Wednesday, May 16, 2012

Tubes, Leak, Airlock and Heat Exchanger

16 May 2012: Tubes: If asked by another GSHP user, I would definitely recommend the use of these swimming pool panels in a Sunbox for low temperature collection, not a high temperature solution like Tubes. I am keeping my tubes, observing them, writing them up for papers etc. But they have proved some useful lessons, taught me a lot about plumbing, and about augmentation methods for Heat Pumps.
  The right amount of Tubes to equal the performance of the Sunbox would have to be more than double or quad of this installation. Since I got things started earlier this month, the 2sqm of Tubes have captured 16 kWh in the time that the 4sqm of Sunbox has captured 140 kWh! OK, the Tubes are on an east facing roof, but we have had a succession of days with sunny mornings, and cooler afternoons.

Leak:  I had a small leak today. I know why, it's because I have used PTFE tape for compression joints instead of plumbers putty, and you don't have to tighten them up so much - meaning easy re-assembly and re-use of olives. However, if there is a bit of tension in the pipe, it can pull out slightly, and I had about 5mm of pull-out, causing a slow overnight leak. Thanks be to the flying spaghetti monster that I remembered to place a good drip tray to catch everything - and had some spare pipe to insert in place of the previous one. It has has been corrected now with a longer section of pipe.

Airlocks:  Getting it all started again, I had to go through 'airlock' hell again. I will buy some more airlock removers to be absolutely safe - it's better than just loosening compression joints to let air out!
  It was alarming to see that in the brief time of an hour to fix this, the temperature in the Tubes manifold zoomed to 101ยบC on a day that has cold air temperature and a not-particularly bright sun. Impressive, but scary. It was a relief to get the circuit working again and cool them down. It worries me that someone who didn't know how to fix this could suffer real problems in summer. It could be massively expensive to keep calling a plumber for small things.
Heat Exchanger:   David Oliver (engineer at our department) explained how the inside of a heat exchanger works. It has a more complex pathway of tunnels than I first thought. It is possible to run the heat exchanger in the upright position, but you have to flush airlocks out of it by running at high speed and pressure, initially. The safest way to use it with a slow flow rate, low pressure circuit is for it to be flat on its back with all the pipes facing upwards, like a dead beetle (above) and put bleed valves or airlock removers above it. I need to get some compression tees and some airlock bottles to make this system even more maintenance free!

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