Rotating heat exchanger
Here shows Hoval on his booth an energy revovery ventilator with show window. In the rotating heat exchanger are many flues.Each flue comes in one turn in the half of the away air and becomes warmed up from the indoor air.
In the second half turn, the flue warms up the cold outside air and becomes cool.
Advantages: high efficiency and also recover ait humidity.
Disadvantages: Smells from indoor air can gather in the flues and come back indoor again by the fresh air.