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Author Topic: Small ASHP (Split system) Install  (Read 18013 times)
M
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« on: April 08, 2017, 06:29:48 PM »

Hiya. Thought I'd start a thread on this, as i finally got a small (3.5kW) ASHP (air con unit) installed, after 4 years of pondering. I actually raised some thoughts questions on this thread in July 2013.

Apologies if all of this is obvious to everyone, or most folk, but I thought it was worth a mention, and also so others could correct or amend, or just polish, some of my ideas and conclusions.

OK, here we go. We have GCH which works well, I don't think we use 'too' much as annual gas consumption is about 7-8,000kWh and that includes hot water and gas oven (hob is induction).

During the 'shoulder months' Feb-Apr & Sept-Nov we often use a 400W oil rad to keep the chill off the living room during the daytime, between morning and evening gas burns, or on the warmer, but not quite warm days to help warm the living room up. Often it's not enough.

The thought occurred to me that getting a COP of perhaps 4+ from that 400W would be a good thing, so I started pondering small split system A/C units. I also started to chat on the MSE website, and one guy on their ran with it, started a discussion thread, and later got a unit installed. Another South Walian also did the same at the end of last year. Following their success, pleasure and enthusiasm, I finally took the leap on April Fools Day.

Some theory:-

Personal economics - If the leccy comes from PV, then until export is metered, it's free (I currently export about 70% of generation). But even if bought, then during the warmer shoulder months when I hope for a COP of 4 or 5, then 1kWh of leccy costs me 12p, v's 2p for 1 kWh of gas. But at 80% efficiency (my boiler is certainly less) 6kWh gives you 4.8kWh of heat, so comparable to the leccy ASHP on price.

But, because I'm only maintaining heat in a couple of rooms, and not heating the whole house (which would mean extra heat loss) then gas consumption will be far less. the other S. Walian, who does have much higher gas consumption than myself, reported these figures for Feb and Mch 2017 v's 2016:
Feb gas consumption down 1,489kWh, leccy import up 64kWh
Mch gas consumption down 882kWh, leccy import up 34kWh

Obviously there could be weather issues, but he checked and thought the years were comparable, and my 1st qtr gas consumptions for the 2 years are very similar.


Environmental issues - It's probably safe to assume that any leccy I fail to export, or any additional leccy I import will be made up by gas generation, so at approx 50% efficiency, the gas plant will burn 2kWh of gas to replace the 1kWh of leccy I used. But the ASHP COP should be 2+, so that should make up for it, plus the greater savings again, from localised heating, rather than a full GCH burn.

The noise from the indoor unit is impossible to hear, though the fan can be heard as you dial up the speed, and I'd probably use the fan most of the time to blow the air through the living room, and out into the hall if warm enough, using the door as a control. The outside unit is also very quiet, and can't be heard from about 10m, so much less noise than I expected, however I did go for an LG model which claims to be very, very quiet.


Costs - I did consider the DIY units, but was too scared in the end, but fully installed, including some additional costs for going through 2 walls, plus a case of lager because the guys were so helpful from the very start, and initial phone contact, it all came to 1,100.


Not sure if it'll ever make the 1,100 back in savings, but hopefully I'll be able to report back some gas savings, which will mean a reduced carbon footprint. Plus the air con part may be highly valued on those rare occasions when the house can't cool down overnight, such as about 1 week in 2015, and 1 day in 2016.

Longer term, when batts become viable, I'd hope to be able to make use of the ASHP, with even less import, during times when generation is fluctuating up and down (above and below demand.)

Lastly, it was installed on 1-4-17, the first truly warm day of the year here, and it's been warm ever since, so apart from having a play with it, and testing it out, I timed it perfectly to be of little to no use till Sept+ ........ oh well. Some April's seem to need lots of heating throughout, and some need next to no heating, this one has actually required the early 'cracking' of windows (locked but slightly open?) to get rid of the heat / solar gain.
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Just call me Mart.     Cardiff: 5.58kWp PV - (3.58kWp SE3500 + 2kWp SE2200 WNW)
GarethC
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« Reply #1 on: April 11, 2017, 09:34:01 AM »

Very interested to hear how you get on. The recent large reductions of grid emissions intensity underpin what you say about only needing modest COPs to achieve lower emissions than GCH.

Unlike even 3-4 years ago, probably means that heat pumps are now a much greener option than GCH even if they provide hot water relatively inefficiently.
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pdf27
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« Reply #2 on: April 11, 2017, 11:32:15 AM »

Average emissions are slightly misleading - what counts is the marginal emissions, i.e. what power station is fired up to meet the additional load on the grid. The virtual extinction of Coal is very good news here though - this summer for instance the national grid are predicting that the marginal plant will all be gas rather than coal, but not by very much: they're predicting electricity prices to be at a level where all the gas plants would make a small profit on running and all the coal plants would make a slight loss. Increase demand somewhat (by adding heat pumps, making it winter-time, etc.) and I think the marginal plant would probably be coal rather than gas.

