature is, thebigger the increase of EER and COP is. The heating COP and cooling EER rise by 41.8% and 45.4%, respectively,at a fixed evaporating temperature of 11 , which indicates the great potential for energy saving of refrigerantrelease besides capacity modulation.Generally, refrigerant release can not only adjust the capacity of the heat pump system with scroll compressoreffectively, but also enhance the efficiency of the system under small compression ratio conditions remarkable.4. BIDIRECTIONAL CAPACITY MODULATION METHODSince the refrigerant injection and refrigerant release technologies can achieve upward and downward capacitymodulation of heat pumps with scroll compressors respectively, the combination of refrigerant injection and releaseis available for bidirectional capacity modulation of scroll compressor heat pump system.0.40.60.81.01.20 2 4 6 8 10 12Evaporating temperature /Relativecapacityheating capacity without releaseheating capacity with releasecooling capacity without releasecooling capacity with release0.81.01.21.41.61.80 2 4 6 8 10 12Evaporating temperature /Relativecapacityheating COP without releaseheating COP with releasecooling EERwithout releasecooling EERwith release(a) Heating and cooling capacity (b) Energy efficiency ratioFigure 4. Effect of refrigerant release on the performance of a heat pump system with a scroll compressor2267, Page 5International Refrigeration and Air Conditioning Conference at Purdue, July 12-15, 2010Figure 5 illustrates the novel capacity modulation method for scroll compressor heat pump combining the refrigerantinjection and release technologies. Actually, it is the integration of figure 1 and figure 3, and the two check valveson the injection and release circuit are replaced by a switch valve for injection and release for easier installation.Bidirectional capacity modulation can be achieved easily with this method. When the capacity of heat pump matchesthe requirement, the adjust valves for injection and release both keep closed, and the system just operates as anordinary heat pump. When the capacity supplied by heat pump is not enough for the requirement, the adjust valvefor injection turns on and the refrigerant injection circuit will be involved to increase the capacity. Throughadjusting the expansion valve and the adjust valve the capacity can be regulated exactly to meet the demand. Whenthe capacity supplied by heat pump exceeds the requirement, the adjust valve for refrigerant release turns on and therefrigerant release process works. Through adjustment of the valve the capacity of the heat pump also can bedecreased to the appropriate value. In addition, the refrigerant injection and release method will not sacrifice theenergy efficiency of the heat pump but increase it to a certain extent.In the experiment above, the maximum modulating range of the capacity is about 70% to 120% by refrigerantinjection and release. However, the modulating range will be larger and the modulating capability will be moreexcellent after the improvement and optimization of valves and pipes of the injection and release circuit. It can bepredicted that the capacity of the heat pump will be adjusted from 50% to 130% under common conditions by thismethod, and the energy efficiency ratio will be enhanced by 5% to 40% additionally.5. CONCLUSIONSA novel capacity modulation method for heat pump systems with scroll compressors based on refrigerant injectionand refrigerant release is proposed in the paper. The experiments indicate that the maximum modulating range of thecapacity is about 70% to 120% by this new technology. After the improvement and optimization of valves and pipesof the injection and release circuit, the capacity modulating range will be enlarged. The technology combiningrefrigerant injection and refrigerant release is a remarkable capacity modulation method for heat pump systems withscroll compressors, which can modulate the capacity continuously within a large range as well as increase its energyefficiency ratio.REFERENCESBeeton, W.L., Pham, H.M., 2003, Vapor-injection scroll compressors, ASHRAE Journal vol. 45, no. 4:p.22-27.Ma, G., Chai, Q., Jiang, Y., 2003, Experimental investigation of air source heat pump for cold regions, Int. J. Refrig.,vol. 26:p.12-18.Figure 5. Novel capacity modulation method for heat pumps with scroll compressors combining refrigerantinjection and releaseEvaporatorScrollCompressorAdjust Valvefor InjectionExpansion ValveHeatExchangerExpansion Valvefor InjectionSwitch Valve forInjection and ReleaseAdjust Valvefor ReleaseCondenser2267, Page 6International Refrigeration and Air Conditioning Conference at Purdue, July 12-15, 2010Park, Y.C., Kim, Y., Cho, H., 2002, Thermodynamic analysis on the performance of a variable speed scrollcompressor with refrigerant injection, Int. J. Refrig., vol. 25:p.1072-1082.Wang, B., 2006, Study on the scroll compressor with refrigerant injection and its application, Ph.D. Thesis ofTsinghua University, China.Wang, B., Shi,W., Han, L., Li, X., 2009, Optimization of refrigeration system with gas-injected scroll compressor,Int. J. Refrig., vol. 32, no. 7:p.1544-1554.Wang, B., Shi, W., Li, X., Han, L., 2007, Variable capacity refrigeration system with scroll compressor,China,invention patent,Grant No. CN101140111.Winandy, E.L., Lebrun, J., 2002, Scroll compressors using gas and liquid injection: experimental analysis andmodeling, Int. J. Refrig., vol. 25:p.1143-1156.Yang, X., Hwang, Y., Radermacher, R., 2009, Two-stage heat pump system with vapor-injected scroll compressorusing R410A as a refrigerant, Int. J. Refrig., vol.32, no. 6:p.1442-1451.ACKNOWLEDGEMENTFinancial support from National Natural Science Foundation of China (Grant No. 50676042) and Key Laboratory ofFunctional Crystals and Laser Technology, TIPC, CAS are greatly appreciated.

A Novel Capacity Modulation Technology for Heat Pump System with Scroll Compressor

https://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=2073&amp;context=iracc

A Novel Capacity Modulation Technology for Heat Pump System with Scroll Compressor

Abstract

Similar works

Full text

Available Versions

Purdue E-Pubs