Summer heating extra

Just to add more detail here - above is the ground loop stable temperature after a few hours circulation with no GSHP operation (menu 5.11 to switch the pump between modes).  I have distinguished years using colour but the plot against month looks right - with years showing no consistent trend. So the temperature in May after a winter's heating is about 8.5C, recovering to about 10C over the summer (it is obviously tricky to do this measurement in winter when the pump is operating).  For what a curve looks like see the previous post, but it is clear empirically that the ground temperature recovers OK, though the known conductivity suggests that this must be due to heat transfer by ground water movement.

Summer heating updated

There was some concern that the boreholes would cool over the years as the conduction-based re-heating times are very long (centuries).  However, checking ground temperature this August by switching the ground loop pump to continuous on (menu 5.11) whilst the heat pump is not in operation shows a ground temperature stabilising at 10C after 36 hours, much as originally (see the diagram above).  This is presumably due to groundwater movements increasing the effective rate of re-heating.  At all events it looks as if no summer re-heating is necessary.

FTR ground loop leaks fixed

Just to note that replacing two right-angle 38mm plastic joints at the top of one of the boreholes seems to have fixed this.  Two months later there is no, or insignificant, leakage.  These underground joints were removed and replaced once with no improvement, but on replacing with new ones all seems well.  I cannot see anything wrong with the old examples, even after careful cleaning, but I suppose something must have been!

The deductions already made as to which loop (that is pair of boreholes) and which borehole (return-side hole because of the no-leakage reaction to continuous pumping) were both correct.  And the green flourescin dye very helpfully confirmed the leakage site, though the amount of dye already in the ground on digging resulted in a green pool which made the exact source of the leak hard to discern.

The sub-contracted plumber has sent the builder a bill, and the builder has digging costs; totalling a few £100, but we have firmly said this is not our problem!

The ground temperature (that is the circulating ground loop temperature with no GSHP working) seems about the same as last year at about 10C - so groundwater movements may be enough to stop it cooling down indefinitely.

The system is otherwise fine and works well.  The similar system installed in our new village hall (with underfloor pipework) also works well - but it has taken us 3 re-submissions, a number of phone calls and £1k worth of heat meter fitted inside the GSHP casing to reach 'level 3' of the RHI (government subsidy) system.  It appears that we are nearly there but we have 'lost' the last winter.  If all goes well the subsidy should about cover the electricity running costs.  We hope the much-postponed domestic subsidy system will prove simpler....

More leakage

The leaking is fairly complex. With some difficulty we have established exactly which valves on the manifold are paired on circuits. Obviously the same order on out and return manifolds would have been much too easy! - so the photographs taken before burying were useful, but one can check by putting the ground loop circulating pump to 'continuous on' (menu 5.11). Then when the second valv of a pair is closed nothing happens, whereas when any other return valve is closed the pipework makes a perceptible sound as it relaxes.

But the actual behaviour is confusing - basically the system does not leak if the (5.11) pump is running all the time, presumably because there is some negative pressure on the return half of the loop. So one needs to go round shutting the loops one at a time in succession, for a week or so each to be sure (the fluid level varies a bit due to thermal expansion). This does look to work and we are moderately confident of which loop, and if the conjecture above is right whcih borehole, is involved.

Leakage

The ground loop continues to leak steadily at about 3 litres/month as it has been doing from January, whether or not the GSHP is operating. It is difficult to locate the leak in the manifold manhole because the ground is wet anyway - but the suppliers now agree that it is feasible to use flourescein dye and a uv 'torch' and we will try this.

Details

The inability of the electricity company to read the meter persists - every reading so far has been accompanied by a phone call asking me to re-read it! The 'smartness' is not enough to enable automatic reading but enough to confuse the people.

The leak on the ground circuit persists - at about 0.25l per week. No-one seems to have any suggestions here and the leak is probably too small to be traced, even if it is visible.

The house monitoring system (at http://www.welserver.com/WEL0412/ ) continues to be extended, now with a rainfall monitor. This is an adapted version of the Oregon unit, with an extra magnetic reed relay (from Maplin) added so that a signal is generated from the WEL's pulse inputs as well as the Oregon readout (which is not compatible). The WEL detects the switch closure and only connection is required. The sensor is a tipping unit with alternate emptying reservoirs, rather like a Japanese fountain, and only detects whole mm.

Still learning!

Well it seems that when the system was installed our electrician mis-connected the external (to the GSHP) house heating circuit pump (P1 in IVT speak, this is the usual circulating pump that all systems have) across the terminals for the ground loop circulation pump (P3), with the effect that it operated (& hence the radiator circuit water circuated) only when the GSHP was running instead of continuously. This explains all the oddities of the temperature movements before and after the accumulator tank, which have now gone away as I have re-wired it! (so much for more complex theories). Also the lounge (fan convector) now works much better. The transition is clear towards the left of the lower image above, after which temperatures hardly vary through the accumulator tank and the lounge temperature (yellow) rises to normal. One does wonder whether this might have been affecting the system last winter when we had high return temperature alarms, though of course the effect will be larger now when the GSHP is only on occasionally.

FTR this was an accidental observation after I deliberately switched P3 to continuous to see more clearly what the ground loop temperatures are doing (the average outgoing had come above the average return - but this is an averaging artifact). They do in fact behave normally top above - purple outgoing, blue return - note the ~10 minute delay for the fluid to circulate round the loop and the return temperature to drop).