Air Source Heat Pump

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Discussion

bangy1

Original Poster:

105 posts

142 months

Saturday 18th January 2020
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Hi folks we moved house in March last year and are getting slowly there so next job being the heating.

Currently we have oil fired heating which has a non condensing boiler which coupled with the general crustyness of the metal fitting on the external tank means investment is needed. However due to the trend of phasing out fossil fired systems we have been looking into heat pumps as our old property had one.

We have had the survey done by energy savings trust scotland and are able to get the interest free loan via MCS so are looking at installers etc just now.

My question is most have quoted LG and Samsung systems which I am not that familiar with as our last one was a Daikin. Are there any brands we should avoid etc I have heard Nibe, Grant and Mitsubishi mentioned as good, we are also struggling to find much in the way of local installers etc here in Aberdeenshire.

I was considering maybe leaving the oil in perhaps to act as a boost if needed but this could scupper MCS/RHI I guess. Regardless we will need a couple of extra radiators in also due to some poor layout decisions by previous owners. I know insulation is key to any ashp install due to lower leaving water temps so will look at that all first.

Sorry for long post,any advice much appreciated as to brands to avoid etc and installs. Thanks

Equus

16,767 posts

100 months

Saturday 18th January 2020
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bangy1 said:
... Regardless we will need a couple of extra radiators in also due to some poor layout decisions by previous owners. I know insulation is key to any ashp install due to lower leaving water temps so will look at that all first.
This sounds like a very half-arsed approach, and is ringing immediate alarm bells as to whether ASHP is even a sensible solution in the first place.

You haven't told us anything about the property it's going into, or your patterns of occupancy, but as a general rule heat pumps only work well if:
  • The property is both genuinely well-insulated and has a high level of airtightness (which most existing properties of an age to be looking at replacement heating systems don't).
  • The house is ideally fitted with underfloor heating; even over-sized radiators often struggle, so the suggestion that you think you'll get away with just a couple of extra radiators to compensate for a poor existing radiator layout sounds very optimistic.
  • The house will have high levels of occupancy. Heat pumps aren't very responsive to changing demand, so only really work efficiently if the house is occupied and heated pretty much continuously.
All the brands you mention are reputable, and at the end of the day a heat pump is basically a refrigerator running in reverse, so it's not rocket science and there's not a huge difference between the manufacturers in terms of cost, reliability and efficiency, but the bigger worry is about suitability of a property for the installation... grant funding of this sort always attracts a lot of shysters and cowboys after a quick buck, who will specify systems even on the most inappropriate properties and make all sorts of extravagant promises to get you to sign up.

JT68S

25 posts

189 months

Saturday 18th January 2020
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Agree with the above.
The property needs to be very well insulated/airtight etc...
Underfloor heating is also instrumental with ASHP.


I have a 16kw Samsung air pump fitted at home, house is a 375m2 open plan new build with UFH and so far its very good/efficient.
Along with the government RHI scheme (quarterly payments paid to us for 7 years) our electric bill for heating/hot water/cooking are more or less even
winter months no more than £300 per annum.

Speak to a company called Joules based near Liverpool,


hantsxlg

862 posts

231 months

Saturday 18th January 2020
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I'd be cautious. Friends did similar, installing air source heat pump. They had huge issues with icing. They are in west Wales which isn't a particularly cold climate (frosts are rare) but is damp. The heat pump freezes up constantly and then stops working. Normally just when you need it most.... it is meant to have heating elements to stop the condensation on the heat exchanger from freezing but they are not man enough for the job and use a lot of electricity (wiping out the savings) to operate.

fastbikes76

2,450 posts

121 months

Saturday 18th January 2020
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We have pulled our more heat pumps than we have ever installed. Retro fitting ASHP’s hardly ever works out as you hoped and eventually end up going to fossil fuels again. If it’s a nice new build insulated to the hills then you are on the right track, otherwise I wish you good luck, you will probably need it !

bangy1

Original Poster:

105 posts

142 months

Saturday 18th January 2020
quotequote all
Thanks for the replies although no need for the tone in the first one I am just after some advice.

