Rethinking the mindset for mass retrofit - a provocative idea

[JamesPa]

I'm being deliberately provocative here to stimulate out of the box thinking, please bear with the explanation and numbers, but then feel free to critique. 

 

In summary I am proposing that, for retrofits (at least in the South of England, where many of the UK houses are), we should abandon the insistence on achieving low flow temperatures in favour of accelerating roll out, which is necessary to mitigate climate change.  So here goes:

 

I think we all know

1. that ASHPs are the way to go for low carbon heating, and that low carbon heating is an essential part of combating climate change
2. that the way to make ASHPs work efficiently is to minimise the flow temperature
3. that the current model, whereby ASHPs are subsidised by government yet still cost up to 3 times as much as a gas boiler to install, is not working, in the sense that it is not gaining the traction hoped, let alone the traction required to meet climate change goals
4. that large ongoing government subsidies are likely to be unsustainable politically, however strong the environmental arguments
5. that most ASHP installations 'require' replacement of at least some radiators, almost all 'require' the replacement of the DHW tank and other sundries, and that this contributes massively to the cost and disruption
6. that, because we 'need' different flow conditions ‘specialist’ design is required
7. that local plumbers, who are surely the mainstay of the retrofit market for gas boilers (which is the retrofit market), are not engaged in the process because its too complex, onerous and expensive and because of point 6.

 

Now if we could fix #5 and #6 then #7 is fixed more or less automatically, #3 no longer need applies and we can achieve actually #1, which is the real goal

 

So what is getting in the way - answer: a) regulation and b) #2.  Regulation is ultimately fixable, but #2 is a function of the physics.

 

Several manufacturers now do high temperature heat pumps which run at 65 or even 70C.  These are much dismissed on this forum because they are less efficient, and the received wisdom (which, until recently, I, physicist by training, bought into) is to design for the lowest possible flow temperature, which is what triggers most of the other challenges. 

 

From a physics point of view designing for low flow temperature is undoubtedly the right answer, but engineering, particularly system engineering, is about trade offs between practicality, performance, cost and other factors.

 

So what if we designed for a flow temperature of say 65 (and a delta T of 5)?  The average radiator temperature would be about the same as the common 70/50 combination, so we almost certainly don’t need to change out radiators.  At a flow temp of 65 you can easily heat the DHW, with a standard coil, to 50( provided that the HP has a decent modulation ratio) so we don’t need to change out the DHW tank.  In many, perhaps most, domestic environments the primaries split near the boiler into 2x22mm (upstairs and downstairs), which is sufficient for 6kW, 7-9kW at a push, on each leg, sufficient for most households, so we don’t need to swap out the primaries.  And we don’t need to upgrade the ‘standard’ 22mm feeds to the DHW tank because they are already good for 6kW at a delta T of 5C, which is sufficient and twice what an immersion heater delivers.  We will have to swap out the existing diverter valve (a few 10s of £) and we will need to connect up the controls differently (maybe half a day for the electrician), but that’s about it.  No need for MCS, extensive replacement of functioning hardware, extensive lifting of floorboards (or solid flooring), replacement DHW tanks etc; a regular plumber and his electrician friend can just do it in a day or two.

 

But, you say, the efficiency will be terrible!  Well sure it won’t be as good as it could be, but there is almost always a trade off between capital investment and long term cost and that trade off is not ‘one size fits all’.  I would suggest that, while a SCOP of 4 or more is desirable, it is sufficient, in the real world, if the SCOP is such that the running cost are about the same as whatever the current system is.  In the case of gas, the predominant heating in the UK, this means an SCOP of about 3 currently (because electricity is 3 times the price of gas), a figure likely anyway to reduce as the Government (hopefully) reduces the wholly artificial weighting in favour of gas that exists at present.

 

Some weeks ago I posted a model of weather compensation (which I attach to this post) and this can be used to estimate the effect of increasing flow temperature.  I have taken, as an example, the LG figures for their 12kW model.  This shows, for conditions in the South of England (where a large proportion of the UKs houses are situated) an modelled SCOP of 4.4 (with weather compensation) and a ‘design’ flow temperature of 45, frequently the target for retrofits where radiators as are present.  If we increase the flow temperature to 65, the SCOP reduces to about 3.5.  That’s a big reduction, but arguably a sacrifice worth making in return for the advantages in terms of up-front cost and disruption.  Most importantly, even allowing for poorer-than-model performance, its good enough by the definition above.  It is dependent on a reasonable (but by no means perfect) setting up WC, but if installers weren't spending so much time on replacing perfectly functional equipment, they could perhaps do this and pop back a couple of times in the ensuing heating season to adjust.

