Wednesday, 17 January 2018

Talking about Passive House. Lesson 14

This low energy building course is really just propaganda in disguise. The whole course has been framing the question, and the answer is Passivhaus. I also like to talk about differences in building culture, and mention my own experience trying to build a low energy house in Japan. I can, with honesty and some innocence, present my discovery Passivhaus as an epiphany on my road to building a house.

As usual term starts running out with too many lessons left over. In week 13 of 15 I had to get them into groups for their final presentations, and then give them some guidelines of what to do, and what not to do, when designing and delivering their own presentations. I could spend a whole lesson talking about preparing presentations. In this class I probably should, focusing on presentation construction as a piece of architecture.

They had put their own presentation ideas into a forum on the online part of the course, and then chosen their top three choices in an online quiz, so I had most of the data needed to make the groups, but of course a few students had not actually added their top choices for a presentation topic, a few others missed the lesson, and as usual a small number of the topics were very popular and they did not fit neatly into seven topics that were the first choices of exactly four students. In the end over half the lesson was taken up discussing their presentations, and I could only get through half of my beautifully prepared full lesson, with its narrative from building cultural differences between the isles on the East and the West of the Eurasian continent, to my own journey into house building, and discovery and application of the Passivhaus standard.
Energy balance for a Passivhaus

Descriptions of standards can be dry, and there's a maximum of ten minutes I can talk to any class in English before they lose attention, so tasks are needed. I like setting them problems to solve, and also want them to practice real-world calculations where possible.

First I had them brainstorm heat gains and losses in a house. They got most of these, but needed a bit of a hint to remember ventilation.

The next task was to get from the definition of Passivhaus in English to the numerical heating load. This is a fairly straightforward calculation from the floor area per person, the volume of air needed per person, the maximum temperature air can be heated to before it burns, and the heat capacity of air.

Next, I wanted them to work out what U value they would need for the walls of a Passivhaus in Matsumoto. This involves several steps, and I made the mistake of giving them too many of the steps to work out in one go. I don't think the calculation itself is particularly difficult, but I guess I'll find out because I've set that for their homework!

The first step, to make the calculation easier, is to assume that the heating load is equal to the loss of heat through the walls. Remembering the energy balance of a building, you can get to this by assuming that solar gains through windows roughly equal heat losses through windows and internal heat gains roughly equal heat losses through roof, ground, and ventilation.

The next step is to work out the wall area of the house. I gave them the volume, told them it was two-story, and assumed they'd just be able to work out the wall area from that. Half of them are studying
architecture so I think I can be forgiven for my assumption. It turned out to be wrong though. Perhaps there were too many assumptions for them to make: the height of the walls, the squareness of the building footprint, the use of square root to get from an area to one of it's sides, the number of sides on the square... Perhaps they were worried about other things: did they need to subtract the windows and doors? What shape was the roof going to be? Perhaps they were distracted from this question because they were expecting thermodynamics rather than geometry. Anyway, I think have learnt my lesson, and will chop the problem into bite-size chunks for them next time.

I should probably have realised this sooner, and modified the task, but while preparing the lesson I had been more impressed by the result of the calculation: 0.162 W/m2K. This number may not mean a lot to you, but as I scrolled down the slides to the introduction to my own house, I noticed that in fact the U value of my walls is 0.162 W/m2K. Perhaps just a coincidence, but it does show you
the power of rough estimates!

Unfortunately I didn't have time to share this bit of synchronicity with my students as the lesson had somewhat dissolved into scratching heads, spurious scribbling and many over-precise, under-accurate sums. The bell was going to go before I got to the happy ending that is Matsumoto Passive House.

Friday, 22 December 2017

Passive House in Canada

While Passive House remains a mystery to most, and a misnomer to many in the building trade, here is some news of steps in Canada. And why wouldn't you?

Tree hugger reports here on a Canadian charity building social housing to Passive House standard.

CBC News​ reports here ​h​ow Canadians are constructing North America's biggest green buildings​.​ And perhaps the greenest big buildings too.

