I have found that enabling quiet mode has a noticeable effect on the DHW efficiency as it throttles the output of the unit. My 4kW in “more quiet” mode will only output up to 4.5kW instead of the full 8kW without quiet mode. I’ve seen COP of up to 5.99 when running at warmest time of day in the recent heat, and 4.41 overnight last night. When I tried in non-quiet mode I got 2.84.
Discovered today that you can set a schedule for quiet mode, but I’ve not tried this out yet. As I’m only using DHW and not heating currently, this will be more useful come autumn/winter, to be able to set one quiet mode level for the DHW run, and a different one if needed for heating.
Things were going well, better and better DHW COPs due to the warmer weather (depends on what start temp is though), however yesterday I noticed the DHW cycle was still running some 2.5hrs in - unusual.
Examining the actuators etc in the MMI info, the direct heater appeared to in action!
6kWs had been used - normally is around 2 for full great up.
I stopped it at just 42C water temp via the app..
Went through things in installer mode.
Nothing obvious, direct heater disabled except for disinfection.
Disinfection disabled.. - its been fine for months of course!
Once out of the DHW schedule I turned DHW back on schedule.
Today at the scheduled 13.00 start, it did its usual thing from 30C tank temp to normal hot setting.
Really strange behaviour yesterday.
Hope it doesn’t do it again.
just tried on the quietest setting and no significant COP difference for me between non-quiet and the quietest modes. Maybe because I am always starting from a low temp.
Similar start temps ~15C
Same end temp 45C
Similar Outside temp, similar weather
Be careful when comparing hot water runs, as performance is very much affected by the starting temperature, i.e. how much hot water was used over the previous day. Drawing from the cylinder during the reheat (as can be seen above) will also skew results.
I recommend checking the total “HP heat output” over the duration of the heating cycle (e.g. 4.5 kWh) which is the amount of heat put into the cylinder (ignoring losses). Only compare to other cycles with similar heat output. If a cycle has significantly more or less kWh of heat when compared to another, that suggests the starting conditions were not the same.
It’s also a good idea to plot the tank temperature too, if that data is available. The recently updated app now accepts feeds for heatpump_dhwT and heatpump_dhwTargetT with an option to display them.
In my charts there was no draw from the tank, not even a hot tap, I was home alone. And I do have the tank temp enabled at least on the most recent one and Home Assistant has the older ones tank temp.
Start dhw temp of non quiet 15.9C
Start dhw temp of most quiet 18.9C
What I would say is it’s just a single tank temp, half way up the 180L slimline and I have no confidence in it representing how much hot water there actually is in the tank. I’ve had perfectly hot showers when it’s been reading ~15C and luke warm showers when it’s read much higher perhaps mid twenties.
In all my DHW runs I’ve looked I have yet to see anything that conclusively shows a significant COP improvement in quieter mode.
