COP - diminishing returns on investment?

michaels

QrizB said:

michaels said:

QrizB said:

michaels said:

Obviously the 10 year time horizon as mentioned is probably too short - I suspect the entire heating system would last 50? years

Just on that point, I didn't choose 10 years as the life of the system. 10 years represents a ~7% return on investment. If you had £1k in a SSISA and earning 7% (eg. you were invested in UKWIND) then over 10 years it would earn you another £1k.

Spending £1k to improve your COP means you're missing out on that £1k of returns over the next decade. So it's an approximate way to judge whether it's worth spending to cut your bills, or whether you should just keep the money invested and buy more electricity.

If I'd chosen 50 years, that's only a 1.4% return which is (in my opinion) unrealistically low.

I acknowledge (again) that you might not choose to look at this in purely financial terms, but this is the Money Saving Expert forum not the Planet Saving one.

Personally I would not expect a risk free real return on investment of more than about 0.5%

That's your choice, but this isn't a *real* return; it's a nominal one.

I'm not competent to explain discounted cash flow, but there are some good articles if you want to read about it on the internet. There's even a Wikipedia page.

It is pretty complicated though, although the investment is a fixed nominal amount (lets assume financed on a fixed rate, the cost of fuel is likely to rise at a similar rate to prices so the nominal size of the savings (relative to the fixed cost of the installation) will increase over time.  Govt index linked bonds return about 0% in real terms, anything else and there is market and counterparty risk.

Solarchaser

Since you tagged me @QrizB I read the thread.

I inadvertently ran my heating system with heat pump levels of flow temperature this year (45c), but keeping the double radiators I've always had.

I found that for all but December all was great, but during the 2-3 weeks of minus temperatures up here, the 45C Radiator temperature was not enough.

All my heating is at 7p/kwh, as it heat the tanks overnight on off peak rates.
During the day that heating would cost 25.6p/kwh, so does that mean my system has a scop of over 3??
🤔😜

michaels

Solarchaser said:

Since you tagged me @QrizB I read the thread.

I inadvertently ran my heating system with heat pump levels of flow temperature this year (45c), but keeping the double radiators I've always had.

I found that for all but December all was great, but during the 2-3 weeks of minus temperatures up here, the 45C Radiator temperature was not enough.

All my heating is at 7p/kwh, as it heat the tanks overnight on off peak rates.
During the day that heating would cost 25.6p/kwh, so does that mean my system has a scop of over 3??
🤔😜

Can you heat your tanks warmer or is the flow temp regulated by a mixer valve?  Perhaps you could control the flow rate if you can't control the temp?

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?!

FreeBear

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.

michaels

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.

I agree but I was just trying on Soulchaser's idea for size....

Reed_Richards

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?    

Solarchaser

michaels said:

Solarchaser said:

Since you tagged me @QrizB I read the thread.

I inadvertently ran my heating system with heat pump levels of flow temperature this year (45c), but keeping the double radiators I've always had.

I found that for all but December all was great, but during the 2-3 weeks of minus temperatures up here, the 45C Radiator temperature was not enough.

All my heating is at 7p/kwh, as it heat the tanks overnight on off peak rates.
During the day that heating would cost 25.6p/kwh, so does that mean my system has a scop of over 3??
🤔😜

Can you heat your tanks warmer or is the flow temp regulated by a mixer valve?  Perhaps you could control the flow rate if you can't control the temp?

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?!

To be fair, I was just being facetious. 

Until a few months ago, I was running a manual mixing valve, but didn't like how hot the radiators would be first thing in the morning, I had a spare hot water thermostatic mixing valve, which has a max of 45C and although I wanted maybe 50C, I thought 45C would be good enough... but its not really.
I've now bought an underfloor heating thermostatic mixer valve which has a max of 60C, and I'll likely set it to 55C and see how I go.

So the tanks are hot enough (about 82C) but the mixer can't go any higher.
The flow rate is controlled by a pump which i don't think is doing its best work either, so I'll be replacing that with a better one at the same time.
I can't complain, I bought 2 pumps for £50 2.5 years ago, so they have done well enough, but adding a loft room, so need a pump with a better pump head height anyway.

Solarchaser

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??

😂

Reed_Richards

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.

michaels

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)