Wednesday, March 10, 2010

A Danfoss Valve to control the drift

March 9th: (also happens to be my birthday).... I chatted to David at Ice Energy for a while, and we reckon that the resistance from the non return valve is encouraging the drift of glycol up to the solar panels at night when the heat-pump is working in the evenings. Left to its own devices this could result in Cooling the Earth in winter evenings if the night-time air temperature drops below the ground temperature.
  We can't have a manually operated regime of opening and closing valves because it should be automatic, and not be affected by human forgetfulness.

•  One answer is either to half-close some of the lever ball valves (after the pump) to create a resistance, but this would increase the workload on the loft pump for years to come, and also could result in a future user misunderstanding this, and moving the levers to open or closed. And the pump might have to be run at a higher wattage.
•  Another answer is to have laid all the pipes with 22mm copper instead of 28mm, but that would require a time machine as I can't really recycle all that 28mm piping now. That is hindsight that we could apply to a future installation - the cost would have been a fraction of the cost of 28mm. In fact, as the Wilo pump is designed for pumping central heating all over a large house, it could possibly have been in 15mm, extremely cheap and easy to lay and insulate. The nightmarish job I had of laying the copper pipes vertically through the house would have been tolerable.
•  The third answer is what I am going to use, an electrically operated valve (with a manual override). You can get ones for 2-way or 3-way, and you can get ones for Hot or Cold systems. The Honeywell is designed for hot liquid (must be more than 5ºC) and would not work in ours. The Danfoss (illustrated) is suitable for temperatures down to -10ºC (which our system would never go down to). These valves are 5 wire, which means that they take a 230V AC power supply, but also will pass power on to the pump a few seconds after they open the valve. This prevents the pump having to pump against a closed valve in case of a failure.
  Looking at the picture of the plumbing below, I have a Real Problem working out where to put it, although the Danfoss is quite happy being positioned on its side. Or I can dispense with one of the copper pipes installed to feed a future thermal battery.

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