Your short cycling is occurring because the heat pump can't modulate down enough to match the demand.

If you increase the system volume as suggested it still won't be able to modulate low enough but the cycles will get longer and less frequent, which is desirable. 

So yes that should help.

Yes exactly, that's what stubborn. Pump doesn't modulate to work in "idle" because that's why the inverter is right? to drop "low rev" consume low power and just try to keep the water temp constant  (so when target water is set to 18C it tries to stay 18.X but in my case it also drops to 17.X which cause a compressor stop.

Would adding an extra pump (apart of HP's internal) will help? By increasing the water flow will be able to bring back more "high" temp water (we are in cooling mode 😀 ).

Manufacturer manual also shows install cases without buffer but my current install is ~ 40L water for 8kW pump (5L/kW instead of 15+L xD )

Thanks James for the heads up xD I will install the tank monitor and maybe contact the manufacturer directly (well not the real manufacturer since the "brand" is inventor but it's built by Midea) 

Do we know how the modulating works? If pump checks the outgoing water temp TW_O or  incoming water temp TW_I or both (ΔΤ TW_I-TW_O)?

Posted by: @immunity

↑

Yes exactly, that's what stubborn. Pump doesn't modulate to work in "idle" because that's why the inverter is right? to drop "low rev" consume low power and just try to keep the water temp constant  (so when target water is set to 18C it tries to stay 18.X but it also drops to 17.X which cause a compressor stop.

Yes but... it can only modulate so low.  If the demand is less than the min modulation the water temperature will overshoot(heating)/undershoot(cooling) and the heat pump will stop for a while, then restart (ie cycle).

Posted by: @immunity

↑

Would adding an extra pump (apart of HP's internal) will help? By increasing the water flow will be able to bring back more "high" temp water (we are in cooling mode ).

No.  Assuming your emitters are large enough the demand is determined by the room temperature in relation to the flow temperature.

Posted by: @immunity

↑

Manufacturer manual also shows install cases without buffer but my current install is ~ 40L water for 8kW pump (5L/kW instead of 15+L xD )

Indeed.  If your system volume is sufficiently large there is no need for a volumiser. 

There are actually two factors which depend on system volume namely defrost and cycling.  Manufactures generally quote the minimum system volume needed for defrost.  At this (quite low) system volume its quite likely the heat pump will short cycle when the demand exceeds the minimum modulated output, but the heat pump can cope with that by having a min cycling time, so manufacturers dont necessarily consider that its necessary to insist on sufficient colume to extend the cycles.

40l is a low system volume for 8kW.  My system volume is 200l for a similar capacity pump.

Note increasing the system volume will NOT stop cycling, it will merely reduce the frequency.  Neither will it significantly change the on/off ratio.  Fundamentally it must cycle to match average output to demand.

40l is a low system volume for 8kW.  My system volume is 200l for a similar capacity pump.

Ye I see you have 7kW pump xD and 200L hm  I might need a bigger volumizer tank xD.

Note increasing the system volume will NOT stop cycling, it will merely reduce the frequency.  Neither will it significantly change the on/off ratio.  Fundamentally it must cycle to match average output to demand.

I've also tried the power limitation with no luck (maybe when I add the extra 80L might work) I see compressor amp 4 when it start the circle, 3A-2A afterwards (probably trying to modulate)

So will probably need to go to smaller HP 4kW or 6kW?

Posted by: @jamespa

↑

There are actually two factors which depend on system volume namely defrost and cycling.  Manufactures generally quote the minimum system volume needed for defrost.  At this (quite low) system volume its quite likely the heat pump will short cycle when the demand exceeds the minimum modulated output, but the heat pump can cope with that by having a min cycling time, so manufacturers dont necessarily consider that its necessary to insist on sufficient colume to extend the cycles.

Thank you very much again for the info 😀

Posted by: @immunity

↑

So will probably need to go to smaller HP 4kW or 6kW?

Whoa.  Is it also used for heating?  If so then it needs to be sized to meet your heating demand.  Also beware, some low output heat pumps are simply high output ones derated in firmware.  That reduces max output but doesnt change min output.  Personally Id fit a tank and let it cycle unless there is a good reason to do otherwise.  Is it cooling sufficiently?

