[Closed] Air source heat pumps, advice please

I looked at ground source heat pumps for my place, we have quite a big solar set up. Very expensive, as this was a vertical one which basically requires a land drilling rig.

I didn't do it in the end, too much initial outlay.

Air source is a lot cheaper but I haven't heard anything good about them, very expensive too run by all accounts and not very reliable.

The other thing to bear in mind, you really need either much bigger radiators or underfloor heating to make efficient, as the water temperature is lower.

Air to air or air to water?

I looked at them about 10 years ago, and was put off by the noise they made (I didn't look in costs/benefits).

As above re ground source, it's very expensive. We're in the process of starting a barn conversion. Plenty of land, so no need to drill down.....it was still so much cash! I know that you recoup that cash, but for us with massive bills coming in right left and centre, and a limited budget, we've had to go with other options.

If you've got enough garden and cash, ground source heat pump with buried pipe is more efficient.
https://smartrenewableheat.com/blog/ground-source-vs-air-source-heat-pumps/
https://www.ofgem.gov.uk/environmental-programmes/domestic-rhi/contacts-guidance-and-resources/tariffs-and-payments-domestic-rhi/current-future-tariffs

They need to be set up correctly to work efficiently and are best in an efficient house. Work well with external wall insulation. Underfloor heating and large radiator panels.

Ground source works better in this country but then you have the expense of the drilling. The Dutch are big into it as part of their retrofit social housing projects. Look up Energiesprong online.

I'm told that they are crap unless you have a very well insulated home. You'll need new rads, but it doesn't sound as if cost is an issue.

Air to water.

Under floor heating won’t be an option, just too much hassle and outlay.

Was hoping that the excess energy stored in the PW2 would be put to some benefit as well.

CoPs are much more variable with air source.

Both have to be sized correctly because it's low temperature heat - best delivered with large emitters in well insulated homes.

Air source is cheaper to install but generally less efficient and if not sized correctly turn into a big electric boiler in the winter, with associated large electric bills. They'll also block their heat exchanger with ice as a result of poor sizing - a real problem in the winter to defrost.

Air source has got a bad name from alot of outfits that add it to their portfolio along with gas, oil, etc... But don't really understand that it's different.

Dunno how feasible it is, but if the efficiency drops in winter to barely better than just electrical heating the water directly. Could you not just do that? Rather than charge up the power wall from the solar, just set it up to dump excess electrical energy into a hot water tank, and use the batteries to run electrical heating.

Could you spend the cost of the heat pump and associated plumbing on more PV panels and gain enough to heat the house in winter? Or even if it's a bit wasteful, feed in enough over the summer to pay the cost of electrical heating in winter?

Also look for a suitably sized buffer tank. Otherwise the heat pump can be constantly switching on and off, which is less efficient and wears out the compressor etc. And the buffer tank can help to defrost the heat pump if necessary.

Remember that electricity is 3x the cost of gas. So unless your CoP is at least 3x, you won't save any money.

Experiment with your existing heating system before you change. I know it's Summer and this would delay your project a year but the results will tell you a lot. Turn the water temperature on your boiler down to 35°C and see if that's enough with you existing radiators during the coldest months. If it is then you'll be fine and have a COP of better than 3 in a typical British January. If it isn't then you need to insulate the house to the point rads at 35°C are enough, accept COP below 3 or think again.

Edit: I also found that the lower the water temperature the more efficient the gas central heating was because it only ever fired the gas at the lower setting. The house temperature was more stable with less overshoot each time it fired up.

Before I took out the gas central heating I got the water temperature down to 33°C (it wouldn't go any lower) and that was enough. In the end I worked out that firing up a wood burner in the evening for an hour or two would be enough and so far haven't fitted the heat pump I had planned.

https://www.cibsejournal.com/cpd/modules/2010-02/

Thanks for the replies.

Looks more likely to go for a high efficiency combi boiler, given the cost factor and some questionable heat loss issues.

Pity, would really like to reduce our carbon footprint.

My brother has had an air source heat pump for a good few years now. i remember he had trouble and had the installers back a few times in the first couple of years but now it seems sorted and he saves money but he was on oil, not mains gas.

We have them at work in a lot of our properties. Very few people have good words for them. Typical electric bills of £200 a month in the winter.
If you have a good array of PV panels, then that will help. Ours are a poor design (or maybe how they've been fitted), as when the ASHP unit fails, there isnt a separate supply to the immersion heater, so no hot water at all.

