Posted by: @jml

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also a 25L CB Heating Expansion Vessel

No you HAVE to install this, otherwise when you heat the water it would over pressure the system. It's a mandatory safety feature.

Posted by: @jml

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scop

SCoP is a seasonal average of CoP. The colder it is outside the lower the instantaneous CoP.

Sorry about that this is the data.

Regarding oil, if my demand was 14000khw based on above figure I've already shared then :

14000kwh / 0.7% (70% efficiency given it is a 15 year old combi oil boiler) would equal 23000kwh (I think?? 🤔 🤪 

I spend about £700 on oil a year

In all fairness, I never have my hot water on given I have an electric shower.

For other sink and kitchen hot water use, given it's a combi I just turn on the hot water when required for those period of use.

@jml So your oil usage is pretty much for heating only and your domestic hot water is heated via electricity for the most part.

£700 of oil is about 1000 litres at £0.70 p/lt which is about 10350 kWh of heating which is very close to the 10572 kWh on your data sheet. That suggests the the heat loss figure is accurate and that the heat pump isnt oversized.

Are you contemplating keeping you electric shower or will it be changed to run from your hot water cylinder? There is an interesting trade off if the shower is a good distance from the cylinder. Although the heat pump is more efficient at heating water (COP=1.75 v COP=1), there are losses to consider from the tank and the pipework run. My guess is on average they might just about even out (perhaps the heat pump might be slightly better) so you can discount your water heating from your overall bill. It should be about the same as it is already.

This leaves 10350 kWh for heating at a SCOP of 3.91 needing 2647 kWh of electricity at £0.245 per kWh giving a yearly cost of £648.50. Just less than your oil price.

If you could post some details of the installation and installer, we would be happy to comment. On first sight though, you have a good heat pump, no gylcol and hopefully no buffer vessel so it sounds good.

If anyone spots a mistake in my calculation please say!

Posted by: @bontwoody

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electric shower or will it be changed to run from your hot water cylinder

Would assume you already have water pipes to the shower room for the sink. Showering experience from an Unvented cylinder will be a night and day change for the better.

We run about 15m from cylinder in 15mm pipe and the wait isn't long for the hot water.

Posted by: @bontwoody

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COP=1.75

I am currently getting closer to 2.5 for DHW. If you use a Vaillant cylinder which has a small coil 1.75 is about as good you will get. Heat Geek has some good videos on DHW heating with a heat pump.

Posted by: @jml

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14000kwh / 0.7% (70% efficiency given it is a 15 year old combi oil boiler) would equal 23000kwh (I think??

Posted by: @bontwoody

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£700 of oil is about 1000 litres at £0.70 p/lt which is about 10350 kWh

If you have only used 10350kWh of oil, your heat input required cannot be 23000kWh. Other your boiler is 200% efficient, not 70%. Which makes no sense.

So taking the energy input (oil) at 10350kWh and the oil boiler being 70% efficiency 

10350 x 0.70 is 7245kWh heat to heating system per year including what ever DHW usage is. Even without the shower, numerous stops and starts every time a hot water tap is used will add up quite quickly. We could get through 5kWh of gas for our fairly new combi, without showers. The showers were quite low users, as it's a long sustained draw and the boiler runs quite efficiently.

From a cost to run perspective 

(7245 / 3.5 (CoP)) X 0.23 (per kWh electricity) is about £500

Thanks. I forgot to take the boiler efficiency into account. Even better running costs then. 

If you have only used 10350kWh of oil, your heat input required cannot be 23000kWh. Other your boiler is 200% efficient, not 70%. Which makes no sense.

So taking the energy input (oil) at 10350kWh and the oil boiler being 70% efficiency 

10350 x 0.70 is 7245kWh

@Johnmo Oh damn, right there is what I did wrong. I divided rather than multiplied! So actually my figures are actually improved. I gave the 0.7 (70% given the boiler is very old and not of new design)

So your oil usage is pretty much for heating only and your domestic hot water is heated via electricity for the most part.

@bontwoody As for hot water, no it is all in fact heated via boiler as it is a combi boiler but I never have the hot water timed or on. I literally flick the boost button which is preset to given an hour of hot water via the boiler. Once we have finished with the hot water we just turn that boost option off again. We don't have a tank nor do we have to heat water via an immersion element. So all heating and hot water is via boiler. 

So based on that assumption with heat and hot water being supplied by ASHP - the data sheet 14617 demand (almost matching my calculation of 14000) 14617 / 3 SCOP x 0.23 kw unit = £1120

Are you contemplating keeping you electric shower or will it be changed to run from your hot water cylinder? There is an interesting trade off if the shower is a good distance from the cylinder. Although the heat pump is more efficient at heating water (COP=1.75 v COP=1), there are losses to consider from the tank and the pipework run

Also @bontwoody not sure I follow. Will getting rid of electric shower be better or not? (Sorry if I am coming across a little dense atm) I am actually considering keeping the electric shower. I can always plumb a shower attachment in to existing hot and cold taps of bath if required at a later stage if the running of the Elec shower runs too much along with the ASHP.

