Heat pump and refrigeration cycle
According to the second law of thermodynamics, heat cannot spontaneously flow from a colder location to a hotter area; work is required to achieve this.
Applications that need to operate at a high coefficient of performance in very varied conditions, as is the case with heat pumps where external temperatures and internal heat demand vary considerably through the seasons, typically use a variable speed inverter compressor and an adjustable expansion valve to control the pressures of the cycle more accurately.
[citation needed] The above discussion is based on the ideal vapor-compression refrigeration cycle and does not take into account real-world effects like frictional pressure drop in the system, slight thermodynamic irreversibility during the compression of the refrigerant vapor, or non-ideal gas behavior (if any).
In the generator, on heat addition, the temperature increases, and with it, the partial pressure of the refrigerant vapor is released from the strong solution.
Absorption refrigeration systems can be powered by combustion of fossil fuels (e.g., coal, oil, natural gas, etc.)
Therefore, for the same cooling load, gas refrigeration cycle machines require a larger mass flow rate, which in turn increases their size.
Because of their lower efficiency and larger bulk, air cycle coolers are not often applied in terrestrial refrigeration.
Several such setups require rotary or sliding seals, which can introduce difficult tradeoffs between frictional losses and refrigerant leakage.
In the first stage of this cycle, the refrigerant absorbs heat isothermally from a low-temperature source, TL, in the amount QL.
Next, the refrigerant is compressed isentropically (adiabatically, without heat transfer) and its temperature rises to that of the high-temperature source, TH.
Lastly, the refrigerant expands isentropically until its temperature falls to that of the low-temperature source, TL.
Thanks to this integration, the device can obtain cooling and heating effects using both thermal and electrical energy sources.
[16] The merit of a refrigerator or heat pump is given by a parameter called the coefficient of performance (COP).
Combining these two equations results in: This implies that COPHP will be greater than one because COPR will be a positive quantity.
In a worst-case scenario, the heat pump will supply as much energy as it consumes, making it act as a resistance heater.
[3] For Carnot refrigerators and heat pumps, the COP can be expressed in terms of temperatures:
