Load Calc for Mini Split System

[liam913]

Ductless Mini Split System: Mitsubishi R454B
- 208V, 1PH
- MCA: 12A
- MOCP: 20A

Looked too deep online and get differing answers on this one. For the load, I am doing 208V * 12A = 2496.

I thought this was Watts but read that it is Volt-Amps based on the MCA? Went down a rabbit hole and got myself confused. I am looking for VA in this situation.

Also, what would the power factor be in this situation?

 

[wwhitney]

The MCA is for sizing the branch circuit wiring. So it includes a 125% factor on the largest motor. With that in mind, 208V * 12A = 2496 VA is the VA, as you've just multiplied volts and amps. The power factor is unspecified, you'd need to seek out further documentation on the unit to find it out.

But a subtlety: if you are doing a load calc, and you have more than one motor on the service or feeder you are calculating, only the largest motor gets a 125% factor. That means if you use MCA as the input to your calculation when the unit is not the largest motor for the calculation, you will overestimate the VA. In that situation, you need to use the other information on the nameplate to effectively backcalculate what the MCA would be without the extra 125% factor, and use that value instead of the nameplate MCA for your load calculation.

Although for an inverter driven minisplit, it is possible that the distinction is minimal to zero. Would need the full nameplate data to determine that. For a central split system design, where the nameplate just shows a fan FLA and a compressor RLA, and the MCA = 125% * RLA + FLA, then the backcalculation is easy, you use RLA + FLA in the load calc when the unit is not the largest motor for the calculation.

Cheers, Wayne

 

[Ragin Cajun]

Another gripe I have about HVAC labels. What's so difficult for the manufacturer to simply add to the label total watts and VA!!!!?????
I waste way too much time trying to dig out the needed data to get it and often it's not there at all.