Beelbeebub

We have some flats using electric vented thermal stores. Work really well. That's said we had one brand of TS where a pin hole developed after about 7 years in the DHW coil. The F&E tank kept filling up about 2lpm then overflowing. Tenant called complaining of high elec consumption, cool showers and "dripping" noises At first I thought the ball cock had failed. But that was all fine. Eventually traced to the only explanation (failed coil). Swapped the whole thing out for another brand in a morning. Biggest balls ache was getting the things up 3 flights of stairs! A HP driven one using high temps (65C flows) from a small capacity (sub 5kw) unit might make sense for small flats. The lower cop for DHW is still higher than direct electric. The smaller HP is then sized for more efficient running at the lower end of the scale (10C external say) where we spend most of the heating season. Only running flat out on a few days if the year, I wonder.if you could set it up so the electric immersion in the vented tank could contribute heat to the CH system?.... Maybe not the highest efficiency, but as long as it can hit 3.5ish that's ok, and a smaller external box and small tank..... Hummm

Yeah, we switched out all the UVCs (we didn't have many) after that. Went to combis and in the case of electric places, electric showers and vented cylinders. It's also why I'm thinking of doing heat only HPs for the electric flats and leaving the existing cylinder/shower arrangement. Any future upgrade would be to vented tank heated by large coil and if pressure is an issue, a pump. The combi flats and houses are tougher. But almost all did have a tank at one point, so it would be possible to refit one. Probably go with vented and pumped.

Problem we had is at very low drips, the water tracked from inside to outside around the arms between the top and bottom halves. It's really poor design, there is no drip feature on the top part of the tundish. Little drips will track down the arm. I modified them by drilling the top "end stop" out and inserting the copper pipe just a few mm further into the tundish so there was a sharp drip feature. And yeah, the pipework can't take full flow. But, in fairness, I don't think they are supposed to. The PRV isn't a blow off valve, all or nothing. It's supposed to "crack" open and allow a dribble of water out, thus bleeding energy. In theory it only needs to bleed a flow rate equivient to the energy input and delta between incoming mains and activation temp. Even a 30kw boiler jammed on full power would only require 5lpm to stay cool. It was part of why we suspected the tenant was playing with the valve. The second time it happened it was an overflow because the valve had opened so far and was stuck on the little "detent" before it snaps back. The resulting flow overwhelmed the tundish pipework and flooded the floor. The floor which the tenant stacked lots of "priceless" papers that he forbade me to move our of the standing water when I arrived. Neither I, the G3 guy or the valve manufacturers could envisage how the valve could be activated to that level of opening without manual intervention. The tenant claimed against our insurance for damage to the papers and items (despite me having written to him previously to warn him not to store items next to the tank). Luckily I had all the communications, and testimony from the manufacturers, engineers etc His claim was denied. 😁

Just seen! It's a typo!😁🫢 Should read "Every single home owner I know with an UVC hasn't had it inspected. Several didn't even know they had an UVC. One didn't even know where the cylinder was!" Basically, apart from me, getting inspections because it's a legal requirement, nobody in private homes seems to be - alot of people don't get their boiler serviced every year. Most people are oblivious

I should add that even the g3 guy thought it was daft, the check was just a check of the expansion vessel then a visual check of the valve and pipework. Could be done by anyone with eyes and a foot pump. Every single home owner I know with an UVC has it inspected. Several didn't even know they had an UVC. One didn't even know where the cylinder was!

As I was responsible for several.UVCs I can answer this. We had an issue with a cylinder, basically the PRV activated and the tundish leaked, it is a design flaw with the common tundish design, water can track down the arms to the outside. We have a suspicion the tenant was fiddling. Anyway, the arse covering recommendation from on high (the manufacturer's and insurers) was we needed someone with a g3 ticket to insect every year. This meant our regular company had to send thier one g3 ticket guy to do the annual boiler services. Rather than any of the regular gas safe guys who had been doing it (mostly they fit combis for us) This was a fact that led us to ditch UVCs where.fitted and go with combis and vented.

Wonder if it is to shepherd you towards their products. If they require a much higher spec for 3rd party stuff than they require for their own it gives them an advantage?

Sensible. But the point is your system is incrementally improving. Right now it is good enough and will no doubt get even better. Imagine if it was all or nothing. No halfway house, see how it goes, tweak a bit more, replace stuff as it ages out. Just do it all in one go because otherwise it won't be efficient enough. We need to make your approach easier (normal even). Support it where required (IMHO, via a price guarantee subsidy for a.limited time).

Electric or HP?

Sound like a good setup. The heating side is, more.or.less the way forward. If (probably when) I do another build, I think I'll go for a HP feeding single zone UFH (it'll prob be a bungalow given other restrictions) with a diverter to a hot water cylinder. Prob unvented, though maybe vented with pump. I don't think I'll use a thermal store just because of the extra temp/volume needed. Only one pump, one valve. Weather compensated flow temps with thermostat high limit. Question, if your boiler had some sort of catastrophic, not under warranty failure.....would you replace it? Do you use gas anywhere else? Eg hob?

