Air Source Heat pump discussion - facts only please

[Zak33]

Hello good people


I think it's time to start pondering long term alternative heating solutions for our homes, and the one that intrigues me the most is Air Source Heatpumps to water radiators

My knowledge is minimal right now and so I ask you all for your input and in each case I ask... no.. I beg.....

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OK - from where I am sitting it looks like it works thus - tell me I'm wrong please, where I am wrong and add detail, experience etc

1. The Airsource heat pump runs on electricity
2. It will only work on a well insulated home as it is a permanent source of back ground heat and not red hot radiators
3. Outside your home is a large unit that looks like and aircon unit, except it is taking ambient warmth from the outside air, and using a refrigerant system similar to an A/C unit, it puts that small amount of warmth into a waterloop that warms your home radiators and potentially also a hot water tank
4. It looks as though it needs to run a long time to take enough warmth from the outside winter air to warm the water loop enough for a result and therefore must be a very efficient system

My confusions arise thus -

If I want my (well insulated) home at say 18C, and the outside air is averaging 5C, just how much electricity does the system need to use to pull enough winter air through to remove the energy from the air?

Ie - elephant in the room.. the temp drops to below freezing and my house is only at 12C ..how long before we all die in our beds as the temp plummets?

[kalniel]

My confusions arise thus -

If I want my (well insulated) home at say 18C, and the outside air is averaging 5C, just how much electricity does the system need to use to pull enough winter air through to remove the energy from the air?

Ie - elephant in the room.. the temp drops to below freezing and my house is only at 12C ..how long before we all die in our beds as the temp plummets?

Some info from EDF: https://www.edfenergy.com/heating/ad...eat-pump-guide

The amount of heat energy you need to put into your house is the same to get to your desired temperature, regardless of method, so you can compare costs per kWh.

At the above link, referencing the energy saving trust, they put the 'typical' cost at 4.7p per kWh, compared to 4.6p for a gas boiler, and 9-16p for electric heaters.

To get the calculations you need for your house, first work out how many kWh you currently use for heating - this will be on your gas bill probably - if you know the efficiency of your boiler then adjust for that too (usually around 90%). Then look up the CoP (efficiency) for the heat pump you are interested in. Divide the kWh you need by the CoP for your possible heat pump and you'll arrive at roughly the amount of electricity you need to achieve the same level of heating.

Hopefully you can get the CoP average across the range of temps you're likely to experience in the UK.

Temperature dropping to below freezing is no problem, there's still a lot of energy that can be extracted. If you get to -273C on the other hand

[Jonatron]

Just googled for a PDF with some CoP's: https://www.lg.com/gr/download/resou...04443_1641.pdf
LWT : Leaving Water Temperature, OAT : Outdoor Air Temperature
LWT 35°C at OAT 7°C 4.60
LWT 55°C at OAT 7°C 2.80
LWT 35°C at OAT 2°C 3.52
It works against you, because the colder it is, the more heat you need, but it gets less efficient. So I guess you'd need to oversize the system to cope with the coldest days.
As the efficiency drops as you increase the LWT, you'd want to keep the LWT as low as possible, but lower LWT = bigger / more radiators needed.
Why would you let your room temperature drop to 12C? You could have cheap (to buy, not run) electric heaters for emergencies.

What makes more sense to me is solar powered air conditioning, because sunnier = hotter = more solar power = more air conditioning.
The UK is unfortunately located where there's little solar power in the winter when you need more power because it's cold. So unless it's windy, there's not a lot of renewable energy about in winter.

[Saracen999]

I have been pondering this for a while, due to gas boliers being 'banned' in a few years. My current boiler works well enough for now but is old enough that I know the clock is ticking. And when the inevitable happens, do I get gas again while I can, or does something (anything) else make more sense environmentally, while still being both effective enough to be pragmatic, and not ludicrusly expensive up-front?

My conclusion, so far, is me=confused.

So will be watching this like a hawk. Nice one, Zak.

[jim]

Ie - elephant in the room.. the temp drops to below freezing and my house is only at 12C ..how long before we all die in our beds as the temp plummets?

The problem here is not so much how good the heat pump is, it's that if your house has dropped to 12C then the insulation is probably not good enough. I do have some electrical things running 24x7, e.g. one of the computers, the fridge freezer etc, which no doubt brings up the temperature of my house slightly, but even when we've been away on holiday it doesn't really drop below 16. It is not detached, which helps greatly. We have only turned the heating on once so far since the summer, and that was for a couple of hours earlier this month. The house is either A or B rated, I can't recall which.

I think this is where you'll see a lot of misleading information - because without doubt, a high powered gas boiler can warm up houses that are so poorly insulated you can feel the draught. A heat pump just isn't going to do that. But especially with grants, we are likely to see people fitting them who full well know they're inappropriate, and buyers will blame the technology.

If you consider houses at the top end of the passivhaus rating scales, the insulation is sufficient that they can in some cases do without any heating at all. If you look, they claim that their "C" rating is less than half as polluting as an "A" EPC. However, my house was designed to be energy efficient and built in that fashion. As far as I'm aware, to achieve high-end passivhaus ratings normally means building to a very careful design with significant investment in insulation and energy recovery. I imagine that trying to turn a Victorian house into a high-rated passivhaus without a lot of money or just knocking it down altogether would be nigh-on impossible. And that will be the challenge for many.