We installed Air Source (NIBE) when we built are house in 2013 as no gas nearby. It works very well and total electric bill (electric, heat and water) averages out at £110 per month for a 4 bed 3 bathroom house. We have a care plan at £30 pm with NIBE which covers for annual service, parts and breakdown. Cost was around £22k but include all the plumbing for the entire build. I think I got a £5k rebate from a government scheme.

However, systems need careful planning as lots of equipment to locate, install, commission and the house must be extremely well insulated as radiators and underfloor run fairly cool compared to traditional systems.

Hot water capacity is excellent and being unvented means no issue with supply pressure when multiple bathrooms in use which you’d get with a combi.

It’s a reliable and efficient system but I don’t think suitable for retro fitting to an existing property unless it is a back to brick renovation to install the right level of insulation and plan in water tanks and controller locations.

May's recent commitment to a carbon neutral in Britian by 2050 is laughable when even one of the most committed carbon footprint reducers on the forum isn't prepared to spend the extra cash needed to cut off the gas.

I know that on a planet of 7.7 billion whatever we do on an induividual level is pissing into the wind but if we all do it... .

I've known three people who have them and all said the pump was noisy and unreliable.

Ground source, I can understand - when the earth is always at the same temperature (14c?) it will suck out warmth and a well-insulated house can be kept warm. But how much energy must it consume when the outside temperature is 0c or less and the system is having to collect heat?

For what it's worth, we have one in our house which was a "back to the stone" renovation, new roof, etc. We did spend 000's on insulation and also benefited from a Green Energy Scheme grant for our installation but it has been brilliant. It's a mitsubishi unit which we never hear or note to be noisy. Granted, the rads are cooler but theyre also slightly oversized (and combined with the significant insulation) which counteracts this fact. We also have a huge woodburning stove which we use to heat the house in preference to the central heating. As has been mentioned, cost of gas v elec perhaps makes them slightly less attractive than the "usual" heating methods but we don't have any mains gas so, for us at least, it was a simple decision. Plus, at the time of installation (about 4 or 5 years ago) oil was up over 65p a litre and we didn't want to be at the mercy of unpredictable prices. (though predictably it has been cheaper than that ever since I believe!)

But how much energy must it consume when the outside temperature is 0c or less and the system is having to collect heat?

See my link above

Thanks again for all the replies and additional info.

Looks like a high efficiency combi boiler, although I really would like a greener alternative.

Just for some background info.

Modern 4 bed detached house.
4 kWh solar panels
Tesla Powerwall 2 battery, plus running a Nissan Leaf EV car for the last 3 years

Our annual bill for

Gas £460

Electricity £440

This includes charging the car at home on a 7kwh plug for about 95% of the time me, so very little spent on 50kwh rapid chargers.

Ideally wanted to be even greener, but looks like the technology isn’t quite ready yet.

The technology absolutely is there and air source pumps have been used for years in other countries. As others have mentioned they are not suitable for a badly insulated house but work very well in very well insulated air tight houses. I think there is an issue with the number of installers that actually know what they are doing, and I am sure this would not have helped peoples bad experiences with them. Air source is not great at heating water over about 48 degrees as the efficiency really drops off so not great on their own for your hot water needs. Lots of info and helpful people here

Thanks

Good thread this.

So assuming ASHP is a non starter for a late 60s house, what is the best option to replace oil (mains gas not an option)? Keep oil, and look to solar and batteries to supplement?
We run the house pretty cool by other peoples standards, but the boiler is getting on (over 20 years old) and probably going to get a beyond economic repair bill some day, and I'd rather not replace but I don't see an option (other than pure electric which I'm not convinced is cheaper or as effective).

I'd always look to insulate before anything else.

Assuming that £110 of the £460 bill is standing charge then you consume £350 of gas which at 2.8p/kWh is 12500kWh; which is about 2500kg of CO2 or about the same as driving 20 000km very slowly in a small ICE car.

The solar panels are just window dressing with that level of gas consumption (I assume that you like me are producing only 3000-3500kWh a year)

Assuming an average COP of 3 and electricity price of 14p/kWh then your electricity bill would go up by £580 a year using air-air rather than gas. So about £200 a year more to roughly halve your CO2 for domestic heat given the current UK energy mix. That's a better reduction in CO2 than driving an electric car instead of an ICE.

