Saturday, 20 August 2011

36 views of Matsumoto Passive House

A couple of weeks ago I clocked the camera memory stick. I've been taking pictures of the site since they first laid out bits of string to mark the footprint of the house, back in December last year. I've been deleting old pictures from the camera each time to make space for the new ones, and just caught up with the first pictures of the plot.

At the beginning I took four pictures, one from each corner of the plot. I'm still taking the same four pictures, adding each one to a separate album.

Actually, there are many more than 36 views. There are now over 90 albums, most with a series of pictures taken each day from a fixed spot inside or outside the house. On a busy day I'll take over 100 photos.

The slideshow above is the biggest album, the view from the South East corner of the land, with 130 photos. To the right is the latest angle, looking at where the boiler as going. I wish I'd started taking this shot sooner. The back wall is already finished. 

You can see all the albums here on picasa.

I've wanted to change the name of an album a few times as the situation changes. Unfortunately, the name of the album is included in the link to the photo, so once I've used the link it's not a good idea to change the name. The names each made sense at the time.


Another thing that seems to happen is that I'll start taking a shot from an angle, then something will appear right in front of the camera, blocking the view.
This happened with two of the original angles, when a wire frame appeared in the shot from the North East corner, and a portaloo appeared in the view from the North West.  
More recently they moved the boiler, still in its box, right into the middle of the shot from the South East corner inside the house. 

I think this view of the four corners of the house is nice, and shows how the walls are developing.  

I really need to go through some of these albums and delete all the pictures that look the same, but having spent so much time adding photos, it will be painful. Editing always takes ten times longer than making things, but probably makes things ten times better. Less is more. Enough said.

More views:
new upstairs and progress downstairs.
(Somewhat crosseyed) stereo view from the north.
The view from the western approach.
This began a view of the foundation, but you can now see the South West corner of the house, from the outside.

Or you could just press "views" in the labels yourself!

Built to last or built to lose

It is sometimes hard for me to come to terms with the disposable nature of house building in Japan. Apparently the average life time of a house in Japan is 17 years. In the UK, it would take 1700 years to replace the entire building stock. Although those two numbers are not equivalent, it gives some idea of the difference. I come from a country where houses are built to last. I grew up in a house that was a couple of hundred years old, which was not particularly unusual. The house we rent here now is about a hundred years old, and it's a constant surprise that it is still here.

It is easy to write this off as bad workmanship or see it in terms of a nation that loves new things and is obsessed with the disposal of the old. It has been suggested that Japan needs a large construction industry as there are periodic needs for mass rebuilding after natural disasters. It seems that the construction industry is a powerful lobby and they can veto any suggestions to improve building standards. There is also no doubt something left over from the post-war rebuilding of Japan where fast, cheap building was the only option. I think there is no simple reason.

There is a vicious circle, as I found when I was asking the bank about loans. As far as they are concerned, and as far as the taxman is concerned too, a house is worth nothing after twenty-five years. The biggest drop in value is the moment you move in. In most cases, the house is worth less than you paid for it as soon as you turn the key and walk over the threshold.

The people at the bank weren't particularly interested in the building specs when they were valuingthe property, instead they look at the houses in the neighbourhood andtake an average per floor area. In fact as far as collateral, they don't really take the house into consideration and just look at the value of the land. So unless you're building with cash, and have lots of it, you're at the mercy of a bank that is not going to encourage you to increase the spec. There is little incentive to build something that will last more than 25 years, although a standard for a hundred-year house has recently been introduced, that can open the door to lower mortgage rates.

Houses in the UK, and probably the rest of Europe, the US and Australia, steadily increase in value. From when they are built, they start to get more valuable. After a while, when they hit an unfashionable or unserviceable age they stop getting more valuable, but even then they will hold their value. A little later they start to go up again. There are certainly stories of people with negative equity and people who lose out, but that's usually short term and a combination of local conditions and some measure of extra bad luck for the house owners, forcing them to sell at the wrong time.

