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Freeze Stat/Defrost setting….Ecodan in freezing conditions

Amanda1 · 2023-06-06T08:32:56Z

Several members have suggested I start a new topic re Freeze Stat (Defrosting) settings on the Ecodan. I should state that I am still an ASHP newbie, and an ASHP ‘layman’, and the technical terminology still evades me. This is specifically about the Freeze Stat setting, and not about the pros and cons of heat pumps in general , or about Weather Compensation Mode, or the other settings. Assume that all your other settings are as good as you can get them. The Freeze Stat setting is possibly overlooked by some ASHP owners because average winter temperatures in the UK rarely fall below zero for very long. With a default setting of 5 degrees C the defrost function of the Mitsubishi Ecodan will start to kick in, meaning that the pump will run frequently to defrost itself. The immersion heater will also be used to heat the house while the pump heats itself. Result =££££££ if it goes on for a long time. So if the outside temperature drops to 5 degrees and you have this setting on, then the pump will cycle more and it will cost you more while it does this. The minimum setting for the Freeze Stat is 3 degrees. You can set it to *. But if you set it to * because you need it to be lower than 3 degrees, you are deactivating the Freeze Stat function and you become reliant upon the concentration of antifreeze in the system preventing icing up. I live in an area of the UK which is famous for its snowfall and arctic temperature in Winter, and the temperatures in December can be as follows: Compare with the rest of the UK: My new Ecodan has the Freeze Stat setting at **. I am currently checking with the installers the % concentration of glycol in my system. I am trying to avoid having to have the defrost cycle of the pump running 24/7 for most of December and January, which of course guzzles electricity. Mitsubishi make big claims for the PUZ WM85VAA ASHP - that it is capable if operating in ambient temperatures of -20C. My question is this: I wonder if there are many Ecodan owners or ASHP owners out there who have a similar problem - that the ambient temperature is below zero for prolongued periods- and who have tried having the Freeze stat set to *, and if this was a disaster, a success, a work in progress….??? Or, if your ASHP has operated on the defrost setting for a protracted period of time, what was the energy consumption per day like in KWh?

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SUNandAIR

(@sunandair)

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Joined: 3 years ago

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17/10/2023 7:26 am

@walkers-heatpump agree. From a practical point of view your comments make sense…. I guess the key is to check the outside pipes are fully insulated right up to the body or the HP and around the isolator levers.
I believe the ambient thermostat is exposed to the air so will get cold more readily.

The anti freeze valves are not supposed to be insulated but they can be sheltered from wind and rain. This should mean the more exposed thermostat will reach 3C well before the valve does.
Is that your post on the Facebook page?

👍

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Linz

(@linz)

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17/10/2023 8:27 am

@amanda1 thank you, great help 😀

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Linz

(@linz)

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Joined: 2 years ago

Posts: 6

17/10/2023 10:42 am

@sunandair thank you. Yes it was me on fb. I hadn't discovered this forum then and they took a while to approve my post. My next dilemma is how to adjust the setting, so I will trawl the manuals. Thanks again 😀

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Walkers Heatpump

(@walkers-heatpump)

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17/10/2023 8:55 pm

@sunandair Cheers. Yes I'd posted on the Ecodan group. I'll see what the installers say. They seem to have done a good job with the pipe insulation. Just dropping it by a degree or two I reckon could reduce freezestat runtime considerably over a winter

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SUNandAIR

(@sunandair)

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16/01/2024 2:20 pm

Posted by: @kev-m

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Posted by: @walkers-heatpump

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-- Attachment is not available --

No pretty sure it's the ambient outdoor temp, states in the manual - see attached screenshot

If you set it to 3 degrees....

When outside air temperature gets to 3 degrees, it starts the circulation pumps and monitors the flow (I assume it uses the RWT sensor) temperature . If the flow drops to 15 deg, the ASHP heats it to 20 deg. And repeats ... The 15 and 20 are not adjustable.

This won't use a lot of energy but may be annoying if you want a silent overnight setback.

That's what mine does anyway. 😀

Surprise on Variable Freeze Stat function. As we know from this thread there are 2 parts to the freeze stat function -

1. To circulate the water so as to displace the colder water in the outside unit and pipework.

2. To reheat the circulating water if it drops below a certain temperature. (Factory set at 20degC.)

And as stated above we had ours starting to reheat at 15c flow temperature and reheating to just above 20c.

However it was -3c last night and I’m monitoring night time reheats at the moment and saw this reheat. So the Freeze Stat Function started a reheat of the circulation water at 20c which is 5c earlier/warmer than expected and took the unit into a defrost 22 minutes later, followed by a reheat up to 40c.

As far as I am aware this was entirely due to the Freeze Stat Function changing its operating parameters based on the protection needs of the system.

the function finished with another defrost then stopped leaving the flow and return temperatures at 30c.

Interesting to note how quickly the temp then drops while the circulation pump continues to operate and it’s -3c outside.

Incidentally I only have MELCloud and I don’t have specialist data collection on our HP but I’ve worked out a way of approximating the HP OUTPUT just from the MELCloud graphs but it requires an accurate flow rate to calculate it. Here is a graph showing some output values..

Obvs. if someone knows these calcs don’t add up or any thoughts let me know.

The full 24 hours outside and inside temperatures can be seen on this graph.

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glpinxit

(@glpinxit)

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17/01/2024 1:29 pm

Our Ecodan was installed 18 months ago and glycol was included in the system. Since then I've been meaning to buy a refractometer so I can check the concentration of the glycol and the temperature that it reduces the freezing point to- see eBay item 354895847827 for example. I haven't got round to buying one so far but would use it by releasing a little water from a radiator drain point (I used to use these instruments many years ago when I worked in a laboratory and they are very easy to use.) Although the glycol in our system should protect it down to about -12C I've still got the freeze protection set at about +5C as it isn't very bothersome.

Supplementary point: reading this thread sent me to look at my Melcloud results in the 'Hourly Temperature' report to find that it had been regularly cycling through the night because even here in rural Somerset it has been cold enough at night (-5C) here to cool the bedroom with the thermostat to the point where it calls for heat. I've relocated that thermostat to our (much warmer) bedroom and need to keep an eye on the temperature downstairs.

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