Gas boiler lobby obstructing heatpumps

[Beelbeebub]

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.

[JohnMo]

1 hour ago, SteamyTea said:

Can they reach 110% reliably?

Mine did on a regular basis, but 100% made the math easy. Unfortunately most are installed badly so don't get to 100% let alone 110%

[SteamyTea]

4 minutes ago, Beelbeebub said:

If someone invented a "super condenser boiler" that could get 125%, 180% efficency Vs today's 90% condensers

I think the physics are against that.

Higher Heating Value of natural gas is14.5 kWh/kg, the Lower Heating Value is 13.1 kWh/kg.

 

[JohnMo]

8 minutes ago, Beelbeebub said:

today's 90%

My boiler had a part load efficiency of 109.8% with a return temp of 30. I often ran it cooler than that, so efficiency should be slightly better.

[JohnMo]

13 minutes ago, Beelbeebub said:

HP is essentially a gas boiler

Not really by any stretch of the imagination is it. Closest relationship would be a fridge.

[Beelbeebub]

3 hours ago, JohnMo said:

Trouble with accepting a CoP of 2.5 could be running cost compared to gas especially with the new prices gas 7.5p and electric 30p per kWh. A well installed gas boiler can achieve 100% + efficiency.

 

You may be better with DHW heating accept the limitation of the normal cylinder, let it heat to around 40 with the heat pump, finish of heating with the immersion to about 50 or as low a figure as you can get away with.  CoP of 3ish for the heat pump.

 

1kWh at CoP 2.5 is 12.5p, so heating bill will 40% higher than with gas, not many volunteers I would assume. Even a good heat pump install achieving a SCoP of 4 will be on parity price wise with gas.  

 

 

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)

[Beelbeebub]

1 minute ago, JohnMo said:

Not really by any stretch of the imagination is it. Closest relationship would be a fridge.

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.

[Beelbeebub]

13 minutes ago, SteamyTea said:

I think the physics are against that.

Higher Heating Value of natural gas is14.5 kWh/kg, the Lower Heating Value is 13.1 kWh/kg.

 

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.

[JohnMo]

7 minutes ago, Beelbeebub said:

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)

Trouble is MCS rules would still apply, even if they changed them, you would still need to go through that or similar scheme to qualify.

 

My heat pump doesn't have a heat meter or record electric used or heat generated, I do have an external electric meter dedicated to the heat pump. Just give a discounted electric rate for those kWh.

[Beelbeebub]

42 minutes ago, JohnMo said:

Trouble is MCS rules would still apply, even if they changed them, you would still need to go through that or similar scheme to qualify.

 

My heat pump doesn't have a heat meter or record electric used or heat generated, I do have an external electric meter dedicated to the heat pump. Just give a discounted electric rate for those kWh.

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.

Edited July 21, 2023 by Beelbeebub

[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.

[JamesPa]

Good ideas.

 

I would add (for retrofit)

 

• the ability to run the flow temp for the DHW at 65/70 so you dont have to replace the cylinder, even if its vented, and as you say leigionella fixed
• a plate heat exchanger 'add on' to an existing DHW cylinder so that you dont need to replace a cylinder just to get a large coil (already offered by Mixergy) (only necessary if you run DHW at a low temp, not necessary if your run it at 70)
• Monobloc option also available

 

All of this and what you have listed is already available from the market, but the installation industry wont fit it!

 

 

 

 

Edited July 21, 2023 by JamesPa

[JohnMo]

If you are doing a split system, you may as well bring refrigerant inside also. Have PHE in the box with refrigerant one side and drinking water the other, do away with the cylinder coil.  Looked at the refrigerant temps the other day and the hot side was 75 degs. That's R32 not propane.

 

Existing setup adds inefficiency, refrigerant to PHE, to heating water, to a coil in a tank of drinking water.

 

So indoor unit has two PHE inside the indoor box and two pumps, and a 3 way diverter for refrigerant. Call for DHW heating, bronze DHW pump starts heats cylinder water directly. When satisfied, 3 way diverter swings to CH DHW pump stops CH starts.

Edited July 21, 2023 by JohnMo
Clarity

[JamesPa]

26 minutes ago, JohnMo said:

If you are doing a split system, you may as well bring refrigerant inside also. Have PHE in the box with refrigerant one side and drinking water the other, do away with the cylinder coil.  Looked at the refrigerant temps the other day and the hot side was 75 degs. That's R32 not propane.

 

Existing setup adds inefficiency, refrigerant to PHE, to heating water, to a coil in a tank of drinking water.

