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.