After the recent issue I had the last time it was really cold, I spoke to Grant and they got me to make some adjustments to the parameters over the phone. It’s been fine since then but last night was the first real test as such. It got down to -4.

woke to around 20 degrees downstairs underfloor and 19 upstairs radiators which is a definite improvement. 

previously it was dropping overnight in cold weather from 21 to 18. This was because of the defrost cycle.

i don’t have an LLH or a Volumiser. I asked Grant about this as I found in the instructions that seemingly these are classed by Grant as essential for all installations.

Grant were a bit evasive of that point, asked me to try what they had suggested for now. 

but riddle me this - should I really try to have everything calling for heat all the time in that kind of weather to maximise volume? Sometimes parts will reach temperature for a while and then click off? And the upstairs I have set back to 18 overnight rising to 21 from 6am.

@marvinator80 I find that with my system UFH and rads I need all circuits open all the time calling for heat 24/7 any setbacks when its 0 or below only cause the house to cool too much and then can't recover.  This means your heatpump is appropriately sized and not oversized which is a good thing.

If I set back to 18C till 6am then asked it to get to 21C from 6 it would probably get to 21C around 6pm and will have been running flat out all day and will have consumed about 40kwh.  Where as leaving it on with no setback may use the same amount of electricity but the house will be continually warm which is much more pleasant.

@gary that’s great Gary, thank you. I’ll set everything to 21.5 so it’s always pumping. Then when it hits 22 it’ll stop, which won’t happen in sub zero cold but will prob maintain 21, which is fine.

then when it’s above 5 degrees there is it will easily reach 21.5 then stop and probably maintain by itself for quite a while. 

Posted by: @marvinator80

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@gary that’s great Gary, thank you. I’ll set everything to 21.5 so it’s always pumping. Then when it hits 22 it’ll stop, which won’t happen in sub zero cold but will prob maintain 21, which is fine.

then when it’s above 5 degrees there is it will easily reach 21.5 then stop and probably maintain by itself for quite a while. 

If you prefer the temperature slightly cooler in the bedrooms you have the choice of adjusting the lockshield valves or using TRV's.

HI folks It feels quite autumnal here in Ayrshire today so I'm back to planning ahead for the winter. Last year the ASHP struggled a bit and seemed to use a LOT of power. I think the power part was because it is a fairly big house and also we added the garage last year which has the heated upstairs. 

There were a few times last winter when the pump struggled to deliver comfort temps. We didn't freeze of course, but coming down in the morning to 19 rather than 21 isn't ideal. The issue seemed to be weak recovery from defrost cycles and the defrost cycles being almost constant for about a month due to temps. 

Grant told me that the system should have a LLH or a Volumiser fitted - it has neither. So I am getting the installer to retrofit a volumiser before this winter. 

I see there is a new Smart Controller - has anyone used this yet? Is it worth upgrading?

Cheers,
Martin

@marvinator80 

We have the Grant LLH/volumiser fitted to our setup. Last winter was our first experience of ASHP and, like you, the cool and damp conditions were not ideal for the heat pump. I fiddled with the settings on the LLH a couple of times but I don't think I ever got it working the way I wanted to. It will be interesting to hear if you can have more success than me 🙏

@dodgyknee With Grant on the phone and changing the settings it definitely improved and got close to what we needed but I think we just need more volume in our system for those kind of conditions. We shall see. 

Grant did say that every system should be installed with either a LLH or Volumiser so no idea how mine has neither.

Posted by: @marvinator80

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Grant told me that the system should have a LLH or a Volumiser fitted - it has neither

The main reason they say that is the ones they install have an immersion in them to provide secondary heating source. So if you are marginal on heat pump output a further 3kW can be used.

I noticed you said up thread when above freezing you easily hit the thermostat, that would indicate your WC curve needs some adjustments.

Do you run on a timer or 24/7? Or have set backs?

The Grant LLH works well for me with the 3kW immersion programmed to give supplementary heating during defrost mode when the LWT drops below a pre-set value. It has greatly helped with flow temperature recovery after defrost, powered for 5-10 minutes each defrost cycle. My 10kW Grant Aerona is marginally sized for our house, should be 13kW but DNO and power issues = 10kW unit. The LLH needs to be well balanced hydraulically, sane flow on primary and secondary sides. 

@dodgyknee this sounds familiar

Posted by: @dodgyknee

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I fiddled with the settings on the LLH a couple of times but I don't think I ever got it working the way I wanted to.

Yup, I played around, got the supplementary heating indicator to appear on the Grant controller, so all appeared to be working, but absolutely no change to the ASHP performance or water temperature. That prompted a closer investigation, and, surprise surprise, I found the 3kW immersion control relay wasn't wired up. The installer had pulled all the cabling, and terminated at the ASHP end, but not at the immersion end. Got that fixed and it's now happily assisting during defrost if the LWT drops below 38degC during defrost, which it usually does, as the flow is normally between 40-45degC in winter temperatures that require periodic defrosts. Defrost can push it down to the mid 20s. The defrost recovery time is much shorter now as the immersion heater energises fairly early on in the defrost cycle and helps pull the temperature back up after for 5 minutes after. The parameter settings are a bit fiddly and complicated, with various delay on/off timers as well to consider.

I also have the immersion set to provide 3kW supplementary heating if the outdoor ambient drops below -5degC until the outdoor temperature rises above -3degC. The confusing bit initially was this was disabling the compressor and only turning the supplementary immersion heater on, but there's a separate parameter for compressor disable temperature which needs to be adjusted down to -20degC. That way, the 3kW immersion and compressor run together.

The Grant Aerona Installation Manual and the LLH Installation Manual make a hash of describing the parameters for Group 46 'Supplementary heating'. They redact some parameters and chop up the others into smaller tables. They make much more sense all together, as Chofu manual shows them in their manual parameter list.

@allyfish 

That's good information for me to work with, thanks. Any chance you could tell me which 46 group parameters you changed and what their new values were?

Posted by: @allyfish

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Grant Aerona Installation Manual

Download the Chofu one, it's pretty easy to read. Grant have just deleted the sections they don't want the installer to read.