PDF Publication Title:
Text from PDF Page: 288
Appendix A – CO2 as a Working Fluid in Heat Pumps With reference to Figure A13 and A14 it can be concluded that: ♦ The optimum high-side pressure rises almost linearly from about 7.5 MPa and 31oC CO2 outlet temperature to about 10 MPa at 40oC. Consequently, the higher the CO2 outlet temperature from the gas cooler, the higher the optimum high-side pressure. ♦ The COP drops off quite rapidly when the high-side pressure is below the optimum value, particularly at CO2 outlet temperatures near and above the critical temperature. Conversely, the COP is quite invariable when the high-side pressure is above the optimum value. As a result, the high-side pressure for a CO2 heat pump cycle should be kept at or slightly above the optimum value. ♦ At CO2 outlet temperatures above the critical temperature, the opti- mum high-side pressure is virtually independent of the evaporation temperature (maximum ±1.5% variance). ♦ When the CO2 outlet temperature drops below approximately 30oC, there is no optimum high-side pressure since the isobars are virtually coincident (ref. Figure A7). However, this is only true as long as the CO2 outlet temperature is constant when varying the high-side pressure. This topic is elaborated in Section A2.4. ♦ At high-side pressures above the optimum value, a deviation in the order of 0.1 to 0.3 MPa from the optimum value will not reduce the COP by more than a few percent. Hence, the influence of the pressure drop in the gas cooler can be neglected when calculating the optimum high-side pressure. ♦ In bivalent space heating systems (ref. Section 2.1), the optimum high-side pressure providing the maximum COP for the total heating system, will in most cases be higher than that of monovalent systems. The reason is that the heating capacity of the heat pump unit can be increased by raising the high-side pressure, thus reducing the need for supplementary heating (Richter et al., 2000 and Aarlien, 2002). The heat from the heat pump will in any case be delivered at a higher energy efficiency that that of the peak load unit. Skaugen (2002) investigated a transcritical CO2 air conditioning system, and concluded that superheating of the suction gas by using an internal (suction gas) heat exchanger slightly decreased the optimum high-side pressure. Only at an evaporation temperature of 20oC, a significant im- provement of the maximum COP could be achieved by introducing superheat. A18PDF Image | Residential CO2 Heat Pump System for Combined
PDF Search Title:
Residential CO2 Heat Pump System for CombinedOriginal File Name Searched:
20559406.pdfDIY PDF Search: Google It | Yahoo | Bing
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
Heat Pumps CO2 ORC Heat Pump System Platform More Info
CONTACT TEL: 608-238-6001 Email: greg@infinityturbine.com (Standard Web Page)