General > General Technical Chat
What is the real story around heat pumps?
Zero999:
--- Quote from: zilp on February 21, 2024, 09:57:05 pm ---Price results from supply *and* demand. Limited supply with decreasing demand still leads to decreasing prices. As the majority of gold demand is from speculators, there is no fundamental reason why demand couldn't decrease (as opposed to technical uses, say, where the practical value of the products that contain gold and where gold is hard to substitute drive the demand). Really, what keeps the value of gold up is exactly such marketing campaigns that mislead people who lack deeper economical understanding into "investing" in it, because that is what generates the demand.
If you buy gold, that's a bet on other people buying gold, and them doing so at a higher rate than gold is supplied to the market, so that you can later sell it to them. That's it.
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Just look at the value of gold over the last 100 years. There are peaks and troughs but there's a clear upward trend. Yes I might lose some money, so I certainly wouldn't put all of my money into gold. On the other hand, I know if I replaced my gas boiler with an electric heat pump, it will lose money, so it would be a dumb investment for me. I'm not going to buy a system which will cost a lot of money and cost more to run. It would be like me trying to persuade you into investing in a new paper magazine publication. It will lose money.
https://www.macrotrends.net/1333/historical-gold-prices-100-year-chart
--- Quote ---There is no need to make up my mind, you just have to pay attention.
I am *currently* (as in: most of February so far) heating with a COP of around 600%. As in: Right now, my heat pump draws 476 W electric (pumps and everything included) and outputs 2786 W of heat, so 2786 W / 476 W = 585 % COP.
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Well good for you, but I've hardly used any gas this February because it's been so mild. It's possible I would get a COP of 600% or higher at the moment, since the UK is milder in winter than Germany, but if I'm not using it, then it's irrelevant. I've used my heating a bit this evening because the temperature has dropped to 4°C, but the boiler didn't run for long.
--- Quote ---Which I mentioned above to explain why an average of 350% is reasonable, even though the COP can be lower during really cold days.
To compare heating systems, you obviously have to use annual averages, and that certainly is not 600%.
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Okay, I accept 350% is a reasonable figure and that I shouldn't just go on the worst case, given others here have told me the same thing.
--- Quote ---
--- Quote from: Zero999 on February 21, 2024, 08:34:10 pm ---Natural gas is a clean fuel, so the exhaust won't be any more dirty than my boiler.
--- End quote ---
Well, it is clean in comparison to other fuels. But it is not clean as in "doesn't leave any residue". Whether it would be dirtier than your boiler isn't really that easy to say, as the dirt that results from the combustion really depends on the conditions.
--- Quote from: Zero999 on February 21, 2024, 08:34:10 pm ---Assuming an electric heat pump would give a COP of 300%, a gas one would give a COP of 160%
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How did you get to that number?
--- End quote ---
Given:
The gas engine has an efficiency of 30%
The heat pump system a COP of 300%, i.e. for every 100W of mechanical power from the engine, I get 300W of heat.
Calculate the total COP of the heat pump, driven from the gas engine:
100W of power goes in:
The engine is 30% efficient, thus produces:
30W power to the shaft, which is delivered to the heat pump, which generates three times as much heat 30W*3 = 90W
70W of heat, which isn't wasted but goes into my home.
Total heat to my home 90 + 70 = 160W, hence a total COP of 160%
--- Quote ---
--- Quote from: Zero999 on February 21, 2024, 08:34:10 pm --- and given gas costs a quarter of the price, it would pay for itself within a few years.
--- End quote ---
What price are you assuming for a gas-driven heat pump, and how did you arrive at it?
I have no idea what they cost, but I would expect them to be even more expensive than electrically driven ones as they are more complex to build (combustion engine vs. electric motor) and more difficult to install (need a gas line i addition to electricity and potentially refrigerant lines)!?
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I don't know what the actual cost of a gas powered heat pump is. Yes it would be more expensive, but typically the cost of the heat pump itself is only a small proportion of the total system. At least with a gas powered system, I know it would pay for itself, unlike an electric one. If I've changed my heating to be heat pump compatible and the market changes, I can always move to electric in the future.
EDIT:
Climate change and politics removed.
Someone:
--- Quote from: tszaboo on February 22, 2024, 09:22:38 am ---
--- Quote from: Someone on February 22, 2024, 02:16:37 am ---
--- Quote from: tszaboo on February 21, 2024, 10:34:44 pm ---
--- Quote from: Someone on February 21, 2024, 08:33:57 pm ---
--- Quote from: nctnico on February 21, 2024, 12:35:33 pm ---
--- Quote from: Marco on February 20, 2024, 11:21:19 pm ---Since PV provides a glut of power in summer, recharging is hardly an issue.
