What comes down sometimes doesn't go up again.

From the beginning of February, when it started getting to around minus ten each night, we were putting down the shutters on the upstairs windows each night. They may have some insulation effect, but their cutting down on heat radiating from the house is probably more significant.

Joe, who is eight, correctly surmised that the best time in the morning to put the shutters up is when the light comes on to show that the solar panels are producing electricity, and the shutters should come down in the evening when the light goes out. According to the passive house software, the heat coming in through the south-facing windows is 790 kWh in February, which is over 20 kWh per day. This goes up to 927 kWh in January, over 30 kWh per day. It's 843 in December and 743 in March. Overall, the south facing windows bring in over three times more heat than they lose, so even if it's very cold outside, any solar radiation coming in is going to make up for the thermal losses, and certainly be more of a benefit than any increased insulation from the shutters.

Anyway, I got back one evening to find that one of the shutters had come down a few centimetres. I assumed this had been partially put down, so I switched it to come down properly. It didn't, but there were whirring noises. I switched it to go up. More whirring noises. 

Now this shutter happens to be outside the window opening onto the balcony. Lucky, I thought, as I can just open the window and try to help it up or down. Actually I got Joe to help with the controls, while I stepped out onto the balcony to try pushing the shutter up while he was switching the shutter to close. I thought perhaps it was a little disengaged.

As it turns out, it was more than a little disengaged, and after some more whirring and a little clunking, the whole of the shutter came crashing down to the bottom, leaving me standing on the balcony in bare feet on a very cold afternoon. It was impossible to get the shutter up again, as it was not coiling properly inside its case. The shutter case uses some kind of six-pointed star screwdriver, so I couldn't open that to get the shutter up. I was stuck.

I considered climbing down from the balcony, but decided it was best to appeal to my better half's better nature and get her to bring a ladder out. The sharp tongue of a wife who is both angry and right, while certain to cause some injury, would be much less painful than potential injuries from sliding and landing on the hard tiles below. 

Before fixing this, the suppliers, who also provided our windows, needed to get parts for the disengaged shutters, and there was a chance that they would not be able to fix it until we got back from our travels. They assumed that we would be leaving the shutters down while we were away, but I was looking at the thermal gain from these windows. Of a total almost 16 square metres of glazing on the south side of the house, the shutter in question was covering a double window, with 1.5 square metres of glazing. That's 10%, so a couple of kWh a day. The equivalent of a heater on for an hour. It can still be quite chilly at the end of March, so we didn't want to be turning heat away while we were away.

As it happened, the parts arrived and it was fixed in time. What had happened, apparently, was that the for the motor to stop when the shutter was going up had been set above the actual level of the shutter when fully wound up. The switch goes three ways: up, off and down. If the shutter is down, when the switch is switched to up, it will go up until you switch it to off again, or if you leave it it will go all the way to the top, then it should switch off inside, even if the switch is still set to up. So the first few times we used it, we had obviously been very careful and attentive, marvelling at the wonder of this technology, and staying to switch it off as soon it reached the top. After a week or so, we switched it to go up and left the switch, confident that it would automatically stop. However, it wasn't switching off and the motor was still working away on the shutters, presently rending them from the axle. 

All is now well, and I'm beginning to wonder what temperature it is actually worth putting the shutters down at night, as the effects on radiation must be minimal.

Luke warm water

It was a beautiful sunny Sunday in February, so we went skiing. There's nothing nicer, after a hard day of skiing, than a nice hot bath. Usually I'd go to an onsen, a natural hot spring, and soak in abundant mineral rich waters, not worrying that they are probably heated with dirty oil because they lose so much heat to the outside air.

There was school the next day, and anyway, we have this fantastic new bath which can supply hot water, and it's only a short crawl to bed from there, rather than a drive. 

I just went with the kids, so I called as we were setting off asking the wife to put the bath on. We didn't get on that you could telephone.

When we got home, looking forward to a piping hot bath to sooth are muscles, the bath was not really all that hot. The first sign of something wrong was that the control panel didn't have the red light on to show that it was keeping the bath water warm. It's set to keep it warm for a couple of hours.

