Determining available capacity in Multifamily building

[Scottrandall]

We are measuring demand in MFH buildings in Minnesota. If measurements occur over cooling season, we see about 104 KW for 48 units or about 2.17 KW per unit. Outside of cooling season we see about 1.65 KW per unit. When we measure outside of cooling season we are forced to calculate A/C demand and add on to measured demand. NEC requires A/C be calculated at 100% of nameplate without demand factor. Each A/C unit is 23 amps at 240 volts or 5.52KW. 48x5.52=265KW. Based our our measured values over a number of jobs we would have expected it to be around 26KW. Calculated versus measured seems to be different by a factor of 10. Is this real or am I missing something?

 

[ptonsparky]

We are measuring demand in MFH buildings in Minnesota. If measurements occur over cooling season, we see about 104 KW for 48 units or about 2.17 KW per unit. Outside of cooling season we see about 1.65 KW per unit. When we measure outside of cooling season we are forced to calculate A/C demand and add on to measured demand. NEC requires A/C be calculated at 100% of nameplate without demand factor. Each A/C unit is 23 amps at 240 volts or 5.52KW. 48x5.52=265KW. Based our our measured values over a number of jobs we would have expected it to be around 26KW. Calculated versus measured seems to be different by a factor of 10. Is this real or am I missing something?

Typically NEC load calculations are not anywhere close to actual demand. I'm not surprised.

Are you using 3 vs 1 phase in your calculations and measurements?

 

[ron]

This is why the utility doesn't meet us at the service drop with the same ampacity wiring that we have (based on the NEC). The utility is allowed to design based on their historical expectations for that type of occupancy, where we design based on hypotheticals that are super conservative.

 

[Scottrandall]

We convert the main service amps to single phase capacity by multiplying by 1.73. Then we convert everything to KW. This way we can subtract measured KW from 80% of main service KW to get remaking capacity. We are just trying to determine how many EV chargers we can add before we run out of capacity.

I think that as a company, we will be recommending that permanent monitoring be installed so that there will always be the info available needed at any time for our customers.

Thank you for your response.