COP - diminishing returns on investment?

Strummer22

michaels said:

Reed_Richards said:

Solarchaser said:

Reed_Richards said:

FreeBear said:

michaels said: If we are allowed to include timeshifting into our scop calcs then what is the scop of my heatpump that is powered by 7p per unit overnight leccy only via the v2h battery?!

Your SCOP would remain the same, but your running costs would be lower.

SCOP is based on the seasonal average of heat output (kWh) divided by electrical energy supplied (kWh). 

A more sensible measure would be the annual expenditure on whatever fuel you use (in pence) divided by heat used by your home in a year (kWh).  So (approximately) if a kWh of electricity costs you 25p (on average over the year) and that gets you 3 kWh of heat on a seasonal average then the ratio would be 8.33 p/kWh.  But if you can bring your electricity costs down to say 7p per kWh by time-shifting then the number would go up to 2.33 p/kWh.  Or if you heat with gas at 6p per kWh using a gas boiler that is 90% efficient on average the number would be 6.67 p/kWh.

All we are really lacking is a snazzy and memorable name for the quantity I am calculating.  Perhaps the Annualised Cost of Heat, ACOH?  Or maybe somebody else can think of a better name?    

Heating Energy Annual Total
HEAT ??
Or to add in the cost
Cost (of) Heating Energy Annual Total
CHEAT??

😂

I like those but its not an annual total.  The closest I can come is:
Cost (of) Heating Energy Annualised Ratio
CHEAR
or. slightly simpler,
Cost (of) Heating Annualised Ratio
CHAR

I quite like CHAR because that sounds like it might be a bad thing and the smaller your CHAR the better.

So developing that idea, I wonder if we can estimate our co2 per kwh and annual total co2 of our heating.

I wonder what the average co2 for UK electricity is between 23:30 and 06:30 which is when my heat pump power is downloaded?

It would seem to be about 150g per kwh on average at night in 2022, if I assume a cop of 3 then that is 50g per kwh for my heating, and about 750kg for the 15,000kwh of heat we use a year.

With gas that would be about 3,200kg (assume 215g per kwh heat delivered)

Probably a decent estimate but the CO2 intensity of electricity varies so much... very cold weather in winter also tends to be still so there wouldn't be much wind power generation when your consumption is highest. 

According to my EPC my household would produce 9.8 tonnes of CO2 per year! EPCs are just worse than useless:

"[the EPC calculation] uses a static baseline carbon intensity factor set in 2012 of 519g CO2/kWh – in reality, the National Grid has become much cleaner in recent years, which the actual up-to-date carbon intensity being 173g CO2/kWh" - https://www.kammaclimate.com/news/2024/06/understanding-sap-calculations-for-energy-performance-certificates/

98,00 kg / 0.519 g/kWh = 18,882 kWh. So that's what the EPC estimates our electricity usage is.

We actually use about 11,000 kWh electricity (no gas). Taking 173 g/kWh this is "only" 2 tonnes of CO2 per year. 

A new 'Home Energy Model' is to be implemented this year apparently, which hopefully won't be as useless. https://www.gov.uk/guidance/standard-assessment-procedure#full-publication-update-history 

Nick_Dr1

Heres a graph showing the decarbonisation of the grid over the last few years. From Energy Dashboard - real time and historical GB electricity data, carbon emissions and UK generation sites mapping

Solarchaser

Strummer22 said:

michaels said:

Reed_Richards said:

Solarchaser said:

Reed_Richards said:

FreeBear said:

michaels said: If we are allowed to include timeshifting into our scop calcs then what is the scop of my heatpump that is powered by 7p per unit overnight leccy only via the v2h battery?!

Your SCOP would remain the same, but your running costs would be lower.

SCOP is based on the seasonal average of heat output (kWh) divided by electrical energy supplied (kWh). 

A more sensible measure would be the annual expenditure on whatever fuel you use (in pence) divided by heat used by your home in a year (kWh).  So (approximately) if a kWh of electricity costs you 25p (on average over the year) and that gets you 3 kWh of heat on a seasonal average then the ratio would be 8.33 p/kWh.  But if you can bring your electricity costs down to say 7p per kWh by time-shifting then the number would go up to 2.33 p/kWh.  Or if you heat with gas at 6p per kWh using a gas boiler that is 90% efficient on average the number would be 6.67 p/kWh.

