Does any one have experience of poor DHW COP on an 8.5kW?
Heating seems to be just achieving a COP of 3 with mild outside temperatures, the DHW COP is 1.6-1.9 only heating to 50C. Heating a 250l tank from 30-50C in about 25 minutes.
I’ve only ever seen sub 2 COP once on my R290 6kW, I understand R290 is better but the performance seems poor for R32.
Recently installed system (last week) logging to HomeAssistant with MQTT bridge. Computed input power and output power at peak of DHW cycle is ~3kW in with ~5kW out.
There is no external monitoring on this system yet.
The tank temperature is getting up to 50°C, yet the return temperature is not. We’d normally see the flow and return temperatures to be several degrees above the tank temperature, as shown in the example in post #2. I would check that the temperature sensors are correctly fitted and insulated.
Has a temperature probe actually been fitted in the upper pocket? This isn’t usually included in pre-plumbed cylinders, and is an optional extra. If there’s no probe, you can disregard this data.
And if there is an upper probe, has it been fitted correctly or is it just floating in the wall of the tank?
I believe the flow is on the left highlighted in blue and the return is on the right highlighted in blue also. The blue wire behind is the DHW upper, I believe it may have been dislodged previously.
The pump on the right is active during heating operation, flashing green. The pump on the left appears to have a button for changing mode between radiatiors or underfloor and three speed settings it would appear.
At a minimum I would recommend wrapping both sensors in a good layer of insulation. For best results, take them out and apply thermal compound before refitting, though I appreciate it’s a tight space to work in.
Plotting flow and tank temperatures on the same graph will make it easier to compare.
Also, look at the period when the compressor is off but the primary pump is running. The flow and return temperatures should be the same while they drop.
All the comments about the thermocouples all look very sensible.
My experience of the estimate of power consumption on Philip Thompson’s mqqt interface over estimates my power consumption for DHW in particular - I can’t track any other way, but it’s often a few hundred watts above what my Octopus Mini is measuring for the whole house (that’s with a 5kW R32 version) - so if that’s typical it’s possible you might have two inputs to the calculation both driving the COP estimate down.
those 2 sensors there are the flow and return sensors. the dhw sensor is in the spare sensor pocket for the immersion. problem with the cylinders used for the ecodan is that this sensor pocket is nearly at the base of the cylinder. that means that if you draw off only 20lt of hot water the system will then try to re heat. to get around this ( although it is not the real solution is to adjust the dhw max temp drop from 10 degrees to 20 degrees. and to also time your hot water so that it can only reheat for 2 or 3 periods each day. you only need 75 mins max to heat a complete tank even if you have it on eco mode. this will change your water COP above 2. ( don’t expect much more from these unless you time the hot water so it is heating a tank that is nearly empty. You may also need to look at the main pump settings. your flow and return delta is way too small. it should be around 5 to 8 degrees. i bet your main pump setting is still on the default of 5 which is max and most systems only need it to be on 2. Try dropping the hot water down to 47 degrees ( this is not the temp that you get from the taps, its the temp at the sensor at the bottom of the cylinder. you actual should then be around 51 to 52 which is plenty hot enough for most).
If you want to try calculating the power consumption yourself, I wrote up a more accurate formula over here, though DHW is tricky still, especially for pre-plumbed cylinders with heat exchanger.
Indeed, a tank can be reading below 20°C yet still has enough hot water at the top. Depending on usage, you may find that heating the tank just once a day (or even every other day) provides sufficient hot water.
Thanks. I’ll give that a go. I’ve got a power meter waiting for configuration during some downtime over Christmas, so it’ll be interesting to compare the two.
