Many thanks for the article and this helpful thread. My install is only 7 months old and no third party monitoring so I don’t have all the figures, but:
Arotherm Model: 7kW
Firmware Version: 351.09.02
Pre-Install Heat Loss: 5.684 kW estimated by installer. My estimate is a bit lower: 60m2 floor area, 1950s ex-council house in the Highlands with external wall insulation, 100mm loft insulation and double glazing so maybe 60m2 * 65 w/m2 ~ 4kW?
Measured Heat Loss post install: TBC
System Volume: Not much. 6 small radiators and a towel rail. All new rads and pipework at install.
Compressor Hours: 594
Compressor Starts: 1174
Average cycles per hour (Compressors Starts / Compressors Hours): 1.9
What outside temp your system goes from constant steady state running to cycling: not sure, maybe around 0 degrees??? I don’t have any monitoring so it relies on me watching the thing.
I have just reduced the energy integral to -100degree mins. I’m hoping the cycles per hour will reduce going forwards.
The sensocomfort estimates our combined cop so far at 4.3 so maybe not too bad considering. This October is up to 4.5 with some tweaks. Granted, these values will be inaccurate.
Any advice in getting the most out of an oversized heat pump is welcome.
Glad you found the article useful Alistair. At least you’re on the latest firmware.
Shame you ended up with a 7kW as it sounds like a 5kW would have been fine.
There doesn’t sound much you can do other than ensure you keep your rads as open as possible to ensure working system volume (use TRV as upper limiters only and tweak curve down instead if rads getting too hot).
COP of 4.5 is good. My combined COP in October was 4.65 (heating 5.2, water 4.1)
Thanks Mick. Yes, I was relieved when I checked the firmware version. Thanks for the tips. I’ve been keeping the TRVs fully open but our bedroom stays too warm at night, so I’ve been experimenting with turning that trv down which is probably bad for cop, but not sure what else to do. I can probably go a touch lower on the heat curve but waiting for cold weather to adjust this.
Fairly limited data but the change to -100deg mins on the temp integral seems to have boosted my combined cop for the first 5 days in November to 5.0 (valiant numbers). This is higher than anything I have seen since the install in April. Anecdotally, and looking at our smart meter usage it seems like the heat pump is doing longer cycles as expected and has made quite a step up in efficiency. I wonder if this effect is exaggerated in slightly oversized and low volume systems? I’m quite surprised and happy to be honest. Will keep an eye on cycles per hour and update as winter progresses.
I have looked at this as well and see very very little difference in efficiency. Be wary of Vaillant’s COP numbers, they include standby pump and electronics use. This means that when you are at the heating threshold you will see a lower COP which is dominated by standby electricity use over the little heat you need to keep the house warm. As it gets colder, COP in the app will rise at first only to drop again as it gets even colder. This is only the total COP looking at all the electricity used vs. heat generated. Looking at just the compressor efficiency you see a steady monotonous increase with temperature as you would expect, but Vaillant’s app doesn’t show you this.
Vaillant changed the board at my expense. The first three weeks of heating this year (from 4th Nov), compared with same period last year resulted in COP changing from 4 to 5.1. Outside temperatures pretty comparable but lower thermal gain in the house. Judging from this result, I suggest it is not just “some geeks making a fuss” and that there has been a notable impact on performance!
Not to discard your experience here, but thats more than 20%, which would be huge if true. The defective energy integral setting leads to roughly 2x the cycles, which according to my own experiments yields slightly lower COP but nothing quite as extreme as 20%. Do you have a link to two comparable sections on the MyHeatpump app pre- and post fix?
No data as I have never managed to get the ebus data into EmonCMS. Simply based on the Vaillant numbers from the controller, recorded weekly by hand. The HP is always running at lowest output at this time of year (<500w input, including pumps) and cycles are down from 6 in 4 hrs to 4 in 4hrs.
I just noticed that Vaillant has managed to restore the historical data from the old board (it disappeared from the app when board was replaced). The energy efficiency for Nov 24 is reported in the app as 5.1 and for Nov 23 is 4.5, so different to my manual figures. There was a cold patch in late Nov last year with some defrosts, so will be interesting to see how full month figures work out after the forecast cold spell this week coming.