As we were looking around Matsumoto for houses and land, we often saw old houses for sale that were very reasonable. If they weren't sold after a year or two, they were knocked down, and the price of the land, without a house, would go up. There is a common wisdom here that renovating old houses is more expensive than building new ones, and I think it may be true if you're comparing a low-cost new-build with restoring a ruin to its ancient form. I think it's more likely to be propaganda by the building trade, a symptom of few people or businesses that renovate, and the prevailing trend of not looking after houses, but letting them wear out until they are knocked down, which is all part of the vicious cycle.

Having said that, if I look at the house we are in now and if we were to bring it up to a comfortable level to live in, we'd have to replace the roof, replace the windows that make up the north and south walls, and pull up the floors and do some work on what's underneath. By the time we'd taken all the bits off that need changing, we'd be left with a wooden frame, and that probably would have to be made earthquake proof as their are no diagonal supports and the whole thing is a mechanism (see here). Also, I'd want to raise all the horizontal beams so the doorways are at least twenty or thirty centimetres above my head rather than two or three centimetres below, just where there is a permanent bruise on my forehead.

One way of looking at this difference is in terms of agriculture. The UK traditionally has pastoral farming, so buildings have been essential to provide shelter for people and animals, so that animals can feed off the surrounding land. Buildings have intrinsic value in this sense. Japanese agriculture is arable, so that land itself is valuable for intensive planting of crops. Any building is going to reduce this value by stopping the production of crops.

Another consequence is in the notion of "home". For the British, a home is a solid thing. An Englishman's home is his castle. For Japanese people, any building seems arbitrary and the sense of belonging is to a community of people.

So while I see what I am doing as an investment, and put myself on a mission to make a small change to the way houses are built and treated here, I'm probably just pouring cash into a hole in the ground, and the main interest of most of the people involved is to catch some of that cash as it falls. I'm sure the house could be built to a similar specification for less cost, and hopefully everyone involved will learn something onthe way, so if another idiot comes along asking for a house that doesn't consume, it'll be easier for everyone concerned.

Wednesday, 17 August 2011

Keeping those panels cool

The people from Caname, the roof makers, and Rooftech, the roofers, came to visit the other day. My concern was with the air channel under the panels, which seems to me to be just too small. I've started measuring the temperature of the air coming out of the top, and it was getting up to 70 degrees centigrade. You can see a graph of the temperatures below, showing also for references the ambient temperature, the temperature inside the house and the temperature at the bottom of the slab, which comes pretty much to a straight line. The heat of the actual panels is going to be more than the temperature of air in the channel. 

So what? I hear you ask. 

I can hear some of you replying that solar panels produce less electricity as they get hotter. With the Suntech STP190S-24/Ad+ panels we are using, the efficiency drops half a percent with each one degree increase in temperature. 

As a thermodynamic system, incoming heat is beating down in solar radiation. This heat is lost in four ways: the panels are losing some heat to the wind from the top of the panels by convection, they are losing some heat by convection to air passing through the channel between the panels and the roof, they are losing some heat that is converted to electricity and they are losing some through the top by radiation. A small amount of heat will be conducted from the panels to the roof, but the roof is well insulated, so this heat is not really going to go anywhere very quickly. Heat that is not lost will make the panels hotter, and the efficiency will go down.

Directly fitting panels onto roofs as solar tiles is a bad idea because of this heat loss. Even conventional arrays that have been added onto a roof with a gap underneath will suffer efficiency loss of around 20% in the summer. 

Caname have done some research with panels fitted directly onto a roof with no air channel, some fitted in the conventional way, where air can flow north to south and east to west, and some fitted in their roof system where air only flows south to north. Their results over a year peg the conventional roof at 100%, find that fitting the panels directly to the roof with no gap drops to around 80%, while their roof is 99.5%. In terms of average panel temperatures, the conventional panels and their panels averaged around 65 degrees, while the tile style was over 70.   

In my opinion, rather than treating the conventional way as 100%, they should be treating ideal output as 100%, and ideal output means either full rating of the panels, or the projected power output at ambient temperature, in other words with perfect cooling.

