ABSTRACT
Heat pumps are thermodynamic devices allowing for the recovery of energy in the form of sensible and/or latent heat from relatively low-temperature heat reservoirs and, simultaneously, supplying sensible heat to higher-temperature heat reservoirs for residential, commercial, or industrial usage. The first law of thermodynamics uses concepts such as internal energy, heat, work, enthalpy, and specific heat. In thermodynamic systems, the heat and work that can lead to changes in the system's internal energy are equivalent variables. Improvements of mechanical vapor compression heat pump technology aim at: reducing the cycle thermodynamic losses; providing optimum amount of vapor superheat at the evaporator outlet and liquid subcooling at the condenser outlet; recovering expansion energy losses; and achieving multistage cycles. Subcooling is usually achieved within the heat pump condenser once liquid refrigerant starts accumulating within the area close to the condenser exit. In practice, the refrigerant subcooling can be realized without internal heat exchanger or other similar devices.