They look exactly the same and even the sw-version is the same.
To me it looks, that you can use both.
Can somebody confirm?
Is it possible to keep the faulty sw-version in the inside unit and just to swap the pcb of the outside unit?
Some replaced both pcbs, some only on the inner or on the outer unit. I‘m a bit confused.
Vaillant swapped just the board in the external unit, yes. P/N 0010033771 on the box of the board they supplied. Everything seems fine since heating season started at beginning of this month.
@tom.delahaye fixed price service visit of £490 incl. Covers any issues they find during the visit. Vaillant did suggest a third party could do it cheaper, but that would have got them off the hook if things were not sorted by just the external board change.
Many thanks for the article - find it useful. Unfortunately maybe not helping with my situation, but would be curious what others think. Our pump was installed almost 2 years ago.
Arotherm Model 7kW plus
Firmware Version: 351.06.07
Pre-Install Heat Loss: 6274kW at -4C
Measured Heat Loss post install: N/A
System Volume: Unsure + 25L buffer
Compressor Hours : 5424
Compressor Starts: 9561
Average cycles per hour 1.76
What outside temp your system goes from constant steady state running to cycling - will be checking my home assistan data to see if I can find the highs
Heating COP / working figure (total) 2,8
Hot Water (DHW) COP / working figure (total) 2.8
I always felt like that my COPs are somewhat disapppointing - but that might be a design issue than anything else I suppose.
@Zarch , thank you for the article excellent writeup.
One thing however maybe I missed but you observe this issue with inactive room temperature mode right? Haven’t tested with active as recently switched over to expanded and expanded mode seems to eliminate both issues at the same time. Not sure why compressor starts basically stop but would appear it goes to a compressor start a day? If that. Find it pretty much unbelievable - unless in expanded mode again is counted different?
Ah that’s fine. Just now when the temperature got up to 4-5°C even with expanded room temperature mode started seeing loads of cycling, where before hardly any.
However I have emailed Vaillant and argued that the pump doesn’t work as described in the manual and apparently will be sent an engineer next Friday.
From the testing i’m still doing now, the Energy Integral internal counter is always adhered to on all three Room Temp Mod settings on the Sensocomfort.
The only difference Expanded will do is turn off the heating if the room temperature is 0.1.25C above target temperature and not come back on again until it drops 0.1875C below.
The manual explains that Expanded deactivates the zone if the current room temperature is 0.125C greater than target and only re-activates if room temperature drops 0.1875C below target.
When the heat pump turns off due to Expanded Target Temp matching, Energy Integral IS IGNORED.
So really, Expanded ‘could’ lead to more cycling than Inactive or Active.
Thanks for this - I had noticed the problems the energy integral so good to see it explained in your article.
Arotherm Model 12 kw
Firmware Version 351.06.07
Pre-Install Heat Loss: 12kW
Measured Heat Loss post install: Est. 9 to 10kW (1930s extended 5-bed house with good loft insulation but with one entire side of the house still solid brick wall)
System Volume: Sorry don’t know this precisely - I have 3 K3 rads, 8 K2 rads and a K1 rad so 26 panels plus 4 WC / towel radiators and a 45 litre buffer tank Assuming 7L per panel (including pipework - http://galaxyens.com/installer-information/water-volume-calculations-in-systems.pdf ) gives an estimate of around 250L, so high volume
Compressor Hours: 6927
Compressor Starts: 9815
Average cycles per hour (Compressors Starts / Compressors Hours) 1.41
What outside temp your system goes from constant steady state running to cycling: I don’t have energy monitoring connected to heat pump but from my Givenergy app I’d estimate somewhere between 6C and 7C at 20C internal temp
I’ve had the heat pump two years now and have an overall COP (measured manually using the consumption and heat generation figures from the Vaillant controller) of 3.4 combined heating and hot water. So not a disaster but would be nice to edge it up a bit. Install is not ideal as it is in a side alley and enclosed on three sides within 1m by wall of house, fence, and back wall of garage so I think I’m probably getting some air recirculation at cold temperatures.