Beelbeebub

My understanding is that VRF system have branch boxes that contain some valving - which is fine but extra expense My "proposal" was for the pipework to be dead simple. Effectively the same layout as a 2 pipe wet central heating system. The major difference would be the indoor units would have a valve roughly analogous to a TRV but electrically controlled that woukd either allow gas to flow through the finned coil (and turn fan on) or not. If you want to add a second indoor unit to a room all you need too is tap into the existing flow return and wire up the electrics. More or less the same as adding a radiator to a room or even extending the system on to a new room. Rather than having to run a new flow/return set from the outdoor unit (assuming you have enough spare ports) Was really just an idle thought on how we could make installing A2A systems easier and quicker (thus cheaper).

Which takes me back to my argument that rather than subsidise the installation and create a closed shop of subsidy harvesters we should subsidise the consumer directly. If the unit is monitored (power in vs heat delivered) basically using a prepackaged meter system provided as part of the subsidy, you can monitor how much heat was delivered. The scheme then looks at the difference between how much that heat woukd have cost if you had used a gas boiler vs how much you elec did cost. It then subsidies that difference - so the consumer never pays more than they would on gas. But also if they are more than 3.5 efficient they actually make money. The subsidy tapers off after (say) 5 years. Any money left unspent from the £7.5k pot would be split 50/50 between the installer and the consumer. This woiod give consumers certainty, 5 years to troubleshoot any problems and an incentive for both the installer to get it right. Would also allow a picture of installers efficency to be built up. The key but woukd be the monitoring package which would be a box with 4 ports (flow and return in and out) plus power in and power to heatpump and a radio/modem unit for sending results. Basically an open monitor but in a tamper proof box Would be adminstered by energy suppliers so all done via your bill. This way the installers have zero incentive to inflate costs as they just won't get the job. It will go to another company who didn't pad the job.. But also an incentive to do a halfway decent job so they might get some windfall split in the future (the scheme might do it annually to improve incentive). As the payments are based on actual performance not estimated we coukd ditch the approved installer approach. The only qualifier beyond basic industry training eg electrician, would be thr installer using the monitor box (supplied by government) Would also build an amazing database of performance

I'm aware of VRF systems and thry are overkill for domestic situations. Which is why I was wondering if there was a simplified version for domestic systems. The need for simultaneous heat and cool is small in domestic situations (the possible exception being DHW production in summer) What would be useful in domestic situations (heating particularly) would be the lower pipework requirement of a "series" system vs the current "radial" systems (aka multi split) For example a typical upstairs would have 4 or maybe 5 rooms to heat. That is towards the maximum of most domestic multi splits and would require 4 or 5 pairs of pipe to be run from the outside unit to the top floor. If a single pair of pipe could be run to the first unit. Then on to the second and so on it woukd reduce installation cost and disruption. I would envisage the indoor units would come with 4 ports as standard, an in pair and an out pair. The out pair would be blanked off with plugs by default and the pipework (basically a post of tee connections) would already be in the unit, avoiding the need for onsite brazing. This would reduce the skills and material for install. It woukd also make adding an extra unit very simple. As adding extra units would be simple there would be less need for a high power density in the units. They could be simple 1kw units with basically a finned tube radiator, simple fan and a valve making them cheaper. If your room needs more heat input, just add another. The lower power density would also mean lower air flow requirements thus quieter. Is there a practical reason why this system doesn't exist? I don't think the system would need variable refrigerant volume or any fancy valves beyond the normal reversing valve in the outdoor unit and a open/close valve on each individual unit to shut off any hot gas flow into the coil if that room doesn't require heat.

The traditional A2A split unit has a AI vke outdoor unit (with compressor) and a singke inside unit with a flow and return line between them and also (usually) a condensate and power/data cable. Each inside u it has a corresponding external unit. In effect each one is stand alone. There are multi splits. These have several indoor units and one outdoor. Crucially they all appear to have one flow and return (plus date etc) lineset to each indoor unit. The number of indoor units is fixed by the number of "branches" on your outdoor unit and you have to pipe a radial system with lots of pipes going to and from your main unit. Is there a resin why there are no systems where the I door units can all be connected to a common flow and return, much like a wet central heating system? Although the flow would be live to each indoor unit, a valve could prevent any gas flow into any "off" units so the heat output would be minimal. It would seem this method would make the piping of such whole house systems with potentially 8 or more indoor units, much easier. Just pipe to unit 1, then on to unit 2 and so on. Obviously the units would need to be designed for this. Is there a reason why this isn't a thing? What am I missing?

