Heat Pumps
Foundation · Bằng chứng và paraphrase khá trực tiếp.
A An air-source heat pump transfers energy from outdoor air into a building. It can provide more heat than the electrical energy consumed by its moving parts because electricity drives a transfer process rather than creating all the heat directly. B The simplified circuit contains four main devices connected by sealed pipework. The refrigerant changes pressure and, at some points, physical state as it travels around the loop. C Outside the building, the evaporator absorbs heat and turns low-pressure liquid refrigerant into vapour. The vapour then enters the compressor, which raises both its pressure and temperature before sending it indoors. D Inside, the hot refrigerant passes through the condenser and releases heat to the building. It next crosses the expansion valve, where its pressure falls sharply. A refrigerant loop carries the cooled fluid back to the outdoor unit so that the cycle can begin again. E Sensors measure temperatures, pressure and electrical input at several points. Frost on the outdoor coil can reduce performance, so real systems periodically reverse or modify the cycle to remove it. F The diagram omits fans, pumps and the building's heat-distribution system. Actual efficiency depends on outdoor temperature, flow temperature, installation quality and operation over a complete season.