Air Source Heat Pumps…

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Hi all..
This is my first forum post!
I am wanting to switch over to an ASHP from my current gas combi (which is perfectly adequate)
Usethesun are a company who came out, surveyed the house, carried out a heat loss calculation etc. They have recommended a 9kw LG unit. All rads will be upgraded. I’m happy with the price, and will potentially receive annual payments from the government to offset the cost. All good stuff.
What I would like to know, are real life electricity costs for running a system.
I have a fairly standard 3 bed semi. Cavity walls have been filled, plenty of fluff in the loft and reasonable double glazing. No underfloor heating, all radiators.
We don’t like living in a sauna.. at the moment the living areas are set at 20, the bedrooms slightly cooler. Gas is obviously set to go mental so some decent savings there.. but I’m concerned the electric bills will skyrocket with a retro fitted system.. then I’ll be stuck with a very expensive system that costs a fortune to run… does anyone run a comparable system??
Sorry for the essay..
many thanks
 
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The current price cap for gas is approx 4p per KWh. Electricity is 21p per KWh, yes over 5 times more.
Both are going mental at the moment.

A decent gas boiler is 90% efficient. An air source heat pump gives out maybe 3Kw for 1Kw electricity, effectively 300% efficient.

Doing the sums to produce 1Kw from gas 4.4/0.9=4.89p. ASHP 21/3=7p.
 
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beware of any payments from the government offered. ask anyone with solar panels etc.........
 
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The current price cap for gas is approx 4p per KWh. Electricity is 21p per KWh, yes over 5 times more.
Both are going mental at the moment.

A decent gas boiler is 90% efficient. An air source heat pump gives out maybe 3Kw for 1Kw electricity, effectively 300% efficient.

Doing the sums to produce 1Kw from gas 4.4/0.9=4.89p. ASHP 21/3=7p.
should that not be 4/0.9 = 4.44p

But whatever, an air source heat pump is going to 50 to 60% more expensive to run than gas,

And from what I have heard they are no where near as efficient as 300% in very cold weather, this being the time you will be using it the most. I have also heard that when we get this very cold damp weather so typical in the UK the whole thing just ice's up and becomes useless. Then there is the noise nuisance of the compressor running 24/7, I have heard them running and I hope none of my neighbours goes for one.

 
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You should average a CoP of about 3.5 if correctly installed, bringing running costs broadly in line with gas boilers. I've got one and I'm very happy with it.

As for that Skill Builder video....


 
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How many kw is your present gas boiler, to cope with your heating needs?
Not really relevant as many boilers are oversized. Our old Ideal Classic was 18kW but the new 11kW heat pump heats the house just fine. 80% of UK homes need less than 10kW
 
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I am responsible for the ASHP at work, and this morning when it's 1 degree C outside, the outdoor unit is continually icing up. For 20 minutes of each hour it produces no internal heat as it it busy defrosting its outdoor coils. Even though the building has been Environmentally Certified as being BREEAM Excellent; once the outside temperature drops to low single figures it struggles to maintain 20 degrees internally even with the ASHP running 24/7.

Because ASHP's work like a fridge in reverse, the indoor coils get warm, and the outdoor coils get cold, so even when it's 5 degrees C outside the outdoor coils will still ice up as the coils themselves are still below 0 degrees C, and the damp British air passing over them turns to ice.

Having watched 'Heat Pumps the Ugly Truth' video referred to by @Munroast, that's my experience to a tee.

When its 10 degrees outside it produces vast amounts of heat and warms the building very quickly, as the temperature falls into single figures and more heat is required, efficiency drops and it produces much less heat, and then when we get below 5 degrees the dreaded defrosting starts.

So in summary, at the point when you need more heat, the ASHP heat output drops dramatically.......
 
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You should average a CoP of about 3.5 if correctly installed

if correctly installed, many are just thrown into place.

Average is good, but can include periods where the CoP is much lower. The average can even include periods of a negative CoP when heat is used to defrost the outdoor unit

When its 10 degrees outside it produces vast amounts of heat and warms the building very quickly, as the temperature falls into single figures and more heat is required, efficiency drops and it produces much less heat, and then when we get below 5 degrees the dreaded defrosting starts.

So in summary, at the point when you need more heat, the ASHP heat output drops dramatically.......

As was predicted by engineers tasked with developing ASHP back in the late 1970's
 
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A decent ASHP is a pretty good bit of kit these days but they always get a slating on forums such as this. I have a "hot" 80 degree ASHP in my own house and it really is excellent in every way. HOWEVER, I have no access to gas so my switch was from oil heating. If I did have access to gas I would have kept or upgraded it, there is no benefit to change from gas to ASHP apart from, possibly, a reduction in greenhouse gas (assuming electricity is mostly renewable).
You would also need to factor in an outside unit with a large fan, it's similar to an AC unit but blows extremely cold air out when heating the house.
 
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Does an ASHP also provide a cylinder full of hot water? Or are you relying on a costly immersion heater?
 
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Does an ASHP also provide a cylinder full of hot water? Or are you relying on a costly immersion heater?
Yes it does, however most systems are scheduled to boost the cylinder temperature, once a week, to a high temperature, to prevent legionaries. The temperature above what the heat pump can produce is carried out by the immersion heater.

Edit, my system does not require the immersion to do this as I chose an 80 degree system.
 
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And don't forget the capital outlay, maintenance costs, etc etc

Yes it does, however most systems are scheduled to boost the cylinder temperature, once a week, to a high temperature, to prevent legionaries. The temperature above what the heat pump can produce is carried out by the immersion heater.

Edit, my system does not require the immersion to do this as I chose an 80 degree system.

Help us out here - 80c sounds good but that's only on the DHW service, the CH still runs at 55 or so
 
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If i may chip in with some uneducated comment.

The issue isn't heat, or lack of it.

The issue is what happens to the heat.

ASHP's need an efficient, low loss building. This means that air flow through the building needs to be strictly managed.
Old buildings and methods of construction often require unrestricted airflows.
You cannot reduce the airflow without having significant impact on the building and its inhabitants.
The forum is full of posts from people complaining about mold, condensation, etc. from the reduced airflow rates of modern buildings.

IMHO, a ASHP needs the building to be designed for it and old housing stock isn't really suitable.
I have friends who have ASHP's in new-builds and they have no issues with them because they are an integral part of the building design.

As for ripping out a perfectly good Gas system, i think if you do a cost/benefit analysis, you may be surprised at the results.
 
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Mine is a Hitachi yutaki s80 but, If I'm honest, it is overkill and I only had it turned up to 80 degrees for a short while.The rads and the water were too hot for my liking.
I'm not sure if any other manufacturers make a similar system? The downside to it is that it has an indoor unit, about the size of a washing machine that needs to go in the airing cupboard. My mother in law has a 50 degrees system and even that is hot enough in my opinion.
 
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