 

Of course radiator and DHW upgrades can, and should, still be offered, but as an option not as a requirement, which is how they are currently positioned.  This decouples the part which is transition to low carbon heating, and the part which is system improvement and, vitally, gives consumers choice. 

 

The upshot is, I think, that we could for a good proportion of households, eliminate much of the ‘compulsory overhead’ associated with retrofit of a heat pump.  Yes it means compromise, but the rewards in terms of climate emissions are enormous.

 

The MCS brigade probably wont like this, but that’s just tough.  The ASHP market cannot possibly continue as a niche sector if it is to achieve our climate goals, and the constraints imposed by MCS confine it to just that place.  This has to change!

 

Discuss! (but in doing so please bear in mind that the objective is to find practical solutions to achieving mass retrofit with existing, or near-existing, technology, not to achieve perfection).

WC Simulation.xls

[JohnMo]

Only thing to add, is we need a wholesale change of mind set, to accept weather compensation is the way forward, whether that's a run 24/7 mode or an extended running period of  8 hours or so, to cover your days heating.

 

Not the on/off like a yo-yo, loads of zones which seems the mind set currently in force.

 

 

[Temp]

9 minutes ago, JamesPa said:

But, you say, the efficiency will be terrible!  Well sure it won’t be as good as it could be, but there is almost always a trade off between capital investment and long term cost and that trade off is not ‘one size fits all’. 

 

Historically electricity has cost roughly three times gas on a per kWH basis. So it's important for most people that the average COP is more than three or running costs will go up. Can that be achieved with 60-65C flow rates?

 

The other problem is the size of the heat pump required. According to this web page...

https://www.boilergrants.org.uk/news/how-much-gas-does-a-boiler-use

The average gas boiler in the UK is rated at 35kW. 

 

It's claimed that lower output ASHP can be used by running them for a higher percentage of the time. But the same argument can be applied to gas boilers. I wonder if we really have enough data about the "load factor" of gas boilers in cold weather?

[JamesPa]

10 minutes ago, Temp said:

 

a) Historically electricity has cost roughly three times gas on a per kWH basis. So it's important for most people that the average COP is more than three or running costs will go up. Can that be achieved with 60-65C flow rates?

 

b) The other problem is the size of the heat pump required. According to this web page...

https://www.boilergrants.org.uk/news/how-much-gas-does-a-boiler-use

The average gas boiler in the UK is rated at 35kW. 

 

c) It's claimed that lower output ASHP can be used by running them for a higher percentage of the time. But the same argument can be applied to gas boilers. I wonder if we really have enough data about the "load factor" of gas boilers in cold weather?

Ive added lettering above so I can refer

 

a) Yes (at least according to the modelling), provided weather compensation is turned on and correctly adjusted

b) Gas boilers are massively oversized because its easy to do so.  The average house needs about 6-8kW.

c) Gas boilers don't have the same characteristics as ASHPs and don't benefit massively from running slow and low (although they probably do benefit a bit).  But so what, we need to make gas boilers history and give people a practical and affordable path to adopting ASHP else we are toast (literally!).  Most gas boilers are set up inefficiently so we have only to do as well cost-wise as an inefficiently set gas boiler and the transition becomes a no brainer!

 

14 minutes ago, JohnMo said:

Only thing to add, is we need a wholesale change of mind set, to accept weather compensation is the way forward, whether that's a run 24/7 mode or an extended running period of  8 hours or so, to cover your days heating.

 

Not the on/off like a yo-yo, loads of zones which seems the mind set currently in force.

 

 

 

Of course, that's a given.  But the result is a more comfortable house so, once people get over it, its not a difficult transition.

 

Edited April 22, 2023 by JamesPa

[joe90]

No mention about extra insulation to negate more heating (and you only buy it once). My heating comes on for maybe 2  months a year and for a large detached house it’s a 4kW ASHP 🤷‍♂️.

