thanks. the volumiser is in the cold loft, but it is itself insulated. I wondered if that, plus the heat lost to the loft from all the pipes running through the loft could be bad for efficiency, but that doesn’t fit in with the data I see, which is the dT being too low (i.e. not enough heat lost, even including the loft).
They left only 2x TRVs when changing from buffer- to piping as volumiser. Those are always on 5. There are now 2x lockshield valves on all other radiators, and I might have missed to fully open one of those. Will check, but I don’t think this is the case. Interesting that you say it’s 2x15mm, in fact there are 2 pipes per radiator going down from each 22mm pipe in the loft. I though that for the pressure loss, the one going in and the one coming out of the radiators it would be the same pressure loss as one long 15mm pipe. The 15mm pipes are rather long, as they go down the >2m from the ceiling and around the corner to the radiator and back. Compared to having 22m under the floor boards, perhaps that means we have a longer run of the 15mm pipes and thus lower flow rate relative to pump power. Note that we DO get the maximum flow rate if I set the building pump setting of the aerotherm to “Auto”, it then settles around 61% pump power to get the 1205l/h.
Yeah, right !? I am glad that I am not the only one wondering about this.
The noise is a loud humming and seems to be due to the compressor vibrating through the primary pipes. These come into our 3rd-bed-/guest-/multi-purpose room. The plan was to use it as the master bedroom so that the kids can each have their own bedrooms, however at the moment I couldn’t sleep well during the winter.
The noise depends on the compressor modulation (speed). It’s fine up to ~35%, more noticeable up to ~45% and rather loud (like having an old microwave running in the room) from ~45% upwards. Interestingly there seems to be a resonant frequency of the pipe, so that the noise is worst between around 60%. The noise during DHW legionella cycle at >90% I would say was quieter than at 60% heating. There is still considerable vibration noise from the compressor through the pipes. The installer kindly did change the previous pipes for nicer looking ones and I think it also improved the vibration significantly, but it is still quite loud. The primary pipes and cylinder are in our largest room, which I thought we could use as a bedroom, but the loud low humming noise is really a problem.
Anyway, I think the point is that it is actually working reasonably hard in cool/cold weather and not short-cycling during lower demands. So I come to think that it is not actually oversized as most people suggest.
But efficiency is still low, so I think something is not quite right:
Either, the efficiency in reality is actually very good and only the sensors are wrong, or something causes it to use too much energy relative to the output.
Sensors: if dT is measured too low (usually below 2K) the generated heat is calculated too low. Same for the flow rate. Obviously, if the consumed energy is read wrong, this also skews it.
dT seems to be OK, as Flow and Return T within 0.1K during “compressor shutdown” phase.
Flow rate: is there a way to check this? I notice that on Auto, the pump power goes to 61%, to achieve 1205l/h, both for heating and DHW, although there should not be any restriction at all. Previously it was at 51%. The DHW circuit shouldn’t have changed at all. ( I need to double check). Setting the pump power to 51% results in 1030l/h flow rate. If that was actually1200l/h, that would result in an actually better COP with the same low dT.
Electricity consumption: I think someone said these are very accurate, and I think the readings look fairly reasonable.
So the Flow rate sensor is currently one of my question marks. But shouldn’t dT be much higher in any case?
Looking at some of the more obscure parameters in the installer level (Test menu-> sensor/actuator test), I see the value “T.0.88. Overheating actual value” seems constantly above 20K (e.g. 22.3K, 25.6K), but the manual says “0.1 to 20K are normal operating parameters” ?!
“T.0.87 Overheating target value” says 0.0K by the way.
Does anyone know what this means?
Could this (or perhaps any other parameter, e.g. “condensation temperature”) indicate something being wrong (or not ideal)?
I have recorded some snapshots just from photographing the display of the control unit and will need to put them in a spreadsheet to look at that more systematically.
