Hot air about ventilation

There's something about mechanical ventilation systems that seems to go against the whole idea of an eco-house. The idea of using electricity the whole time to pump air in and out of a hermetically sealed box just seems downright un-environmental.

But of the options it's probably the best one available.

To survive comfortably and healthily, you need the house to be substantially higher or lower than outside temperature. That's assuming that human health and survival are compatible with ecology, but that's a different discussion.

So, unless you're sitting on or near a source of heat that is free, or very cheap both financially and environmentally, you're going to need insulation.

For insulation to work well, it should also be airtight. However well insulation works, you're going to lose heat if air can escape in and out.

And if you're in an airtight envelope, you need some kind of ventilation, unless you're in a few acres of thermal envelope with trees purifying the air, or you use oxygen tanks like they do in submarines.
Ventilation means air leaving as well as coming in, and the leaving air is going to contain a lot of heat. So unless you recover heat, you're going to have to produce or procure a lot more, and unless it is controlled by a fan, you are often going to be exchanging too much or too little.

Natural ventilation depends largely on external weather conditions, so if it's windy, more air will change, and if it's still, less air will change. Pressure fluctuations will also change the amount of air coming in and out, and this is likely to mean loosing too much heat or not having enough fresh air.
So this leaves two options. The simplest is probably the Passive House solution of a ventilation system with a heat exchanger. This pumps the appropriate amount of air in and out of the house and, in the winter, transfers most of the heat out of the expelled air into the incoming air to keep the house warm, and in the summer, transfers the heat from the incoming air into the expelled air to keep the house cool.

The other option, which I thought about before deciding on the Passive House approach, was to recover heat from the extract air using a heat pump, and make hot water with it. In this case, as long as the air was being extracted in suitable locations around the house, airtightness becomes less critical. In fact relatively thick, permeable walls would have a temperature gradient and may warm the air as it comes through them, although unless it was arranged carefully, most of the air would leak in through specific gaps.

This may be less efficient than the Passive House method, as the heat exchanger is passive, while the heat pump is active. It would also mean more heating in the winter, since the ventilation system is not going to contribute to the heating any more. More heating means more losses through the heating system. The heat pump would be working on air at a higher temperature—20 degrees above freezing rather than the -6 outside that it was struggling against last night—so would be more efficient.

Rather critically, there would only be a fixed amount of air leaving the house, and this may not contain enough heat to meet the needs on a cold winter day. At first sight, it would seem that there is not going to be enough heat in the expelled air, since you're going to have to heat the air coming in up to that temperature, but first of all there is solar gain, so the house is gaining heat. Secondly, if the hot water tank is over-sized, and you are storing heat a large thermal mass like our concrete slab, it would be possible to store heat for a few days. Thirdly, it's possible to get more heat out of the air, but the temperature will drop below outside temperature.

At the moment, the heat exchanger is getting heat out of night-time air well below freezing. I'm not sure how fast the fan is blowing the air over it and what kind of volumes we're talking about. The amount of heat in air depends on change in temperature but, unlike humidity, the actual temperature makes practically no difference, so if you change the temperature of some air from 30 to 29 degrees, it's going to release the same amount of heat as a similar volume dropping from minus 9 to minus 10 degrees. The difference is in the amount of energy you need to get that heat up to the temperature you want, which is going to be over 70 degrees to be sure to wipe out those legionellas.

Also, recovering heat to make hot water would need 24-hour energy use to run the heat pump since the house is being ventilated 24 hours, and so we would not be using cheap night time electricity, and the bills may be higher.

Another advantage is that you could perhaps turn the fan the other way in the summer, so you can cool the house while making hot water from incoming air.

This all makes sense in terms of design simplicity for the overall system, but in terms of economics would end up much more expensive than getting separate systems for hot water and for ventilation. Air conditioners are becoming standard in Japanese new-builds, and atmospheric heat pumps a popular way of producing hot water, but it's rare to find systems that combine these two, rather than throwing away the heat from the air conditioner.

The house sucks...

...air in when the extractor fan in the kitchen goes on. This makes the pressure drop, and there are two consequence. One is that the front door is difficult to open. It's not impossible to open, but can be quite hard work. The first time I tried to open the front door when the fan was on, I thought it was locked.

The other problem is cold air coming in through the bottom hinge of our big window. Already the floor seems to be a few degrees lower around it as cold air is leaking in, but when the extractor fan is on, you can feel a draft. I think the window could be fixed so there is no draft, but this problem perhaps seems worse because the rest of the house, including all the other windows, is so airtight, and the air has to come in somewhere.

I imagined that the ventilation system would be able to accommodate this somehow, so I've been looking at the controls again. The two pertinent settings, I think, are "Fixed pressure imbalance" and "Constant pressure off".

For the latter, the default setting is zero, "No". It can also be set to 1, which is presumably "yes". The manual explains, "This enables the determination whether the fans should run at constant flow rate at all times or whether, if a certain pressure drop has been exceeded, the fan changes to constant pressure."

I changed it from the factory default, zero, to one. Then I wasn't sure if that was correct. Presumably it was trying to balance the pressure before, but was not doing well enough. For a start the ventilation system is set to shift 160 cubic metres of air per hour, whereas the kitchen extractor fan can shift over 500. There's no way it can compete. At the medium setting, the kitchen extractor moves 380 cubic metres per hour, and at low it shifts 160. It also has a regular ventilation function which shifts 90, at a power usage of 18 watts. This may be useful in some seasons. Also, it will take a while before the "certain pressure drop", whatever that is, has been exceeded, so the ventilation system is not going to start compensating as soon as the fan goes on.

A few days later, with constant pressure off, the door is being sucked in, and is getting increasingly difficult to open. I guess what is happening is that the ventilation system is diligently pumping in and out equal quantities of air, but every time the kitchen fan goes on more is pumped out and the pressure is dropping. Previously this would have reached an equilibrium after the ventilation system realised the pressure was different. Now it does not care. 

The other setting, "Fixed pressure imbalance" was at the default of zero, so I'm thinking that this should perhaps be set to some positive number, so the pressure inside is slightly higher than the pressure outside. This would mean that any leaking air was going outwards, so drafts would stop coming in. All of the windows open outwards, so increasing internal pressure would probably strengthen the seals. The two doors open outwards, so they may become more leaky. With an over-pressure house, when the extractor fan went on, for a while it would just be bringing the internal pressure down towards the external pressure. "Fixed pressure imbalance" can be set anywhere between -100 and +100, but I wasn't sure what the unit was. Further reading suggests that it is the difference in cubic metres per hour of the fans blowing in and out.

As a  complete thermal system, less heat is probably wasted if the house is at a lower pressure to the outside, and cold air is leaking in rather than warm air leaking out. If the house is over-pressure and air is leaking out, it will be room-temperature air, whereas if it's under-pressure, the air leaving the house will have passed through the heat exchanger, and be at a lower temperature. But, this is going to make the heat exchanger less efficient. The heat exchanger can only exchange as much heat to one side as it takes from the other. If the air going in and out are at different speeds, they won't be able to exchange the same amount of heat.  My head starts hurting when I try to work this out, although that may just be because of the low pressure.

The morning after fixing these settings, the front door was still sucking in, and I went to see what the controls said. You can call up all the settings on the machine, so I saw it was expelling air from the house at 19 degrees and drawing in fresh air at minus 5. I also noticed that the flow rates were very different. It was expelling air as per the setting of 159 cubic metres per hour, but only bringing in air at 77 cubic metres per hour. 

This is a frost prevention technique. As the air leaving the house drops in temperature, it will reach saturation somewhere above freezing, then if it's cold outside it will hit the freezing point saturated, so it's going to start snowing in there, or icicles will start forming. This is a bigger problem with more efficient heat exchangers. The solution they use is to change the rates of flow going in and out, which makes the heat exchange less efficient and means that the air going out will not drop much below freezing. Now I understand how the frost prevention works, but I'm still not sure whether we're going to get back to atmospheric pressure!

Is proper tea theft?

