General > General Technical Chat

What is the real story around heat pumps?

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nctnico:

--- Quote from: pcprogrammer on February 25, 2024, 07:00:25 am ---
--- Quote from: nctnico on February 24, 2024, 09:21:38 pm ---Just out of interest: Are there any ways you could reduce the amount of heat you need without sacrificing comfort?

--- End quote ---

Not really as it is already set reasonably low. I'm thinking about heating up more during the night at a reduced rate, but not sure if the offered pump will supply enough energy to reach the needed temperature rise on the coldest days when profit would be biggest.

--- End quote ---
Sorry I wasn't clear, I was hinting at adding insulation so you can reduce the amount of energy going out of the home.

tszaboo:

--- Quote from: Siwastaja on February 24, 2024, 08:29:08 am ---
--- Quote from: pcprogrammer on February 24, 2024, 08:00:33 am ---Paving the planet with solar panels or harvesting all the lithium in the world, etc, might only make things worse.

--- End quote ---

Don't take it too extreme, but there is something to this. Efficient solutions should be preferred and e.g. a simple air-to-air heatpump which costs 500€ to buy and uses a few dozen kg of common materials like plastics, iron, aluminum, copper, yet harvests 1kW (input power) * 2 (SCOP-1) * 24*365 * 0.5 (duty cycle) * 12 (years lifetime) = 100 000 kWh of free, renewable energy. A 4-5kWp PV system would then harvest say 5000 kWh/year * 20 year lifetime = roughly the same 100 000 kWh of free, renewable energy.

But the environmental cost of manufacturing the heatpump is probably smaller, it is significantly cheaper to buy, and it harvests energy during winter nights, too. This doesn't mean PV is bad, just something to think about for the priority list.

Lithium ion battery storage is then again at least an order of magnitude worse again. Especially if you have any low-hanging fruit like controlling the usage of electric hot water production which can easily store 20kWh worth of energy by just adding 500€ worth of control to an existing system. Compare the ecological footprint and install cost to li-ion battery system of the same size!

Then again, maybe such low-hanging fruit is not available. I'm not saying never to install battery systems. Just something to think about for priorities.

--- End quote ---
See, this is what makes sense. Using easy to install technologies to save energy on the existing houses. Building new houses with the new technology in mind. Leveraging technology without bankrupting ourselves.
The same way, we don't want to ban spark plugs for cars, just because we want people to switch to electric. And tell people who need a new boiler "just buy electric".
If OP installs an air to air heatpump maybe he can reduce the heating season here from 4-5 month to say 2 month. Buy installing heatpump on 2-3 rooms and using it additionally to the heating he has. Save 40-50-60% of the bill (and reduce CO2) with 1/20th the investment.

Siwastaja:

--- Quote from: tszaboo on February 25, 2024, 11:19:56 am ---See, this is what makes sense. Using easy to install technologies to save energy on the existing houses.
--- End quote ---

Fair enough, but in specific case of OP, air-to-water heatpump is such easy-to-install retrofit. It's a perfect match because of the existing under-floor and low-temperature radiators. The problem is only navigating past overly expensive turn-key solutions and either do-it-yourself or find the right contractors to do it with sensible cost. Total cost should be only marginally larger than 2-3 room air conditioner units (1000EUR each installed). If price difference is more than 2-3x (let alone 20x as you suggest) then something is wrong and you are not looking hard enough for the right supplier.

Zero999:

--- Quote from: pcprogrammer on February 25, 2024, 07:00:25 am ---
--- Quote from: nctnico on February 24, 2024, 09:21:38 pm ---Just out of interest: Are there any ways you could reduce the amount of heat you need without sacrificing comfort?

--- End quote ---

Not really as it is already set reasonably low. I'm thinking about heating up more during the night at a reduced rate, but not sure if the offered pump will supply enough energy to reach the needed temperature rise on the coldest days when profit would be biggest.

That is part of the experiment.


