Initial results from the Cardiff Passiv Haus

The house was completed in late 2007 and people have been living in the flats since then. The owner and architect have been monitoring the performance of the building both from the energy perspective and the 'live-ability' angle.

The comments that have been received to date are:

We did an air tightness test which resulted in 1.8 cum/sqm = 2.7 ach for the ground floor and 1.3cum/sqm=1.7ach for the first floor. This is not up to Passiv Haus standards but according to the PHPP spreadsheet it still achieves 17 kWh/sqm/a and 14kWh/sqm/a for the ground and top floor respectively. (101kWh and 93kWh primary energy). There are some questions about the air test in particular the fact that there is leakage between the flats, so it may actually be marginally better than measured.

The measured energy consumption over the winter for the ground floor suggests a total yearly consumption of ca 40kWh/sqm/a for everything (cooking included). So that actually is similar to the PHPP calcs. But we really need to wait a full year to tell.

The heating element (in the MVHR unit) had to be used in December- February for the ground floor flat but not continuously, just once in a while (probably related to the weather). The first floor has never even had the MVHR on and in the winter is was always comfortable, and we suspect the MVHR could have been omitted and it could have been ventilated naturally. But again wait another winter.

As for overheating we expected the top flat to overheat and the mezzanine does get hot. But by opening the windows the problem is solved as there is very good cross ventilation that also cools the mezzanine. So that was very positive.

On the ground floor with the concrete floor we didn't expect it to overheat and when we were there it did not. But the girl in there now was suffering from being too hot at night because she didn't feel safe enough to open the window (even tilted open). Now we have installed a window lock that locks the window in an open position so she can ventilate the space at night. Night ventilation is a key aspect especially in the bedroom  - even though it faces north.

It is interesting that in the end what counts is whether the windows allow safe ventilation. 

We are monitoring the internal temperatures and relative humidity as well so we'll have a good picture of how the flats perform in six months time.