​And here's an article from High Performance Building Supply about why smart cities need passive house buildings, which is not really about Canada​, but they do mention a project in Toronto.

Monday, 18 December 2017

Carbon payback in a month not three days: Check those facts!

It looks like a simple arithmetic mistake has struck again.

In preparation for my lesson, I noticed my slides proudly announcing that five jerry cans of paraffin will put out two hundred times more carbon emissions than ten square metres of glass wool insulation. I had the carbon emissions for paraffin at a quarter of a tonne, which at first seems like a lot, but it's pretty much all carbon, and each one of those atoms is going to bond with a couple of oxygens from the atmosphere as they set of heating up the planet in their cosy little threesomes. You have to remember that fossil fuels are worth more than their weight in carbon dioxide emissions! Adding this to the extra density of the paraffin, a factor of two hundred is reasonable.

To give a little extra support for my students who are good with numbers but less good with foreign languages, I wanted to add a more precise weight of carbon equivalent to the glass wool. I could have just divided the quarter tonnes by two hundred, which would have given me one and a bit, but I wanted to get a more precise figure.

My first port of call for fact checking, as usual, was google. I assumed I could just ask it how much embodied carbon was in glass wool, and it would tell me.

I quickly found this greenspec.co.uk, which doesn't have any actual numbers, but has a few graphs. Very sensibly, it starts with different thicknesses of insulation to reach a respectable wall U value of 0.15 W/m2K, which would be about 23cm for glass wool. Then it has the embodied carbon value for a square metre of wall. If my I've read the graphs right, and my sums are correct, this gives 25 kg of carbon dioxide equivalent for my ten square metres of glass wool. Not two hundred times less than the paraffin, but ten times less.

I started looking for my own workings or references, but didn't find any. Usually I add a reference somewhere nearby, in the last few slides of a presentation or as a footnote of a blog post. At least it's good practice to do that, and I always expect it from my students!

So back to google again for a second opinion. I found a carbon footprint of 1.35 kgCO2/kg for glasswool in table 4.3 on page 118 of Sustainable Construction Processes: A Resource Text, by Steve Goodhew, which is the same as the University of Bath figure I wrote about before. The density is 25 kg/m3 here on engineering toolbox, which gives a slightly higher figure. But if I go with the spec on google shopping of 10kg/m3, I get to about 13 kg of carbon dioxide equivalent for the roll. Twenty times less, not two hundred times less.

There's a factor of ten error somewhere, but since I didn't keep my original workings, I can't see exactly where it is. I've checked a few times, and I'm pretty certain that the roll of glass wool is 10 square metres, and since it's 100 mm thick, it's going to have a volume of one cubic metre. I can well imagine a factor of ten error sneaking in somewhere around there.

Anyway, in terms of the return on carbon investment, instead of a three day carbon emissions payback for switching from paraffin to insulation, it's actually a month. Still seems like a pretty good idea!

This does go to show that it's always a good idea to double check calculations.

When I prepared the lesson two years ago, I was comparing an 11-metre roll of 910-mm wide, 100-mm thick glass wool with five 18-litre cans of paraffin, both of which cost 6000 yen. I'm not sure if it's a trend, or there is some fluctuation, but now the glass wool is a thousand yen cheaper, and the paraffin a thousand yen more expensive.

Monday, 11 December 2017

Lesson 10: Take 3: Standards

It's a challenge making building standards interesting. The topic seems as dry as a highly insulated house in the middle of winter with heat recovery ventilation and no humidification. As I started brushing the cobwebs off last year's presentation, my first thought was that I should teach this lesson later, and tackle the altogether more exciting topic of energy generation first. I stopped myself, thinking that I was just trying to put it off, and I've just noticed now that I'd moved it two weeks later last year. A lesson on comfort had been added to the original plan, and Windows 2.0 came after the lesson on standards the first time.

This lesson should really work as a revision of what I've been telling them about low energy building, since standards ideally reflect the essence of low energy building, and promote improvement.

