Some like it hot? Data up to the solstice

Last time I posted temperature data was in April and it covered the period from the winter solstice to the spring equinox (for an explanation of the solstices take a look at the BBC's website here). We've now got data for the next three months as the sun reached its highest point in the sky. Of course this has also coincided with pretty dismal weather here in the UK but we are getting a bit of a feel for the pros and cons of this particular house so first I'll give you the scientific data and then I'll give you the low-down on what that data feels like. 

Before I begin, I ought to say that I do love this house and largely enjoy its quirkiness, but as a recent school visitor said, houses are for living in, so apologies in advance to any readers who won't be happy with what I say.

Here's the temperature data from the winter to summer solstice. We've changed the graph to show fortnightly averages to make it fit on one page:

As before the green bars show the amount of energy we've generated (so you can see how much heat we got from the sun that day) and the blue, orange and red lines show the floor temperatures but I've changed the external temperature record to a purple line so the graph is clearer. 

If you compare the peaks at the beginning of January, end of March and end of May you can clearly see how much stronger the sun is as we approach the solstice and each peak pushes the internal temperature of the house up to a new plateau. In the winter the internal temperature was running at an average of 18-19°C, by the time of the equinox in March it was 20-21°C and by the end of June this had become 22-23°C.

In the winter the house felt too cold and we assumed this was because it was drying out after the build so we were delighted when the weather warmed in the spring and we were able to switch off the heating boost but by the end of May I was tweeting that we were having problems with cooling the house and this has been a big issue now for a couple of months.

If you google "passivhaus overheating"  there are a number of sites that tell you that passive houses don't overheat and, technically, this house doesn't very often because the point at which overheating is defined seems to be when the internal temperature exceeds 25°C (that's 77°C in old money). But, whilst our internal averages have been in the low 20s Celsius we have had days when several days of sunshine or the combination of sunshine and high temperatures outside has caused the temperature on the top floor to rise to 25 and beyond. It may not technically be overheating but you try sleeping in 25° heat when you've been trained for donkey's years to keep your house thermostat on 21° to save the planet!

I jokingly posted on twitter that our house may be passive but we're having to be rather actively engaged with it and that's certainly been the case since it started warming up. We've obviously been keeping the blinds closed to exclude direct sunlight (and, irritatingly, block the views of my garden) but that wasn't enough. We've sought advice about how to cool it down but there's a lot of advice out there and what works in theory doesn't necessarily work in practice in this particular house and, in the process, we've discovered ancecdotally, about other passive houses experiencing similar problems. 

There have been elements of farce involved in reaching a modus vivendi with the house temperatures but at least the Jubilee and Olympics have bought me time by postponing summer. One suggestion was that we turn off the MVHR and open the windows to cool the house down. I tried that but we ended up with the 'wet' areas of the house (the bathrooms and utility room) reaching jungle levels of humidity so I battled through the lianas and leeches to the MVHR control panel and abandoned that idea. Another suggestion was to switch the MVHR to summer bypass mode. Sadly we didn't know what that meant so I wasted a day or so working it out and then trying to find out how to do it as the only manual we'd been given was all auf Deutsch. Well, you can't say you don't learn stuff in this house - not just physics and engineering but linguistics too. With a combination of German dictionaries, google and sheer bloody-mindedness, I managed to sort that but it only reduced the temperature by half a degree and I'm not even convinced that it was a key factor in that. So, at the moment, the only thing that is working is to open as many windows as we can on the top floor without the rain pouring in and keep the MVHR on the lowest possible summer bypass temperature. With all that going on the temperature on the top floor is now about 23°C and it's not as warm as I'd like downstairs so any sensible suggestions about how to vent the house further will be gratefully received.

This house only has external shading on the south facing windows and this, I think, is one of our key problems. We had to have rooflights on the top floors to counter planning objections and they only have internal blinds on the south-facing roof so some heat obviously gets into the top floor through this route. In addition, since May, the sun has been high enough in the sky to shine through the rooflights on the north side of the house and they have no shading at all. We are also finding that a lot of heat has been coming through the east and west windows since the equinox so probably those windows needed external shading too.

So, architects/engineers reading this, may I suggest some things to consider when planning a passivhaus?

1. Please put external shades on all the windows
2. Don't make a three-storey house unless you've got very efficient ventilation for the top storey
3. Consider designing the house upside down - you want bedrooms to be cool and living rooms to be warm so perhaps bedrooms should be on the lowest floor and the living rooms at the top floor. Thus, ideally, you should be designing houses for south-facing slopes which are accessed from above not below!
4. Give people manuals in their native tongue unless you feel that self-improvement is an integral part of living with your design

Next time I post I will write about the financial efficacy of the solar panels and probably be busting a few myths but I will wait and see what, if anything, we get in the way of our first FIT payment compared to the amount of electricity we've been generating.... I might be pleasantly surprised but don't hold your breath!

And because all the above may be received as criticism rather than the words of a critical friend let's finish with a pretty picture of the house because it may be a bit mad, but I am rather fond of it.

