Living in the Denby Dale Passivhaus still feels like something of a physics lesson to owners Geoff and Kate Tunstall (but in a good way). Here they give an update on how they have found their first summer and autumn in the house and their thoughts as they head into winter
Six months in and we’re finding that life in a Passivhaus is suiting us very well. The air quality and temperature is good – there’s a pleasant warmth in the air – it’s not hot, it’s just comfortable. There’s also a serenity about a Passivhaus, thanks to all the insulation and triple glazing. We’re actually finding that we are oversleeping some mornings because of the absence of outside noise.
As for the MVHR system – myths about which abound – you would actually have to make a supreme effort to hear it at all. We’re also enjoying the solar space and the feeling of having the outside inside. In different lights and on different days, you see it differently – we like effect of the light playing across the room. We’re growing a passion flower up the inside of it which is flourishing, although we found that growing tomatoes and cucumbers inside it didn’t work for some reason.
We had a lovely first summer in the house. We had been slightly worried about how it would go as the solar space (our idea) has larger amount of glazing than in a typical Passivhaus. It had all been modelled in PHPP of course (and a certain factor of overheating allowed for) but we were still a bit anxious as to how it would perform in reality.
Fortunately the external blinds and large roof overhang really helped keep the internal temperature cool and we don’t think we’ll need to bother building an extra pergola/ vine outside for more shading.
During the summer, the MVHR also has a “summer bypass” button which can be used and means that the heat in the outgoing air is not passed through the heat exchanger so that incoming air is a bit cooler. We only did have overheating on a couple of really hot days in the summer. However, we have learnt a really effective way of dealing with it called “Mediterranean purging” (recommended by Passivhaus expert Mark Sidall at one of the Green Building Store training days).
Apparently in Germany “Mediterranean purging” is often used to prevent Passivhaus’ overheating on really hot days. This means that during the day you close windows, close blinds etc (but keep MVHR on) but from dusk onwards you open the windows so that the cooler night air comes in and cools the thermal mass through the night. So you bring the thermal mass temperature down at night and then you keep it down by not letting the warmer air in during the day (apart from what the MVHR brings in).
Once we’d started to do that we didn’t have any problems. The MVHR was still bringing in the hot outside air but because it takes a long time for the thermal mass to change it wasn’t until late afternoon that it was beginning to have an influence. So we’re learning how to fine tune the house.
To further help keep the house cool in the summer we could have had the air supply pipe leading into the MVHR unit underground which actually lowers the temperature – but that would have been another £10,000 on top of the price of the house. So for the hottest 3-4 days of the year, you can compromise and use the purging technique to stabilise the temperature. That’s what the Mediterranean do – they have shutters.
Temperature variation and thermal mass
We’re also finding that temperature is not completely constant throughout the house and that there can be variations between rooms. This is often to do with the heat gains from the sun. The other day was a lovely morning and we left the shutters open to let the heat in. If you sat directly where the sun was radiating the temperature was around 26 degrees – and it felt warm as if you were sunbathing almost. But if you moved somewhere else, away from the windows the temperature was between 22 and 20. It will be interesting to see what happens over the winter with this as the sun is beginning to lose some of its strength now.
The other interesting thing that we’re noticing is to do with thermal mass of the building. You’d think that when you opened the window the house temperature would go down rapidly – it does while the window is open obviously but as soon as you close the window the heat’s back up again – thanks to the thermal mass inside the house retaining the heat. We’re interested in how our house – built using cavity wall construction – would compare with a timber framed one in terms of temperature changes. We’ve heard that timber frame Passivhaus buildings can have much steeper changes of temperature. If you open the doors here in winter for 20 minutes, it wouldn’t make a difference. Whereas if you did that in a timber frame Passivhaus you could lose the temperature very quickly. This could be a case for heavyweight construction like cavity wall as a way of offering thermal mass as a buffer against rapid temperature changes.
Where’s the manual?
We’ve had to give the MVHR control panel some minor tweaks now that the autumn is here. In the early morning the downstairs was cooler than the upstairs (around 18 degrees celcius). This was something to do with the “night lowering” setting on the MVHR – designed to help ambient temperature go down to 2 degrees to 18 degrees at night – which we’ve now adjusted for the autumn.
Although a Passivhaus is simple to live in in many ways, it would be really good if a Passivhaus came with a manual, as things do change subtly with the seasons. It would also be really valuable to have a forum for people who live in Passivhauses to share ideas and experiences – there are still so few of us in the UK that this would be a valuable resource.
Monitoring and bills
LeedsMet University have put various temperature and CO2 sensors around the house. They are also taking measurements of the outside temperature -– because you need to relate what’s happening inside to what’s happening outside. They came and took readings a couple of weeks back and they could tell from the readings when we’d been away for a few days. Because we weren’t living in it the temperature slowly decayed because we weren’t putting any of our own body heat into it. Fascinating stuff.
Our first quarter bill for gas has been £31 (46 units of gas), some of which was for the standing charge not gas. We also keep a note of the meter readings per month. Our other utility bills have also been very low – due to installation of low water WCs and taps, and showers and use of LED lights. The solar thermal and solar PVs on the roof are also contributing to this. We haven’t needed to use the boiler from April to September as we got all our hot water from solar thermal panels – the boiler has just sat there wondering whether it’s been connected. The only gas we used was for cooking. The gas for August that we used was 59p. We really got riotous in September – it went up to £1.32.
We are really pleased that Chris Huhne and Jonathon Porritt have recently given their support to the Passivhaus approach which will help raise awareness and put Passivhaus onto the political agenda.
Since the recent launch of Green Building Store’s technical film on the Denby Dale Passivhaus and “Future Passiv” documentary we’ve also found that we’ve become minor celebrities (accent on the minor) in the Dale. It is good that the information is getting out there. We hope that we can help dispel some of the myths about Passivhaus. We wanted a comfortable home and that is what we’ve got – it’s a smashing home.
As part of a Passivhaus Trust organised event, the Denby Dale Passivhaus will be open to visitors (by pre-arranged appointment) from Friday 12 to Sunday 14th November between 11-5pm. To arrange a visit please email firstname.lastname@example.org or ring Chayley on 01484 461705.
For a lively and up-to-date discussion about the practicalities of Passivhaus go to the Building Network