The property is a 3 bedroom detached brick property built in 1993 with approximately 180m2 floor space split over 2 floors. The windows I believe were all replaced 5 years ago to new double glazed units and there is approx 120mm insulation in loft which will need upgraded. There is also a supplementary log burner in the kitchen. My initial thoughts is to maybe just upgrade the tank and boiler but this is a finite solution perhaps.

Equus

16,767 posts

100 months

Saturday 18th January 2020
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bangy1 said:
...no need for the tone in the first one I am just after some advice.
Aimed at whoever suggested that solution to you, rather than you directly.

As I said, these Government funding initiatives invariably attract a feeding frenzy among the cowboys.

The basic shell of an early 1990's property will be very poorly insulated compared to modern standards; if it's masonry, it may still have an uninsulated cavity, which will be at best 50mm (twice that would now fail to meet current regs). It will almost certainly have been built with an uninsulated ground floor, and no attempt at airtightness. Be aware that increasing loft insulation too far can cause its own problems (do a search for loft condensation, on this forum).

My advice (as someone who has been designing houses since before yours was built) would remain that it's not a suitable property for an ASHP install, especially using radiators as the heat emitters, and especially not on the North East Coast of Scotland, but it's your funeral...

fastbikes76

2,450 posts

121 months

Saturday 18th January 2020
quotequote all
Equus said:
Aimed at whoever suggested that solution to you, rather than you directly.

As I said, these Government funding initiatives invariably attract a feeding frenzy among the cowboys.

The basic shell of an early 1990's property will be very poorly insulated compared to modern standards; if it's masonry, it may still have an uninsulated cavity, which will be at best 50mm (twice that would now fail to meet current regs). It will almost certainly have been built with an uninsulated ground floor, and no attempt at airtightness. Be aware that increasing loft insulation too far can cause its own problems (do a search for loft condensation, on this forum).

My advice (as someone who has been designing houses since before yours was built) would remain that it's not a suitable property for an ASHP install, especially using radiators as the heat emitters, and especially not on the North East Coast of Scotland, but it's your funeral...
As a Heating company operating 40years plus ... absolutely everything above !!

Equus

16,767 posts

100 months

Saturday 18th January 2020
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fesuvious said:
Why is the airtight nature so crucial to ASHP?
Simply the rate at which heat is lost from a property, versus the rate that the heating system can transfer heat to replace it.

In crude terms, the rate of heat transfer from a heat emitter (be it a radiator or a floor, with an underfloor heating system) is basically a function of the difference in temperature between the heat emitter and the air it's trying to heat, multiplied by the surface area of the heat emitter.

Heat pumps aren't capable of generating the such high water temperatures as conventional boilers, so you need to make the surface area of the emitter much larger, to compensate. Hence UFH is ideal, as it gives you the entire surface area of the floor as a heat emitter.

But if you have poor insulation and high levels of air leakage, the house will simply be losing heat faster than the ASHP can put it back (or so close to it that it takes forever to respond to changes in demand).

It's not the air leakage on its own that's a problem - it's the overall heat loss from from fabric and air changes combined - but you will appreciate that (to take an extreme example) you can have all the fabric insulation in the world, and it still won't help much if you've got a howling gale blowing through the property because the front and back doors are left open. A very leaky house approximates to that scenario.

Modern houses are air tested upon completion. I won't use the units measured, as they'll just make it look more complicated, but to put simple numbers to it, a modern house might typically be achieving an air test figure of 3.5 (some are much lower - PassiveHaus requires below 0.6), whereas a house of the OP's age will typically be somewhere between 10 and 15.



Edited by Equus on Saturday 18th January 15:34

finlo

3,731 posts

202 months

Saturday 18th January 2020
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Because they produce low grade marginal heat output at the best of times so you need to retain 99% of there output.

Kawasicki

13,041 posts

234 months

Saturday 18th January 2020
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I rented a new house when I returned to Germany in 2015. It had an air source heat pump..it worked very well except on one occasion where we thought we would turn the heating off because we were away for a couple of weeks. When we got back it took about a week for the house to warm back up!

The other slightly worrying incident is that the unit in the garden failed when it had been running 2.5 years. It cost the landlord over 8000€ to replace. The warranty was 2 years.

