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Author Topic: Small ASHP (Split system) Install  (Read 17518 times)
M
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« Reply #15 on: April 12, 2017, 05:50:26 PM »

The problem though is the millions of badly insulated existing homes...

In terms of whether a heat pump is better than a gas boiler or not, why should the level of insulation matter? Not sure I follow.

I think it's a game of two halves. Countrypaul and pdf are almost certainly right that for a new build I'm over thinking it, and good insulation is the key.

For older houses like mine, I'm pretty convinced now that the use of a HP as a secondary targeted heat source should be a positive move regardless of the house condition (as you say), though improving insulation where possible is always an important first step.

Hopefully April 2017 to Apr 2018 will be comparable to 16/17 and I'll be able to report some interesting gas consumption figures next year.
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pdf27
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« Reply #16 on: April 12, 2017, 05:51:56 PM »

In terms of whether a heat pump is better than a gas boiler or not, why should the level of insulation matter? Not sure I follow.
Two reasons:
  • Heat pumps only really show significant gains if you run them at low temperature - with a badly insulated house it's probably impossible to run the temperature low enough to provide adequate comfort, so you'll end up with them performing no better than a gas boiler.
  • The load on the grid is significant - unless we insulate at the same time as fitting heat pumps, you'll need to spend megabucks on strengthening the grid and increasing power supply. Insulating to good standards cuts the required grid works down to something sensible.
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dhaslam
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« Reply #17 on: April 12, 2017, 07:57:01 PM »

The main difference between using electricity and fossil fuels is that it can be renewable.  By using a renewable supplier all the money you pay goes into new renewable sources and maintaining existing ones.
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« Reply #18 on: April 12, 2017, 08:25:32 PM »

Thanks pdf, but I'm still struggling!

On point 1, HPs give their rated output and COP (say 15kW and 2.5) at a low flow temp (say 40 degrees?) as you say, but I thought that simply means you have to increase emitter sizes. I. E. if your 15kW GCH was running at 60 degrees, moving to an HP means you'll need to increase your radiator sizes by 50% to transfer the same heat to the house at the same rate. In which case they're equivalent, aren't they? 15kW is 15kW isn't it? I dunno.

On point 2, yes I see the load on the grid would certainly increase, but is drawing 5kW of leccy for a 15kW HP that bad? A lot less than one electric shower draws, and less than a couple of kettles. Sorry for all the questions!
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pdf27
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« Reply #19 on: April 12, 2017, 08:58:54 PM »

On point 1, HPs give their rated output and COP (say 15kW and 2.5) at a low flow temp (say 40 degrees?) as you say, but I thought that simply means you have to increase emitter sizes. I. E. if your 15kW GCH was running at 60 degrees, moving to an HP means you'll need to increase your radiator sizes by 50% to transfer the same heat to the house at the same rate. In which case they're equivalent, aren't they? 15kW is 15kW isn't it? I dunno.
The problem is that radiators end up being massive at low temperatures (halving the temperature difference means you need the radiators to be rather more than twice the size). Even underfloor heating starts to have problems at low temperatures and high heat demand, which is in any case very disruptive to fit.
Insulation solves both the problems - improving things to say the EnerPHit standard takes the peak demand from a few hundred W/m2 down to 25 W/m2, meaning that a (small) standard radiator can still heat it at low temperatures.
Edit: note also that heat pump performance starts to crash above 35C - gas boilers typically operate at 60-80C, meaning a temperature difference of 15 .vs. 40-60C, so it's more like 4:1 than 2:1.

On point 2, yes I see the load on the grid would certainly increase, but is drawing 5kW of leccy for a 15kW HP that bad? A lot less than one electric shower draws, and less than a couple of kettles. Sorry for all the questions!
The problem isn't individual demand, it's everybody for extended periods of time. There are what, 20 million households in the UK? 20 million x 5kW is 100 GW - approximately twice the current UK peak demand - on top of the existing demand which is already happening in winter evenings anyway. It isn't just a matter of building more power stations either - the transmission infrastructure is sized to provide 50GW, and simply won't cope with having to provide 150GW instead. That means the only option is to massively increase insulation levels and switch to some sort of smart grid in order to keep a lid on peak demand.
« Last Edit: April 12, 2017, 09:00:54 PM by pdf27 » Logged
marshman
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« Reply #20 on: April 12, 2017, 10:12:16 PM »

Interesting discussion, a few points/considerations I would like to add for furtehr comment/discussion Smiley.

1. A 15kW output heatpump is quite a big heatpump in domestic terms. My ground source one is 10kW output and that heats a very large detached house easily, but the house is very well insulated.

