Ventilation and heat recycling
All buildings need ventilation for renewal of breathing air and change of air when doing activities and to prevent rotting and fungus. Heat recycling saves energy, unfortunately it turns out that heat recycling through ventilation air has a bad efficiency in small houses compared to larger buildings. The low efficiency is caused by the small flow (40 l/s) of air done by the fans in small houses. The recycling unit consumes about 1000 kWh electricity annually and is only able to recycle 2000 to 2500 kWh of heat annually. The same saving is possible by making the insulation better or use the heat of the sun and so on.
There are three types of ventilation systems:
- Type S draught by itself
- Type F mechanical exhaustion
- Type FT mechanical suction and exhaustion
Type S meaning the ventilation is done by the natural way of heat leaving the house thru the roof. Thus the indoor air is warmer (in Sweden) during long periods of the year the draught works fine by itself.
Type F is a fan that exhausts the same level of air constantly, the air is renewed through valves beneath windows and so on. Type FT meaning fans are used to suck and exhaust air, this system is mainly used in houses with heat recycling.
From energy stand of view type S and FT have a lower efficiency than F. The inflow of air is more or less large when using type S and FT. Type F does not stop the inflow of air but instead becomes a part of it and controls the amount of air flowing, thus Type F is the most energy efficient of the three systems.