A house into a home and a home into a house

It's amazing how quickly our old home has turned back into a house.

There is still some tidying and cleaning to do there, and when we go back it seems strange to think that we actually lived there a few short weeks ago. 

 

The moment we moved the stuff out of there, it lost that essence of home, and our new house seems to have very quickly become our home.

I wonder exactly what it is. Perhaps the fridge. Like the nourishing mother of the modern family. Perhaps the TV, like a father who speaks and everyone shuts up to listen. 

Or is the essence of home there in the details? That jar of pens, most of which don't work. A pair of pajamas with a button missing. An odd sock hanging up, waiting to find its partner. A chip in the woodwork, or a stain in a carpet.

Too bloody hot

December and January could be the hottest months in the house. At least, somewhat counterintuitively, they are the months with the highest solar gain. It's not that the sun is hotter in December and January. In fact, the sun is more or less the same temperature all the time, and cares little whether it is winter or summer in the northern hemisphere on Earth, but of course there is a difference in how much of that heat reaches the surface of our planet.

In terms of the radiation from the sun, there is more in the summer than in the winter. There are two reasons for this. First, the days are longer, so there are more hours of sunlight. More hours of sunlight mean more heat. Second, the angle of the sun is higher. This has two benefits. First, more sunlight is going to hit a given area of the earth. If the sun is directly above, a square metre of sunlight is going to hit a square metre of the earth. If the sun is 60 degrees below vertical, 30 degrees above the horizon, a square metre of sunlight will be elongated over two square metres of the earth so the incident radiation is halved. Also, the higher the sun is, the less atmosphere it has to get through, so the rays are stronger when they reach the ground.

The point with a house is that the windows are on the walls, so we aren't really interested in how much sunlight reaches a square metre of the ground. We want to know how much reaches a square metre of window. And this, almost by some divine intervention, means that in the winter, when we may expect it to be coldest outside, we get the most heat coming in through the windows. And when it gets warmer in the summer, less heat comes in. If we are careful with balconies and eaves, then we can try to keep this radiation to a minimum. Reflection is another thing that may lead one to believe that God invented windows, or at least that God was a double glazing salesman. The smaller the angle between solar rays and glass, the more is reflected and the less heat comes in. This means that more of the low winter sun will get through, and more of the high summer sun will be reflected.

So this is why it got up to 28 degrees centigrade in the living room at lunch time on 12th January, even though it was only one degree above freezing outside. The bottom line on this graph of temperatures over the first few weeks of our residence shows outside temperature (green - averaging more than one degree below zero). The highest temperature is inside temperature south (red at the top), and inside temperature upstairs north is pinkish below that, but dancing to the same tune. The others are slab temperatures. The big leap in inside ambient temperature was when we closed the windows and switched on the ventilation system on 23rd December, but you can see the jump in the temperature at the middle of the floor (light blue) as the underfloor heating started working on 26th December three days later. The effect at the bottom of the foundation slab (middle - dark blue) is slower, with about a three-day delay. At the North West corner of the foundation, the temperature change is much slower.   

Obviously it would be churlish to complain about the house being too hot, when all around are pouring gallons of oil into theirs and still freezing, and of course there are a few things that we can do before resorting to opening windows and letting the heat out. According to the thermometer in the upstairs north room, it is significantly cooler there, so if we open the inside windows from the atrium into the bedroom, the heat should go in there. Also we can open the door into the genkan and washitsu, which are to the north and significantly cooler. 

Part of the reason the north side is cooler is that the slab is much cooler there. This is by design. Kind of. The underfloor heating passes from the boiler to the south side of the floor, then to the north side of the floor, then back to the boiler, so the south side is being heated more effectively. Eventually the slab will probably have a constant temperature, but it actually seems like a good idea to have some temperature difference in the house. It would be nice to be able to control it a bit better, and I'm sure there is something we could do with the ventilation system. At the moment we are using a fan to blow air from the cooler northern parts of the house. 

But, going back to emissivity, I can't help feeling that it may have been a good idea to have had a higher emissivity for the floor and the walls so that they would have been absorbing more heat. What I guess is happening is that the radiation is just bouncing around the floor and the walls and getting the air really hot. The white terrace outside is probably helping by reflecting more sun into the house.

We're going to get some blinds soon anyway. I'd really like Venetian blinds with white on one side and black on the other, but I'm not sure if they are available or aesthetically pleasing. 