Not much of a saving for him.

bangy1

Original Poster:

105 posts

142 months

Saturday 18th January 2020
quotequote all
Cheers for the replies confirmed my initial thoughts as many have said it's better suited to new builds which have good insulation. As the lwt is a good bit lower than the oil fired system we have. Dont want to start oversizings rads etc so will look at getting a condensing boiler. Thanks folks

anonymous-user

53 months

Saturday 18th January 2020
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My parents have one in their house in Crete, wouldn't reccomend it at all. It's supposed to heat the house in winter and then cool the floors in summer. It does pretty much nothing of the sort.

Biomass or Peacoal is the way forward. I heat a 200m2 house with Peacoal and it costs around £800 a year (our winters see -20 too) it's also very clean as it's effectively a blast furnace.

caziques

2,567 posts

167 months

Saturday 18th January 2020
quotequote all
Excellent summing up by other posters, so I will only address this issue (I do underfloor heating in NZ exclusively with air source heat pumps)


hantsxlg said:
I'd be cautious. Friends did similar, installing air source heat pump. They had huge issues with icing. They are in west Wales which isn't a particularly cold climate (frosts are rare) but is damp. The heat pump freezes up constantly and then stops working. Normally just when you need it most.... it is meant to have heating elements to stop the condensation on the heat exchanger from freezing but they are not man enough for the job and use a lot of electricity (wiping out the savings) to operate.
All heat pumps freeze below about 7 degrees. Units should then reverse cycle to defrost - all our heat pumps are set to defrost every thirty minutes. Any longer can be a real problem.

Excessive icing can be a sign of low refrigerant, or simply the coil temperature sensor is faulty.

If the heat pump thinks the cold refrigerant temperature is say 30 when it is in fact 3, it doesn't work properly.

Coil temperature sensor failure by reading incorrectly is common, even on named brand machines.

Equus

16,767 posts

100 months

Saturday 18th January 2020
quotequote all
caziques said:
All heat pumps freeze below about 7 degrees. Units should then reverse cycle to defrost - all our heat pumps are set to defrost every thirty minutes.
... Of course, when they do so, they're reducing their own efficiency - they're literally dumping energy back out to defrost their own external workings.

Couple this to the fact that their basic efficiency (Coefficient of Performance) drops off at lower temperatures, anyway, and it means that they're least efficient when you need them, most efficient when you don't. nuts

And in terms of the rate of heat delivery from the heat pump vs. the rate of heat loss from the house, you also need to remember that that, just as a radiator will transfer heat more quickly if there's a big difference between its water temperature and the room temperature (hence heat pumps perform poorly because of their low water temperature), the same physics means that houses lose heat faster when there's a big difference between their internal temperature and the air temperature outside. So when it's cold out, they're losing heat at a faster rate.

This graph shows that there''s a crossover point where the increasing heat loss from the house meets the reducing efficiency of the heat pump... beyond which the heat pump just can't keep up any more. What the graph doesn't tell you directly is that as you approach that point, you've also got less in reserve to be able to cope with changing demand, so they become even less flexible:


Skyedriver

17,655 posts

281 months

Saturday 18th January 2020
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I usually agree with Equus his knowledge is good BUT

We moved into a 1999, 4 bed bungalow near Oban two and a half year ago, last year we ditched the 20 year old brick filled electric storage heaters.
ASHP installed NIBE pump (which has had some bad press in the past). We had increase loft insulation to 300mm.

You'll need larger rads than the ones for oil/gas or whatever as they don't heat up quite as much but our place is set to 19 degrees C and it's plenty warm enough although we have a slight balance problem where living area is warm and bedrooms less so. It's down to placing the wi fi stat in a house that is a large L shape with the bedrooms at the north end.

We got the £10K interest free loan from the Scottish Govt, which we pay back monthly and get the RHI three monthly which covers the repayments. Total installation cost, SSHP, all pipework, new rads throughout was £14910 so we effectively are paying under £5K for a total heating and hot water system. There is plenty of hot water for three really good showers off the tank with mains pressure with loads more for washing up etc. Never run out.

And finally with the awful storage radiators we were tied to SSE with THTC (Total Heat Total Control) where you get cheaper electric for the storage heaters at the expense of silly high priced electric for the rest.