To be fair,.we.had some tenant who moved from a coal fire in each room and immersion to a combi and they struggled with how little they had to do. At one point they were having issues and it turned out they were leaving it off and turning it on each time they wanted hot water! They complained it was too inconvenient to walk from the bathroom to kitchen to turn the boiler on to wash their hands! 😁 It took a while to impress upon them that they just needed to leave it on and not touch it at all.

For better or worse, the combi is the yardstick. I don't think people really need actually infinite hot water. They just want to not have to think about it. They also want the space a big cylinder takes up for other things. Right now the relatively big cylinder specified by manufacturers and installers is a bit of a barrier. Both in cost and size. The HG system is a good attempt at making the installation a bit lower friction. As long as the hot water delivery is good enough - ie the times where the customer has a tepid shower or has to wait 20mins for the cylinder to recharge are very few, then it's a great idea. A 9kw instantaneous water heater (variable power controlled to just top up the temp if too low) afterwards would extend the hot water delivery time and not fall foul of g3 regs.

But it's DHW cycle is limited. For true combi performance we need to produce hot water for an infinite time. If you don't defrost you HP the capacity and efficency drop (which is why we do defrost them). That will eventually mean the amount of hot water you can instantaneously heat will fall and your bath or shower will become tepid.. You already get this if you have to many hot water draws on a combi. If someone is showering and someone else fills the bath, the flow rate and temp fall. What people really want for a "just like a combi" heat pump is an installation that takes up similar internal room to a gas boiler. As HG identified the issue is more the storage of hot water. Current approach is a large UV cylinder. This is OK if replacing a large UV cylinder but when you are swapping a vented cylinder you get the g3 issues and when you are swapping a combi you get the G3 and space issues. A combi or at most,. Kitchen unit or kitchen cupboard hot water storage and delivery system that could operate efficiently on a HP (ie no high temp bricks or phase change) woiod be very useful.

I think Heatpumps are inherently incapable of continuous DHW production in a gas boiler fashion. The 2 points are the power demand of instantaneous DHW production - typically 20kw and more - vs the typical maximum heating load means you end up massively oversizing for what is a small% of the use time. Unlike gas boilers, the peak power output of a HP is proportional to the size of the unit. A 40lw gas boiler isn't much bigger than a 12kw one. The mass of metal, plastic etc aren't much bigger. So whilst a gas boiler can be oversized easily and cheaply, you pay a much higher upfront cost for a bigger HP. The second point is that there are times of year when a HP will need to defrost. This means the HP cannot guarentee to always supply hot water. With heating, the 10 minute pause to defrost is unimportant. With instantaneous DHW production it is a deal breaker. Thats not to say that we cannot have a sensible amount of hat water availble with a quick recovery time that gives an identical experience to a combi 99% of the time.

Reverso fan coils seem reasonably well built - the cost is fairly high though. One thing to note is they have obviously been designed for their home market (Italy?). The mounting system is not like the UK rad hangers. You have to mount directly to the wall, which makes for almost zero adjustment for getting them level. You have to be dead on with your drill holes. Also the pipe entry on the bottom isn't quite right for the standard UK pipe clips. The pipes have to kink a bit awkwardly to get round the frame. Noise wise, the standard setting is audible, but not loud. You can change some dip switches to lower the speed and at the bottom end (200rpm) it is near inaudible. Your output is lower (obviously) but still many hundreds of watts. Might be over 1kw I'd have to check.

The other option is fancoil rads. I've been trying out a reverso fancoil. Not been able to fully test it as it was installed in the spring and it hasn't been that cold, but (when set to minimum) very quiet and seems to punt out quite a bit of warm air at 40C flow temp. Had to do some fiddling to get it to work with my system - it is replacing the failed UFH in a room, but so far so good.

