Hi Joe - I just found this site. I don't know if this is any help but... I have had a Vaillant Arotherm (not -plus) 8 kW ASHP for about a year now. Do not believe those figures! There are so many variables that the only reliable data comes from actual kWhs consumed, and kWhs produced in heat. But remember this; you must look only at the power the whole installation consumes, not the mere heat output. It may be tempting to compare heat-only data with kWh input, but you will be kidding yourself! Vaillant have a reputation - maybe all other manufacturers do too, but - for being hopelessly optimistic with their figures. Nb. car manufacturers given mpg equivalent numbers vs your actual experience. I would be very interested in how your apparent data looks now we have had some proper cold weather. Btw, I am on the NW coast of Scotland, where it is not actually any colder than where you are - Bristol? which is where I lived before moving north - except it tends to be cooler for more of the year. I am getting real figures of a COP of only 2 when the temp is around zero, and maybe 3 when it rises above 7 or 8 c. Cheers, and good luck with it.

That does seem pretty amazing. How do you calculate? Is it (Environmental Yield + Electrical Consumption) / Electrical Consumption? My AroTherm 5kW was installed last March, so that's (5823+3056)/3056 = 2.905 which seems painfully low. They have wired the thermostats incorrectly so that upstairs and downstairs both turn both on, if you know what I mean. So we have to choose between being too cold downstairs or being too hot upstairs. Is that going to affect the COP?

I only have the data on the controller which I painstakingly manually track every day. My kingdom for an app 🙁 

Possibly relevant to OP also, how do Vaillant calculate Environmental Yield anyway?

@dangermousie Hi. Hmm, not sure your calculation is right there. COP is simply power ie kW of output, divided by kW consumed. My figures come only from the wall unit/controller (not sure which one it is, poss. V700/senso-something).

Reading everything I can find, it seems the data from the controller is not definitive, but not far off either, and the main figures I am tracking - until I can't be bothered anymore, or my obsession with the thing fades! - are 1) kW of power consumed to create heat in the rads, 2) Total kW consumed inc. DHW plus power used to pump the CH water round, and the power the fan and compressor consumes ie, the whole installation and 3) The CH heat output figure. During Dec 2022 and Jan 2023 I was getting a COP of only about 2.0 for the whole installation and 2.2 for heat only. So far this month, Feb 2023, I am averaging 2.3 for installation COP, and 2.5+ using the heating only figure.

I have, since my last post, discovered my unit is an 11 kW unit, Arotherm, not the newer Plus model. My house is a small 2 bed semi-detached, and until July 2022 I used to use 3 tonnes of coal and a similar money value of hardwood every year in a solid fuel CH system (NW coast of Scotland). Even looking at the slightly eye-watering figures for Dec and Jan, I am clearly quids in compared to soild fuel costs, especially given that both coal and wood has gone up by way more than 50% since last winter. I think everyone gets a tad too fixated on COP, when SCOP is a much more important number ie, the comparison between heat output the whole year round and power consumed (vs whatever your previous system consumed, for comparison's sake too).

One thing now clear to me is that ASHPs use MUCH more power when the outside temperature is around zero C +/- but much less when it is around 10 c +/-, and much, much less at 15 c +/- (figures from Aug/Sept 2022). The higher the flow temperature of a system, the less its consumption varies almost regardless of ambient outdoor temps (and a solid fuel system has a very narrow band of consumption because anthracite only burns at above 430C! Wood is nearer 350C, so flow temps within the back-boiler/rad loop were usually nearer boiling than not!! Toasty house, aching bank account!!!) while really low flow temps create a much steeper spring/autumn vs winter gradient.

I fully expect my overall annual electricity consumption for this heat pump to cost less than the old solid fuel system, even after the unit/standing charge price hike of last year. My case is a tad apples to bananas, one extreme to another, whereas you might have gone from gas CH/DHW to ASHP, and might find this costs a little more to run. But do wait for a whole year to pass before calculating actual seasonal COP (SCOP). I expect 2.5 for mine, which is 2.5 times better than eg, night storage heaters or an electric wet CH system. These can never get better than a S/COP of 1, so you are still better off with a heat pump, cost of said system installation notwithstanding.

In Scotland we have no coal power stations left, and are often self sufficient in wind/hydro(/PHV, although this will be tiny as yet), so I'm not complaining. (For what it's worth, I only have a State Pension, no savings, and the heat pump was totally free to me! I had no choice over make or model of heat pump, take it or leave it. I took it! If my monthly DD lecky bill, year round, is less than the cost of wood and coal USED to be, I know I am massively quids in, possibly spending about 30-40% less than I used to, and no more lugging of 120x25 kg bags of coal and half a dozen or more dump bags of wood from the road-side to my back garden storage every naffing year. Not to mention dealing with the toxic coal ashes (-:)~

@yogabob 

I edited your post to split into paragraphs.  A lot of people wouldn't bother reading it as it was (I nearly didn't!), which would be a shame as it's quite interesting. 🙂 

Hi @Yogabob

"@dangermousie Hi. Hmm, not sure your calculation is right there. COP is simply power ie kW of output, divided by kW consumed."