2. As pdf says the COP does "crash" at higher (above 35 deg C) temepratures.

3. The volume house builders are notoriously conservative and anything other than night storage heaters or oil/gas boilers and radiators and the bare minimum of insulation are all they will consider.

4. The general public need educating. They just don't get energy consumption or the concept of saving energy, be it lighting, heating or cooking. You can start with your "it's cold outside so I need to turn up the thermostat" type person, to the its too hot in here I'll open a window. They won't consider insulation, there's no point - they can't show it off to their neighbours - a shiny new car is more important, or the huge Smeg fridge, 50" T.V. etc.

5. Even if you could persuade the general populus to insulate you would then hit the next problem - ventilation, or understanding it. The number of people I know that will spend pounds and pounds on mould removers for their bathrooms, kitchens and even bedrooms. When you say to them open a window to get some ventilation after a bath or shower or cooking they look at you and say but its cold. You explain it doesn't take long to get rid of the moist air and the house will feel warmer after and they think you are mad. They then go on to tell you the dry all their washing indoors. Some people hgave no choice, I accept that, but a lot just don't get it.

6. The government needs to change its approach and a) educate the masses b) change the building regs to up insulation, sort ventilation - preferably MHRV, and ensure wet heating can run at lower temperatures allowing for heatpumps to be used. c) reintroduce the Green Deal or what ever offering cut priced insulation like they did a few years back, but put in some extra money to ensure it is done properly. Even some allowance for double glazing for those in houses with single glazing that can't afford it. Also look at ways of a getting  proper EPC for houses that identifies "easy" wins for the occupier and has some sort of inducement to do them. (carrot or stick could be used).

7.  To be honest I don't think ASHP are a viable option on crowded housing estates - the external unit fans are too noisy.

8. Enticing any sort of retrofit option for heatpumps will be a disaster - cowboy firms will jump on the band wagon of the latest government backed scheme and con people into paying a fortune for inadequate, poorly designed systems that will never work. There are already plenty of examples of that - undersized ground loops being a common problem.

9. I think the PDF fag packet calculation of 20 million households x 15kW is way too high - I know it was just an illustration of the electricity distribution problem but a proportion are electric heating anyway as they are not on the gas grid. The 15kW is not continuous. My last property, a large detached bungalow only had a 14kW boiler. Many smaller terraced places have much smaller boilers. If the government were serious they could legislate to install a proper smart grid,  proper smartmeters and heating systems where turn on was staggered and controlled to limit and manage demand. If houses had enough insulation and thermal mass you could even use it to smooth out the peaks and troughs, effectively storing energy as heat in peoples houses.

At the end of the day I think a combined system would just be too complex for the majority and the expense could/would not be justified.

Roger
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Countrypaul
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« Reply #21 on: April 12, 2017, 11:51:10 PM »

Edit: note also that heat pump performance starts to crash above 35C - gas boilers typically operate at 60-80C, meaning a temperature difference of 15 .vs. 40-60C, so it's more like 4:1 than 2:1.

Do you have any reference for that figure of 60-80C by any chance as it what I thought too, but have no hard evidence for it? From what I recall for a condensing boiler to work in condensing mode it should be below 55C. It could be that an education program on how to use a gas boiler cut not only save a lot of gas and therefore reduce CO2 output, but could also save people an awful lot of money. Maybe an option for future gas boilers should be to not allow then to run at a higher temperature than condensing mode will work at stir more nanny state perhaps, but I think too many people need help as they just don't get it as stated earlier.
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marshman
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« Reply #22 on: April 13, 2017, 08:59:32 AM »

Edit: note also that heat pump performance starts to crash above 35C - gas boilers typically operate at 60-80C, meaning a temperature difference of 15 .vs. 40-60C, so it's more like 4:1 than 2:1.

Do you have any reference for that figure of 60-80C by any chance as it what I thought too, but have no hard evidence for it? From what I recall for a condensing boiler to work in condensing mode it should be below 55C. It could be that an education program on how to use a gas boiler cut not only save a lot of gas and therefore reduce CO2 output, but could also save people an awful lot of money. Maybe an option for future gas boilers should be to not allow then to run at a higher temperature than condensing mode will work at stir more nanny state perhaps, but I think too many people need help as they just don't get it as stated earlier.

They operate in condensing mode as long as the return water temp is below 55C. The lower the better. So if you have a 20 dec C temp diff, flow to return, you can in theory have a flow temp of 75 de C and still achieve condensing and hence higher efficiencies. Trouble is, as you say, people can and do turn up the boiler temp and I suspect many so called high efficiency boilers do not run in condensing mode as the temps are too high. Again a problem with education and peoples understanding, or lack of it, about how stuff works.