The other day I went into the teachers room and pressed the reboil button on the pot to make a cup of proper tea. There are a couple of two-litre insulated electric kettles there, of a kind very common in Japan, but not that I've ever seen in the UK. I think this goes down to point number 6 of George Orwell's eleven essential points to making a good cup of tea.

George and I agree on ten of them. I have to confess to being a mif, no doubt having been handed down the practice of putting milk in first from some of my proletarian forebears, who had to use milk to protect their inferior quality porcelain or earthenware from cracking upon impact of hot tea. I completely agree on the absolute necessity of the water being on a rolling boil as it is poured into the teapot, or at least soon before. 

This is the part that sets thermo-economic alarm bells going, knowing that electrical heating is expensive, and that converting water to steam requires the input of a lot of latent energy. According to this blog by Ro Randall, which PJ sent me along with the George Orwell essay, 4% of UK domestic carbon emissions come from the kettle.  This is an astounding figure, so I traced Ro's link to Chris Sherwin's blog on Green Alliance, which in turn gives you a link to Chris Goodall's book How to Live a Low-Carbon Life: The Individual's Guide to Stopping Climate Change on Amazon. I presume this is a reference not an advert. I know from George Monbiot's Heat that when it's half-time on the FA cup final, and half the country get up to put the kettle on, the extra demand on the system is more than the capacity of any one conventional power station, and, since mains electricity is instantaneous and cannot be stored, the load must be made up by a hydro-electric station in Wales that spend the rest of the time skimming excess supply from the grid to pump water uphill for such emergencies.

I like Japanese tea, but there was some milk in the fridge in the teachers' room, and there is nothing like a cup of proper tea. When I say proper tea, I mean English tea of course. The kind that's grown in India. Not the kinds you can actually identify leaves in. Not the fresh green tea they have in Japan or the naturally-fermented Chinese kind, but tea fermented by yeast. It's called koucha (crimson tea) in Japanese, and getting badly made cups of proper tea in Japan is very common. The main reason, I think, is that Japanese tea brews at a lower temperature. In fact to make a good cup of Japanese tea, you should pour water from the kettle into a cup, then from the cup into the teapot, onto the leaves which it will meet at around 70 degrees C, then straight from the teapot back into the cup to drink. Also, they have the dreadful non-British habit of putting cream in, or, perhaps worse, heating up the milk before adding it, but this gets back to Orwell's essay rather than the main point. It also gets onto milk which is a whole different area of ecogeddon.

The point is that making a cup of tea uses a lot of energy, but it is part of a ritual, as Ro Randall points out. Boiling the kettle and then waiting for the tea to mash gives you a valuable break from work, and the process takes you through a routine that is comforting in its familiarity. Technology can perhaps give us some answers, but I'm not sure whether it will stop people from over-filling kettles, or drinking tea in the first place. One of the most compelling reasons to drink tea in the first place, at least from the point of survival, was that boiling the water kills the germs in it. In many ways, with our current infrastructure, cold tap water is about the best thing you can drink, except of course its absence of psycho-active drugs like caffeine.

So we should always remember what Marx said about proper tea being theft. Actually it wasn't Marx, it was Proudhon who said that all proper tea is theft. And it wasn't proper tea either.

New LED strip light

I just saw this for 2,180 yen. Is it a no-brainer to buy, or would I be another sucker?

We have four fluorescent lights in the house. Fluorescent tubes are cheaper to buy than LEDs for the moment, although they use more electricity and don't last as long. We used fluorescent tubes in three store rooms in the house. We seldom use these, perhaps once or twice a month for the ones upstairs, so the electricity usage is tiny, and the difference in lifetime is insignificant. The underfloor storage is more marginal as we use this more. 

The other fluorescent tube was ready-installed in the bathroom sink and mirror unit. This is used a few times every day and is often left on. There are four advantages to switching it to LED: Lower electricity costs, no need for replacement, instant switch on, and less heat in the summer. 

In terms of electricity usage, we're comparing 9 watts for the LED with 20 watts for a 20-watt fluorescent tube. If we use it for two hours a day, which may be a bit generous, the difference will be around 600 Watt hours per month. At an average 20 yen per kWh, that's around 12 yen per month. Those yens are certainly going to add up, but will take almost 7 years to reach 1000 yen. In a living room or kitchen, and more so in shops or offices, the payback in electricity cost is going to be much shorter. 

I always scratch my head in wonder when I go to the local electrical appliance shop and see the LEDs being promoted and on offer, but looking up at the ceiling there is row upon row of fluorescent tube. Perhaps they get a special deal from the electricity company as they do so much to boost their business!

In terms of replacement, I can pick up a regular 20 Watt tube for around 100 yen, which, relative to the price of the LED is free. The lifetime of an LED is not twenty times longer. Even if it were, the lifetime of the fluorescent tube is still going to be a few years. They are rated with a lifetime of around 9,000 hours. This is 10 times longer than incandescent bulbs, so switching from incandescent to fluorescent is a no-brainer. LEDs are about five times longer again. In the case of our house, the fluorescent tube should last over ten years. That's a theoretical figure, but one practical bit of evidence is a house my parents built twenty years ago, which used all compact fluorescents. It was eight years before they had to change a bulb.

So after a couple of replacements, LEDs are likely to be cheaper than fluorescent tubes as the economics of their inherently lower resource use take over. So in terms of replacement, getting the LED and replacing it now is going to save perhaps a couple of hundred yen in ten years time. Of course, in ten years, fluorescent tubes may have been banned and there may be no choice, since another issue is the pollution from the production and disposal of the fluorescent tube. 

If I had the choice of buying a fluorescent tube or an LED tube for this, then I would go for the LED. This is not really a direct financial cost in my pocket now, but a more general trend of picking the pocket of the planet, and increasing the problems and shortages that our children and grand children will face. Having said this, LEDs are not made out of sunshine and rainwater, and have their own range of dirtily-mined precious metals and toxic chemicals, but there are undoubtedly going to be less of them. The choice is whether to carry on using a tube I already have, or replacing it.

The instant switch on is not a major issue as everyone has lived in Japan for quite a while and is used to that flicker. The summer heat is also marginal. It's brighter in the summer so we use it less, and it is only putting out an extra 10 watts. 

So, for now there is no need to spend 2,000 yen. When the bulb goes, it's going to be sensible to replace it with an LED. Until then, or unless LED-style tubes get to be much cheaper, or threaten going off the market as everyone is installing LED light units, I can put away my wallet. 

Steamy breathing

We've now got three new humidifiers in the house, each with a performance of 300 ml/hour, so if they're all steaming away they can put out 900 ml/hour, which should be enough to keep us at 50% relative humidity when it's bone dry outside. It may now be possible to over-humidify the house, so I'm just going back to the question of how much humidity is added to the house by other means. I know we have some plants in the house, but since we're watering them every few days with a single wine bottle, and the house is losing that much water every hour, they are not making a massive contribution. 

We can easily estimate how much humidity we breathe into the air. Our lungs are moist and at body temperature, so we can assume exhaled air is saturated and around 37 degrees C. After a little googling, and avoiding the contentious red herring of how many breaths we make a minute and the futility of trying to count your own breathing rate, I found this site on normal breathing.

Apparently 6 litres per minute for a 70kg adult. That's 360 litres per hour.

From this site on humidity and anaesthesia, just in case anyone is still conscious out there, they have figures for water content in mg/l at 20-degree room temperature and 37-degree body temperature: 18 and 44 mg respectively. These figures correspond with the g/kg figures I was talking about  in my humidity blog. 

If the air going in is at 20 degrees at 50% humidity, holding 9 mg of water per litre, it looks like a standard adult will add around 35 mg/l, a total of 12 grammes of water to the air per hour. Two adults and two children will add around 40 grammes. So this is something like 5% of the humidity we're loosing on a day when it's freezing outside and 20 degrees C inside. 

Another reason for humidifying is that apparently it makes the ventilation system exchange heat more efficiently. Presumably humid air carries more heat, so the heat exchanger will work better. I'm not sure how big an effect this is going to have. Stopping to think about this for a couple of seconds, once the air has been cooled ten or fifteen degrees, it's going to be saturated anyway, so it's only going to make a difference for the warm part of the heat exchanger. Perhaps the actual condensation of the airborne moisture in the heat exchanger improves the transfer.

