Posted by: @crimson

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Cycling has always been stated as happening by the specialist and by the installers. S

It will inevitably.  If your heat pump capacity is perfectly matched to your house loss you can expect the heat pump to cycle from an OAT of roughly 11C and above.  If your heat pump capacity exceeds your house loss the onset of cycling will be lower.  It may also be lower if there is distortion in the LLH.  Added system volume will increase the 'on' time for the cycling, but not the on/off ratio which is determined by the ratio of min output of the heat pump to demand.  There are some other tweaks which can change the on or the off time, but again not the on/off ratio.

Posted by: @crimson

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Previously I’ve just increased the min or max temp beyond the system design to compensate but the cycling is always consistent.

It will be, there is no reason for it to change materially unless the house loss changes or you change one of the parameters that affects the cycling period!  Given you are operating open loop cycling is not the cause of your rooms not getting to temp, and at current mild temps is almost inevitable anyway.  Thus recommend you ignore cycling for now

Posted by: @crimson

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Night mode was forced constantly. So not just at night but at 60% constantly, assume that's 60% modulation or whatever the manual states. This was done with a wire on the terminal and setting. So nothing in the terminal stating night or not if that makes sense

That will be night mode AKA quiet mode, which imposes a cap on compressor modulation.  This may have the effect of reducing cycling for the reason stated in my post above and will definitely cap the max output of the heat pump, which may or may not be what you want!

Posted by: @crimson

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I’ll look at the 4 probes across the LLH when get back but am pretty sure top right (flow from ASHP), to top left (through LLH) to just before heating zone, to just before first rad in run would see temp drops. Likely readings further back in thread. Installers havent once looked at temps. Literally never.

I recommend we just get new data following recent changes (both deltaTs and absolute Ts), and then work out from that whats happening. 

Heating is a matter of energy generation and energy transport, the temperatures tell you about both of these (if you had flow rates it would tell you everything).  Failure to heat is because either energy generation is failing or energy transport is failing or both.  Given how long it has taken to track down the problem the fact your installers never bothered to measure anything merely proves that they don't understand heating.

Thanks James, will get back to you.

as a reminder theret 3 zones. Ground floor front (5 rads), ground floor rear - UFH and first floor (rads - 8 Stelrads, 2 towel, 1 tall).

so I dont think open loop. Its first floor and ground rear stop calling leaving 5 Eskimos and a towel rad calling for heat in Ground front.

Posted by: @crimson

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Thanks James, will get back to you.

 

as a reminder theret 3 zones. Ground floor front (5 rads), ground floor rear - UFH and first floor (rads - 8 Stelrads, 2 towel, 1 tall).

 

so I dont think open loop. Its first floor and ground rear stop calling leaving 5 Eskimos and a towel rad calling for heat in Ground front.

 

Thanks.  I had forgotton that particular feature.  I presume the call for heat switches secondary pumps on/off not the heat pump.

All of this is going to be much easier to diagnose if its treated as a single zone fully open by setting all thermostats and TRVs to max.  The heat loss calculations are, after all, done on this basis. You will also reduce your cycling by doing this, engaged system volume is key!   The state of the zones (open/closed) will change the characteristics of the LLH, which could easily confuse measurements unless we know exactly what is happening when any measurements are made, and when any problems occur.  Is there any material reason not to do that?

@jamespa 

i think the challenge is in the house, its an existing 1970s structure thats been highly insulated, basically gutted and celotex up to 100mm on internal walls and a tone of loft insulation and other works.

But the rear is underfloor and extended, with 1 new bedroom on first floor (as 2 floor extension). Thats largely “new” construction.

Upstairs just doesn’t even need heating it seems, passively it gets a lot of warmth to get to 20+C. In actuality its hard to make it keep to 18-19C for sleeping.

There’s a large hallway in ground floor that adjoins the upper landing and that’s where heat flies up.

So in effect you have 40-45sqm underfloor at rear ground being easily heated. Upstairs getting tonnes of passive heat. Then 2 large ground floor front rooms struggling as the other zones just don’t need the heat. Balancing those down is very difficult it seems. I honestly tried and tried and got nowhere. The living rooms have the most external wall space in effect with 2 slight overhang roofs (also replaced and insulated).

The way the specialist put it upstairs is hugely oversized as smaller rooms, so is the rear with the underfloor. Leaving the front ground as the unique challenge. As the most external wall space in ratio to the room. So the heat pump in effect becomes almost oversized due to often solely that zone needing heat. Hence him attempting the 60% forced lower power via nightmode.

His thought was the LLH could be effecting the delta to point that ground front just keeps meaning it cycles off. It seems Eskimos cant function a very low delta. Hence him wanting the LLH off the main flow.

However the installers had this design so should have thought this through.