@JamesPa WRT the DHW: I am happy that is working OK and the heat loss is acceptable. The circulation pump runs so that there is always hot water at the kitchen sink, and we accept the heat loss to achieve it. The heat-up times are set to utilise off-peak electric as much as possible, or solar during the day. As shown on the schematic, the DHW tank is a 250lt Tempest, and power consumption just for DHW is less than 7kW / day.

WRT the property,

heating was assessed as “space heating annual demand” = 48,176kWh/yr

insulation standard = not specified

Property shape = 3 linear wings, with 2 adjacent to a square pool area. (Think of an L shape, with a wing of rooms off the bottom of the L and the pool in the middle of the L)

Pool insulation – unspecified

The area quoted was from something the estate agent produced, and I see in the heat calculations doc that they said the area is 278mSq, but do not include the pool.

Posted by: @jamespa

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Can you clarify exactly what the figures of 60kWh and 264kWh both of which you quote above, cover.

The 60kWh is what the total daily consumption sensors of the 2 pumps report, of which 7kWh are attributable to DHW. As shown on the graphs, the 264kWh was a rough tot up of a days energy produced by both pumps (heating & DHW) and quoted as a sanity check that energy consumed and heat generated with a COP around 4 was about where you would expect it.

@bobflux Yes the thermostat graphs are shaded = heating, and look to be working as they should. The pool heating uses a Heatmiser timer as a timer, so I have online control for pump running times, but the temperature and control is a proprietary set up that there is no online control over, so no monitoring. I could put a temp sensor onto the pipe either side of the heat exchanger, but my gut feeling is the pool heat loss is not likely to have changed significantly in the last few weeks.

The Grundfos pump is UPM3S Flex AS 25-60 130 AZA

I do appreciate your efforts on this, as the original question was just of the buffer tank - is it appropriate in its current configuration, but if there is something obvious that would reduce the power consumption, that would be good. The 40C flow to heat the pool to 29C might be OTT, but it is in use quite a bit so I can not easily drop it down to experiment with. It seems incredible, but the red unit on the right, is the heat exchanger for the pool heating (the other red tubes are UV anti-bacterial tubes). Nothing has ever been looked at regarding the flow rate to that heat exchanger - again, a 3rd company was responsible for the pool, that did not talk to the other 2...

@fosterl2, ah, that changes the picture somewhat. I’d assumed the two Ecodans were still operating as a cascade, but having two independent controllers feeding into a common buffer raises another question for me… what happens hydraulically when one heat pump is running and the other isn’t? Are there non-return valves preventing unwanted circulation between the units, particularly when one is producing hot water while the other is heating the pool or house.

I’m also curious whether simply removing the cascade controller and repositioning the sensors was sufficient to convert the original design into two genuinely independent systems. It may be absolutely fine, but given everything else you’ve uncovered, I’d want to know whether the revised configuration was actually designed and checked or simply ‘made to work’.

And as for Britain’s Heat Pump Shitshow, I bet your early experiences will mirror the first half of the book rather closely! That initial excitement about getting a heat pump, putting your faith in the people designing and installing it, followed by the gradual realisation that things aren’t quite right and that you’re somehow becoming responsible for diagnosing problems you paid professionals to avoid. It’s a depressingly familiar story.

What makes your experience particularly interesting is that you’re clearly doing a lot of the investigative work yourself, and I suspect there are still a few surprises waiting to be uncovered. Hopefully the discussion here will help you get some proper answers.