Another Chiller Feeder Calculation

[philly]

I am looking at another Chiller feeder calculation and wanted to make sure that I am on the right track as I get familiar with Chiller calculations.

A new 480V 1200A Switchboard is being provided which will feed a 235kW chiller along with some small auxiliary pumps that will support the chiller system. There will be a feeder breaker in the Switchboard to feed the Chiller directly and there will be another feeder breaker which will feed a small MCC which contain the small pump starters.

The Chiller schedule from the manufacturer shows the chiller as having an "MCA" of 530.6A, a "MOCP" of 700A and an "IF" of 2028.6A. It also lists a "IPLV/EER" of 12.29/10.08. I'm not sure what the "IF" and "ILPV/EER" are?

In terms of the feeder calculation for this chiller do I simply use the 700 listed OCPD to size the feeder breaker at 700A and have (2) sets of 500MCM cables for the feeder? I'm assuming that the listed MOCPD and MCA already factor in the requirements of 440.22 and 440.33 and thus there are no further multiplying factors needed for these (the manufacturer already did these calcs for us)

In terms of the load calculation for the switchboard would I simply use the MCA (530.6A) value for the chiller load or do I need to add any adjustment factors to this for the load calc.

There will be four small 10hp pumps connected to a small MCC which if fed from the switchboard. For the load calcs for these pumps I simply use 4 x 14A (FLA) plus 25% of 14A (largest FLA) to come up with 59.5A. I then add this 59.5A to the 530.6A chiller value above to come up with the total Switchboard calculated load. Am I on the right track here?

 

[philly]

The Chiller schedule from the manufacturer shows the chiller as having an "MCA" of 530.6A, a "MOCP" of 700A and an "IF" of 2028.6A. It also lists a "IPLV/EER" of 12.29/10.08. I'm not sure what the "IF" and "ILPV/EER" are??

I did some further investigation and found that "ICF" (mistyped as "IF" above") is essentially the Instantaneous current flow related to the chiller starting or essentially the locked rotor current. I also found that the "EER" term is related to the energy efficiency ratio.

In terms of the feeder calculation for this chiller do I simply use the 700 listed OCPD to size the feeder breaker at 700A and have (2) sets of 500MCM cables for the feeder? I'm assuming that the listed MOCPD and MCA already factor in the requirements of 440.22 and 440.33 and thus there are no further multiplying factors needed for these (the manufacturer already did these calcs for us)

I am used to seeing a "RLA" value on the nameplate which define the maximum continuous current which would be used for the load calc. However this was not given so do I need to use the "MCA" value and add any multiplying factors?

440.32 indicates that "Branch circuits supplying a single motor-compressor shall have an ampacity not less than 125% of either the motor-compressor rated-load current or the branch circuit selection current, whichever is greater". Since the motor-compressor rated-load current is not given do I need to use 125% of the branch circuit selection current which I'm guessing may be the "MCA" value thus I would need to take 125% of this value?

 

[GoldDigger]

The MCA calculation already includes the 125% factor for the largest (or only) motor.
For an air source chiller the unit would typically include both compressor and condenser fan motor under one label.

 

[steve66]

I would use the 700 amp breaker, and I believe you can actually use (2) sets of 300 KCM, since that would have a 570 amp capacity (and that is above the 530 MCA).

You could also make sure the instantaneous trip on the 700 amp breaker is greater than the 2030 amps, but I don't think it will be a problem.

 

[JoeStillman]

I would use the 700 amp breaker, and I believe you can actually use (2) sets of 300 KCM, since that would have a 570 amp capacity (and that is above the 530 MCA).

You could also make sure the instantaneous trip on the 700 amp breaker is greater than the 2030 amps, but I don't think it will be a problem.

Ditto that. Don't be fooled by the MOCP. Your ampacity doesn't have to match the MOCP. Your cables are protected from overload by the starter heaters, not the feeder breaker.

 

[philly]

The MCA calculation already includes the 125% factor for the largest (or only) motor.
For an air source chiller the unit would typically include both compressor and condenser fan motor under one label.

I have done some more reading and see that MCA includes 125% of the largest motor (usually compressor motor) plus the sum of all other motors (fans, etc...). So you cannot simply take this number and divide it by 125% to get the RLA of the compressor unless that is the only motor. If there are multiple motors then dividing MCA by 125% will not provide the correct RLA if for some reason you were trying to back calculate that.

As far as what number to use for load calculations I have seen some people say they use the RLA of the chiller if it is given. In this case that is not given so I would think that the MCA would be the best conservative number to use for a load calculation since the 125% in this value follows the same rules for other motor feeders outlined in Section 430. Do others agree? No need to add on any more multiplying factors?

Ditto that. Don't be fooled by the MOCP. Your ampacity doesn't have to match the MOCP. Your cables are protected from overload by the starter heaters, not the feeder breaker.

Yes I have also found that the ampacity does not have to match the MOCP.

 

[Ingenieur]

Starting i 2040 A
CB 700
or 300% or 3 x i rating of CB
Typically should hold for 30 sec cold decreasing to 10 sec hot for a molded case CB
should not be an issue

 

[topgone]

I did some further investigation and found that "ICF" (mistyped as "IF" above") is essentially the Instantaneous current flow related to the chiller starting or essentially the locked rotor current. I also found that the "EER" term is related to the energy efficiency ratio.

I am used to seeing a "RLA" value on the nameplate which define the maximum continuous current which would be used for the load calc. However this was not given so do I need to use the "MCA" value and add any multiplying factors?

440.32 indicates that "Branch circuits supplying a single motor-compressor shall have an ampacity not less than 125% of either the motor-compressor rated-load current or the branch circuit selection current, whichever is greater". Since the motor-compressor rated-load current is not given do I need to use 125% of the branch circuit selection current which I'm guessing may be the "MCA" value thus I would need to take 125% of this value?

I did some quick calcs and here's what I got (using your MCA = 530.6 amps and MOP = 700A):
Greatest motor load amps = 169.4 amperes
Sum of the other loads = 318.85 amperes

MCA = 1.25 X 169.4 + 318.85 = 530.6 A --> checked out with your 530.6A
MOP = 2.25 X 169.4 + 318.85 = 700 A --> checked out with your 700A MOP.