This is pursuant to another thread. And I’ve touched on this before. It’s an interesting thought experiment. I’m sure it’s full of holes, but if not, there’s a knighthood in there for someone. Discuss!

“How to reduce UK space heating and hot water carbon emissions by 56% compared to current levels over twenty years, subsidy free, cheaply and with no other government intervention (maybe).”

An air source heat pump system which provides heating and hot water for £3k at an SCOP of 4.0 would reduce space heating and hot water C02 emissions by 42% (see note 1) compared to a high efficiency natural gas boiler at current grid intensity (0.519kg/kWh, 2) and cut running costs by 25% (3).

The average household gas bill is £752. A 25% decrease saves £188 per year, £940 in five (say £1k). A replacement boiler costs £2k installed. Our system costs £1k more, but savings would cover this in 5 years – an excellent payback incentivising homes to adopt just for financial, let alone green, reasons. Note, no subsidies anywhere here, in fact delivering long term reductions in domestic heat bills.

Gas boilers last about 20 years. Almost all must be replaced by then. All boilers might be replaced with our new systems over that period without forced ditching of working boilers. This would deliver a 42% cut in total UK domestic heating and DHW emissions by the end of the period.

If some of the gas displaced (wouldn’t need all of it) instead generated electricity in new gas power stations, they would deliver electricity with marginal emissions of 396kg/kWh (4), 24% lower than current grid intensity. Powering our systems with this electricity would deliver emission cuts of 56%. It should also lower electricity costs, improving system payback and incentives to adopt.

If, over that 20 years, other measures reduce grid intensity, as they will, then emissions cuts would be even larger. These measures might raise electricity costs by a third, and homes would still pay no more than today for heating and hot water due to the lower running costs of the new systems.

We need to cut emissions by 90% vs. 1990 to be sustainable. If domestic heating + DHW emissions have already fallen by 15% (don’t know!), then our systems would help cut emissions by 1-0.85*0.44 = 63% vs 1990 by, say 2035 (if we start replacing soon). With cuts in grid intensity, better heat pumps and fabric improvements (lower demand) by then, we could be done for domestic heating + DHW (businesses too?).

So, we need to design a system fitting the requirements chaps! Really should be doable.

1. Natural gas space heating emissions are 0.184 kg/kWh (http://tinyurl.com/nwc4rlq) divided by 82.5% efficiency = 0.224 kg/kWh. Therefore a system with an SCOP of 4.0 will deliver emission reductions of 1-0.519/4.0/0.224=42%.

2. Not 0.462kg/kWh and 47% as used previously. Previous figure used doesn’t include 7% grid losses, and the emission intensity of imported energy. Although advised by DEFRA, I can’t think why you would exclude these.

3. Average domestic price of gas in Q1 2015 was 5.0p/kWh, and price of electricity was 15.6p/kWh (http://tinyurl.com/o8zybas). So 4 SCOP delivers 1-15.6/5/4=25% saving.

4. Taken gas turbine emissions as 370 kg/kWh from the 2014 IPCC report (http://tinyurl.com/nub25kr)*1.07=396kg/kWh including grid losses. Divided by 4.0 SCOP= 0.099. 1-0.099/0.224 = 56% reduction. This intensity figure doesn’t include ‘life cycle’ add-ons, but I don’t think other figures I’ve used do either. Should they?? If so, gas boiler emissions figures should probably have a life cycle figure included too if not already. Check IPCC report for figures.

Posted By: jamesingramFirst thought, what is the mean carbon intensity of electricity during the heating period (high demand time)
this needs to be used rather than a yearly average figure

Can get that from GridWatch.

One way would be to reduce usage, so use less hot water (put people on a meter maybe), basic draft exclusion, thermal curtains.
I think most people could cut usage by 25% for no investment, just good management.

Technical solutions not only need a short pay back, but also need to be affordable in the first place.
No good saying to people that if they spend x, they will save y, when they only have a tenth of x to spend.

Grid CO2 reduction/intensity is probably best left up to the big boys, rather than individuals. This is becoming more apparent with the reduction in FITs, there is no incentive to share your power, but there is a big one to waste it yourself.

You can always change your car too.

Yes, the -slight- problem is that the system doesn't exist yet... But I think it should be doable, if not now, then soon.

I'm confident that you can heat an average UK home with AAHPs (simple air conditioning units) with an SCOP of 4+ for about £2k installed without upgrading insulation or using radiators (I don't think these are a good way to deliver the heat for ASHP systems - too lossy and expensive). Better air tightness would help greatly though.

