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CHAPTER 2: LITERA TURE 33 increased. This makes CO2 a promising candidate for use in these kinds of applications (Neksa, 2002). Most studies on the use of heat pump technology for space heating concentrate on combining it with tap water heating. This contributes to a more efficient system where one application covers two heating demands. With the temperature glide found in the gas cooler it is made possible to make full use of heat pump applications for combined space heating and tap water heating (Neksa, 2002). 2.5.4 Heat pumps for Domestic Hot Water Heating 2.5.4.1 Conventional Heat Pumps for Domestic Hot Water Heating In a typical heat pump system as shown in figure 2.21, the evaporator extracts heat from a heat source at a low temperature. Through the evaporator, heat is absorbed by the low temperature fluid turning it into a low temperature gas as it absorbs the heat. The gas pressure is then increased by means of a compressor causing the fluid temperature to rise drastically, producing a heating effect which is exploited in heat pumps. The hot gas flows to the condenser where the heat is rejected from the working fluid and changes it from a gas to a liquid. As the working fluid is still at a high pressure it is passed through an expansion valve which reduces the pressure, producing a cooling effect which is used for refrigeration. By doing this the fluid returns to a liquid phase at low pressure. The working fluid then returns to the evaporator and the cycle starts over again (ANON (b), s.a.). In conventional heat pump cycles which may use HFCs or HCFCs the liquefaction process occurs below the critical temperature of the refrigerant. The critical temperature is the point above which liquid cannot exist thus there it is referred to as a subcritical cycle. This cycle requires that the refrigerant critical temperature must be above the temperature at which the medium is rejecting its heat. Thus condensing of the refrigerant vapour yields a condensing pressure that is also below the critical pressure. condensing pressure and temperature are linked by a unique relationship that depends on the nature of the refrigerant (Bensafi & Thonon, 2007). A subcritical cycle using R-22 as refrigerant is discussed because it gives a good idea of a cycle operating in its subcritical region and because is the refrigerant A Techno-Economical Analysis of a CO2 Heat Pump. School of Mechanical Engineering, North-West UniversityPDF Image | CO2 HEAT PUMP Analysis
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CO2 Organic Rankine Cycle Experimenter Platform The supercritical CO2 phase change system is both a heat pump and organic rankine cycle which can be used for those purposes and as a supercritical extractor for advanced subcritical and supercritical extraction technology. Uses include producing nanoparticles, precious metal CO2 extraction, lithium battery recycling, and other applications... More Info
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