Friday, 29 June 2012

Awnings and shade

At some point, probably in a couple of weeks, we're going to want some shade over the terrace. Otherwise we may get hot feet. There is 20 cm of concrete under the tiles, which should sink some of the heat, but in direct sunlight, it's going to get hot. The range of options, and corresponding range of costs is quite wide. 

The ideal solution would be a shop-style awning, that can be drawn in or out as we like it. My feeling is that we should put up some semi permanent shade over the terrace at the beginning of the summer, and take it down at the end of summer. My wife prefers something much more variable, which may be a cultural difference. The same thing seems to happen with heat in Japan and the UK. In the latter, houses usually have central heating, so you set the temperature you want, then it is warm enough. Japanese houses typically have fan heaters and air conditioners, so if the temperature is not how you want it, you can press a button.

I'm not sure whether it's enough to have a button like the one next to the traffic lights that you press, and it says "please wait". These are often not connected to the traffic lights, but people feel much better if they have something to press. 

Or there's the joke about the Englishman, Scotsman and Irishman stuck in the desert. I must apologies for the mild racial stereotyping in this joke. If anyone takes offence, they should just remember that the Irishman was from Kerry.  

Anyway, they walk through the heat for a while, and meet a genie, who gives them a wish each. The Englishman asks for gallons of water. The genie grants the wish, the Englishman drinks and is cool and happy. The Scotsman asks for gallons of whisky. The genie grants the wish, the Scotsman drinks and is happy. Then the Irishman asks for a car door. The Englishman, Scotsman and genie look at him, and ask what on earth he wants a car door for. "Well," he replies, "If I get too got, I can wind down the window."

In our situation, of course, when it's really hot outside we will want to shut the windows. We could still do with something outside to stop the heat getting in by radiation through the glass. I think we underestimated the effect of the white-tiled terrace to the south reflecting more heat in through the windows. This probably increased the solar gain in the winter, and of course it will increase the solar gain in the summer unless we shade it.

Trawling the internet, mostly Amazon and Rakuten, the cheapest solution is canvas strips, anchored at the top to the balcony above and at the bottom pegged into the garden. There are some framed awnings for a few thousand yen, but usually only 2 or 3 metres wide and not so sturdy. Our terrace is almost 6 metres wide.

These people, Minowada, make them much wider. This place seems to sell their awnings for 400,000 yen. Tostem also has some, about half the price, but not as wide.

As an option, for another 120,000 yen, they have a wind detector, that will automatically close the awning if the wind gets up. We're not in a particularly typhoon-prone area of Japan, and actually the terrace is probably well sheltered as it's surrounded by houses. Perhaps we can design ourselves not to put the awning out when there's any chance of wind. 

My wife's biggest worry is the heat, and influence from the terrace into the house. According to calculations, the windows will let in some of the heat of the sun when it's low and shining through them in the winter, but much less in the summer when it is higher. This is for about three reasons: one is that as the sun gets higher the angle becomes more acute, and more sunlight is reflected from the window. Another reason is that as the angle gets more acute, there is more glass to go through, so less heat gets through. At the best of times, the south-facing windows will only let in 60% of the sunlight, and that's because they are special high-g glass. Another reason is that in the summer the sun rises north of east, so it won't be shining into the south-facing windows at all in the early morning, and the balcony above the terrace should form a complete block of direct sunlight, at least until the end of August. Some heat may be reflected off the terrace, but it's still going to be the same acute angle. As for heat getting in by conduction, this should be very small, and hardly worth bothering about. The only difficult thing will be to keep windows closed during the daytime, so the heat exchanger will start working to cool down the incoming air, rather than letting in hot air.

At the moment we have a camping flysheet over the terrace, but may go for a slightly more sophisticated set of canvas pieces for this year at least.