The former I think. AA pushes the lower end up and the higher end is constrained by my 43 deg upper limit. If I remove the upper limit, the upper end increases. This makes the variation more but also the average. When I'm back home I'm going to turn the thermal diff off and keep the upper limit (which is the same as my WC curve upper limit. It may start to cycle but let's see.
@sunandair I'm not sure I fully understand all the maths, but that's very useful, thanks.
As a side note; I notice you have three towel rails. The reason I mention this is we have two, and it dawned on me fairly recently that towel rails are not really heat emitters. I started thinking that most of the flow going through these was just 'passing through' (raising the RWT) rather than dumping heat into the room. I turned the valves right down to give the minimum flow possible - I have two K3's in the circuit that were not receiving adequate flow/even heat before, they now do. I think my LWT/RWT delta has increased a little as a result.
@sunandair I'm not sure I fully understand all the maths, but that's very useful, thanks.
As a side note; I notice you have three towel rails. The reason I mention this is we have two, and it dawned on me fairly recently that towel rails are not really heat emitters. I started thinking that most of the flow going through these was just 'passing through' (raising the RWT) rather than dumping heat into the room. I turned the valves right down to give the minimum flow possible - I have two K3's in the circuit that were not receiving adequate flow/even heat before, they now do. I think my LWT/RWT delta has increased a little as a result.
I've left my system in AA mode for now. Here's a representative hour from last night. Interestingly the target temp appears to have dropped by one degree (despite the OAT being two degrees colder) compared to the graph I posted yesterday - it seems to be adapting quickly. Overall it took 7.5 hours to raise the house temp by one degree (a which point the remote stat turned the heating off). Worth noting the 'on' cycles are quite short as it cannot hold the temps that low for long. OAT was 10C last night.
@derek-m I guess not (or with not enough attention to detail) lol. I've also sussed out since that they also left the pump on a setting that gave a flow rate outside of the operational parameters in the Ecodan manual.
The former I think. AA pushes the lower end up and the higher end is constrained by my 43 deg upper limit. If I remove the upper limit, the upper end increases. This makes the variation more but also the average. When I'm back home I'm going to turn the thermal diff off and keep the upper limit (which is the same as my WC curve upper limit. It may start to cycle but let's see.
From my experience the upper limit was ignored when thermo diff was OFF (I'd set it to 42C - it blasted through to 48C in one test). It will be interesting to see how you get on.
@derek-m I guess not (or with not enough attention to detail) lol. I've also sussed out since that they also left the pump on a setting that gave a flow rate outside of the operational parameters in the Ecodan manual.
If you haven't already done so, I would suggest balancing your system.
@derek-m What did Toyah once say, 'It's a mystery, I'm still searching for a clue..' 😀 .
My system needs 40C+ flow temps when OAT is in the 12-15C range to reduce cycling. The logic behind trying the inverse curve was to give the system what it wants as such (without excessive overrun) the 38-42 combo was working pretty well.
I knocked up a modelling tool for your system today and it shows the following results based upon the data you supplied.
The results would indicate that your heat pump will commence cycling at an OAT of 8C and above, with a LWT of 38.6C. This is at a fixed water flow rate of 10 lpm giving a DT of 4.1C.
At an OAT of 12C the heat pump would probably be running for 67% of the time.
I knocked up a modelling tool for your system today and it shows the following results based upon the data you supplied.
The results would indicate that your heat pump will commence cycling at an OAT of 8C and above, with a LWT of 38.6C. This is at a fixed water flow rate of 10 lpm giving a DT of 4.1C.
At an OAT of 12C the heat pump would probably be running for 67% of the time.
How does this compare with your findings.
Thanks.
Quite accurate - in fact I ran at a fixed flow of 38C last spring as a happy medium of still being able to heat the house at minus temps, but also resulted in an 'acceptable' amount of cycling at milder temps (say 3-4 cycles per hour once air temps were around 12C and above).
Just to provide some additional info; flow rate is 16lpm, with a DT nearer to 3.5.
Note: yes I have rebalanced the rads since having the towel rail lightbulb moment a few weeks ago. All rads now have even coverage/temps etc that would be hard to improve upon imo.
The importance of 28mm primary pipework taken right to the first junction where 2 X 22 mm pipework takes over and the split of the radiators is approximately symmetrical down both branches to ensure water volumes are more or less balanced.
So we’re hoping all this attention to detail will help avoid excessive cycling. You may have noticed there is some 10mm microbore however only one rad is fed off each branch. This hasn’t caused too much resistance - there is a flow rate of 22 lpm on the DHW circuit and 19 LPM on the heating circuit with the microbore. All the TRVs are now left fully open so that maximum heating capacity is available at all times.
In the knowledge that our capacity is limited to around 32 to 35 we have edited our WCcurve to have a lower limit of 30 LPM at outdoor ambients of 9C and above since any lower will probably invite rapid cycling.
**Correction **
the last paragraph should read:
‘In the knowledge that our radiator capacity at lower temperatures may restrict the HP operation to around 32degC to 35degC we have edited our WC curve to have a lower limit of 30 degC at outdoor ambients of 9C and above since a lower flow temperature will probably invite rapid cycling.’
Operating in AA. We have been getting reasonable ‘on’ time yesterday since we extended the ‘Room Temp. control’ interval. This is the interval period between self monitoring points.
The interval was 20 minutes. It is now set to 30 minutes. We have been getting over 80 minutes ‘on’ time. Followed by possibly 1 or 2 hour off time.
But the flow temperature is still rising to nearly 40c see attached.
Does anybody have a suggestion which might result in lowering the flow temperature and reducing the off time? The WCcurve is set to 30c @ 9c Ambient and above. It’s 10c outside atm.
<img src="https://renewableheatinghub.co.uk/wp-content/uploads/wpforo/attachments/4924/thumbnail/4936-D1077371-41D8-4560-857B-31EA8BE31654.png" style="max-width: 400px; max-height: 300px;" alt="D1077371 41D8 4560 857B 31EA8BE31654" title="D1077371 41D8 4560 857B 31EA8BE31654" />