All we are really lacking is a snazzy and memorable name for the quantity I am calculating.  Perhaps the Annualised Cost of Heat, ACOH?  Or maybe somebody else can think of a better name?    

Heating Energy Annual Total
HEAT ??
Or to add in the cost
Cost (of) Heating Energy Annual Total
CHEAT??

😂

I like those but its not an annual total.  The closest I can come is:
Cost (of) Heating Energy Annualised Ratio
CHEAR
or. slightly simpler,
Cost (of) Heating Annualised Ratio
CHAR

I quite like CHAR because that sounds like it might be a bad thing and the smaller your CHAR the better.

So developing that idea, I wonder if we can estimate our co2 per kwh and annual total co2 of our heating.

I wonder what the average co2 for UK electricity is between 23:30 and 06:30 which is when my heat pump power is downloaded?

It would seem to be about 150g per kwh on average at night in 2022, if I assume a cop of 3 then that is 50g per kwh for my heating, and about 750kg for the 15,000kwh of heat we use a year.

With gas that would be about 3,200kg (assume 215g per kwh heat delivered)

Probably a decent estimate but the CO2 intensity of electricity varies so much... very cold weather in winter also tends to be still so there wouldn't be much wind power generation when your consumption is highest. 

According to my EPC my household would produce 9.8 tonnes of CO2 per year! EPCs are just worse than useless:

"[the EPC calculation] uses a static baseline carbon intensity factor set in 2012 of 519g CO2/kWh – in reality, the National Grid has become much cleaner in recent years, which the actual up-to-date carbon intensity being 173g CO2/kWh" - https://www.kammaclimate.com/news/2024/06/understanding-sap-calculations-for-energy-performance-certificates/

98,00 kg / 0.519 g/kWh = 18,882 kWh. So that's what the EPC estimates our electricity usage is.

We actually use about 11,000 kWh electricity (no gas). Taking 173 g/kWh this is "only" 2 tonnes of CO2 per year. 

A new 'Home Energy Model' is to be implemented this year apparently, which hopefully won't be as useless. https://www.gov.uk/guidance/standard-assessment-procedure#full-publication-update-history 

I'd say that very much depends on where you live also.
It's currently snowing and so fairly cold, but this is my area right now at 2g, while I'm taking 22kw from the grid.



However south Wales is currently the worst at 216g



South Wales doesn't tend to be generally, it's more often west and east Midlands which are the dirtiest in my random observations

ed110220

Solarchaser said:

Strummer22 said:

michaels said:

Reed_Richards said:

Solarchaser said:

Reed_Richards said:

FreeBear said:

michaels said: If we are allowed to include timeshifting into our scop calcs then what is the scop of my heatpump that is powered by 7p per unit overnight leccy only via the v2h battery?!

Your SCOP would remain the same, but your running costs would be lower.

SCOP is based on the seasonal average of heat output (kWh) divided by electrical energy supplied (kWh). 

A more sensible measure would be the annual expenditure on whatever fuel you use (in pence) divided by heat used by your home in a year (kWh).  So (approximately) if a kWh of electricity costs you 25p (on average over the year) and that gets you 3 kWh of heat on a seasonal average then the ratio would be 8.33 p/kWh.  But if you can bring your electricity costs down to say 7p per kWh by time-shifting then the number would go up to 2.33 p/kWh.  Or if you heat with gas at 6p per kWh using a gas boiler that is 90% efficient on average the number would be 6.67 p/kWh.

All we are really lacking is a snazzy and memorable name for the quantity I am calculating.  Perhaps the Annualised Cost of Heat, ACOH?  Or maybe somebody else can think of a better name?    

Heating Energy Annual Total
HEAT ??
Or to add in the cost
Cost (of) Heating Energy Annual Total
CHEAT??

😂

I like those but its not an annual total.  The closest I can come is:
Cost (of) Heating Energy Annualised Ratio
CHEAR
or. slightly simpler,
Cost (of) Heating Annualised Ratio
CHAR

I quite like CHAR because that sounds like it might be a bad thing and the smaller your CHAR the better.

So developing that idea, I wonder if we can estimate our co2 per kwh and annual total co2 of our heating.

I wonder what the average co2 for UK electricity is between 23:30 and 06:30 which is when my heat pump power is downloaded?

It would seem to be about 150g per kwh on average at night in 2022, if I assume a cop of 3 then that is 50g per kwh for my heating, and about 750kg for the 15,000kwh of heat we use a year.

