PassivHaus Verification Sheet

A piece of software called PassivHaus Planning Package (PHPP) has been used to model the thermal properties of the retrofit, and will be used in the certification procedure. The image above shows the final “verification” sheet that the model has produced - i.e. how it thinks the building will perform.

This verification sheet is the result of a fairly complex simulation which includes weather data, house geometry, shading from houses opposite, heating and cooling loads, water heating, the energy consumption of appliances and even heat that people in the house give off.

The most important result (in the red box, cell D31) is the space heating demand, measured in kilowatt-hours per square metre per year. In order to be a PassivHaus, a building must use less than 15kWh/m2 per year; our preliminary results suggest we will need only 9kWh/m2 per year. This would be pretty impressive.

Another key result is the specific primary energy demand, shown in cell D33 which includes the energy used to generate electricity supplied to the house as well as the energy supplied directly (e.g. in the form of gas). For example, water heating, powering appliances and doing the cooking are included in this figure. At 61kWh/m2 per year, this is only slightly over 50% of the PassivHaus target of 120kWh/m2 per year. Again, if we achieve this, it will be very impressive.

The third key number to note is in cell D32, which shows how airtight the house will be. In order to qualify as a PassivHaus, this number needs to be 0.6 or below, so we’re on the borderline here. Because we are renovating and have to fill lots and lots of gaps and cracks, this component is likely to prove the biggest challenge. About halfway through the build, we will bring in a special door called a blower door and test the whole house for air leakage. We hope to fill or tape up any leaks that we find.

A bit about PHPP

The German PassivHaus standard embodies a philosophy of very low energy design and is widely seen as a gold standard for efficiency in buildings. The key principles include:

• Super insulation
• Very low air infiltration (<0.6ach@50Pa)
• Passive solar gain
• Mechanical ventilation with heat recovery
• Compact form

PassivHaus follows specific design principles to with the goal of creating comfortable, pleasant living environments with the lowest energy use possible. In contrast, the UK Code for Sustainable Homes specifies reductions in the carbon emissions associated with energy use (and also includes a plethora of regulations involving bicycle sheds, bin storage and other issues).

From an energy point of view and in light of the years of experience of PassivHaus building on mainland Europe, we believe that PassivHaus is the standard that the UK should be adopting.