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7 – Discussion and Analysis 7.1.3 High-Side Pressure Control 7.1.3.1 The Optimum High-Side Pressure At each temperature program and operating mode for the prototype CO2 heat pump unit, there was a maximum COP which corresponded to an optimum high-side pressure (ref. Section 5.1.3.5, Comparison of the Measurements in the Different Heating Modes). The experimental results regarding the optimum high-side pressure can be summarized as follows: ♦ The combined mode – At constant DHW temperature and 33/28oC, to 40/35oC supply/return temperatures in the SH system, the optimum high-side pressure ranged from approximately 8.0 to 9.0 MPa (60oC), 8.5 to 9.5 MPa (70oC) and 8.5 to 9.5 MPa (80oC). ♦ The combined mode – At constant supply/return temperatures in the SH system and 60 to 80oC DHW temperature, the measured opti- mum high-side pressure ranged from approximately 8.0 to 8.5 MPa (33/28oC), 8.5 to 9.0 MPa (35/30oC) and 8.5 to 9.5 MPa (40/35oC). ♦ The DHW mode – The optimum high-side pressure rose from 9 to 10 MPa when the DHW temperature was incresaed from 60 to 70oC. ♦ The SH mode – The optimum high-side pressure increased from 8 to 9.5 MPa when the supply/return temperatures in the SH system was altered from 33/28 to 40/35oC. The experimental results demonstrated that the higher the temperature level in the SH system and the higher the DHW temperature, the larger the optimum high-side pressure. In the combined mode, the temperature level in the SH system had a greater impact on the optimum high-side pressure than the DHW temperature, i.e. 0.14 MPa/°C vs. 0.03 MPa/oC. This was due to the fact that the SH gas cooler unit gave off heat in the pseudo- critical region, where the specific heat capacity of the CO2 reach large peak values, and the temperature glide for the CO2 is relatively moderate during heat rejection (ref. Appendix A2.1, Temperature Gradients During Heat Rejection). As a consequence, even small variations in the high-side pressure had a considerable impact on the temperature difference between the CO2 and the water, and with that the heating capacity of the counter- flow gas cooler unit. Figure 7.3 shows the correlation between the pressure and the pseudocritical temperature for supercritical CO2 (RnLib, 2003). 214PDF Image | Residential CO2 Heat Pump System for Combined
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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
Heat Pumps CO2 ORC Heat Pump System Platform More Info
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