Ventilation Heat Losses - Summary
Ventilation heat losses occur when warm indoor air leaves the building and is replaced by cold outdoor air. They typically account for 20-40% of the heating load – in very well-insulated buildings even more.
The Principle
Air is a heat carrier. When 20°C warm indoor air is replaced by -10°C cold outdoor air, the heating system must compensate for this temperature difference.
Air Change Rate: The Decisive Factor
The air change rate n indicates how often the room volume is exchanged per hour:
- n = 0.5 1/h: Half the volume per hour (well-sealed building)
- n = 1.0 1/h: Entire volume per hour (average)
- n = 2.0 1/h: Double volume per hour (leaky old building)
Heat Recovery
Modern ventilation systems can recover 60-95% of the heat from exhaust air. With 85% heat recovery, ventilation heat losses are reduced by 85%!
Two Types of Air Exchange
- Infiltration (uncontrolled): Air exchange through leaks in the building envelope
- Mechanical ventilation (controlled): Targeted air exchange through ventilation systems, ideally with heat recovery