Things to avoid in a water storage system

There are a few things to watch out for in designing a rain water collection system. These probably include mosquitos, algae, freezing, over flow, first flush, noise, leaks and condensation.
watercache.com gives some great information on first flush devices, and there's more here.

The basic issue here is that between rainfall your roof can accumulate a lot of crap. Some literal, of the avian variety, some more in the engineering sense of the word. So when it does rain the first few millimetres will be dirty. This is likely to be a bigger problem when there are longer dry periods, and is probably affected by local pollution.

Research in Tokyo found the first 1-1.5 cm from the roof is dirty, and it seems a rule of thumb is that you should throw away the first 40 litres per 100 square metres of roof. There is no definitive amount of rain needed to clean the roof, and it has been pointed out that rain often starts as a trickle so if the first-flush strategy is to divert a fixed volume of rain at the beginning of a rainfall, then this may all be drizzle, and when the heavy rain comes and stats washing the roof it will go straight into the tank.

The important point is that keeping the water going into the tank as clean as possible will keep maintenance and cleaning easier and make the system last longer. Filters obviously come into this too, and I should probably have put that in the list.

Also obviously, there must be a strategy for the tank overflowing. Since this is likely to happen when it's raining heavily, the overflow pipe should be as big as the pipes going in, and possibly bigger since the pipes going in could be full of water, but the overflow pipe, at least at the beginning, will be full of air.

Even if the tank doesn't leak, there may be a fair bit of condensation on it in the summer, and there is likely to be a pool of water at the bottom, so getting a well drained area below the tank is a good idea.

There's a good site here from the Australian government and lots of information just in this thread on the Alternative Technology Association. They cover most points.

I'm not sure about noise but if there is a lot of water moving around, it's possible that it could be be dripping, hissing or humming. It's probably going to do most moving while it's raining so this is unlikely to be a serious problem.

Freezing is likely to be a challenge when the average temparature is below zero for at least a couple of weeks of the year, so either the system needs to be drained, insulated or set up so the water can freeze without breaking anything. 

Harvesting rainfall

There seems to be a lot to write about water, whether suspended in the air or precipitated.

I've been thinking about harvesting rainfall for a while, with the usual constraints of elegant design, low cost, and aesthetic beauty. In fact it was on the list of things to incorporate into the building of the house, but it soon went onto the back burner along with all the others. It's not a good idea to leave water on a back burner for too long as it will evaporate and you'll burn the kettle.

We need water for the garden and rather than switching on the tap and pouring rainwater down the drain, it would probably save us a fair bit of money to collect rainwater and use it for the plants. 

Just to deconstruct the problem, we'd mostly be looking at collecting water from spring, and using it mostly in the summer. If we could collect enough then, we wouldn't need to worry about the winter, and could use that time to empty the system, which may be preferable to having a collection of ice. 

Looking at the supply side, there's roughly 100 mm rainfall a month, a little bit more from May to July, and we have a total roof area of around 100 square metres. Technically speaking, the roof area is bigger than that, since it's at an angle, but that's the area as far as the rain is concerned, which I guess we have to assume is coming down vertically. 

Anyway, down the four drainpipes we'll get a total of 10 cubic metres of rain water per month, or 10,000 litres. So we'd have no trouble filling a 500 litre tank from one of the drainpipes. 

We could get a big tank somewhere, but would probably want to put it underground to save space, in which case we'd need a pump to get the water out. What would be more useful is something tall and thin that could stand against the wall, right next to the drainpipe. 

A 500 litre tank could be 80 cm in diameter and a metre tall. Or if you had two 250 litre tanks, they could each be 60 cm in diameter and 90 cm tall. At least those are the internal dimensions. You'd probably want to add a bit for the thickness of the walls. 

Since we don't really want water tanks in front of the house, and the gap between the side of the house and the fence is only a little over a metre, we wouldn't really want 80 cm tanks along there. We could make them taller though. 

A 5 metre tall tank of 25 cm diameter would hold 250 litres. We could tip it onto it's side, and run it along the whole width of the house, north to south along the west wall, so that it could fill from two of the drainpipes. Then one tank could be 8 metres long and 20 cm in diameter.

