@robertoi where you live will make a big difference. I live down on the south coast and I am averaging a COP for heating and hot water of 3 with radiators. If I went to UFH I expect I could get more like 4+ as I could drop the flow temperature by a pretty large amount. If you live in the highlands, might be a different story. Have a look in my signature if you want to see how my ASHP is performing.

Solar will help in the shoulder seasons - minimal benefit at the moment. A battery might also be useful depending on your tariff and solar PV system.

PV production per month is pretty easy to calculate and there are a few websites. This one is pretty good - https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html

@batalto Many thanks - Ive done the solar PV calcs from that website already, very useful.

I live near Oxford but where we are is a bit of a frost pocket.

@robertoi There is a calculator in my signature which is from Freedom heatpumps. Have a crack at that and you should get a better idea of your costs. You'll need to do a room by room heat loss assessment, or you can fudge the numbers if you have a ballpark idea - just make a copy and off you go.

Oxford should be fairly warm - use the London baseline. 

Posted by: @robertoi

Hello everyone

I'm new to the forum, and dont yet have a ASHP but have been very interested to learn about the technology recently, alot of it from Mars's website and this forum.

I'm currently weighing up my options around installing a ASHP. I can't pretend this is purely environmentally driven as I would like to save money ultimately, ideally whilst also eventually stopping using gas entirely and reducing my CO2 footprint...

I have been doing some calculations and from what I can tell it only really makes financial sense for me to go for a ASHP if I also install PV panels at the same time. In order to convince my better half of the pros of this it would be nice to say how quickly the install would become cost neutral.

To try and estimate this I need to have a guess at what my COP is likely to be...

I have a 135m2 detached 1990s house with loft and cavity insulation, and double glazed windows throughout. We currently have 14 radiators, although I am considering getting rid of the downstairs rads and switching to UFH throughout. As we are having an extension built shortly we had SAP calcs done which suggest a total space heating requirement for our house of around 11500kwH per year, plus probably around 4000 for hot water - which matches quite closely my annual gas use of 15500 kwh last year.

I wanted to get an idea of what kind of average COP I might achieve over the course of the year. Am I being too optimistic to think that I might achieve a COP of 3.5-4, particularly if I move to UFH???

What sort of avearage COP are other forum members getting from their systems???

 

Many thanks in advance!

 

Rob

Hi Robertoi,

welcome to the forum.  3.5-4 is at the higher end of the SCOP that most people achieve.  It's definitely possible but you'd need to have a well designed, low temperature system and use it like an ASHP should be used.  UFH will almost certainly help you achieve this.  I'm getting about that but it's taken a lot of tinkering to get there.

The most important thing is to find a good supplier who knows ASHPs and doesn't treat them like boilers. 

I would also caution against assuming too much input from PV for an ASHP.  It will help a bit in Spring/Autumn but not much at other times elsewhere.  Batteries can help but that's more outlay.

Good luck and keep us updated.

One other thing to think of is possible location of the heat pump. 

If you can get it on a south wall it will benefit from solar gain on cold but clear frosty days. Also good ventilation is paramount for high COP. 

Posted by: @robertoi

Hello everyone

I'm new to the forum, and dont yet have a ASHP but have been very interested to learn about the technology recently, alot of it from Mars's website and this forum.

I'm currently weighing up my options around installing a ASHP. I can't pretend this is purely environmentally driven as I would like to save money ultimately, ideally whilst also eventually stopping using gas entirely and reducing my CO2 footprint...

I have been doing some calculations and from what I can tell it only really makes financial sense for me to go for a ASHP if I also install PV panels at the same time. In order to convince my better half of the pros of this it would be nice to say how quickly the install would become cost neutral.

To try and estimate this I need to have a guess at what my COP is likely to be...

I have a 135m2 detached 1990s house with loft and cavity insulation, and double glazed windows throughout. We currently have 14 radiators, although I am considering getting rid of the downstairs rads and switching to UFH throughout. As we are having an extension built shortly we had SAP calcs done which suggest a total space heating requirement for our house of around 11500kwH per year, plus probably around 4000 for hot water - which matches quite closely my annual gas use of 15500 kwh last year.

I wanted to get an idea of what kind of average COP I might achieve over the course of the year. Am I being too optimistic to think that I might achieve a COP of 3.5-4, particularly if I move to UFH???

What sort of avearage COP are other forum members getting from their systems???

 

Many thanks in advance!

 

Rob

Hi Rob,

Welcome to the forum.

If you want my honest opinion, if you are on mains gas then stick with it, otherwise you will be spending a large amount of money installing a system that will cost you more to run. On the present tariffs for gas and electricity, for an ASHP to be cost neutral would require it to operate with a COP of 5, which at the present cannot be achieved. You would be better off spending some of the money on improving the insulation of your home.

