A heat pump consists of an evaporator that recovers heat from the environment (water, air, soil). In the evaporator, a refrigerant passes from liquid to gaseous state and then travels to the compressor. There, the vapours are compressed to increase pressure and temperature. Hot vapours are liquefied in the condenser unit, emitting the condensation heat to the heating medium. Then the refrigerant passes through an expansion valve where its pressure is again lowered, and continues back to the evaporator where the process is repeated. All heat acquired from the environment is free.
Raising its temperature requires some energy. Hence, electric power is required for heat pump operation to power the aggregate/ motor. The ratio between input power (electrical energy) and output heat (thermal energy) is normally between 1/3 and 1/5. The ratio between input energy and output heat is called Coefficient of Performance (COP). The value of COP depends on the type of heat pump and source of thermal energy in the environment. On average, annual COP for heat pumps is between 3 and 5 or more.
There are three basic versions of heat pumps according to the medium (environment) being cooled and the medium being heated: air/water, water/water, and brine/water (geothermal heat pumps). When designating the type of heat pump, the sources from which the heat is taken away is indicated first, followed by the medium being heated.
For optimum operation, heat pump requires effective insulation of the building and high-quality windows.
In essence, the heating system provides the input of energy that the building is unable to retain. Hence, it actually replenishes the thermal energy of the building, compensating for the energy losses. In the building, the heat is dissipated through outdoor bordering surfaces (external walls and roof) and by ventilation. In efficiently insulated houses, heating of sanitary water represents a major part of consumption. Thus, annual amount of energy required for heating depends on the characteristics of the building, i.e. the specific thermal losses of the building and the building location. Building location is indicated with the number of hours that the heating system was in operation. To this, average energy required for heating of sanitary water per person must be added.
Initial investment costs are a major factor for the systems and the break even period of investment therein. In newly constructed buildings, the chimney and the fuel storage represent a major investment; a system with a heat pump renders such investment unnecessary.
Coefficient of performance (COP) depends highly on the type of fuel and heating system. In floor heating, coefficients of performance are very high; in radiation heating, these coefficients are lower since the input water temperatures in the system are much higher.