This is my point. The current system makes HP installs expensive so this charge is leveled at them (I'll be honest, I think some of this is down to the current political climate and culture wars - some wish to stop all progress on the climate front and it is convenient to use "but what about the poor working class salt of the earth bloke?! - all this climate stuff is for middleclass metropolitan tofumunching wokerati!" attack line.) The idea is to make swapping to a HP, which is good for society, also good for the majority of people. At the moment we are trying to make a change good for all of us at a national and global level whilst making it hard on an individual level.

Yes, plenty of rubbish installs, especially the older ones with r410a and badly sized (over or under) But yes I am fixated on ASHPs as the main (not only) solution, because they are. Sure, some people will still be on oil or gas or electric for various reasons (unusual location, unusual usage patterns, unusual buildings etc) but the vastajority of houses, flats, offices etc could swap over from gas boilers to HPs. Not always air source and not always air to water (UK moving straight to A2A systems is an option) but given our infrastructure and preference for wet heating systems A2W ASHPs will be the default choice, like a combi gas boiler is often the default now and if not a combi then a boiler and UVC. But if we want to reduce our carbon output the gas boiler has to go. There is no way we can get a combustion boiler to emit much less than 200gCO2 per kWh*. Many emit more. HPs can already get below that value and as the grid decarbonises the figure drops lower and lower. Already a well setup HP running on a good day for our grid will emit less than 25gCO2/kwh The funny thing is we already had a huge stimulus subsidy that was pretty effective with the boiler scrappage scheme. People had old boiler ripped out, and got cash towards a new boiler. We need a similar setup to boost our heating fleet's efficency again. The current scheme isn't working. Our rates are slow. *Theoretically we could if we used Hydrogen, and central carbon capture for any H2 made with gas, but if you examine the logistics of that route it's clear it is pure fantasy, whose only purpose is to delay the switch from combustion boilers.

That is an extremely well set up system. It can only achieve the apparent the high efficiency because the UFH g WC provide very low return temps to allow maximum latent heat extraction. If you were to use a modern HP on such a set up (when the current boiler expires) you would need a DHW tank, so would fit a large coil model and, alongside your low flow temp heating, would be getting efficencies of 150%+ (with respect to the base gas) A modern HP will, in most cases, burn less gas for the same heat output than a boiler attached to same system. Yes, some really bad systems with tiddly little rads that need 75 or 80C flow temps just to keep you warm enough, will need upgrading because they won't reach a.SCOP over 2.5 But if your system can run flow temps below 55C, you will almost always end up with less gas burn via HP

I don't think it would. 1. There are alot of boilers installed that can't do weather compensation. 2. There are a lot that can't do this either - at least in a way that improves efficiency. 3. Yes heating controls are a mess, but I'm it sure boiler short cycling is major issue efficency wise other than it indicates you are running at higher than needed temps. Even then, the most optimised boiler and system can only approach 95% efficency. Unless you screw your HP install up badly (have flow temps over about 55C or lots of cycling) your overall efficiency (gas to heat, via operation and grid) will be 100%. And that's before you factor in the decarbonisation of the grid. It doesn't matter how efficient you gas boiler is, it's really hard to run it on anything other than gas (it's not even easy to run it on hydrogen) Fun fact I found out, 10 years ago, the best the national grid ever achieved was above 400gCO2/Kwh, and was often over 500. Now the worst week we've had this year is under 250 and we've been aslpw as 100 (week 12) For reference a gas boiler hits about 200gCO2/kWh. So all those heatpumps, even the really badly installed ones, are massively ahead of gas in carbon terms. We're nearly at the point where a 3bar fire beats a gas boiler! Of course, if we do a massive switch to HPs our elec demand will rise, probably quicker than we can add renewables. But we can still just build some CCGT stations, burn the gas we would have burnt in our boilers and end up ahead.

Yes different discussion but the route "renewable electricity -> hydrogen -> boiler -> heat" is several times less efficient than "renewable electricity -> heatpump-> heat". Scotland would genuinely be better off providing 3 bar electric fires to heat than hydrogen boilers.

Taken from data table of a r32 York unit (the vaillant tables are similar) A 16kw unit can put out a 60C water at better than 2.5CoP anywhere above 5C external temp. And 65C anywhere above 10C. Ok that doesn't include cycling losses etc but it shows its not too far from what is needed I've dm'd you.

The bit that the carbon capture (either from direct gas combustion of from hydrogen manufacture) lobby miss out is that capturing carbon is very energy intensive. It is thermally driven, you dissolve the CO2 in a solvent, then heat it to extract it, before recycling the solvent. There is also the not insignificant energy to pump it back underground etc. It takes something like 25% more gas being burnt per kWh produced to capture the carbon So as soon as you fit you magic CO2 capture tech to a thermal power plant (or a "blue" hydrogen generation plant) your gas consumption goes up by 25% So of course the gas lobby are very keen on this tech, it not only enables them to keep selling their product but actually increases demand!

