PassivHaus

The fundamental objective of Dr Wolfgang Feist’s PassivHaus design is to cut energy consumption and to provide accurate design tools to measure the expected energy consumption in a clear, accurate, numerical way. The essential PassivHaus requirement is to produce a building designed to use less than 15kWh/m²/annum supplementary heat and no more than 120 kWh/m²/annum primary energy, including heating, lighting, hot water, appliances and any cooling.

Typically a UK building, like a German one, uses an average of 200kWh/m²/annum for space heating. Most of that energy requirement is supplied by imported fossil fuels.

However, the first ever PassivHaus development, DA-Kranichst, has achieved an average of 9.2kWh/m²/annum in monitoring from 1991-2008. This is less than 1/20th of the typical German new-build house. In the UK we have the same potential to reduce energy consumption.

The simple techniques necessary to achieve PassivHaus design are:

• Insulation (typically 30cm thick)
• PassivHaus windows (airtight, triple glazed with thoroughly insulated frames achieving an overall U-value of 0.8 including the frame)
• Airtight construction (max 0.6 air changes/hr under 50 pascals pressure) with very efficient mechanical heat recovery ventilation.

Assuming that these three main performance targets are met, together with detailing to remove cold bridging and other requirements, it is possible to eliminate the need for space heating equipment, such as a boiler and radiators or underfloor heating. In fact, manufacturers are already beginning to produce all the mechanical kit required to ventilate, heat water and top up the air temperature of a PassivHaus in a single compact unit. The heat pump required to maintain 21 degrees centigrade, in sub-zero outdoor temperatures, is the size of a refrigerator pump!

In addition, architects and builders have a great deal of style freedom with PassivHaus design, whether constructing houses, schools, offices or factories. Already some beautiful designs are emerging from PassivHaus architects’ offices.

The picture above shows a thermograph of a PassivHaus – which demonstrates the difference in heat lost between a conventional house (on the left) and a house built to PassivHaus standards (on the right).