Author Topic: UK Heat Pump/Exchanger Heating.  (Read 2788 times)

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Offline paulca

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Re: UK Heat Pump/Exchanger Heating.
« Reply #25 on: March 16, 2019, 12:52:56 pm »
So electrical powered heating of any form...  He's a few indicative numbers based on a bit of research into power plants and electrical grids.

For every 100 units of energy you extract from fuel at a power plant, be that oil, coal or nuclear, only approximately 30-40 are converted to electrical power.  This means that a 1GW power plant is actually producing closer to 3GW of heat energy.  Some indicative figures here: https://www.brighthubengineering.com/power-plants/72369-compare-the-efficiency-of-different-power-plants/

Of those 30-40 units, up to 10%, are lost through the electrical grid.  (Based on https://data.worldbank.org/indicator/eg.elc.loss.zs)

So having taken the (often fossil fuel based) hit of releasing 1GW of heat, you only end up with around 300MW reaching homes.  Even if the heating system is 100% efficient, your overall efficiency is 30% or so.

Conversely, burning the fuel and using the heat directly as the primary product of the system the efficiencies are far, far higher with the only losses I can think of are the heat absorbed into the boiler system, the electrical power for pumps et al and loses through chimneys.  I'd poke a finger in the air and say at least 60-70% efficient.  Although, one would need to account for the energy requirements to supply that fuel to the homes rather than to a single power plant.
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Offline apis

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Re: UK Heat Pump/Exchanger Heating.
« Reply #26 on: March 16, 2019, 12:59:57 pm »
Here the ground temp BELOW 2m is 18oC.
I actually thought that was universal.  The lower you go the better apparently. Not sure it gets warmer but probably you have a better buffer on top.
Here it's about 7-8°C below ground. In many parts of the world, it was (and still is) common to build a root cellar, i.e. a room a below ground level, which would have had a good temperature for refrigeration. But as you noticed, how effective it will be depends on where you live.

If you start going really deep the temperature starts rising again, about 2-4°C per 100 m, so at 3 km depth you can be at above boiling temperature of water (at sea level pressure). But near the surface (below 1-2 meter) the temperature will be close to the yearly average.
 

Offline george80

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Re: UK Heat Pump/Exchanger Heating.
« Reply #27 on: March 16, 2019, 02:11:53 pm »

I'd poke a finger in the air and say at least 60-70% efficient.  Although, one would need to account for the energy requirements to supply that fuel to the homes rather than to a single power plant.

The spa Boiler I am going to use in gas form at least is very High efficency, 85% from memory.  Won't change much with Oil.
It was a while ago since I did it and would have to check the vid but from memory I think I was able to burn 20-30Kw worth of oil using a 12V Bilge blower pulling 4A. For this I'll call it 12W Max.
 I'll use an electric fuel pump also 12v Which from memory is 3A intermittent as it's a pulse type pump. 36w
Controllers etc wouldn't even be 1A so 12W.
Fan for house, 18w, Circ pump, probably 30W solar pump.

Call it 120w as over kill. For this electrical input I'll be getting 5Kw+ out of the burner with the oil. Not a bad result.
If I run it 10hrs a day, 1.2 Kwh or what 2 solar panels will easily produce and then some through winters days.

Oil is roughly 10Kw/h L , I reckon 3 Kwh average output, 4L day should allow for inefficiency and desired output.
Geez, had to recheck that, seems so low. Probably because I am more used to playing with burners cranking out 200-600KW worth of heat.  Call it 5L day for the hell of it,  35 Wk, 12 weeks say, 420L.

And here I am thinking I'd need a couple of IBC's.  ??? This is going to be more economical than I ever thought!

