Experience with Air Source Heat Pump

Following my recent thread about storage batteries I thought that it may be helpful to share some of our experiences as new user of an Air Source Heat Pump.

The short version is that using a heat pump reduces energy use but not cost if you are currently using mains gas for space heating. If you are using coal, oil, LPG, storage heaters or other similar heating technologies then heating cost may be reduced.

The drive to install heat pumps is driven by two factors as I understand it. Firstly heat pumps produce approximately 3kW of heat for every 1kW of electricity consumed, like a fridge in reverse. Secondly electricity can be generated by renewable sources. Together these facts significantly reduce the CO2 emissions compared to other heating types.

We has a Mitsubishi ECODAN heat pump system installed in October to replace our mains gas space heating system. Major components of the system are manufactured in Livingston, Scotland which is less than 20 miles from my home so a local sourcing bonus. The full installation was funded by the UK Government Electrification Of Heat project which aims to install systems such as heat pumps in a range of properties and monitor their real world performance to inform future strategy. This was a wonderful opportunity for us to install a heat pump system at no up front cost so we went for it.

Our experience with the heat pump has been wholly positive so far, keeping the house at a comfortable temperature for me to work from home. The energy consumed by our house so far this Winter is significantly lower than last Winter:

November 2019 45kWh/day gas only, >50kWh gas and electricity
December 2019 49kWh/day gas only, >55kWh gas and electricity

November 2020 19kWh/day electricity, 60% reduction
December 2020 26kWh/day electricity, 50% reduction

Energy consumption is significantly reduced, which is my objective. Cost of space heating will actually increase as electricity is more expensive per kWh than mains gas. We have been told that our total energy costs may increase by approximately £100 over a year which we are OK with to achieve the energy use reductions above.

We are happy with what has been achieved by changing to a heat pump however it seems obvious that in a wider roll out support should be concentrated on new build homes (already planned) and those not heated by mains gas.

Thanks for sharing. Might be worth adding that the current proposal for the next big building regulations update is for new homes to not be connected to mains gas.

We’re having one installed in our new home – super insulated, timber framed construction. Advice of builder wasn’t to go for Ground Source Heat Pump as the added costs and complications take 20-odd years for extra payback. We had option of a solid fuel stove as well but decided not to. Will maybe look at PV solar at some point when they come up with a more discrete solution.

Is your ASHP supply separately metered? If not, we’re you wfh before?

Hi Metalheart, no separate metering, the heat pump is on the regular supply and draws a little over 3kw at max usage for short periods.
WFH is new for me as many others. I would expect the gas use to be higher than last year if we were still using it as the house is kept warmer.
Heat pumps are ideal for WFH as they provide lower amounts of heat for longer periods compared to gas.

LitteDave could you expand further on details, is your house old/new inbetween…i.e. what modern insulation standards, what heating emitters UFH and/or rads or something different. Interesting research as you mention to learn more, especially if cost goes up (especially in winter when ASHP less efficient) so will public be sold if costs more to save Carbon, easier to sell the future by saying we will save £££, but not so sure, being cynical and all…my interest is what we can do with old buildings but with long term view.

We installed an air source heat pump as ground source ones require either a large land area or a deep borehole.
We do not have the land and don’t fancy a borehole as there are lots of old mines in my area so drilling is risky as well as expensive.

We’re on Economy 7 atm, toying between heat pump and pellet burner, bungalow is 90s build with decent insulation.
ASHP will be cheaper to install, but pellets have the RHI payments.

Thanks, the point of asking about wfh is presumably your non-ASHP electrical consumption will also have risen?

I’m interested in actual/real world ASHP experience from a professional viewpoint (experience hadn’t been completely positive and I’m trying to get to the bottom of things as a result). Condensation and frost cycles being main bugbears (albeit in more commercial based environment).

Cvilla, my house is recent build, well insulated 4 bed detached.
We use conventional radiators throughout, larger for use with heat pump.

I agree that heat pumps to replace mains gas will be a hard sell, many will not spend money to increase their costs! We should start with new build, this us happening and other fuels. Ulimately only an increase in cost of gas relative to electricity will drive adoption, CO2 reduction will not do it.

ASHP will be cheaper to install, but pellets have the RHI payments.

Pellets will require significantly more ‘maintenance‘/cleaning…. been a lot of issues with this in LA housing, so much so biomass systems are being replaced.

