How dose the heat pump transfers from cold to hot body ?
When your running the heat pump in heat mode, you have actually switched the routing of the freon so that the outside unit becomes the evaporator and the inside unit becomes the condenser. Knowing this, the outside unit, even though it is in the cold air is picking up heat from the cold air because the coil is colder then the outside air. Then, in addition to this temperature gain, the compressor adds heat due to compression and you get the warm air inside.
The heat pump uses work to transfer heat (Q) from a body at a lower temperature to a body at warmer temperature.
Normally heat flow direction is high to low temperature zone when no work is input . But if external work is spent, then heat may flow in reverse direction also as per the thermodynamic principle. Heat pumps ( refrizerator, air conditioners etc.) follow above principle
Heat cannot flow from cold to hot under any circumstances. A refrigeration system in an air conditioning unit, when used as a cooling system, uses the expansion of a liquid refrigerant to produce the cooling and exchanges heat with (removes heat from), the circulating air of the building. The refrigerant after doing its work is fully re-vaporised, compressed, cooled and condensed to begin the cycle of cooling again. As a heat pump, the difference in the cycle is that, the compression of the refrigerant gas causes an increase in temperature of the gas. Instead of the gas then being cooled and condensed, the cooler/condenser becomes the heat exchanger between the circulating air of the building and the hot gases. The refrigeration expansion stage is by-passed. The hot gases simply exchange heat with (transfers heat to), the surrounding air as it is circulated and passes over the coils containing the hot refrigerant gases. This cools the refrigerant gas therefore decreasing its pressure. It is then re-compressed and thereby re-heated and begins the cycle again.
