Wednesday, May 12, 2010

Why have Sunboxes?

12 May 2010: I was asked by David Atkins of Ice Energy, and by a student today, why have Sunboxes? (getting heat from the microclimate in the sunbox), when we could simply hang black panels out on the wall, simpler and cheaper (getting heat directly from the air).
    If we had bare black panels externally they would have to be encrusted with Ice to work effectively in Winter (using latent heat of freezing), and would not be possible to control thermostatically - they could work all day and night, and use a lot more loft-pump energy (longer hours and a more powerful wattage of pump), and the thermostatic control would be by the GSHP - and to me they would negate the point of using Ground Source because the GSHP would be working long hours putting glycol out at below freezing - and perhaps we would need 8 panels not 4 - this hasn't been tested (need another house and a lot more plumbing!). (A small advantage is that they could be on the roof, not wall)
   We have no wish for below-freezing pipes to run around the loft, dripping bucketloads of condensation in the house and risking us dry rot - and causing a higher workload for the GSHP than it already has because temperatures would have to be seriously low.

    The Sunboxes work by exploiting the principle of the 'Sunspace' (solarium)....  contain very warmed up air that works all year round (even in winter on bright days with cold exterior temperatures), and the thermal sensor can hang in the airspace just above the black collector to monitor the performance and know when the thermostat should trigger the pump - consequently the pipes are never below freezing, and the pump is never working when there is no heat worth downloading. The thermistor has a bonnet of reflective foil to make sure it responds to air temperature not merely to direct sunshine.

  Millions of Solar Cookers work on the same principle in India, and I must post more information about those.

   The ground remains our prior source, but for the small amount of time that the sun shines in Dec / Jan / Feb, there is still going to be restoration of the heat into long term storage, thus avoiding chilling. Actually, being vertical on the wall, we have found during March that the Sunboxes were still quite effective at lower sun angles.

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