The majority of AirMaster units contain one or more aluminium heat exchangers, which enable AirMasters to recover heat from the room air, therefore cutting energy consumption when compared to a natural ventilation solution.
Aluminium has been chosen for its high conductivity (237 W/m K) compared to other materials commonly seen in heat exchangers, such a plastic (0.2 W/m K). This results in a high efficiency of recovery: typically, 84-90% dry bulb efficiency.
Due to the ΔT between intake and extract, the by-product of heat recovery is water. As plastic is inefficient in comparison to aluminium, plastic heat exchangers must have a comparatively high density of plates to maximise surface area and therefore heat recovery efficiency. When water forms in the heat exchanger, there is a risk of capillary action, which will reduce the surface area of the heat exchanger, reducing its efficiency. In contrast, aluminium heat exchangers can have wide pathways between plates due to their high conductivity enabling any water formed to leave the heat exchanger, maintaining the high heat recovery efficiency.
There are two exceptions: the AM 150 has a low flow rate and therefore a plastic heat exchanger has been found to be more efficient than using aluminium in this instance (80 – 87%). The AM 900 has a three-part heat recovery process, which results in a higher heat recovery efficiency (86 – 96%).