The Crookes radiometer shows the difference between black and white, invented by the eponymous Victorian chemist, William Crookes, who was pleased with himself for being able to make vacuum tubes. It was supposed to work as a kind of light mill, the white sides of each panel reflecting the sunlight, the black sides not reflecting anything, and spinning accordingly. When it started spinning, it went the wrong way; the black panels going away from the sunlight. The simple explanation is that the black sides get hotter than the white sides, and heat up the air molecules next to them, because actually the vacuum was far from perfect, which push the wheel around. A more detailed and accurate definition can be found 

here on wikipedia, unless the US government has shut it down. The difference the vacuum makes is to greatly reduce the resistance, so the effect of the heat becomes more significant. 

Black bodies and getting my head around emissivity

There's something about emmissivity that doesn't seem to have made sense, and probably should have done much sooner.

My attention to thermodynamics regarding the house has mostly been concentrating on conduction. Of the three ways heat gets around, this is probably the most significant. Obviously convection is important, but I think if you're dealing with a wall with inside on one side and outside on the other, and you treat the air as being at a constant temperature, then you won't be far wrong. What is actually happening, if the wall is hotter than the air next to it is that it is heating up that air, then that air is moving away and is replaced by a new bit of air which needs heating up again.

The resulting heat flow is more or less the same. 

Probably.

Anyway, I haven't really been thinking about radiation. I can remember a physics teacher telling us that radiators don't really radiate, they transfer heat by convection. And that seems to have stuck in my mind. I have, of course, been thinking about solar radiation, as that is how the sun gets its energy to us. We worry about nuclear power and radiation in the hands of humans, but in the case of the sun, it's an important part of life. If you want to see how much radiation nuclear power produces, you just have to look at the sun, as that is basically a big nuclear power station. In fact it's probably not a good idea to look at the sun as it will make you go blind. 

So the solar heat coming into the house is coming in by radiation. The windows are low-e, which everyone who knows about windows will tell you is important, so that you keep the heat in the house. The "e" is for emissivity, and it doesn't really fit into my idea of common sense. As far as I can tell, "low e" just means that it reflects heat. 

Emissivity, on the other hand, is a measure of how much a body radiates. It is a number between 0 and 1, or zero and a hundred percent. For a black body, which I'll get to in a moment, the amount of radiation is proportional to the fourth power of the absolute temperature. This corresponds to emissivity of 100%. You can read more about that here, if you're really interested.

The black body is a theoretical object that will absorb all the radiation that falls on it. What confused me for a while is what exactly this has to do with windows reflecting heat. It seems that three things are going on when radiation hits glass. First, some of the radiation is reflected by the glass, second some it it goes through the glass, and third, the rest of it is absorbed by the glass and warms it up. These seem to be independent ideas. Obviously all the parts are going to add up to 100% otherwise we'd be breaking the law of the conservation of energy, but what does radiation have to do with absorption?

I've given in to what seems a much simpler reality. It just comes down to one number - the emissivity. Bodies are like mirrors. If they absorb a lot of heat, they can also radiate a lot of heat. If they reflect heat well, they radiate heat badly. 

Polished metals have very low emissivity, which is why the lunar module was wrapped in tin foil. Not necessarily what you'd want around your house as it would conduct the heat away, but in space there is no atmosphere, so conduction is not an issue, and heat is lost, or gained if you're in the sun, through radiation. Radiation and emissivity are issues in buildings on earth, as we shall see in the next post. 

Ten good things about the new house

To make sure I'm not just finding fault with everything, so that I don't sound like a miserable git, and so that I don't turn into a miserable git, here are some things that are really good about the new house. In no particular order, and all little details, but life is made up of little details. Usually little details interspersed with boring bits. The details can be a bit tedious at times too, but here you go!

1. The kitchen counter is at the right height.

2. I don't have to stoop to get through each doorway either. This will be good for my back, once it recovers from moving all the boxes.

3. No parts of the house get scarily cold and become no-go areas in the winter.

4. The handle of the kettle doesn't get hot. We have an IH heater, so the heat is going straight into the water inside the kettle, rather than warming up the sides of it and the handle on the top. We used to need a towel to pick up the kettle in the last house because it got so hot. Now it doesn't get hot at all. IH must be a lot more efficient. It also seems a lot cleaner as the flames and fumes from the gas are not carrying particles of grease around the kitchen.

5. I can park the car in front of the house.  I just changed to snow tires and don't have to wheel them all the way from the car park to store them in the garden.

6. I don't have to worry about coming home to a cold house. It will never get cold, even without the heating on. And even if the heating is on, I can leave it on, and not worry about the house burning down too.

7. I don't have to wear socks inside.

8. I can see outside from in the house. It's nice being able to see snow on top of the mountains, or watch it fall. Also this means I can stay inside all day without getting cabin fever.

9. I don't have to walk through the kitchen after having a bath. The bathroom in the old house was the other side of the kitchen.