Posted by: @jamespa

↑

Whoa.  Is it also used for heating?  I

Yeap also for heating (25-26C room temp, set water temp 27-28C, renovated appartment 15cm isolation, very good isolated windows etc :D)
Heating is working better xD I have 2-4kWh consumption per day. the Cooling is that hitting 10-12kWh per day and I want to fix this (it short-cycling every 10-16 mins)

Posted by: @jamespa

↑

Is it cooling sufficiently

Nope. On hot days 40C I wasn't able to drop room temperate under 30C and that's because it short-cycling so the indoor floor (ufh only, no fan coils) can't drop temperature under 23-25C. I have added ceil fan/lights (reverse sucking) which helped drop the room temp 1-2C. I tried to switch from uhf to fancoil and set the water temp 12C for like 1-2 hours which then dropped the temp and was "able" to cool but the power increased to 1.6kW (from ~700kW) and of course I feared water will start developing in surcafes and don't know if the tiles develop any problem with that low temp xD [compressor didn't stopped water reached till 14C before I stop it my self]

Posted by: @immunity

↑

Heating is working better xD I have 2-4kWh consumption per day

Do you mean kWh/day?  Thats essentially nothing unless its just for DHW?  You arent doing any material space heating on 2-4kWh/day!

Is it possible you are confusing kW with kWh?

Posted by: @immunity

↑

the Cooling is that hitting 10-12kWh per day and I want to fix this (it short-cycling every 10-16 mins)

Thats not necessarily unreasonable

Posted by: @immunity

↑

On hot days 40C I wasn't able to drop room temperate under 30C and that's because it short-cycling so the indoor floor (ufh only, no fan coils) can't drop temperature under 23-25C.

Short cycling shouldn't really affect that much how low the floor temp will go, the heat pump is simply not seeing sufficient load hence the cycling and if you want it lower you will need to reduce the flow temperature to increase the load (which will also help with short cycling). 

There is debate over how effective UFH is for cooling, practically it seems to be OK in the UK but of course we don't generally get as hot as you.  The problem you have (same with radiators/coiling) is that cool air sinks, so (unlike with heating) there is no convection current to mix up the air in the room, so the cool air stays near the floor thus limiting the output of the emitters.  Adding fans just to circulate the air may well help.

Posted by: @immunity

↑

I tried to switch from uhf to fancoil and set the water temp 12C for like 1-2 hours which then dropped the temp and was "able" to cool but the power increased to 1.6kW (from ~700kW) and of course I feared water will start developing in surcafes and don't know if the tiles develop any problem with that low temp xD [compressor didn't stopped water reached till 14C before I stop it my self]

Whats the dew point at your location.  if you run a couple of degrees above dew point your shouldnt get too much condensation.  Some heat pumps can measure the dew point so do this automatically, not sure if Midea has this feature.

It sounds like you have two problems namely 

1. Insufficient output from your cooling to give adquate cooling.  To fix this you have to cocus on increasing the output from the emitters by (a) fans, (b) lower flow temperature (c) increasing the area of the emitters

2. Short cycling.  If you fix this then problem (1) may go away.  If not then a volumiser will help.

I would concentrate on (1) before getting too hung up on (2)

Yeap 4kWh/day for heating (not DHW) for keeping room temp 24-26C (water target 27-28C)

(2340- 2093kWh  in 31 days in graph there is also the power consumption for DHW although some days solar cylinder had enough hot water so HP didn't heat its DHW boiler)

Heat pump short-circling also on winter (HEAT mode) but need to work much less times in a day so that's why the low daily comsuption.

Of course uhf is worst for cooling (cold air acts as isolation at the bottom, the opposite in heating that helps circlulate hot air in room) That's why I added the ceiling fans(a) 😀 to add that circulation and it helped.

(c) is not possible since can't modify the ufh now 😀 and (b) I am not that afraid of dew point more of doing damage overtime to tiles, tile's glew etc + it's not that nice to feel 15C on your feet xD

I have dehumidifier trying to keep humidity 50% or lower (getting full 1-2 times per day [5l tank])

So 1(a) and (2) 😀

Thanks again!

Posted by: @immunity

↑

it's not that nice to feel 15C on your feet xD

True!

Posted by: @immunity

↑

So 1(a) and (2)

I think so, or fit fancoils!  From your figures the system is more for cooling than it is for heating.

I switched to "fan coil mode" to be able to set water temp lower than 18C.
I used 15C to increase the load as you mentioned together with power limit and currently it modulates ? 😀 (outside it's 32C)