Monday, September 5, 2011

Solar charging a Conservatory

4 Sept 2011: I had an email and call from John, one of the West Bridgford Ecohouses group. He and partner Rachel are doing major extensions to their house, and this will include a 20 sqm conservatory. He has been reading my blog and got interested in the idea of solar charging. They've no intention of using a heat pump, the idea is to dump heat into the slab under the conservatory. It will then be comfortably keeping the conservatory warm or tempered in the winter. The conservatory slab is to be totally new build, 300mm of tiled concrete on 150mm of rigid EPS foam.
   The storage capacity of the slab is only a day or two, so the idea is to use sunny days and sky infra-red during the equinox and winter months to just lift the temperature a bit in daytime. (During the summer it would be too hot, so either the solar panel will be closed off, or its heat will be diverted to a water tank). All the electrics and plumbing conundrums have been tackled on the Peveril Solar house and I will be able to adapt the thermostat and other elements to suit his installation.
   The conservatory is a good source of fresh air for a MVHR (Heat Reclaim) system, which they are likely to use. For the rest of the heating, the house will be very well externally insulated and will need little heating if the MVHR works well. For evenings, there is a source of firewood so they intend to use wood burning stove.
  John is such a can-do man (even has his own digger and dumper truck) that buying a commercial flat plate panel is out of the question - it must be self build! We talked about building a sun box type structure, using the same plastic panels that I already used, but as the panels are not intended for summer use, they may get too hot with stagnation. We discuss metal radiators, easily available second hand. We finished with a discussion of using his underfloor heating piping (or copper) used with the aluminium spreader plates (for underfloor heating), and then boxing them up with a cover made of the polycarbonate that was in the conservatory they took down. (This is the same stuff that I have used on the Surya-3 Sunboxes.).

PS. There is an interesting comment below from Chris Wood. He is approving the idea, but because this is intended for winter and diurnal use only, he is identifying Vaccuum Tubes as the best mode of collection  because they have a fast pick up (and of course are not affected by cold air temperatures). I note that they are also scaleable. If you have a large manifold to start with, you can add more tubes. We have plenty of tube arrays set up in the school if John wants to call in and view.

3 comments:

  1. Hi David,

    Interesting - So you intend to put heat into the slab in winter days as diurnal store? Like you say it will only hold 1 to 2 days of heat max. Why do you suggest using a self made collector? Remember I have done a lot of testing with using alu spreader plates and pipes - ok performance in the summer for interseasonal strorage but in winter the irradiation is so low, I suspect you will be facing a losing battle. You would need a very substantial area of pipes and plates. Unfortunately in winter months you have to extract heat very quickly due to the short bursts of sun, the vacuum tubes are the only way of doing this to any decent efficiency. Flat plate panels and other variants are fine for summer but in winter they just lose to much to the ambient. Also I wouldnt expect to heat water directly as the losses would be substantial from the array and you will find that to get above 30degC would be a struggle. But I guess its all good experimentation if everyone is willing!
    Chris

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  2. Hi Chris, I did strongly suggest getting a commercial quality panel at the best possible deal from one of the friendly companies I know (like Sasie or Carbon Legacy), but John seems determined to try to build his own. But you're right, tubes would probably be cheaper and offer higher performance . One great advantage is that they are scaleable - more can be added. Also, they are not particularly expensive now. I presume the thing is to get a large manifold at the start, and have the means to add more tubes. They would be in a position where nobody can chuck stones etc. On my own house, I could never have used those on my south wall, nor a flat plate panel as they would be target practice for kids on the field. One of the original reasons for using polycarbonate was that stones would bounce off.

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  3. Just a note on the vacuum tubes: yes they would be good at providing heat for tempering the air temperature in the conservatory in the shoulder months of winter, and perhaps to some degree in the deepest months of winter.... but the problem will lie in how to deal with the excess heat in the summer delivered by the array... perhaps the best method is to have solar thermal system for heating domestic hot water and in winter use this for heating the floor slab instead. The heat delivered to the slab is likely to be greater than that which would be delivered to the DHW tank in winter. (due to the low irradiance, there will be many days when the tank can never reach temperature as the solar system will not circulate fluid due to low temp lift across the array. But if this is diverted to a floor slab, say at 25-30degC then more potential for heat delivery. So in essence - late spring, summer, early autumn then solar thermal heats DHW. late autumn, winter, early spring then prioritse slab heating and let alternative boiler heat DHW.

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