Beelbeebub

Proposed "good enough" HP Split system. Outside, very basic unit. Little more than a split air to air unit with a plate heat exchanger, some sensors and a simple control board. Inside, boiler sized enclosure containing pump, valves, heat meter, and optionally control box (could be remote mounted) The inside box replaces the boiler and two insulated pipes run out (maybe via the old flue hole) to the external fan unit. The existing CH and DHW connections are fitted to ports on the inside box. Unit can provide 55C flow for water cylinder and CH if required. The external and internal boxes and the control system all adher to an open standard (especially control box to external unit) so you can mix and match from suppliers. Now my idea about DHW cylinders An unvented cylinder is a great thing. Simple and good performance (assuming decent mains pressure and flow). The main reason for not fitting one (imho) is cost and the regulatory requirements (which I think feed into cost) The regulations around them stem from the potential to explode if the heat input gets stuck on and they "boil". So there are lots of elaborate "fail safes", emergency vent plumbing and regular checking to make sure they are all working. So swapping out a vented cylinder for an unvented is not simple or cheap. If we were able to guarantee it couldn't ever boil, a large amount of the regulations and safety equipment could be ditched. It becomes a metal cylinder with two ports, a coil, expansion vessel and a pressure relief valve discharging to the main drains. Fortunately a HP.is such a heat source. You can guarantee never boiling a cylinder with a HP - in fact this is common criticism of HPs!.😁 At this point the legionella regs are brought up, but modern r32 and r290 pumps can hit high enough temps to sterilise cylinders without immersion heaters. So if we had HP certified UV cylinders that were cheaper and simpler than normalmones because they don't need the safety gear, and they have big coils for efficency HP use, they would be paired with the above system to bring down the costs of an install.

That's the point. MCS doesn't have to apply. We could chuck it in the bin if we liked. It's just a political creation. MCSz is sort of well meaning. Trying to make sure systems are well designed and work to avoid disappointment. To try and make sure we don't have cowboys ruining the reputation of the industry before it can get started. I think it is self evident it isn't helping. It's slow, restricts choice, increases price and we still seem to get bad installs. So my proposal was a replacement. The "quality control" is via the approved HPs (makes sure they are decent quality and can provide reasonable output and efficiency even when straight swapped) The method of stopping customers getting bill shock is via the price guarantee. Then the army of boiler installers can just get on with it. There may need to be some tweaks to planning and building regs, for example the noise requirements should be ditched so long as a qualified HP (which would already beow noise to qualify) is used, and heating zoning should be scrapped for HP installs. I have another idea around UV DHW cylinders that would make them cheaper to install. The final point about just discounting the electric used for the HP. I considered that, but the incentives don't quite line up. There is no incentive to hit any type of efficency. Your HP could run a SCOP of 1.1, why do you care? You could even just run you heat pump on the backup direct electric heater! Plus there is the issue of people inevitably wiring their whole house to the HP, or charging their Tesla from the HP feed. Measuring heat prevents all of that though at the cost of a bit of extra hardware. Mind you that hardware is off the shelf and widely available.

Sorry I have probably confused things. I'm talking about at a high level "black box" technology 99% of people don't know or care how a boiler works. They know gas goes in, heat comes out. A flame is probably involved. All the stuff about combistion ratios, modulation, condensation heat recovery is just "science stuff" It could be a magic goblin in there for all they care We might like to geek out on the intricacies of heating systems. Most people want to be warm, have hot water and money in their pocket. In the quest for high COPS and ultimate efficency we may miss the wood for the trees. We just need a system that people can easily get fitted, that keeps them warm, prices less CO2 than a gas boiler (wherever that gas is burned) and costs noore to run.

I mean from a high level, just looking at the primary energy input (gas in a pipeline) to final output (heat in the home). The nitty gritty of compressors, fans, expansion valves, vapour pressure, latent heats etc is irrelevant at the national level. It's just how much gas do we need to get out of the ground and burn to keep our population warm.

An excellent point. So this is my solution..... HPs are fitted with fairly accurate heat meters. Ones fitted with this tech are approved for the scheme. If you fit one, you register it with your energy co. The meter monitors the thermal kWh delivered per month/week/day. Your smart meter monitors the electric use over the same period and both are sent to electric co. Whilst you are on the scheme (which light be say, 10 years from registration) the energy co takes your thermal kWh and divides by 2.5 to get your assumed elec use for heating. They then calculate the difference in price between the kWh of assumed elec and equivalent gas and pay you back the difference. The upshot is if your HP is running a SCOP of 2.5 your heating costs will be the same as if you had a gas boiler. But if you beat 2.5, you actually used less elec than they assume so end up ahead Worked example 100kwh⚡ used at 35p = £35 100kwh delivered via HP, assumed 40kwh for heating which is £14 of the above was for heat. 100kwh of gas at 10p is £10. So you would have paid £10 for the same heat using gas. Therefore you get £4 knocked off your bill and are roughly the same place as of you has gas. But say you HP SCOP was 3! You really only used £11.67 of electricity but you still get the £4 rebate. Towards the end of the 10 years the target SCOP might move up or a taper out be applied. Various checks and limits would be put in place, like checking if your kWh/m² was crazy high etc. The money for the subsidy would be paid by for by a premium on gas unit price. This would jack the price of gas up a bit (and self regulate as thendiffernec between gas and electric would shrink)