 

So indoor unit has two PHE inside the indoor box and two pumps, and a 3 way diverter for refrigerant. Call for DHW heating, bronze DHW pump starts heats cylinder water directly. When satisfied, 3 way diverter swings to CH DHW pump stops CH starts.

As an option yes, but forced not sure.  In a retrofit situation the win is a simple water connection to the existing primaries at the existing boiler location, retaining the dhw tank if there is one or colocating a small tank where the combi was (or very nearby).  Or have I misunderstood (perhaps a diagram would help!).

 

Further thought, so are you suggesting repurposing the primaries between boiler and cylinder for carrying heated cylinder water?  If so then I can see where you are going, depending of course on where existing diverter valves are located.

 

Also, let's factor in that 15l of stored hot water doesn't need all the safety precautions.  Can we make a heat pump combi replacement using your ideas and this?

Edited July 21, 2023 by JamesPa

[JohnMo]

24 minutes ago, JamesPa said:

Further thought, so are you suggesting repurposing the primaries between boiler and cylinder for carrying heated cylinder water?  If so then I can see where you are going, depending of course on where existing diverter valves are located

Use original cylinder, use primaries after a good clean, connect to top and bottom of the cylinder. Use pump inside indoor unit to circulate through top and bottom connections of the cylinder and the PHE. Cap existing cylinder coil off.

 

No diverter valve external of the indoor unit. Common refrigerant two PHEs the diverter valve inside indoor unit moves refrigerant to one or the other PHE (DHW or CH).

[JamesPa]

Just now, JohnMo said:

Use original cylinder, use primaries after a good clean, connect to top and bottom of the cylinder. Use pump inside indoor unit to circulate through top and bottom connections of the cylinder and the PHE. Cap existing cylinder coil off.

 

No diverter valve external of the indoor unit. Common refrigerant two PHEs the diverter valve inside indoor unit moves refrigerant to one or the other PHE (DHW or CH).

Sounds sensible.  What will it take, I wonder, to persuade installers to reuse primaries for hot water?

[JamesPa]

17 minutes ago, JamesPa said:

Sounds sensible.  What will it take, I wonder, to persuade installers to reuse primaries for hot water?

But ... Are any systems plumbed with separate flow for dhw yet common return.  Probably, if so better not get that mixed up!

[sharpener]

22 minutes ago, JamesPa said:

Sounds sensible.  What will it take, I wonder, to persuade installers to reuse primaries for hot water?

 

I proposed doing this and was met with a flat refusal on grounds of hygiene.

 

3 minutes ago, JamesPa said:

But ... Are any systems plumbed with separate flow for dhw yet common return.  Probably, if so better not get that mixed up!

 

Yes, mine are commoned somewhere above ceiling level, haven't yet investigated further. But the DHW coil flow pipe might well be  sufficient as there is a separate CW feed in the utility room to pressurise the existing CH circuit. Not sure if it is 22mm though, mains pressure is well adequate for 15mm but not entirely confident about the rainwater supply.

 

Edited July 21, 2023 by sharpener

[JamesPa]

7 minutes ago, sharpener said:

proposed doing this and was met with a flat refusal on grounds of hygiene.

Well that's almost certainly Bow Locks.

 

So, after a good wash, it's got traces of copper, iron, rust and very, very, very dilute inhibitor in.  Probably a lot safer than your local swimming pool on kids day!

[sharpener]

2 hours ago, JamesPa said:

So, after a good wash, it's got traces of copper, iron, rust and very, very, very dilute inhibitor in.  Probably a lot safer than your local swimming pool on kids day!

 

After a day or two with acid rainwater in it it will be clean as a whistle.

[Beelbeebub]

3 hours ago, JohnMo said:

If you are doing a split system, you may as well bring refrigerant inside also. Have PHE in the box with refrigerant one side and drinking water the other, do away with the cylinder coil.  Looked at the refrigerant temps the other day and the hot side was 75 degs. That's R32 not propane.

 

Existing setup adds inefficiency, refrigerant to PHE, to heating water, to a coil in a tank of drinking water.

 

So indoor unit has two PHE inside the indoor box and two pumps, and a 3 way diverter for refrigerant. Call for DHW heating, bronze DHW pump starts heats cylinder water directly. When satisfied, 3 way diverter swings to CH DHW pump stops CH starts.

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.

[JohnMo]

17 minutes ago, Beelbeebub said:

Split systems like that exist.