Combined cycle gas turbines are in the region of 50% efficient, so for all seasons except winter it looks to me like a heat pump with any COP above 2 would be the best option right now. For winter use I'm not so sure - as you need to assume that the marginal load will come from coal for a big chunk of the time and gas the rest the required COP to be better will go up significantly. I **THINK** this means that for well insulated houses heat pumps are probably the best option, and for badly insulated ones gas probably is: that also fits with the economics (big heat pumps are expensive, small gas users get hammered by the standing charges).
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M
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« Reply #3 on: April 11, 2017, 12:39:35 PM »

Hi guys, that seems to fit with my reasoning, and the use of a secondary heat source for selected use. I based all my grid impact thoughts on gas gen as that will be the marginal source ramped up (theoretically) to meet my increased leccy demand, or to cover my reduced PV export.

The big lightbulb moment though, and I agree that this will also be outside of the coldest days/months, is the large reduction in whole house GCH from targeted heating, as experienced by the other MSE poster and the large gas savings - they are not direct savings of less gas v's more HP, but rather avoided gas consumption from allowing most of the house to cool down more than normal, and thereby reduce heat loss (reduced heat differential).

I'm not sure about the efficacy of running the HP and GCH at the same time, to use spare PV generation. I'd never do it with the oil rad, but perhaps the HP COP makes up for it. My assumption here is that if there's spare generation, then there's probably semi-decent sun, and whilst cold outside still warmer than nighttime when COP will be lower.

I don't know if duplicating heating capital costs, and an extra 1k spend can be justified, but I suspect at worst it won't be too bad. I'll need to see what impact it has on both leccy and gas consumption (and comfort) then try to rationalise all of it at some point in the future. That'll be fun!
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Just call me Mart.     Cardiff: 5.58kWp PV - (3.58kWp SE3500 + 2kWp SE2200 WNW)
pdf27
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« Reply #4 on: April 11, 2017, 02:09:21 PM »

The big lightbulb moment though, and I agree that this will also be outside of the coldest days/months, is the large reduction in whole house GCH from targeted heating, as experienced by the other MSE poster and the large gas savings - they are not direct savings of less gas v's more HP, but rather avoided gas consumption from allowing most of the house to cool down more than normal, and thereby reduce heat loss (reduced heat differential).

I'm not sure about the efficacy of running the HP and GCH at the same time, to use spare PV generation. I'd never do it with the oil rad, but perhaps the HP COP makes up for it. My assumption here is that if there's spare generation, then there's probably semi-decent sun, and whilst cold outside still warmer than nighttime when COP will be lower.
Actually, I'm not sure how much is from targeted heating and how much is from the fact that boiler efficiency will suffer (possibly quite badly) when working at a small fraction of capacity and short-cycling. I've certainly seen data from the US where oil fired heating used for hot water in summer was horrifically inefficient because it was operating at a small fraction of design load - gas fired boilers should be significantly better, but I still suspect the efficiency will be pretty poor.
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GarethC
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« Reply #5 on: April 12, 2017, 10:07:51 AM »

Good points pdf.

One thing though, if we all switched from GCH to heat pumps, net we would consume less gas overall.

That's if the gas previously used for heating was instead used to produce leccy in 50% efficient power stations (and used to power heat pumps) AND the heat pumps averaged COPs of greater than two.

If on average they achieved 2.5 (which I think is realistic to conservative), all other things being equal gas consumption would be 20% less.

Of course, if uk demand for gas for GCH declined by 20% (which would be a hell of a lot if you think about it), it should reduce the price of gas. And cheaper gas would increase the chance the gas met marginal increases in electricity demand instead of coal.

Does that all scan??
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M
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« Reply #6 on: April 12, 2017, 10:19:28 AM »

Actually, I'm not sure how much is from targeted heating and how much is from the fact that boiler efficiency will suffer (possibly quite badly) when working at a small fraction of capacity and short-cycling.

Good point.

Messy question, but where full HP heating and super insulating may be hard to promote, do you think developers promoting new builds could successfully market a property with dual heating such as a slightly undersized GCH, with a 1 or 2 room heating/cooling boost given the extra cost isn't massive?

Would folk understand the principle / tricks and benefit, or would it be a pointless diversion away from the doing the job 'properly'?
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Just call me Mart.     Cardiff: 5.58kWp PV - (3.58kWp SE3500 + 2kWp SE2200 WNW)
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« Reply #7 on: April 12, 2017, 10:25:30 AM »


Does that all scan??

Interesting. I'm trying to find an annual average COP for ASHP in the UK, but they do seem to vary from site to site. I think estimates are 2.5+ with a few suggesting 2.9-3.5, so that would seem to support your figures. Location is presumably important too, say a southerly heat sink city, v's rural Scotland.