As usual, somebody has already thought of tall this. Rainwater hog make a chunky modular system, and there's Jackson in the UK.

But going back to the tank, as it gets longer it's starting to turn more into a pipe than a tank, so if it is going to be a pipe, then perhaps it could run through the garden towards the plants where it is going to be used. Then it could be 15 metres long and only 15 cm wide. Of course we'd be back to needing a pump again. 

So the best ideas are probably a couple of thin horizontal tanks, or thick horizontal pipes, running along the side of the house, or a few vertical ones, possibly cascading like pan pipes.

So it's time to start looking around for parts and construction techniques. The question is, do they have them in a nice colour? I don't want grey pipes on the side of my house. 

Water is not going to collect in the summer... or is it?

Back to the mystery of the dripping ventilation system, at first I was worried about the lack of a drainage channel for condensate from air coming into the house in the summer. We've had enough problems with the channel for water dripping from the air leaving the house in the winter. 

If it's very hot and humid outside, as the air comes into the house and through the heat exchange element, it's going to drop in temperature, and as it does so the relative humidity of the air will go up and over saturation, then water will start dripping from the air. 

For example, it could be thirty-five degrees outside, 80% humidity, and twenty-five degrees inside. As the air comes in from outside through the heat exchange elements, it's going to drop from 35 degrees to about 26 degrees. If the heat exchanger were 100% efficient it would drop to 25 degrees, but it's around 90% efficient. The dew point for air at 35 degrees, 80% humidity is 31 degrees. It's going to hit that temperature inside the heat exchanger, and water is going to start precipitating.

At first I thought this would be a problem, but I was assured that it would be fine since the water is going to head towards the chamber of the ventilation system where the temperature is the same as outside, and the extra heat will allow the air to absorb the moisture. 

But then I realised that actually it is going to be a problem, because water is going to be accumulating there, and while it might be fine in a steady state if you add some water to hot air, this is not a steady state. Humid air is constantly coming in, and water is going to be added to that chamber and will not be able to leave, so sooner or later it is going to push the humidity up and over 100% and water will start dripping. 

Hot and humid may be difficult to imagine in Europe, where the ventilation system was designed and is usually sold, but it does happen elsewhere. Japanese summers have both heat and humidity, and with discomforting frequency in some places. According to an article about Heat Index on Wikipedia, in Dhahran, Saudi Arabia on July 8, 2003 the dew point was 35°C while the temperature was 42°C.

However, just looking at the temperature and humidity here in Matsumoto in July and August 2013, the outside dew point never went above the inside temperature, and the closest it got was still three and a half degrees lower. Over those two months, the highest the dew point reached was twenty-two and a half degrees, and the lowest the temperature got inside was twenty-one degrees, ten days earlier. So it's possible to imagine that we'd get a saturation problem, but in practice when the temperature goes up the relative humidity drops and we're safe. This part of Japan is acclaimed for having dry summers, so I'm sure the story would be different if you were closer to the Pacific coast, not surrounded by mountains which do a good job precipitating humidity from the air themselves.

References

I know pictures add to the readability of a blog, but that equations reduce it. So here's a picture of an equation.
(TD is the dew point, f is the relative humidity, T is the temperature.)

Online dew point calculator

Humidity charts

Should be the consistency of thick brownie batter

So here's my recipe:

• 1 part cement,
• 2 parts sand, 
• 3 parts gravel.
• A little water

You will also need:

• A wheelbarrow to mix in
• A strong form to pour into
• A pointy stick for rodding

Mummy may not want you to do this in the kitchen.

A plasterer was there doing the wall when I was pouring the first section of concrete. It's always a mixed blessing having someone standing over your shoulder giving you advice.

I'd already got the frame so that I thought it would hold the concrete. There's a good You tube video demonstrating the result of not properly keeping the two sides together.

The plasterer wandered over and told me that it was no good, and I'd have to push soil down the outside edges. I was just about to do that.

Later he came over when I was just about to start mixing. "You mix the cement and sand first, then add the gravel later," he told me. I was going to do that, but I thanked him politely.