--- Quote ---Well you did start this thread on the basis that you had to get something to replace the wood burning, or perhaps you'd like to add labour for someone to come and cut/dry/handle/load the wood for you?  ;) We've seen this before with people claiming they get their wood for "free" so it's not a cost.... in their shallow analysis.

--- End quote ---

I never claimed the wood to be free, but do still have about 12m3 from one of our own trees. It was a hell of a job to take it down, partly due to my disease, but also because it was a very big oak tree to close to the house. Cutting up all the branches and the trunk took us weeks. Apart from that labor and the petrol for the chainsaw and electricity for the splicer it is "free" wood.  :-DD

The thread was started to find out if sales people are lying about air to water heat pumps having far worse performance then ground to water heat pumps, and what the noise levels are.

And as with everything on the net you have to filter and analyze the given answers to get to the bottom. Conclusion is that the two systems are not far apart and definitely not the factor two that one of the sales people claimed.

--- End quote ---
Oak is quite expensive. It might have been more economical to sell the wood and use the money to by pellets, or scrap offcuts, than burn that tree!

It's not just sales. I don't completely trust everything people say on forums such as these, when it comes to heat pumps, because it has the potential to be shaped by ones political stance. I'm not accusing anyone of lying, just bias, which many people are unaware off. This is true for both those who are strong advocates, as those who are against. Another thing is everyone's usage and climate is different.

It's very difficult to find objective data. Not only does COP, of an air source heat pump, depend on the inside and outside temperatures, but also the relative humidity.

I had a bit of a Google and found lots of contradictory information.

This laboratory test shows a COP of between 3 and 5, at 5°C, but it was done under very dry conditions. I live in a very humid climate and COP does down with high relative humidity, when the air temperature is 5°C.
https://www.nrel.gov/docs/fy23osti/85081.pdf

This Italian study is probably more relevant, as inland areas of Northern Italy have similar winter temperatures and relative humidity as Southern England. The downside is it's over ten years old and heat pump efficiency might have improved since then.
https://www.sciencedirect.com/science/article/pii/S187661021400071X?ref=pdf_download&fr=RR-2&rr=85afe559b8a379b5

A quote which I find concerning.

--- Quote ---The energy consumption due to the defrost cycles has to be considered in calculating the heat pump performance but the calculation methods proposed by the European standards ignore this effect.
--- End quote ---

Given this can I trust data based on European standards, or is this not the case and this is out of date information?

This one from Strathclyde shows slightly lower COPs.
https://www.esru.strath.ac.uk/EandE/Web_sites/10-11/ASHP_CO2/ccl-potential.html

Someone on a British forum complaining about a COP of 2.3 for space heating and 2.5 for water.
https://forum.buildhub.org.uk/topic/34775-is-my-cop-rubbish/

I think those who estimated a COP of 3.5 for me were optimistic. 2.5 seems more likely, given the data I've seen.

I've also realised I didn't take into account the fact that if I can stop using gas, which would also involve replacing my cooker with an induction hob, I can reduce my standing charge (a flat rate daily connection fee, which independent of usage), but then I have to factor in the fact it probably costs a bit more to run.

tszaboo:

--- Quote from: Siwastaja on February 25, 2024, 11:52:15 am ---
--- Quote from: tszaboo on February 25, 2024, 11:19:56 am ---See, this is what makes sense. Using easy to install technologies to save energy on the existing houses.
--- End quote ---

Fair enough, but in specific case of OP, air-to-water heatpump is such easy-to-install retrofit. It's a perfect match because of the existing under-floor and low-temperature radiators. The problem is only navigating past overly expensive turn-key solutions and either do-it-yourself or find the right contractors to do it with sensible cost. Total cost should be only marginally larger than 2-3 room air conditioner units (1000EUR each installed). If price difference is more than 2-3x (let alone 20x as you suggest) then something is wrong and you are not looking hard enough for the right supplier.

--- End quote ---
"Should be" is a keyword. It's not.
I've quickly looked up air to hot water pumps, they start at 3500. You get a subsidy, but only if they install it.

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