Posted by: @mikefl

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HW would be better run during the afternoon (say 3-4pm) rather than overnight, as it's when the LWT is highest so you want the warmest external air you can. Although this might depend on your usage - if you use most HW in the morning, you want to ensure you have enough.

The 'wasting half an hour' thing is an issue with Grants - it's the hottest water you're losing too, if the LWT is 55C during the HW phase. I listen for when my HW has hit the target (I can hear the HP "turning off") and then just go and hit the 'advance' button on the HW timer - which switches the HP back to CH mode (or rather, ends the DHW cycle early). I'm hoping this is something the new Grant controller (or Homely) is smart enough to do. It's a very obvious improvement.

Thanks Mike, I'll give 3-4pm a go tomorrow to compare against today on our usage.

@crimson you refer to "only just reaching 21". are you turning it off for a long period? the thing to remember is that the most efficient running (at lowest water temp you can get away with) is when you just slowly replace the heat at the same rate that the house is losing it .  if you start the house from "cold" , it may well take a long time to reach "comfort". 

Posted by: @mikefl

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The 'wasting half an hour' thing is an issue with Grants - it's the hottest water you're losing too, if the LWT is 55C during the HW phase. I listen for when my HW has hit the target (I can hear the HP "turning off") and then just go and hit the 'advance' button on the HW timer - which switches the HP back to CH mode (or rather, ends the DHW cycle early). I'm hoping this is something the new Grant controller (or Homely) is smart enough to do. It's a very obvious improvement

Totally agree @mikefl. The way Grant runs the CH and DHW is dumb, with no intelligence between the two. It's basic S plan stuff from 40 years ago. There's no sophistication when using 3rd party DHW timers and cylinder thermostats. I dare say if it was all run through the Chofu controller, as it should be, it would be cleverer. I have my heating timing set to 'on' throughout the DHW scheduling, which is timed from 1-2:15pm each day when the outdoor air temperature is highest for best ASHP COP at 60degC LWT. If the DHW tank temperature is satisfied, it drops straight back to CH. I say 'straight back', but the system stops, restarts, the compressor idles for 5 minutes, before re-energising..... But that way the residual hot water in the primary circuit gets pushed into the CH circuit. It's only a small fraction of the secondary circuit volume however, which has significantly cooled during the HW charging.

Posted by: @crimson

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Posted by: @mikefl

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HW would be better run during the afternoon (say 3-4pm) rather than overnight, as it's when the LWT is highest so you want the warmest external air you can. Although this might depend on your usage - if you use most HW in the morning, you want to ensure you have enough.

Thanks Mike, I'll give 3-4pm a go tomorrow to compare against today on our usage.

"better" needs caveating. Its most efficient when the air is warmest. It may or may not be the least cost. If for example on a TOU cheap night tariff, its almost always cheaper to do HW at night even if the kwh electricity for kwh of hot water efficiency is worse , the £ for kwh of hot water is better. So "it depends".

Posted by: @iancalderbank

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@crimson you refer to "only just reaching 21". are you turning it off for a long period? the thing to remember is that the most efficient running (at lowest water temp you can get away with) is when you just slowly replace the heat at the same rate that the house is losing it .  if you start the house from "cold" , it may well take a long time to reach "comfort". 

I had it at 22c on and 21c 'off'.  So technically it just never reached 21C at all - the zone always calls for heat.  I'd not seen 21c in the room itself before.  It also would appear the ASHP would just turn off as the out and return temps would match, so the zone never got a chance to hit temp, which they indicated might be a sizing issue.

Tomorrow I'll have to see throughout the day how it fares.  Mornings will be more for me a tell that something has improved

Posted by: @crimson

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I had it at 22c on and 21c 'off'.  So technically it just never reached 21C at all - the zone always calls for heat.  I'd not seen 21c in the room itself before.  It also would appear the ASHP would just turn off as the out and return temps would match, so the zone never got a chance to hit temp, which they indicated might be a sizing issue.

ah ok. if the zone is always calling for heat, but the ASHP is shutting off because the ReturnWT is too high,  then something is meaning that not enough cool water from radiators / too much warm water  gets back to the LLH . Could be radiator sizing , one of the zones closing, flow rates , balancing, or even a bypass valve. quite a lot for them investigate on your unfortunately rather complex system.

