Part of my homework on the AECB’s Passivhaus “Bitesize” course was to take a brief look at a project I had worked on and assess it in terms of PH criteria. The exercise can be downloaded here:
The assessment appears to show that the basic form of the block could allow a Passivhaus approach. However the south-west facing glazing which isn’t shaded by balconies would benefit from solar shading, and the arrangement of glazing in the block as a whole could be improved.
In terms of building fabric the overall insulation amounts are good, and there is triple glazing, but the nature of the construction (light gauge steel framing on a concrete base) and the known quality (sadly very poor) mean that airtightness in the finished building is likely to be low, ie it will be leaky.
At the same time, even though the building has Mechanical Ventilation with Heat Recovery (MVHR), the actual performance of this will be constrained by the thin section ductwork and long and sometimes complex duct routes. This usually means the system is both less effective and noisier – and if it’s too noisy people may try to switch it off. Then they will either suffer poor air quality or by using the windows in cold weather, excess heat losses.
The design performance if it was all built well gives an energy use of 56.5 kWh per m2 of floor space per annum. This compares with the Passivhaus standard of 15kWh per m2.
Reducing the number of flats on the site to allow better disposition of glazing, more dual aspect flats, and simpler built form, together with a more generous floor-to-floor height with more space for high quality, quieter ductwork, would have allowed a massively better energy performance (using about a quarter of the energy required now), and improved wellbeing.
That would be seven times more than the photovoltaic panels (PV) currently contribute. Or put another way, if PV panels were extended slightly they could contribute more than half the total energy use of a Passivhaus block.
These are all my estimations based on a limited training in Passivhaus, so not to be taken as evidence, but rather food for thought.