TuftedPuffin.co.uk

Behaviour of the Solar Heating System

Something we don't want to see is the tell tale signature of the gas boiler heating the cylinder after one or two days with little sunshine.

But at least this only heats the top of the cylinder

On the other hand a sunny day is very effective at heating the water

And it does heat the tank all the way through

And does add a significant amount of energy into the hot water cylinder

One thing that does intrigue me is the fact that the pump comes on during the night, as can be seen from the plot below

At first I thought that hot water may be convecting around the loop and therefore taking energy out of the cylinder. I mentioned this to my solar installer and he assured me that the use of 10mm copper pipe keeps convection down to a minimum. He thought that it was more likely that residual heat in the collector was triggering the controller as the temperature of the hot water cylinder dropped throughout the night. In order to test this theory I've added two sensors, one on the feed and one on the return, about halfway between the cylinder and the collector, so that I may be able to tell which way the heat is flowing!

Mine is a modern insulated tank and yet there is still quite a considerable heat loss during the night, this can be seen in this plot, the sudden drop is water being run for a shower, and the dramatic rise is the gas boiler kicking in.