Friday, 8 January 2016

Lesson 11, Part III: Passivhaus

Passivhaus is a voluntary standard based on super insulation, high levels of airtightness, a heat exchange ventilation system. The windows must be of good quality, and mostly on the south of the building to consider solar gain. The standard is largely based on comfort, so the whole house is warm, there are no drafts, no cold surfaces, no overheating, and the air is always fresh. 

The standard came out of collaboration between German Wolfgang Feist and Swedish Bo Adamson in 1988, leading to the Passivhaus being built in Darmstadt, Germany in 1991. The Passivhaus institute was founded in 1996 and between 1998 and 2001 the CEPHEUS project--Cost Effective Passive Houses as European Standard--monitored several building from the top of Finland to the bottom of Spain to ensure their calculations of building performance were working. And they are working, which puts the Passivhaus standard into stark contrast with other building standards that typically only deliver half of the promised energy savings.  

By 2010 there were 15,000 Passivhaus buildings in Europe, and the first certified Passivhaus in Japan was built in 2011, the same year as my house, which meets the standard, but is not certified.

The big idea behind Passivhaus is that if you increase insulation, at some point a central heating system becomes unnecessary, and heat can be delivered by small scale heaters or by adding a bit of heat to the ventilation system. This reduces the building cost, especially in Europe where central heating is standard. In fact you can calculate how much heat can comfortably be delivered through the ventilation system, taking into consideration a volume of 30 cubic metres of air per person per hour, floor space of 30 square metres, a maximum air temperature of 51°C to avoid burning smells in the air, or on your skin or hair. As everyone knows, the heat capacity of air is 0.33 Watt hours per cubic metre kelvin, giving us about 10 Watts of heating per square metre of floor space. 

This is a fixed standard, unlike many other standards that keep changing in attempts to become more stringent and lower energy. Passivhaus is based on comfort and the human physiology that we inherited from the savanna and have taken to the four corners of the world, which we now know to be round. The extent that the standard changes is that the modelling and simulation become more accurate, and applicable to more climates and situations. The heating load is not arbitrary, but at some kind of optimum where any more will require a heating system and increase costs, and any less will probably put the extra insulation costs beyond the potential gains from reduced heating bills.