CoP of a modern unit is likely to be more like 2.5 Vs 3.5 So 26Mwh needs 10Mwh or 7.5Mwh (round figures) at 30pkwh that's £750 difference over 15 years. I'd agree if your looked at an existing setup and calculated the DHW cop was really crap (let's say below SCOP 2.5) you'd want to change the cylinder. But as long as it's not *too* bad, let it be. The hurdle should be projected overall SCOP of 2.5+ The caveat here is we would need a subsidy regime which meant the cost of heating (at least in the short term) was similar to gas. If that was put in place I would expect installs to rocket. You'd have an option that was about the cost of a gas boiler replacement, would definitely not cost more to run than gas for the next however long the subsidy lasts (say 7 years) which gives time (and feedback and experience) to get the system up to the financial break even point of 3.5 (ish.

Yes fitting a new cylinder and all the ancillary work will make for a more efficient set up in the long run. But the question is "better rather than best" The high level goal is to swap out as many gas boilers HPs because that will reduce the consumption of gas. The additional upfront cost that required moving from a typical existing system to the ideal system Vs going part of the way is a barrier. Would you suggest that MCS mandating UFH being retro fitted throughout is a good idea? UFH has superior performance to radiators for HP installations in every way. It is very expensive and disruptive to retrofit though Or do we say "ok UFH is best, but upgrading one or two rads is good enough" The same logic applies. By all means change the cylinder if the householder is prepared to. But don't virtually mandate that you do unless the existing system is so subpar as to not function at all. At a high level, swapping lots of gas boilers for HPs with CoPs greater than 2.5 is better than a few with CoPs of 4

No problem with making sure the system works, but there is a whole bunch of backside covering going on. If there is no cylinder then you need to fit one and you should get the appropriate one. The point is, with new HPs it looks like most existing cylinders are "good enough". They won't be the highest efficiency but they will function as well as the previous set up (the exception being undersized high recovery units supported by a large boiler , effectively combis). By more or less mandating a cylinder swap you are increasing the cost and disruption of the job and thus reducing uptake. To get more uptake HP swaps need to become cheaper and quicker. The current MCS system is, self evidently, not working. HP installs have a reputation of being a middle class luxury - "only rich people can spend the money to get one and get the grant, poor people have to stick with gas". It's used as an attack against HPs in general I, and some others, think there needs to be a change to "good enough" to speed adoption. For the same subsidy cost you could get much higher uptake, with minimal drop in performance.

It seems that the advent of new refrigerants has more or less removed the need for "high temp" heatpumps as they are HT almost by default. As we have discussed this actually opens up alot of possibilities for making retrofits more attractive. Not every DHW cylinder will be left in situ, and a good chunk will give worse performance than a new one (if only because of batter insulation!), but it's back to "good enough" and it would save at least a couple of grand on an install.

Is it just a case of hangover from previous generations of.tech where replacing the cylinder was more important? Removing the requirement from the manufacturer spec would require paperwork and internal testing *and* reduce sales of their cylinders. So I don't expect there is a lot of internal pressure to do so.

Regarding CoPs, If you can run your (modern) HP at 50C to get your cylinder up to 45C (IE you have a big coil) then the CoP is likely to be above 3.5 all the way down to 10C again, most of the year. Don't forget your HP will not spend all the.time at 50C it will creep up from the lowest temp it can sustain with sufficient heat transfer not to cycle. So you COP should.be better than 3.5 and it should be cheaper than gas.

I had a look at a table for an R32 York machine, it can produce 60C water from -15C to 30C (so all usual UK situations). At 0 it's min output at 60C is 3.6kw at a rather poor 2.3CoP So we would only be getting "worse than gas" performance on the few days of the year we are below 0. It only has to rise to 5C to start being more efficient than a boiler. At 20C the min output rises to 7kw but the cop is 3.6 A standard cylinder coil should be easily able to handle 6kw transfer at 60C

That would be true of an older pump using r410 similar. I think they tended to top out in the low 50's sometimes below. But an r290 can go up to 70+, basically the same range as a gas boiler. So it starts at 45/37 flow/return. But the coil is too small and the return is 42C (say) As you say, it ramps up, maybe tries 55/47. Still no good, the return is 49! At this point an old HP would just quit (as you say). But newer ones just try 65/57 At which point the cylinder can't tell the difference between 65C flow from.a gas boiler and 65C from a HP. The only issue I can see is the higher flow rate of the HP might cause hydraulic issues. But, as I said, 22mm pipes should be able to handle the 65/57 flow rates required to dump 6kw or so. There may be some cases where the run is long, has many bends and valves etc where we start to run into issues.