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It is an issue as there is a relatively short peak power output from solar panels. A common solar panel setup with 12 panels, can deliver around 4kW of output for a couple of hours per day. So either you need a large heatpump capable of taking in 4kW of power and convert this into heat that goes into the ground (assuming the ground can absorb it quick enough) OR have a large battery pack which can smear out putting the energy into the ground over time. Neither is cheap / cost effective. And then you'll still need electricity to get the heat out of the ground again. Where is that coming from? My estimation is that conversion to/from hydrogen (in some form) you can store above ground is more cost effective.
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Again with your pushing of solutions and completely ignoring/side stepping the practical ones (pretending like no other options exist).
Oversize the solar array, then it will produce enough energy in winter.
Sure not everyone has the physical space for that, but few have the physical space for ground source thermal storage/dissipation.
--- End quote ---
Almost nobody has place for that here. I have a system that covers my yearly electricity consumption, in fact makes an extra MWh. And I needed 5 GJ heat this december, which is 1400KWh, while my solar made 52KWh, which is a factor of 27. Even with SCOP of 5, it's just not going to be worth it to install 6x the solar on my roof, no space, no money for it.
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Which you know... I said (and you quoted). The size of that setup is comparable to the sustainable footprint ground source heating in those cold places where little to no air-conditioning is needed (and solar production falls way off in winter).
Why go straight to extremes with a pure solar setup? its a convenient strawman? Energy supply is almost always cheapest as a mix of things.
Sizing solar arrays to the inverter or export limit is old thinking. Panels are cheap and adding more capacity (vertical for winter production for example) can be cost effective for many.
Also to be pedantic you don't need 5 GJ of energy for heating, you want 5 GJ of energy for heating. That's a choice and how you supply it is up to you (and you can pay for it).
--- End quote ---
I'm a bit confused, in one comment you say we should oversize solar system to cover winter energy needs. When I show you it's not practical, you say that's not what you said. So then what is your suggestion?
--- End quote ---
Ok, so I add back in the original quote tree above rather than your cherry picking and dithering (since you claim to forget why this has happened).
Marco points out that thermal ground sources can be cheaply recharged recharged with solar power when it's running in excess and the price of energy is at its lowest.
nctnico proposes there are only two possible solutions and says since neither of those is economic then the entire idea is a non-starter
I point out that's a dumb simplification as there are other solutions, and include an example
You argue that won't work for you and say it is not practical for the majority
I point out that your generalisation is over dramatic and, wrong on several points.
There are many ways to get more thermal energy when it's needed. But there are no universal solutions that fit all, or situations that apply to all (beyond the laws of physics...).
Always jumping to single solutions for energy are putting up strawmen, 100% solar, 100% wind, 100% CO2 capture, heating only from seasonal storage. They're all as dumb as each other. Most people can and do leverage the diversity of the gird to provide their energy needs, backed with things that are impractical on a domestic level like pumped hydro and nuclear power.
Talking about thermal ground sources without considering the energy recharge is just abusing another finite resource, which has little to no oversight. Pretty much the same as logging national parks to burn the wood (there are people doing that too). Tragedy of the common.
--- Quote from: tszaboo on February 22, 2024, 09:22:38 am ---And yes, I do need 5GJ for a winter to be bearable in my home, dropping temperatures lower than most people keep here would be a respiratory hazard.
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You're not needing that, its a want. As has been said repeatedly and in this thread even if heating is a need for health, heating the whole house is still a want.
But it seems this thread is now just the (outlier) UK gas price discussion, and the rest of the world still cant talk openly about heat pumps.
NiHaoMike:
--- Quote from: Zero999 on February 22, 2024, 09:24:50 pm ---I don't know what the actual cost of a gas powered heat pump is. Yes it would be more expensive, but typically the cost of the heat pump itself is only a small proportion of the total system. At least with a gas powered system, I know it would pay for itself, unlike an electric one. If I've changed my heating to be heat pump compatible and the market changes, I can always move to electric in the future.
--- End quote ---
How about compare it to just a CHP generator? If gas is so cheap compared to electricity, you could make a profit heating your house. It also wouldn't need any redesign of the plumbing for lower temperature, actually engines don't like to run too cool and so there would be valves to regulate the temperatures.
m k:
--- Quote from: Zarhi on February 22, 2024, 08:53:28 am ---That's is situation with air source heat pumps from this morning:
Outside temp 2°C, humidity about 60%, clear sky, no rain, no clouds, no fog.
Pictures taken 3-4 minutes after defrost cycle completion.
--- End quote ---
Looks can be misleading.
The structure is what it is because air is not dense enough that lesser surface area would be enough.
Actual operation happens between refrigerant and inner wall of the pipe.
So the machine doesn't know that there is frost, generally it only knows that compression is fine or not.
Condenser/evaporator can be insufficient when general operation changes from the normal sufficient operation.
It can still be fine with visually not so fine looks.
tom66:
Depending on the model, some heat pumps just detect that they have fallen in efficacy (due to airflow drop) whereas others do actually measure for ice on the fins.
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