But then the bells of legionnaires disease start ringing again.

Cost of solar panels in the US drops by 80% in five years

Yes, that means it was five times more expensive five years ago. And apparently there is 14 times more installed solar generating power since 2007. That sounds much more impressive as 1400%. Interesting how percentages and rates seem different. 

I learnt this from Proud Green Home who were announcing a report "Tracking the Sun" from Lawrence Berkeley National Labs. Berkeley labs have apparently won 13 nobel prizes, so I'm reluctant to doubt their science, and there should be no need to worry that this wishy-washy propaganda from the solar lobby. They do have an infographic though.

Apparently, "The report also finds that the installed price of residential PV systems on new homes has generally been significantly lower than the price of similarly sized systems installed as retrofits to existing homes, that building integrated PV systems have generally been higher priced than rack-mounted systems, and that systems installed on tax-exempt customer sites have generally been priced higher than those installed at residential and for-profit commercial customer sites." So, in terms of cost, we got two out of three right.  

I still think whole-roof solar panels are a better bet, aesthetically, when the south facing roof of an average house is going to produce around 10 kW. 

But this is not America, and I'm not sure how this translates to Japan. Costs have certainly been trending downwards, but a number of factors probably mean that the reductions are more modest. For a start, Japan has been doing solar for longer, so many of the US gains are probably comparing the frontier times of solar cowboys with developed businesses. Also, Japan has a lot more protection in its markets, so to a large extent costs depend on what the local solar giants are charging. Having said this, our panels came from China, so the Japanese companies do not have a stanglehold. But we did not get Turkish hybrid PVT panels because installation grants were not available and we wouldn't have been able to sell them into the grid, because the company in Turkey had not paid the millions of yen demanded for a license to sell in Japan.

One thing that is difficult to find in the report, although is perhaps somewhere in the small print, is the percentage of total solar generation that this represents. In the absence of a number, I suspect is it a very small drop in a large ocean, which is dirty and getting gradually warmer with fossil fuel emmisions, and glowing slightly from nuclear radiation. At least the solar drop is relatively clean and growing.

Winter's coming, but not too close!

The temperatures are starting to drop below zero every night, and the other day it was trying to snow outside.  The garden is often tinted with frost as we look out over breakfast. On clear evenings the moon reflects on the snowy tops of the mountains, under a starry sky that seems to suck heat from your face as you look up.

November has come and gone and winter is definitely here, destined to get colder and colder for the next couple of months. Meanwhile, inside the house, we haven't put the heating on yet but the low temperatures are still a degree or two over 20. When the sun shines, it gets into the high 20s around midday with all that solar radiation.

On the last day of November, we put away the thin blankets we've been using since summer and got out the winter futons. In the old house, the stoves came out and the thick futons went on at the beginning of October. By now we would probably have added a blanket on top, and hot water bottles inside. We'd be facing icy corridors, and a real struggle to get out of our warm cocoons in the morning. In the new house, the kids sometimes jump out of bed before the sun even comes up. 

Using more electricity

Another record electricity bill came through. 9,000 yen. Almost 2,000 yen higher than any bill since last February. Deja vu. And we haven't put the heating on yet. Once again, this inspires me to look through the numbers and work out exactly what they are charging us for. The electricity bill doesn't say what the rate per kWh is, which I eventually found on the electricity company's website. 

Day time: 31.43 yen/kWh

At-home time: 21.23 yen/kWh

Night time: 9.33 yen/kWh

Then there is a fuel surcharge. This started the year at 1.3 yen/kWh and crept up to 1.8 in August, then dropped a little. It's going to be 1.64 in December. How careless of the electricity company to forget about the cost of fuel when deciding their tariff. I blame the airline companies for this practice, and I'm worried how far it will go. Perhaps the next time I go to the cinema they will charge extra for the film, or the next time I buy a carton of milk they will charge me extra for the milk.

Even so, this only makes at most  700 yen of the bill, and the difference between the higher rate and the lower rate is a less than 200 yen. 

Then there is a solar surcharge, which lets the electricity companies pass on the burden of paying people like me with solar panels for our electricity. This is only a tenth of a yen. 

Since August, they've added a renewable energy generation surcharge. Not sure why they need to do this as well as the solar surcharge. I thought solar was renewable, at least in the long-range future, if not aeonic future. This similarly makes a difference of tens of yen. Writing this paragraph probably cost me considerably more.

So we're no nearer explaining the 2,000 yen hike and it must be down to consumption. I can't compare with the previous year yet, but compared with the previous few months, the at-home consumption went up about 150 watts, night time 300 watts. That's a 40% an 45% increase.

Part of the reason is probably the humidifier, which I'll go into more later. We got a cheap humidifier at a second hand shop in preparation for the dry winter. If that accounts for the 150 watts at-home time, and some of the night time increase, then it was an expensive bargain!

I don't know if we're using more hot water, but heat pumps are less efficient at lower temperatures, so the drop in night time temperatures may account for the higher usage of night time electricity. 

Passive House Days

Our house was one of six houses in Japan that were listed in the worldwide Passive House Days. Low energy buildings around the world were open to visitors.

I'd been waiting for almost two years to get our house certified as a Passive House, spending many hours of discussion with the Passive House lady about the certification process. In the end, I registered it myself on the database held by the Passive House Institute in Darmstadt. Perhaps we will get certification in another year or two.

People didn't exactly beat a path to our door for the Passive House Days, although that was probably because we only opened the house on Friday, not the weekend, and we didn't do any publicity. I suspect they are a bit more organised in Europe, especially in Germany, and possibly less factional and cliquey. Having said that, cliques and factions are probably not limited to Japanese architecture, and probably apply in all areas of alternative technology and architecture in any country. Also, I was adding the building as a home owner, not an architect or a builder with an agenda of increasing my customer base.

I did ask Passive House in Germany about publicity for Passive House Days in Japan, and they told be about a person who I know indirectly, and have spoken to on the telephone who I'm going to call Mini Me. They said Mini Me knew me, so I assumed would be in touch. Mini Me had prepared a webpage announcing all the Passive House Days buildings in Japan, and I guessed that our house may be added to it, with it being on the Passive House database, and one of the houses open for Passive House Days. I think the list was not so much of Passive House buildings in Japan as Mini Me Passive House buildings in Japan. Not houses meeting an international standard, but buildings that Mini Me had been involved with the construction of, advertising Mini Me's services.

The list of "Passive Houses" in Japan on Mini Me's website page about Passive House Days had nine houses, although if you read carefully, and had some insider knowledge of the Passive House database, you could work out that only three of them were actually part of Passive House days, while they other six had "Passive House" in their names and claims that they had applied for certification, or planned to apply. Among them, this one looks similar to ours, at least in southern profile.


Actually, I didn't really expect to hear anything at all from Mini Me. I keep wondering whether I've been talking to the wrong people, or whether the world of Passive House is filled with unhelpful people. Being of a scientific disposition, I have not yet made a decision on this, and am waiting for more evidence to come in.

Not enough humidity in the winter

To try to get an idea of the size of this problem, we need to think about the amount of water that the air can hold, which very roughly, and to keep the numbers simple, is 4 grammes per kg of air at freezing. This halves each time it gets 10 degrees colder, so is 2 grammes at -10, 1 gramme at -20. It doubles each time it gets 10 degrees hotter: 8 grammes at +10, and 16 grammes at +20. There are some more precise figures at the bottom for anyone needing to do exact calculations.

The volume of the house, again in the roughest of ballparks, is 500 cubic metres. A kg of air takes up about 0.8 cubic metres, so let's over-compensate for our overestimation of the amount of water that the air can hold, and say that a cubic metre of air can hold 4 grammes of water at freezing, 8 grammes at +10 and 16 grammes at +20. In a house we're not really interested in the weight of air, and the volume is going to be pretty constant.

