In a ventilation system in a house or building, it is very profitable to recycle the heat contained in the exhaust air and use it to heat the supply air. There are several methods for achieving such heat recovery.
Water, or water mixed with glycol, circulates between a water battery in the exhaust air duct and a water battery in the supply air duct. In the exhaust air duct, the liquid is heated to then deliver the heat to the air in the supply air duct. The fluid moves in a closed system and there is no risk of transmitting contaminants between exhaust air and supply air. This type is therefore preferable if you have to be absolutely sure that no transmission takes place, for example. in hospitals, laboratories and businesses with very smells. The battery heat exchanger is also suitable if the supply air fan and the extract air fan are not placed in the same unit without the extract air fan eg. sits on the wind and the supply air unit sits in the basement. The heat recovery can be regulated by increasing or decreasing the water flow. The battery heat exchanger has no moving parts. Low efficiency (45-50%).
A chamber is divided by a damper in two parts. The exhaust air first heats up one part of the chamber, then the damper switches the air flow so that the supply air can be heated by the heated part. There is a great risk that contaminants and odors can be transferred between exhaust air and supply air. The only moving part in the chamber changer is the damper. High efficiency (80-90%).
The cross-flow heat exchanger, which has a square cross-section, has a temperature efficiency of about 60% for equal air flow on the supply air and exhaust air sides. 60% of the exhaust air heat is thus transferred to the supply air. One way to improve the efficiency of cross flow exchangers is to connect two pieces in series. Then the pressure drop increases slightly and the efficiency increases to about 70%.
COUNTER CURRENT HEAT
The counter-current heat exchanger which is becoming the most common alternative is the further development of the cross-flow heat exchanger and a very good compromise with high recycling, usually over 80%, relatively low pressure drop and no moving parts. It has a cross section that allows the air streams to have a longer path to switch the heat. In order to obtain as much heat exchange as possible, the air flows need to be supplied in the opposite direction, hence the name "counter-current heat exchanger".
ROTATING HEAT EXCHANGER
In a rotary heat exchanger, heat is transferred between the exhaust air and the supply air. The system is not complete and there is a risk of contamination and odor being transferred between exhaust air and supply air. There should be a so-called clean-blowing sector built in which makes the air transfer as small as possible. The degree of heat recovery can be controlled by increasing or decreasing the rotational speed. The freezing risk in the heat exchanger is small. The rotary heat exchanger is driven by an electric motor with belt drive to the rotor. High efficiency (75-90%).