Beelbeebub

No but the HX coil sizing is based on a 65C or higher water temp. If you ran lower (which you could) your heatuomtimes would be slower. Of course, part of the optimisation would be to get the flow temp for heating the DHW (which is not the same as the DHW supply temp) as low as possible. It might be the slower reheat time and lower capacity of using a lower flow and DHW store temp don't impact the user, so could be used. But if the HP can deliver 65C you have a much lower risk that you *have* to change the setup. Note that you may still need occasional 65C flow for weekly pasteurisation cycles.

I agree. If designing from scratch a lower storage temp (with occasional pasteurisation cycles) would be better. But this was specifically about swapping out the gas boiler with a HP unit with the minimum faff Changing the water cylinder is often cited as a negative. It probably adds at least to 2k to the overall price. If you are willing to accept the efficency hit of running high (say 65C) you can leave the existing cylinder and DHW system as is. The goal is to make the swap over take no longer than swapping a gas boiler. Typically that's 2 men for a day. Maybe day and a half if you're unlucky. At the mother grant is 5k, but you need to jump through hoops to get it and some of those hoops push thr overall cost up so you end up paying £7k or more after the grant. Compare that with a new boiler for 2, 3k And after spending double or triple, you can still end up paying more. But if we made the swap cheaper. Got the price of the parts down below 5k and the labour below 2 days we could install for similar price to a gas boiler swap. That means not replacing the cylinder if we don't need to. Sure, the system won't be super efficient but as long as it beats a scop of 2.5 we are ahead in terms.of CO2. If there is a price guarantee scheme so you definitely won't pay more for your heating than gas I reckon uptake would shoot up.

Could you send me some info, the only ones I've come across are big and expensive Siemens ones.

the valve bit of the trv (not the detachable head) is designed to be on/off. it's just a flat rubber disc that pushes down on an opening. That said it can operate as a linear valve *if* the actuator can move small amounts (total travel from on to off is around 3mm) A screw actuator driven by a small motor and some fairly basic electronic would do it. Just needs to respond to "up a step" or "down a step" How about this. each room/zone has a thermostat with an unnumbered scale for set temp, an indication if the thermostat thinks you are at that temp or is trying to get you to that temp and two buttons for "i'm too hot" and "i'm too cold". These are just a temp sensor, basic display (could just be leds), two buttons and a wireless comms link. This should be fairly cheap Each rad has a clicky manual control knob with fine adjustment, so one click is a small change in flow rate. These should be dirt cheap. The pump is set to constant pressure so each rad should stay at same flow rate regardless of others. The central controller monitors zone temps and user demands for more or less heat. it then decides if that zone needs more or less flow and puts a suggestion to the user via a screen. "Increase zone 1 by 1 click" or "decrease zone 2 by 1 click" The key part of my pitch for a very open control system is that this could be just one of many options, you wouldn't be tied into whatever systems the HP manufacturer provides. One control system maker might have a complex system using variable trvs, controlling the pump output and deciding the HP flow temps with it's own web enabled AI. Another might be a dumb box that takes an old school on/off hall thermostat and commands a flow temp based on the external air temp flowing into the HP. Both could be interfaced easily with whichever HP is currently fitted (or any HP could be fitted and interface with the exisiting control system).

Auto blancing trvs would be useful. Ones that can micro open/close to control the flow rather than on/off. If they were paired with a room stat, which just tweaked the weather comp'd flow up or down a bit you could balance the rooms if that fed back to the main controller itncouod work out if the curve was too high or too low. So room stat looks at set and actual temp (plus the history) works out if the room is getting too warm because of too much flow, and then tweaks the flow down a tad. Waits a day repeats. Goal is to get a flow rate on each room that results in the least adjustments needing to be made.

For whole house load any system that requires measuring walls, estimating construction, guessing air changes will always be error prone. There are direct measurement methods, basically heat the room up mrleasuring the power input then let it cool down measuring the temps If you could do it passively, just measuring inside and outside temps and maybe smart meter consumption data that would be good Just leave the sensors in each room and one outside for a week or two and then the computer crunches the numbers and spits out some specs. The big problem is these techniques only work in the winter!

