Posted by: @boycey

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Hi, Ecodan system with UFH.and using MELcloud to look at data. i've attached 3 graphs 2 from 4 and 5 am and one from 4pm, the 4pm one represents most of the day, well today anyway. Question:- what do these tell you? is one good and one bad? let me know what you think please?

 

hi Boycey

There needs to be a few bits of other information to be 100% sure. Most importantly is the heat pump operating…

4am looks like hp is off (though not 100% sure) then starts at about 4.40am operating at 30c flow (LWT) and straight into cycling.

5am looks like continuing to rapid cycle at 30c 

3pm looks promising until you see a half degree fall on both flow and return lines. With no rises despite a 5c DT. This would suggest that the HP may have reached room temp target and is on standby.

• @sunandair hi, HP is on all the time, as in it's on weather comp and not on timer etc, all stats set to about 19.5c from 10pm til 6am, then they change to about 20.5c 6am to 5pm. Then 21.5c 5pm til 10pm. HW at 11am and 11pm at 49c. What is cycling ? Is it bad, is it avoidable? I'm aiming to try and set the flow temp so it hardly ever quite reaches the stat setting, so calling for heat and ticking over. I guess this is impossible when moving to set back of 19.5c as its lower than the previous 21.5c setting in the evening

@boycey hi,

So if your schedule was set back then it would appear the thermostat dropped below the setback temp at 4.40am and started heating but the system was heating then stopping, heating then stopping every ten minutes that might be considered as rapid cycling. Ideally the rapidity of on/off cycles need to be reduced to around 2 or 3 off cycles per hour.

the good news is you only lost 2c room temp overnight. (6 hours, 21.5c down to 19.5c by 4.40am when the hp started again) Your last post suggests you only need a few hours heating to get up to daytime target temp. 
perhaps under floor heating may need a different strategy than what I do with our radiator system.

@sunandair thanks for your replies, yes I think your right, in what little I know so far, I'm just trying to understand and find the right strategy. Maybe I need to set the stats at night a bit lower so it's not cycling, I'm not sure how to best feed the system so it's ticking over nicely, as it is then does the cycling at 4am mean it's just topping the heat up every 10 minutes, is this a bad idea?  Would it be better to setback to maybe 18c then at 6am set to go back to 20.5? Maybe someone with more experience with ecodan and UFH could point me in the right direction?

@boycey in terms of understanding MELCloud here are a few graphs from our radiator system

we are reheating on a low and slow WCcurve after a 12 c setback. This graph shows the first 24 hours you can see the reheat slows down as it approaches 20 c target. To the point that it hardly reaches the set temp in the first 24 hours.

the DT IS 5c with 1 or 2 cycles per hour.

we have a good cop 

of around 4.5

our most comfortable flow temperature to avoid rapid cycling is 35c esp when it’s mild circa 10 to 15c outdoor ambient temp. We have an 8.5 model.

@sunandair thanks again. So my graph where the flow and return are straight across, contant delta T more or less, do you think that's good or bad? With yours cycling once or twice an hour, what causes that? Is it the room getting to temp, and being shut off by stats? Mine is running flow temp of 25c with current oat at about 10c, the flat is warm and is pretty much calling all the time during the day and room temp is not quite reaching target temp, so I thought I'd nailed the westher curve, well this end of it, ie lowest flow temp possible whilst the flat stays warm and constantly feeding the system? But I am getting short cycling sometimes.  It's tricky this isn't it lol.

Hi @boycey 
I don’t think the graphs you posted where they are straight and parallel are actually showing the HP in operation. If you look at them closely you can see the lines dropping slowly which probably indicates the HP is in standby mode. 
I tried to explain this in my previous message and modified it for clarity below:

Posted by: @sunandair

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Graph 1

The 4am graph looks like hp is in stand-by mode then starts at about 4.40am operating at 30c flow (LWT) and starts cycling on and off.

Graph 2 (5am) looks like the HP is continuing to rapid cycle at 30c flow temp.

graph 3 (3pm) May look as though it is working with a 5c DT but is in fact in standby. If you look at the flow and return lines and see a half degree fall on both flow and return lines. With no rises despite an apparent 5c DT. What this graph is really showing is the HP in standby with no circulation at all. This would suggest that the HP has reached room temp target and is on standby. 
MELCloud will still show temperature graph even if the water is not circulating and the hp is not generating heat.

 

graph 3 is shown below.

so you can check when the HP is operating by seeing the HP icon on the FTC screen or on the “Internal Temperatures” 24 hour graph on MELCloud graph option list.

hope this helps

Just to add my 2p, I have an Ecodan and UFH, to avoid cycling on and off then we need set the flow temp at a minimum of 32C, from your plots it looks like you are lower than that at 29C so it may be worth increasing the minimum flow temp a few degrees, cycling on and off rapidly like you have is bad for efficiency and bad for your compressor.

Cycling on and off occurs when the Ecodan can't keep the flow temp within about 1C of the set point as it can't reduce the input power any lower so it has to shutdown for a few mins till the flow temp cools then its starts back up again, this is what you are seeing numerous times an hour.

@gary hi, thanks for your input, I've just been flicking through the ecidan set up booklet, just cage across flow temp range, in service menu/operation settings/heating operation. The minimum flow temp default is 30c, but can go down to 25c. I'm wondering if this would help on the short cycling. 🤔

That will just prevent the heat pump from setting a temperature lower than 30C, its easier just to adjust your weather compensation curve.  Can you post a picture of the curve you have set currently?

@gary ive set it 25c til it gets to down to 15c, and 34c at -6c. its a modern well insulated flat, south facing, also has heat recovery ventilation.