Thats the thing with liquid fuels, there is so much energy in them compared to electricity.
Last year my main 9KW array made 15000Kwh. That's 1.5 IBC's worth of oil. I could pick that up in a day, weekend at the outset.
To put it in another perspective, a LARGE car battery holds about 1Kwh of power. Imagine the space  1500 of the things would take up! Oil, 1.5 Cu m. batteries, 157.5 Cu m.
Oil would weigh about  1.275 ton. Car batteries, about 375 Tons !!  :wtf: 

Going to get a HE so I can run the domestic hot water feed through that with the output from the oil heater on the other side to preheat the domestic hot water. that should in itself take quite a few KW off the hot water demand.  I calculated on a full tank there would be about 4 Kw of energy needed just to bring the incoming water from the winter temps to the same temp it enters in summer.
If I can bump the hot water input to even 40oC, will save a lot of power right there.

Other alternative is I have a lot of roof left and a lot of smaller panels so if i can find a suitable electric HWS, I might just hook it to a stand alone array and pre heat the water that way.  Won't need to get up to full temp , any increase will lessen the load off the main heater.
 

Offline f4eru

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Re: UK Heat Pump/Exchanger Heating.
« Reply #28 on: March 16, 2019, 06:23:52 pm »
Quote
The spa Boiler I am going to use in gas form at least is very High efficency, 85% from memory.  Won't change much with Oil.
Yep.

Direct flame heating at home is much more efficient that resistive electrical, due to the bad efficiency of power stations.

Flame at home is approx. on par with heat pump if the electricity comes from only fossil.
 

Online coppice

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Re: UK Heat Pump/Exchanger Heating.
« Reply #29 on: March 16, 2019, 11:57:14 pm »
Double glazing is VERY rare here, Maybe a bit more popular down south where it's colder but still not typical by any stretch.
If you are in place with high temperatures in the summer, double glazing can be a problem. The greenhouse effect in the warm weather can incur more energy usage to cool the place than it saves in the cold weather. Various glass coatings can help reduce the greenhouse effect, but they can't eliminate the problem. If you are in a place where the summers are not hot enough to demand air conditioning, double (or triple) glazing is always a win.

In a few hot places, like Southern China, lots of new homes have double glazing, required by the building regulations. Its not for thermal insulation, though. Its for noise reduction in homes near highways.
 

Online james_s

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Re: UK Heat Pump/Exchanger Heating.
« Reply #30 on: March 17, 2019, 01:33:21 am »
I assume double glazing is double pane windows? As far as I know they have been a universal requirement in the USA since the mid 70s, I've seen a few old houses without them but most have been upgraded by now due to the substantial energy savings. In a warm climate it probably wouldn't matter as much but here houses with single pane windows feel cold and drafty.
 

Offline paulca

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Re: UK Heat Pump/Exchanger Heating.
« Reply #31 on: March 17, 2019, 11:50:23 am »
Yeah, double or even tripple glazed windows have two (or three) pains with a gap in the middle, can't remember if it's just air or a vacuum.
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Offline paulca

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Re: UK Heat Pump/Exchanger Heating.
« Reply #32 on: March 17, 2019, 12:09:18 pm »
Direct flame heating at home is much more efficient that resistive electrical, due to the bad efficiency of power stations.

Flame at home is approx. on par with heat pump if the electricity comes from only fossil.

The worst bit about the UK's plans is that it intends to replace gas with heat pumps.  Which when you read a bit of several charity energy advice websites and the like, none say it is a good replacement for gas.  Few even mention oil heating.  They say the primary target is to replace coal heating and electric storage heaters.

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Offline Towger

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Re: UK Heat Pump/Exchanger Heating.
« Reply #33 on: March 17, 2019, 04:12:47 pm »


The worst bit about the UK's plans is that it intends to replace gas with heat pumps. 

That makes as much sense as Brexit.  The house needs to be build to extremely high insulation standards and even still they are not great.
 

