Hot air collectors

Air collectors currently do not have a large market share (e.g., 0.5% in Germany in 2009). Nevertheless they can be considered as an alternative in certain situations (e.g., space heating, when an air heating system is used). As the type name indicates air collectors use air as the heat transfer medium (instead of water and glycol). This has some advantages:

• Air does not freeze or evaporate and air does not degrade when exposed to high temperatures. Freezing and stagnation thus does damage the system. Air collectors are usually intrinsically safe.
• Fresh air may be used directly as heat transfer fluid; a volume of air has no cost and is nontoxic. Leakage in the system does not cause damage to the system nor the environment.

On the other hand some disadvantages are:

• Air has lower heat transfer attributes and a lower heat capacity (a factor of 4 times lower compared to water and glycol).
• Higher driving power by a fan is needed for a comparable mass flow [kg/h] to a fluid pump.
• Larger cross sections for conduction pipes are necessary.
• If water is to be heated, an additional heat exchanger is needed.