Aerothermal and hydrothermal | Idae

Directive 2009/28/EC of European Parliament and of the Council, of 23 April 2009, on the promotion of the use of energy from renewable sources and amending and subsequently repealing Directives 2001/77/EC and 2003/30/EC, recognises as renewable energy the energy captured by heat pumps, under certain conditions. Article 2 of this Directive provides the following definitions, among others, according to the nature of the medium with which such pumps exchange heat:

Aerothermal energy is energy stored in the form of heat in ambient air.

Hydrothermal energy is energy stored in the form of heat in surface water.

A heat pump is a thermal machine which can pump heat from a cold source to a hot one. In the case of aerothermal and hydrothermal heat pumps, they extract heat from the natural environment (air or water) through an evaporator and transfer it to the interior of a building or to industrial processes through a condenser. If they are reversible, the cycle can be reversed, and heat transferred from the interior of the building to the natural environment.

Within heat pumps, we can distinguish between the following categories: electrically driven, such as the most widespread model, where the energy required to move the compressor is obtained by means of an electric motor; gas powered, where the compressor is driven by an internal combustion endothermic engine; and thermally driven, where the state of the refrigerant is changed by means of a thermal absorption or compression cycle.

To account for the share of renewable energy set out in the Directive, energy captured by heat pumps shall be considered provided that the final energy production significantly exceeds the primary energy input needed to power the heat pump, i.e. only part of the energy can be considered to be renewable.