The fact that they are building a roof system should mean that they can do better than panels that are added to an existing roof. Setting this as their target seems to be aiming too low. For example, they mount the panels on corrugated steel. Corrugated steel roofing may sound like a really bad idea, but it should work very effectively to cool the panels, both by channeling the air from bottom to top of the roof, and by increasing the surface area to conducting the heat from the panels.

Temperature and heat of the slab

So we're getting all this temperature data from the thermometers in the slab. Not sure exactly what to do with it, or exactly what it all means yet!

There are ten thermometers in the slab: two in each corner, and two in the middle. One at the bottom in the foundation slab, and one in the screed floor.  They are numbered from 1 and 2 in the middle, 3 and 4 in the north-east corner, then clockwise until 9 and 10 in the north west corner. Odd numbers are at the bottom and even numbers at the top. 


You can see eight of these on the graph. The software from T&D will only show eight bits of data at a time. If you look at the graph you can see the lines at the top moving up and down rapidly, fluctuating with the temperature in the house, in turn affected by the outside temperature. The bottom lines, at the bottom of the slab, are much more sedate. 

One highlight is 6th July when the windows were installed and the fluctuations at floor level were quelled. 

The weather changed after the middle of July and it got a significantly cooler. Luckily this was just after we got back from a camping trip. You can see the peak of the temperature at the top around 20:00 on 16th July, which didn't reach the bottom of the slab until 05:00 on 19th July, two and a half days later. 

As a thermal system, I think there are nine ways in which heat can move:
Going in:
1. From the sun to the screed
2. From the boiler to the screed through the under floor heating pipes
3. From the air in the room to the screed (when the room temperature is above floor temperature)

Going out:
4. From the screed into the room (when the floor is warmer than the room)
5. From the screed through the walls around the foundation to the external air.
6. From the bottom of the foundation to the ground under the house.

Within the slab:
7. Up and down (depending on temperature difference between top and bottom)
8. North-south (especially when the sun is heating the floor in the winter.)
9. Through the underfloor heating pipes (when there is a big difference between north and south).

This heat will all pass according to the second law of thermodynamics, that you can hear more about here on you tube from Flanders and Swann.

According to the calculations in the Passive House software, for the heating season between October and April, 5,195 kWh of heat are going to come in through the windows on the south. January will get the most heat. This is a combination of fine weather and a low angle of the sun. On average there will be 31 kWh per day. January also has the coldest temperatures. 

I'm not sure how much of this heat is going to go straight into the slab. Some will hit walls or furniture, some will be reflected from the slab and the heat that does reach the slab may leave it quickly.

Also according to the Passive house software, most heat will be lost through the slab in February, and the figure it gives is 4.6 kWh per day. 

The slab is like a box, representing the structural foundation, filled with some gravel and topped with a screed floor.  According to the builder's invoice, there is around 40 cubic metres of concrete; 16.5 at the bottom, 4 standing up around the edges and 20 on the floor. At a density of 1600 kg per cubic metre, that's 65,000 kg. 

There's around 22 cubic metres of gravel in it, which amounts to 26 tonnes, if the density is 1200 kg per cubic metre. 

It's difficult to be sure of the specific heat capacity, but 0.8 kJ/kg seems a reasonable estimate. 1kWh is 3,600 kJ, so the whole slab holds around 73 kilowatt hours per Kelvin. In other words, if it drops one degree it will release 73 kilowatt hours.

In the very worst winter weather, the whole house will lose 55 kilowatt hours in one day, so even with no sunlight or heating, the temperature of the slab should drop by less than one degree. 

Shimo bashira

Now that we're in the middle of summer, it's a good time to publish some pictures of ice.  They're called Shimo bashira in Japanese. Apparently "needle ice" in English.

I think these are quite unusual, geographically speaking. I heard somewhere that they need volcanic soil that's wet and above freezing,  and air that is below freezing.

Obviously we haven't had any for a while.  
Charlie has a better picture. Have a look!