Refrigeration/HVAC Loads Diversity Factor

B

blake1008205

Member
Location
Powder Springs, GA
Occupation
Electrical Engineer
Hello everyone, I have a job that's getting push back right now on the way I sized the refrigeration/condenser/HVAC loads that need to be backed up by the generator set. I sized all of the loads based on the nameplate on the motors. I used MCA × sqrt 3 x 480 for the 3 phase motor loads and used the MOCP for the breaker sizes. They're telling me I need to use a diversity factor for the loads but I have never used a diversity factor for emergency backed refrigeration/HVAC equipment. I can't find anything in the NEC about it (I did see where it talks about lighting and receptacles but not motor loads), can anyone help me
 
blake1008205 said:
Hello everyone, I have a job that's getting push back right now on the way I sized the refrigeration/condenser/HVAC loads that need to be backed up by the generator set. I sized all of the loads based on the nameplate on the motors. I used MCA × sqrt 3 x 480 for the 3 phase motor loads and used the MOCP for the breaker sizes. They're telling me I need to use a diversity factor for the loads but I have never used a diversity factor for emergency backed refrigeration/HVAC equipment. I can't find anything in the NEC about it (I did see where it talks about lighting and receptacles but not motor loads), can anyone help me
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MCA is NOT the load ampacity of a given piece of equipment.
 
The MCA was given for 125% of the largest motor added to the heater load. From the code it says to use the nameplate information but it doesn't break the loads apart. Just gives me the MCA total. How would you do a load calc with this information differently than I did?
 
blake1008205 said:
The MCA was given for 125% of the largest motor added to the heater load. From the code it says to use the nameplate information but it doesn't break the loads apart. Just gives me the MCA total. How would you do a load calc with this information differently than I did?
Click to expand...
Have the equipment reps provide you with the TOTAL amps for cooling vs heating for each item and work from there.
 
blake1008205 said:
It's existing equipment being moved to a new facility, they don't have spec sheets. I only have the nameplates to work with
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The tags on the equipment only provide you an MCA?
If there is a MECH, ME or MC, on the project I would put the information gathering in their lap.
You asked what I would do…if I have the job, I am calling the equipment manufacturer.
You need all this info so the generator can be sized properly, so I would place a detailed list of loads on the plans so each gen rep can do their thing.
 
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