I would certainly recommend having a solar PV system installed, but doing so to assist an ASHP is of limited benefit, since the solar PV will not provide a great deal of energy at the time of year when a heat pump would require it.

Posted by: @derek-m

 

....

I would certainly recommend having a solar PV system installed, but doing so to assist an ASHP is of limited benefit, since the solar PV will not provide a great deal of energy at the time of year when a heat pump would require it.

Not sure I'd want to outright disagree with you, @derek-m, but I would be prepared to debate the point if the solar PV system includes a battery. We have found the combination of even limited generating during the day with the system's habit of recharging the battery at night means in practice that very little of our ASHP's consumption has been electricity drawn from the grid at the daytime rate. That's meant a pretty significant offsetting of the heat pump's running costs so far even on overcast days.

Hi @majordennisbloodnok 

I'm afraid I was performing my usual role of Devil's advocate.

You can correct me if I am wrong, but what it would appear that you are suggesting, is that Rob should spend £5000 to £10000 of his own money, along with £5000 of electricity consumers money, to install an ASHP. Then spend a further £5000 or more for a solar PV system, and then a further £5000 or more for a battery storage system, so that his running costs would be about the same as if he had stuck with his gas boiler.

If money was no object then I would encourage everyone to insulate and draft proof their home to at least passivhaus standard, then install a ground source heat pump. Also install a large solar PV system and a large battery storage system.

Since one of Rob's objectives was to save money, then I think my advice was quite sound.

Posted by: @derek-m

Hi @majordennisbloodnok 

I'm afraid I was performing my usual role of Devil's advocate.

You can correct me if I am wrong, but what it would appear that you are suggesting, is that Rob should spend £5000 to £10000 of his own money, along with £5000 of electricity consumers money, to install an ASHP. Then spend a further £5000 or more for a solar PV system, and then a further £5000 or more for a battery storage system, so that his running costs would be about the same as if he had stuck with his gas boiler.

If money was no object then I would encourage everyone to insulate and draft proof their home to at least passivhaus standard, then install a ground source heat pump. Also install a large solar PV system and a large battery storage system.

Since one of Rob's objectives was to save money, then I think my advice was quite sound.

“Happy to debate”, says I. You’ve certainly taken me at my word.

Actually, I’m not suggesting any of what you outlined. All I was suggesting is that IF someone chooses to install an ASHP and IF they decide for whatever reason to install a solar PV system that there is a bigger synergy than just thinking of the solar panels powering the ASHP there and then.

How one stacks up the costs and ROI is quite the black art, and one can use the figures to justify almost any stance. However, from ballpark figures our install looks as follows

• The ASHP and related work cost about £15,000
• The 18 solar panels, inverter, 6kWh battery and installation cost about £7,500. It was done through a council partnership bulk buying scheme, hence coming in significantly below our other quotes.
• Our RHI, if the first payment is a good indicator, will total about £11,000
• Our annual oil bill for the coming year, based on December prices, would have been about £1,400
• Based on our location, the house price and latest surveys, the solar PV could have increased the house value by anywhere between nothing and about the installation cost. Some estimates suggest far more, but their assumptions are suspect, so they are ignored.

Putting all that together, I have some justification if I were to claim our installation cost about £4,000 net. The running costs, thanks to the battery (and better thermostatic control to be honest), have definitely dropped compared with oil boiler, and the latter definitely needed changing due to age.

One thing I totally agree with you about is the importance of sorting out the insulation first. Irrespective of heating technology, the less heat is actually needed the more efficient everything will work.

@majordennisbloodnok 

Even if Rob was able to receive all the benefits that you managed to achieve, he would still struggle to equal his present fuel costs, let alone lower his fuel bill. ASHP's can possibly make economic sense when replacing an oil boiler, but certainly not a mains gas boiler.

The other thing that should be considered is the servicing and replacement costs, particularly for inverters and batteries, which would soon eat into any potential savings that may have been made.

Whilst I do my best to help people get their systems working in the most efficient manner, I cannot recommend that people spend their hard earned money, on a system that may not be suitable for their needs.

Posted by: @derek-m

…

Whilst I do my best to help people get their systems working in the most efficient manner, I cannot recommend that people spend their hard earned money, on a system that may not be suitable for their needs.

Nor would I suggest you should.

The point I’ve been making is that an ASHP may enjoy more benefits from a solar PV installation than just the energy generated. Whether or not that makes it a good idea for the prospective customer is for them to decide.

Unfortunately, this discussion has turned into a rabbit hole that is detracting from the rest of the good advice you’re giving, and that I agree with. I’m debating a detail and not even certainly disagreeing, so perhaps better if I step back and let us focus again on Rob’s situation.