If we start with 50% humidity at 20 degrees inside the house, that means there are 500 * 0.5 * 16g = 4kg = 4 litres of water in the air. If we imagine it's a steady zero degrees outside, also 50% humidity, and we switch on the ventilation system to shift 120 cubic metres in and out per hour, that's going to bring in 120 * .5 * 4g = 240 grammes per hour, and expel 120 * .5 * 16g = 960 grammes. A net loss of 720 grammes.

The humidity outside is going to make a difference, but even if the air is dripping with mist and it's 100% humid, we're still going to be losing twice as much water as we gain, around half a litre per hour. If it's bone dry, we lose almost a litre. Britain tends to be dryer in the summer and wetter in the winter, while Japan is the opposite, with humid summers and dry winters. In the summer, the opposite effect happens, so if it's 35° C outside, even if there's only 50% humidity when the temperature drops to the 25° C inside temperature, it will be saturated.

To maintain the humidity in the cold winter, then, we need to be emptying something like one wine bottle of water into the air in the house every hour. Of course, there are some sources of humidity within the house, for example bathing, washing clothes and cooking. If we use a tumble dryer, or hang out washing inside, this will help keep the humidity up. As humans respire and perspire, we're giving out water too. The air we breathe out from our moist lungs is saturated and above room temperature. That's why mirrors and spectacles steam up when we breathe on them. House plants can also keep the humidity up as the water we give them evaporates. This is all good, but I'm not really sure how big the effect is.

Burning fossil fuels gives off moisture, as the hydrogen atoms within the hydrocarbons combine with oxygen in the air. Our cookers are electric, so they don't help us.

The other place humidity is going to come from is the building materials. This is not such good news, if the building is drying out.

At the moment we have one small humidifier which gurgles away noisily and empties its 2 litre tank in about six hours, which is not going to keep up with the ventilation system's dehumidifying effect.

One option when we were choosing a ventilation systems was whether they maintain humidity going in and out, or ignore humidity. We chose one that ignores humidity, probably for reasons of hygiene as the moisture that it's passing from the outgoing air to the incoming air could contain bacteria. Legionnaires' disease has been known to thrive when moisture is circulated in a ventilation system. We usually just hear about this from hotels, rather than private houses. This may be because hotels have bigger systems, or maybe because it affects more people and is bigger news. Since this disease kills one in ten healthy people it affects, the stakes are high and caution is warranted.

The US Department of Labor offers some useful tips on designing HVAC systems to avoid legionnaires' disease. Very simply, if a system avoids bodies of water, especially any between 25 and 45° C, and only allows clean air in, it should be OK. Perhaps we could have followed these to make a built-in system to regulate the humidity safely. Getting another humidifier is probably much easier and cheaper though.

More precision (than you probably need or want)

Temperature	Maximum possible water vapour grammes per kg of air
-10° C	1.79
0° C	3.84
10° C	7.76
20° C	14.95
30° C	27.69

Too much humidity in the summer

Some of the thermometers in the house have been dutifully recording humidity for over a year now, but for the first few months I was largely ignoring that, much more interested in the temperature. Humidity is, of course, important for the health of the building and of the people in it. If the humidity is too high, there will be condensation. Condensation provides an ideal habitat for molds and mildews. Dust mites also like humidity, so high humidity means more dust mites, which in turn cause more allergies and asthma for people.

If the humidity is too low, the wood in the building can dry out and shrivel up. This may not have huge structural consequences, but can lead to warped plaster board and cracks in the paint work.

The comfort level for humidity is between 30 and 50%, apparently. Or between 40 and 50% or between 35 and 45% depending on which website you're reading. Our house was usually in that range in the first winter, but over July and August was in the 50 to 70% range. 

The human body generates heat at around 100 watts, and has to lose it somehow to avoid overheating. The main method of heat loss is evaporation, and the more humidity is in the air, the less effective this is. This means that if air is very humid, it feels a few degrees hotter because we judge temperature by the amount of heat we lose. If the air is very dry, it can feel cooler, but this can also lead to dry skin and respiratory problems.

Humidity is not presented as an absolute quantity of moisture in the air, but the amount of moisture relative to the maximum the air can hold. As air gets hotter, it can hold more moisture, just as hotter tea can hold more sugar, although technically speaking the humidity is not dissolved in the air as the sugar is in the water. So as the temperature goes up, we can expect the relative humidity to go down, and vice versa, as we can see on this graph of the temperature and humidity inside and outside on a couple of days in the summer. The total amount of moisture in the air, both inside and outside, is not changing very much.

Drip drip drip

I already mentioned pools of water and houses and the question not being if it will happen, but when. It seems a bit soon to get another one, and a little inconvenient that it was on a Sunday when I had to work.

When I was making breakfast I saw the small puddle and the drips coming from the ceiling in the utility room. The utility room is directly under the bathroom, so that's where any water is going to end up. Although it doesn't have much respect for a house free of fungi, water does at least obey the laws of gravity.

The first reaction was to call the plumber. Actually the first reaction was to get a bucket for the drips and a cloth for the puddle as it still hadn't got very far. Also, since it was dripping quite slowly, I thought we should let the plumber finish his breakfast.

I finished my work early enough that the plumber was still working, searching for the source of the leak. When I spoke to him on the phone, he hadn't found it, and was about to give up and go home. He said the water was not coming from the bath or any leaks in pipes there, but from the wall between the bath and the boiler.

Thinking about the mystery on my way home, like a Poirot of plumbing, it increasingly seemed that the ventilation system was the problem. In the process of exchanging heat, the ventilation system takes a lot of water out of the air, which must find its way through a drain out of the house. This seemed the most likely source of the water.

The night before had been the first below freezing, and I wondered whether the outside drain from the ventilation system had frozen over, stopping the water from escaping. Of course the temperature had only just dipped below freezing, so it wasn't cold enough for pipes to freeze, and there had not been enough time for a dam of water to build up and get through the ceiling.

When I got home, the first thing I did was look at the drain as it leaves the house on the East side. There was no ice there. In fact the drain pipe itself was dry.

The plumber showed my the pipes above the utility room when I got into the house, and the one that water was dripping down the outside of. We went upstairs to the boiler, which was installed by different tradesmen and was not really his responsibility. There were pipes coming in from the external heat exchange units for the boiler, and the air conditioner that we don't use. There were just two pipes for each: a supply and return for the coolant. No drains.

I then suggested the room upstairs, which he had had nothing to do with, and was unaware of. Above the bath is the machine room with the solar power conditioners and the ventilation system.
And there was the smoking gun. Or at least the dripping pipe, and a pool of water underneath the ventilation system.

The pipe coming out of the ventilation system had come out of the drain in the floor. It had not been fixed in there, but was just pushed in, the ventilation "experts" no doubt hoping for the best. I go into that room about once a month, and it could well have been knocked out when I was vacuuming the floor last time I was in there a month before. Water had been slowly dripping onto the floor, gradually increasing in flow as the outside temperature dropped. As it found its way down past the bath, following the pipe, it would gradually have evaporated back into the house. For the last couple of nights, as the temperature dropped to around zero and the amount of moisture coming out of the air in the house increased accordingly, more or the moisture got to the puddle above the ceiling of the utility room, and in the morning it finally got through the drywall. In fact the dry wall was now a wet ceiling.

It's a good thing we'd just used drywall for this room rather than a plastered and painted ceiling. A screw driver is enough to take a panel off, and it can easily be replaced without needing to call in a procession of tradesmen. The drywall panel is now propped against the wall to let the ceiling dry out, and I can put it back again in a couple of days without having to call the plumber out again.

An extra 2,000 yen

Talking electricity again: this time the bill we have to pay. After the delight of earning ten thousand yen more than expected in July-August, it was a surprise to see the amount we pay go up by a couple of thousand yen in August-September.

There is only one wire going in and out of our house, and two meters outside measuring what goes in and what goes out, so if we use electricity during the day time while the panels are generating, we will use our own power and sell less. 