Are you away from home a lot?

I see this in the future at my house (no mains gas option)

This is why I’ve gone for solar PV and a battery currently……while.my current oil boiler and tank do their thing. When the boilers up for renewal ashp will look a whole lot more attractive with PV and battery behind it than if standalone.

at the same time I’ve been beefing up the insulation on the house so we need less energy input

The piss annoying thing about ashp is that I’ll have to put the unit in my front garden due to building aspect.

RHI payments are available for heat pumps I think, worth checking out.
Metalheart, in he recent cold snap we have seen the heat pump go into defrosting mode only on one day so our system seems to be working well so far.
My energy use now will be higher than last year at home for lots of reasons, no holidays, home at weekends, no meals out, wfh, more hot drinks so the energy reduction is even more impressive to me.

Do you have any data for the efficiency that it’s achieving? Looks like a bit over 200% from the numbers, but obviously wouldn’t account for seasonal variation. If the controller had any data, it’d be interesting.

We’re here most of the time Metalheart, cleaning and maintenance wouldn’t be an issue.

How are you heating your hot water?

We’re under increasing pressure to design large healthcare/commercial with ASHP but it is a hard sell, 3kW heat for 1kW electric is only in mild/temperate conditions, you’ll be no better than direct electric in winter. Radiators and heating coils all need to get a lot bigger as well!

Requires instantaneous electric heating of water although there are a lot of efficiencies in this that mitigate moving off gas.

We’re under increasing pressure to design large healthcare/commercial with ASHP but it is a hard sell, 3kW heat for 1kW electric is only in mild/temperate conditions, you’ll be no better than direct electric in winter.

Most of the manufacturer data I looked at reckoned on at least 200% efficiency down to around freezing.

I believe the cancellation of new build domestic gas installations has been rowed back on thanks to pressure from house builders. Tories innit? 🤷

@trail_rat how is solar pv and battery meant to help an ashp? At the times of year you generate pv you aren’t really going to need to heat the house.

I think the main problems users have with ashp is that they are often not matched to the spec required in older houses. If you used to need a 25 kw gas boiler to heat the house in winter you will need to replace it with an ashp with a 25kw output.

how is solar pv and battery meant to help an ashp? At the times of year you generate pv you aren’t really going to need to heat the house.

The sun stops shining in winter ?

Solar still works there is just less of it as less sunlight hours. It still removes a portion of the cost -i have solar on my camper already and have witnessed it working and giving good amps in winter for prolonged periods.

How ever I do have the advantage of a south/south east 50degree sloping roof with zero shadowing so it’ll do all it can for me….certainly more than if I didn’t have anything on the roof. The battery helps me get and store power when it’s cheap to heat my house at periods when it’s expensive to use the grid…….

Ashp (daiken altherma) fitted to late my 1980’s 1 bed bungalow by housing association (DGHP….you useless ****) about 8 years ago, **** hate the thing as fitting it to a bungalow with no wall insulation, no under floor insulation and minimal (same insulation from when built) in attic along with 35yr old thin air gap double glazing means it doesn’t bloody stand a chance to offer any heat – in the summer my lecky bills are <£10 week, last week they were £42 as the bloody air pump has to run all the time just to keep the chill out of the house. Within two weeks of it being fitted I opened up the fireplace as the housing association removed it when fitting ashp and fitted a wood burning stove.

@trail_rat the sun does not shine enough in winter to provide any useful amount of power for an air source heat pump. If you have been told otherwise the advice is wrong. I have a 5.5kw solar pv that on most days in winter barely produces more than a couple of kWh and that is just used in the base load for the house. Couldnt you just heat the house at night on cheap power with an ashp and not need the battery?

Not sure what your getting at. Does it or doesn’t it generate power?

Net reduction in power is what I’m looking for before I go and start adding further load.

No one said it would power all the ashp.

How ever the battery on the other hand to shift the ashp load largely to offpeak hours.

Couldnt you just heat the house at night on cheap power with an ashp and not need the battery?

Have you ever had storage heaters. Unless it comes with a Chrystal ball you’ll end up cold on cold.days and charbroiled on warm days.

The sun stops shining in winter ?

Solar still works there is just less of it as less sunlight hours

Well yes, it does!
In December PV generation falls to about 10% of that generated in June.