Offline richard.cs

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Re: UK Heat Pump/Exchanger Heating.
« Reply #34 on: March 17, 2019, 05:52:07 pm »
For every 100 units of energy you extract from fuel at a power plant, be that oil, coal or nuclear, only approximately 30-40 are converted to electrical power.
No argument there. Mid 30s are pretty typical except for combined cycle gas turbines which can be significantly over 50%
Quote
Of those 30-40 units, up to 10%, are lost through the electrical grid.
In my part of the world it's closer to 7% but I'll use your numbers. 10% loss on 40% is 36%, 10% on 30% is 27%. And for reference a 54% efficiency CCGT power plant with 7% loss would be 52%
Quote
Even if the heating system is 100% efficient, your overall efficiency is 30% or so.
Given the above 30% seems a little low, 40% would be perhaps more typical in areas where a significant amount of generation is from gas. In any case this discussion is about heat pumps which have a typical coefficient of performance around 3, varying depending on the inside and outside temperatures. 2 kW of heat is moved from outside to inside for each 1 kW used to move it, and 2+1 kW is dissipated inside. With 30% fuel-electricity that would give 90% heating efficiency, and with a more typical 40% fuel-electricity it would give 120%. Those numbers are sounding pretty good to me. More so when not all of the input to the grid is from burning fuel.*

For optimum performance the temperature difference should be minimised, so higher COP is achieved with ground source systems (warmer outside heat source) and heated-air or heated-floor inside (lower heat pump output temperature compared with wet radiators).

* Right now the total fuel-burning contribution to the UK grid is 1% coal, 35% combined-cycle gas, and 5% wood. A further 14% is from nuclear, but then "burning" uranium at home and using the heat directly is not a practical option for most of us.
 

Online james_s

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Re: UK Heat Pump/Exchanger Heating.
« Reply #35 on: March 17, 2019, 07:33:55 pm »
Direct flame heating at home is much more efficient that resistive electrical, due to the bad efficiency of power stations.

Flame at home is approx. on par with heat pump if the electricity comes from only fossil.

The worst bit about the UK's plans is that it intends to replace gas with heat pumps.  Which when you read a bit of several charity energy advice websites and the like, none say it is a good replacement for gas.  Few even mention oil heating.  They say the primary target is to replace coal heating and electric storage heaters.


That depends on the cost of gas and electricity. Here in the Northwest USA heat pumps work great, my mom's house has one in tandem with the gas furnace that was present when she moved there. I've set it up so the heat pump is used down to an outside temperature of around 30F at which point it switches over to the gas furnace which serves as the air handler for both systems. Even a pure heat pump is somewhat cheaper to run year round here as the climate is mild. Gas is around $1 per Therm (100k btu/hr IIRC) and electricity is approximately $0.08 per kWh.
 

Offline richard.cs

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Re: UK Heat Pump/Exchanger Heating.
« Reply #36 on: March 17, 2019, 08:35:56 pm »
That depends on the cost of gas and electricity.

Indeed it does, and the effect is calculable. If you compare a modern condensing gas boiler with an efficiency around 90% with a heat pump with a coefficient of performance around 3, then if the electricity:gas price ratio for a given amount of energy exceeds 3/0.9=3.3 then gas heating is cheaper. Prices per kWh in the UK are around £0.124 and £0.028 for electricity and gas respectively, so a ratio of 4.4. Here gas works out cheaper than a heat pump (with these COP and efficiency assumptions).

You can turn this on it's head and calculate the COP you need to achieve to break even. COPmin= PriceE/PriceG * EfficiencyG
With the numbers above you get a minimum COP of 3.95.

I am struggling to find measured real-world data for domestic style heat pumps, the COP I have used is a bit of a guess really. This: https://www.researchgate.net/figure/Average-heating-coefficient-of-performance-for-air-and-ground-source-heat-pumps-left-and_fig7_255759857 suggests 3.3-3.9 for air source at space heating temperatures (40 C hot side) and 4.5-5.4 for ground source where the cold side is significantly warmer. That would make ground-source cheaper than gas with current UK prices.
 

Offline paulca

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Re: UK Heat Pump/Exchanger Heating.
« Reply #37 on: March 18, 2019, 06:09:55 am »
That depends on the cost of gas and electricity.

I think this is the nub of the problem.  It's cheap to carry on as we are.  If you give people cheap fuel bills they will burn whatever and at the same time cry about Big Oil ruining the planet.  If you make it cheap and profitable for big energy companies they will burn lorry loads of grannies to make money.