"You weren't going to do that, were you?" He said next. I wasn't sure what to say. It's a fine line to tread between idiot and expert.

He also told me the stones in the gravel were too big, which other people have also said, but I've mostly been ignoring their advice. I've been using what gravel has been lying around, and not overly worrying about finely grading it. Certainly when I have used smaller gravel it's been easier to mix and pour, but I hope that it won't make much difference structurally.

Over the past couple of years I've been steadily producing gravel while getting a little half-decent top-soil for the garden as a by-product. It's not so much that the soil in the garden has a lot of stones in it, more a case that the stones in the garden have a little bit of soil mixed in with them. So it's been nice to find a use for them, and I've been loathe to pay money at the DIY store or pay trucks to bring a load to the house.

I've also been following various bits of advice, for example from Oli who suggested that washing the gravel was important.
This site has some useful ones, including this:

"Your cement should be the consistency of thick brownie batter. You want to have to scoop it into your mold, not pour it."

There's another good one about putting your concrete mould on top of a washing machine after you pour the concrete. Great idea as this will get the bubbles out, and the bubbles are air, and air will make the concrete crack. The reason it will make the concrete crack is that as the concrete heats up, everything in it will heat up, and that includes any air. As concrete heats up, it will expand at about 12 parts per million per degree. This is not a lot, although it adds up to one centimetre over a 25 metre length and a temperature rise of 40 degrees, which you'd get over the year. Air expands a great deal more as it gets hot, and any bubbles are going to be little pressure bombs adding forces in all directions, some of which are going to crack. I expect to see a few cracks forming in my earlier attempts at concrete, but the later ones should be OK.

Putting the poured concrete onto a washing machine is a great way of shaking all those bubbles out, unfortunately impossible for my 1.6 metres lengths, which I hope are bonding with the rubble below them.

"The only generation participants intend is that of profit"

There's an article on Solar generation in the 9th April, 2014 Japan News, formerly known as the Daily Yomiuri, AKA the mouthpiece of the LDP.

http://the-japan-news.com/news/article/0001194163

It seems broadly based on fact but has a bit of a derisory tone to it, with comments such at "the ultimate cost of this problematic situation will be shouldered by ordinary people throughout Japan, via their electricity bills."

It also seems to skew the view of businesses engaged in building solar farms who are locked in to a favourable rate for a 20-year contract, by first naming a Chinese company that is investing heavily in Japan, then talking about other foreign investors rubbing their hands with glee at the investment opportunities in Japan. So foreign investment in Japan's solar industry is a bad thing? Seems quite clever to me! 

Meanwhile at the end of the article it alludes to companies that are fiddling the system by claiming tax rebates for green investments. This is certainly a serious issue and the kind of thing a newspaper should be writing about, on the basis that news is something that somebody doesn't want you to hear. But there should be a little more depth, some expanation of the underlying theories and discussion of the actual carbon savings from solar. And perhaps they could give actual examples of companies playing the system, as they did with those foreign companies guilty of investing in Japan.

This does very neatly lead up to the quote that I put in the title of this post, but I can't help thinking that the article was written to lead up to that, rather than in a quest for truth and understanding.

Free trees

When we built the house, the city offered us two free trees. If we'd got the application straight in, there was a chance we could have had them in March 2012, a couple of months later, but the deadline was the end of January so we had to be quick. We weren't quick, and a year later we missed the deadline, again, so it's only now that the trees have arrived. 

There were several choices, with translations below.

Sarusuberi Lagerstroemia Indica or Crepe Myrtle

Grows to 6 metres. Flowers in August.

Originally from China.

When I hear this name I always think it must be a transliteration of Salzberry, which of course does not exist. Saru means "monkey" and suberi means "slide" so it is a tree which monkeys slide down.

Hanamizuki  Benthamidia Florida, Flowering Dogwood

Grows up to 10 metres. Flowers from the end of April.

From Eastern US. Apparently the state flower of Virginia. 

Hana means "nose" and mizu means "water", so hanamizu usually refers to the liquid that runs from your nose. Not an immediately appealing name for a tree. I'm sure that's not what it means.

