In the Passive House the home ventilation system plays a key role. It provides clean, pollen-free, dust-free air and eliminates moisture and odours where they occur. Opening windows to achieve this would result in heat losses greater than the total energy demand. That is why heat recovery from exhaust air is indispensable in the Passive House. It reduces ventilation heat losses considerably because inside the heat exchanger, heat from the warm exhaust air is passed on to the cold fresh air. Depending on the efficiency of the heat exchanger, over 90% of the heat from the exhaust air can be passed on, which brings the incoming air almost up to room temperature.
High quality systems ensure that the exhaust air ducts and supply air ducts in the heat exchanger are leak-proof, so that the fresh air and exhaust air are not mixed. These high-quality ventilation systems use much less energy than the amount they are able to save by preventing heat loss. The ventilation system as a whole needs to be carefully designed and laid out. Air flows (imperceptibly) into the living room and bedrooms of the house and is extracted through the kitchen, bathroom and WC. These two areas are connected by so-called transferred air zones (e.g. hallway) that direct the air flow through the home and allow the fresh air to be used several times. To ensure that closed doors do not hinder the air flow, appropriate air transfer openings (e.g. covered panels with acoustically optimised vents) are installed above the door frame. A high-quality Passive House ventilation system is super silent, in passive Houses the maximum sound level is 25 dB(A). To comply with this limit, the supply and exhaust air ducts are fitted with silencers that prevent sound transmission between the rooms.
Operating and maintaining a comfort ventilation system with heat recovery is very easy. For reasons of hygiene (prevention of contamination), the system must be fitted with high-quality filters in the fresh air inlet and coarse filters in the exhaust air valve. These filters should be replaced regularly (one to four times a year). Experts and specialised companies are at your disposal for planning and installation information, advice and support. Even a Passive House requires some heating, but the heating demand is so small that the ventilation system can also be used to distribute heat in the house. Heater coils heat the incoming fresh air. Compact heat pump units have been approved for this purpose, because they combine all the building services functions (ventilation with heat recovery, heating, hot water supply and storage) in one unit. These space-saving devices are industrially manufactured and optimised and are easy to install.
Other solutions are also available – the Passive House is flexible. Gas, oil, district heat or wood can be used for heating and hot water. Active application of solar energy, using solar collectors to provide hot water for household use, is an interesting option that can reduce energy consumption even more.