I followed the plan at the beginning, giving them several reasons for low energy building. An obvious reason is to reduce environmental impact, although unfortunately this is a relatively low priority for a lot of people. Money is often a higher priority, and the fact that low energy buildings are cheaper to run, long term, is perhaps a more powerful incentive. Even then, a lot of people are concerned with the immediate costs, and less worried about possible future savings. Grants or tax breaks are another reason people may build low energy, but the most powerful reason is probably where there are laws that oblige people to build low energy.

Then I tried to introduce the idea of standards, with a few examples and their logos, including the JIS (Japan Industrial Standards) logo, which they all knew, and the logos for European Standards, British Standards, and Forestry Stewardship Council (FSC), which they did not.

In order to breathe some air into the topic, I put them into groups and had them imagine they were government committees who had to come up with their own standards to ensure low energy buildings.

First they had to brainstorm for things they could look at. I had to steer them away from things like giving grants, which is a good idea but not actually a standard.

Their ideas mentioned insulation materials, windows, form factor and solar power.

After some brainstorming, I got each group to choose two or three ideas, and come up with some details of what exactly they would stipulate.

They came up with a few concrete suggestions, such as using wood rather than aluminium for window frames, and a minimum percentage of glazing to frame. Other ideas were a bit vaguer, like making the air gap thicker, and having "really thick" walls. There were very few actual numbers, and nobody mentioned U-values, which makes me think I haven't talked about that enough times.​ Also nobody mentioned ventilation.​ One group came up with the two ideas of adding solar panels, and adding a battery to store the power. These are both interesting ideas but have absolutely nothing to do with what we've been talking about for the previous nine weeks. That did make me think I should have done the lesson on generation first.

The lack of detail also made me wonder whether I should have given them that task later in the lesson, after I had given some examples of actual building standards. As often happens in teaching, there is a difficult balance to reach between giving students information and getting them to come up with their own ideas. Perhaps I should start off by introducing some of the early low-energy building standards and then get them to think about what is missing, how they could be improved, and what they would do now.


This may have been a good lesson to produce a multi-dimensional gap fill, or jigsaw activity for. There is a smartphone app called Quizlet Live that lets you add several questions and their answers, which are then scrambled for students to match. The teacher gives students an access code, then the app puts students into groups of three or four, so they have to go and find their partners. Then each student gets around four answers on their screen, and the questions come up in turn. The student with the correct answer must select that, then they will all get the next question. If someone gives the wrong answer, it goes back to the beginning again, shuffling the answers. This may not make the content any less dry, but it could socialise its delivery.

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Thursday, 30 November 2017

Building Jokes

There was a tweet a while a ago from Nick Grant @ecominimalnick with a picture of a structural engineering joke.

I didn't get it at first, but the joke is that the round black things with the bolts in are supposed to be stopping the walls from bulging, by bolting them onto the floor. Clearly the floor is not in the middle of the windows. This may be a deliberate joke, but I don't think the other pictures are.

A couple of my students did start laughing when I showed them this picture, which Sam sent me. I'd been talking about the relative merits of glass, air and aluminium in window construction, and they found this very funny, although I doubt the joke is deliberate.


I asked them to calculate how much glass and how much frame there was. They all guessed around 70% glass and 30% frame, but actually it's closer to 55% frame and 45% glass.

It's even funnier when you notice the unmelted snow, and see where the sun is coming from and realise this is a North-facing window. So not only is the aluminium going to reduce the performance of the glass, it's not going to get much sunlight coming in. It's possible there is some fantastic view that these windows look at, but even then, most of the view will be obscured by frame.

Of course traditional houses in the UK aren't much better.


I also showed them the windows below from a brand new concert hall in a nearby city. Due to my photographic inability, it's a bit difficult to work out what's going on, but basically the external surface area has been needlessly increased by around 20%, and it's aluminium too.


This time the joke is on the city tax payers, who will be getting the heating bill.