Air source Heat Pumps any good?

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Heat pumps as a retrofit to an existing house don't make sense to me, but I do wonder about simple aircon fed from our solar, as a supplement to the gas boiler.
A quality 6kW mitsubishi split with two indoor units cost about £2k plus installation.
These can be run as a cooler or a glorified fan heater with (by the look of things) a 300% COP most of the year in the UK. A lot of asia uses split aircon units for heating through winters colder than ours....
For just a modest outlay I suspect I'd get quite a lot of free heating from one of these and a useful reduction in the gas bill over the year. Once you have solar PV it's all about using up what it generates.

The issue there, is that the sun doesn’t shine in the evening ie when heating is more likely to be required and so you’re then either dependant upon the grid or, if you can afford it (more below) a battery backup system.

We had a 4.2kw solar system fitted about 3yrs ago and it works as well as we expected…..payback between 8-10yrs.…..so much so that a few weeks back I contacted the same fitting company and enquired about adding battery backup. Their own estimator/designer gave me some very basic cost info as well as technical specs and sent me away to do my own simple monetary calculations. A few days later I confirmed (to his agreement) that it was NOT a financially viable project for us…..he then pointed out that he has several enquiries per month where he has to, unfortunately for the company, burst bubbles by illustrating how much the sums simply do not stack up at current costs. He genuinely doesn’t want customers wasting money.

We have a 3 bed bungalow (now with attic conversion) and in the warmer months it only uses ~3-4kw per day (the solar panels obviously helping by doing their thing as they regularly produce 20+ kw/day). However, from roughly mid October to January, when we’d need even more electricity for evening heating, there are numerous days where we don’t even produce 5 kW!

Based on a rough 5kw battery cost of £4k the simple calculations (for us) are as follows:-

If our house needed 5kW in an average evening (highly unlikely but let’s run with it) then, in theory, we would be charging and discharging the 5kw battery once (ie one cycle) per day. At £0.20 per kw, this would mean a saving of £1/day = ~£350\yr……meaning that over ten years we would save ~£3500……given that over this period we may have to change the inverter the overall cost (battery and inverter) would be roughly the same as the savings…..And so, for us anyway, it isn’t worth the financial risk?

I’m also concerned (having read up on the battery’s chemistry etc) that in the winter months, when the battery isn’t being charged fully, would this lead to battery degradation over time resulting in a reduced battery life?

When you sit down and actually think about it (in our case anyway ) we’d only be saving £1 per day which, on first impressions, seems crazily low given current electricity prices but everything adds up when you multiply it by 30 or 365 days.
 
We’ve just had a Mitsubishi ’Ecodan’ 11kW ASHP installed (6 months ago) when the RHI was slightly better, ie, not a £5k one-off.

We’re not millionaires, but we are able to do our ‘green bit’.

Chris
It's nice when other people pay for your green credentials, isn't it? (Not meaning to be personal in any way - I don't blame you.)
 
We've had a 3-phase GSHP here for 17 years and it's never missed a beat. It's been serviced once in that time with only minor tweaks needed.

Post in thread 'Suggestions for future heating system' Suggestions for future heating system


We installed it at the same time as doing our self-build, so had the machinery onsite, thus keeping the cost down a bit. At the time, it cost about 5K to install with an RoI of about 3 years.

Firstly, the hot water that a heat pump delivers is just about right for 99% of uses - the sterilisation cycle every week or two costs a couple of quid at current rates.

We have a measured average cop of 3.5 and I have fairly sophisticated power monitoring on all aspects of the site, based round an Emporia system (see elsewhere on this site). If needed, we easily get 300lts of 40-45C water every hour day or night, summer or winter. Since the kids moved out, our hot water usage has plummeted anyway.

For ANY heat pump to be effective, you need good insulation and a house designed for it. Retrofitting is always a compromise and is highly unlikely to be anywhere as efficient as a system sized and designed alongside the property its intended for.

Heat pumps are not a panacea, but they are a step in the right direction, especially when used in the right building and with "green" electricity.

