Extractor fan hot water units

The more I think about it, the more sensible seems the idea of pumping heat out of extracted air into hot water tanks. Given a reasonably well sealed thermal envelope, the places you want to extract air from a house are kitchens, bathrooms and toilets. These are also places where hot water is used. 

And if you don't have a well-sealed thermal envelope, then extracting air is not an issue.

If you extracted 50 cubic metres and dropped the temperature by 20 degrees, 1,300 kJ would be available. If you did this every hour, you'd get about one kWh every three hours, 8 kWh per day. According to Without Hot Air by David Kay, in Sustainability without the hot air, a bath takes about 5kWh and a shower 1.4 kWh. He estimates 12 kWh of hot water per day per person, although he seems to include cooking, refrigerating and freezing in his sums. 

The problems, of course, are in economies of scale and system complexity.

In the summer, rather than cooling the air going out, you would want to cool the air coming in, but you probably wouldn't want to be drawing air into the house via the kitchen, bathroom and toilet! 

Air conditioners are now pretty much standard fittings in Japanese houses and models are available that heat water as they cool the air, but these are not widespread, and in installation they work out more expensive than buying separate units for heating water and cooling air, and since the air conditioner is not on for most of the year, another means of water heating is necessary anyway.

Useful physical characteristics of air: 
Air holds 1 kJ per kg per degree change in temperature. 
In cubic metres, that's about 1.3 kJ per cubic metre kelvin. 

Bog standard

Until relatively recently a lot of the houses in this city would have had dry lavatories, not connected to the town sewage. The one in our old house seemed to have moved three times, most recently from the North East to the South East corner. Where they had running water, they were squatters and I imagine for the first half of the twentieth century, sit-down toilets were about as common as thrones, and no doubt considered with the same admiration. In fact around a hundred years ago a sit-down toilet was installed in a nearby town in anticipation of a visit by the Meiji Emperor.

From the second half of the twentieth century there has been a dramatic movement from squatters to sitters, and the toilet seat has burst into Japanese culture. Japanese toilet seat design lacks the wondrous assortment of colours, materials and patterns available in the UK market, but makes up for it with the availability of gadgets. Many houses may not have running hot water, but their toilet seats do. They are on display and available in electric shops, since toilet seats seem to be more electrical devices than plumbing. 

The first attraction for the consumer is perhaps warmth. Most houses are not centrally heated, and buildings are often assembled in a modular way, rather than rooms being fit into the thermal envelope of a house. The lavatory itself has not completely been accepted as a room in the house anyway, as evidenced by the toilet slipper. This humble piece of footwear will surprise the visitor to Japan and often embarrass him as he walks back into the rest of the house with "toilet" written on each foot. I believe the toilet slippers are there because the toilet remains conceptually "outside" in the complex world of uchi to soto (inside and outside) that informs a lot of Japanese culture but very little of its thermal efficacy. When it is freezing outside, it is freezing in many lavatories.

The result is that the seats can get pretty cold. With a squatter this is not an issue, since there is no seat and no contact, and not so much heat is lost through convection or radiation, but electrical heating elements can soften the thermal shock of conducting heat away from the fleshy behind. Since these heating elements are electrical, these devices must also be very attractive for electricity companies, as they put several hundred yen on each month's electricity bill for each house. Now they are advertising low-energy seats, but they still use substantially more than a seat with no plug on it.

The hi-tech toilet seat that we have has a low-energy function, which makes a light come on saying "low energy". It has a "super low energy" function too. This makes the light flash. 

There are also elaborate washing and bidet functions with hot and cold running water, elevating the humble toilet seat further and further above a hole in the floor. These are not considered particularly luxurious and you can find such toilets in shops and restaurants and even some public conveniences.

Of course the seat heater in our house is switched off, but if we ever need it I suspect it would do a good job heating the whole room.

Another possibly meaningless experiment in solar snow clearing

There was about a centimetre of snow outside this morning, making the ground crisp and clear beneath the blue sky. I postulated that there would be a coating on the roof too. This postulation, at least, was correct.

I also postulated that clearing this snow off the roof would increase the generation, and sure enough it did. Before I cleared the snow, it was generating 1.5 kW, which is not bad for 8 o'clock on a winter morning. I cleared the bottom  row of panels of its thin covering of snow, and it went up to 1.8 kW, an increase of 300 watts. The array is 8 x 6, so I'd cleared 1/6, which presumably had been generating 250 watts before, more than doubling when I removed the snow. Another way of looking at it is that the panels generate a little less than half as much electricity when covered with a thin layer of snow.

They will also be absorbing half as much heat, so, as before, clearing these bottom panels speeds up the clearing of the whole roof. Ten minutes later, we were generating over 5 kW.

One interesting thing was that the cosmetic panels, which run up and down each side of the roof to make up the difference between the width of the roof and the dimensions of the panels, were already completely clear of snow from the melting effect of the sun. 

