A heating system in a building can be based on radiators, convectors, floor heating, air heating or a combination of these. Using air heating is a fast but expensive way to heat up a building.
In air-heating systems, a heating surface in the AHU heats the air in the ventilation system intake before it is circulated throughout the building. If there are different heating needs throughout the building, heating surface zones can be set up so the inlet temperature can be adjusted for each zone.
The advantage of air heating is that it reacts quickly to changes in demand. The inlet temperature can be regulated very quickly to meet varying heat demands, unlike a water-based system of radiators and/or underfloor heating.
However, air heating is significantly more expensive than water-based systems both in terms of construction and operation.
The specific heat capacity of air is approx. 1000 J/kgK, which is significantly lower than the specific heat capacity of water (4200 J/kgK). This means that 4.2 times as much air needs to be moved to have the same heating effect as 1 kg of water. In addition, the ventilation ducts require significantly more space than a water-based system of radiators, convectors and underfloor heating.
One way to offset the higher cost is to set up fan-coils that are heated via a water-based system. This reduces the cost of transporting air, but noise emissions can be a problem if fan-coils with built-in fans are used.