I fully concur that the government simply don't understand the complex issues involved.
 
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Who needs heat pumps?
Screenshot 2022-08-06 at 10.52.23.png
 
My wife likes it at 22 C you say.

New law in Spain.
Air conditioning cannot be lowered below 27 degrees in summer and heating cannot exceed 19C this winter, while shop fronts must go dark by 10 p.m., according to the decree passed Monday.

Similar measures have already been put in place for public administration buildings, while they remain voluntary for houses.

https://www.politico.eu/article/spain-order-temperature-limit-business-energy-saving-decree/
I think similar legislation should be adopted in this country, if we are serious about reducing global warming.

I agree that air source heat pumps make no sense commercially or even ecologically at this time. We have had to re-open coal fired power stations to provide electricity to 'not' heat our homes.

https://www.theguardian.com/busines...er-station-open-nottinghamshire-west-burton-a
I live in a detached house built in 1865 the only option is plenty of thermal layers..
 
It is funny the electric boiler I am going to install is stated as 100% efficient BUT it is only gets a "ErP Rating D(Heating) A(Hot Water)"

Solar panels are only 20% efficient when new dropping to 18% after a couple of hours of use.

Though as I recall steam engines were only 9% efficient..
 
I’ve been asked by the head of our household to look into air source heat pumps. We are hopefully moving shortly, and she would like to have an eco friendly heating system in the new residence. I’ve done a little bit of research, and it would appear that financially they don’t financially make any sense even including the £5K government grant available.
My initial work looked at the Kw/H generated from 1 litre of oil and 1 cu ft of gas, I’ve used 60% and 90% boiler efficiency to work out how much it will cost for 10.35Kw of heating energy (equivalent to 1 litre of kerosene which my existing property uses). I’ve looked at heat air source heat pumps and used the optimistic 300% efficiency, however, my reading suggests that this drops down to say 200% (and lower) which I haven’t used) when the air is cool in Winter. The saving with todays high energy costs means that it won’t break even for say 15 years. In fact if the house is highly insulated I will be dead before it breaks even. If I look at energy prices before Ukraine, and oil is going back down in price, the payback is again ridiculous / if ever.

It seems that an efficient air source system needs to run as c40C which is too low for hot water so you need an immersion heater to top up the hot water tanks to stop legionnaires growing (which isn’t I believe included in the 300% efficiency figures quoted). The radiators need to be much larger than for a gas / oil boiler and preferably it should be underfloor if you are to attain the same room temperature. Now my wifey likes it warm (a career running hospitals has made her acclimatised to the heat before anyone suggests running the house at a lower temperature)…..around 22C which isn‘t a big temperature differential for a 40C system, I’m actually wondering in a house that may not be very thermal efficient if it will be possible to attain this room temperature.

Has anyone else looked at how cost effective moving to air source is? Am I missing something?

Whats people experiences, the good the bad and the down right ugly in installing and running such systems?
I've been in the industry for 27 years. There are many factors to consider prior to making an informed decision. Don't listen to you mate down the pub who has watched a YouTube video on ASHP. Firstly you need to do heat loss calculations for every room in the house. All 4 walls and the window(s) sizes. Are walls solid, cavity, cavity with insulation, internal, external etc. Once calculated this will give you the total heat loss of the property thru walls. Windows, are they single glazed, double glazed etc. If double glazed what's the air gap? It used to be 16mm now it's 20mm. Are the frames wood or Ali. This will give heat loss thru the windows. Once calculated this will give you the heat loss for every room.

Next look at every radiator in the house. What type are they (K1 single, K2 double, K3 triple (panels)) Then look at the relative heat output from each radiator at 80deg C, 60deg C & 40deg C. Next look at you loft insulation and floor types. Is the ground floor solid concrete, suspended, etc, first floor is usually suspended floor boards or chip board. How much loft insulation do you have. Once you have calculated all the above this will give you the total heat loss for the whole property.