I should probably warn you not to try clearing snow off your solar panels yourself. The only reason it's easy and relatively safe in our house is that we have a balcony running along the south side of the house, so I can step onto it from upstairs and easily reach the roof from there with a brush. The biggest danger is bits of snow falling down my neck.

On design

Everyone has an idea of what is good design and what is bad design. Each person's ideas are different. They are usually not articulated, and we just have strong but unclear ideas of what we like and what we don't. We pick up on one detail or another, either turning us on or off, and we are ambivalent towards wide ranges of factors. 

For many people, energy efficiency and environmental impact fall into that blind spot that doesn't make the slightest difference to their stylistic appraisal of a product. 

In building our house, inevitably my wife and I did not have the same ideas, and the architect's ideas were different to both of ours.

Here's a list of things that I think I believe are criteria for good design. As I said our ideas about design come more from the gut than the mind, and even if they are from the mind, they're from the bit that doesn't do rational thought or logical organisation. Or lists of criteria. So these are criteria that I think I should be using to decide what is good design.

Simple

Sympathetic

Worth what you pay

Uses what you've got

Uses as little as possible

Doesn't need much looking after

Disobeys rules if there is a good reason to do so

They're ordered more on aesthetics than in order of priority, but the number, seven, was not chosen for it's luck. This is an exhaustive list. That's as many things as I could think of, although there may be some criteria that I've forgotten. 

Loads of snow and no generation

For the first time we had zero electricity from our panels for a whole
day. Until then the least we'd generated in a day was 3 kWh. There's
no particular mystery as to why we had no electricity. It was snowing
all day, starting at around midnight and not finishing until after 4
pm. jma.go.jp reckons it snowed 22cm. This was a very
snowy day.

Also, the timing was not very good. It had been clear before it
started snowing, so the roof had been chilled below ambient
temperature, radiating its heat beyond the stratosphere. The first wet
snow falling onto it would have frozen on impact, making a perfect
foundation for the later snow to stick onto. So as well as opaque snow
falling while the sun was coming up, there was a layer on the roof
making the panels impenetrable to the sun's radiation.

The following day the sun was out, and I was hoping it would clear
some of the snow off the roof. When I got home most of the snow was
still there, and we'd only clocked up 3kWh for the day. A bit of the
snow had fallen off the bottom, south edge, and the first two or three
columns of panels from the west side of the roof were all clear. One
reason I can imagine for this is that the west side of the roof sticks
out from the side, so it will have been warmed by the air underneath
it. The rest of the roof, on the other hand, is a victim of the
insulated roof, and its bottom layer will have been kept nice and
cool, stopping the layer of ice from melting and helping the snow
sticking firmly to the panels.

Two days later, the sun is beating down from a beautiful blue sky, and
under normal circumstances we'd be generating seven kW. But only
around two were coming out.

Now I'm as concerned about de-glaciation as the next person but I
don't particularly want one forming over my solar panels. So I went up
to the balcony to try to help some of the snow down. I have a plastic
snow shovel, good for snow, and a metal spade, good for ice. The spade
helped some of the snow above the bottom row coming down.

When the first row of panels was clear, I went back to check and the
generation had gone up from 2.5 to 2.9. Of course this difference may
have been due to the higher angle of the sun, as this had taken about
half an hour, clearing the ice and snow off the balcony too, and may
have had nothing to do with my work. I went back up again with the
snow shovel, which has a longer handle and is less likely to smash the
panels, and this got some of the snow off the second row of panels.

I went back to check the generation and it had gone up from 2.9 to
3.2. At first sight this seemed a pretty poor return for my work.
Financially speaking I would have been better off spending the time
giving out tissues in front of the station. Also, this seemed a poor reward
for the risk of falling off the balcony and breaking my neck, or
accidentally putting the spade through the panels and causing them
permanent damage. But then, a few minutes later, there was a rumble
and a crash as half the snow slid off the roof. The generation shot up to 6
kW, and then over 7 when a second load of snow crashed down from the
middle of the roof. The panels at the bottom had heated up, in turn
heating up the air passing under the panels. After clearing the bottom
of the roof, I noticed it was over 25 degrees in the air channel. This
must have helped melt the snow further up the roof. Or perhaps this
was going to happen anyway, whether I'd been clearing snow or not. I
like to think that this bit of snow clearing was not entirely
pointless. Ironically, if we had less roof insulation, the snow would
have melted much quicker.

But this kind of snowfall is pretty rare so it's hardly
worth worrying about anyway, unless the climate shifts significantly
and snow starts getting over the protective ring of mountains and
falling more heavily and more regularly, or unless we get to a
situation where there's no grid and we have to rely on our own
electricity. There's a lot to be said for connecting to solar panels
and going off the grid if you're in a sparsely populated area or have
unreliable generation, but where we are, we stand to gain a lot more from
being connected.