It's not either or tho. We can (and should) do both But back to the discussion about "good enough". My feeling is getting the gas burned down is a good thing for a variety of reasons. If someone invented a "super condenser boiler" that could get 125%, 180% efficency Vs today's 90% condensers, I think everyone would be in favour, even if they put out a lower flow temp and had some capacity limits. The gas boiler industry ("big boiler" 😁) would be falling overitself to push this tech. Even then there were issues with the swap out, putting condensate drains in, sometimes upping gas pipe capacity (ok mainly for combis), redoing flues and plume kits etc. Remember the boiler scrappage scheme? A HP is essentially a gas boiler that can achieve an even higher efficiency than a condensing boiler, it's just the combustion chamber is really big and remotely located! If we can start with a straight swap (or near enough, just changing the smallest rads) the emmiter side can always be upgraded later, in fact there will be a greater push for it as the gains from chanignyour rads will be more visible.

I am coming round to the idea of good enough. As long as the SCOP is better than about 2.5 you get more heat from your gas by burning it on a power station to run the HP than in a boiler. 2.5 should be achievable by a modern pump with a flow temp below 55C. The cost break even is closer to 3.5, which require flow temps closer to 35C. That, in turn, requires careful system design and setup and probably upgrades for retrofits. The cost break even can be addressed by changing the electric unit price structure in relation to gas and by a price match to gas guarantee for X years after installation. The price march guarantee gives 3 big advantages - is it removes the uncertainty factor from the buying decision. - It also allows the actual performance to be measured - it gives time for any upgrades to be identified (from actual monitoring) and carried out before the subsidy tapers away. Once caveat with this is, and this might be a PR issue, we may need to build more gas.power stations! Our overall gas consumption (and this carbon) would fall but the amount that get turned into electricity would increase hence we might need more gas generators in the short term. Fortunately, gas stations are quick and cheap to build and pretty clean (apart from the co2).

From my reading of the specs, the r744 (CO2) unit really only comes into its own providing high temp (65+) water from cold mains, as @markocosicsays, they are different from normal heatpumps in that the COP is very dependent on the return temp being low. I.e. they work more efficiently providing a flow of 75 from a return of 20 than if the return was 55 - wierd I know. So the advantage is you can create a store of very hot water, which means you can have a smaller cylinder. I guess that's why they are popular in Japan. If you don't need blisteringly hot water and might need some heat, a r32 (split or monoblock) or r290 (monoblock only) heatpump is probably better. The cops are similar but it's less "exotic" tech from more suppliers. Oh and the other option for air to air would be a multi split, one outside unit and 2 or more inside. Daikin do a system where one of the inside units can be a (specially designed) hot water cylinder.

I'm pretty sure it's possible to install HPs for about the same as a boiler. Maybe not the absolute cheapest "15kw whatever the merchants had a clearance on Regular boiler" but on a par with a top brand combi. the costs of any changes to the system like rads would be extra, but they are one time. the magic number (I believe) is 2.5. if the scop can beat that, you get more heat burning gas in a power station, transmitting it to a house and using a heatpump, than to burning the gas in a boiler. as long as any heatpump replacing a gas boiler can beat 2.5, it's a carbon reduction. That should be possible for most modern units as long as the flow temps are below 55C If it can hit about 3.5 (much harder need flow temps in the low 40's) you could end up costing less to run. If we can get simple HPs that can (near enough) plug into existing heating systems and beat 2.5 we are good. if we can create a subsidy regime where such an install would end up costing the customer no more to run than a gas boiler we can sort out the efficency later.

Willing to bet any tinkering to improve MCS (or replace it with something that works) would be interfered with by the boiler lobby. I spoke to our regular gas contractors, they aren't training any of their guys on heatpumps because they aren't getting any signals or encouragement to do so. A friend's son is an apprentice heating engineer with a small firm (a couple of guys). One is LPG and oil, another concentrates on gas. They were thinking of training the apprentice up on Hydrogen "because that's what's next". It isn't, it never will be. It's just a fig leaf to allow the boiler industry to keep selling. And it's working, the apprentice won't be trained on HPs, so the firm won't be able to (really) offer HPs so nobody will buy HPs because it's difficult to find a fitter.

