Poorly performing R...
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Poorly performing R32 LT Daikin monobloc - is this normal?

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I’m hoping you can all help me with our new Daikin EBLA09DA3V3 i.e. 9kW, low temperature, R32. I think it’s performing much worse than it should and I’d like you to tell me I’m not being unreasonable. Apologies for the long post but I thought I would get as much information out there to start with.

The heat pump installed behind a garage feeding a hot water cylinder inside the garage. The DHW and CHW are both fed into the house underground a few metres in insulated pipes.

The house is a 1930s semi-detached inCambridge with a recent loft extension. The loft extension is well insulated and the rest is pretty good given the age - internal insulated plasterboard up to 50mm thick in many places and insulation under the suspended wooden floor. The ground floor is UFH and the 1st & 2nd floors are feed via air ducts from an water -> air heat exchanger ( https://www.invisible.ac/), so we are able to run at low temperatures. I currently have the WC curve set to 40C at -5C ambient and 25C at 15C ambient. The reason I’ve got that slightly odd curve is that Daikin’s minimum temperature is 25C and so I can’t set any value on the curve lower than that. I’m on dumb thermostats across multiple zones in the house, but they’re each set back by only a couple of degrees overnight. I did have the flow temperature set back overnight on a schedule but that option seems to have disappeared in a firmware update to the Daikin controller (a real pity since that feels like the best way to reduce temperatures overnight i.e. don’t use thermostats, but instead dial back your flow temp). We also have the thermostats set back during week days since we’re at work, but again only a couple of degrees.

There is no low loss header or volumiser. A LLH was originally planned and partially installed before I queried it. The installer then did the sums and concluded that there was enough volume in the under ground pipes (never mind the house) to meet Daikin’s minimum volume requirements. That exchange didn't fill me with confidence to be honest.

I don’t have a full heat loss survey but the performance estimate has a required heating capacity of 6.1kW at -5.9C i.e. we’re comfortably sized with our 9kW unit (to be honest one of my concerns is that we’re oversized since I don’t think the full heat loss calcs take into account the upgraded insulation).

DHW is set to heat to 47C between 0230 and 0400 in the morning, and heat to 45C if it ever drops below 40C - which happens surprisingly often in a two person household. I also think we have far too much heat loss from the DHW cylinder, but that’s not my most pressing problem.

Anyway, the Daikin controller will tell us a total energy produced and consumed for each of CH and DHW. I’ve been recording those every evening and so I’m able to calculate a daily average COP. There are obvious problems with that since I don’t know how accurate the Daikin’s temperature and flow rate sensors are for the heat production and it only reports in whole kWh so there is obviously some rounding error. Over the last month I’m seeing CH COPs of between 1.9 and 3.3. There is some correlation between ambient temperatures and the measured COP - the better numbers are more recent but I attribute that to the warmer weather. However, given the flow temperatures we’re running that feels far too low.

A good example would be 4 February, which was a Saturday so the heating was on all day. The ambient was vey steady, between 6.0C and 8.0C, according to the weather station just down the road. That feels like very good heat pump weather and on our WC curve flow temps would be 31C or 32C flow temps so we ought to be getting amazing performance. Yet we used 7kWh electrical and generated 18 kWh thermal for CH, for a COP of 2.6 on that day. According to the Daikin data sheet here (page 56) we should be getting a COP of around 5 at those temps:

The COPs for DHW are similarly dismal, down as low as 1.2. Of course these will be lower given the higher temps for DHW, but still that feels far too low.

One thing that is abundantly clear to me from these forums is that the whole system design should be examined. However, I would expect problems there to manifest themselves in lots of compressor starts and I’m not seeing much sign of that. Unfortunately the Daikin controller doesn’t have a restart counter, which I think is incredibly dumb because it would be a great tool for them to point the finger of blame at the installer. However, just looking at the screen it looks to me like the compressor is typically on for extended periods of time and there is no sign of cycling that I can discern.

I understand that the real world and the data sheet numbers will be different but I would expect us to get much closer to the data sheet than that. Is that an unreasonable expectation?

Side note: I actually asked for a Daikin engineer to come out a little over a week ago since I think they need to take a look at this. I still don’t have an appointment for that.

This topic was modified 1 year ago by mark-h



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