@murchison2003

Sounds like it might be setup with a fixed flow temp without weather compensation? Might be best to set up a new thread and post the link here so we can hop on and get into the detail of your install. There will be lots of people who are happy to help you investigate. 

Posted by: @murchison2003

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Hi all

Just read this through this topic and looks like there are alot of yous with the same issue as i have and hopefully someone can help with the high running costs i'm experiencing. 

Some basic background information, i have a timber frame kit /block bungalow, heating area 267m2 with underfloor heating, highly insulated, A rating EPC. Replaced a 14 year old ground source pump with a Vaillant Aro Therm 12 kw air source pump approx 3 months ago and haven't touched any settings that the installation team set up. I have tried various timings, on all time / timer etc to try and get this running as efficiently as possible. DHW set at 48 deg on manual to top up when water drops 5 deg. All underfloor manifolds open and inside thermostat set at 21.5 with fallback at 21 deg. I normally run this for 4 hours  at night on the cheap tariff to heat the house which retains the heat for about 10 hours then it kicks in for approx 4-5 hours, this is the time it takes to increase the inside temp by  .5 to 1 deg.

What i have noticed is this, no matter what the outside temperature is, i've seen it at -3 ranging to + 9 deg, the flow temperature is always 32-38 deg, i haven't seen above 38 deg no matter how long the pump has been running. When heating DHW, i've seen the flow temp up as far as 69 deg which tops up the 300 ltr water tank in about 30 mins. Another thing i've noticed too is that the pump runs at 5 kw/ hr all the time, again no matter how long the pump has been running, it ran for 7 hours solid once, all at 5 kw/hr. Is this correct as i would have thought that when it gets up to temperature it wouldn't take so much energy to sustain that temperature. Am i right or have i got this all wrong? I'm hoping a few setting adjustments will remedy this running costs but not holding out much hope. I am grateful that i have solar and battery storage to compensate for the running of this pump, if not my December bill would have been £980 which is a bit worrying. I appreciate electricity prices have risen dramatically however this pump is running way more expensive than my ground source pump did. My old system used to run at 34 deg and that kept my whole house at 22 deg where now i have cold ceramic floors at this flowrate temperature which i just can't understand. 

Any input would be appreciated. 

Thanks in advance. 

Why didn't you replace the old GSHP with a new GSHP, since they are more efficient?

I would suggest that you read through the manual, particularly the section on weather compensation (WC), and check that your ASHP is set to operate in WC mode, and report back the actual settings of the WC curve.

Derek M

i would have if I could have but due to new regulations, all the house demand now has to come completely from the source. My old pump had an immersion back up whereas now the pumps do not come with such backup. I would have required to double the length of my ground coil which wasn’t viable hence why the air source pump is fitted.

@derek how is your COP looking for DHW when the heating is switched off in April/May? We had our Glycol levels adjusted and would like a comparitor.

Ours is 3.15 for May heating 250l to 47 degrees once per day.

I also noticed the heat pump uses 1kwh every few days for 'heating' even though heating is switched off. Does yours do similar? 

Posted by: @webcmg

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@derek how is your COP looking for DHW when the heating is switched off in April/May? We had our Glycol levels adjusted and would like a comparitor.

Ours is 3.15 for May heating 250l to 47 degrees once per day.

I also noticed the heat pump uses 1kwh every few days for 'heating' even though heating is switched off. Does yours do similar? 

We don't have an A2W heat pump we have an A2A one that cannot heat the DHW. At the moment our DHW is provided exclusively by our solar PV system via a power diverter.

Sorry, getting confused I meant @colin! 

@webcmg  Pretty busy at the mo and also getting solar + battery installed so not been paying attention to heat pump. We had family staying so had to tweak the DHW temp to accommodate more. Not had time to look at COP but here's a dump of my May DHW screens. 

Posted by: @saz

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I'm also trying to get to the bottom of my high running costs. It is arduous to say the least. Have you had an independent inspection @webcmg?

@saz whatever happened to your issues? I know you were really stressed out, with no obvious resolution. 

@derek-m I have re-read this thread because @colin and I were discussing our respective ASHP efficencies. Quite early on in the thread you suggested measuring the flow and return temps across the buffer which I didn't really understand at the time and did not have the equipment to measure. The buffer was subsequently re-piped so the flow was through the top and the return was through the bottom (both pipes on direct opposite sides for flow and return).  I thought I would measure the temperatures across the buffer today and noticed that there is only Delta-T of 2 degrees between flow and return, but that there was also a 1 degree loss on the outward flow across the buffer. The system flow temp via the Vaillant app was reporting 29 degrees at the time the photo was taken. 

I'm interested in whether this all look as expected? My 2024 COP was 4.82 (5.5 CH, 3.73 DHW)  Total usage for the year was 4181 kwh.

Thanks

Posted by: @webcmg

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I'm interested in whether this all look as expected? My 2024 COP was 4.82 (5.5 CH, 3.73 DHW)  Total usage for the year was 4181 kwh.

Posted by: @webcmg

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I thought I would measure the temperatures across the buffer today and noticed that there is only Delta-T of 2 degrees between flow and return, but that there was also a 1 degree loss on the outward flow across the buffer. The system flow temp via the Vaillant app was reporting 29 degrees at the time the photo was taken. 

!C drop across the buffer is small, and might cause an efficiency degradation of ~3%.  But 2C flow to return is also small so was this at a time when the heat pump wasnt working particularly hard?

SCOP of 4.82 means that your heat pump will be quite a bit cheaper than oil or gas so probably not worth worrying too much!