The electricity bill gives a breakdown by time, and we usually buy the most electricity at night time, about 50% more than we buy in "at home time"  which is in the morning, 7am to 9am, each evening, 5pm to 11pm, and all day Saturday and Sunday 7am to 11pm. We buy very little during the day as we are usually generating far more than we need. Night time is 11pm to 7am, which is 8 hours per day everyday. Considering weekends, at-home time averages a little over 10 hours per day, and day time a little under six. Although we use much more electricity at night, we pay much less for it, and at-home time is the most significant part of the bill we pay.

From the solar panel monitor we can also see how much we consume and how much we generate. At the moment this has to be copied manually, and detailed information is lost after a month, but I hope one day to be able to download the data onto a computer. That's another story.

So why did we use so much more? I don't think we did a lot of cooking or washing, which are two of the main power users. We'd need to charge a few hundred phones to make that difference, and leave the TV on all the time. If we had been using a lot more hot water, the night time usage would have gone up but not the at-home usage, as the boiler heats water at night time. 

Another thing that appears from the bill is that this was a 33 day period, containing two weekends, so there were several more hours of at-home time than usual. Perhaps this is part of the answer. Also, while it was a couple of thousand yen higher than the August bill, that was almost a thousand yen cheaper than the bills for the past three months,

I wondered whether it was the extra load on the ventilation system because we hadn't changed the filters. A closer look at the numbers shows that the main difference was in the at-home time, where we were using around 140 watts more than the last few months. In fact at night time we were using less, if anything, so it doesn't look like a constant electricity user. The ventilation system is on all the time, so we would expect to see both night time and at-home time consumption increase. Day time consumption, as far as the electricity bill is concerned, would be lost in the fluctuations of generation. 

The only thing I can think of that we had changed was switching off the monitor from the solar panels. Before, it had been set to switch on whenever we were generating, and part of the display was encouraging us to save more electricity, or praising us if we were meeting a target. I've switched it back on again, and perhaps that will encourage us to use less electricity.

This echoes something David MacKay said in his fantastic book of energy exposition and explanation,   Without Hot Air, available in full online: "Since I started paying attention to my meter readings, my total electricity consumption has halved" (p. 156)

I had only switched off the monitor to save electricity!

Passive House Days

Here is the press release from Passive House International about an event our house is involved with.

Residents and users of sustainable buildings open their doors

The Passive House Days, 9-11 November 2012

Darmstadt, October 2012 – Affordable, comfortable, environmentally friendly  - Passive House embodies the best in sustainable building. The Passive House Days, taking place internationally from 9-11 November, provides the perfect opportunity for anyone wishing to see this first-hand. For this event, hundreds will open exemplary buildings constructed to this intelligent building standard to the general public. Those with experience in such buildings can pass their expertise on to interested visitors taking advantage of the event to actually experience Passive House first-hand.

Whether residential, office building, kindergarten or swimming pool, there are very few restrictions as to the type of building and building use possible with the Passive House Standard. During the second weekend in November, buildings of almost all types will be open for viewing. With more than 40000 Passive House units in existence globally, Passive House has come a long way since the completion of the prototype more than 20 years ago. This successful concept is becoming increasingly popular.

"Excellent indoor air quality, consistently pleasant temperatures and affordable energy costs guaranteed over the long term: these are the advantages to be gained by building owners and investors," explains Dr. Wolfgang Feist, Director of the Passive House Institute and co-initiator of the Passive House Days.

Besides being cost-effective, this building standard also minimises impact on the environment. On account of the excellent level of insulation and a ventilation system with heat recovery, Passive House buildings can do without conventional heating and cooling systems. The potential savings in energy costs, in contrast with buildings requiring active conditioning, are often greater than 90 percent. "With Passive House, it is possible to manage real estate in a sustainable way and thus contribute significantly to the energy revolution, even today", states Feist.

The Passive House Days, supported by the EU Comission's Intelligent Energy Programme through the PassREg project (www.passreg.eu), are an initiative of the International Passive House Association (iPHA) and its worldwide affiliates.

Information about Passive Houses in specific regions open for viewing from 9-11 November 2012 can be found online at www.passivehouse-international.org. Should you have any questions, the International Passive House Association will be pleased to provide further assistance.

Contact:

Sarah Mekjian | Angela Werdenich

Rheinstraße 44/46

64283 Darmstadt

Germany

+49 (0) 6151 826 99 55

+49 (0) 6151 826 99 54

info@passivehouse-international.org

www.passivehouse-international.org

Endangered Buffalos - Only you can save them!

Once again I digress from the immediate topic of building houses that leave small footprints and don't cost the earth.

At work I was looking through some electronic archaeology and have been trying to resuscitate some old Buffalo Linkstation external hard drives. When I say "old" I mean more than five years old. There were three altogether, each 500 gigabytes. That was when 500 gigabytes was a lot. They were LAN drives, so could be accessed from any computer connected to the network. This is usually a sure way to let them fill up with crap and corruption.

Anyway, all three of them are broken. They flash seven times for an error message that the disk is knackered. I think that's just the way things are with disk drives. The guarantee is for a year or two, they may work for five, after ten they are rubbish. The moral of the story is probably not to buy storage devices together, otherwise they will probably all fail together. Instead you should get one at a time, over a period of time.

I asked my friend John about these, knowing him to be technologically savvy and also concerned about the fate of the planet and all it's little creations.

This was his reply:


Not sure if those external hard disks can be revived. On the continent I come from, whiteys and buffalo, they just didn't go well together. ;-)

I recommend ... kneel over them, utter the words:

"oh holy beast, you roamed this great LAN, 

you served us, you gave us sustenance, 

and your blood, and 500 gigabytes of storage, 

for the good years and the bad, 

thanks for the memory, 

the bits and bytes now forgotten, 

we see your red lights, 

they blink, faintly;

and to you our fading friends, 

this final data to each of us must come, 

goodbye and an eternal power down. 

amen"

Under Pressure

The door was sticking a little the other day. It felt a bit like it does when the extractor fan is on in the kitchen. Because the house is very airtight, when the extractor fan in the kitchen goes on, it's difficult to open the front door. As is traditional in Japan, the front door opens outwards, so the decreased pressure sucks the door in and makes it feel like the door is locked. If all the windows are closed it's almost impossible to open.

The flow of the extractor fan is several times more than the ventilation system. There was an option to get an extractor fan which also lets air in to replace the air that is being extracted, but we decided against it as it was likely to reduce the airtightness. The doors and windows are all carefully sealed, and the vapour barrier and outside layer of tyvek have been carefully installed to get an airtightness around ten times better than the average house being built in Japan. The extractor fan is not designed to these exacting standards. In fact during the airtightness test the extractor fan was taped over, which apparently is standard practice, but seemed to me more like cheating. Regardless of the test result, throughout the life of the building an extractor that sucked air in as well would have two holes in the wall rather than one, and twice as many gaps. 

Anyway, the extractor fan wasn't on, and it didn't seem quite like a pressure issue, so I thought it was another problem with our front door. We've had problems with the key on our front door, making me wonder whether it is a big crooked door to go with our big crooked window that we all got from what I worry is a big crooked German. Then I remembered the ventilation system. 

I used to clean the filter every month, at the same time as my monthly collection of the temperature data from the thermometers around the house, and my monthly inputting and uploading of power generation and consumption data from the solar panel monitor. Since they put in the new ventilation system with the bypass, I haven't actually cleaned the filter. 

When I went into the machine room, which was up in the thirties due to the power conditioners in there and the boiler below, and the insulation around the room keeping that heat from getting to the rest of the house, I saw "FIL" flashing on the ventilation unit. I had heard stories of people with ventilation systems very happy with them until they open them to clean the filters and are attacked by swarms of insects. No insects swarmed out, but there were plenty in there, mostly dead, and several fat spiders scurrying around. One moth flew out. The vacuum cleaner took care of them all.

The filter for air coming from outside had evidently become rather clogged, leading to less air being pumped into the house than being pumped out of it and, in spite of a few windows being open most of the time, lower pressure inside than outside. This was enough to suck the front door in and make it harder to open. It took a few hours for the pressure to balance, but the front door now opens normally. 