[JamesPa]

10 minutes ago, joe90 said:

No mention about extra insulation to negate more heating (and you only buy it once). My heating comes on for maybe 2  months a year and for a large detached house it’s a 4kW ASHP 🤷‍♂️.

No, that's a separate issue.  Necessary I grant, but not the problem I'm trying to discuss/solve, namely that the transition to ashp isn't happening (and as things currently stand isn't going to happen) because it's too difficult, too expensive, and too disruptive in the way we currently do it.

[JohnMo]

16 minutes ago, JamesPa said:

c) Gas boilers don't have the same characteristics as ASHPs and don't benefit massively from running slow and low

I think there are a good correlation, the typical boiler installation is around 80% efficient, the typical low temp weather compensation gas boiler efficiency is 110%, which is a big drop in running costs, but not many installs are complete so that advantage can be taken, instead the installer uses a Y plan or similar.

 

 

27 minutes ago, joe90 said:

My heating comes on for maybe 2  months a year

 

Living in the sunny south also has some advantages, well insulated here means I only have my heating on for 5 to 6 months a year, instead of on most of year.

 

[Temp]

Found this although I'm not sure the way they calculate averages is correct. Should be weighted by the number of houses in each age band?

 

It's also worrying that for detached houses it seems to have gone up after 2006?

 

https://tools.bregroup.com/heatpumpefficiency/dwelling-heat-loss

 

Edited April 22, 2023 by Temp

[ProDave]

There is clearly a lack of joined up thinking.  We have to get to net zero. Somehow.  The current approach really only skims around the edges of the problem.

 

Lets fit heat pumps in place of all fossil fuel boilers.  That will do it.  No matter that for a good many people that will mean more expensive heating.  Oh they don't seem to be queuing up in sufficient numbers to pay £000's just so they can have more expensive heating.  I wonder why that is? 

 

Assuming they all do choose to get an ASHP, just like electric cars, where is the green energy coming from to power them?  We still burn a lot of fossil fuel to produce electricity.  We need to make sure we add to the electricity demand less fast than it is being turned green.  No point adding extra demand faster than we can build and commission wind turbines or nuclear power stations, otherwise each additional heat pump gets powered by additional probably gas fired power stations.  Now which produces less CO2, a gas boiler burning in a house to heat it, or an ASHP powered by a gas fired power station?

 

And we appear to be completely ignoring the elephant in the room, or rather in the walls, lack of insulation and air tightness.

 

I don't have the solution and it seems nobody does, but unless there is a proper plan to upgrade the old housing stock, then we are not solving the problem, just kidding ourselves that we are.

 

Having built and now living in a near passive standard house, heated by a small ASHP with low heating bills, this is what we should be aiming for already for every single new build, not just a few geeks that choose to do so, but still we are not demanding that of the mass market house builders.  If we can't even get all new houses built NOW built properly m what hope is there ever to get all the old poor houses upgraded?

 

It is a problem that needs to be solved in a way that everyone can manage, and like it would seem everyone else, I don't have a clue how we are going to manage it.  I am just glad for once to be ahead of the curve with my own house.

[ReedRichards]

I actually have a 12 kW LG heat pump and (replacement) radiators.  It was designed for a flow temperature of 50 C and I was promised an SCOP of 3.2 for heating.  Now using Weather Compensation I get a SCOP of somewhere around 3 overall (heating and hot water).  I don't have a high temperature model, mine can get up to about 55 C.  But unless LG have made vast improvements to their efficiency in the two and a half year since I got my heat pump then the idea that I could achieve an SCOP even approaching 3 whilst heating the water to 65 C seems wildly overoptimistic.  But I'm in the far north of England where outdoor temperatures are lower so I'm not going to achieve an SCOP as good as I could in the south.  If what you are proposing really would work in the south then it's just yet another north]south divide.  

[gregh]

I'm convinced air-to-air has to be an answer here. Even if the government isn't willing to subsidize it!

1. Generally more efficient (SCOP >5 in many cases)
2. Usually less expensive, and can be done incrementally

If you want to fully electrify, DHW can be a bit of a challenge, but there are options depending on individual circumstances.

 

[SteamyTea]

TL;DR

 

This may have been answered, but shall say it anyway.