"Gas boiler lobby trying to delay UK’s heat pump plans, leak shows Trade association, which promotes hydrogen for home heating, called for clean heat market mechanism to be pushed back to 2026...." https://www.theguardian.com/environment/2023/jul/20/gas-boiler-lobby-uk-heat-pump-plans-leak Shocked! I tell you! 😱 Shocked!😱

I thought CO2 heatpumps were supposed to be good for situations where the majority of the demand is DHW. I believe they have been used for quite a while in Asia where there is no heating demand. AFAIK the only unit readily available in europe is a mitsubishi one https://les.mitsubishielectric.co.uk/products/residential-heating/outdoor/ecodan-quhz-monobloc-air-source-heat-pump

Ah! Thought I'd missed something! I don't know if CO2 will catch on here. It seems great for hot water heating but not so good for heating due to the requirement for a low return temp. I can see maybe it might be good for those all in one extract/heatpump/hotnwater cylinder things.

Those are listed as r32 on the website? Is there an r744 variant? Special order?

Which model is that? Do you mean an r744 pump? I'm quite interested in those, they have very different characteristics from usual pumps but apart from a mitsubishi unit seen any others.

As I mentioned earlier, if the HPncan achieve pasteurisation temps (65C or so) on it's.own then we no longer need any immersion booster. That means it is physically impossible for the heat source to overheat the cylinder and cause a catastrophic event. Which means the safety features aren't needed, just a PRV, venting to the drain in case the expansion vessel fails. Which simplifies the installation back to that of a vented cylinder (DIY) probably easier (thus cheaper)

Sorry about ☝️ couldn't get rid of the boxes Anyway.... Yeah something like that. I did wonder if we stored the DHW at about 35/40C and then used the HP to instantaneously heat up the DHW.flow by another 5-10C? The power required to lift a shower flow from 10C to 45C is too much for a HP, without it being oversized for heating. But the power required to lift a shower flow from 35C to 45C is much closer...

Higher thermal mass housing construction would help. I've got a UFH concrete slab, about 20 tons IIRC. During the winter, when I operate my woodstoce, it dumps heat into the slab at about 7kw which then rides us through the night and next day no problem. When I eventually get round to fitting a HP, I imagine it will do the same, run for a few hours then shut off for a day or so.

The flexibility of the system is the important bit. Where.we.get that from, fancy HP with wide operating range or a buffer to provide that flex instead, is not important. I'd note that any buffer needs to be compact for retrofit. I can see milage in combining the DHW tank with a buffer and even the expansion - this is more or less what some of the indoor modules are. But the big issue (from a retro fit pov) is the size. They are fridge sized. What we really need is a unit about the size of a boiler, somkitchen cupboard. At an absolute pinch washing machine sized.

Yeah, tge cheapness of gas combined with the very high power density mean you can pack way more power in to a boiler package than any house is likely to use. This has allowed installers to get away with sloppy installs, eyeballing the rad sizing, knowing they can get round any cockups by just turning the wick up on the boiler. Rhe same approach comes unstuck with Heqtpumps. Dumping a load of cash into R&D to develop HPs with a broader operating range would be useful. If hearing installers and retro fitters just need to go and grab a white label "3-15kw" unit and know it will work pretty well for most homes, it would be very beneficial. What would enable that? Twin compressor models? Maybe smaller units (like 2-3kw) that can be installed in parallel to boost power? Just keep adding units until you get the right power and gives much more "turndown" than an individual unit can offer?

From reading @markocosic it seems that heatpumps (despite recent advances) are rather inflexible beasts. The combo of compressor characteristics and working fluid charge mean there is a narrow range of efficency power/temp pairings for any given external air temp. If you stray from this zone your efficency starts to drop away. Would this be correct?

I suspect there is a seasonality element. The price of gas fluctuates lower in the summer The price of electricity will often go higher as it is generator constrained and southern Europe is guzzling electricity for cooling. I had a look at what makes up unit prices. Both gas.and electrify have a "per unit green tax" If you look at the absolute amounts Gas - about 0.2p/kWh Elec - about 1p/kwh You can see elec has a much higher level of taxation We could move almost all the cost of green taxes to gas. That would help. But this is where my subsidy pegged to the gas.price.wouid come in. It would effectively make the swap risk free. Even if electricity Soares away from gas your bill.woiod be capped at what it would have been if you remained. You may (if your setup beats the official COP) make a little.from it (winks). Human nature being human nature that fact may motivate people to increase efficiency. People will often work extra hard to get "free" stuff. This will remove one of the barriers to switching "what if is spend all this money and my bills go up?"

Seems.lije a good system, are you happy with it? Strikes me that could be packaged in a pretty small, neat unit. Also strikes me, it could be used as a defrost volumiser. If heat was pulled from the PHE. You have a huge reserve of heat for the defrost cycle. Ideally the system would simply work via back thermosyphon. the cold water sinking tgrougbt the PHE to the bottom of the tank and fresh warm water coming from the top.

I'm not sure! Ultimately it's a question of PHE size. You'll get heat transfer, but it's a question of how much Vs the modulation of the HP.