Abstract: The invention relates to a heat transfer liquid for ventilation and air-conditioning installations to be used at low temperatures, in which installations heat is recovered from the exhaust air and conveyed to the supply air by means of a heat transfer liquid. For lowering the costs and eliminating environmental risks, the heat transfer liquid contains potassium formiate and water.

Abstract: The invention relates to an arrangement for cooling supply air in an air-conditioning installation, comprising a heat transfer device for transferring heat between supply air and exhaust air by means of heat transfer surfaces; and a humidifying device for humidifying heat transfer surfaces on the exhaust air side. In order that supply air could be cooled more efficiently, the heat transfer surfaces on the side of supply air and exhaust air are separated into separate heat exchangers; and the heat transfer surfaces are selected in such a way that the surface temperature of the heat transfer surfaces on the exhaust air side is close to the dew-point temperature of exhaust air.

Abstract: A method and an arrangement for controlling heat transfer in a ventilation apparatus or an air conditioning apparatus, in which heat contained in exhaust air is recovered into supply air by means of a heat transfer circuit having fluid circulation. Additional heating or additional cooling energy is supplied to the heat transfer circuit when the heat transfer is insufficient for maintaining a desired temperature of the supply air. To optimize the heat recovery, the supply of additional heating or cooling energy is minimized by measuring the temperatures and fluid flows of the heat transfer fluid and of the additional energy.