Heat recovery Ventillation

The principle is simple: The stale air and the fresh air are passed through a grid of capillary ducts in opposing directions. The heat naturally passes from the hotter air to the colder air. In good systems the fresh air entering the home will only be a degree or so cooler then the room it enters. Beware of systems which do not reach this level of efficiency. The system itself is simple enough too: There is a heat exchange box containing the capillary ducts, a pair of fans and a control unit. There also needs to be ducting to carry the air around the building. To be effective the unit itself needs to be finely engineered while the system for any given house must be carefully designed, installed and tuned.

A typical Heat Recovery Ventilation (HRV) configuration would be as follows:

• stale air taken from bathrooms and kitchens and fresh air injected into living and bedrooms
• volume of air in house replaced every 2.5 hours
• HRV located in internal press (they range in size from that of a storage heater right up to something like a large fridge) or somewhere where fans will not disturb occupants
• air carrying ducts are located under floor, in wall cavities and in attic
• unit should be connected to ducts with flexible pipe to decouple vibrating components; cold air ducts should be insulated to stop condensation; baffles need to be installed at certain points to eliminate cross-talk between rooms

Comfort ventillation Explained

In new houses with good insulation against outside noise there is hardly any natural ventilation. This can lead to high humidity and low oxygen levels. To eliminate the possibility of harmful effects developing, it is essential to introduce fresh air.

Our comfort ventilation system generates a steady, slow stream of fresh air (5–10 times slower than conventional air conditioning systems). This guarantees a pleasant and hygienic indoor climate with no draughts. The fresh air is filtered and, according to season, can be pre-heated or pre cooled. The energy from the waste air can be recovered and then used to pre-heat the fresh air, for the water heating system or for central heating. You can enjoy an ideal indoor climate and yet all this consumes hardly any energy.

Our ventilation equipment extracts air from specific rooms and channels fresh air into them (e.g. kitchens and bathrooms).

Why a mechanical ventilation system is recommended - at least in Passive Houses

The health and comfort of the inhabitants are the most important objectives of a Passive House design. Excellent indoor air quality is indispensable. But this can only be achieved if stale air is exchanged with fresh outdoor air at regular intervals. This can definitely not be done by just opening windows twice a day.

Ventilation will work accurately only if polluted air is removed constantly out of kitchen, bathrooms, and all other room with significant air pollution. Fresh air has to be supplied to the living room, children’s room, sleeping rooms, and workrooms to substitute the removed air. 
The system will supply exactly as much fresh air as is needed for comfort and for good indoor air quality; only outdoor air will be supplied – no recirculated air. This will lead to a high level of indoor air quality.

What has been discussed so far could be satisfied by using a simple exhaust fan ventilation system, where the air is supplied through direct vents in external walls. These vents allow fresh (cold) air to enter the room at the required rate. However, for a Passive House, the heat losses caused by such a system are much to high.

In Central Europe Passive Houses will only work with highly efficient heat recovery. Heat from the exhaust air is recovered and applied to the supply air by a heat exchanger. The air flows are not mixed in the process. State of the art ventilation systems may have heat recovery rates of 75% to more than 95%. Of course this only works with counterflow heat exchangers and very energy efficient ventilators (using so called EC-motors with extraordinarily high efficiency). With this technology the recovered heat is 8- to 15-times higher than the electricity needed.