Whilst building fabric is the key to Passivhaus performance, it is important to pay attention to building services. Mechanical ventilation with heat recovery (MVHR) poses the most challenges but it is also important to design heating systems appropriate to the level of heat demand so they run smoothly and
economically. This section looks at the principles of building services design.
There can be a temptation to think of a Passivhaus as an opportunity to deploy the latest renewable heating systems. However, having put the effort into a high performing fabric, there is little need to spend a lot on heating systems, and the heating demand is so small that extra investment in expensive heat sources may not be worthwhile. The challenge is to deliver systems that don’t cost a lot, respond well to small and erratic heat demands, and are still effi cient in terms of primary energy and carbon emissions.
On the other hand inexpensive ventilation systems do not usually meet the performance requirements needed for Passivhaus. The importance of heat recovery effi ciency in the PHPP energy model means that high quality Passivhaus certifi ed components are justifi ed, and the expense can be offset against additional fabric insulation costs that a poorer MVHR would require.
Excerpt from “How to build a Passivhaus: Rules of thumb”, Passivhaus Trust, April 2015