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3.15kWpk (15xSharp ND210)/SB3000. & 3.675kWpk (15 x Suntech 245WD)/SB4000TL, 10kW GSHP driving Wirsbo underfloor heating from 1200m ground loops. 10' x 7' solar wall (experimental). Clearview 650 Wood Burning Stove. MHRV - diy retrofit. Triple glazing.
M
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« Reply #23 on: April 13, 2017, 09:50:14 AM »

7.  To be honest I don't think ASHP are a viable option on crowded housing estates - the external unit fans are too noisy.
Hiya, just to say this was one of our considerations, and made a bit easier by the fact that it would be in daytime use when 'the world' is a little noisier. However, the outside unit is extremely quiet (as marketed), and when I tested it, by walking down the garden, I couldn't hear it at all at 10m.

I was told they aren't as bad as folk suggest, but it's actually much better still than expected, which the installers promised.
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pdf27
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« Reply #24 on: April 13, 2017, 09:56:12 AM »

Hiya, just to say this was one of our considerations, and made a bit easier by the fact that it would be in daytime use when 'the world' is a little noisier. However, the outside unit is extremely quiet (as marketed), and when I tested it, by walking down the garden, I couldn't hear it at all at 10m.

I was told they aren't as bad as folk suggest, but it's actually much better still than expected, which the installers promised.
Remember that you've got a small unit running at small temperature differences in temperate weather - exactly the conditions required for minimum noise. Try to get a similar sized unit to provide heating and hot water for the whole house on a cold day and it'll have to work a whole lot harder - not to mention that on modern housing estates you aren't going to be able to get 10m away without being in someone else's living room!
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Countrypaul
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« Reply #25 on: April 13, 2017, 10:18:59 AM »

Surely for a modern(crowded) housing estate the heating beng supplied centrally in a "district" heating system should be one of the considerations rather than the assumption that each place should have its own boiler? Whether this would be a GSHP, ASHP, Gas boiler, Solar thermal, PV, CHP system etc. or more likely a combination should almost be a secondary consideration. However again as stated earlier, this would require the estate developers/builders to be a little more adventurous and think a little bit more, so probably little chance  Sad
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M
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« Reply #26 on: April 13, 2017, 10:43:38 AM »

Hiya, just to say this was one of our considerations, and made a bit easier by the fact that it would be in daytime use when 'the world' is a little noisier. However, the outside unit is extremely quiet (as marketed), and when I tested it, by walking down the garden, I couldn't hear it at all at 10m.

I was told they aren't as bad as folk suggest, but it's actually much better still than expected, which the installers promised.
Remember that you've got a small unit running at small temperature differences in temperate weather - exactly the conditions required for minimum noise. Try to get a similar sized unit to provide heating and hot water for the whole house on a cold day and it'll have to work a whole lot harder - not to mention that on modern housing estates you aren't going to be able to get 10m away without being in someone else's living room!

Regarding large units, and less optimal running times, please see thread title and the premise behind it. I suppose for larger units and full heating and hot water noise does need consideration. For us, noise wise, it's very quiet standing right in front of it, far less than quiet conversation and impossible to hear through any windows. The indoor unit is silent, sort of, but you get more noise as you dial up the fan speed.
« Last Edit: April 13, 2017, 12:51:51 PM by M » Logged

Just call me Mart.     Cardiff: 5.58kWp PV - (3.58kWp SE3500 + 2kWp SE2200 WNW)
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« Reply #27 on: May 01, 2017, 08:28:12 AM »

1 month in, and loving it. Didn't expect to get much use in April, especially with the lovely warm start we had, but as the arctic weather came in 'HiPpie' got to do its thing. Probably ran for 100+hrs in April, and the GCH didn't need to come on though the upstairs has gradually cooled down (lost all it's thermal mass) with a week or more of outside temps at between 3-13C ...... so ...... with great regret ...... the GCH has been put back on today to warm the house back through. Hopefully that'll be the last day till Sept, or Oct ..... or Nov  fingers crossed!

Total leccy import for April was 96kWh, last year was 82kWh, and the year before 97kWh, so too tricky to work out how much of HiPpie's work came from import, but certainly looks like the vast bulk was from PV.

Very pleased, and so are the cats, who've moved from the bedroom, and now curl up under HiPpie.
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« Reply #28 on: May 04, 2017, 12:59:11 PM »

Sorry, probably a stupid question, but what is the ASHP feeding? Does it have a radiator or two plugged into it?
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« Reply #29 on: May 04, 2017, 01:05:11 PM »

Sorry, probably a stupid question, but what is the ASHP feeding? Does it have a radiator or two plugged into it?
An indoor fan coil unit, typically wall mounted. It acts as a refrigerant to air heat exchanger and a small built in fan increases the rate of heat exchange achievable with it.
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