I’m on IOG at 7p off peak have heatpump, solar and battery my total peak electrical consumption last year was 200kwh costing £60.  I was looking at getting a 2nd power wall but payback was beyond my kids lifetime never mind mine.  So in short I don’t worry about the cost of running the heat pump any efficiency gains have minimal financial impact.

Frankly, @bontwoody, I'm not entirely convinced by either metric. If cost is one's overriding concern - and for most people it will be - the only metric that matters is "how much will it cost me to heat my house and domestic hot water to a comfortable degree over a year?"

Obviously, all other things being equal, a better COP (i.e. better efficiency) will use less energy than a worse COP, but things aren't always equal. Only using cheap rate electricity - either by heating offsets or by use of a battery and/or home-grown energy - may well in the long run work out cheaper than a great COP heat pump running constantly. Only a particular home owner's location, personal preferences and tariff choices will be able to tell. Of course, only using cheap rate electricity and maximising as far as possible the heat pump's COP will inevitably give a better financial efficiency still, but it just demonstrates they are two metrics that neither tell the whole story.

That said, that's not the only concern for some people, me included. I personally don't want to consume all the cheap leccy I can if the carbon intensity of that power is high. No matter how good the COP is, a constantly running heat pump will not differentiate between sustainable electrons and fossil fuel ones. Nor can one extrapolate how green the power is from the unit price.

Overall, I believe that chasing a good COP and trying to avoid expensive electricity are both good and helpful techniques for bringing down the overall yearly cost of heating one's home but that neither should be followed at the expense of the other; they both play their part along with other factors as yet not mentioned.

Not a fan of the league tables as you are comparing apples with oranges.

Our heating needs are very different from a house down the road, let alone the other end of the country. Most the summer we cool, so get a negative CoP anyway.

Cost to run as you say is the important bit. Getting the system setup for your house needs and tariff is also key. We are on E7, have a battery and PV. So can load shift quite well if we need to.

Last year we were way cheaper than gas, using mostly cheap rate periods. This year I am trying the low and slow approach to see how things compare. When really cold (we get -9) the immersion may come into play and cylinder heated in the cheap periods so we don't need to, in the expensive bits and the heat pump not playing catch-up.

Where I think COP is immensely useful is in giving a snapshot, either instantaneous or over time, of a system's performance, which can be useful in comparing against other similar systems or a known reference (manufacturers data) to determine if the system is operating correctly and/or as expected. Measurement of COP could also be useful for fine tuning a system to understand the effect of any changes or tweaking to it's operation. If I change X, I need to be able to measure it's affect on Y otherwise what was the point of changing it.

When selling a house and producing a sellers pack, what do buyers want to see? Do they want to see that a heating system is 400% efficient (SCOP) or that it consumed 4,000kWh of electricity, or that it cost £1000/year to heat the property, or a lot less if you have large solar/batteries installed.

@majordennisbloodnok 

"I'm not entirely convinced by either metric. If cost is one's overriding concern - and for most people it will be - the only metric that matters is "how much will it cost me to heat my house and domestic hot water to a comfortable degree over a year?""

Is cost per kWh of heat produced an exact measurement of just that? All you would need was you annual kWh consumption to work that out.

Also isnt the price of electricity a reasonably good indicator of how green it is? I guess many of us using heat pumps are already on 100% green tariffs.

@Johnmo

"Not a fan of the league tables as you are comparing apples with oranges."

True, but I think they serve a useful purpose in allowing comparisons and pushing good design and practice.

I was running my heat pump for on/off periods last year, but this year will also being seeing how low and slow compares.

@old_scientist

I agree entirely and much of the improvement I have been able to make on my system has been driven by good COP monitoring

Posted by: @old_scientist

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When selling a house and producing a sellers pack, what do buyers want to see? Do they want to see that a heating system is 400% efficient (SCOP) or that it consumed 4,000kWh of electricity, or that it cost £1000/year to heat the property, or a lot less if you have large solar/batteries installed.

