Wednesday, August 19, 2009

Do it with black plastic pipes?

19 Aug '09: I had a wonderfully advancing conversation with David Atkin of Ice Energy, which has also reduced the cost enormously and is likely to increase the efficiency of the installation.
      We want this to be a research project, and an exemplar for future house design, so affordability is part of the requirement. Solar charging is worth doing in his opinion, because deep down, the earth does get colder. A heatpump working for 25 yrs will gradually lower the ground temperature until it reaches a new equilibrium - the precise time depends on the soil and the depth of hole, size of house, so 25 yrs is an estimate. So, Solar Earth Charging is going to prevent that temperature decline.
     Pro-quality Solar panels are heavily insulated with a glass top, so only collect heat when the sun shines. They are aiming for a high Delta-T in order to make hot water, but we are not doing that - we don't need glycol at 60-80ยบ. The solar panels do nothing if the sun is not shining - which can be several days in a row in British summers.
     On the other hand, If we have an array of uninsulated black plastic pipes in the open air (like a swimming pool heater) this will pick up ambient air temperature, so it will be able to charge the ground with low grade heat throughout summer nights, long rainy days etc., so long as the air temperature is hotter than the below ground temperature - more than eight months of the year, day and night. Whenever the sun shines, it will of course harvest even more heat. The black surface of the pipes will reduce UV degradation.
     As 4 sqm of pipes costs less than £ 200, it can be replaced after 10yrs if need be, and not even require scaffolding. This can be mounted on the South wall, not on the roof, so that is it getting more solar heat in Equinox and Winter, but benefitting from air temperature as the wall heats up in summer sun. There is a zone of very hot air over the surface of the wall when the sun is shining. For summer hot water heating, the heatpump will benefit directly from this higher temperature panel.
      The idea that an industry standard Solar panel would actually reduce the efficiency of our idea shook me, but in a most beneficial way. Getting heat on rainy summer days and balmy nights from the ambient air temperature is an enhancing idea.
    The compact collector can be fixed to the South wall right next to my bedroom window (for easy inspection). There is a small tree opposite which does not shade the wall yet, but we will keep its height trimmed. There is a direct route from there to run the insulated connecting pipes through the loft to the position above the heatpump and the storage cupboard where we would want the displays, datalogger, pump etc located.
      It simplifies things because the PV installation by EvoEnergy has more roof area to work with and it totally self contained as a package of work, and need have no connection with the Solar Charging project.
     The Solar Charging project - compact collector on the South wall and the connection to glycol loop - would become a totally Ice Energy-DNC-University of Nott'm project.

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