We're discussing what to do about hot water in another thread, to which I'll return after my sojourn day dreaming about saving the UK environment. But it does seem harder. A 4+ SCOP must be maintained and the marginal cost can't exceed £1k.

James' question might relate even more to seasonal, rather than daily, grid intensity variation - is grid intensity higher in winter? I'll look into it. I'm not 100% confident of the sums on gridwatch. The hypothetical proposal to use displaced gas to provide electricity -might- provide for the concern.

ST - if your boiler's condemned, you have to replace it somehow. I know many homes would struggle to find even £2k and so choose straight replacement. But 'green deal thinking' should work here - a £3k loan to install the hypothetical system, repaid over five years, would cost the same as £2k for a boiler, and deliver savings thereafter.

Posted By: GarethCST - if your boiler's condemned, you have to replace it somehow. I know many homes would struggle to find even £2k and so choose straight replacement.

The problem here, is the firms offering new gas combi boilers for £17 / month.

<blockquote><cite>Posted By: jamesingram</cite>Id suggest using worst case figures for grid intensity. If it still adds up then great</blockquote>I have just does a very quick calculation of Grid Intensity (by the week and from 4 years data and only on coal at 1 kg/kWh, gas at 0.39 kg/kWh, nuclear and wind at 0.001 kg/kWh).
Worse case is 0.53 kg/kWh and best is 0.39 kg/kWh. Mean is 47.5 kg/kWh.

Not really enough of a difference to worry about.

Not sure we have ever fitted an ASHP system for £3k!.

Also generally modern condensing boilers only last around 10 years possibly a little more if you fit a decent one and the system is also well designed downstream.

We have never had issues with the stored temps of hot water in our installed ASHP/GSHP systems. Typically we target 48 degrees in the cyl and pasteurise every 2 weeks. Dishwashers take care of grease and the bigger properties have a point of use boiling tap.

Not sure about the AAHP option either.

We have fitted plenty of these in hotels, offices, studies, conservatories, summer houses etc. but generally in a single room application.

If you need to heat multiple rooms, doors or free flow of air is required which negates some functionality in a house and depending on the layout would mean some areas don't heat, unless you start chopping bits off doors etc.

There is also no option to zone, maintenance is required via a fridge engineer, and they are bloody ugly inside and out!

JonG, where do you get this myth from that 'modern' condensing boilers only last 10 years?
I have fitted WBs and Vaillants from '97 onwards, and not had one fail as far as I know.
They do not fail as a matter of course.

Other mfr's whose names end in 'i' may be less well made, or susceptible to faults.... but this does not apply to all condensing boilers....

Daryl it's an average obviously but it is pretty much an industry accepted figure TBH.

The problem with multi splits is the cost and the fact that they are pretty industrial and require ceiling distribution or wall distribution and fridge pipework routing around.

It may be ok if you are undergoing major renovation or new building but retro the costs would soon negate the benefit.

Reduce heat demand. Insulate and improve airtightness (while ensuring appropriate, adequate ventilation).

Reduce heat use (turn thermostat down, change programming so it's only used when needed - improved controls to prevent it coming on when not needed).

Heat pumps are great for off-gas, but for now electricity is over double the C02 of gas and electricity is a more costly fuel, which counters a lot of the real world COP (COP also drops withn outside temperature, so in coldest periods, you aren't going to get a COP of 4).

Lower hot water temperatures mean it works best with oversize radiators, or better still an underfloor heating system below chipboard or in a screed over a lot of insulation.

A GSHP seems to come out typically better than a good gas boiler overall; A good A2W HP comes out around the same as a good gas boiler; A good A2A HP comes out a bit worse than a good gas boiler - all based on equivalent emissions / costs for a well insulated property.

The key advantage of heat pumps comes when/if the grid is actually decarbonised, or electricity used to power them is from a low carbon source.

As it stands though, grid electricity is 'dirtier' (and doesn't seem to be getting considerably less so any time soon) and a COP of 4 is optimistic.

That said, presumably gas carbon emissions will be worse once we start shale extraction.

Posted By: Sigaldryunderfloor heating system below chipboard

I would not want chipboard in my build...
especially with UFH below it - too many nasty chemicals !

gg

Thanks for the input all.

+1 for gravelld's first point from his last post. With great regret, I just can't see it happening to the extent we need. Beyond green 'no brainers' (loft insulation etc.), it's too much hassle and cost.

Sigalrdy and gravelld, we've discussed the evidence that AAHPs can achieve SCOPs of 4 in this thread: http://tinyurl.com/puh2jnt, and why that translates into significant C02 cuts.

