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Figure 2-13 outside air evaporator EVI enabled compressor fan outside air vapor injection port electronic expansion valve condensor water out water in solenoid valve (main) TXV thermal expansion valve refrigerant "sub-cooler" sub cooled liquid refrigerant Figure 2-14 operating range of a vapor injection compressor 140 120 100 80 60 40 20 0 -60 -40 -20 operating range of a typical 2-stage scroll compressor 0 20 40 60 refrigerant evaporating temperature (oF) refrigerant temperature entering the evaporator, the better it can absorb heat from cold outside air. The vapor formed as part of the refrigerant expands within the sub-cooler is at a pressure higher than that at the suction port of the compressor. This medium-pressure vapor is routed back into the refrigeration cycle using a specially designed scroll compressor with a medium- pressure vapor injection port. The medium-pressure refrigerant vapor enters at a specific location within the scroll set. That location prevents the injected vapor from flowing toward the low-pressure side of the scroll set. This effectively increases the compression ratio beyond the mechanical ability of the compressor alone. Figure 2-14 compares the refrigerant temperature operating range of a typical 2-stage scroll compressor versus a scroll compressor using EVI. Notice that the vapor-injected compressor can achieve much lower refrigerant evaporating temperatures. The lower the refrigerant evaporating temperature, the lower the outdoor air temperature from which useable heat can be extracted. One characteristic of air-to-water heat pumps using EVI refrigeration systems is an increase in heating capacity as the temperature of the water leaving the condenser increases. This is shown in Figure 2-15. This characteristic is counterintuitive because it is opposite from the decrease in heating capacity of non-EVI refrigeration systems as the water temperature leaving the condenser increases. However, as is true with non-EVI refrigeration circuits, there is a significant drop in COP as the water temperature leaving the condenser increases. Since the principal goal is to keep the heat pump’s COP as high as possible, it’s always best to operate the hydronic system at the lowest water temperature that maintains comfort in the heated space. Many contemporary air-to-water heat pumps, especially those intended for use in cold climates, now use EVI refrigeration systems. These heat pumps are sometimes called “cold climate” or “low ambient” heat pumps to emphasize their suitability 17 refrigerant condensing temperature (oF)PDF Image | Heat Pump Systems 2020
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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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