Most ill informed people think that they'll have to change every radiator in the house for some super sized monstrosity. Not so. Example, if the heat loss for a room is say 700 watts and you have a 600 X 600 K2 radiator in there and the heat output for that radiator at 40deg C is 800 watts then why change it? Do this exercise first before even thinking about an ASHP.

Next, hot water cylinder. Legionella grows at temperatures below 55deg C. A typical 200litre cylinder will change it water volume around once every day in a typical household. The temperature of a cylinder only needs to be set at between 38 & 43deg C max otherwise you have to blend in cold water to get it to this temperature. Any hotter and it will burn you. For safety sake we set cylinders to achieve 61deg C once a week to eliminate legionella risk.

Next look at your heating circuit pipe sizes. If it's this new 8mm micro bore plastic forget it. You'll have to change all your pipework. Most properties have 22 & 15mm copper pipe. If that's the case then your good to go although I would add that power flushing the heating circuit is always recommended to remove any crud in the system therefore increasing efficiency. There are other options to help with efficiency, flow rates, heat distribution, headers or buffer zones, weather compensation etc but don't want to get too technical here.

Without trying to offend, your average plumber wont know or cant do the correct heat loss calculations nor will they be able to size and design a system to run at max efficiency at 40deg C. Most of them can fix a shower or a WC or install a new boiler, (all they do is look at the current boiler kW rating and install a new one of the same rating)

To sum up. It's a highly technical exercise to see if a domestic ASHP is suitable for a property. Government make all these outrageous claims that we'll be a nation of heat pumps by 2030 but in reality we need to look firstly at the correct training, sizing and installation methods before embarking on this journey.

Systems are getting better and we can get water temperature of 70+ Deg C on some systems now but those systems are not suitable for all properties. Hope this helps some of you.
 
The potential (we havent yet signed our lives away just going through the process) new property was built I think around 1900, it’s recently been fully renovated and extended. Triple glazed, loads of roof insulation and some parts (extension) has underfloor heating. It has a LPG tank and boiler as living in Cheshire mains anything is very rare other than in the towns. All rooms have a due south facing aspect so lots of solar gain. However the EPC is E, I’m told a lot of why it’s so low is due to the LPG??
 
For ANY heat pump to be effective, you need good insulation and a house designed for it.
I don't think you can generalise like that. I seriously doubt that our house, built in the 1890s, was designed for a heat pump but our GSHP works better than any alternative available to us.
 
I live in an old timber frame house with extensions. I spent a lot of time improving the insulation, fitting high performance sashes and other household improvements when I took the plunge of my first ASHP 10 years ago, getting rid of an lpg boiler. My first ashp only heated the water to 50 degrees. It mysteriously failed and had to be replaced after 3 years with a generous help from the Swedish manufacturer CTC. The replacement can heat the water to 60 degrees (I only set to 55 tho as efficiency declines as temp increases). Servicing cost is minimal. It is controllable from my phone as many things are nowadays. It doesn’t blast out heat like a traditional radiator, but if you insulate your house you don’t actually need that. I run the old radiators @ 35 degrees and the underfloor heating area at 30.

Overall It is brilliant, I was lucky enough to get an RHI grant which helped with the cost too. Would I go back to an LPG or oil boiler….er no. It has saved me thousands in energy bills over the years.
Would I consider anything else? Maybe a wood pellet system, but they can be more fraught with problems of pellets getting moisture damage and clogging feed mechanisms.
Over all it’s a sensible way forwards but you need your house not to leak heat (but who wouldn’t want that?)
 
@deema Yes probably the same as I posted about our boiler. It will be the cost of producing the LPG and probably the cost of transporting as well.
So, while an electric boiler can heat water with little to no heat loss, giving the unit a 99-100% efficiency, the fuel factor sees the ErP rating appear low as the generation back at the power station produces high volumes of carbon.
 
Firstly you need to do heat loss calculations for every room in the house
This suggests I'm on the right track. Thanks.
I decided to write an excel sheet to do exactly these numbers in detail so that I could look at what changes would have the biggest bang for my buck and exactly how much heat I need in each room. Work's in progress but it's already interesting.

