Pre-heating/pre-cooling is implemented via installation of a duct coil in the outdoor air duct before the ventilation unit. A fluid-filled coil can function both as a pre-heater and as a pre-cooler; in other words, its purpose is to pre-heat the incoming fresh air in winter and to pre-cool the incoming air during summer. Ventilation pre-heating/pre-cooling can be implemented on all sites that have mechanical supply and extract ventilation and where installing a ground circuit is possible. The type of heating system used in the house is of no
consequence. Therefore, the system can be installed for an older building too.

The pre-heating/pre-cooling coil is usually connected to a specially built collection circuit. The pre-heating/ pre-cooling coil can also be connected to the ground circuit of a ground-source heat pump, if the building has a ground-source heating system. In any case, the coil needs to have its own fluid circuit, which is separated from the fluid circuit of the heat pump via a fluid-heat exchanger, because the fluid in the heat pump ground circuit freezes in winter if it comes in connection with outside air. Therefore, a different fluid circulates in the heat pump circuit from that in the coil circuit. The coil-circuit fluid is usually a waterglycol mix (e.g., Dowcal 100) or an ethanol solution. Pre-heating/pre-cooling helps to even out the effects
of extremes in outdoor temperatures during winter and summer. The system provides significant energy savings by decreasing the energy consumption required to heat and cool the ventilated air. In addition, preheating reduces the need to defrost the ventilation unit and the demand for defrosting energy. The preheating system has a very good COP (i.e. efficiency). There is no need to design the ventilation unit for the region’s most extreme temperatures; this translates into savings on the purchase price and energy consumption. At the same time, the reliability of the ventilation system is improved in extreme temperatures: when there is extremely cold or hot weather. Heating outdoor air via a ground circuit is much more
energy-efficient than using an electrical resistor, because the energy obtained from the collection circuit is free. Pre-cooling provides some level of cooling even if the ventilation unit has no other cooling devices. The pre-cooling also dehumidifies the supply air blown inside, which makes it feel more pleasant. In houses where cooling devices have been installed as part
of the ventilation system, pre-cooling decreases the amount of energy required for cooling by reducing the temperature and humidity level of the supply air. The pre-heating/pre-cooling coil has a class-G3 coarse filter. The filter pre-filters the outside air to the ventilation unit, thereby extending the life of the ventilation unit’s supply-air filter.