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Appendix A – CO2 as a Working Fluid in Heat Pumps where p is the absolute pressure, V is the internal volume of components and tubing, n is the number of moles, R is the universal gas constant, T is the absolute temperature and Z is the compressibility factor. Eq. (A2) shows that the supercritical pressure is determined by the internal volume and the momentary CO2 charge in the high-pressure side of the system, when assuming constant average temperature in components and tubing. The most commonly used method to control the high-side pressure in a transcritical CO2 heat pump system is to use a low-pressure receiver (LPR) installed at the evaporator outlet (Lorentzen, 1990). Figure A8 shows the principle of the LPR system. SUCTION GAS HEAT EXCHANGER Oil return GAS COOLER COMPRESSOR Heat sink EXPANSION VALVE EVAPORATOR Heat source LPR Figure A8 Principle of a CO2 heat pump system equipped a low- pressure receiver (Lorentzen, 1990). The high-side pressure is controlled by adjusting the opening of the expansion valve, thus temporarily changing the balance between the mass flow rate in the compressor and the valve. By reducing the valve opening, more CO2 will accumulate in the gas cooler and piping, and the high-side pressure will rise until a new balance point for the mass flow rate in the compressor and the valve has been reached. The extra CO2 charge needed to increase the pressure is boiled off and transferred from the liquid reservoir in the receiver. When reducing the opening of the expansion valve, the high-side pressure will be reduced, and the surplus CO2 is stored as liquid in the receiver. A12PDF 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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