Thursday, 9 June 2011

Bare pipes

I did ask where the insulation around the hot water pipes was, before the pipes were buried and sealed under the concrete screed floor. The cold water comes into the house on the north side, running under the store room, then shoots up the pipe space in the middle of the house to the boiler. The blue pipes have cold water pipes in them, already plumbed in, and the red are for hot water pipes to be sent through later. 

This is the utility room looking East. The cold blue pipes are coming from the storeroom to the left. Five red hot water pipes are coming down the pipe space on the left. One is going to the sink, which you'll be able to see on the left against the far wall. To the right of the sink is the washing machine, which is fed by one hot water pipe from the boiler, and another carrying bath water, which in Japan is usually used in part of the clothes-washing cycle. Another pipe heads off south to the kitchen.

This is the view from the utility room, standing on the left of the last photo looking to the right. You can see two blue cold pipes coming to the dish washer and the kitchen sink, and a red pipe for hot water to the kitchen sink. The drain (grey) runs in a lovely straight line, which is a jolly good idea. The hot and cold water pipes meander about a metre to the left, adding to their length and heat loss, which doesn't seem such a good idea.

Hot water pipes loose heat in two ways. First, as hot water is flowing through them, it conducts out of the pipe. This increases as the pipe gets bigger and longer as there is more surface area, and decreases with more insulation around the pipe. I can remember doing a maths problem at school to work out the optimum width of insulation, which showed that there is a point after which more heat is lost than gained because more insulation is increasing the external width of the pipe, and this has a greater effect than the reduced heat loss through extra insulation.

The other way heat is lost is because hot water is left in the pipes after the tap is switched off. The longer the pipe, and the greater the diameter, the more hot water is left inside. This hot water will likely cool down to room temperature before the tap is turned on again, so all the heat in it is lost. This will also mean that when you turn the tap on, cold water will come out at the beginning, and, depending also on the level of insulation, it will take a while to get to the desired temperature. So generally short, narrow, insulated pipes are a good idea. There's an excel file here that can calculate all of this for different pipe lengths, widths, amounts of insulation and temperature differences.

Anyway, this all seems to be a digression from what's happening in my house. I asked the architect at least twice about the insulation, a week or two before the screed went down, then more urgently a couple of days before. I also sent him an email on 15th May, which has yet to be replied to. He told me that the actual hot water pipes would be sent through the red tubes and that they would be insulated. I've since asked for details of the insulation on these hot water pipes, and he's told me each time that he'll find out and get back to me.

I asked the site manager yesterday and he told me that there wasn't going to be any insulation on the hot water pipes. Evidently we share different notions of energy efficiency, and the importance of keeping hot water pipes short and well insulated that I've been talking to the architect about for two years now has not registered. Maybe this is just a Japanese architecture thing, where stuff like electricity and water should not really be in a house in the first place, so are not really part of the equation and should just be quietly ignored or hidden as best they can. Most of this theory goes back to Newton's law of cooling, so it is not particularly revolutionary, new-fangled or controversial.

Anyway, I'll be encouraging them not to use the underfloor pipes, and save about three metres of pipe length by going across the ceiling and down the wall, rather than down one wall, under the floor, then up another wall. Rather than two separate hot water pipes going to the sink and the washing machine next to it, the same pipe can take hot water to both. This may result in lower pressure, but usually both are not going to be used at the same time, so that is not a major issue.

To be honest, I would have been happier to see some insulation around the cold water pipes. In the winter we're going to be sending hot water through the floor to heat it up, and the cold water pipes are going to be doing exactly the opposite. With the hot water pipes, as well as the simple question of efficiency and the fact that any heat loss means less hot water coming out for each kWh of electricity we put in, a bigger problem is in the summer when this heat loss is going to be warming up the floor slab that we'd rather stays cool.