Shidekobushi Magnolia Stellata or Star Magnolia.

So that's what a magnolia is! I didn't know that. Heard the word loads of times and always wondered. 

Flowers late winter before the leaves come out. Grows to 5 or 6 metres in height.

This species is native to Japan.

Akamatsu Pinus Densiflora or Red Pine.  

That's a literal translation. Japanese Red Pine is a more natural translation. Or Korean Red Pine. Grows 20-35 metres.

Renge tsutsuji  Rhodedendron Molle subspecies Japonicum

I never knew "tsutsuji" was Rhodedendron! 

Grows 1-2 metres and flowers April to June. Since they are small we get two of these for one of the others.

Chishio kaede  ?

Seems to be a very local species of maple. Also known in Japanese as momiji. Also known in English as acer. Maybe acer is kaede and maple is momiji. My first guess was that etymologically speaking, the acer is Latin, and Kaede is the Japanese reading of the Chinese character. Without going into too many details, there are semantic similarities between words of Latin origin in English and words of Chinese origin in Japanese. Maple is English, while momiji seems to be Japanese, meaning "red leaves", although in some different dialect, as "red" is usually aka and "leaf" is ha. 

As usual, my first guess is largely wrong. Kaede, while written with a single Chinese character, is also Japanese, meaning "changing hand" from kaeru "change" and te "hand". I guess the leaves look like hands. Momiji is a more general word for changing colour, and applies to a whole host of things from vines to deer meat.

Apparently there are around 130 species of maple, mostly trees growing 10-45 metres high, but some shrubs. 

The Japanese maple, Acer Palmatum, grows 6-10 metres high and has 1,000 cultivars. Presumably the chishio kaede is one of these. chi means "blood" and shio means "salt" and in this case it does mean "blood and salt". When I googled it, most of the hits mentioned Matsumoto City, so it's clearly a very local species, or at least a local name.

There was a maple in the garden in the last house, and we brought a few of its baby seedlings, but none of them survived the short journey, or my clumsy gardening. 

In the end we chose one Hanamizuki and one Chishio Kaede. Now they've arrived we need to decide where to plant them quickly. 

Low voltage circuit... is it worth it?

They were selling double adapters with USB ports in the supermarket the other day, so you can plug in your phone to charge and still use the socket for something else. Great idea. It made me think about something I wanted to do in our house.

Since we have solar panels on the roof and since a lot of electronic appliances work on DC, I wanted to have low voltage outlets. One problem with this was deciding the voltage and the plugs to use. This was not clear a short couple of years ago when we were building the house, but if we were building a house now they would be USB sockets. The eponymous "universal" has become a self-fulfilling prophecy, and the U could also stand for "ubiquitous". Not only do USB cables charge phones, tablets and cameras, there is also a range of appliances that can plug into computers, such as fans and lights.

Although a USB socket would be the way to do it, I have to wonder whether it would be worth it. Intuitively it seems that sending low voltage electricity around the house would save power lost in the inverter converting DC to AC and in all those inefficient chargers converting it back again.

But, power losses over wires are proportional to the square of the current, so 5 volt USB voltage is going to lose 400 times more power over the house wiring than 100 volt AC mains.

That sounds terrible, but is it a lot? Is it more than what you'd lose in the devices?

It depends on how much power the devices draw. If it's a 500mA camera charger, ten metres of wire away from the power source, then it's only going to lose half a percent of the power. Some chargers go up to 5 amps, in which case you'd be losing 5% of the power. This is comparable to the inefficiencies of converting at each end, so it's probably not worth the extra cost of putting the wiring in.

I've been assuming the same gauge of house wiring used for AC and DC, at something like 5 milliohms per metre, although obviously not the same actual wires.

Of course if the DC wiring were thicker, the line losses would be less. Perhaps you could turn your house into some kind of a battery where you had one strip on one side of the walls and another on the other side, holding charge between them. This seems like a recipe for disaster since all you'd need would be a nail through it and it would short out. With increasing numbers of houses with solar panels, some kind of embodied electrical capacity in the building materials may be worth investigating though.