Of course attempts at costing environmental damage (carbon tax et al) have typically been exploited but at least it's trying.  Although, generally, in the UK anyway, those taxes get levelled at the consumer, not the energy companies.
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Offline paulca

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Re: UK Heat Pump/Exchanger Heating.
« Reply #38 on: March 18, 2019, 06:15:03 am »
In any case this discussion is about heat pumps which have a typical coefficient of performance around 3, varying depending on the inside and outside temperatures. 2 kW of heat is moved from outside to inside for each 1 kW used to move it, and 2+1 kW is dissipated inside. With 30% fuel-electricity that would give 90% heating efficiency, and with a more typical 40% fuel-electricity it would give 120%. Those numbers are sounding pretty good to me. More so when not all of the input to the grid is from burning fuel.*

Not sure about the 2+1kW as I'm fairly sure the compressors are usually mounted outside due to noise and space.  A lot of the energy from the compression is doubtless lost.

But fair enough.   What about the issue with "idle time"?  During the work week, I can leave my heating off for 8 hours a day when I'm out and 7 hours at night when I'm asleep.  Only because I can heat the house in under 30 minutes when I switch it back on.  If I went for a heat pump solution I can't really do this anymore.  I would need to leave it running almost constant to keep the heat in the house.  It's too early in the am here for me to crunch those numbers, I'll maybe try later.
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Offline richard.cs

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Re: UK Heat Pump/Exchanger Heating.
« Reply #39 on: March 18, 2019, 10:14:31 am »
Not sure about the 2+1kW as I'm fairly sure the compressors are usually mounted outside due to noise and space.  A lot of the energy from the compression is doubtless lost.
Most of that 1 is mechanical energy that is transferred into the working fluid, not motor inefficiency. Often the refrigerant is the motor coolant so much of the motor losses end up inside too.
Quote
But fair enough.   What about the issue with "idle time"?  During the work week, I can leave my heating off for 8 hours a day when I'm out and 7 hours at night when I'm asleep.  Only because I can heat the house in under 30 minutes when I switch it back on.  If I went for a heat pump solution I can't really do this anymore.  I would need to leave it running almost constant to keep the heat in the house.  It's too early in the am here for me to crunch those numbers, I'll maybe try later.
Yes, clearly if you can heat with much higher power then you can heat only when occupied. Your unoccupied temperature is then lower and you loose less heat in that time because of the lower delta-T. This depends a lot on occupation patterns, insulation, etc. so will be quite variable.

I suspect however that the effect is quite small, my house when unheated falls perhaps 1-2 C in about 10 hours when I am at work with a delta to the outside of around 15-20 C. This means that the delta-T and therefore the heat flux out of my house is only about 10% lower than it would have been had I heated the house during that time.
 

Offline awallin

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Re: UK Heat Pump/Exchanger Heating.
« Reply #40 on: March 18, 2019, 06:01:18 pm »
I am struggling to find measured real-world data for domestic style heat pumps, the COP I have used is a bit of a guess really. This: https://www.researchgate.net/figure/Average-heating-coefficient-of-performance-for-air-and-ground-source-heat-pumps-left-and_fig7_255759857 suggests 3.3-3.9 for air source at space heating temperatures (40 C hot side) and 4.5-5.4 for ground source where the cold side is significantly warmer. That would make ground-source cheaper than gas with current UK prices.

here up North where we need a lot of heating in the winter they say the COP also depends on what kind of heat you want the pump to deliver.

If you have 'normal' water-filled radiators where the pump heats the radiator-water then it needs to be up to +50C in the winter when it's -10..-20C outside. ground-source COPs maybe in the 3-4 range.
OTOH many new homes are built with water-circulating floor-heating where the water in the floor only needs to be heated to maybe +25..+35C to keep that same +22C room-temperature in the winter. ground source COPs in the 4-5 range (?).


 

Offline richard.cs

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Re: UK Heat Pump/Exchanger Heating.
« Reply #41 on: March 18, 2019, 06:47:51 pm »
Yes, those numbers sound believable, and a clear demonstration of why heat pumps are best when coupled to underfloor heating or to warm air circulation - conventional water filled radiators just have too little surface area so need to be hotter, although I suppose they could be oversized if you were designing for a heat pump. It does mean heat pumps may be a poor choice to retrofit in place of a gas boiler unless that boiler was already heating floors.