When I sold my last house, I think it required a certain type of buyer to appreciate the advantages. It was even a struggle to explain just how much a year the solar panels on the FIT tariff were worth!

Posted by: @old_scientist

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Measurement of COP could also be useful for fine tuning a system to understand the effect of any changes or tweaking to it's operation.

Two images over a 6.5 hr period so DHW doesn't confuse things. Both images are after some changes, OAT very similar, but cooler on the second image.

First image CoP 4.97 over 6.5 hrs, but heat delivered and kWh used is high - compared to the one below

Lower CoP of 4.47, so looks worse, but delivered heat and supplied electric way lower (32%) than above - house is actually warmer as well.

Conclusion - Some changes may give you a better CoP, but result in wasted energy as its not being efficiently being used to heat the house

Posted by: @bontwoody

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Posted by: @majordennisbloodnok

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@majordennisbloodnok 

"I'm not entirely convinced by either metric. If cost is one's overriding concern - and for most people it will be - the only metric that matters is "how much will it cost me to heat my house and domestic hot water to a comfortable degree over a year?""

Isn't cost per kWh of heat produced an exact measurement of just that? All you would need was you annual kWh consumption to work that out.

Also isnt the price of electricity a reasonably good indicator of how green it is? I guess many of us using heat pumps are already on 100% green tariffs.

...

Unfortunately no in both cases. Annual kWh used combined with a time of use tariff means the time a heat pump kicks in (particularly after someone had a shower) does not necessarily align with cheap prices. That muddies the waters a lot since not all kWh are equal.

As for the price of electricity as an indicator of sustainability of production, that's far more complex. If there is a lot of green energy, the price is likely to drop due to plentiful supply. However, there are also plenty of recorded cases where sustainable energy production is paid to switch off so that a fossil fuel plant doesn't have to (along with the associated expenses of starting up again later on). As a result, there are situations where electricity is cheap whilst the carbon intensity is surprisingly high; not exactly what we want. Obviously there is a link between low price and low carbon intensity but the relationship is not strong enough to be reliable.

Posted by: @bontwoody

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Posted by: @johnmo

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@Johnmo

"Not a fan of the league tables as you are comparing apples with oranges."

True, but I think they serve a useful purpose in allowing comparisons and pushing good design and practice.

I was running my heat pump for on/off periods last year, but this year will also being seeing how low and slow compares.

They do allow comparisons and push for better design and practice but I rarely see conversations about COP and/or unit price comparisons that also keep the bigger picture firmly in sight. It's a bit like car nuts talking about either performance or fuel economy without keeping in mind the overall reason the owner bought the car and whether it's fulfilling that purpose.

@johnmo Yes by COP I was really envisaging a stable COP rather than more instantaneous peaking. Ive noticed that overall COP is high on my heat pump when its cycling quite badly, but I wouldnt like to run it like that.

@majordennisbloodnok 

"They do allow comparisons and push for better design and practice but I rarely see conversations about COP and/or unit price comparisons that also keep the bigger picture firmly in sight. It's a bit like car nuts talking about either performance or fuel economy without keeping in mind the overall reason the owner bought the car and whether it's fulfilling that purpose."

I have to disagree with you there, I was listening to a good podcast yesterday (which I cant find) with the OpenEnergyMonitor guys and installers talking about exactly that and how the league table had enabled improvements and debate amongst installers, leading to better installations and cheaper bills.

Posted by: @bontwoody

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I have to disagree with you there, I was listening to a good podcast yesterday (which I cant find) with the OpenEnergyMonitor guys and installers talking about exactly that and how the league table had enabled improvements and debate amongst installers, leading to better installations and cheaper bills.

 

You misunderstood my point which is not surprising since I didn’t say quite what I meant. Ho, hum…

What I was describing with car nuts was something of a stereotypical generalisation where enthusiasts can become wrapped up in detail and forget the wider context. My experience is that conversations about optimising all sorts of tech - heat pumps included - can suffer from the same treatment. However “often” is certainly not “always” and if the OpenEnergyMonitor guys have managed to avoid the characteristic myopia then they’re obviously doing all the right things.