Hi Mike,
It’s good to see another NIBE owner on here. While NIBE systems are nothing like as common (in the UK) as Daikin or Vaillant they’re well-engineered and have robust control algorithms.
I also have a NIBE heat pump (though it’s an older Ground-Source unit) in a Passivhaus with MVHR. Mine’s an 8kW unit which is plenty big enough for 315 square metres of floor area at Passivhaus levels of heat loss. Out of interest, what’s your floor area and what’s the capacity of your F2040? (Tim mentioned 12kW but I wonder if that was inherited from the previous thread.)
For comparison, over the past 24 hours my heat pump used 12.75 kWh of Electricity and delivered 48.725 kWh of Space Heating and 2.65 kWh of DHW Heating - which is what I’ve come to expect, given it was only just above freezing here overnight. If you’re nearly double that Electricity input the implication is that either your efficiency is lower or you’re needing a lot more Heat. myUplink should show you an “Energy Log” which will let you (roughly) calculate your CoP - even without a separate Heat Meter.
I completely agree with Tim that cycle durations measured in hours are not considered ‘short’ and provided you don’t have multiple cycles per hour that’s nothing to be too concerned about by itself.
There’s a thread from a couple of years ago from another F2040 owner in a Passivhaus which might be worth a read: Cost of running a Nibe ASHP , controlled by SMO20 for DHW only. The principal issue there was a two-cylinder DHW setup which led to the space heating drawing heat from the DHW cylinders, which then kept running DHW cycles at high temperatures resulting in very low efficiency. You won’t have that same issue but the discussion might help your understanding of NIBE systems.
That’s completely normal for a NIBE system, with 30% being the factory-default speed in ‘Wait Mode’. The consensus from users on these forums is that a lower speed is generally adequate - 20% or even 10%, which slightly reduces the heat lost via the outdoor unit when the compressor is off. That’s more ‘fine tuning’ than a fundamental configuration requirement though.
Note that the NIBE control algorithm is based on the “Degree Minutes” principle:
- The Outdoor Temperature reading is used to calculate the required Target Flow Temperature
- In myUplink this is called the “Calculated” supply temperature
- The Measured Flow Temperature reading is compared with the Target Flow Temperature and the extent to which the Measured temperature is Above or Below the Target is accounted for in the Degree Minutes running total:
- If the Measured temperature was e.g. 3C too low for 2 minutes then 3 x 2 = 6 gets Subtracted from the Degree Minutes
- If the Measured temperature was e.g. 2C too high for 5 minutes then 2 x 5 = 10 gets Added to the Degree Minutes
- When the Degree Minutes running total drops to -60 (or a different configurable value) the Compressor switches On
- When the Degree Minutes running total rises to 0 the Compressor switches Off
If you add both Degree Minutes and the Calculated temperature as Custom Tiles in the myUplink app that should give you more insight into why the compressor is stopping and starting. You might also want to track “External supply line (BT25)” which is what I called the Measured Flow Temperature above.
David