Our place is a small 1979 detached with a disproportionally large roof (hence the long term desire to exploit it with solar). We don't have any damp problems since I rectified the original builder's habit of bridging the DPC with plaster (shoddy workmanship) but I've heard too many horror stories and I've avoided cavity wall insulation ever since we bought the place.

The down side is that you have fat chance of receiving any government RHI or grant if you won't install cavity insulation. I believe that these schemes just allow approved contractors to hoover up tax payers money and frankly that you can get a better job done outside them if you take time to educate yourself. Still, I want to learn what my decision not to install cavity insulation is costing me.

In my searches for U values for a range of housing elements and construction materials I found a real interesting report by the BRE that measured actual U values of walls across a good number and range of UK legacy houses. It's always nice to find data where the authors are prepared to document their methods to justify it.

https://assets.publishing.service.g...file/409428/In-situ_u-values_final_report.pdf
 
How much did that all cost?
It was part of an extension rebuilding with lots of new windows so it was a little hard to quantify in flat terms.
I doubled the square footage of the house and reduced the heating bill… and the house feels warmer.
 
if you have a passive NZEB house then maybe they make sense, if not then the upgrade to that level would be your 1st priority.
 
Woodworkers need woodburners. I don't do a lot nowadays but even that can produce sawdust, chippings, offcuts to keep the fire burning for some time. I also collect anything going including pallets and old bits of furniture and people bring it in knowing we'll have it.
The burner is a Dowling Sumo which is supposed to do 12kw and gets hot in a few minutes. The squat shape suits sawdust as well as everything else. Also coal, though never tried it.
The only prob could be storage but I've got lots of room luckily.
Also does old cardboard, paper etc which get the room hot very quickly.
Very efficient, hot, zero carbon, free fuel
PS and a smaller Dowling Firebug in the workshop
Forgot to add - bigger wood stoves are better - a small fire burning hot in a large stove with a larger surface area is more efficient than the opposite.
Also much faster in terms of heat generation - you can get a room warm very quickly with small stuff packed loosely with the vents open to burn it fast.
This is roughly what is behind a rocket stove at one end of the scale, or a gasification boiler at the other, i.e. fast hot burning for greater efficiency.
 
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Next, hot water cylinder. Legionella grows at temperatures below 55deg C. A typical 200litre cylinder will change it water volume around once every day in a typical household. The temperature of a cylinder only needs to be set at between 38 & 43deg C max otherwise you have to blend in cold water to get it to this temperature. Any hotter and it will burn you. For safety sake we set cylinders to achieve 61deg C once a week to eliminate legionella risk.

agreed with everything you said until you got to that point ..!! If it is a sealed unvented cylinder then the legionella risk is nil. Legionella requires air entry to the system along with moisture. It will not grow in a closed chlorinated water source and there are no reported cases anywhere of it in a domestic environment in the last 20 years. Legionella cycles just cost money, they do not actually do anything.
 
Depends on the details but generally not a problem.

We insulated our chapel conversion with stud linings plus 100mm Kingspan to all the external walls , with 50mm in window reveals and 250mm in roof spaces.
Not really a problem.
Listing is generally about outside appearance and internal details only rarely specified.
Sold floors is a prob but much less important than insulating walls and roofs - heat goes up.
Re - “listing is generally about outside appearance” I wish that was the case. My listed buildings officer will not allow any insulation to be fitted to the inside of the walls as it “hides and damages the historic fabric” this historic fabric has been hidden to the world for 250 years but she will not be moved. This means I cannot insulate the house to a point where UFH / GSHP/ASHP are viable so despite my desire to be green I have reluctantly purchased a new oil boiler. The listed buildings police just don’t get that the buildings need to be practical if they are to be lived in and therefore maintained. I am all in favour of preserving our heritage, that’s why I took on the challenge of owning a listed building but a slavish adherence to “everything that’s old must be left untouched” will lead to empty buildings that fall down, some sensible pragmatism is required. Rant over!
 

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