8th March: The system is working! It is on a timeclock at the moment from 0930 to sunset (1730 at the moment). On its first day, it buried 17 kWhr into the ground. Without the Energy flowmeter, this experiment would be impossible to verify.
I discovered one problem that we hadnt thought of that makes me wish I had used smaller pipes. Or it may be the non return valve represents some resistance. I presume that there is enough of a pressure drop either side of the non return valve for the liquid to find it easier to go upstairs to our panels than through the valve.
The circuit to the panels is soooo frictionless with 28mm pipes everywhere that when the pump is turned off at night, the heatpump pump still sends liquids round the panels, the rate is about a 1/3 or 1/4 of the rate when the loft pump is going. But it will be enough to cause a problem as it is going up cold and could be returning colder still, and causing condensation. We didnt have much of a condensation problem in daytime as it was returning distinctly warmer.
I tried closing a lever ball valve partially, to simulate friction in the pipe, eg as if we had used only 22 or 15mm copper. It did stop the flow eventually. but it is too closed and will force the Wilo loft pump to have to work unnecessarily hard during the sunny days. If I had used 22mm or even 15mm, would this have balanced the system better so that the GSHP didnt pump up to the loft when the loft pump is off?
I had hoped when the Wilo pump was Off, it would act as a valve, but it seems to be open circuit when off. So how can we get a valve to close the circuit when the pump is switched off? They have to be on the same electric supply, operated by the same thermostat or timeclock. Is there such a thing as a switchable closing valve that can come on and off simultaneous to the Wilo pump??