10. I can get to the post box without having to cross any roads. From the last house, we had to wait at the really long traffic lights to get across the busy main road, or walk across the river to the one near the new house, or go much further to get to the local post office. Not that I have to post letters very often, but I did say that it was in the details.

Japanese airtightness measurements suck

Apparently in Germany, when they do an airtightness test on a house, they test both over pressure and under pressure. In other words, they shut all the windows and doors, and put a blower on one of them to blow air into the building until the pressure gets to be higher than outside, then they measure how quickly the air starts leaking back in again. Next they blow air out so the pressure is lower inside, then they measure how quickly the air starts leaking in again. They take the average of the two values to get the airtightness of the house, which is measured, at least for Passive House certification, in the number of times the air will change per hour. The passive house standard is 0.6.
In Japan, they usually only have the equipment to do the under pressure measurement, which apparently is usually a little better. So, in a sense, Japanese airtightness measurements suck.
They did another airtightness test in December, which I'm still waiting for the results for. I should have done this months ago, but I've just now started looking carefully at the results from August. The experts said that we needed a C value of 0.2, but we only got 0.3 which was not good enough. They said that this was a reverse calculation, making it sound really difficult.
Never trust experts, especially if they make things sound really difficult and complicated. If they do that, it's a sign that they don't know what they're talking about. If they do know what they're talking about it, they should be able to explain it and make it simple.
Anyway, as a result of this 0.3 that should have been 0.2, we became very sceptical of the Compriband's effectiveness, and added caulking around each window to improve airtightness. We had previously planned to add a layer of insulation around the inside of the window frame, on the few centimetres of wall perpendicular to the window. This insulation would have reduced the thermal bridge effect of the window from something like 0.04 W/mK to 0.03 W/mK. This doesn't look like a lot, but when you think of all the windows in the house, and measure around each frame, there are something like 80 metres, and there are 70,000 degree hours temperature difference over the part of the year that needs heating, so it amounts to about 50 kWh per year.
Anyway, it was basically presented to me as a choice between putting caulking around the window frames, to improve the airtightness, which wasn't good enough, or carrying on with the plan to insulate around the frames and improve the thermal bridges. The caulking was going to work out more expensive than the insulation, but the builders offered to cover the extra cost, so it would make no difference to my pocket.
The decision had to be made quickly as other parts of the wall were about to go up, and the frames would no longer be accessible. I agreed to them adding the caulking, which the airtightness and insulation people went ahead and did.
But, while waiting for the results of the latest airtightness test, I started looking a little more closely at the figures of the last one. I should have done this ages ago, and in fact I've been waiting for an opportunity to talk with them and find out more details of this devilishly difficult conversion between the C value and the number of air changes per hour.
According to the figures the airtightness experts emailed me 4th October, almost two months after the test, the result was 259 cubic metres per hour at 50 Pa pressure difference. The bit of the form where the number of changes per hour should have been was blank, I guessed because they didn't have the figure for the volume of the house. According to the Passive House database, the volume was 500 cubic metres. Obviously this is not the exact volume, but it's close and serves as a design volume. Taking this, and the 259 cubic metres per hour, that looked to me like 0.52 times per hour, which meets the PH standard.
So, I surmised that either 1) my calculations are incorrect and it's much less straightforward than [volume per hour / total volume]; 2) the design volume of the house (500 cubic metres) is a lot more than the actual volume; or 3) the architect or airtightness experts were too lazy or too incompetent to perform a straightforward calculation. My money was on 3.　
I spoke to the architect on the phone, broken into two or three calls as he kept having to find information, or calls back because he had found more information. The figure he had was 0.542 exchanges per hour at 50 Pa. The actual volume of the house is 478.1 cubic metres. I'm beginning to wonder whether the airtightness people sent him a different copy of the results to the one they sent me... Why would they do that?
After first denying that the caulking had anything to do with the insulation and suggesting that the airtightness people had done it as an act of charity, he later came back and conceded that yes, the first airtightness test had met the standards, although they had told us that it had not, and that no there had been no need to add caulking on top of the Compriband, and yes, we could have had the extra insulation around the inside of the window frames and reduced the thermal bridge effects.
Another factor prejudicing them against extra insulation was that in some places the insulation would have stopped the windows from opening. As far as I was concerned though, it was a fairly straightforward choice.
Not sure exactly whether he's going to do anything about it, but he did at least say sorry, and not really related but he would get us a ventilation system with a bypass, and would cover the cost for it.
Maybe a complete coincidence but the airtightness and insulation people did the caulking work, and also did the airtightness tests.
There's something very satisfying about letting people know that they have done you wrong, but perhaps only relative to the much deeper dissatisfaction of feeling that you have been done wrong to.