Posted by: @trebor12345

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I didn't run the heating over night.  Only just now switched on.

OK thats a pity it would have been good to see if/how defrost changed as a result of switching off night shift and overnight there would have been plenty of opportunity.  Next time!

Posted by: @trebor12345

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Posted by: @jamespa

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Posted by: @toodles

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My Vaillant was defrosting every 45-60mins overnight (chart shows FT).  As you can see it doesnt fully recover from the defrosts because noise reduction mode is set from 11pm-71m, and struggled particularly to recover from the deep defrost following the DHW cycle.  As a result IAT fell 1C overnight, but is now recovering again.  Some would of course program this behaviour deliberately and call it 'setback'.

 

 

You can also see how the temperature rose during the evening as the OAT was falling.  Also a deep defrost at midnight, prior to the DHW cycle, following the DHW cycle and then again at about 7am.

Yes, you can work out a lot from a plot of FT.  Interesting that there were both deep and shallow defrosts, for reasons I dont understand.

I have been experimenting with different flow temperatures to help facilitate the setting up of WC.  Todays run was the lowest temperature I have used.  Temperatures above 30C have produce a level run with no Thermo Offs. 

Todays result showed 4 Thermo Off's over 7 hours.  It did increased the temperature of the bungalow from 21.5C to 22.5C and held steady at this level in the evening. The HP did drop to it's minimum power level of about 3 Amps or 750 watts. Used about 5Kw.

The HP was manually turned on at 2pm and off at 9pm.

To me it looks like my minimum flow might be around 30C with an outside of 10C and above.

Should I be happy with todays result? Any comments?

That level of cycling is normal and absolutely nothing to worry about, the important point being that the on periods are long enough for it to reach good efficiency.  Here for comparison is what mine does

As to whether you should be happy, I think your aim is probably 'zero touch' ie not having to adjust it at all, and you are clearly making good progress so I would say yes.  To fully achieve zero touch you will have to tolerate a degree of cycling for sure.  Based on everything you have said I think there are two ways it could probably be done:

1 Program the heat pump to be on 24x7, adjust lowest FT down to whatever it takes so that the house doesn't overheat (Im guessing 25-27 @ OAT15).  It will certainly cycle at higher OATs

2 Program the heat pump to be on for say three, roughly equally spaced, periods every 24hrs.  This will require higher flow temperatures, but you will get less cycling (you will still get some!).  

The risk of (2) is that it struggles at low temperatures, particularly when its defrosting.  That shouldn't be the case of course because its oversized, but we have seen already what defrosting does so Im not so sure at present

Personally I would start off by trusting the heat pump to do its thing and go with (1).  You have an enormous buffer in your floor so its quite likely that cycles will remain long even at low FT.  If it turns out they don't (having tried it for a few weeks) or want to work a tou tariff then you can experiment with (2) from a solid baseline.   The important thing is to choose and stick with it, adjusting the WC curve so that you don't have to turn it on and off manually.  Unfortunately there is no substitute for time to do this particular part of the process

Yesterdays run 8th Dec.  Chart is showing flow temperature.  The HP didn't like a set temperature of 29C.  Very little on periods.  Lots of temperature overshoots, level run point was about 40C as per 4/5pm.  Plus 2 defrost cycles even with an outside of 12C.  Bungalow this morning 21.5C.

Posted by: @trebor12345

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Yesterdays run 8th Dec.  Chart is showing flow temperature.  The HP didn't like a set temperature of 29C.  Very little on periods.  Lots of temperature overshoots, level run point was about 40C as per 4/5pm.  Plus 2 defrost cycles even with an outside of 12C.  Bungalow this morning 21.5C.

Thats not the greatest profile although the energy consumption is probably tiny so it doesnt actually matter that much.  Also it looks like its targeting 40C not 29C, are you sure about the settings?

If you are then I suspect its bumping up against a slab temperature which has barely dropped at all (because of the high OAT) between cycles and thus it has nowhere for the energy to go, hence cycling.  That may be a signal to try option 2 above ie

"Program the heat pump to be on for say three, roughly equally spaced, periods every 24hrs.  This will require higher flow temperatures, but you will get less cycling (you will still get some!)."

Personally, before changing anything, I would run as is for another couple of days at least to check the results.  If they are similar Id consider having a play with option 2, the idea being to give the slab time to lose some heat between the programmed bursts, but still have the heat pump on for enough time that it can cope with the coldest days.

At least the bungalow is at a comfortable temp though!

@jamespa My mistake this was not the flow temperature chart, but my refrigerant temperature, it shows better what the heat pump was doing.  

Below is the actual flow chart for yesterday.  You can see it's hitting its target set temperature of 29C (my probes record about 1C less). It does show a lot more off time than on.

I have noticed these overshoots in refrigerant temperature before.  They seem to occur more at low setting temperatures.  Below is an example:

Regarding the 2 defrosts.  These occur when only the bottom 100mm of the evaporator is being used by the heat pump.  You can see from the UI when this is going to occur because the evaporator temperature goes -10C(ish), whilst the OAT is 12C.  I am told:

"The reason is that during compressor stop the liquid refrigerant settles at the lowest point, (in this case the evaporator lower section) it won’t settle in the compressor because the crank case heater is designed to keep the compressor warm to avoid this. So when the system first starts up, until the refrigerant has started circulating around, the bottom section of the evaporator would be observed to be cooler than the top".

But this does occur whilst the heating is in use (not start up) as per yesterdays 2 defrosts mid way.  So I don't know if this is a valid explanation.

@trebor12345 

Ok that makes more sense and leads is in a different direction. The cycles are about once per hour and there is a distinct plateau.  Basically I can't see a problem.  As such I wouldn't worry about them.

I would now program a basic WC curve as previously suggested, leave it on 24x7, and monitor.  It would be useful to monitor oat and return temp if possible at the same time