The filter for air coming out of the house, there to protect the other side of the heat exchanger, had grey dust growing from it like small drifts of snow. 

Once a month seems to be the right frequency for cleaning the filter, especially in the summer!

Getting through the paperwork to get rid of a car

Diverging once again from the topic of houses, I got a call from the garage that took away our old car. In order for them to scrap it, they need a document showing that it was my car. Documents in Japan are often very precise. You can't just show a passport or driving license to show who you are. You need to go to the city hall and get a document showing where you live. This is called a juminhyou. 

The important point with the paperwork for scrapping my car was that I needed to show that I lived in the house where the car was registered. Since I moved last year to my new house, I had to a get a juminhyou showing my previous residence, which is normally kept in the city hall's records and can easily and quickly be added to the form. 

At this point I should say how helpful and efficient Matsumoto City Hall have become over the time I've lived here. You used to have to wait for about an hour to see someone, then get looked down the nose at and met with surly grunts, then sent away to be called up again at their whim. Another hour later they would tell you the document was ready, and then you had to pay for it, which was at their convenience and would take another hour. This usually meant taking half a day off work. Heaven forbid you try to go in your lunch hour. 

Now they have become much more efficient. Often the person at the counter simply presses a button on their computer, walks a few metres across the room and collects the document from a printer, then hands it over and asks for the fee. It's like being in a shop.

Perhaps this is the benefit of new technology, but I think it's more than that.

They smile. They say thank you. They are helpful. This also adds to the impression of being in a shop, rather than being a pitiful peasant paying homage to the king of the local castle, or presuming to seek audience with him. I think the change came about when the mayor changed from an old-school bureaucrat to a doctor who had spent some time in Chernobyl helping children with thyroid cancer. 

Anyway, going back to the documents for my car, the problem was that the law changed in July so instead of being registered as foreign residents, foreign residents are now registered in the same way as Japanese citizens. Previously we didn't get juminhyou, but some other document, the name of which I could never remember, and now I no longer need to. Generally speaking this is good news as a layer of discrimination between Japanese nationals and foreigners has been removed, and a layer of fog has cleared. 

Unfortunately, I'm now only registered as having lived here since since the new system started in July, and all previous records, including my previous address, have been sent away to the Ministry of Justice in Tokyo. 

So, the very helpful staff at Matsumoto City Hall carefully talked me through the process and the five things I needed to send to the Ministry of Justice: the form I had to fill out, a 300 yen revenue stamp, a juminhyou, a photocopy of some form of ID, and a self addressed envelope. They said it should take two to three weeks, but maybe longer as it's a new system and they probably don't know what to do.

Back at the garage they seemed to be happy with this. I suppose if they'd been in a hurrry they would have contacted me a couple of months ago.

PCMs in the house and in the pocket

So the beauty of phase change materials is that they store heat at constant temperature. One of the challenges in our house, with its passive solar design and extensive south-facing windows, is the daily temperature difference in the winter, when it gets warmer from the sunshine in the day, then when the sun sets cools down from the loss of heat over the massive, thirty-degree temperature difference. Because of the insulation, it doesn't cool down so much, but insulation does not stop heat from moving—it just slows it down.

Building thermal inertia into the house is important—our slab of concrete and stuff under the floor has been doing a great job—but if the thermal mass were in phase change materials, that would be even better. When we were looking at solar thermal collectors, we looked at underground phase-change storage to transfer the heat of summer to warm the winter.

The principle is a bit like the pocket warmers we send the kids to school with in the winter. You put them in a pan of hot water until they melt. They stay molten in your pocket until you need the heat, and when you do, you click the metal strip inside. This causes the liquid to freeze, and in the process release a lot of heat. You can see the liquid freezing in the photos, taken in rapid succession.  Somewhat counterintuitively, they are giving out heat when they are freezing, and taking in heat when they melt. Because of hysteresis, the freezing point is a little bit lower than the melting point. Water will freeze when it is below freezing, and ice will melt when it is above freezing. Some hysteresis is very helpful because we want heat when it gets colder, and we want heat to be taken away when it is hotter.  As long as the liquid is not interrupted, its temperature can cool well below the freezing point, which I guess is a little over 40 degrees C. It's ready to freeze, though, just like the moisture is ready to freeze in the cold winter air. There needs to be a catalyst for the molecules to solidify around, and a clicked metal strip will act as that. Then the molecules will all freeze onto each other, like a rapidly growing crystal. A bit like snow crystals growing from the moisture in the air. As the molecules freeze, they release heat, warming up your pocket. I guess snow is releasing heat too, if the flakes are growing and taking moisture from the air. Perhaps that's why it feels warmer when it snows. I'm not sure whether snow counts as a phase change building material. You'd have to ask an Inuit.  One possibility for using PCMs in the house was inside the hot water tank. Effectively the hot water tank has a load of wax floating around in it. When heat is coming into the tank from the solar panels, the wax gradually melts, absorbing the heat but staying around its melting point. When hot water is drawn out of the tank, the water cools, forcing the wax to freeze and release heat in the process, just like the pocket warmer. The combination of hot water and PCMs floating around in it, is very effective for increasing the thermal mass of water, and avoiding some of the issues of PCMs such as super-heating and hysteresis.  I suggested that we use a hot water tank with PCMs when we were negotiating with the Solar thermal people, but they didn't seem to understand what I was talking about. I may as well have been suggesting that we build the foundation out of blancmange. Perhaps it was my language inability, or it may have been their reluctance to grasp the science. It was probably their stance as experts preventing them from listening to a technical opinion from a potential customer.

Here is a paper on a system in India using cans filled with paraffin, storing and releasing solar heat.

This is one of the tanks that I would have liked to get for our solar thermal system, which works on the same system.  I suggested this to the people who were trying to sell us the solar thermal system, but they didn't seem to understand. 

Another interesting idea with PCMs is this one from China.  Solar vacuum tubes are filled with phase change material. When the sun shines they change phase and charge up. When you run water through them, they draw off the heat and charge down. 

So the pieces are all there. They are just scattered around on the floor rather than coming together into the plans of buildings. 

Prince Pondicherry and the Phase Change Palace

Those familiar with the works of Roald Dahl, or even just the Johnny Depp film, will no doubt remember Prince Pondicherry, who had a palace in India made out of chocolate. Every part was made from chocolate. Even the taps, from which would flow hot chocolate. Mister Wonka did warn the prince that he should start eating quickly as it would likely melt in the heat of summer, which sure enough it did.
A couple of pages before this palace is mentioned, Dahl tells us that Willy Wonka could make ice cream that wouldn't melt, even in hot sunshine. So the obvious question is, why not make a tropical palace out of chocolate that didn't melt?
The only sensible answer is that he was using the phase change of chocolate to maintain room temperature in the palace. While the phase changes of water, at zero degrees to ice and 100 degrees to steam, are too high and too low for a comfortable ambient climate or efficient heat production, chocolate changes its phase at a much more useful temperature.
The melting point of the best chocolate is around 34 degrees Celsius. This is an ideal temperature from a culinary perspective as it is low enough to melt in your mouth and high enough not to melt in your pocket. Unlike water, which is predominantly H2O molecules, chocolate contains a variety of substances in various forms of crystalinity, so the melting point will vary. The art of great chocolate making is to get the right kind of crystals of fat in there, but hearing about this suddenly makes its taste much less appealing.
There's also likely to be a lot of hysteresis. This means that it may melt at 34 degrees, but you have to cool it down below 28 degrees to get it to solidify again. I usually put it in the freezer.
So if Mr Wonka, who elsewhere exhibits a  great mastery of the physical sciences, was indeed trying to make a phase change building, it would work something like this.
The temperature inside would stay below the melting point of the chocolate. On a hot day the chocolate would start melting. As it melted, it would absorb heat from its surroundings, therefore having a cooling effect. Later, the melted chocolate would solidify, emitting heat into the inevitable coolness of the night.
If he was trying to make a phase change palace, though, he didn't do a very  good job, and shouldn't really have been advising Prince Pondicherry to eat this thermodynamic wonder.
In the winter, chocolate could work in the opposite way, absorbing heat from the sun in the day time, and melting in the process. As it cooled later inside the building, it would solidify and release heat as it changed its phase.  The best thing to do with this chocolate would be to line a south-facing internal wall with it, so that it would catch the sun coming through south-facing windows. Painting a wall with chocolate is probably not to be recommended as it would run down the wall when it melted, and all end up at the bottom. Fixing chocolate in sealed bars, preferably in heat-absorbant black, would be much more effective.
And if it got really cold, you could always eat the chocolate.