With gas that would be about 3,200kg (assume 215g per kwh heat delivered)

Probably a decent estimate but the CO2 intensity of electricity varies so much... very cold weather in winter also tends to be still so there wouldn't be much wind power generation when your consumption is highest. 

According to my EPC my household would produce 9.8 tonnes of CO2 per year! EPCs are just worse than useless:

"[the EPC calculation] uses a static baseline carbon intensity factor set in 2012 of 519g CO2/kWh – in reality, the National Grid has become much cleaner in recent years, which the actual up-to-date carbon intensity being 173g CO2/kWh" - https://www.kammaclimate.com/news/2024/06/understanding-sap-calculations-for-energy-performance-certificates/

98,00 kg / 0.519 g/kWh = 18,882 kWh. So that's what the EPC estimates our electricity usage is.

We actually use about 11,000 kWh electricity (no gas). Taking 173 g/kWh this is "only" 2 tonnes of CO2 per year. 

A new 'Home Energy Model' is to be implemented this year apparently, which hopefully won't be as useless. https://www.gov.uk/guidance/standard-assessment-procedure#full-publication-update-history 

I'd say that very much depends on where you live also.
It's currently snowing and so fairly cold, but this is my area right now at 2g, while I'm taking 22kw from the grid.



However south Wales is currently the worst at 216g



South Wales doesn't tend to be generally, it's more often west and east Midlands which are the dirtiest in my random observations

But does it make much sense to use regional carbon intensities? I know there are certain bottlenecks in the grid, but it is essentially one system. Thought experiment - if you switched on a heat pump in Bristol and at the same time switched off an identical one in Swansea, would the carbon intensity change? I would argue for accounting purposes it wouldn't.

Solarchaser

I'd say if there were no bottles necks, then you would be 100% correct, but in reality in Scotland, wind is curtailed rather than used in Bristol due to those bottle necks and so it's better to use it at very low grams of c02 than curtail it.

NedS

Reed_Richards said:

FreeBear said:

michaels said: If we are allowed to include timeshifting into our scop calcs then what is the scop of my heatpump that is powered by 7p per unit overnight leccy only via the v2h battery?!

Your SCOP would remain the same, but your running costs would be lower.

SCOP is based on the seasonal average of heat output (kWh) divided by electrical energy supplied (kWh). 

A more sensible measure would be the annual expenditure on whatever fuel you use (in pence) divided by heat used by your home in a year (kWh).  So (approximately) if a kWh of electricity costs you 25p (on average over the year) and that gets you 3 kWh of heat on a seasonal average then the ratio would be 8.33 p/kWh.  But if you can bring your electricity costs down to say 7p per kWh by time-shifting then the number would go up to 2.33 p/kWh.  Or if you heat with gas at 6p per kWh using a gas boiler that is 90% efficient on average the number would be 6.67 p/kWh.

All we are really lacking is a snazzy and memorable name for the quantity I am calculating.  Perhaps the Annualised Cost of Heat, ACOH?  Or maybe somebody else can think of a better name?    

Absolutely. COP (or SCOP) is a great way to determine your system is running in the right ballpark, and great for identifying when something changes or breaks (e.g, you suddenly go from a COP of 4 to a COP of 2), but ultimately we all just want lower running costs.

I get annoyed when people tell me the cheapest way to run my heat pump is slow and steady, 24/7. That's not a bad way to run a heat pump, but for us it is far cheaper to turn it off for 9-10 hours overnight and reheat the house from cold the following day. We use around 10-12kWh less electricity by turning off overnight. Unless the external temp is below 2C overnight, the house is too warm overnight, even set back to minimum. So for us it's cheaper to turn off overnight, save that 10-12kWh usage, and then run a slightly higher flow temp during the day (which is likely offset by the ambient temp being a few degrees warmer) achieving a similar COP and lower running costs. Having cheap electricity slots on the Cosy tariff helps where we can bump up the flow temps at half price.

Unfortunately we have no way of determining our Cost (of) Heating Annualised Ratio (CHAR) as, although we know our heat pump electrical input usage, we don't know the price per kWh for that usage, only the overall price per kWh for our whole house usage on that day.

michaels

NedS said:

Reed_Richards said:

FreeBear said:

michaels said: If we are allowed to include timeshifting into our scop calcs then what is the scop of my heatpump that is powered by 7p per unit overnight leccy only via the v2h battery?!