The reason that heat pumps are being promoted is that they are mature technology.

The reason that heat pumps are going to be fitted is because they can reduce, quite significantly, our domestic CO₂ emissions.

The rate of fitting HPs will go hand in hand with renewable electrical generation.  Global emissions from electrical generation may well peak this year.

https://www.newscientist.com/article/2368526-emissions-from-global-electricity-generation-may-have-now-peaked/

 

I think most high temperature HPs use supplementary resistance heating for the final 10°C or so, so not really high temperature at all.

 

It has been a long day, but I try not to smoke too much hopium or unobtainium.

[Iceverge]

1 hour ago, JohnMo said:

Not the on/off like a yo-yo, loads of zones which seems the mind set currently in force.

 

 

 

This yo-yo method is the only way I imagine most could afford to get some heat into their houses. 

 

Most houses could get by on electricity today. An A2A or two and an immersion for the hot water, maybe an ESHP for high DHW users. 

 

 

 

 

 

 

 

[Big Jimbo]

I've got a vented, timber floorboard floor. 9 inch solid brick walls. Single glazed old metal framed windows. Concrete tiled roof with no underfelt. The truth is that the house leaks like a sive, has zero insulation. When the weather is really cold it is actually warmer outside than inside. To be honest the house is not fit for purpose. However, the majority of our uk housing stock is like this. I know some very rich people with stupidly large houses. Heating is on 24 hours a day. If it gets too hot indoors they open all the windows and doors. Thats how they adjust the heating ! That, while some old person on a state pension sits with a blanket over themselves. People with low incomes (The majority) are not going to pay out thousands of pounds to have thier houses upgraded. They struggle to find hundreds of pounds to pay the monthly bills. If put into the position of broken heating, and you say i can sort you a new boiler for a grand, or a new Carlos fandango system that will save the planet for 2 grand. 99% are going for the grand option. .......It's a mess, and i don't know what the answer is.

[Radian]

I think my experience shows the aims of the OP may be achievable - at least for those of us living in the South.

 

I've been on a mission to range-rate my 30kW gas boiler down as far as possible to emulate replacement with an ASHP. The first step was to implement a digital interface to gain control of flow temperature to run separate DHW and radiator temperatures. Surprisingly to me, over the last winter, I managed to get down to 15kW max. power output and run the existing radiators at 55^oC without any great drama. This is significantly lower than the original design levels. Less than 15kW didn't work out too well for the DHW when asking for 65^oC so I caved in at 15kW (but I may re-visit this as I was under pressure to 'fix' things at the time). Now I've got full control over flow temperature I need to look at load or weather compensation to see if I could improve the projected SCOP.

 

The house is detached 4/5 bed built to slightly worse insulation levels than should have been in force for 1998 although the empty cavity walls have recently had an EPS fill. Annual gas consumption has remained fairly consistent over the last four years (including this year's experiment) so the losses remain fairly constant but are replenished over a longer period.

[JamesPa]

Thanks for all the responses, keep them coming, they help innovation. 

 

I'm not going to comment on the 'politics', that's for another forum altogether and for an election within the next two years.  Nor am I even going to try to solve every problem (eg insulation , north-south climate differences...) at once, that's too difficult, which is why we generally partition things into manageable chunks.  However:

 

21 minutes ago, Big Jimbo said:

They struggle to find hundreds of pounds to pay the monthly bills. If put into the position of broken heating, and you say i can sort you a new boiler for a grand, or a new Carlos fandango system that will save the planet for 2 grand. 99% are going for the grand option.

 

Which is sort of the whole point of the post.  ASHPs are actually pretty simple, they are basically a fridge,  but we make the installation complicated by trying to optimise them, leading to ridiculously high installed prices (2 grand -  more like 10-15 grand at present).   Worse still the 'rules' and the 'established practice' mean that we are bullied into making the installation ridiculously complicated, with the result that hardly any actually get installed.  The thinking needs to change otherwise not even those who can afford to pay a little extra will bother.

 

30 minutes ago, Iceverge said:

Most houses could get by on electricity today. An A2A or two and an immersion for the hot water, maybe an ESHP for high DHW users. 

 

53 minutes ago, gregh said:

I'm convinced air-to-air has to be an answer here. Even if the government isn't willing to subsidize it!

