Posted by: @harriup

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Posted by: @ecodan-efficiency

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Posted by: @abernyte

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If the overnight temperatures are seriously sub zero, as in recently, then the auto adapt seems to bring on the heating to maintain the house at 16C regardless of set back until the next heating period hoves into view.

This sounds kind off odd. I run my ASHP on a room temp schedule, with a setback during the night to ensure it's off until morning (13 degrees because the house loses heat so quickly), and I've never witnessed this behaviour. Where would this figure of 16 be coming from? Have you activated Frost Protection on the melcloud app perhaps? (not to be confused with frost stat function).

I wonder if this related to the Holiday setting in the controller menu which sets a room temperature below which the heating will come on with a modest flow temp when the normal heating pattern has been turned off after Holiday Mode is activated. This has caught me out before when I expected the heating to remain off when I was on holiday only to see it running - I have lowered this temperature from its default setting of 15° since then.

Perhaps this particular setting also acts as a default lower room temperature even when the heating is following its day-to-day schedules?

 

well I guess there  might be some magic dust after all... even in weather compensation it’s happening. Not just Auto Adaptive.

we have put our system on a massive setback (12c room temp) and the system seems to be making sure things don’t ever get too cold for either a defrost or frozen outside pipes - but also for a preset crossing point into a low internal water pipe where the minimum is thought to be 20c.

last night we had 2 Auto boosts of the system water temperature. One at 4.20am and another at 8am. Both were triggered when the freeze stat thermostat crossed 3c.

There was no water heating at 20c as per the assumed auto reheat... interestingly the internal water temperature was well below 20c. It was closer to 15c. So there’s a puzzle.

so the first pic shows the early reheat and note the flow temp and low output. There’s was no defrost but the graph suggests there might have been one.? 

This second pic is a shorter reheat 

And this last graph shows the overnight temperatures when these occurred.

It can be seen that 4am and 8am were around the 3c outdoor ambient temp.

So what made our system happy not to boost the heating at 20c?

and why not reheat up to an internal water temperature of 20c?

Something to Mull over.

@judith 

@abernyte

@jamespa 

@ecodan-efficiency 

@westkent 

@editor 

@sunandair Hi, you're simply witnessing the operation of the Freeze Stat function. Most people turn this off, since it seems to be almost the norm to add glycol to the system. (but adding/not adding glycol, using freeze valves etc. is wide open to debate in my opinion)

The temp at which it kicks in is configurable - the lowest being 3 degrees (the thread was created to discover how configurable this figure was for other manufacturers). The water temp is also configurable - the lowest being 20 degrees. It only heats the water in the cyclinder heating circuit (ie you're radiators will not get warm).

I was under the impression that when @abernyte was describing their situation the Freeze Stat function was turned off?

As an aside, your heat loss is much better than mine. I live in a detached 1970s ex-local authority house, with dubious cavity wall insulation retrofitted. I don't fully understand why it's so awful if I'm honest and would love to improve matters. I've added insulation under the suspended floor and there is copious amounts of loft insulation.

@ecodan-efficiency 

Hi and thanks for your reply.

just to clarify, over the past 2 years there have been several discussion threads on the Ecodan Freeze Stat Function . And my comments were somewhat tongue in cheek since  there’s been novel interpretations along the way.

perhaps the best clarification was made by @derek-m back in June 2023 see extract below.

“Freeze stat function *1 -  An operational function to prevent the water circuit from freezing when outdoor ambient temperature drops.

          Flow t  -  The target outlet water temperature at water circuit when operating in Freeze stat function. *2

          Outdoor ambient temp.  -  Minimum outdoor ambient temperature which freeze stat function will begin to operate,
(3–20ºC) or choose**. If asterisk (**) is chosen freeze stat function is deactivated. (i.e. primary water freeze risk)"

*1. When the system is turned off, freeze stat function is not enabled.

*2. Flow t. is fixed to 20°C and unchangeable.

As you have correctly stated, the defrost cycle is performed to remove ice formation from the Evaporator coils at the rear and side of the heat pump unit, but this process must be carried out whether the ambient temperature is above or below the Freeze Stat setting, and even if the Freeze Stat function is disabled.

The Freeze Stat function is to prevent the water circuit from freezing, not to prevent the Evaporator from icing up.”

My comments related to the “fixed flow temperature of 20c.”  I was observing that in the graphs I had posted the graph showed the start of the freeze stat reheat the water flow temperature was not per the manual - 20c it was a lower15c It seemed to only put a very efficient 20 minute operation at a very modulated output of a delta T of around 3c. This did however adjust the flow temp upwards to around 20c which does correlate with the Freeze Stat target temperature. So I was very pleased to see @abernyte comments on the 15c and low reheat levels.

So my comments were to clarify that Freeze Stat becomes active at 15c and not 20c. However it raises the fixed flow temp until it reaches 20c. Which is a subtle but nonetheless important clarification. Sorry if this sound s a bit pedantic it’s  not intended.

Regarding glycol of course if you have chosen to use it and manage the concentration levels there’s is no need for this function at all. However I believe the heat transfer is a little less efficient when using glycol and and management of spills and leaks is something of an environmental challenge. I believe there are many non glycol installations.

I was curious about your comments that freezeStat only reheats the cylinder circuit. I’ve not heard that before. Can you let me know where that is stated? 

I hope your home heating gets better and better as you find out more. It sounds like you’re doing all the right things in the insulation you’re  applying.

best wishes.

@sunandair Hi, apologies I didn't read your post very carefully.

It's hard to say what algorithm Mitsubishi uses in relation to this target temp. of 20. It might be more akin to "periodically heat it to 20 degrees".

And you're right: it's the radiator circuit that's pumped. Although it might be nice to have that configurable.

I personally think that glycol does affect the performance (it wasn't my "choice" - was that of the installer and I was ignorant at the time) and that was really the nature of the original post. Have a small amount of glycol to cover the vast majority of low temps, and then have the freeze stat for the very infrequent low temps. Can you see any issue with that?

For me the sole purpose of the glycol or antifreeze valves is to provide backup protection if the power fails for any length of time; the freeze stat function is the primary protection.  But you could of course consider it the other way round if you want.  Freezing is, after all, only a problem if its very cold and the heating is off for a long while and passive protection survives a power cut.