Tuesday, 20 October 2015

The timelessness of the Passive House standard

I was lucky enough to participate for a few days of a training course for Passive house designers and consultants led by Nick Grant in Herefordshire. I learnt many things, as well as reinforcing the knowledge I had, and brushing the rust off some maths skills. A couple of things really struck me. 

One was that the Passivhaus standard is timeless and objective. Many standards are somewhat arbitrary, and most standards are revised and changed from time to time. Passivhaus is based mostly on objective criteria that will not change, and most of those criteria are based on human comfort. Passivhaus guarantees that room temperature and humidity will stay around what we are physiologically suited to. The standard should guarantee good air quality, and prevent moulds and bacteria from building up.

The energy part of the standard is set to a low enough energy demand that the house can be kept at a comfortable temperature just by adding heat to the incoming air. This doesn't mean that the house has to be heated by the incoming air, but it does mean the heating demand will be very small. So whatever the heat source is, it's not going to use very much energy, and the house would not be too uncomfortable if it stopped working.

Although the standard is fixed, Passivhaus is not standing still. Where the changes and innovations are being made is in how to better estimate the performance of a building from its plans. This has been going on for at least thirty years and means that the Passivhaus estimation of a building's performance is within a few percent. Other energy estimations are often out by a factor of two.

In implementation there are always new technologies and techniques that can meet the standard at lower cost, and there are still locations and types of building that have yet to be made to the Passivhaus standard.

Passivhaus is neutral on a lot of things. In the goal to reduce energy use, most significant is perhaps embodied carbon. The Passivhaus standard is just looking at the building in its lifetime. Other standards are needed to reduce the carbon footprint while it is being made, and of course many people involved in Passivhaus are also looking for building materials and techniques that will reduce carbon from cradle to grave. Such buildings should still be trying for the Passivhaus standard so that energy use during the lifetime is kept low.

Also the standard is neutral on renewable energy. You can use wood pellets for a boiler, or burn fossil fuels. Whatever heat source you use, you will need less of it. If you're aiming for zero-carbon or plus-energy, starting with a Passivhaus makes it much easier when you stick some solar panels on the roof.