Beelbeebub

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.

Exactly, and I reckon that you could make most (not all) existing cylinders work with a (modern) HP. Initially you would use the "boiler emulator" setting of 65 or 70C flow and thermostat. Not very efficient, but it works and the switchover job is much faster. Then you could tune the system to work best with existing setup. Once you've got to maximum efficiency then, if it's still not high enough, you look to fitting a "HP coil" cylinder. As I said, the magic number is around 2.5 As long as you overall scop is better than that the.UK burns less gas.

From what I have seen if HP performance tables the minimum power output is relatively flat as flow temp increases, actually falling abit. All the coil caers about is the temp coming in. The temp going out is a function of flow rate. Eg if you pumped 1lpm of 65c water in it would come out at whatever temp the s DHW was. If you pumped at 200lpm the water would come out at about 64C. The power dissipated is just the average dT between the DHW and the coil (and the area). If you double the average dT you double the power dissipated. So a regular boiler might flow 65c water in at 10lpm and the return is 45C. For 14kw If our HP could supply 65C at 10lpm with a return of 55C the power would be a bit above 7kw (because the average coil temp was now 60C and not 55C) The issue was always that the little coil couldn't provide enough SA to dump enough power at 50C or whatever the old HPs could pump out. The HP needed to raise the temp to dump enough heat to stop cycling, bit couldn't. Yea the cop of hearing a cylinder using 65c flow temps is it good, maybe 2. But, so what. It just drags the SCOP.down a bit. And, in time the cylinder cam be changed. Meanwhile the heating is much more efficient. The point is it is probably better for the UK to get more HPs in even if they aren't being super efficient at DHW, than people sticking with gas boilers because the cost of swapping is too much (because of the cylinder swap)

I get the point but a 16kw r32 HP has a minimum output of 6kw at 65C water temp. 16kw should be enough for most properties From the cylinder's point of view, all it knows is that it's connected to a 65C flow source and will extract the same heat. If anything, it will extract more with a HP as the return temp is lower thus the average coil temp is higher.(65/58 Vs 65/45) 6kw is well below the output of any gas boiler so any coil that works with a gas boiler, IE can dump enough heat to stop the boiler cycling, should be fine with a HP. The only thing I can think that might cause a problem is the follow through the coil being higher if the resistance is to much. But 22mm copper should be big enough and I can't imagine anyone using 15mm feeds for the coil in a large house. With old r410a pumps limited to lower temps, so I get the issue. But r32 and r290 especially can replicate the flow temps of a gas boiler. The could even do a legionella cycle and do away with the immersion heater. That would mean there is no possibility of the cylinder boiling. That works mean we won't need expensive g3 cylinders, installer ticket or annual checks.

I get why I vented and a booster seems less attractive. And I have experience with a really noisy crap old booster. But recently (about 2.years ago) I have fitted the pump linked to provide cold water mains pressure for 8 properties (from one pump!). It has an additional 50l expansion vessel to buffer it's output a bit, but to be honest it probably doesn't need it. It's very fast responding and just a mild "rustle" sound. If it was on an insulated pad in an airing cupboard you probably wouldn't notice it at all. It made me rethink my strategy for DHW cylinders a bit. For less than the cost of an unvented cylinder you can get a vented cylinder and pump and not have to bother with any invented regs or checks.