They don't - the inside unit is just same bits as a monobloc, the cylinder still has a water coil in it, so it has two levels of heat transfer not one that am speaking about.

 

19 minutes ago, Beelbeebub said:

water split system

Don't really see any advantage of a water split system. Just use a monobloc, keep all the noise and bits outside in a single box, then you only need a 3 way valve inside to connect to cylinder and heating.

 

My heating system is as simple as it gets, monobloc ASHP, a 3 way valve, UFH manifold (no pump or mixer, no actuators or wiring centre), single house thermostat to give stop, start permissive to heat pump and act as overheat protection. No internal controllers, everything on the outside unit, set to run WC. Once commissioned out of the user eye sight, so would have little or no messing about changing setting. Anything important hides behind an installer password.

 

I have a small thermal store hooked up for DHW, but that gets a little complex as I heat via a PHE for heating the cylinder, and have a return booster pump, due to less than ideal pipe sizes and lengths. So pretty much replicates a retrofit  of using what you have.

[Beelbeebub]

7 hours ago, JohnMo said:

They don't - the inside unit is just same bits as a monobloc, the cylinder still has a water coil in it, so it has two levels of heat transfer not one that am speaking about.

 

Don't really see any advantage of a water split system. Just use a monobloc, keep all the noise and bits outside in a single box, then you only need a 3 way valve inside to connect to cylinder and heating.

 

My heating system is as simple as it gets, monobloc ASHP, a 3 way valve, UFH manifold (no pump or mixer, no actuators or wiring centre), single house thermostat to give stop, start permissive to heat pump and act as overheat protection. No internal controllers, everything on the outside unit, set to run WC. Once commissioned out of the user eye sight, so would have little or no messing about changing setting. Anything important hides behind an installer password.

 

I have a small thermal store hooked up for DHW, but that gets a little complex as I heat via a PHE for heating the cylinder, and have a return booster pump, due to less than ideal pipe sizes and lengths. So pretty much replicates a retrofit  of using what you have.

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.

 

 

[JamesPa]

2 hours ago, Beelbeebub said:

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.

 

 

Lots of good ideas here, many of which are readily implementable!.   Fundamental goal for me is

 

1. If there is an existing stored DHW system, it should not be necessary to replace it

2. If there is a combi, then the replacement needs to fit in the same space as the combi, or thereabouts.

 

If we can achieve this then the installation should come down to 2 men*2 days, or even 2 men * 1.5 days, as opposed to 2men*1 week which seems to be the current norm.

 

Sadly I'm not optimistic about a common protocol for communication, but surely they could at least agree on a common physical layer.  Currently some require 2 wire, some 2*5 wire, and doubtless there is everything in between and more besides.  At least if they could agree on that, only boxes not infrastructure need to be replaced when something fails.

 

In addition to the packaging questions, I believe that there are two other matters which need to be addressed namely:

 

• A quick, robust way to estimate whole house load, the current gigo spreadsheetery is not helping at all. 
• A less time consuming and more robust way to balance emitters

 

The whole house load thing has been aired on this forum several times; I don't think we have found a universal solution yet but there are a couple of options.  The most robust is probably to use smart meter readings where they are available, and some intelligence around the patterns of consumption and local weather data.  It needs some software eventually, for now some people to play with it and develop some simple techniques (which some are doing) and acceptance that the current method cant work for retrofits where you have no reliable way to determine the fabric.

 

Balancing radiators seems to take on more importance with ASHP than with fossil fuel, because of the drive to low and slow.  The first question is, what are we balancing for?  Heat Geek does a bit on this and eventually they come down to 'balance for equal room temperature (with open TRVs)'.  This makes sense, balancing for equal delta T assumes rad sizing is correct, which we know it isn't.  Balancing for equal (or correct) room temperature takes out this error so Im going with that as the actual requirement.

 

There seem to be all sorts of auto balancing valves around, but none I know of actually do this.  To my mind an adapted TRV (certainly an adapted electronically driven TRV) must surely be able to achieve this.  What you need is some kind of slow reaction linear adjustment of the flow, which settles on a flow that delivers the correct temperature over the long term.  The problem of course is that you have multiple control systems fighting each other and the risk of oscillatory behaviour is clearly real.  I haven't yet got my mind round this, and to be honest don't know enough about valves to do so from a solid knowledge base.  More thought needed.  Perhaps a 'fit for a week then remove' solution is appropriate, however, so far as I can see, this will only work during the heating season which creates an issue for installers that probably rules it out.

 

 

Edited July 22, 2023 by JamesPa

[Beelbeebub]

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.