You would think that is the case, but @dangermousie is indeed correct.  For Vaillant systems the calc suggested is correct.  I have attached a screenshot of one of Vaillants documents.  

I to am in Scotland, the North East to be specific.  If I check the NG ESO app I can see that we are regularly supplied by 100% renewable energy.  In fact I am struggling to remember the last time I saw that we weren't.  Very lucky to live where we do, very frustrated to be ripped off by the wholesale price of gas and the fact its tied to electricity generation!!!

Out figures for our install for COP are as follows

2023 so far "4.61"

Since install "4.06"

2023 - hot water "5.34"

since install minus hotwater "5.05"

Ive got our installer coming back to make some further changes to try and improve this even further.  

ATB

Drew 

Thanks, both!

I'm delighted with my ASHP. I'm so grateful every time I wake up to a warm house. Using the data in the heat loss calculations, I have determined that it would cost £1700 more to achieve the same DHW and CH with a modern "efficient" gas boiler.

It was installed on Mar 19 last year, so almost a year. If I take the total yield and total consumption, the COP is 2.9 - or is that the SCOP?

Like everyone, our energy bills are higher. So in an attempt to do a like for like comparison, I'm comparing what our bills would have been without an energy crisis.

There are many caveats:
- The weather
- Data missing from Octopus, so estimates are used
- We are warm now
- Before the heat pump, we used space heaters instead of gas when possible.
- The installers made a mistake in the wiring that meant we have used excess heating upstairs.

In the charts, we had gas for year 1 and the ASHP for year 2.

You should see the spreadsheet behind this 😀

G’day 👋🏼

I am delighted that you are delighted! I too am delighted with mine! Although I haven’t gone to the lengths you have to work out your COP – probably not far off, but - I would be surprised if my average for 12 months wasn’t pretty much the same as yours.

I don’t know where it was that I read it, as I can’t seem to find the original post, but somebody posted their COP figures based on a strange equation that is clearly incorrect. And I am hoping they find this post as it must be in the same general thread. COP is most definitely calculated as: kilowatts produced divided by kilowatts consumed. Simple as. Any other equation is a contrivance, and does not represent kilowatts consumed versus kilowatts returned in terms we can understand ie money! 

Hi @Yogabob,

Is this the quote that you were on about? \

"The energy yield is the excess heat generated, on top of the electricity used. So you have produced (222+444) or 666 kWh of heat from an input of 222 kWh.

The calculation is (input + yield) / input. See page 10 here: 22006-heat-pump-leaflet-v05-web-2-2343880.pdf (vaillant.co.uk)"

Many thanks

Drew

@Yogabob, I was using the simple A/B for a long time as it seemed to make sense to me, but my COP was 1.3! When I asked my consultant ( https://yourfutureenergy.co.uk/ - highly recommended), he told me to add consumption to the yield, as per @Drew Pa and docs. For my purposes, as long as I use the same formula as everyone else, I get the comparison I need to determine if my system has an issue. I'm going to have Vaillant do the end of Year 1 service rather than the original installer. That should give me peace of mind!

@dangermousie good idea to have fresh set of eyes on your install by getting Vaillant to do a service. Although my physical install was pretty competent. the settings we rubbish. 

Too many engineers are just told to make sure the house is warm and don't worry about the cop. So they set it very conservatively. i was left with the DHW at 55 degrees and the weather compensation  curve of 1.8, we turned down the DHW to 47degrees  (we don't run out of hot water so this is plenty for us.) by turning down the heating curve bit by bit and testing is for a few days, if the house maintained temperature, turn it down a bit more until the house cant quite reach you desired room temp, and put the curve up a fraction. we ended up with a heating curve of 0.6 - which results in radiator temps of 26- 36 degrees for typical December outside temperatures. More importantly we have had a huge increase in COP.

we have only had it in since September so i have no SCOP. but the working figure for February has been 5.8 and hot water has been 4.2 (working figure is an over approximation of COP as Vaillant slightly under measure the electricity use.) i would estimate this to be a cop in the region of 5 and hot water of 3.5. 

I don't know if other people have noticed this , although the cops are good, i think our overall delivered heat has gone up compared to our gas consumption (without a full year its more difficult to tell) I don't know if the HP is over estimating the delivered heat (and therefore inflating the COP figures.) or perhaps its a combination of having a generally warmer house than we did and now not using the wood burner as much as it seems like the dirty option compared to HP, whereas it used to feel greener compared to gas. 

it feels there is a market for a specific tune up service. in which the main purpose of the visit is to boost SCOP. I would certainly be drawn to a service company offering this service. saving could easily pay for the service. 

Good idea! I'd be in the market for an ASHP tune up service. 

The installer is coming back soon to install a gateway so I can use the app. I don't seem to have separate yield values for heating Vs water. What controller do you have?

My house is infinitely warmer and very dry! I have minim thermometers in most rooms because I can't tell if the house if cold, or if it's just me being hungry or tired, or need more exercise. I drink more water and use more hand cream 😀 My house plants are loving it! Except the winter Jasmine, I might have to give that a new home.