The international body that certifies a passive house is the Passive House Institute, based in Germany. Of course it is perfectly possible to build a passive house and not get certification, or to build using passive house principles and not quite attain the standard for certification but still have an extremely efficient house, and both those options are equally honourable. Gary and I are aiming for certification, partly as we think the certification provides an independent quantifiable measure of the house’s efficiency, partly as we see that certification adding value in the future, but also partly because we are the kind of people who like to tick the box when we do something! Just because we are going for certification does NOT mean that everyone ought to do so too, and part of the purpose of our blog is to raise awareness and encourage others to join the passive house “movement” and incorporate the principles into their house design or renovation.
In order to qualify as a certified passive house, we will need to ensure that our house meets the following standards. It must meet all of them, no exceptions and no “almost there” qualification. The nice thing about the standards are that they are binary – you either meet them, or you don’t.
Here are the standards (copied verbatim from the Passive House Institute documentation):
- Space heating demand does not exceed 15 kWh annually OR 10 W (peak demand) per square metre of useable living space
- Space cooling demand roughly matches the heat demand with an additional, climate dependent allowance for dehumidification
- Renewable primary energy demand not to exceed 60 kWh annually for all domestic applications (heating, cooling, hot water, and domestic electricity) per square metre of usable living space
- Airtightness of a maximum of 0.6 air changes per hour at 50 Pascals pressure (as verified with an onsite pressure test in both pressurised and depressurised states)
- Thermal comfort must be met for all living areas year-round with not more than 10% of the hours in any given year over 25 degrees C
You might be wondering how on earth you know that your heating or cooling demand will be within tolerance, and that is where the PHPP software modelling comes in, and is why we have been using the model right from the (almost) get-go to check that the design will comply.
In New Zealand the space heating demand criteria are met easier than the thermal comfort criteria. A well insulated house with a compliant airtightness barrier and some north and west facing windows will achieve that. It is harder to keep the house cool and to comply with standard #5 as those very windows which provide solar gain on sunny but cold days, can provide too much solar gain when the sun is low in the (western) sky in winter or on the cracker 30 degree plus days we often get in a Cantabrian summer. In our case we didn’t have many windows on the west, but removing one (who needs a window in the walk in robe?!) and shrinking slightly the others on the upper floor, has enabled us to be compliant. Other options are to have shading (e.g. pergola, sail shade, shutters) on problematic windows and French doors.
The criteria have been developed to ensure that the house is actually efficient – after all, a passive house is supposed to have minimal draw on energy for the purposes of heating and cooling and is supposed to be highly comfortable to live in.
In late 2015 the Passive House Institute released further refinement for certification. The above standards remain in place for certification as a Classic Passive House and two further classes have been created called Plus and Premium. These two classes reduce the maximum amount of primary renewable energy demand whilst also allowing for “credits” when the house generates and uses renewable energy for the domestic purposes, which is in alignment with the passive house philosophy of sustainability and energy efficiency. The primary renewable energy requirement is influenced by the way energy is generated in the country/region itself, which works well in NZ as a lot of our power is hydro or geothermal. The PHPP software works all this out.
Here’s the requirements to achieve the higher classes:
I find it easy to think that in order to achieve Plus classification the house needs to generate some/most of its own energy through renewable sources, such as solar PV panels. To achieve Premium classification the house needs to not only generate enough energy for its own needs but also add some back into the grid and this energy must be obtained from renewable sources. This link and this link give more background information on the primary renewable energy factors
In a future post I will talk about the various things we are doing with the house to comply with the standards and how we might even achieve a Plus category through our inclusion of solar PV panels for electricity generation.