Posted By: Gavin_A300l dual coil cylinder

Would be interested how you got to that size as I was looking at a much bigger tank especially for the cold season to keep the tank as cool as possible (which is an odd thing to say!) and also to avoid stagnation in the summer (if we ever get one).

Hi Gavin, thanks for the nice comments, would a drainback solar system allow you divert solar heated water between the tank and the floor without efficiency losses through heat exchangers or trying to collect heat when the tank is already hot?
Could you turn down the temperature of the cylinder to 25 degrees in winter so its the same temperature as the Underfloor heating, hot tap water could come through a coil in the cylinder with an electric or gas after heater. When you have solar heat in winter heat up the house with it straight away and insulate your house sufficiently so that it stays warm for a few days.

Posted By: Viking HouseHi Gavin, thanks for the nice comments, would a drainback solar system allow you divert solar heated water between the tank and the floor without efficiency losses through heat exchangers or trying to collect heat when the tank is already hot?

I've considered this, but I don't think there's a practical place for the drain back tank to be located that's higher than the rest of the heating system given that it's a warm roof / open to the rafters, with no loft to locate the tank in.

Is this how you're able to circulate the same fluid through the panels and the under floor? I don't think I can do that with the panels specced anyway as they're a double harp pipework, which I suspect would be prone to retaining fluid in the lower sections of the harp, which could then freeze if not anti-freezed up.

If I have to use a sealed system, then I want to disconnect it from the UFH system as I don't think it's wise to add a more viscous fluid that's got lower heat carrying capacity to the UFH circuits, as they're pretty long already, plus potential issues with over pressure in the system as we didn't spec or install the UFH system. The heat exchanger is a compromise to avoid potential problems with the UFH system coming back to bite me really, apart from anything else.

Posted By: Viking HouseCould you turn down the temperature of the cylinder to 25 degrees in winter so its the same temperature as the Underfloor heating, hot tap water could come through a coil in the cylinder with an electric or gas after heater. When you have solar heat in winter heat up the house with it straight away and insulate your house sufficiently so that it stays warm for a few days.

I went off the thermal store / indirect water heating idea as it was adding several hundred to the price, plus you actually need the store temperature 5 deg or so higher than the water temperature, so it doesn't particularly help in that respect.

I am considering the idea of setting it to prioritise the space heating if it can't get hot enough to make a difference in the cylinder, but I'm not entirely sure if this is going to be possible with the controls, certainly not if I want to set it and forget it instead of expecting the customer to reprogram the controller for winter / summer mode.

I suppose though that if it only ever heated the lower portion of the tank in winter to 25 deg (24 deg to be safe), then this is below the legionella breeding temperatures, and it would be going through a hot top heated by the gas boiler anyway, so that could be an option so that it operates at the most efficient temperatures through the coldest period.

I'm sure if it was my house then I could change the controller as the seasons change in order to absolutely maximise the output, I'm less sure about being able to set it up in this way in a customers house so that they're able to make the changes themselves from one season to the next. It could be possible though. The other problem being if the gas boiler is heating the UFH to 35 deg, then this is probably what the solar will need to be running at as well.

There's still some of the finer details to iron out if / when I get the go ahead, but something like this arrangement may well be possible.