@tasos — Also, the set LWT never mind the actual LWT seem rather high for the OAT, mine might be 10 degrees lower, in fact i might even turn the heat pump off altogether in those OATs!
I think I am short of radiators, as I have not done any changes after switching to heat pump from oil burner. Or I am doing something else wrong.
Midea MHCV10WD2N7 R290, 5.8kWp energy community solar power.
In wc curve 9, the lowest LWT I am allowed to set from the wired controller (not Serviceman menu) is 35 degrees. Is that the same for you?
Is this (setting the LWT, where the lower limit is 35 degrees) on the home/main page? If so, this has sort of come up before and I think it may be important. On my R32 unit, if I have set the weather curve end points inside the FOR SERVICEMAN menu to say 30 @ 15 for the right hand end (higher OAT end) and then put the unit on WC using curve 9, then two relevant things happen:
(1) when the OAT is 15°C and above, the set LWT will go down to 30°C, and the actual LWT will cycle, but the average will be about 30°C, see this chart which also has just about everything else as well including steady state and defrost running plus overnight setbacks):
(2) I cannot set the LWT on the wired controller home/main page. If I attempt to do so, I get the 'Weather temp. set function is on. Do you want to turn it off? message, 'weather temp. set function' being Midea-speak for weather compensation. In other words, it will only run in weather compensation mode. I cannot separately influence the set LWT. To do that, I have to turn weather compensation off.
But on R290 units, it seems you can set the set LWT even when on weather compensation (which I still think is odd), and if the unit's default lowest manually set LWT is 35 degrees, then that over-rides the weather compensation setting?
Midea 14kW (for now...) ASHP heating both building and DHW
Still however I do not understand why actual LWT is almost always below the target LWT as set by the wc (for the 10 to 14 hours the unit operates daily). Don't get me wrong, I am happy our unit does not cycle. But I am also curious as to why this is so.
I cant explain that unless either (a) the heat pump is working at its maximum capacity (which could be the case given you are operating part time and possibly never reach equilibrium) or (b) there is somewhere a programmed offset, perhaps a 'correction' factor.
Far from it, it reaches >16kw for some time after switching on and then it drops to <6kw and subsequently modulates depending on OAT and LWT/RWT feedback, hardly ever exceeding 10kw though.
And my theory of not cycling because it does not surpass the set LWT has crumpled with @tasos diagram: his LWT is constantly above the set LWT, yet his midea does not cycle either.
I think we need a sizable sample of midea R290 units to observe behavior, establish a pattern and construct a theory as to their cycling behavior. Our meager n=2 sample seems to have an ultimate mandate: never, ever cycle.....
(2) I cannot set the LWT on the wired controller home/main page. If I attempt to do so, I get the 'Weather temp. set function is on. Do you want to turn it off? message, 'weather temp. set function' being Midea-speak for weather compensation. In other words, it will only run in weather compensation mode. I cannot separately influence the set LWT. To do that, I have to turn weather compensation off.
But on R290 units, it seems you can set the set LWT even when on weather compensation (which I still think is odd), and if the unit's default lowest manually set LWT is 35 degrees, then that over-rides the weather compensation setting?
Indeed I can set the end points of our wc 9 curve from the main menu of the wired controller. I have never entered for Serviceman menu yet in our installation. The 35 degrees I was mentioning is the lowest temperature I am allowed to set at either points of the wc 9 curve (with 74 degrees being the highest), at least from the main menu. Not an arbitrary set LWT value while wc is running.
And even though I have not entered for Serviceman, I have skimmed through various midea R290 manuals and have not found a relevant entry in the Serviceman menu (i.e. defining wc parameters from Serviceman menu). But I may well be wrong on this.
(1) when the OAT is 15°C and above, the set LWT will go down to 30°C, and the actual LWT will cycle, but the average will be about 30°C, see this chart which also has just about everything else as well including steady state and defrost running plus overnight setbacks):
Indeed the chart has just about everything, including consistency in behavior. How do you explain the increasing gap between actual LWT and set LWT in the time intervals around midnight? Is this a constant pattern?
Indeed I can set the end points of our wc 9 curve from the main menu of the wired controller. I have never entered for Serviceman menu yet in our installation. The 35 degrees I was mentioning is the lowest temperature I am allowed to set at either points of the wc 9 curve (with 74 degrees being the highest), at least from the main menu. Not an arbitrary set LWT value while wc is running.
OK, got it. I've also checked the R290 manual @tasos kindly made available, and I too can't see anywhere in the FOR SERVICEMAN menu to set the WC end points. I also searched the same manual for 74 and 35 ie the limits but got no relevant finds.
The modbus table for my wired controller does give the limits and defaults for the custom curve 9 T1SetH1/2 values, limits 25-60 for both, H1 default 35, H2 default 28°C. I think this is going to need more research, including n>2!
How do you explain the increasing gap between actual LWT and set LWT in the time intervals around midnight? Is this a constant pattern?
It's the setback (2100 to 0300). The unit sets the set LWT, but (obvs) doesn't use it when it is not running. The same thing happens during the summer.
Midea 14kW (for now...) ASHP heating both building and DHW
It's the setback (2100 to 0300). The unit sets the set LWT, but (obvs) doesn't use it when it is not running. The same thing happens during the summer.
So you switch it off for some hours daily.... I thought you belonged to the 24x7 school and I was the black sheep... 🙂
So you switch it off for some hours daily.... I thought you belonged to the 24x7 school and I was the black sheep...
I have been both a black sheep and a white sheep, as part of my attempts to determine whether setbacks save energy/money. At the moment I am a sort of a grey sheep that cannot get to a black and white answer to that question.
Midea 14kW (for now...) ASHP heating both building and DHW