Regulators could be brutal and just mandate rs485 or ethernet or whatever. A 2 wire system with no defined poliairy would be good, but go to industry body and say - "sort it out amongst yourselves, we don't care but pick one". Then mandate the Comms protocols are published and free to implement. You are right, making the installation easy is key. For retrofits the option to run the DHW flow at 65c accepting the lower efficency for easier installation. The flow temp could always be turned down when a new cylinder was fitted. For combi replacements a simple UV cylinder with the absolute minimum safety features (overpressure to internal waste) because the heatsource (HP) can't ever boil it or an instantaneous electric water heater. https://www.superlecdirect.com/8829-redring-108kw-power-stream Tho, you now need a sparky to run a dedicated spur and breaker and your hot water flow isn't going to be as good as a 28kw combi. But it should be plenty for a shower, washing up etc.

Sorry, i meant systems that pipe the refrigerant onto the building and do the heat transfer to water inside exist. I don't believe your suggested system exists. The closest i's seen is a.daikin cylinder heated directly via a refrigerant coil supplied form a multisplit outdoor unit. Your system sounds very good and what I would say should be a target to aim for. Nice and simple and efficient. The idea in packaging a monoblock with everything in is very attractive. There are some units I've seen that have expansion vessel, air bleed, pump, flow sensors, the lot all in one unit. I would suggest they are the way forward for mass retrofits but for one wrinkle (which may not always be a problem) Size. All that gubbins makes the monoblock unit bigger. The mono bloc units are a chunk bigger than the splits (which are.just standard outdoor Aircon units) Finding space outside a house or flat for them outside unit is not always easy. If it is a boiler retrofit you already have a dedicated internal boiler sized space where the various pipes come to. So we can shift the volume of all the compomemts not needed outside, back inside and make the outside unit a bit slimmer and cheaper. As has been said, all the components are readily available. It's just a case of packaging or up and making it as easy as possible for someone to swap out a boiler. Swapping the boiler box on the wall for another box then plumbing that box with 2 pipes and 2 wires back to a box outside is fairly simple.

Oh and I would second not bothering with a wood stove. I have very well insulated house. (8" wool insulation, high speed windows, air tight etc). To be fair one IKEA bag of wood does heating and hot water for 24h and I have access to free wood. And there is something nice about a.fire on a cold winter's night. But..... We can only use our small 4kw to room, 6kw to water stove once a day if it is near or below zero. Otherwise we overheat. We run the stove a few dozen times a year. If the wind is in the wrong direction we can't run it because the plume goes towards the MHRV intake.....😱 The dust from loading/unloading is a pain. As is storing the wood and lugging it in and out. If I was building again, I wouldn't bother.

The CO2 unit's efficency is critically dependent on the return temp as mentioned. For heating the return temp is typically too high, say 35, 45C and the efficency crashes It might just work with a fan coil or UFH *if* you could get the return down to 22C or so. With a DHW the "return temp" is whatever the local water supply is, typically well below 20C, maybe even 10C in winter. The CO2 manual says it's critical to hear the cylinder in a stratified fashion, so you always have a very cold base to cool the return right down. If you try and run it like a typical heat pump it is very inefficient.

Split systems like that exist. The refrigerant enters the building and exchanges heat with the water in a "hydro box" inside. The issue with split systems.like that is 2 fold. 1) you need a F-Gas certificate and specialist tools (vac pumps etc) to fit one. The joints all have to be high pressure brazed or flare nuts. R290 (propane) is the probable future fluid. As you can imagine the regulations around people installing high pressure propane lines in the home are fairly strict. 2) the inside and outside box are effectively one machine, split in two (hence name). They need to talk to each other fairly comprehensively. This is often by proprietary protocols and interfaces. If you have a brand X outdoor unit, you need a brand X indoor unit. You can't just rock up to a merchant and grab whatever they have in-stock for repairs. Imagine if you needed Worcester Bosch radiators and cylinder to use a WB boiler. It would be hard to replace a rad or cylinder, particularly in an old system. So you end up replacing the whole lot. Which is more expensive. The goal is a system that is dead easy to install with little qualification required. A water split system could be plumbed from inside to outside in speedfit by a DIYer. The refrigerant circuit would be a sealed non-user serviceable item. So could be r290 with no additional risk or regulation. The inside and outside boxes could be different manufacturers because the outside box is only being instructed to control compressor and fan speed to achieve a set output parameter (flow temp) the interface would be a protocol probably modbus.

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?