Obviously the long term solution is insulation, but I have no idea how much that would cost you. From personal experience I can say that in both Winter and Summer it makes the house much more comforatbale.

I've seen cops below 1 in a typical UK winter.

Daikin Altherma fitted to my 1 bed ex council now housing association bungalow (30yrs old) and it's utterly ****ing useless, costs me £100 per month for heating/hot water which is prob due to the bungalow having no wall insulation/ no underfloor insulation (wooden suspended floor) and 30yr old loft insulation. Got 5 normal radiators in the house and occasionally they get tepid to the touch but as for heat?, nah....you've got more chance of getting warm by lighting farts.  I've had the engineers out a dozen times this year as the valve that switches hot water/heating sticks all the time and the system looses pressure and drops its guts, anything under 10C outside and the heating doesn't work - i'm getting an independent EPC report to force the housing association (DGHP dumfries & galloway) to come up with a better solution as the heating system is not fit for this type of poorly insulated property.

They may work well in a new build with modern insulation standards but in older houses they're ****ing useless.

Somafunks experiance mirrors that of a couple of folk I know in Aberdeen who have them in new builds.

They have have had to use suplimentary heating (think electric oil radiators and fan heaters )in the winter and still end up paying through the nose to get hot water from the system.

Certainly research real world for your direct area and climate rather than Dr google links.

@ Edukator

Thanks

We consistently produce just over 4000 kWh per annum in sunny South Wales .

Surprising really given how much it rains and the overcast Dec, Jan, Feb months.

I’ve seen cops below 1 in a typical UK winter.

What is the temperature of the water people are circulating to get that low? (see my link above) There isn't that much difference between the Winter climate in Pau and the southern UK. People here get good results with very reasonable bills. The best though is a friend with a ground-sourced heat pump with a claimed COP of 4.5-5 that costs cents to run. The whole system in a new build with low temperature under-floor heating did cost 18 000e though.

55 degrees. HW and heating. To be fair, that was a system that was clearly sized incorrectly, and installed in a 1960s brick apartment of a little old lady that wanted her house temperature at 25 degrees day and night. The heat exchanger was a permanent block of ice because it was drawing so hard and was using the electric heater to heat and backwash into the heat exchanger to try and defrost it, in a permanent cycle of freeze/thaw. In fact, it's backwash cycle was completely insufficient to make an appreciable difference.

She was effectively trying to heat her whole house and hot water using a 3kw element, and trying to defrost a 75 X 75 cm block of ice all at the same time, hence the less than 1:1 CoP.

I've never seen a COP of greater than 4 for a UK specced ASHP, but I did only spend 18 months in the industry.

In that time, I drew the conclusion that most of the systems were specced too small for the heat demand, with individual models generally too close to maximum draw, with insufficient attention spent on the energy performance of the dwelling.

I think they can work, but even now, nearly 10 years after I was doing it, heat pumps are still regarded as quackery, and the UK expertise is in short supply.

55c as the supply temp for the heating circuit is way to high. Our AS typically supplies at 35c to maintain 20c for a 0c outside temp. 55c for hot water is very hot as well given most showers set default maximum to 38c for safety. 55c is scalding hot.

Given age and build I think most heating would struggle / massively expensive to run so definitely an outlier use case for AS.

IIRC 55°C for a hot water tank is the temperature to kill legionelles bacteria so many installers set it too that. For a domestic tank with no stagnant feeds or exits over 45°C is generally considered OK.

I use a solar thermal panel and tank for hot water which supplies all our domestic hot water needs for about 7 months of the year and is used as a pre-heater for a second conventional tank with immersion heater when not hot enough. The washing machine is filled direct from the solar system on the fill cycle.

Following this post, different situation but I have just started a new build 1 1/2 storey 150m2
UFH on both floors insulated to current regs.
Going for a Grant air source heat pump as no mains gas. We will have a log burner in living area downstairs. I have visited a couple of new builds with similar systems and generally the owners are really happy with them. As long as sized and fitted correctly. RHI payments can be claimed back for 7 years.
As I said different situation with well insulated new builds or renovations. I would be interested to hear any feedback from anyone running ASHP in newer homes

NIBE controller does a heat to 65c in both heating and water every two weeks to ensure Legionella build up doesn’t become a problem.