1. Generally more efficient (SCOP >5 in many cases)
2. Usually less expensive, and can be done incrementally

If you want to fully electrify, DHW can be a bit of a challenge, but there are options depending on individual circumstances.

Absolutely I agree.  Its a harder sell because the internal fittings are not what we are used to, and the A2A merchants round here at least seem to be a bit reluctant to fit splits (multiple indoor units, one outdoor), but A2A is definitely part of the 'mix'.  

 

1 hour ago, ReedRichards said:

I was promised an SCOP of 3.2 for heating.  Now using Weather Compensation I get a SCOP of somewhere around 3 overall (heating and hot water).

I would say that's pretty good, 3.0 actual vs 3.2 modelled/sold!  Makes me, if anything, more confident about the plausibility of getting to 3 at 65C based on -2/-3 design temp.  Bear in mind that 3 is basically good enough to match the running costs of gas, and that's with the current ratio of gas prices to electricity, which is artificially tilted in favour of gas (and likely to change) and the model was based on technology available today (actually since 2019), which can only improve, thus extending the range north.

 

37 minutes ago, SteamyTea said:

I think most high temperature HPs use supplementary resistance heating for the final 10°C or so, so not really high temperature at all.

That certainly used to be the case, but not so with more recent devices.  The modelling was based on LGs specifications and this does not use a supplemental heater.

[MikeSharp01]

1 hour ago, SteamyTea said:

unobtainium

If that glows in the dark it may be the solution to all our problems - no hang on.

[ProDave]

10 hours ago, JamesPa said:

Which is sort of the whole point of the post.  ASHPs are actually pretty simple, they are basically a fridge,  but we make the installation complicated by trying to optimise them, leading to ridiculously high installed prices (2 grand -  more like 10-15 grand at present).   Worse still the 'rules' and the 'established practice' mean that we are bullied into making the installation ridiculously complicated, with the result that hardly any actually get installed.  The thinking needs to change otherwise not even those who can afford to pay a little extra will bother.

Octopus seem to be trying to break that mould by offering simple cheap ASHP installs.  I await hearing from anyone who has had one fitted to see how successful that is.  Hopefully this is the start of cheaper, simpler installs.

[JamesPa]

10 minutes ago, ProDave said:

Octopus seem to be trying to break that mould by offering simple cheap ASHP installs.  I await hearing from anyone who has had one fitted to see how successful that is.  Hopefully this is the start of cheaper, simpler installs.

Agree.  I know one person who has had, and is pleased with, their Octopus install.  More power to their elbow if this is typical, and they probably have some clout with Government as they have bailed out quite a few electricity companies.  

 

However Octopus alone wont cut it (in fairness they probably know this) and they are still dependent on the 5K grant to get the installed price down to the price of a gas boiler.

Edited April 23, 2023 by JamesPa

[SteamyTea]

9 minutes ago, ProDave said:

Octopus seem to be trying to break that mould by offering simple cheap ASHP installs.  I await hearing from anyone who has had one fitted to see how successful that is.  Hopefully this is the start of cheaper, simpler installs.

They are probably only going to pick the very easiest installs, the ones that could be done by almost anyone.

[RichardL]

Seems like original idea was replace the gas/oil boiler with an equivalent & ideally an equivalent skillset to fit it.

 

ASHP A2W - nearly fits the bill - but not quite - needing carefull sizing and ancillary works - insulation/radiator sizing etc to guarantee success.

 

The next shift should be some sort of admission that the swap out gas/oil boiler and swap in something doesn't fly - which leads to opening up the market for other ideas rather than one size fits all. It feels like this sort of forum is already there with that open thinking - it needs to filter up to whomever drives the marketplace;

 

I don't know who that is

   Subsidy drivers/politics?
   Manufacturers risking take-up?
   Word of mouth? 

CH and DHW options for moving off carbon should be a simple consumer level selection of a few options - A2W, A2A combinations etc on a level playing field.

[ProDave]

In recent years I have concluded the whole "heating industry" in the UK is in pretty poor shape.

 

I have given up counting how many heating systems I have worked on that have never been working properly since installation, the usual faults are original plumbing or wiring simply done wrong so the system is not shutting off when reaching desired temperature.

