rgledhill

There's one pump inside the Daikin internal unit, which circulates through the heat exchanger inside the same unit, through the 3-way diverter valve, then through the second heat exchanger and back again. There's then a standard Danfoss CH pump which circulates heat through the other side of the second heat exchanger and internal the existing central heating pipes. The 3-way valve seems to be working fine, in that the pipes to the DHW tank remain warm from conduction of heat but only get hot when it's switched to DHW, as you'd hope.

Thank you both and as I'm not the installer, just the user (albeit a fairly knowledgeable engineer one, but certainly no ASHP expert), I don't know the answer to many of those questions... but I'll try: The water loop from the internal heat exchanger is running at 1.1bar it appears. No idea about the loop to the outside unit which is using R32 refrigerant, rather than water+glycol so there should be no issue with freezing. The heat exchanger that's gone (twice) is in the one in the inside unit, not outside. The system has both backup and booster heaters installed and configured correctly (as far as I can tell) and if the system goes from a relatively low cycle (e.g. overnight, when the whole house is at 18C target temperature) to suddenly needing a bit more (e.g. one bathroom is set to 21C) then the booster comes on to get the temperatures up more quickly. There's a single heating zone but programmable TRVs everywhere, though none is set to be hugely different to 18C-20C, so it's not like they're completely off, then completely on. Most of the time the system trickle heats the house at about 18C very effectively, it seems. I've tried reducing the flow temperature and it has no noticeable effect; running around 37C and we're at a SCOP of less than 2 so far today. I tried disabling both boost and back-up heater as they would obviously drag the SCOP down but it had no noticeable difference. The system is a low-temperature split, so it has an outdoor unit with a short run of about 3m (well insulated, outside feels room temperature) to the inside unit, using R32. The inside unit has a heat exchanger to a relatively short 28mm pipe run, either going through another heat exchanger to pass heat to the CH circuit, or diverting through the coil in the hot water tank. Return temperature appears to be around 30C which corresponds to the read-out from the sensors. I will try dropping the flow temperature down to 30-35C and keeping the booster and back-up heaters disabled, because really this should result in a decent SCOP. Outside temp today is around 9C and breezy so fairly good conditions really. The outside unit has a good amount of space to breathe too. Thanks again, very helpful!

(Apologies to anyone who's already seen my post on this on RenewableHeatingHub) Hello everyone, Last March, we had a Daikin Altherma LT R32 8kW system fitted last year, with a 160 litre DHW tank, running CHW for a 3 bedroom recently built house with good insulation. Radiators are all properly specified, flow temps set at about 42C in current 5C outside temps. The house gets warm with no problems, with 18C set-back temperature, and occasional rooms up to 21C (e.g. bathrooms in the morning, lounge in the evening). It's configured to use weather compensation, so dropping to 30-35C flow temperature as the outside temps warm up. Hopefully this is pretty much an optimal system. The only thing is, I get poor SCOP - see below: Looking at the CHW, this seems really low, and has since dropped to around 1.5! Back in April, we started hearing fizzing sounds, and basically the heat exchanger had sprung a leak and coolant gas was fizzing into the water loop. As there was less and less coolant going round, the system had to work harder and so the SCOP dropped. The heat exchanger was replaced at the end of April and the SCOP went back up from 2.58 to 2.93, and on DHW 1.78 to 2.34. Well, back in October, it started fizzing again and the SCOP's on the way down too. So... any ideas firstly what's causing the poor SCOP? This system is supposed to be about 3.5 to 5.5 SCOP, so 2.5-2.9 is pretty rubbish. Secondly, any idea why the heater exchanger has failed again (so that's two brand new heat exchangers now that have gone)? I'm thinking the only reason they could fail is over-pressure or over-temperature. I do notice the hot gas inlet from the external unit is really hot, probably 55-60C - is that normal? Any advice or experience with these Daikin units would be really appreciated. The original dimensioning seemed very sensible, with about a 5kW heat input required in really cold temperatures, so 8kW seems well-dimensioned. As I say, the house is warm, it's just really inefficient (and breaks heat exchangers!). Thanks Richard