Holy crap! That was the problem!? Red faces with the installer it think! Still glad it's sorted.

The isolator valves are shut off?

Need more facts, but if the valve, either diverter or 2 port, is letting by just a tiny bit, then the first few rads in the loop would get a bit warm. The OP states they are getting to maybe 30C during DHW cycle, but the flow temp would typically be higher, which points to a little flow sleeping past. Possibly because the valve is damaged of maybe a little bit of crud from the power flush is stuck on the seat.

Or the power flush has damaged the little ball in the valve (if you have that system) and it's letting a bit by. But the culprit is likely in the valve(s) as JohnMo says

I have to say, the wooden baths I've seen seem to be a little thicker sided, though how much is necessary and how much is looks I don't know

Very cool! Is the bath overflowing continuously (ie constant water input) or is it just that it is designed to be tolerant of overflowing? I know wood baths shouldn't dry out or they start leaking so will you be keeping it full all the time?

As your storage volume goes up, the required input power of your heating device trends to whatever the daily power requirement is. Eg a 1000l tank might only need a 2kw heater as it can produce 48kwh a day. The smaller the tank the closer your input power needs to be to the maximum instantaneous power requirement. A combi boiler might need to be 28kw to produce a decent flow. Unless the OP planned to use more than 300l in a sitting, then pretty much any HP should do.

How big is this bath?

Here it is Daikin multi+ 120l tanks so might need 2!

I'm sure I saw some manufacturer makes an invented cylinder heated by a refrigerant loop that you hook up as one of the head units to a mumtisplit. The cylinder has the necessary electronics in to interface with the outdoor unit. So get a 2 or 3 head 5kw multi split and have one head as the cylinder and the other 2 as heating or cooking as required. Probably cost less than the a2w setup.

Sorry I can't help, I haven't got around to trying one yet. Mulling over this or just biting the bullet and going for a full HP job.

The other option, which we've discussed here before, would be a small HG cylinder this no G3 with a 9kw instantaneous heater after it. Ideally the 9kw unit would be modulating so you can bring whatever the HP delivers (say 3kw on a cold night) plus another 9kw. As it's an instantaneous heater no G3 either. And the instantaneous heater is only needed occasionally so most of the time you get the high cop of a HP.

Yeah, the inclusion of an immersion heater would come with a small chance of overheating (but very small now the units all have built in non resetting cutouts as well as the usual thermostat and presumably the actual control relay as well). But if there was no immersion in the system then zero chance of overheat.

For what it's worth, my large TS seems to (generally) cool equally from top to bottom ie I lose 5C from top and bottom as I draw off water. Of I only stored water at 45C I wouldn't get much out *However*, the coil area of the store isn't huge as it was designed for a 65-75C store temp and IIRC it's distributed towards the top of the volume. I can imagine, if you had a very big coil, running from top to bottom, you might get closer to a bottom up draw off. You would still have the issue that, as you got towards the end of the store capacity, your effective coil area would fall and you wouldn't be able to access the last bit of restored energy. I agree with the assesment that this is more of a work around the UVC regs than anything else. Which does beg the question, why couldn't we just have the regs amended. As has been pointed out before, a UVC hooked up solely to a HP, especially without an electrical booster, has zero chance of overheating. If the regs just carved out an exception for that circumstance then we could fit small "under counter" UVCs that would potentially perform a little bit better. Edit & slightly off topic - in the same way if the regulations on grants for A2A were changed to allow them to collect grants as long as they were firmware locked off from cooling below (say) 30C it would massively help uptake

If the regs allow an immersion heater in the buffer/store without bringing the whole weight of G3 into things that would be fantastic. Another 3kw on top of the HP would probably make it near indefinite for showers and taps. My thermal store set up is similar albeit with a very big tank for solar and solid inouts. The gas boiler is maybe 15kw (might be 12, not sure) and that acts more or less as a combi for showers. The trick is having enough stored capacity to provide hot water whilst the system is "ramping up". I've found it I make the storage volume too small (I have a home brewed virtual thermostat on the tank that allow me to set how much volume to store) there is a dip in shower temp before the boiler manages to catch up and hit steady state. If I get the volume right then it effectively works as a combi