The previous day, we'd used too much hot water in the underfloor heating in the morning, and so there was no hot water in the evening and we didn't run the bath. That meant that it was starting from cold. 

I pressed the button again, and it announced that it was going to start running the bath, and the red light came on, and the little bath icon with lines floating up. A few minutes later it just stopped. No warning, no error message and no bleeping. It just gave up, put the lights out and the icon vanished. There were three bars when we'd got home, and these were starting to go down to two and then to one. 

When I checked the bath, it was not getting much hotter, but did seem to be getting fuller. 

The problem is the strategy for filling a bath. 

If the bath is empty, it's easy. It just needs to fill the bath with how ever many litres we've told it, at whatever temperature it's set for. Simple calculation based on the temperature of water coming out of the tank. 

Usually the bath is not empty though. As we get clean outside the tub, we don't need to change the bath water every day. I guess it measures the amount of water in the tub by the water pressure at the fancy jet thingy where it sends water in and out. If there is less than the required amount of water in the bath, it can get the water to the right temperature by adding hot water. Again this is a fairly simple calculation.  100 litres at 30 degress needs 50 litres at 60 degrees to make 150 litres at 40 degrees.

If the water in the tank is not hot enough to do this, then it can go to plan B, which is to circulate the water from the bath through the boiler, and re-heat the water in the bath. This is known as Oidaki.

The problem with this strategy is if the water in the boiler isn't hot enough, it will just take away heat from the boiler, and still leave the bath luke warm. Remember the second law of thermo dynamics. 

So I suspect what's happening is that the Eco cute tries to add hot water to the bath, realises that it can't get it hot enough with hot water, then tries Oidaki, and then gives up.

We just have to make sure that there is enough hot water, and in this case there wasn't for about four reasons.

First of all, the night before had been very cold, minus 11 in the morning, and not ideal conditions for an atmospheric heat pump. Exactly how unideal is an ongoing concern.

Second, we'd left the underfloor heating on for rather too long in the morning and run off a lot of the heat from the boiler. This left it in a situation of abundant water at low temperature.

Third, we had a full bath of cold water that had not been heated the previous day. Part of the reason why it  was full is that the washing machine is not working properly. It's supposed to be able to reuse the bath water in part of its cycle, but doesn't seem to be working. The bath water, controlled by a special tap and with a separate hose into the washing machine, keeps running into the washing machine when the tap is on, while the washing machine should actually be switching it on or off itself. That's another story though.

Fourth, and this may have been fairly critical, the temperature of the boiler was set to low. I'm not sure why, but I remember showing the wife how the temperature setting worked a couple of days ago, and maybe I didn't set it back again. If the boiler had been set to a higher temperature, in fact, everything would have probably been OK. It is now.

at least influencing 

Difficult decisions... Counting the number of angels that can dance on a pinhead

February 19th. One of those really cold mornings after a bitter snowy day that was followed by a starry night, and weather that seems to have come straight from the Arctic. Minus eleven when I got up and looked at the data logger in my room that's connected to the outside thermometer. It was under 14 on the thermometer on the window sill, strategically placed in the coldest spot in the house.
The panels were already making 0.7 kW just after 7 am, highly efficient supercooled by the ambient temperature and then some by radiating beyond the stratosphere with nothing coming back.
And I wanted to make a cup of tea.
Usually I turn the IH stove onto a high middle setting to boil the kettle. There are ten bars, and I'll put it to number seven. I think gas stoves are most efficient at a middle setting. They may boil the water quicker if you turn it right up, but they will use more energy to do so. I assume the same for IH heaters, although they may be equally efficient at any level.
Anyway, I was thinking about all those lovely kilowatt hours, and wanting to sell as many of them as possible. Putting the kettle on at any level was going to exceed the 0.7 kW we were generating, and mean buying electricity. Given this, the logical thing to do was to turn the IH stove up as high as possible, and while it was on, put the shutters up, which use a couple of hundred Watts, to keep the time that we were buying electricity short, and we were back to selling electricity as quickly as possible.
This must have saved at least some fraction of a yen.
These are the kinds of calculations that we are forced into by the economics of solar power. Surely I have better things to do. The best thing, of course, would have been to drink water rather than tea.
I did notice, after switching the kettle off and setting off proudly with my tea, that we were still using 400 Watts, which seems strange when everyone's still asleep and nothing's on. I realised it was the pump for the underfloor heating, which I'd set to come on from 7 to 7:30 as well as an hour before 6. This was because I'd left it on too long the previous morning and it had used up all the hot water, so it didn't come on in the evening, as I'm mean and didn't let it start working till cheap electricity rates kicked in at 11pm.
With the sun already beating down, we aren't going to need heating until tonight, so it's a good thing I noticed it. That will actually have saved a few yen.

