Posted by: @painter26

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although I take the petrol pump to mean the compressor is running to actively heat whatever it should be

Exactly, the petrol pump icon, or left handed one armed bandit as I sometimes call it, indicates the compressor is running (and so active heating is taking place, unless it's in a defrost). 

@cathoderay @jamespa I did a controlled experiment this evening:

• Manually turned on DHW to heat to 55 degrees
• It took 80 minutes to heat the tank from 36 to 55 degrees
• The radiators went from being lukewarm to completely cold during this period
• As soon as the tank hit 55 I heard the system switch over and the compressor kicked in for space heating
• Within seconds all the radiators were filled with (presumably) 55 degree hot water
• 20 mins later the rads are back to their usual lukewarm temperature in line with the weather comp curve (34 flow temp at 8 degrees outside)

Posted by: @painter26

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@cathoderay @jamespa I did a controlled experiment this evening:

• Manually turned on DHW to heat to 55 degrees
• It took 80 minutes to heat the tank from 36 to 55 degrees
• The radiators went from being lukewarm to completely cold during this period
• As soon as the tank hit 55 I heard the system switch over and the compressor kicked in for space heating
• Within seconds all the radiators were filled with (presumably) 55 degree hot water
• 20 mins later the rads are back to their usual lukewarm temperature in line with the weather comp curve (34 flow temp at 8 degrees outside)

Interesting and sensible behaviour by the heat pump, prioritizing DHW as one would expect and ensuring no colder water flows through the DHW coil.

Based on that I would say nothing to worry about, and thanks for exposing the sequence that this heat pump follows!  I'm now wondering what mine does.

Is there anything else thats concerning you?

Posted by: @jamespa

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Posted by: @painter26

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@cathoderay @jamespa I did a controlled experiment this evening:

• Manually turned on DHW to heat to 55 degrees
• It took 80 minutes to heat the tank from 36 to 55 degrees
• The radiators went from being lukewarm to completely cold during this period
• As soon as the tank hit 55 I heard the system switch over and the compressor kicked in for space heating
• Within seconds all the radiators were filled with (presumably) 55 degree hot water
• 20 mins later the rads are back to their usual lukewarm temperature in line with the weather comp curve (34 flow temp at 8 degrees outside)

 

Is there anything else thats concerning you?

 

Not at the moment, thank you. I'm still not quite sure of the tolerance point at which the under 5 degree rule kicks in a reheat for the DHW - it appears to work fairly accurately some days but others it lets the tank cool quite a bit more than 5 degrees of target temp. I think it's still trial and error as I work out its quirks.

Posted by: @jamespa

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My DHW cycle happens at night so I wouldn't notice it, but it would make a lot of sense sense for the heat pump to switch the diverter  before changing the flow temperature (at the end, other way at the beginning),

This is certainly what my system does. At the end of the DHW cycle, the diverter valve switches back to the radiator circuit, whilst there are quite a few litres of very hot water in the primaries, which is then dumped into the rads. In my case it's very noticeable due to a long pipe run to the outdoor unit. 

I don't yet know what happens in summer if the CH is off. I would to think that diverter would stay in the DHW position? It'll soon be warm enough to find out.

Posted by: @painter26

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Posted by: @jamespa

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Posted by: @painter26

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@cathoderay @jamespa I did a controlled experiment this evening:

• Manually turned on DHW to heat to 55 degrees
• It took 80 minutes to heat the tank from 36 to 55 degrees
• The radiators went from being lukewarm to completely cold during this period
• As soon as the tank hit 55 I heard the system switch over and the compressor kicked in for space heating
• Within seconds all the radiators were filled with (presumably) 55 degree hot water
• 20 mins later the rads are back to their usual lukewarm temperature in line with the weather comp curve (34 flow temp at 8 degrees outside)

 

Is there anything else thats concerning you?

 

 

Not at the moment, thank you. I'm still not quite sure of the tolerance point at which the under 5 degree rule kicks in a reheat for the DHW - it appears to work fairly accurately some days but others it lets the tank cool quite a bit more than 5 degrees of target temp. I think it's still trial and error as I work out its quirks.

 

 

I have mine set for a daily timed reheat.  For reheat to occur two conditions must be met

• The time of day is correct
• The tank temperature (at the designated time of day) < target-hysteresis

This means that it can skip a day from time to time.  I reduced my hysteresis from 10C to 5C because if it skipped a day because the tank temp was only just over target-hysteresis, it was too cold by the following day.  Im guessing yours will do something similar.

