I was being optimistic the heat pump might set the flow rate, etc. based on the schedule / max charge time.
I was also forgetting the outside temperature was colder last night so the heat pump would have had to work harder.
Cylinder charge offset is on 5K. What would you suggest reducing it to, please?
Yes, cold plays a part
Nope. I’ve got my flow rate high to it keeps the DT narrow so the heatpump doesn’t have to work as hard.
If you’re only wanting 48C, you might as well put it down to 1K. ie, end temp should only creep a little over 48C (offset + DT), especially if you keep the flow rate high and the DT narrow.
Might be worth just making small changes each night and seeing what happens.
One final thing, are you sure you’re in Eco? Cos the graph looks like Balance to me (ie, Normal to 45C and then Eco beyond that).
Thank you.
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.
It’s not on the sensocomfort, it’s on the heat pump controller.
I detailed where on here
Perfect, thank you.
I’ve dropped the Cylinder Charge Offset to 3K and switched the DHW to Eco, it was on Balance.
Will see how that goes tonight.
The most obvious difference with having the “set-back mode” set to Eco, was the flow rate dropping to zero, rather than sitting at 8.8 l/m
How does keeping dT narrow mean less work for heat pump?
Far more gentle power consumption this morning. Peaked at 1226 W towards the very end of the DHW cycle. Previous nights would see power consumption peaking around 2800 W after the first ten minutes.
Flow temp peaked a little below 60°C. Will see how these settings fair for a few days before trying a lower offset.
Flow goes out 40C and comes back 30C, heat pump has gotta raise the water by 10C before sending it back out.
Flow goes out 40C and comes back 35C, it’s only gotta raise the temp by 5C, so less energy / work required?
My understanding anyway. 
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.
This makes no difference. It was highlighted on the heat geek mastery course.
It was recommended to have faster flow. Will need to go back and check what his reason was.
The can be tons of combinations of DT x SHC x flow rate to get to the same heat output.
My theory is that the combination with the lowest DT may stress the controller the least?
Perhaps a test is required (if you/we are able to track compressor speeds/power).
ie, one run with wide DT and one run with narrow DT
I’m running mine at just over 2 DT (with 100% pump speed) and i’m getting the best DHW performance i’ve seen.
DHW COP of 3.4 this morning. (2.8 yesterday)
Heated water from 14.5°C to 43.5°C
Flow rate peaked at 55°C
Two hours not quite long enough for it to reach the target temp of 48°C in Eco mode.
Check what you got DHW anti cycling time set to. If you put this to 0 it should run past 2 hours if required.
It will be interesting to see it run to completion to see what flow/return ends up at. You’d hope that you can set it to be not too much past 48C eventually.
Much nicer COP though. 
Something wonky goes on with flow rate on the graph though? Have you got any air in the system?
Graphs suggest that erratic flow rate has been there for a while. Only with DHW though.
New cylinder coming in a couple of weeks so will ask the installer when he returns.
Yep, common issue. Usually air in the system.
Have a look around the site so you’re armed with the right info.
heat meter location and air valves etc.
You need to get this sorted as it can screw output (and cop) data. See how the heat output drops at 03:20 there in line with lack of flow reading.
flow x dt x shc = output.
if the input values aren’t there, the output comes out screwy.
We got an efficiency of 3.17 to heat our 300L tank to 52c.
We set the flow temp to 4C over the tank temp. So it does take a while to heat up.
@gck303 could you explain how you set the flow temp for the DHW? Am I correct that you have an Ecodan?
I have a loxone miniserver that controls the ecodan (via modbus), circulator and the CH/DHW valves. The miniserver sets the flow temp and operates the valves based on demand.
The miniserver collects the Kamstrup data (via modbus) and publishes it via MQTT after splitting it into DHW/CH based on what is operating. See my feeds below.
Ah, so I’m assuming the Ecodan has no idea that you have switched from heating to hot water and back it is just delivering a fixed flow temp that you are changing when needed?
It has no idea. It is just heating the water to the temperature requested.
I only use two things on the ecodan controller via modbus:
All the relays and external controls on the FTC are unused.
