Here's the scores on the doors for day three in AA mode (quite interesting - sad but true).
Target temp appears to have been dropped by a further 0.5C (day 1 it looked to target 32C, day 2 31C, day three 30.5C). The heating came on last night around 1am - it stayed on until 1pm this afternoon. That implies AA mode has within three days learnt the flow temp to keep the house at a constant temp (the stat is set for heating to come on at 18C, AA mode brought IAT up to 18.5C and held it there for some 11 hours, only when OAT increase during the afternoon did the IAT reach 19C and stat turn the heating off).
I actually thought the heating was off when I got up this morning, but then realised it was on very low (just a trickle of heat out of the rads) all rooms sat perfectly at design temps, it really is the radiator version of UFH. I like it.
Interestingly the 'on' cycles only last 20 mins, that coincidentally (or not) matches the Room Temp Control - Interval I have set. It's almost as if after 20 mins it checks the various temps and decides there is nothing to do (IAT is stable, and I've already reached target flow temp) so cycle off. If that is the case, that would explain why sometimes it does not reach for the +3 overshoot.
Derek is right in saying that IAT and OAT are needed to provide full context. I've also included that chart from Melcloud below.
+3 would be my choice. How long have you been in AA mode (I'm wondering if it has started a little high in term of target temp and needs a few more days of learning where it will gradually bring it down)?
Interestingly the 'on' cycles only last 20 mins, that coincidentally (or not) matches the Room Temp Control - Interval I have set. It's almost as if after 20 mins it checks the various temps and decides there is nothing to do (IAT is stable, and I've already reached target flow temp) so cycle off. If that is the case, that would explain why sometimes it does not reach for the +3 overshoot.
hi, I’m pretty sure it’s no coincidence. Earlier in the month I was getting 20 minutes cycling but, like you, I also had the period set to 20 minutes. As soon as I set it to 30 minutes the cycling stopped. The HP would either modulate down to a lower output after 30 minutes or carry on running for 45 minutes, ramp up the output then decide there was enough heat already in the room and switch off for possibly an hour or more.
I believe the control interval is the moment the HP is supposed to adjust the heating trajectory. I’ve avoided a longer interval than 30 minutes because a longer interval period might take a lot longer to adapt if the output was set too high. Ideally I’d like it to not switch off which does seem to be the outcome now we have a 30 minute interval set.
It would be interesting to see what your cycles would do on a longer interval but your short cycles appear to keep your flow temperature down to an efficient output somewhat.
Regarding your comment on IAT and OAT information I did supply this on my opening 12 graphs at the start of this discussion but I didn’t record them yesterday.
It would be interesting to see what your cycles would do on a longer interval but your short cycles appear to keep your flow temperature down to an efficient output somewhat.
My thoughts are on the same lines. Also, once OAT decreases, it will result on longer 'on' times and shorter 'off' times. I'm inclined to leave things as they are and wait for colder temps.
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.
Our Thermo Dif was set to +5 and -7 yesterday.
Today we have moved it to +4 and -5.
any suggestions?
No suggestions yet but your AA settings are now the same as mine. What I can see happening in my system is that the IAT is varying between the setpoint and 1.5 deg over. The ASHP spends most of its running time raising the IAT, followed by idle periods as the IAT drops. The fact that it's raising the IAT leads to (I think) my relatively high LWT (average 40 deg atm).
I'll try switching thermo diff to the minimum tonight (leaving everything else the same) and report back.
No suggestions yet but your AA settings are now the same as mine. What I can see happening in my system is that the IAT is varying between the setpoint and 1.5 deg over. The ASHP spends most of its running time raising the IAT, followed by idle periods as the IAT drops. The fact that it's raising the IAT leads to (I think) my relatively high LWT (average 40 deg atm).
I'll try switching thermo diff to the minimum tonight (leaving everything else the same) and report back.
Thanks that sounds interesting Kev
Meanwhile, I’ve changed to WC curve it is set at 31c at today’s outside temperature of 8c. So I’ve added +2 to bring the output to 33c. The graph shows it stopped at exactly 33c.
So I may increase it to 35c and see if it modulates rather than just switches off.
thanks again! 👍
oops.... I spoke to soon - it has modulated and at 32 ish.
What is the water flow rate? It would be interesting to see what effect reducing the flow rate would have.