I did a little research myself on this last year.

As a retrofit proposition, on your typical thermally-inefficient and gas-heated British home, they are problematic.

On the practical front, you need room for the outdoor unit which is also noisy, room for some kind of hot-water storage, room for some kind of instantaneous heating element (for shower, etc), and then you need larger radiators because it’s not efficient to boost the water temp as high as gas combi-boilers go (~70 deg C) Having said that, there are numerous configurations and ideas knocking around including the use of dual-stage heat pumps which supposedly can supply hot water for a shower, etc., but they are still bound by the laws of thermodynamics which is the main problem here; heat pumps become less efficient the colder it gets, and for an air-source heat pump specifically you will have to burn electricity to prevent the evaporator from frosting up when the weather gets to low temps in addition. Expect massive bills and it possibly not even working properly when it’s very cold.

Having said, for a thermally efficient home where the house and heating source are designed as a combined system, then they are an excellent idea although water-source and ground-source are functionally superior to air-sourced due to the higher specific heat capacities and more stable temps of their heat-source. As a ‘bolt-on’ retrofit they aren’t a great idea in my view for most homes in the UK.

My south facing 5.5kw array regularly produces over 30kwh on a summers day and rarely produces more than 3kwh in winter and often below 1kwh. That is not a useful amount of power for an ashp. The only reason I jumped on the pv heating the house crap is because that and the usual battery providing all your energy needs crap was spouted to me by my installer and often gets repeated. Insulation and air tightness with proper ventilation makes the most sense to lower heating bills but people tend to want to buy kit instead.

Yeah if you were going to throw some money at me, I’d externally insulate my period terrace and put new triple glazing in.

We’re under increasing pressure to design large healthcare/commercial with ASHP but it is a hard sell

Someone (pretty well known in the industry) asked me: ‘what happens to the cold air?”.
I’d say you need to ask yourself the same thing. Drop over the coils is approx 6 deg C, if you don’t disperse this properly it will short-circuit and be drawn back in… not so problematic on a 3-4 kW job, not so good with 100kW….

As ever, correct plant and equipment selection is paramount. Select the wrong thing or install it incorrectly/badly it’ll never work properly. There are examples of systems working properly in Scandinavia (which is colder, but mostly drier…). I’m not sure we have sufficient knowledge and experience currently in the Uk.

If you need a 25kW boiler to serve your house you either have a McMansion or poor thermal performing fabric/leave the doors and windows open. Or you have multiple baths/half hour showers…
Money would be much better spent on energy reduction measures.

Also, Nobody is proposing running an ASHP off PV, so please drop that straw man.

PV and batteries are Smart Grid items (to make best use of renewables that generate excess electricity that currently costs a fortune to dissipate). There are some tariffs that will actually pay YOU to take electricity at certain times. Batteries help lop peak/trough usage, and EV’s can also be part of that mix.

But I’m way OT…

Evening all,
Lots of good questions and points above so some responses are due:
I have no direct efficiency data however I can confirm that efficiency is maintained at low temperatures. We are using 20-30kWh electricity while last year we used >50kWh daily gas only.
This is in below freezing temperatures
We heat all hot water including shower using the heat pump, water temperature is lower but the shower does not mix as much cold, still hot enough for a shower, washing up etc.
Our outdoor unit is not noisy, the next door neighbours complain about absolutely everything and have no issue with the heat pump noise!
The heat pump has provided heat and hoot water perfectly well with consistently below freezing temperatures, defrost only activated on one day

i_scoff_cake, you may wish to repeat your research as several of the points you raise are simply not true in many cases. My house is well insulated, however:
My heat pump supplies water for a shower, no supposedly, it does 🙂
No massive bills or not working when cold, see above
A heat pump may not suit you however to dismiss in the terms you did does not provide a balanced service to other forum members, hence why I started the thread to bring forward some real experience of using a heat pump in UK winter for those who may be interested.

The only reason I jumped on the pv heating the house crap is because that and the usual battery providing all your energy needs crap was spouted to me by my installer and often gets repeated. Insulation and air tightness with proper ventilation makes the most sense to lower heating bills

Which we have done and have more in the pipeline. But don’t let that stop you. As metal heart says – no one’s proposing to run ashp off a solar PV or a battery but it’s all part of the system to reduce energy COST at END USE which is my driver….