Phase change materials - an introduction

Under the category of things we thought about doing, didn't, and now wish that we had, comes PCMs, or phase change materials. You probably think you don't know what they are, but I'm sure you have used them many times. The planet has also been using them to stabilise its climate, although perhaps it won't be for much longer. In fact that I'm just talking about one phase change material: ice.

We should probably also call it water, as the point of phase change materials is that they change from one phase to another, for example ice turning to water, steam condensing to water, or dry ice subliming into gaseous carbon dioxide. What is happening in all these cases is a transaction of heat at well above the regular exchange rate per degree change in temperature. 

Some languages don't have separate words for the different phases of water. For example, Malay apparently has the word air for water, confusingly enough, and air batu, roughly "solid water" for ice. Strong evidence for the Sapir Whorf theory that language depends on culture. Japanese, on the other hand, has four words for di-hydrogen oxide. Kohri is ice, mizu is cold water, (o)yu is hot water and jouki is steam. Actually you could argue that jouki is not really one word, but two Chinese characters, hence as foreign a concept as when Malay speakers say aisu. But I digress.

The beauty of phase change materials is that they save up heat, either in credit or in debt, and release it at a constant temperature. So when you put some ice cubes in a gin and tonic, you're ensuring that the temperature of the beverage, as it reaches your lips, will be the same from the moment it reaches the table, until the last drop pours out of the rattling ice. That is as long as you finish drinking it before the ice melts. My grandmother was never a big fan of ice as it diluted the alcohol. I seem to be digressing again. 

What is happening in your gin and tonic, or even lemonade, is that the ice, being ice, stays at around zero degrees centigrade. If you work in the Farenheit system, then all you need to know is that zero corresponds to the freezing point of water and 100 to the boiling point. The glass and liquid in it set up some kind of equilibrium so that the temperature of the water is between room temperature and ice temperature. Heat, dutifully obeying the second law of thermodynamics, flows into the liquid from outside, leaving drops of sweat from condensed airborne humidity in its wake. It then flows from the water into the ice. Rather than changing the temperature of the ice, part of it changes from ice into water. 

On a molecular level, this means that rather than sitting in neat rows, either in starry crystals or glass-like blocks, those di-hydrogen oxides are all getting up and boogying around. Getting them all up takes a lot of energy. When they all sit down in their neat rows again, that energy is released. A similar level of energy is needed to change them from the pedestrian liquid state, where the molecules are at least in close proximity with each other, to the jet-set gaseous state where they fly around at great distances to each other. 

The United States have been instrumental in the propagation of ice around the planet. In the nineteenth century there was a huge trade harvesting ice from New England lakes and transporting it as far afield as India and Australia. This trade was finished off by the 1920s at the hand of plant ice, based on technology that went in to the refrigerator that became a part of every kitchen from the 1930s in the US, and in later decades around the world. 

As a phase change material, ice works by first having the heat taken out of water, either in a cold winter or with the refrigerating cycle of a heat pump. Later it absorbs heat from its environment, bringing down the temperature accordingly. Steam can also work in the opposite way, as used in heating systems of large buildings, taking in heat when the water evaporates in the boiler, and releasing heat when it condenses in radiators around the building. 

As a phase change material for buildings, water is rather limited as the freezing point, zero degrees C, is much too cold for the building, and the boiling point, 100 degrees C, is much too hot. There are other materials with melting points around ambient temperature, for example chocolate. More about that later. 

Outdoor goods - don't use them outdoors

It's been windy the last few days. Not a typhoon or anything, but a strong wind blowing right through our garden.

The house doesn't seem to mind this, but the tarps we've been using to provide shade have been flapping like they're literally three sheets to the wind. That expressions refers to the setting of sails--a sheet, as is not at all obvious to the non-nautical, is a piece of rope tied to the loose end of a sail. This can change the sail from being close-hauled, almost in line with the ship when you're sailing upwind, or let right out for a broad reach or a dead run.

The house doesn't look drunk, but the strong wind has been pulling pegs out and letting the tarps wave around.

The wind was blowing so strongly the other evening that I undid the guy ropes from the pegs, went up to the balcony and furled the tarp, rolling it up and tying it along the top of the railing so that it would not flap any more. I started thinking about getting a more ship-shape arrangement out there, so the tarps can more easily be drawn in and out to suit the sunshine and wind.

The sound of wind is not a bad sound, but there is a lot of energy in the wind, and hopefully the balcony which the tarps are tied to will not sail away from the house. At night we don't need the tarp, but if it's a sunny and windy day in September, we want to keep the sun out. Perhaps I can rig up some halyards for next year, so that the tarps can go up and down with the weather, and possibly be set differently for the sun. Low and in the East for breakfast; high and to the south for lunch; letting the stars in at night.

One issue is that the guy ropes have been breaking a lot over the past few days. This is probably a combination of the heavy wind and fatigue over a month of holding the tarp through all weather. The points of failure were not at places with friction, at the knots, in the eye connecting to the tarp or at the peg, but in the middle of the rope.

I wonder also whether UV radiation has been breaking down the material of the rope. I know that UV can be very damaging. This would be ironic as the tarp is called a "UV Hexagon Tarp" and claims to "protect UV". No doubt "UV" is more of an advertising slogan than an optical description. And anyway the tarp claimes to protect anyone sitting under it from UV; it does not claim that the ropes holding it up are UV resistant. Or perhaps "protect UV" is literal, and it is doing as little as it can to impede the ultraviolet raise on their long journey from the sun to our subcuticular carcinomas.

Anyway, I'd hoped all the parts of these outdoor goods would last more than a month outside, rather than being good for a couple of weekends and being stored away in a cupboard for years in between.

The first tarp we used tore in two on a very windy day at the beginning of August. We'd had it for years and it didn't owe us much. It was a good excuse to buy a newer tarp to add to our camping inventory. After some sewing we can now use the original as two different tarps, which I suspect will be less susceptible to wind than one large piece of cloth.

A certified ventilation system

A side benefit of the reinstalled ventilation system is that we now have a unit that has been certified by the Passive House institute. They replaced the Stiebel Eltron LZW 170 with an LZW 270 Plus. The "plus" means that it has a bypass function, which is the part we wanted to help get rid of that summer heat. The 270 is more powerful than the 170 so it can ventilate more volume, although we already had enough with the smaller system.  The other features are the same and it's difficult to beleive the efficiency has changed in any way.

As far as data entry is concerned, though, if you're entering manufacturer data for parts that have not been certified by PHI, you need to take off something like 12%. This is probably entirely justified, but in our case we can now increase the heat recovery efficiency from 78% to 83%. This doesn't sound a lot but brings our score down from 14.6 to 13.8 kWh/m₂a.

Further investigation online shows that Stiebel give a heat recovery up to 90%, and they say that the Passiv Haus Institute has a figure of 86%. The database on the PHI website passiv.de, on the other hand, gives a figure of 83%. There is a mistake somewhere!

I suppose a lesson to learn, if the calculations are to be believed, is that ventilation and air tightness make a big difference, and having a well insulated house is not enough.

Talking about my generation

August was definitely a good month. About 150 kWh more than May, which had been the best month before then. You can see how well we're doing here, with the actual monthly generation in green and the simulated monthly below it, for the whole year. As I write the September generation is just based on the first week, so it may get better or worse. The simulation is quite a lot worse than August, although August was not the best month in the simulation.


