I bought a Heat Pump

QrizB

04/02/19 to 05/02/20 is 367 days and a total of 1990 degree-days on the same basis. If that period required 17936kWh of heat, each degree-day needed 9.013kWh of heat output.

13/12/20 to 12/12/21 was 365 days and 2165 degree-days, and took 6931kWh of electricity. Each degree-day needed 3.201kWh of energy input.

Assuming (and it's a flawed assumption) that everything else is comparable, that's a synthetic CoP of (9.013/3.201) 2.816.

shinytop

I thought it wouldn't matter if you were comparing two time periods.  If you want an absolute value for your house then it would.  The MCS calculator just uses an average value for each area. 

Cardew

Reed_Richards said:

In order to qualify for the Renewable Heat Incentive you must have an electricity meter fitted that monitors the power consumed by your heat pump.  I took my first reading (172.04) on 13th December 2020 and read it again at the same time past the same hour today (7102.90).  So the amount of electricity consumed in exactly a year was 6930.86 kWh.  I had some teething troubles with my heat pump in the first week, a blocked filter that was a "known bug".  Thereafter I haven't had any problems  

Before that I had an oil boiler, installed in 2012, a condensing combi.  The oil tank was "filled" on 4th February 2019, twice more and then again on 6th February 2020.  The total oil used was 1936 litres.  If you assume 10.35 kWh per litre of oil that is 19928.4 kWh per year.  But that would be if the boiler was 100% efficient.  I am going to guess that it was 90% efficient in which case I would have used 17936 kWh during the year in question.

Is it a fair before and after comparison?  I heated most of my house to much the same temperatures before and after.  But I took the opportunity to put the two bathrooms on a second zone so I could heat the towel rails when I wasn't heating the rest of the house; that will have increased my energy consumption.

The hot water is completely different before and after.  Before I had a combi with such long pipe runs that if you wanted to wash your hands you would lose patience waiting for hot water.  And if you waited long enough then a large quantity of water was left in the pipe, typically over a bucket full.  Now I have a hot water cylinder and a re-circulation pump that runs for 5 minutes every hour from 7 am to 11 pm.  This pumps hot water round a loop of well-insulated pipes and back into the cylinder.  As a result all the hot taps now give hot or warm water very promptly. But this will be costing me energy.  For around 6 months of the year I can also use spare solar electricity to heat the tank via the immersion heater on sunny days.  This is saving me electricity.  I don't know how the increased costs and increased savings balance out.

Then there is the weather.  Memory tells me we had a milder 12 months from February 2019 than we have just had for the last 12 months.  I know there is data you can look up but I have not yet got my head around "degree days".

So superficially I used maybe 17936 kWh of oil before and 6931 kWh of electricity with the heat pump.  A straight ratio gives me 2.59.  The data I was given indicated I should achieve and average Coefficient of Performance for heating and hot water of around 3.  So 2.59 falls short of 3 but it's not really a fair comparison for the reasons I have stated.

The oil I bought for the 367 days I am comparing cost me £870.  The electricity would have cost me £900.50 had Symbio, my electricity supply company, not gone under and electricity prices skyrocketed.  At the moment the average price of heating oil is about 59p  per litre.  The average I paid was 44.94p per litre which means that the price I pay for electricity has gone up more than the price I would be paying for heating oil.

So all that I can really conclude is that a heat pump can indeed use a lot less energy that other means of heating, the performance can be fine and the running cost is broadly comparable to that of an oil boiler.  But I have given dates and figures that would allow anyone who wishes to delve deeper and I am happy to answer questions.         

                      

Thanks for this, it is good to have some ‘real world’ results. However it seems to me that there are too many unknown factors for a realistic COP to be estimated.

As you state, you will have increased consumption by using heated towel rails and a more convenient supply of hot water. Surely the supply from the solar panels to the HW tank will more than compensate for that increased consumption?? My son has solar panels and they provide all the HW for a family of 4 during the summer months. Several posts on this forum indicate they also switch off CH and immersion heater. I believe some have meters that measure how much of the panels output is fed to the HW tank for their system. 500kWh?? 1,000kWh?? It would be interesting to hear their results.

If I understand QrizB’s post  on degree days correctly he is making the assumption* that if the current period is 12% colder(2165 to 1927) then an extra 12% energy will be consumed to maintain the same heat in the house as the previous period. Is that assumption sound? I have no idea. On that assumption* he has raised the estimated COP by 12% from 2.59 to 2.9.

* I did read the caveat about a ‘flawed assumption.’

Notwithstanding the above, of more interest to most people on a money-saving website is a comparison of the cost to run an ASHP against oil or gas CH.

As stated, current cost of oil is 59p a litre. For my area(midlands) and supplier(OVO) the current Standard Variable Tariff(SVT) charges are 20.59p/kWh electricity and 4.04p/kWh gas.

