An instrumental role in energy recovery
Whether rotary or plate, a heat exchanger functions within a framework of energy recovery. It is pivotal in transferring heat or cold, facilitating heating or cooling processes. However, the thermal energy transferred from an air-to-air heat recovery system to the supply air is not classified as regenerative heat. Heat pumps are defined as renewable despite the heat exchanger’s instrumental role in energy recovery, which is often up to three times more efficient than heat pumps. The seasonal performance factors of an air/air heat recovery system are between 12 and 25, while the seasonal performance factors of a heat pump are between 3 and 6. As a result, the narrative veers toward classifying it as non-renewable, contrary to its heat pump counterpart.
The intricacies emerge when considering the source of heat or cold for these systems. Drawing from naturally replenishing sources, a heat pump aligns with the renewable energy narrative. The issue is that it is not the source of the heat energy that determines whether heat energy is regenerative or not but the system that makes the heat energy usable. Moreover, when a heat pump utilises return air from a building’s ventilation system, the extracted heat transforms into a renewable resource capable of heating water and power boilers. This is the case, for example, in toilet exhaust air units. These units have only one exhaust air volume flow and use the waste heat via a heat pump to heat drinking water, which is classified as regenerative heat. However, the delineation blurs when this extracted heat from return air is employed in plate heat exchangers or regenerative air systems to heat supply air.
In some markets, the temperature level at which the heat is recovered influences its classification as renewable. Heat exchangers tend to operate at lower temperatures than the sources from which they harness energy. This divergence in temperature levels seems to play a defining role in the classification of renewable heating energy.