@bontwoody Sounds as though someone is speaking through their headwear to me! The normal arrangement is that DHW heating cycles are achieved by the three way valve being closed so that flow is to the water tank only and (as you say), the flow temperature is increased [reducing the COP of course] so that the water is heated to perhaps 45 degrees or more. Most setups will isolate these cycles to nightime operation so that impact on space heating is minimal. Regards, Toodles.

Posted by: @bontwoody

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@editor @toodles @deano @iancalderbank @derek-m @kev-m

So we had the meeting today with an Andrew Lloyd and whilst we didnt agree on everything it was a useful meeting. Access to the heat pump settings via a local website page was achieved and changes made to the settings to allow a reduction in running costs. Agreement was made to sort out the snagging issues with insulation etc.

Where we couldnt agree was over the size of the heat pump with Andrew insisting the the larger model would be able to successfully modulate low enough to avoid cycling in the shoulder seasons. In the end I asked for a written commitment from them to this effect and what they would do about it if it did. We shall see what I get!

Out of interest Andrew insisted that that it was the norm for heatpumps to heat DHW all through the day using a setpoint. say a drop of 5C. This isnt my experience, what is the experience out there please? I would have thought this arrangement would increase thermal losses from the cylinder and be more expensive to implement due to always heating water at the highest temperature

kudos to yourself for helping your neighbour this way.

on DHW, I do the exact opposite of what your chap said. I let the cylinder get as cold as I can get away with then do a full reheat. fortunately this works out at once a day, my cylinder is big enough to do 4 showers plus the washing up on one reheat. Starting from cold provably gives the best COP. thermal losses less of an issue with a modern well insulated (including the pipes!) cylinder.

with a smaller cylinder / higher usage that doesn't cover a day, I'd expect a different strategy.

@toodles Well I think the mode of operation is just the same, its just the frequency that is different. It makes sense to heat your water at night if you have a cheap tariff or dont want to switch off heating during the day but otherwise the best time is when OAT is highest, i would think

@bontwoody if you''re on a cheap night tariff the cheapest time to fully heat DHW is at night (less efficient but costs less). If no cheap tariff then efficiency swings it in which case best middle of the day of course with highest OAT. but regardless of all that , the COP is ALWAYS going to be better if starting from a cold cylinder than a warm one, so the statement of "leave it always on and reheat if drops by 5C" is demonstrably wrong in COP terms. But that of course requires that you can get away with letting it drop in user acceptance terms : without running out of hot water and causing those taking showers to jump about the bathroom shouting that its "****** gone cold 😉 " . the strategy he talks about is guaranteed to never fail the user acceptance test which may be why he as an installer uses it, i.e. to  minimise complaints and callbacks ... we've seen this installer strategy elsewhere methinks! 

@iancalderbank very true Ian, that may be the reason but I take it you dont use the strategy either?

@bontwoody no (as per previous post) I optimise for lowest cost at "decent but not best" efficiency by doing 1 full reheat a day, during the night. But it does mean I had to make sure that 1 cylinder full "lasts the day". it all depends on the household + cylinder size....

his strategy is guaranteed to work in any household / cylinder size. But will also cost more to run.

Posted by: @bontwoody

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@editor @toodles @deano @iancalderbank @derek-m @kev-m

Out of interest Andrew insisted that that it was the norm for heatpumps to heat DHW all through the day using a setpoint. say a drop of 5C. This isnt my experience, what is the experience out there please? I would have thought this arrangement would increase thermal losses from the cylinder and be more expensive to implement due to always heating water at the highest temperature

My DHW is 'on' 24/7, as is my heating. DHW recharge setpoint is target -12.5 degrees, target is set to 50.

Mainly because the Carel controller is quite complex to configure for time schedules, and we only have a 150ltr tank, heated by a 9kW unit. Recovery times are short, 15-20 mins maximum.

Immersion is also left on 24/7 with the stat for that set at 60 degrees. Heat pump does the heavy lifting (coil is in the base of the tank) and immersion gives us a bit more stored heat capacity.

@hughf Thanks Hugh

So the latest is that the company Thermal Earth are refusing to do full handover until the client has paid the bill in full with no guarantees that the 16kW heat pump will work efficiently in warm weather. That includes giving the client the ability to alter the heat pumps settings. I would advise people to say well clear of them.

@bontwoody, what is your neighbour going to do?

@editor Im not sure Mars, she isnt very clued up on the technical aspects and tends to send long email rants to the company about stuff she is confused about. Im trying to pressure the company with the threat of bad reviews including the one Im going to write for you :-). No cracks showing so far though. If I cant get her control of the heat pump I think she might have to cave in.

@bontwoody, it's bizarre how established companies just don't care about the quality of their work or bad reviews. Ironically, these guys are training other installers: https://www.thermalearth.co.uk/niceic-training-course

It blows my mind how this can even happen and this got me thinking. There's quite a lot of knowledge we've all accrued on the forums. Anyone want to start an installer training course with me? 🤣