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Solar thermal recooling option (holiday mode)

  • 17-12-2022 11:02am
    Registered Users Posts: 2,553 ✭✭✭

    Hi all,

    Solar thermal systems commonly have a holiday mode/ summer / recooling mode. From my limited knowledge they work by cooling the store during the night in order to prepare it for solar loading on the following day by pumping back to the store. I have experienced installer recommend to leave it. I understand that that would cut down on maintenance costs as people might forget to turn it off but how much lost hot water could be lost I wonder, for example in winter with a sole occupant house? Has anyone done any calculations? Thanks in advance.


  • Moderators, Education Moderators, Home & Garden Moderators Posts: 8,037 Mod ✭✭✭✭Jonathan

    This explains the issue fairly well. Holiday mode allows the cylinder to dump some heat during the night, in the hopes that it doesn't reach stagnation during the following day. Turn it on when you'll be away for a few days in the height of the summer. Leave it off otherwise.

  • Registered Users Posts: 2,553 ✭✭✭Yellow_Fern

    That is interesting, thanks. The thermal dump is an interesting idea. Would be nice to have that as a outdoor hot tub.

  • Moderators, Education Moderators, Home & Garden Moderators Posts: 8,037 Mod ✭✭✭✭Jonathan

    If you can avoid the glycol stagnating, the glycol will be good for 5-7 years. Perhaps the installer wants a few bob for annual service calls.

  • Registered Users Posts: 2,553 ✭✭✭Yellow_Fern

    Thanks for the info. If the recooling option was left switched on, what would happen? A lot of waste energy?

  • Registered Users Posts: 1,376 ✭✭✭dathi

    in winter the temps wont get high enough for the cylinder to dump heat back out through the collector unless you have a frost protection on the controller . in summer it would dump heat at night to prevent damage due to the system shutting down because cylinder was to hot .so you would dump some of todays energy in order to collect energy tomorrow, or keep todays energy and not collect any tomorrow so no great waste of energy. my own system dumps the heat through the central heating radiators but that only fires up 5 or 6 times a year as we have high shower usage (girls)

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