Undercapacity A2A outdoor unit - possible? advisable?

[puntloos]

With a Mitsubishi MXZ-6F120VF2 - which has 6 connectors for indoor units, however with its 11.2kW, the simplest math says that my 3x 2.5kW and 1x3.5kW indoor units already add up to 11kW. 

 

Does this mean that this unit can't add more units because the total demand would exceed 11.2kW? Or would it be totally fine, it's just that in the extreme (rare?) case that all units demand cooling, the actual temperature drop for each given unit would be less than optimal?

 

Happy to hear advice on this.. even in the peak of summer last years, only 2-3 units were working at any given time, and even that was rare.. 

 

[crispy_wafer]

They’d use diversity factor, I had the same conversation with my installer after I scoured the manufacturers documents for compatibility qty and combinations of units.  The manufacturers documents should have compatible combinations for the outdoor unit.

[puntloos]

Yup. I'm running into one very weird one, which is that it says my particular outdoor unit - Mitsubishi MXZ-6F120VF2  - and (of course, figures.. ) - my selected indoor unit type, the SEZ-M25DA can't exceed the ratio of 1:1 max power usage. 

 

 

This makes very little sense. Why would only one specific unit type not be able to exceed 1? Either it's a limitation of the outdoor unit (apparently not), or they deliberately broke the M25DA and not the M35DA? 

[pudding]

I installed a Daikin System a few years ago in my extension. I went for a 5kW outdoor unit, feeding 3 indoor units, 2x2.5kW and a 3.5kW, and its fine. Theres actually a page in the Daikin manuals that tells you what actual effective cooling/heating power you'd get if you were to run them all at the same time full power, which obviously is not the 2.5/3.5kW, but that just never happens and it's all good.

 

Here's a screenshot - 

 

Edited February 4 by pudding

[puntloos]

Has anyone tried this with Mitsubishi units?

[puntloos]

Anyone? Or am I out of luck?

[pudding]

I think it'll be absolutely fine, even if Mitsi dont have the page like I had in the Daikin manual. With the 11.2kW outdoor unit you mentioned above with 6 connections, is it even possible to connect 6 units and stay under 11kW? Even with small 2kW indoor units, that's 12kW and over the 11.2kW max from the outdoor unit. All that will happen is the outdoor unit just wont be able to keep up with the demand on that 0.0001% chance all indoor units are running and demanding max cooling/heating at the same time.

[puntloos]

On 17/02/2025 at 07:49, pudding said:

I think it'll be absolutely fine, even if Mitsi dont have the page like I had in the Daikin manual. With the 11.2kW outdoor unit you mentioned above with 6 connections, is it even possible to connect 6 units and stay under 11kW? Even with small 2kW indoor units, that's 12kW and over the 11.2kW max from the outdoor unit. All that will happen is the outdoor unit just wont be able to keep up with the demand on that 0.0001% chance all indoor units are running and demanding max cooling/heating at the same time.

Exactly, I feel the same way, it'd just be very strange if it wouldn't work at all. And 2.5 is the lowest powered indoor unit in the entire range, so 6x2.5 is already way over.

But somehow it's listed as 'wont work'. Hm I should call mitsu to confirm.

[pudding]

Yeah, fire off an email to a technical dept address if you can find one to get clarification, then you can try and persuade any installer it'll be fine with hopefully a good email reply.

 

If you can reassure any installer it'll all be fine and you're not likely to be harassing them to come back because the units are not all working full chat at the same time, then they'll hopefully be happy to go ahead with that unit.