Posted by: @painter26

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Within seconds all the radiators were filled with (presumably) 55 degree hot water

Presumably? Did you actually feel them, I am sure you did, just confirming you did. 55 degrees is getting into almost to hot to touch territory.

Posted by: @jamespa

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Interesting and sensible behaviour by the heat pump, prioritizing DHW

This is an explicit Midea setting, when on, DHW takes priority over space heating. Sometimes the compressor icon switch on the home page on the wired controller is instantaneous, circulating pump stays on continuously even as the valve switches across, sometimes there is a bit of a lag, and I think the circulating pump may stop briefly. In a normal start up from cold, the circulating pump is set to run for a few minutes before the compressor starts up.

Posted by: @painter26

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I'm still not quite sure of the tolerance point at which the under 5 degree rule kicks in a reheat for the DHW

I've noticed the same variability, eg my trigger for a reheat is 40 degrees and below, yet on some days it can be at 39 degrees, and a reheat doesn't happen. I think it is probably just a Midea thing.  

@cathoderay yes I kept touching the radiators every few mins as they got colder and colder during the DHW cycle. They then, almost instantly, became *hot* to touch once the 55 degree was reached and the system kicked over to space.

Another point of note today, at 11am the daily schedule to reheat hot water came on as planned. I think the tank temp was c.46 degrees after having had a bath and shower since the 55 reheat last night. 

The scheduled DHW heating cycle only lasted about 20 mins this morning rather than the scheduled 2 hours and heated the tank to 51 degrees before switching back to space heating (despite the fact that the squiggly tap symbol was still visible. I'm imagining that this is due to it hitting 51 degrees (i.e. within the 5 degree reheat tolerance) so it's decided it can stop at 51 and switch back to space? Whereas, last night's cycle was a manual one to hit 55 so it will power through to 55 regardless?

So if I wanted to hit an actual 55 degrees each day rather than theoretical I would need to set the temp on the schedule to 60?

As expected it also did the same 'dump' of hot water into the rads at the point it switched over.

@painter26 welcome to the forum. However, I don't really get what you are trying to do with your DHW- why are you trying to heat the cylinder so high? A set point of 48, or certainly 50, would suffice. We have ours set at 48 and the outlet flow temp from our unit will reach 57 to get it there. Therefore to try and get it to 55 you're pushing the unit quite close to it's limits I'd imagine without using the backup heater.

With our wired midea control panel in weather comp mode the reading on the left will reflect the set curve point at that time.

@benson hi there. My aim has been to try and keep the tank at or close to 55 a few times a week so that it keeps the legionella danger zone out of reach.

I don't think my wired immersion is working so I'm doing this in lieu of a weekly 60 degree cycle.

How does one find out the outlet flow temp and what is this in relation to the tank temp?

Posted by: @painter26

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My aim has been to try and keep the tank at or close to 55 a few times a week so that it keeps the legionella danger zone out of reach.

Ah ok. There's obviously different schools of thought with respect to the benefits of disinfect cycles but guess you have probably done your own research on that.

Posted by: @painter26

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How does one find out the outlet flow temp and what is this in relation to the tank temp?

Parameters on the wired controller. Plate outlet and inlet ring a bell I think? The trouble is you'd have to continuously stand by the controller to see what is actually going on. This is why a number of us have ended up connecting various things to our ashps via the modbus connection to plot all of these values on graphs.

Here's mine- showing 2 DHW runs in the last 24hrs. The actual peak outlet temp run is quite short in duration so might be tricky to capture if manually trying to read the values at the right time. Red line is the tank temp and green is the outlet flow temp.

To be honest I'm not concerned for myself but as I've got family staying at the moment I wanted to be a bit more diligent at keeping a slightly more regular 55 temp. When you say pushing it to its limits - is this harmful to the external unit or just making it work at its hardest?

In regards the tank heater, I'm still not totally sure if 'tank heater activated' (which is what I've seen once or twice on my wired controller) is an actual thing. I've read some comments suggesting it's a phantom indicator? I'm guessing it refers to an independent heater element rather than the coil or the electric immersion that Midea supply?

Would the Disinfect cycle on the Midea controller activate said tank heater or would it do nothing other than try to get the pump to heat to 65?