Beelbeebub

Split units are basically a "normal" air to air unit outside (including the compressor) and then inside, instead of an air to air room unit, an air to water room unit with a conventional central hearing pump, plate heater exchanger, some valve and other gubbins. I believe Panasonic are confusing things with "hyro split" which is a mono block outside unit and an inside unit with some pumps etc in. The main characteristic of split systems is the fluid that goes through the wall is refrigerant not water. As such you need an F-gas installer. I don't believe there are any R290 systems as r290 is a bit of a grey area in Europe and america so the big players are holding back For what it's worth, most of the effort in the UK seems to be towards monoblock as they don't require fgas certs to install. I know other countries are going down the split route as f-gas trained installers are. More common due to higher air con usage.

Why not swap out the 15mm pipes? As a thought, switching to 22mm speed fit would get you a boost in flow/reduction in velocity with) potentially) easier installation. Yes 22mm plastic isn't as big a bore as 22mm copper but it is still bigger than 15mm copper.

I found massive turbulence corrosion in a 15mm cold water copper pipe running around 8lpm albeit after about 9 years 24/7 and just downstream of a restrictor that would have generated significant turbulence. The pipe was paper thin and full of pin holes for about 40mm downstream of the restriction.

I think the instantaneous Cop figures are pretty solid (not that many manufacturers provide these). The issue comes that the outside temp and inside temp demanded are continuously varying so rather than getting one point on the graph, you wander around it sometimes getting good cop and sometimes not. The Scop tries to capture this, but is (like the car mpg) only ever an approximation based on idealised standard conditions. Part of the problem in the UK is that our elec/gas unit price ratio is around 3.5 to 1. In order to achive price parity your installation needs to be fairly well done. Typical industry practice (sloppy heat calculation, buffers, zones etc) does not reliably hit this performance - hence tales of disappointment. If the ratio were (say) 2.75 to 1 then many more installs would better that and we would have far fewer "my heatpump costs more to run" stories for the daily mail and telegraph to print. If we had a ratio closer to 2 to 1 then people woukd be falling over themselves for Heatpumps as even a fairly sloppy install coukd save you money and a good one woukd save significant sums.

Is it to protect against any crud in the heating system? Are their units particularly susceptible to dirty water? Most manufacturers seem happy with a good flush and then filters.

Is the heat exchanger also being used to isolate a glycol circuit for the HP?

My 2bobs worth.... Is your HP set to weather compensated? You don't mention it. That will help. Not keeping you warm in the cold periods: you may need to up the flow temp for the cold periods. Weather compensation will ensure that the flow temp is lower during the milder periods. The plate heat exchanger won't help. It means your HP will need to run a few degrees hotter than it migbt otherwise. You mention it was installed to allow a boiler to also be used (it may also be to allow glycol to be used in the HP side) Is it possible to get the system replumbed so you run the HP direct and the boiler is connected via the heat exchanger? Given you have an (oil?) boiler backup - you could use that for the few very cold periods when you estimate it's cheaper to run or the HP struggles. Running the boiler a few times a year will help keep it working well and you mihbt as well use it of you've paid for it.!😁

As pointed out before, if there is a fault with the diverter valve setup so that there is flow through the tank coil during heating mode, the hotter water in the tank will be cooled by the water passing through that coil at the cooler heating flow temp. Symptoms would be Your tank swiftly loses temp only when the heating flow is on. The return flow out of the tank coil (usually the lower pipe) is warmer than the feed flow in (usually the upper pipe) If your controller is set to hot water priority it will start heating the house, then notice the tank has cooled, switch to heating the tank, then go back to heating the house, then notice the tank had cooled.... And so on. Try setting your hot water to timed. At this point the above won't happen outside of the hot water times but you would quickly see the tank temp drop to the heating flow temp and then stay there. If there is not a diverter fault then another possibility is the tank is losing temp naturally. Because the prove is at the bottom it can only "see" the temp there. As the tank loses temp naturally the cooler water sinks to the bottom. Your probe will "see" cool water but be unable to know the water above is still hot. My tank can be half full of 65C water and the bottom be at 20C (I have multiple sensors). Again, if your hot water us set 24/7 it wouldn't take much demand or cooling to trigger another heating cycle even though there is ample hot water left

Just a thought. A return water temp of 28C implies either your slab is at 28C - that is pretty warm for a floor slab, what are your floor finishes? My bare concrete slab hits maybe 24C for a 20C air temp though we are very well insulated. If you have wood or carpet then your slab temp. May be higher but 28C is the recommended max floor temp for UFH so I would be surprised. The other option is that the flow is too fast for the water to give up enough heat. Have you checked the flow rates? I believe the Grant installation kit has a flow adjuster with a sight glass in it so you should have an idea. The Aerona Heatpumps come from the factory with the pump configured for maximum. Grant say this is almost always too high and usually needs to be set back to med or low. If your builders aren't very knowledgeable about the HPs, they may have missed that step. Combined with the fact the bedroom zones are mostly off, the flow in the other zones will be higher than may have been set anyway.

That's a fairly unique set of circumstances. Basically an extended power cut and temperatures in the "mushy glycol" zone. I'd imagine, if you arrived back to an ongoing power cut you would want to conserve your battery power for things like Internet, phone charging, lights etc. and off using your precious power to run the heating pump and using your aga as the heat source. The only downside of glycol is the expense, which can be countered by not using giant buffers and the mess issue*. The efficency and viscosity in normal operating conditions seem to be very close to water. *as someone who regularly has to deal with small leaks from heating systems and small spills of water when fixing them, this is the biggest drawback for me.

I notice the first pic says Inlet backup heater water temp 43C ... Refrigerant temp. 37C I may be wrong but this would imply some of your heat is being generated by the backup heater?

Glycol/Antifreeze valves are very much for the chance combination of rate events (though power cuts are often correlated with very cold weather). I understand the reluctance for glycol especially if you have a huge system volume, but I do think the case against it has been overstated - especially regarding efficency. For me the biggest "downer" is the potential mess from leaks, either during use or spillages during maintance, but then again spilling water from a cruddy open vented system is pretty nasty anyway.

But we're only interested in freeze protection if there is no power. If there is power then the fluid temp won't ever be below zero so the increced viscosity at very low temps isn't an issue.

Not in a flat you can't! 😁 The big issue is the space needed to store the heated water, especially as it will be stored at near use temperature rather than high temps and blended down to a lorger volume of use temp water. An unvented cylinder could be made cubic to help give extra 25% volume and if a pressure booster pump was included that might do.

Is glycol so bad? Here's a table (chofu) of the correction factors for glycol Even at 40%, which gives protection below -20C the loss of capacity is only 2.6% and the pressure drop only 3.3% more. I'd argue that a system designed so that those margins are critical is maybe top close to the edge. I do see the reluctance to using glycol in a system with a huge (say 100l) buffer or volumiser but we should be aiming to remove those anyway