So the cost last year at current oil prices would be £1,142  (1936 x 59p)

For gas at current SVT charges it would have been £896 (19,928kWh x 4.04p + £91 daily standing charge)

The cost of 6,931kWh electricity for this year at current SVT charges would be £1,427

The SVT charges used are the cheapest available and if the predictions are correct, they will increase drastically next year; but of course oil prices could also increase.

michaels

Cardew said:

Reed_Richards said:

In order to qualify for the Renewable Heat Incentive you must have an electricity meter fitted that monitors the power consumed by your heat pump.  I took my first reading (172.04) on 13th December 2020 and read it again at the same time past the same hour today (7102.90).  So the amount of electricity consumed in exactly a year was 6930.86 kWh.  I had some teething troubles with my heat pump in the first week, a blocked filter that was a "known bug".  Thereafter I haven't had any problems  

Before that I had an oil boiler, installed in 2012, a condensing combi.  The oil tank was "filled" on 4th February 2019, twice more and then again on 6th February 2020.  The total oil used was 1936 litres.  If you assume 10.35 kWh per litre of oil that is 19928.4 kWh per year.  But that would be if the boiler was 100% efficient.  I am going to guess that it was 90% efficient in which case I would have used 17936 kWh during the year in question.

Is it a fair before and after comparison?  I heated most of my house to much the same temperatures before and after.  But I took the opportunity to put the two bathrooms on a second zone so I could heat the towel rails when I wasn't heating the rest of the house; that will have increased my energy consumption.

The hot water is completely different before and after.  Before I had a combi with such long pipe runs that if you wanted to wash your hands you would lose patience waiting for hot water.  And if you waited long enough then a large quantity of water was left in the pipe, typically over a bucket full.  Now I have a hot water cylinder and a re-circulation pump that runs for 5 minutes every hour from 7 am to 11 pm.  This pumps hot water round a loop of well-insulated pipes and back into the cylinder.  As a result all the hot taps now give hot or warm water very promptly. But this will be costing me energy.  For around 6 months of the year I can also use spare solar electricity to heat the tank via the immersion heater on sunny days.  This is saving me electricity.  I don't know how the increased costs and increased savings balance out.

Then there is the weather.  Memory tells me we had a milder 12 months from February 2019 than we have just had for the last 12 months.  I know there is data you can look up but I have not yet got my head around "degree days".

So superficially I used maybe 17936 kWh of oil before and 6931 kWh of electricity with the heat pump.  A straight ratio gives me 2.59.  The data I was given indicated I should achieve and average Coefficient of Performance for heating and hot water of around 3.  So 2.59 falls short of 3 but it's not really a fair comparison for the reasons I have stated.

The oil I bought for the 367 days I am comparing cost me £870.  The electricity would have cost me £900.50 had Symbio, my electricity supply company, not gone under and electricity prices skyrocketed.  At the moment the average price of heating oil is about 59p  per litre.  The average I paid was 44.94p per litre which means that the price I pay for electricity has gone up more than the price I would be paying for heating oil.

So all that I can really conclude is that a heat pump can indeed use a lot less energy that other means of heating, the performance can be fine and the running cost is broadly comparable to that of an oil boiler.  But I have given dates and figures that would allow anyone who wishes to delve deeper and I am happy to answer questions.         

                      

Thanks for this, it is good to have some ‘real world’ results. However it seems to me that there are too many unknown factors for a realistic COP to be estimated.

As you state, you will have increased consumption by using heated towel rails and a more convenient supply of hot water. Surely the supply from the solar panels to the HW tank will more than compensate for that increased consumption?? My son has solar panels and they provide all the HW for a family of 4 during the summer months. Several posts on this forum indicate they also switch off CH and immersion heater. I believe some have meters that measure how much of the panels output is fed to the HW tank for their system. 500kWh?? 1,000kWh?? It would be interesting to hear their results.

If I understand QrizB’s post  on degree days correctly he is making the assumption* that if the current period is 12% colder(2165 to 1927) then an extra 12% energy will be consumed to maintain the same heat in the house as the previous period. Is that assumption sound? I have no idea. On that assumption* he has raised the estimated COP by 12% from 2.59 to 2.9.

* I did read the caveat about a ‘flawed assumption.’

Notwithstanding the above, of more interest to most people on a money-saving website is a comparison of the cost to run an ASHP against oil or gas CH.

As stated, current cost of oil is 59p a litre. For my area(midlands) and supplier(OVO) the current Standard Variable Tariff(SVT) charges are 20.59p/kWh electricity and 4.04p/kWh gas.

So the cost last year at current oil prices would be £1,142  (1936 x 59p)

For gas at current SVT charges it would have been £896 (19,928kWh x 4.04p + £91 daily standing charge)

The cost of 6,931kWh electricity for this year at current SVT charges would be £1,427

The SVT charges used are the cheapest available and if the predictions are correct, they will increase drastically next year; but of course oil prices could also increase.

What level of efficiency have you assumed for the gas?

Cardew

michaels said:

What level of efficiency have you assumed for the gas?

The same as Reed_Richards gave for his 9 year old oil combi i.e. 90%. So input 19,928kWh for an output of 17,936kWh.

