Was having a nose at the graphs for Heat Geek’s Mytchett heat pump and noticed that for yesterday (1st Jan 2023), it’s showing “Water Heating” as 5.62 but there do not appear to be any DHW sections on the graph.
Might it have been too short a period to render the light blue background for? If their DHW was already at desired temperature perhaps?
Following your guide, I dropped my heat curve to 0.5 yesterday from 0.6 but back up to 0.55 when our guests noticed it being cooler. Will give 0.5 another try later this week as the outside temperature is forecast to drop a few degrees.
Our current cylinder is only 150L. On Normal mode it took an hour last night to heat the water from 20 to 48. I have just amended the “Max cyl. charging time” from 60 min to 120 min and changed the “mode on setback” from Normal to ECO.
The water wasn’t as cold as the previous night so I’m not able to really compare the outcome yet but it looks like it still ran for an hour, despite me increasing the charge time setting to 120 mins and amending the schedule in the weekly planner from 03:30-04:30 to 03:00-05:00.
In some respects, the outcome was worse as the COP was 2.46 heating from 34°C to 48°C, with the previous night COP of 2.41 heating from 18.5°C to 48°C.
I agree with your observation that it is not on Eco for DHW yet.
The setting I found was for “set-back mode” (under Circuit 1) which I switched from Normal to Eco. I did not spot anything similar in the DHW menu.
If the controller is able to adjust the flow rate to target a specific dT, then it’s able to do this without changing the power it uses. Same if you’re fixing the pump speed to achieve a certain dT. Faster flow = lower dT for same heat produced.
What’s more efficient, with respect of consumed energy?
If the water is flowing slower, is there more opportunity for heat to transfer into the cylinder?
I’ve learned here that the pump uses significantly less power than the compressor but, pumping water that’s already warm (low dT) repeatedly to save the compressor working as hard feels like it might be a waste of energy.
Of course, there’s long term wear and tear to consider. If the compressor is an expensive part to service/replace then perhaps the high flow rate and low dT is the better option.