 

I find heating controls pretty simple and logical, having spent my life working on "control systems" mostly for industrial machinery, the usual domestic heating controls are really down at the simple end of the spectrum.  But it astounds me how many plumbers and even more so how many electricians have no basic understanding of the principles.  They just wire them in a "painting by numbers" fashion, connect the cables from the valves and thermostats into the terminals marked for them in a standard wiring centre, job done.  I think many of them never actually test that the controls are actually working properly, and if they did would not have a clue how to fault find and correct the problem.

 

If so many installers cannot get the controls for a standard boiler install correct, then what hope of getting an ASHP install correct?

 

The mass adoption of ASHP's does require a lot more installers who understand how the controls work, and how to test that they are working properly.  Of course this is not helped by the fact that each make of ASHP has a completely different set of electrical controls and operating philosophy to the next one.  Perhaps trying to get the manufacturers to standardise the electrical interface and make it more like a standard boiler controls input would help?

[Dave Jones]

Heating method is not really what should be the focus. Its  insulating the fabric of the building.

 

This means Ground floor, walls and roof.

 

This really cannot easily be done while the building is habited. The floors need to come up, insulation, dpc and screeded. Not cheap, not easy.

 

pre- cavity wall properties that are suitable for external insulation are the low hanging fruit. Council housing etc. The rest are hard to do and £££.

 

Doest matter how hot or what type of boiler/pump used, if the heatloss is too great your never going to win. Just boosting the heat temp to keep up with the heat loss is pointless.

[RichardL]

11 minutes ago, ProDave said:

heating controls

+1 This
Ideally the controls market would be separate from the A2W/A2A (Whatever) systems like they broadly are with gas/oil.
Granted currently an on/off dry contact for a boiler is a bit crude - but its simple and doesn't fail when the internet/cloud/wifi/firmware version buggy (choose any) is down

but
The added value this time round should have been standard ways to talk to the smart meter and work out current cost export import etc - I mean talk to the smart meter direct - not some fancy integration across the cloud which a techie can keep working but joe public has no interest or time (quiet rightly) in fiddling with.

No one wants to call a software engineer to fix their CH.

[JamesPa]

23 minutes ago, SteamyTea said:

They are probably only going to pick the very easiest installs, the ones that could be done by almost anyone.

They do filter installs yes.  I think its by house size (demand) and whether there is a convenient location for the HP.

 

20 minutes ago, RichardL said:

Seems like original idea was replace the gas/oil boiler with an equivalent & ideally an equivalent skillset to fit it.

 

I would characterise the post as suggesting to replace the gas/oil boiler with an ASHP configured to be sufficiently close to equivalent that it doesn't necessarily need ancillary works. 

 

Currently we make it necessary to do all the ancillary works, in many cases it isn't if we accept a modest loss of efficiency.   

 

Sizing (of the system not individual radiators) is a bit of an issue, but we have data here - the existing gas/oil consumption .  This, based on my personal experience, is at least as reliable as full, paid for, surveys.  Even if you do a full survey its only £300, not several 1000s which the ancillary works cost.

 

28 minutes ago, RichardL said:

The next shift should be some sort of admission that the swap out gas/oil boiler and swap in something doesn't fly - which leads to opening up the market for other ideas rather than one size fits all.

In the way its currently done, no, it doesn't and wont (IMHO) ever fly.  Hence the post

 

29 minutes ago, RichardL said:

which leads to opening up the market for other ideas rather than one size fits all.

Hence the post.  Essentially I am suggesting way to change the way we do things so that the conversion from gas/oil to A2W is relatively straightforward, and results is approximately the same running costs (at current price ratios).  The tweaking to make it super efficient, which we currently insist on bundling with the conversion, is essentially what results in all the ancillary works.  this can be offered as an optional upgrade, not bundled.  It requires a change of mindset (and of regulation) which is what I am tilting at.

 

32 minutes ago, RichardL said:

It feels like this sort of forum is already there with that open thinking - it needs to filter up to whomever drives the marketplace; 

Agree, lets continue the debate!  Once we have some well formed ideas we might be able to find ways to filter up/out.

 

32 minutes ago, RichardL said:

CH and DHW options for moving off carbon should be a simple consumer level selection of a few options - A2W, A2A combinations etc on a level playing field.

Precisely, that's the only way forward.