Kiertoilma

Kiertoilma is a term used in building ventilation to describe the air that is circulated within a space or building as part of the ventilation system, rather than air that is exhausted to the outdoors or newly supplied from outside. It is typically drawn from indoor spaces, routed through the building’s air handling unit, filtered or conditioned, and then supplied back into the spaces. In many systems, kiertoilma is mixed with outdoor air to form the supply air.

In operation, a portion of the indoor air is recirculated to improve energy efficiency, especially when outdoor air requires substantial heating or cooling. The exact proportion of kiertoilma vs. outdoor air is controlled by dampers and sensors, and the mixed air may pass through filters, heat exchangers, and cooling or heating coils before being reintroduced. This approach aims to balance energy use with required ventilation and indoor air quality.

Considerations for kiertoilma include energy savings versus potential buildup of indoor pollutants if outdoor air intake is too small. Poorly controlled recirculation can raise CO2 levels, humidity, odors, and volatile organic compounds. Modern systems often rely on filtration and, in energy‑efficient designs, heat recovery or energy recovery ventilators to condition kiertoilma while reducing the need to treat all air from outside. Proper design, operation, and maintenance are essential to maintain indoor air quality while managing energy use.