My house has a relatively inefficient non-condensing gas boiler and a plumbing arrangement that was obsolete the day it was installed (sometime in the 1970s). "Single pipe" heating is interesting, a single loop of pipe from the boiler and back with radiators tapped off it such that they are in parallel to a short length of pipe. The boiler and pump keep the loop of pipe hot, and the radiators thermosiphon off the loop - the pump alone cannot force any significant flow through them. Each radiator on the loop is larger than the one before because of the dropping temperature, but the first one is tiny and means I have to keep the boiler outlet temperature right up to keep that room from getting too cold. It's not inherently a bad system, but I don't think they really got the ratio of radiator sizes right on mine.
 

Offline paulca

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Re: UK Heat Pump/Exchanger Heating.
« Reply #42 on: March 22, 2019, 08:31:08 am »
I am buying a house which has a similar heating system.  What is worse than how the radiator circuit is fed is how the hot water system works.  Before those single pipe can get to the radiator they are first pumped through an exchanger coil in the hot tank in the "hot press" cupboard.  So whether you wanted hot water or not you are still exchanging the heat into it.  The hot tanks are insulated, but that doesn't go very far.

If you DO want hot water, even to wash the dishes you have three choices, use the kettle, run the heating for 45 minutes to an hour to heat the hot tank (as well as the radiator circuit which would be a waste in summer) or turn the immersion heater on for at least 20 minutes and I'm sure some of that leaks into the radiator circuit in the water and copper piping.

Currently I live in an appartment build in 2004 to high insulation standards with a gas  combi boiler which can heat hot water and radiators completely separately.  Hot water is instant and only runs the boiler when the tap/shower is on.

I am already planning to upgrade the new house built in the 1970s, to a gas fired combi boiler, but at a cost of £3,000-5,000, in addition to renewing the insulation standard.
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Offline richard.cs

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Re: UK Heat Pump/Exchanger Heating.
« Reply #43 on: March 22, 2019, 09:23:19 am »
I am buying a house which has a similar heating system.  What is worse than how the radiator circuit is fed is how the hot water system works.  Before those single pipe can get to the radiator they are first pumped through an exchanger coil in the hot tank in the "hot press" cupboard.  So whether you wanted hot water or not you are still exchanging the heat into it.  The hot tanks are insulated, but that doesn't go very far.

That system is very unusual (at least in the UK), are you totally sure that's how it's plumbed? Much more common is having the hot water tank thermosiphon off the boiler then have the radiators in parallel with it but pumped. You get either hot water or hot water and radiators, but can't do heating without hot water. By the '70s single-pipe was nearly dead, mine is oddball enough, something like yours is pretty much unheard of, especially post-war.

You could almost certainly rearrange the plumbing to allow independent control of hot water and heating for much lower cost than a new boiler, I suspect easily sub-£1000.
 

Offline paulca

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Re: UK Heat Pump/Exchanger Heating.
« Reply #44 on: March 22, 2019, 03:02:45 pm »
Yea, fairly sure it has a single pipe in and single pipe out.  You may be right the hot tank might be in parallel but I'm pretty certain it only has a single "ON/OFF" function for the boiler, although I haven't checked that closely.

Other houses I have lived in with oil fired heating have been the same, just an ON/OFF for radiators and hot water.  Was the same for coal fired heating in the 80s.

If I managed to get my offer accepted I'll know more, but I fully intent to modernise the energy rating and heating in the house to gas fired combi system.  Looks like with government incentives it could be much cheaper than the worst case 2-3k.
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Offline richard.cs

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Re: UK Heat Pump/Exchanger Heating.
« Reply #45 on: March 22, 2019, 04:56:37 pm »
I fully intent to modernise the energy rating and heating in the house to gas fired combi system.

Sure, although combis are not the best solution for everyone, depending on the house and the usage patterns.