Regarding Installer, they are 1314 renewables based in Scotland near Stirling. Installation is exact yet but my positioning of Cylinder I understand - based on my research and on what the installers have said, the shorter distance pipework from ext ASHP to cylinder the better so there isnt heat loss over distance (again increasing efficiency) Subsequently, the ext unit will actually be outside the bathroom so that distance to cylinder would likely be the same distance back via pipework running hot water back to shower from cylinder if i do use hot water for shower also.

@Johnmo & @Bontwoody You have both mentioned the SCOPs 3.5 & 3.91 (or even higher say 4-6 in summer months and on clever alterations of settings) these are best case scenarios right? Also on my data sheets it states that under Space Heating Annul Heat Demand but under Proportions, Energy Consumption its a combined SCOP 2.91, could you explain this and do you expect that is what I will get albeit it a varying COP throughout the year??

I'm guessing if I am conservative with my figures (like i were in my calculations) its makes for a sensible approach to factor in under performance and so higher running costs. I understand I expect to pay more for energy but on return of efficiency i will in the long run be yielding far more energy for what I am paying for based on the SCOP values return that in percentage over what any boiler would return.

I would say I am pretty tech savvy so will do my best to squeeze what I can out of my system based on Heat Geeks advice and playing with weather compensation and in ambient settings but could you express on what you have read whether I would actually be getting a decent SCOP or as good as possible COP without facing crazy electrical costs? 

Also guys, I just wanted to say how helpful and thorough you have been. Its very much appreciated. 😉  

@jml LOL, im the one who is a little confused now 🙂 If your shower is electric, isnt that the main use of hot water in your house? It is in ours, although there is the occasional dish washing in a sink and bath. How many people live there?

Im also not quite sure how your boiler works as with gas combi there is now need to switch on the boiler. Is it different for an oil boiler?

Im sorry if I confused you about whether to keep the electric shower or not. Its a largely academic debate and no need to concern yourself with it. Its probably better to let the heat pump do your hot water and lose the electric shower. As JohnMo mentioned it is possible to get better COPs than 1.75 when heating water. That why I was asking for details of your install such as cylinder make etc. Not all cylinders are equal.

I think you are a little confused about the difference between COP and SCOP. COP is the instantaneous efficiency of the pump so if at this moment it is heating your house and is using 1 kW of electricity and producing 4kW of heat, then it has a COP of 4. SCOP is just an average COP over the whole year. So in spring and autumn you might be getting average COPs of 3.5 and in winter 2.5 for heating. So the SCOP over the year might be say 3.1 or something.

You will have different SCOPs for heating and hot water. That is because the temperature the pump is working to is different. Higher for hot water and therefore lower SCOP.

From your document your predicted heating SCOP is 3.91 and hot water SCOP 1.75. Your overall SCOP will be a combination of the two. As you will be heating a lot more water for room heating rather than hot water the combined figure will be nearer to 3.91 than 1.75. Your predicted combined SCOP is 2.91. As I said before, this seems a little poor to me, but it will depend on how much hot water you use, the type of cylinder you have and also how you choose to heat it.

Dont forget there are savings to be made on Time of Use tariffs.

I think you realise the predictions may not be all that accurate but be assured that if the installation is of a good standard (and it sounds like it will be, although I cant find many reviews of the company) you shouldnt have any problems with higher bills. My own installation is cheaper than gas and I installed it myself.

If you can post your installations details (such as an itemised list) and perhaps start a new thread with the title of the company asking for users experiences of them. That would be sensible.

The CoP of 2.9 is closer to what you would get at -3 and 45 flow temp. Most the time it's nearer 7 degs and your flow temp came down to 35 the CoP would be closer to 4.5, if you have an open system

So yes it combi but at programmable thermostat it can be on, timed or off. I have it off so it's not continuosly heating the exchange so saving electricity and only put it on when I want to use the sinks or run a bath. There is 2 currently living at property with the odd Airbnb guest.

I think you are a little confused about the difference between COP and SCOP. COP is the instantaneous efficiency of the pump so if at this moment it is heating your house and is using 1 kW of electricity and producing 4kW of heat, then it has a COP of 4. SCOP is just an average COP over the whole year. So in spring and autumn you might be getting average COPs of 3.5 and in winter 2.5 for heating. So the SCOP over the year might be say 3.1 or something.

No, this is how I understand it also...phew, glad I'm on same page. Sorry if my phrasing of wording suggests otherwise.

 Here is the quote and list of items.

There are plenty of good reviews on the MSC accredited website for 1314 renewables. Over 100 reviews from happy customers

That's good to know regarding your costings. How well insulated if your bungalow?

I also checked the link you sent hestpumpmonitoring.org...and some of the larger area size of people's homes Vs the same system seems to be delivering well so can't see mine not doing so.

Also the fact I will be fossil fuel free as I use a supplier that is 100% renewable makes me feel good about the decision.