I'm obviously looking at the better end as I'm avoiding nighttimes, and the very coldest daytimes in mid winter when GCH will almost certainly be needed to maintain temps, so my average should shift upwards by 'cherry picking' usage.
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Just call me Mart.     Cardiff: 5.58kWp PV - (3.58kWp SE3500 + 2kWp SE2200 WNW)
GarethC
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« Reply #8 on: April 12, 2017, 10:31:01 AM »

Frankly, for a small, modern split system used for heating only not hot water I'd be amazed if you didn't manage a COP of 3+ even if you didn't cherry pick. It's the hot water element that bashes the COP below that.

There's a decent government report with the best data, but these are for systems including hot water (and even they had a median of about 2.5). I'll try to find it if I have time. I've got data from a Swedish government agency which showed that modern air conditiomers actually managed nearer 4 in a much colder country.
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GarethC
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« Reply #9 on: April 12, 2017, 10:50:48 AM »

https://www.gov.uk/government/publications/detailed-analysis-of-data-from-heat-pumps-installed-via-the-renewable-heat-premium-payment-scheme-rhpp

A new one hot off the press! Haven't looked in detail, but I - think- it suggests you should get at least 2.75 (mean of their results) since it's not doing hot water.

The overall mean for systems inc hot water was 2.65. Not too shabby. With new r32 systems (only recently available and about 7% better than the previous r410a iirc), 3 should be realistic. These things are now a pretty good way to cut emissions.
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Fionn
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« Reply #10 on: April 12, 2017, 12:09:05 PM »

I'm looking at putting in one of these myself for a home office where it doesn't make sense to run the gas boiler to heat one room.
Another benefit is that it's nice to have an alternative relatively inexpensive heat source available should your boiler pack in at short notice.
A separate CO2 based heatpump (COP of 4 approx) for hot water is probably the best option if one didn't have PV diversion or solar thermal available.
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PV - 2.75kW East, 1.5kW South, 2.5kW West. 3 x Flat Plate Solar Thermal with side arm FPHE on 268L cylinder
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« Reply #11 on: April 12, 2017, 12:41:50 PM »

These things are now a pretty good way to cut emissions.

Also hot of the press, had some totals for 'the other guy' in S. Wales who had the install last November, and I'm truly staggered.

Jan to Mch 2016 gas consumption was 6,423kWh
Jan to Mch 2017 gas consumption was 2,804kWh

[ For comparison and to hopefully exclude weather differences, I'm about 20 miles away and my consumption for the 1st quarters was
2016 352 units approx 3,900kWh
2017 357 units approx 4,000kWh ]

Extra leccy import comes to 124kWh, and a total guess at diverting another 124kWh of PV leccy, makes it 248kWh of leccy, and about 500kWh of gas burnt for leccy generation.

I knew the theory here, but have to admit to being shocked.
« Last Edit: April 12, 2017, 12:44:30 PM by M » Logged

Just call me Mart.     Cardiff: 5.58kWp PV - (3.58kWp SE3500 + 2kWp SE2200 WNW)
pdf27
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« Reply #12 on: April 12, 2017, 01:15:03 PM »

Messy question, but where full HP heating and super insulating may be hard to promote, do you think developers promoting new builds could successfully market a property with dual heating such as a slightly undersized GCH, with a 1 or 2 room heating/cooling boost given the extra cost isn't massive?

Would folk understand the principle / tricks and benefit, or would it be a pointless diversion away from the doing the job 'properly'?
I think that's an awful lot of money and complexity for not much benefit - far better to force them to go for heat pump heating and proper insulation via the building regulations instead.
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Countrypaul
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« Reply #13 on: April 12, 2017, 03:58:20 PM »

Messy question, but where full HP heating and super insulating may be hard to promote, do you think developers promoting new builds could successfully market a property with dual heating such as a slightly undersized GCH, with a 1 or 2 room heating/cooling boost given the extra cost isn't massive?

Would folk understand the principle / tricks and benefit, or would it be a pointless diversion away from the doing the job 'properly'?

Given that many people don't appear to see the benefit of running the GCH at a lower temperature for longer to promote the condensing mode - and I am told that many plumbers installing GCH set the boiler for >60 routinely, I suspect having 2 systems in place to warm a house is likely to result in both running suboptimally and consequent higher total costs.  facepalm Maybe I'm too cynical, but I strongly suspect there is a huge difference between those on a forum like this and the majority wth GCH that just see a thermostat to allow their lounge to be 25C within half an hour with no idea on how to reduce the amoun of gas they use.

I agree with pdf, force builders to build better homes with heat pumps, probably mvhr systems, integrated PV and lots of insulation properly installed.
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GarethC
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« Reply #14 on: April 12, 2017, 04:51:57 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.
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