Admittedly that is the same 'wet finger in the air' estimate. I believe that as gas boilers can modulate their output, and oil boilers cannot modulate, this is an advantage in operating the boiler in condensing mode and hence achieve a a higher efficiency.

However even if I had assumed an efficiency of only 78% for the gas boiler and thus used an extra 2,000kWh gas to achieve an output of 17,936kWh it would have only added £80 to the cost of gas.

Reed_Richards

Cardew said:

...of more interest to most people on a money-saving website is a comparison of the cost to run an ASHP against oil or gas CH.

As stated, current cost of oil is 59p a litre. For my area(midlands) and supplier(OVO) the current Standard Variable Tariff(SVT) charges are 20.59p/kWh electricity and 4.04p/kWh gas.

So the cost last year at current oil prices would be £1,142  (1936 x 59p)

For gas at current SVT charges it would have been £896 (19,928kWh x 4.04p + £91 daily standing charge)

The cost of 6,931kWh electricity for this year at current SVT charges would be £1,427

The SVT charges used are the cheapest available and if the predictions are correct, they will increase drastically next year; but of course oil prices could also increase.

This is a reasonable comparison of prices but the best comparison of the data I can manage does involve a lot of caveats. 

The other way I look at the data is that I was told I should achieve a SCoP of around 3 and there is nothing to suggest that this is seriously wrong.  If I had achieved a SCoP of 3 then I would have required £1317 worth of oil (2233 l x 59p).  That's closer to the cost of running the ASHP but still significantly cheaper.  Electricity prices have risen more than oil prices (in percentage terms) since the ASHP was installed.   

Cardew

Reed_Richards said:

Cardew said:

...of more interest to most people on a money-saving website is a comparison of the cost to run an ASHP against oil or gas CH.

As stated, current cost of oil is 59p a litre. For my area(midlands) and supplier(OVO) the current Standard Variable Tariff(SVT) charges are 20.59p/kWh electricity and 4.04p/kWh gas.

So the cost last year at current oil prices would be £1,142  (1936 x 59p)

For gas at current SVT charges it would have been £896 (19,928kWh x 4.04p + £91 daily standing charge)

The cost of 6,931kWh electricity for this year at current SVT charges would be £1,427

The SVT charges used are the cheapest available and if the predictions are correct, they will increase drastically next year; but of course oil prices could also increase.

This is a reasonable comparison of prices but the best comparison of the data I can manage does involve a lot of caveats. 

The other way I look at the data is that I was told I should achieve a SCoP of around 3 and there is nothing to suggest that this is seriously wrong.  If I had achieved a SCoP of 3 then I would have required £1317 worth of oil (2233 l x 59p).  That's closer to the cost of running the ASHP but still significantly cheaper.  Electricity prices have risen more than oil prices (in percentage terms) since the ASHP was installed.   

Not sure I understand the first part of the second second paragraph.

The overall point I have been trying to make for a long while is that, in financial terms, an ASHP is more expensive run than oil and particularly gas CH. That applies even if if an ASHP has an overall COP of 3.0, which is very difficult to achieve when the system is retrofitted.

It is the Government's declared intention to phase out gas/oil CH and house owners will be expected install a heat pump and pay in excess of £8,000, after the current government subsidy, for the privilege of paying much higher charges than their gas/oil CH.

Something has to give!!

Meanwhile on a Money Saving Website surely the sound advice would be to hang on to gas/oil CH for as long as possible.

Reed_Richards

When I installed my ASHP in December 2020 I was able to buy electricity at 13p per kWh and I had paid an average of 45.2p per litre for my oil since we moved in in September 2018.  Now my electricity costs me 20.46p per kWh (up 57.5 %) whilst oil at 59p per litre is up 30.5% on my average price.  This has swung the balance in favour of heating oil.  Who knows what will happen in future.  You could envisage that gas prices will continue to rise, pushing up electricity prices and heating oil becomes the cheapest option!

I took advantage of a subsidy for installing a heat pump that gives you considerably more money back than the subsidy that replaces it after the old one ("RHI") finishes at the end of March 2022.  A Money Saving website would ideally compare the full life cost of your heating, not just the running cost.  This would include the cost of replacing the boiler (or whatever) periodically and other ancillary equipment you need (like an oil tank for oil).  Had I stuck with oil I would have needed a new tank costing over £1000 and I don't know how much more in labour.  

Verdigris

On the other hand you probably can't drill an oil well in your garden but you can put solar panels on your roof and buy a share in a wind farm.

Cardew

Reed_Richards said:

  A Money Saving website would ideally compare the full life cost of your heating, not just the running cost.  This would include the cost of replacing the boiler (or whatever) periodically and other ancillary equipment you need (like an oil tank for oil). 

100% agree.

In existing houses, factors for full life comparison costs should include:

A. Running costs.

B. Replacement cost of a gas/oil CH boiler(if needed) and installation of a heat pump system. - taking into account subsidies for a heat pump.

C. Future repairs/replacements.

At the moment it is surely a 'no contest'.

However in the future things could change - either way