While slightly less got done in the house while we were away than we would have liked, the Heat Recovery Ventilation (HRV) system installation is now proceeding quickly.
Along with the thick insulation and sealed building shell, the HRV is one of the most important features of any Passive House. An HRV system is really very simple. In essence, it is a ventilation system with a heat exchanger, so that in winter, when cold air is drawn into the house, it is warmed with the heat from the stale outgoing air (and vice-versa in summer). However, it is also more than this. The HRV ensures a uniform temperature throughout the house, taking the air heated by the sun through the large south-facing windows and distributing it to other rooms.
Our systems is also a little bit more than this. With the addition of a very small thermostat-controlled heating element (about the power of a toaster), it also becomes a low pressure forced air heating system. This will be the only artificial heat in the house, and we don’t think we’ll need it that much even in Ontario winters.
It’s worth noting that not all HRVs are created equal. Most of the manufacturers make claims about their efficiency, but few of these are actually independently tested and verified, and this includes the leading companies in North America. This doesn’t mean they are bad, but you can do so much better. Our HRV is the ComfoAir 200 system from Swiss company, Zehnder, which is pretty much the best manufacturer of HRVs in the world. Their real tested efficiency is the highest, their systems are the quietest and their ribbed plastic Comfo-Tube ducting is much better than the old square section metal ducting you might be used to. Our system was supplied, with minimal fuss, by the excellent Hans, from Zehnder’s Ontario dealer, Pinwheel Building Supplies.
You need to plan for the installation properly from the beginning though. We didn’t but we got lucky. The units themself take up a fair bit of room. However they can be mounted on walls or ceilings. Since we have massively over-engineered CLT ceilings, we did the latter, mounting them up, out of the way, in our machine room, which just happens to have enough room up there. There are a lot of ducts too – intake and exhausts in different parts of the house – and the ducting goes up through what would have been our chimney openings. Again, this was luck rather than judgment. We also didn’t get the design for the HRV system ducting done before we ordered the CLT, so rather than having pre-drilled fittings, the builders are having to drill through the thick ceilings to make the vent holes.