Passivhaus – does it work for offices?

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I have been lucky enough this week to be able to inspect one of the East Midlands most energy-efficient office buildings. The property which is just north of Leicester has been built as Interserves new regional headquarters building. It has been constructed to the Passivhaus standard. This standard was developed in Germany in the early 1990s with the first dwellings to be completed to the Passivhaus Standard constructed in Darmstadt in 1991.

What is a Passivhaus?

“A Passivhaus is a building, for which thermal comfort can be achieved solely by post-heating or post-cooling of the fresh air mass, which is required to achieve sufficient indoor air quality conditions – without the need for additional recirculation of air.”

…meaning the heating requirement in a Passivhaus is reduced to the point where a traditional heating system is no longer considered essential. Cooling is also minimised by the same principles and through the use of shading and in some cases via the pre-cooling of the supply air.  Night purging and the use of natural cross-ventilation through open windows is encouraged during the summer months.

The Passivhaus Standard requires:

  • a maximum space heating and cooling demand of less than 15 kWh/m2.year or a maximum heating and cooling load of 10W/m2.
  • a maximum total primary energy demand of 120 kWh/m2/year.
  • an air change rate of no more than 0.6 air changes per hour @ 50 Pa.

To achieve the Passivhaus Standard in the UK typically involves:

  • very high levels of insulation
  • extremely high performance windows with insulated frames
  • airtight building fabric
  • ‘thermal bridge free’ construction
  • a mechanical ventilation system with highly efficient heat recovery

In accordance with the Passivhaus approach, the Leicester building has a superinsulated, super airtight building envelope, triple glazing and insulated foundations. The fully glazed south-facing narrow aspect will make the most of solar heat in winter, while blinds will provide summer shading. Other features include a mechanical ventilation heat recovery (MVHR) system, with ventilated air being warmed through earth tubes.

The new building should reduce energy costs in the 6,000 sq feet development by about 90 per cent compared to traditionally built properties – the expectation is that it will cost £3000 a year to service, that is not a lot for a building this size!

So, that’s the theory – but what is it like as a building to actually occupy?

Well, having experienced it for a few hours on a warm autumn evening I have to say it’s quite good. The space is light and comfortable. It was warm upstairs but that may be due to the building still ‘balancing’ itself (and the tenants opening the windows when they shouldn’t have!).

Could I work in the space – yes, I believe it would be comfortable and it is a bit different – which I like.

The developer was also indicating that they were able to offer an inclusive rental to tenants – including heating and electrical costs – at the same rate per square foot as a normal building in the area. A definite attraction to tenants in their decision-making process for new buildings.

Whether or not the building makes long-term financial sense for a landlord is another matter – the jury is still out on that question!

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