Can a ventilation unit cool the air on hot summer days?

Ventilation and air conditioning are not the same thing. The primary function of a ventilation unit is exchanging the indoor air, not cooling it. Therefore, its cooling efficiency is limited. In hot weather, the best way to keep the home cool is to shield the windows from the sunlight and use a separate ventilation unit.

In summer, heat recovery from extract air is not desirable. The Vallox MC, SE and MV models feature an automatic heat recovery bypass: outdoor air is led in cool but filtered. The Vallox MV ventilation units also feature a cooling function, which automatically boosts ventilation in summer when the outdoor air is cooler than the indoor air.

However, sun protection is the most efficient means of keeping the home cool. If the sun can shine unobstructed through the windows, the cooling power of ventilation is usually not enough to keep the indoor temperature at a comfortable level. It would be best to prevent the heat radiation from entering the house by means of long eaves or canvas awnings. Blinds are helpful but cannot completely prevent the warming of the inner surface of the window.

If the supply air to the bedroom of two persons is 10°C cooler than the air in the room, the cooling power of the ventilation unit is approximately 150 W. The same cooling effect is achieved by covering a 20 cm high strip of a one metre wide window facing the sun. This demonstrates the usefulness of sun protection.

The supply air should also not become warmer in the ventilation ducts. If the supply air ducts are installed in a space with a high temperature, the temperature of the supply air will also rise. Such spaces may include, for instance, the ceiling of the bathroom or sauna, which may also house radiator pipes or hot water pipes. In such circumstances, the temperature of the outdoor air may rise considerably, increasing the thermal load of the home.

If the thermal load of the home is high, a separate ventilation unit is an efficient means for keeping the temperature comfortable. The unit circulates, dries and cools the indoor air. Air conditioning may also be connected to the ventilation system of the home by means of a duct radiator installed in the supply air duct. The duct radiator cools and dries the supply air coming into the house by using a coolant, such as the cold circuit fluid of the geothermal heat system.