[Jonj1611]

I am not sure what you currently have but if you are seriously looking at heatpumps, ask how you will heat your water.

We have a combi-boiler, which obviously does both but heatpumps as far as I understand any heated water has to go to a insulated tank(like the good old days) and even then its not that hot.

[Zak33]

OK lets answer some of my own statements


My house is often at around 12C downstairs becaue I refuse to pay for oil for heating unless its very cold weather. Jumper and shirts, multiple layers of clothing are default in my home, there are no t-shirt days in winter
Upstairs is always warmer as you would expect naturally.

I have a well insulated home and I heat it on colder evnings through Oct and Nov with a wood fired stove until the heating finally needs to go on, around about December.

I have an insulated hot water tank and have never owned a combi boiler. Hot water is heated by the oil powered boiler and is quite cost effective. It has an Immersion for low oil times/emergency

I am researching this simply because IF it's cheaper to run long term I will budget a swap.

But I fear it isn't from the above prices. With electricity prices at an all time high and going up I fear it will be as expensive as oil

[Zak33]

J
What makes more sense to me is solar powered air conditioning, because sunnier = hotter = more solar power = more air conditioning.
The UK is unfortunately located where there's little solar power in the winter when you need more power because it's cold. So unless it's windy, there's not a lot of renewable energy about in winter.

Air con has no interest for me. It's a luxury in the UK

I want to get a warm house for as little money as possible, low maintenance and it MUST be rock solid and reliable.

[Zak33]

Kal's link to EDF is interesting.


Air source heat pump pros and cons
Air source heat pump advantages

Highly efficient source of heat and hot water
Zero carbon if used with a renewable tariff
Can closely match the running costs of other home heating systems
Installation cost offset by Renewable Heat Incentive payments
Low-maintenance with a long service life
Some systems can provide cooling in the summer


Air source heat pump disadvantages

Lower output temperature than conventional boilers – you may need to update your insulation and invest in bigger radiators too
May work best in older homes as part of a hybrid system with a conventional boiler
Need outdoor space, and can be noisy
Expensive to install and works best with a water tank
Don’t work as efficiently in extremely cold weather

[Zak33]

the surface area of the radiation items seems key...

ie underfloor heating or enormous radiators

[Zak33]

as a secondary thought.....

do we consider the COP (Co efficient of Performance) as a trustable figure?

I mean... few cars ever hit their MPG or CO2 figures in any normal use. Do we trust them?

A quote from a website today for example

"For every 3Kw of heat that an air source heat pump produces, it uses only 1Kw of energy.
This measurement is an example of Co-efficient of Performance, or “COP”.
While the average COP for air source central heating is 3:1, traditional boilers only have efficiency rates of around 75-80%."

So are we to believe that it's really 3 times out for every 1 in? And if so.. at what outdoor temp?

[pp05]

I have been pondering this for a while, due to gas boliers being 'banned' in a few years. My current boiler works well enough for now but is old enough that I know the clock is ticking. And when the inevitable happens, do I get gas again while I can, or does something (anything) else make more sense environmentally, while still being both effective enough to be pragmatic, and not ludicrusly expensive up-front?

My conclusion, so far, is me=confused.

So will be watching this like a hawk. Nice one, Zak.

Unless the govt lets gas price rip so as to make moving to heat pump system sensible there is still niggles that need ironing out. I don't think everyone can do it logistically or financially.

If you have a boiler on its last legs you could always replace with the same model as a like-for-like and save on plumbing. The other thing I'm noticing in marketing literature of new gas boilers is the sticker 'hydrogen ready' which will allow them to be modified in the future to move off gas. The infrastructure isn't there yet but will be down the line.

Another downside I'm hearing is heat pumps as it presently stands will lower your epc rating based on current way its done. So if you're renting, that might be an issue.

For now it's gas boiler > heat pump > electric boiler.

[jimbouk]

If you have space then ground source heat pumps make a lot more sense. Space can either be a lot of land (seen one going under a field where I used to live) or down if you can get a big drill in.

Recent BBC article was light on numbers but the thing that stood out for me was

Will it be cheaper to run than a gas boiler?

Right now, given the soaring price of gas, it's possible, but it's not clear whether heat pumps will be cheaper to run in the long run.

Citation needed to be fair, but given all the other work needed for them even to warm a house with larger radiators and an improbable amount of insulation in many homes in not sure where the push is coming from other than "there's nothing else viable on the market"?

[kalniel]

the surface area of the radiation items seems key...

ie underfloor heating or enormous radiators

Yep - this is just a side function of having cooler water going around them so less heat will get transferred to the room for the same surface area.

For my condensing gas boiler that's somewhere around 70C so that the water gets back to the radiator below 55C and can be used to extract energy from the gas exhaust.

For heatpumps it's more like 35C which if I used the same radiators, would take a lot longer to heat rooms (I can't remember the maths for how proportional it is - how much larger the radiators need to be to account for the difference, but it's quite a lot, hence heatpumps might be always on).

[Zak33]

I wonder if there is a system of storage... where the house is split into zones, and you only warm the ones you need and to do that quickly, you have a large store of hotter water or a ... large lump of stomething that is getting warm all the time for such needs

[Zak33]

bumping this up to the top - hoping for real life experience of these pumps