Jumped ship, went with Bulb, cheapest rate for electric, we reckon about £80-90/month for heating/electric cooking/hot water and all the gadgets.

A new electric storage system was priced at £10k nor RHI of course, a new wet system would have been similar I think and again no RHI and stinky oil.

And our NIBE pump is quieter than a neighbours Dunsley(?) one.

Equus

16,767 posts

100 months

Saturday 18th January 2020
quotequote all
Skyedriver said:
We moved into a 1999, 4 bed bungalow near Oban two and a half year ago, last year we ditched the 20 year old brick filled electric storage heaters.

...we reckon about £80-90/month for heating/electric cooking/hot water and all the gadgets.
To be fair, comparing ASHP against electric storage heaters is a bit like saying that Mussolini was an enlightened liberal, compared to Adolf Hitler.

You're still paying more per month than it's costing me on an oil-fired wet CH system on a 19th Century cottage with solid brick walls and no insulation worth speaking of (except a bit in the loft), though of course differing lifestyles preclude a direct comparison. I do work from home, though (so heating on continuously all day), and sleep with windows and doors open at night, which means I'm re-heating the place from flat cold every morning.

Jambo85

3,311 posts

87 months

Saturday 18th January 2020
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Fit like bangy. Just to make sure you’re aware the HES loan can also be used for a condensing boiler upgrade, I managed to sneak a new unvented cylinder into it too.

Happy to recommend a local Grant installer if you’re North of Aberdeen.

Davie

4,732 posts

214 months

Saturday 18th January 2020
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I can't really offer much on this front as I'm very much learning about the pros and cons of an air source pump. Prior to us meeting, my wife built her house and had an air source pump installed however latterly, we've since moved back in so I've inherited the system and its issues so this has been quite interesting reading for me too.

We have a Grant air source pump and perhaps rather oddly, it's supplies our house and the house next door (also ours, technically) and whilst we had lots of issues when we moved back, most was due to our then tenants not using the system as it should be. Ie, cranking up the thermostat when they got in and wondering why it took days to warm up, something I wasn't aware of either.

However, we have a unit in the garden that supplies underfloor heating downstairs in both properties plus two radiators in our house and two next door, plus supplies the hot water tank. Initially I could only ever get around 26degs out of the unit, thus the heating was pretty much non-existent but Grants attended and despite it being a 6 year old unit, seemed happy to assist. The short of it is, the actual installation isn't that terrific in hindsight... for example we have a hot water tank with an immersion but it's on a manual switch so to boost the water up to bath worthy levels, you need to flick the switch in advance but I'm going to have it rewired back in to the main control unit.

We also had issues with a couple of sensors and this time Grants seemed a little less keen to get involved, saying that the unit wasn't sufficient to supply the size of the house/s although I'm lead to believe, it was they who spec'd the unit at the build. Anyway, I digress and I managed to diagnose a faulty gas discharge temp sensor and replaced it and immediately we're back up to a water temperature output of about 50 to 55degs which has made a huge difference and granted, yes the system is very slow to respond but we just leave underfloor heating running constantly and regulate the bedrooms with the manual stats on the radiators.

We've also got solar panels that feed directly to the pump itself so that massively offsets the costs though it does vary but it's still proving to be cheap month to month despite also being in Scotland. As for icing and such like, not had any issues to date and bar a couple of temp sensors failing, the unit itself is proving to be very reliable. We're looking to split the system now however so also debating a second heat source pump or to fit a combi boiler but trying to get good advice is proving difficult.

So, probably of little use to you but thus far, I'm pretty happy with what we have.

caziques

2,567 posts

167 months

Sunday 19th January 2020
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I'm not a great fan of heat pump radiator systems, all systems I do (a few hundred so far) are air sourced heat pump with the energy going into a 100mm concrete slab.

This acts as a giant storage heater (holds about 1 kWhr of energy per square metre), hence heating is done during the day, fortunately in NZ it is never below freezing hence defrosting is a factor but not that relevant.

I often do 150 sqm pipes lays, which can be 150 kWhrs of stored energy - or the equivalent of 15 litres of oil.