For copyright info on the image of Stonehenge see http://en.wikipedia.org/wiki/File:Stonehenge2007_07_30.jpg

In nuce: new readers start here

I've had a couple of school visits from our local secondary recently as they are studying sustainability in geography.  With children and teenagers you have to fit your patter into a restricted time, partly because they are not shy about exhibiting boredom and partly because they have to leave for the next lesson. With that in mind I've had a crib sheet so I don't forget the pertinent parts of this house and it occurred to me that it might be good to post it here as continuous narrative blogs like this don't always easily work backwards......et voilà, click on the links and it should take you to the most relevant post (sorry if the colours come out strangely with the links):

...... Oh and before I forget, we've had absolutely no heating on since 19th March despite the dismal weather and mostly we're swanning around the place in T-shirts, so I think we can give the design and build teams (plus everyone I don't have links for) a round of applause because the technology really is working and it occurs to me that the passivhaus is a bit of a no-brainer really.

reducing the energy load through design * Passivhaus: 90% less heating * Insulation * Triple glazing * Airtight * South facing * External blinds * Painted white through technology * Eco/A* products * Solar photovoltaic & thermal		reusing waste materials * Glass * Concrete * Paper * Cardboard * Books * Wood
	recycling * Sun * Rain * Earth’s heat * Interior heat * 100% renewable electricity * Carbon neutral * Off-setting CO2

Temperature Data

Here's another data graph for you, covering the period from the winter solstice to the end of March.

The green bars correspond to the amount of energy being generated by the PV and thus the amount of sunshine. The purple bars show the external temperature and the brown the hours the heating has been boosted inside when the temperature has dropped. These are plotted against the lines for the house temperature on the top (red), first (yellow) and ground (blue) floors.

I should point out now that this is a domestic record of what's happening in the house: the energy records are accurate but they aren't always taken at the same point each day and the temperature readings come from a normal thermometer rather than a more scientific instrument. Nonetheless this records what's been happening in this particular Passivhaus over the past three months.

The house has been good at maintaining its base temperature but although that has been 20 degrees on the top floor it was too cool to sit in the rooms on the ground floor for several months without adding an extra heater. The ground floor temperature is closely linked to the external temperature, but it takes about 24 hours for changes outside to be felt on this floor. It was only once we had the high temperatures and sunshine at the end of March that the temperatures on all three floors reached much the same level. The house's heating doesn't have much impact on the ground floor and only slightly more on the first floor, but it has a direct (and immediate) effect on the temperature of the top floor, presumably because the warm air rises to the top of the building and, despite the coanda effect, doesn't hang around to heat the rooms on the lower floors. Is it supposed to work like that? Perhaps one of you Passivhaus engineers can let me know...

The graphs suggest the first floor is the most responsive to sunshine and it certainly receives more than the floor below where the wall and house of a neighbouring property shadow the windows for more of the day. On the other hand, it's also the floor containing the kitchen so the extra warmth from cooking may be what's keeping it warmer than the ground floor.

The top floor is the most responsive to the internal temperature of the house and less affected by sunshine. The temperature on this floor climbed at the end of March as the lower floors became warmer and the warm air rose but we got into the habit of opening the rooflights to cool the rooms and kept the blinds closed to exclude direct sunlight during the day. The question, of course, is will this be enough to keep the house comfortable in the event of a heatwave in the summer?

PS: Do note how little we've actually had to have heating on this past three months - a bit different to a 'normal' house

Springtime...

Well this has been the fortnight the house woke up from hibernation and it wasn't a gradual sleepy start either but a very definite throwing off the covers and flinging back the curtains approach to spring.

Two weeks ago, in my previous post, I was writing about how cool (in the temperature sense) the house was and how we were waiting for it to come up to temperature; then the weather changed. For all but one of the last fourteen days the solar panels have been generating more power than we've used and the average temperature inside the house has gone from 18 to 22-24 degrees (for the less scientific amongst you that's the difference between wearing a fleece in the evenings and grumbling to wearing a T-shirt).

The chart here is our record of how much energy we've been using each week (the brown bars) and how much energy the PV has been generating (green).

You can easily spot the time round the winter solstice because the PV produced the least energy then. The combination of short days and the sun being at its lowest height in the sky meant that the panels didn't receive enough direct sunlight to work much. You can also see the icy weather in early December and the cold and snow in February because the energy consumption goes up as we run the heating more. The fluctuations in the brown consumption bars are caused by the amount of sunshine and illustrate clearly what I've said before about the sunshine warming the rooms and reducing our need for backup heating. Then, of course, there is the green trendline that shows how as the days get longer and sunnier our energy production increases. 

The sunshine has also made a difference to how we've been working with the house. As the days got warmer at the beginning of the month we were opening the porch door and blinds to let the sunlight into the house. In the past week, when the external temperatures here were around 20 degrees, we started closing or tilting the blinds to reflect the light away from the rooms as it was getting too hot inside. We're also now opening some of the roof windows at night to cool the top floor as 24 degrees is too warm to get to sleep. If we didn't have blinds on the south-facing windows the house would be getting too hot already and as it's working rather like a greenhouse we're improving our environment even further by getting more houseplants.

We still don't know what will happen to the consumption-production balance on grey days as the days get longer but, so far, the data from the eco frontier suggests that solar energy is beginning to look like a no-brainer even here in the grey West Midlands. This begs the question of  why the UK government isn't doing more to encourage its adoption, though after the recent newspaper reports one wonders if perhaps the solar industry simply lacks the lobbying power of its energy competitors; a depressing thought.