Back on topic for this thread you could even have a heat pump, especially if you're ripping everything out and re-plumbing anyway. The economics depend a lot on what you expect the relative prices of electricity and gas to do in the future, a few posts back we got numbers for current UK prices that make it slightly cheaper to run ground-source heat pumps than gas boilers especially when coupled to underfloor heating.
 

Offline paulca

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Re: UK Heat Pump/Exchanger Heating.
« Reply #46 on: March 22, 2019, 05:12:23 pm »
Back on topic for this thread you could even have a heat pump, especially if you're ripping everything out and re-plumbing anyway. The economics depend a lot on what you expect the relative prices of electricity and gas to do in the future, a few posts back we got numbers for current UK prices that make it slightly cheaper to run ground-source heat pumps than gas boilers especially when coupled to underfloor heating.

I expect due to the age of the house (even with improved insulation) the ROI on the heat pump might not be viable.  Unless as you suggest the government start ramping up the price of gas, which is plausible in the next decade.
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Online IanB

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Re: UK Heat Pump/Exchanger Heating.
« Reply #47 on: March 22, 2019, 05:26:00 pm »
Yea, fairly sure it has a single pipe in and single pipe out.  You may be right the hot tank might be in parallel but I'm pretty certain it only has a single "ON/OFF" function for the boiler, although I haven't checked that closely.

Other houses I have lived in with oil fired heating have been the same, just an ON/OFF for radiators and hot water.  Was the same for coal fired heating in the 80s.

A system I am familiar with has separate timers and on/off controls for heating and for hot water. There is a circulating pump followed by diverter valves to feed the output from the boiler either to the radiators, or to the hot water tank, or to both. Obviously in the summer you don't want the radiators on, so the system can provide hot water alone without heating. There are also thermostats for the house and for the hot water, so even if the hot water is "on" by the timer, the tank thermostat will turn off the water heating when there is no demand for hot water. The boiler only runs when there is either hot water demand, or heating demand, or both.
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Online IanB

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Re: UK Heat Pump/Exchanger Heating.
« Reply #48 on: March 22, 2019, 05:30:15 pm »
the "hot press" cupboard

That's a new one on me. I've never heard it called that before. It's always been the airing cupboard.
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Online nctnico

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Re: UK Heat Pump/Exchanger Heating.
« Reply #49 on: March 22, 2019, 05:40:16 pm »
So electrical powered heating of any form...  He's a few indicative numbers based on a bit of research into power plants and electrical grids.

For every 100 units of energy you extract from fuel at a power plant, be that oil, coal or nuclear, only approximately 30-40 are converted to electrical power.  This means that a 1GW power plant is actually producing closer to 3GW of heat energy.  Some indicative figures here: https://www.brighthubengineering.com/power-plants/72369-compare-the-efficiency-of-different-power-plants/

Of those 30-40 units, up to 10%, are lost through the electrical grid.  (Based on https://data.worldbank.org/indicator/eg.elc.loss.zs)

So having taken the (often fossil fuel based) hit of releasing 1GW of heat, you only end up with around 300MW reaching homes.  Even if the heating system is 100% efficient, your overall efficiency is 30% or so.
As usual thinking in terms on efficiency isn't getting people anywhere.
The trick of a heat pump is that it moves more energy than it consumes. This is specified as the COP value. For example: if you put 1kW of energy into a heat pump with a COP of 2.5 you'll get 2.5kW worth of heat moved using that 1kW of electricity. For an electric heater you'd have to burn 2.5kW/0.4 (power plant efficiency)=6.25kW worth of fuel (gas/coal/whatever). A gas boiler needs to burn around 2.5kW/0.95=26kW worth of fuel. Using the heat pump you have to burn 1kW/0.4=2.5kW worth of fuel. And that is where the savings are coming from when using heat pumps. In theory. In practise you'll have to be very careful to check whether a heat pump delivers the COP value in the operating temperature range you need it the most. Quite often the name plate COP value is the most optimal one. The example also shows that you'll need a heat pump with a COP well over 3 over the entire operating temperature range to make a significant difference in CO2 output.
« Last Edit: March 22, 2019, 05:46:16 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 


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