Going into it with my eyes open having seen the numbers off a colleague’s set up who lives near by. sorry if your installer sold you the dream.

Little Dave. Out of curiousity Which aspect of your house is your heatpump situated ?

i_scoff_cake, you may wish to repeat your research as several of the points you raise are simply not true in many cases. My house is well insulated, however:
My heat pump supplies water for a shower, no supposedly

I’m assuming you have a two-stage system or two heat pumps then? Again, more capital cost.

Do you have a brief summary of how your house is constructed and insulated? I do stand by my claim that air-sourced heat pumps are not a good ‘bolt-on’ solution for your average crappy British home. As you imply, you need a well insulated home and even then it’s not particularly economic because of the large capital cost, even if from a carbon POV it’s a decent solution.

As ever, correct plant and equipment selection is paramount. Select the wrong thing or install it incorrectly/badly it’ll never work properly. There are examples of systems working properly in Scandinavia (which is colder, but mostly drier…). I’m not sure we have sufficient knowledge and experience currently in the Uk.

I believe that Germany has led the way re heat pumps for several years now, but specifically ground and water-source. Local/district heating systems with heat sourced from rivers or ground-water are very good solutions.

Interested in this as we hopefully move into a new build in summer with decent insulation and an ashp. Bit disappointed the small developer hasn’t also gone solar pv in place of tiles on a nice south facing bit of roof.

How “smart” are your ashp controls? Does it do things like run more in the winter daytime when ambient air is warmer? I’m considering that as a strategy as there looks to be decent internal thermal mass in the construction (don’t think it would work well in say a timber frame where there is minimal mass inside of the insulation).

A guy at work lives in a country cottage backing onto a canal. I keep trying to persuade him to go gshp and lob the coil in the nice ready made water filled trench 🙂

Interested to read of your real experience of living with an ASHP littledave. How big is the heat pump and size of dhw tank?
We are in the middle of a self build and going for air source heat pump with ufh on both floors. House very well insulated.
One concern I have is our hot water requirements as we have 3 kids and all like showers.

Trail_Rat, my heat pump is fitted on a north facing wall, no issues so far.
i_scoff_cake, no we have a single, single stage heat pump, properly sized for the house. All hot water for the day is heated on low rate overnight power for about 2kW. My house is about 10 years old cavity brick, double glazing etc, well insulated but normal not passivehaus or similar.
There is no such thing as an average home, each installation will be different.

For avoidance of doubt for the wider community, heat pumps can operate effectively in below freezing temperature and heat hot water also. No special tricks, just a suitably specified system for the house.

I am not a heat pump salesman, just sitting here in cold weather, warm and with plenty of hot water while reading opinions to the contrary. 🙂

Local/district heating systems with heat sourced from rivers or ground-water are very good solutions.

Absolutely, buts as I said before

I’m not sure we have sufficient knowledge and experience currently in the Uk.

Local area heat networks is the way forward. Needs to be done properly though… 🤪

Thats interesting because neither of the installers would fit to my north facing garden when I replaced my oil boiler 10 years ago.

Ultimately the cost of the unit wasn’t too bad the extra electric was relatively manageable the final straw was them insisting on sticking it in my front garden where it would benifit from.higher temperatures lost them the work

Has the technology moved on that much in 10 years.in another 10 when my boiler needs replaced again maybe the local engineers will have caught up

Oh, and thanks littledave, nice thread. 👍

Local/district heating systems with heat sourced from rivers or ground-water are very good solutions.

At the time 2011, the largest GSHP installation in Europe was the one for the One New Change shopping centre in the City of London, this used the underground aquifer to the provide the heat which was transferred using collectors Incorporated into the piles upon which it was built.

no we have a single, single stage heat pump, properly sized for the house. All hot water for the day is heated on low rate overnight power for about 2kW.

As you say, you’re not a salesman. A single pump, fixed compressor ASHP won’t be efficient at two output temps. Maybe you have something fancier like refrigerant reinjection, variable speed, or something?

There is no such thing as an average home, each installation will be different.

Sure, but from the POV of a mass roll-out, what a constitutes an average home in the UK matters greatly. One appeal of a gas-combi is that you can more or less rule of thumb size it and then just drop it in. ASHPs in contrast demand better planning and specifying. Not an easy thing for your average Bob.