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Sustainable heating in Brisbane

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This is a bit of a departure from my regular blog topics, but I thought people might be interested in a sustainability project that I undertook at home.

I live in a tin and fibro house in Brisbane. While this sounds unattractive, the house itself is architect designed from the late forties and looks out onto a magnificent rainforest. It has nearly three stories of windows facing East and is beautifully light and breezy.

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Unfortunately what keeps us delightfully cool in the summer becomes an ice-box in the winter. We have a log fire and thick down duvets so in the evenings there is no real problem with this. It is in the mornings that we really suffer.

The inside of the house remains significantly colder than outside until about 3PM. Then finally the sun through the windows has warmed it up enough to be pleasant. I am talking about an inside temperature between 12 degrees and 16 degrees through the mornings. Brisbane typically gets to 21 or 22 degrees.

I saw a solar air heater on the internet and decided to install it as a way of heating inside on winters mornings. I bought a┬áSolar Powered Solar Air Heater – Large (1m x 1.4m) for $1,499.00 from Negergy. This arrived promptly in a big cardboard box with some installation instructions.

I had found a place high up in the house to install it. The wall gets the morning sun early and remains in the sun all day. I bolted some wooden mounting bars into the studs with 10mm self tapping bolts, recessed into the bar. I made the bottom bar wider than the top one to give a 6 degree upward tilt.

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I drilled the holes for the two penetrations. This is tricky because the holes have to be exact (the instructions give the spacing). It was then a matter of hoisting the unit into place. I used a climbing rope slung from the other side of the house and a pulley. I tied myself on with an ascender and a climbing harness (I recommend using these having seen so many people fall from ladders in 24 hours in emergency).

One of the penetrations (air inlet) comes straight into the upstairs room. The other is into the roof cavity and I decided to pipe the hot air 8 metres using insulated ducting I bought on the internet. This goes through the roof, down 100mm storm water pipe at the back of a cupboard and to an outlet vent in the ceiling below. Needless to say this was also pretty tricky.

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When the sun came out I was really disappointed. The amount of air coming through the outlet was small and not very warm. When I checked in the roof I didn’t have leaks, but the inlet area was really hot. I believe what was happening was that the inlet air is compressed into the ducting and heats up. By the time it reaches the outlet it expands again and cools down having lost most of the energy on the way.

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Undaunted I bought a computer fan from Jaycar and set at it with my multitool to make it fit in the 100mm plastic pipe. I then connected this to a 10W solar panel next to the solar heater (direct connection, no capacitors or anything).

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Now, come 9:30AM, the fans are both on and there is a steady stream of hot air coming out of the ceiling. Unfortunately most of it rises up, so we put on the ceiling fans to gently waft it back down. The heat keeps coming on a sunny day until about 3PM.

So does it keep the house warmer? I believe so, but have not been through a complete winter. To really test I would need to get some thermocouples and measure the temperature profiles on similar days with it on and off.

Total cost was about $1,600 but if I charged for my time it would be a different story. I am pretty good at DIY, but I found this a challenging project. I believe it was worthwhile, although the fans are a constant background noise. I can turn them off with the thermostat and a separate switch for the computer fan.

I’ll try to remember to give you an update as we get to the depths of winter.