Your SCOP would remain the same, but your running costs would be lower.

SCOP is based on the seasonal average of heat output (kWh) divided by electrical energy supplied (kWh). 

A more sensible measure would be the annual expenditure on whatever fuel you use (in pence) divided by heat used by your home in a year (kWh).  So (approximately) if a kWh of electricity costs you 25p (on average over the year) and that gets you 3 kWh of heat on a seasonal average then the ratio would be 8.33 p/kWh.  But if you can bring your electricity costs down to say 7p per kWh by time-shifting then the number would go up to 2.33 p/kWh.  Or if you heat with gas at 6p per kWh using a gas boiler that is 90% efficient on average the number would be 6.67 p/kWh.

All we are really lacking is a snazzy and memorable name for the quantity I am calculating.  Perhaps the Annualised Cost of Heat, ACOH?  Or maybe somebody else can think of a better name?    

Absolutely. COP (or SCOP) is a great way to determine your system is running in the right ballpark, and great for identifying when something changes or breaks (e.g, you suddenly go from a COP of 4 to a COP of 2), but ultimately we all just want lower running costs.

I get annoyed when people tell me the cheapest way to run my heat pump is slow and steady, 24/7. That's not a bad way to run a heat pump, but for us it is far cheaper to turn it off for 9-10 hours overnight and reheat the house from cold the following day. We use around 10-12kWh less electricity by turning off overnight. Unless the external temp is below 2C overnight, the house is too warm overnight, even set back to minimum. So for us it's cheaper to turn off overnight, save that 10-12kWh usage, and then run a slightly higher flow temp during the day (which is likely offset by the ambient temp being a few degrees warmer) achieving a similar COP and lower running costs. Having cheap electricity slots on the Cosy tariff helps where we can bump up the flow temps at half price.

Unfortunately we have no way of determining our Cost (of) Heating Annualised Ratio (CHAR) as, although we know our heat pump electrical input usage, we don't know the price per kWh for that usage, only the overall price per kWh for our whole house usage on that day.

I guess for the majority either the HP is not powerful enough to recover an overnight setback in a sensible number of hours or can only do so by running at an inefficient high temperature.

I am surprised you save so much via the set back.  Maths says for example if you lose 1c per hour in room temp without 5kw of input then you will need an extra 5kw to raise the temp back by 1C so you will only actually get a saving in terms of the reduction in heat loss resulting from a lower difference between the set back temperature and the external temperature.  Your 10 hour colder period is quite long and I guess reducing the interior to exterior temp difference by 4C for all that period could reduce the heat loss from 5kw to 4kw.

On another board there is discussion of the same LG I I have and how the controls do not actually support using a higher flow temp to restore the temp from a setback followed by a return to a lower temp to maintain the desired temp once reached.

Reed_Richards

I have an LG heat pump and I also use a night-time set-back.  If I used the manufacturer-supplied controller then the "Air + Water" setting would give me Load Compensation as well as Weather Compensation.  Load Compensation should give you a higher flow temperature to restore the internal temperature from a set-back. 

I have a third party controller so use my own method.  From 15:00 my interior set temperature is 20.5 C.  This changes to 18 C  at 22:30.  The temperature falls overnight but has rarely reached 18 C by 04:00 when the heat pump comes back on targeting 20 C.  If it's not too cold out, it can get back to 20 C by 07:00 when my cheap-rate electricity finishes.  I target 19.5 C from 07:00 to 09:30, 20 C from 09:30 to 15:00 and that completes the cycle.

I think the idea of running a heat pump 24/7 slow and steady only works if you want the house at a constant internal temperature 24/7.  I certainly don't want that.          

michaels

I think with an external thermostat though you are limited to a flow temp based either on weather comp or a fixed temp?

We just use constant temp at the moment basically because our rads/balancing/rather thin upstairs pipes seems to give us 18 upstairs and 21 downstairs which works for us or be it at the price of excess heat and therefore heat loss downstairs overnight.

Reed_Richards

michaels said:

I think with an external thermostat though you are limited to a flow temp based either on weather comp or a fixed temp?

Yes indeed, with an LG Therma V heat pump that is the state of play.  How I wish heat pumps used the same OpenTherm system as many gas boilers so you could choose the controller you want without sacrificing control features.