The trend to passive housing forced people to build an air tight envelope. The importance of this tightness is already shown in a previous post. But the consequence of air tightness is that we have to check the quality of the indoor air (IAQ).

The first method to improve the IAQ is to avoid emitting dangerous gases and particles. No smoking inside  is trivial but also diluting by ventilation with (clean) outside air is a must. Ventilation standards in Belgium (always inspired by Europe) give as general rule 3.6m³/h  per m² floor surface or 720m³/h for a 200m² house (10×10 with 1 stock).

Heating 720m³/h air from 0°C to 20°C takes about 4800W. This is unacceptable for passive housing and for that reason heat recovery ventilation is needed with a heat exchanger, which can have an efficiency larger than 85% in case a cellular one is used.

Passive housing means a huge thermal insulation (40cm thickness and more) and an expensive (cellular) heat exchanger for the necessary ventilation with high efficiency recuperation of the heat. The large thicknesses of the thermal insulation are in conflict with elegant architecture and increase largely the building cost besides thermal insulation.

On the other hand, ventilation through permeable thermal insulation with an under pressure (generated by a fan) is a another way. The heat, leaking away in the insulation is used to heat up the ventilation air. The exhaust of the fan has an heat exchanger to recuperate the heat, reintroduced in the envelope.

In case of a windless day, an extreme small U-value can be obtained. In case of an efficient heat exchanger, the heating power will be negligible, reaching the lowest passive values possible. On the other hand, on a windy day, a large under pressure must be generated to avoid that air is going outward through he insulation.

The last system (ventilation through permeable insulation) guarantees a very high IAQ (Indoor Air Quality) and a perfect ventilation of the structure, avoiding any problems associated with humidity. In case open celled cellular glass is used, we obtain a system with an extreme long lifetime. This system can withstand extreme low temperatures with negligible power on a windless day, but is more sensitive to wind.

Swimming pool ventilated through the thermal insulation

Open cellular glass was already discussed in this blog with recipes based on CRT glass and Manganese oxide. That seems to be a good starting point. I guess that this application, dynamic thermal insulation, will induce a lot of competition with impermeable insulation if open celled cellular glass will be available soon at prices around 150€/m³.