Multiple HVAC split system load calculation

[2l84me1]

I have 11 condensers (RLA 25.6) and 11 AHU (FLA 6.1)
Do I take 1.25x 25.6 + the sum of the other condensers + the sum of all FLA on the AHUs to get 355.1 amps?

 

[hmspe]

It depends on what the calculation is for. Is this a service load calculation? Is if a panel/feeder load calculation? Are all the units on the same panel?

Technically the 125% should be only for the largest motor (which would be the compressor), not the largest unit, but it is common to do the calculation the way you show it. The difference in the totals for the two methods is typically 1/2 amp or less. The difference in the totals between Carrier equipment and Trane equipment would be more than 1/2 amp.

 

[2l84me1]

Service load calculation, I’m just trying to figure out if I include air handler FLA with compressor RLA or are the AHUs omitted? I know it sounds like a dumb question.

 

[Tulsa Electrician]

Service load calculation, I’m just trying to figure out if I include air handler FLA with compressor RLA or are the AHUs omitted? I know it sounds like a dumb question.

Yes, include unless the power for the AHU is supplied by the condenser.
Some mini split systems pull the AHU power from the condenser.

 

[2l84me1]

Thanks

 

[wwhitney]

I have 11 condensers (RLA 25.6) and 11 AHU (FLA 6.1)
Do I take 1.25x 25.6 + the sum of the other condensers + the sum of all FLA on the AHUs to get 355.1 amps?

Is 25.6 the compressor RLA, or the condenser MCA?

Presumably the condenser has other loads in it besides the compressor (at least a fan) so it will be labeled with an MCA equal to 1.25 times RLA plus all the other loads.

Then in your formula above you need to further add all the non-compressor loads of all the condensers.

Cheers, Wayne

 

[2l84me1]

That is the RLA I am not using MCA I want the design load to be as cost effective as possible, and yes adding the condenser fan FLAs as well

 

[wwhitney]

So you can double check your calculation as follows: both the condenser and the AHU should be labeled with MCA as well as labeled with the largest motor (RLA for the condenser, fan FLA for the AHU). Then each unit's total connected load (without any factors) is just MCA - 0.25 * largest motor (as the largest motor gets a 125% factor when calculating MCA), call that number TCL (to make up an acronym).

That means your service load is 1 * condenser MCA + 10 * condenser TCL + 11 * AHU TCL. Which is equal to 11 * condenser MCA - 10 * 0.25 * condenser RLA + 11 * AHU MCA - 11 * 0.25 * AHU FLA.

Cheers, Wayne

 

[2l84me1]

Cheers brother