There is quite a variation between the simulation and the actual results, and we are doing much better in the summer, and were doing a little worse in the winter, so the overall the simulation seems pessimistic. Of course this year's weather may have been exceptional, and the differences could be accounted for by that. We'll need a few years' data before we can really know how accurate the simulation was.

To get an idea of why August was so good, you can see from this chart that there were just very few days with low generation. Also there was relatively little limitation of the power output, in fact the least since records began. Less than two hours over the whole month, compared with almost twenty hours in May.

Guaranteed power for quarter of a century

On the same day that the 54,000 yen electricity bill came, we got the warranties from the installers of our solar panels. The power conditioners are guaranteed for ten years, and the panels are guaranteed to produce electricity for 25 years. If the house falls down, and all the bits in it stop working, at least we will still have a small power plant, which should be worth something unless somebody starts making free electricity. The guarantee is for between 5.5 kW and 10 kW, which means at least 60% of the rated value.

Of course a guarantee is only valid as long as the company giving the guarantee is still there. That company is Suntech, which according to Wikipedia is the largest manufacturer of solar panels in the world, with an annual production capacity of 1.8 giga watts, and over 13 million panels sold in 80 different countries. 

For a while we were looking at solar thermal, or to put it in earthy Germanic terms rather than fancy Latin, hot water from the sun. We would have been lucky to get a five year guarantee on a system, and probably would have had engineers coming round every month or two to fix it, or at least pretend to fix it while each time making it worse.

With no moving parts, photovoltaics are much more reliable, and these will probably be generating electricity long after I stop generating carbon dioxide. 

Why is the electricity company paying us so much?

The arrival of bills is not usually the high point of joy, but in our house, each time an electric bill comes, there's a burst of excitement.

The electricity bill for August is 54,240 yen. That's what they are going to pay us. The only thing I wonder is, why so much?

This compares with 44,976 for July--about 10,000 yen more. We sold 1130 kWh, which is a record. July was 937, which is typical, so we sold about 200 kWh more than usual. Either we must have made a lot more, or used a lot less in the daytime. We used less than usual, or at least paid for less. We are being billed for just 5,205 yen compared to 5,935 yen for July, which gives us an idea of how much we used in the evening and at night. This was for the period 24th July to 23rd August, which corresponds pretty much exactly to the school holidays, so in fact I'd expect three people to use more electricity in the day time than just one.

As the meter is read by a human being, with daily generation up to 60 kWh, it could make a difference of a couple of thousand yen on the monthly bill whether the person comes to read in the morning or the evening. 

I'll have to wait until the end of the month and my ritual of copying numbers from one computer screen to another before finding out for sure, but I think there was a lot of generation in this period. Judging by the graph on the display panel, there was at least 25 kWh everyday. Usually there are a few days every month when it's cloudy or rainy all day and there is a single figure generation. 

Not complaining of course!

Recalculating the windows

Solar gain is a massive part of the passive house philosophy. It is probably no coincidence that the word "passive" is also used in "passive solar" design, whereby the natural radiation of the sun is used to the maximum benefit. Positioning, size and G-value of the windows makes a huge difference to the amount of direct solar gain, as do any obstacles outside.

So it was with some trepidation that I started adjusting the figures in the PHPP file to take account of the houses to the South and South West, and have a more careful look at the numbers in there.
For each window, you start with the dimensions, U Value of frame, U Value of glass, Psi value of frame and Psi value of installation. The U value is a simple, one-dimensional heat loss per unit area per degree of temperature difference between inside and outside. The Psi value is the thermal bridge effect, which is the extra heat loss per unit length along a boundary between two insulators, per degree of temperature difference. For example a square window, one metre on each side, has an area of 1, but there are 4 metres of boundary between the window and frame, and 4 metres of boundary between the window frame and the wall into which it is installed, so there are 8 metres of thermal bridge to take into account.

Those figures are enough to calculate the heat lost through the windows, over the year. As a rough guide, there are 70,000 heating degrees hours in the Matsumoto year, compared with 80,000 in central Europe. That's the total of the temperature differences for each hour over the year, so if it's freezing outside and 20 degrees inside for an hour, that's 20 heating degrees. Just as you can multiply a U value by the temperature difference to work out the instantaneous heat flow, you can multiply the U value by the heating degree hours to get the number of kWh of energy you need to replace the heat.

That's the heat being lost through the window. Window U values are based on the area of the frame and take into account the U value of the glass and the U value of the frame. Solar gain of course will only come through the glass, and not the frame. The heat being gained also depends upon the angle and orientation to the sun, depth of overhang on the top window sill, depth of sides to the left and right, and any obstacles in front. A south-facing window will get the most solar gain, and if the window is tilted from the vertical it will also increase the gain. All obstacles and overhangs will reduce the heat gained.

As far as the PHPP software is concerned, as well as the straightforward orientation and angle, which for most of our windows is due south and vertical, we need to put in the depth and distance of window reveal, depth and distance of overhang, and height and distance of shading object.

We started off with the house to the south as a shading object for all windows, 16 metres away and 5 metres above the ground floor windows, 3 metres above the upstairs windows. This makes a surprising difference even though the sun is never behind them. For the window reveal, which is to the left and right of the window, we put in a depth of 100 mm, and distance of 100 mm. The upstairs overhang we put in as 100 mm deep and 150 mm high, while the downstairs overhang is set as the balcony which is 600 mm deep and 600 mm high.

This gives us a total Passive house score of 12.3 kWh per square metre of house area per year, with a total solar gain of 5,392 kWh per year.

Actually the ground floor window panes are all at a depth of 140 mm. This change of 4 cm on the south facing windows wipes 0.3 off our score and loses us a total of 76 kWh per year. The middle concertina window panes are 120 mm from each side. The window to the West, a double tilt turn, dreh-kipp as they say in German, has panes 100 mm from each side.

Actually, they are not all at a depth of 140 mm. The west side of the kitchen window is fixed into the frame rather than into a leaf inside the frame, and is only 125 mm deep and 65 mm from the side.
It's actually not so simple, as there are wooden pillars supporting the balcony, right next to the reveal, so should we be looking at the reveal for the right side of the middle concertina as 140 deep, 120 mm away, or 300 mm deep, 150 mm away? Or in fact 800 mm deep as there is another pillar further out on the terrace supporting the balcony. I think putting in these details is going to give us a mean score as there is only one figure for reveal, which it presumably puts on both sides of the window pane. For the middle concertina pane, we can put the reveal a metre away, which should help our case.

For the furthest west window, the house next door should probably be treated as the reveal, which would be 10 m deep and 3.4 m away, were it a part of our house, which it most definitely is not, event though it is so close that it seems as if it wants to be. There are also a couple of balcony pillars there, 180 mm away and I suppose 800 mm deep, or 300 mm deep depending on which pillar you take. Perhaps these should be treated as the reveal. There is daylight between them, so it seems mean to treat it as 800 mm deep, but probably little radiation gets through that as there is a solid house beyond. The next house gives a figure 50 kWh per annum worse than the two pillars, which is another 80 kWh/a worse than one pillar.

I wonder whether it takes reflected radiation from the reveals into account. Also there's probably a considerable amount of heat reflected off the stone tiles on the terrace and into the house. It would be great to measure all of this with a solar radiation meter. I don't happen to have one though!
And the balcony is actually 800 mm above and 800 mm away from the top of the window panes, rather than 600 mm. This is the same angle, but the further away overhang leads to less solar gain, presumably because less indirect radiation from the sky above gets through. This is a difference of 47 kWh/a.

More accurately, the upstairs window reveal is 170 deep and 100 distant, taking into account the rails for the shutters, and the overhang is either 125 deep and 75 high, or 350 deep and 350 high depending on whether you take the plaster or the box for the shutters as the cutting edge of the light. That makes a difference of 97 kWh/a.

So having started with a total score of 12.3 kWh per square metre of house area per year, putting all these adjustments in, in the worst case of each scenario, we lose 541 kWh per annum solar gain, and get a score of 14.6, still within the Passive House limit of 15 kWh/m²a. There are plenty of places we can argue the toss, if necessary, especially with our double-leafed windows where the strict conditions have been applied to both sides of the window.