Adding load to an existing electrical service

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gsherman

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Hi There! My company is working on an electrification project at 12 unit apartment building. We hired an MEP to determine if the existing 200A service, which serves both the house meter and all (12) 60A apartment panels, has sufficient capacity to handle the new load. However, I am concerned that the electrical engineer is not familiar with the appropriate methodology or calculations, so I decided to turn to this community to get a second opinion.

We are planning to install a ducted mini split in each apartment (NTXDKS18A112A & NTXSKS18A112A) to replace the existing fan coil (~ 3 amps). The fan coils are supplied with heated and chilled water that comes from a central plant that is on a completely different electrical service. We are also planning to install a central heat pump hot water heater to serve all 12 units. Once again, domestic hot water was previously supplied by a central plant. We performed a load study of the existing 200A service and measured the peak demand over a 7 day period. According to the electrical engineer, the max load was 25.12 kW, or 87.26 A.

My first, and primary question, is likely a simple one. When calculating the added load of the new equipment, what number should we be using from the attached spec sheets? My understanding is that he should use the MCA, but he is using a value that is a good deal below MCA. Thanks in advance for your help!
 
Section 220.87 discusses existing loads. The NEC wants 30 days, of the maximum demand, meaning heating or cooling load. Review this section and you many need to discuss with AHJ. 200A and 12 apartments, 200 seems small, You can always do a load calc per 220 ( not sure if can do optional for multifamily), keep in mind load calcs are typically way more then the connected load - but with a 60 amp panel, maybe not.
Also see 220.16 loads for additions.
Multifamily is not my strong area but we have many other experienced here that will add to this.
 
Thanks for the reply Tom. I am aware of Section 220.87 and have read it a few times now and I believe the electrical engineer is following the 3 step process outlined in that section. The part I am confused about is what value to use from the spec sheet for the new equipment we are planning to install. For example, the HVAC system we are planning to install is a Mitsubishi ducted split system. The submittal data we received from the distributor shows a few different values for power consumption and amperage. What keywords on the spec sheet should I be looking for? A few options include:
  • Max power input (watts) - different values are provided for different outdoor temperatures
  • Rated power input (watts) - different values are provided for different outdoor temperatures
  • Recommended breaker size
  • MCA
  • MOCP
 
MCA for load calculations. Don't quote me, I would have to check but I don't think you have to worry about 125% of anything because it is already included in MCA
 
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