Yeah, I'm hoping between the lagging and some balancing done today that won't keep happening.

Removing 2 of the hot water cycles helped as well.  Will see how getting down to 1 goes.

@allyfish I think this slow handover between DHW and CH (and even this isn't the Grant way as per installation) is because LWT on the DHW cycle (say 60C) is in excess of the target LWT on the CH side (say 40C). Probably so far in excess it's beyond the capacity of the lowest compressor frequency to modulate to, so the Grant says "turn everything off until we've cooled down". My idea to improve things at handover, is to artificially set the target LWT to a point between the actual LWT and what it should be, such that the compressor stays on. This would enable that high residual energy to be used by the CH, until it gradually drops to the 'real' target LWT; then go back to standard running. I intend to look into this more when it's warmer.

@crimson

Correctly adjusting WC is a marathon not a sprint, also try to limit adjustments to small steps rather than large ones.

It is also a matter of matching the slope of the WC curve to your particular home's heat loss. The slope for our home is approximately 1, hence for every 1C that the Outside Air Temperature (OAT) reduces, the LWT needs to be increased by 1C, to maintain the Indoor Air Temperature (IAT) at the desired 21C.

You could try starting with the WC curve set for a LWT of 25C at an OAT of 20C, and a LWT of 45C at an OAT of -5C, that would give a slope of 0.8, i.e. 45C - 25C / 20C - (-5C). Allow plenty of time for the IAT to stabilise.

If the IAT is too warm then reduce the 45C setting to 44C and wait for the IAT to stabilise once more, or vice versa if the IAT is too low. Also be aware that on sunnier days the heat loss is reduced due to solar gain even if the OAT remains the same, so be careful that you are not chasing your tail.

Once the correct slope has been established, it may be necessary to move the 20C OAT setting to the appropriate value at say an OAT of 15C, this may help to reduce cycling during milder weather conditions.

Posted by: @iancalderbank

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Posted by: @crimson

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I had it at 22c on and 21c 'off'.  So technically it just never reached 21C at all - the zone always calls for heat.  I'd not seen 21c in the room itself before.  It also would appear the ASHP would just turn off as the out and return temps would match, so the zone never got a chance to hit temp, which they indicated might be a sizing issue.

ah ok. if the zone is always calling for heat, but the ASHP is shutting off because the ReturnWT is too high,  then something is meaning that not enough cool water from radiators / too much warm water  gets back to the LLH . Could be radiator sizing , one of the zones closing, flow rates , balancing, or even a bypass valve. quite a lot for them investigate on your unfortunately rather complex system.

 

Ian,

If you read back within the thread you will discover that the problem was the LLH had been installed with the flows reversed. This has now been corrected.

I’d forgot to change the leave temp to 21c downstairs. Heatmiser showed 19.8c first thing. That’s after 2 hours of 21.5c temp call for.

House was very warm last night, other half said perhaps too warm.

I’m going to allow a week before I accept completion. Am still concerned about downstairs emmiters. Something at back of my brain with plumbers yesterday saying perhaps those aren’t right size and Grant did calcs and architect did sizing (outright lie, they did sizing), makes me think they’ve just gone with suggesting run the downstairs 24/7 and set ASHP to 53.5C to get this across the line with no thought of is it running efficiently.

Seemingly yesterdays changes does get it to 21.5C. So I’ll need to see what I can alter to work to that without burning electricity.

Plumber clarified his changes (he never mentioned he’d upped 2102 to 53.5C)

ASHP pump speed changed to 1

At manifold - each loop set to 1 litre a minute