Key evidence I shoudl have included, was this Swedish field data http://tinyurl.com/o7tz2je. Note that units like the LG unit, available here for £704 http://tinyurl.com/omsseja, achieve COPs of about 4.0 in Malmo. Note that even the latest results are over two years old, and if you plot a line through the data by time, performance has improved steadily, so hopefully will continue to do so. Other useful info in there, such as that COPs benefit greatly with oversized systems.

Anyway, the previous thread discusses why they should manage at least this in the UK. I wish I could prove it, but I'd eat my hat if you can't manage 4.5 in England. And data here (which includes the LG unit for comparison with the new, top rated Daikin unit) http://tinyurl.com/ojrevge shows that R32 should provide further certainty.

Unfortunately, this the report linked to in this thread http://tinyurl.com/pmz9osj shows that neither conventional ASHPs, nor GSHPs, are cheaper to run than a modern gas boiler, even high performing ones. And their capital costs are prohibitive. I believe that using large radiators or UFH, and other complexities, contributes to inefficiencies in space heating compared to A2A.

Hence my interest in trying to find a DHW that achieves similar COPs at modest cost. Struggling on that one though to be honest...

So, JonG, I'm fairly sure a system such as that outlined in the OP should be possible. If you can deliver it you will be rich as well as saving the planet. What's not to like?

Gareth you may be right, but we have priced A2A for several jobs for whole house heating...........still not done one though!

Part of the issue is that they are not a pack solution, to go A2A and A2W as you want to is probably such a negligible market that it hasn't happened and in fairness warm air heating went out of fashion in the 70s in the UK (remember the trench heaters, we once combined a water to air heating unit with a GSHP against our better advices and it didn't end well) although Johnson and Starley still make domestic gas to air boilers.

UK climate is different, not got anything empirical but when the Danfoss launched the AQ after extensive Baltic testing they fell over on a spectacularly regular basis. It turned out that the defrost software parameters needed some fettling in the UK. Our island environment does impact humidity and therefore defrost.

Posted By: GarethCI'm confident that you can heat an average UK home with AAHPs (simple air conditioning units) with an SCOP of 4+ for about £2k installed without upgrading insulation or using radiators (I don't think these are a good way to deliver the heat for ASHP systems - too lossy and expensive). Better air tightness would help greatly though.

I'm afraid I don't share your confidence, especially after living in several average UK homes. A leaky, poorly insulated home would lose heat faster than it was created, especially if that heat was at a low temperature. I was interested in GSHP technology for our curent home, but all of the research I found agreed that it was suited to homes with better than average insulation and airtightness (ideally with UFH). The same must hold true for A2A systems. You'd also have to look at ducting to try and distribute the air in a more uniform manner.

Existing housing stock would have to be upgraded with insulation and airtightedness, they would more than likely have a wet heating system that you'd have to remove, you'd then have to retrofit ducting, which may be difficult and unsightly in a home not designed for it.

New builds could be designed with ducting in mind, and would already have improved levels of insulation and airtighness, but you wouldn't see anything like the savings for the whole of the UK with just the small number of new builds.

Even with newbuilds, I'd suspect people would prefer UFH off a ASHP or GSHP than ducted A2A. Much nicer having wam feet, uniform heatng in all rooms, much more controllable with different temperatures in different zones (bedrooms at lower temps than living areas, unused bedrooms at minimum 'frost' settings). Importantly, no drafts moving dust about and exacerbating asthma, hay fever suffers, and other resparatory issues.

I just don't see the the benefts air over UFH, especially in a country that generally doesn't need ducted cool airconditioning in summer.

I certainly started at the "throw technology at the problem" path when I first got interested in this stuff, but I began to realise simplicity is better. The trouble is that incentives from government tend to be focused on green bling because the politicos don't really understand. Or maybe it's the lobbyists with more influence.

Posted By: gravelldI certainly started at the "throw technology at the problem" path when I first got interested in this stuff, but I began to realise simplicity is better. The trouble is that incentives from government tend to be focused on green bling because the politicos don't really understand. Or maybe it's the lobbyists with more influence.

Same here. I quickly became disillusioned when I looked into 'green tech' and found that none of them seemed to give a complete solution. I concluded that the only green tech that actually delivered (and keeps delivering) was insulation.

I'm quietly installing IWI and ceiling/floor void insulation one room at a time in our house. It's a slow process because its all DIY and I don't have much free time, but I can really feel the difference in the room that is complete, and that's before I have finished lime plastering the walls.

I