Not so Eco and not so cute

The electricity bill for the month of March just came through, and the good news is that we only used 147 kWh. The bad news is that we were away for all of the covered period--23rd February to 25th March--so most of this energy was being used while we were out of the house. Maybe not a big deal in the grand scheme of things. This only added about 1800 yen to our electricity bill, which is little compared to the repayments on the loan, or on the amount they are paying us for our solar electricity generation, which was 45,000 yen for the same period. 

It seems a lot compared to last month when we were in and used 573 kWh. 25% in fact. 29 kWh were used in at-home time, and 117 night time. Only one kWh was used during day time, but this is not surprising as the panels will have been producing electricity for most of this time.

At-home time is 7 am to 9 am and 5 pm to 11 pm; 8 hours per day. For the 32 days, that's a power consumption of around 110 Watts. Night time is 11 pm to 7 am, also 8 hours, and you'd expect the same consumption, but it averaged 460 Watts. The only difference is the eco cute, programmed to come on at night.  Taking 110 Watts as the background consumption of the house, mainly the ventilation system and the fridge, which we left running, but also the circuitry and leds on display panels, and maybe some phantom consumption on the light bulb sensors, that means the eco cute used 88 kWh over the month. That's almost 3kWh per day, and we didn't use any hot water, and the underfloor heating was switched off. The energy it was using was just making up for the heat it was leaking into the house.

I'd set the tank to low temperature while we were away, but when we came back the display said it had one bath and 50 minutes of shower. I suppose this is less than one bath and 90 minutes of shower that it usually has, but this still seems to be a lot of heat. The exact meanings of the high, medium and low temperature settings are far from clear or explicit, and it seems like it's impossible to set them to actual temperatures, for example having the water in the tank at 50 degrees. Also, having thought that I could vary the amount of hot water in the boiler, it suddenly clicked that the setting of full tank, 50 litres or 100 litres is just for the amount of hot water it will add to the tank when you press the re-heat button. It doesn't make any difference to the amount of heat in there.

Without knowing the COP of the heat pump, it's difficult to know exactly how much heat this represents. I can maybe get some ideas by looking back over the temperature each night, and the electricity consumption data, and work out the relationship between the two, assuming that it's losing the same amount of heat each day from the constant set temperature of the tank (whatever that is) to the more or less constant temperature in the boiler room. Heat loss is proportional to temperature difference.

In a way this is the worst possible conditions for heat loss, as the tank was left full. But it was set to the lowest setting, and the boiler is inside. Imagine the usual situation where the boiler is outside, and it is left set to high. 

And they all lived happily ever after...

Actually the lack of posts for the last few weeks has been because we've been away in the UK, concentrating on family and friends rather than work and house building. There are still several issues unresolved, ongoing and upcoming. Regular blogging service will resume shortly.

The big window is still not right, and I believe Pazen made a serious design flaw with the hinge.

We still haven't got any blinds or curtains in, or put pictures up on the walls.

Electrical generation is hopefully going to keep coming and it would be really nice if the data could be accessed electronically rather than having to write everything down from the display.

It's going to take a couple of years to work out exactly how much we will need the heating in winter.

The thermal performance of the house will take at least two winters and two summers to get a proper grasp of.

And I need to sort out the photos. 

The good news is that we got back to the house and it was still fairly warm after a month of winter with no heating on. The middle of the slab had cooled to 17 degrees. It was freezing outside.