Also what is happening with the IAT and OAT?
Here is a challenge for you Derek:
One of these graphs is recorded during a flow rate of 19lpm and 2 of the graphs are recorded at a flow rate of 14lpm. Which is the two at 14 lpm?
Our ecodan 8.5 has a flow range of 11 lpm to 24lpm the room temp was 20.5c on the last picture and 19c rising to 20c on the other two. Outside temp is 10c.
I have been surprised how adaptable the Ecodan is at maintaining a deltaT of 5degC within these changing flow ranges. Our circulation pump allows flow settings of 14, 16 and a max of 19lpm when in CH heating mode. And a top flow rate of 22lpm in DHW mode.
However I have been planning to operate the HP on the assumption that the faster flow rate will enable the heat pump to reach the higher outputs when the weather is especially cold say at -8. Do you have a view on this? Our HP CAN Seemingly modulate up to around 12kwh at max output.
Meanwhile ive been thinking that operating the pump when it gives a modest 16 lpm flow should give the HP most flexibility in modulating down or up when in moderate winter weather. Do you think this would be the case? I don’t have any evidence of this view just an intuitive idea that it might.
@sunandair this is really interesting. I've been a bit nervous to alter the flow rate on ours! But suspect it would help us during the milder weather.
My uneducated guess would be the first pic is the higher flow rate. dT looks bit more consistent.
I was looking at 'mass flow rate' - from what I understand (and a shaky understanding...) that would mean you need a flow of 24l/m to achieve 8.5kw(?) (8.5/(4*5))*60. Ours (6kw) is set at 14l/m and a tad noisy so wouldn't want to push any further (would.prefer lower if anything) , but same calc would suggest we can hit 4.9kw which is a little shy of our 5.2kw heat loss at -2
I would say that the 11:00 and 15:00 charts are at a flow rate of 14 lpm, since a higher flow rate would normally reduce the DT. Of course if you have the water pump speed controlled by the controller, as it sounds that you have, then the controller should be varying the water pump speed to maintain a constant DT, so my assessment may be wrong.
It is all a balancing act dependent upon how your system is being operated.
The DT between LWT and RWT is dependent upon how much thermal energy is being absorbed by the heat emitters at a given water flow rate. If say the LWT is 35C, the RWT is 30C, giving a DT of 5C at a flow rate of 14 lpm, with an OAT of 10C, and the system balanced with the IAT at 21C. If the OAT now reduces to 5C, the heat loss and hence heat demand would be increased and start to lower the IAT. If the LWT is fixed at 35C, then the RWT will start to reduce as more thermal energy is being absorbed by the heat emitters, until the IAT is reduced to the point where the system is once more in balance, with a DT of possibly 6C.
To bring the DT back down to the desired 5C, one of the options is to increase the water flow rate. This carries the thermal energy away from the heat pump at a faster rate, so causing the heat pump to work harder to produce more thermal energy. At the heat emitter end the additional energy increases the RWT and hence the average heat emitter temperature, which in turn supplies more thermal energy into the home. This of course is limited by the LWT, which will also need to be increased in colder weather conditions so that the heat emitters can actually emit more thermal energy.
In cold weather conditions it will be necessary to increase both the water flow rate and the LWT, to be able to transfer more thermal energy from the heat pump to the heat emitters.
I was looking at 'mass flow rate' - from what I understand (and a shaky understanding...) that would mean you need a flow of 24l/m to achieve 8.5kw(?) (8.5/(4*5))*60. Ours (6kw) is set at 14l/m and a tad noisy so wouldn't want to push any further (would.prefer lower if anything) , but same calc would suggest we can hit 4.9kw which is a little shy of our 5.2kw heat loss at -2
Hi Walker, Thanks for your thoughts.
The good news about the rating of Ecodan is that the output range of the compressor is quite a bit higher than the size quoted. The rating value in their literature is a mid point output. I’ve attached the output table for our 8.5 heat pump. You can see in the highlighted part of the chart that the output goes up to over 12 kWh for an 8.5 rated HP.
You can also see the lower output that they can operate at in the same chart.
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.
Agreed. It didn't do it immediately; in fact for the first couple of days it looked the same as before. But yesterday after the HW cycle it sneaked in a 48.5 deg burst. Next change today will be turning back on but with minimum settings both ways.
