2014 NEC Handbook article 220.86

[electrified1980]

First time post. Referencing the notes in blue in the 2014 nec handbook for article 220.86. there is an example given for a school in optional load that states. A school building utilizes electric heat and air conditioning. The total calculated load for the building is 1.5 mVA (1,5000,000VA). The floor area of the building is 100,00 square feet. Ive read this and done my on calculation on this and im not getting the same answer the book is. If i could get some help here it would be greatly appreciated.

 

[Dennis Alwon]

It is hard to answer without knowing what you did.

From the book- 2011- I believe it is the same

Calculate the overall demand factor for a 100,000 ft2 school
building (based on outside dimensions and the number of
stories) using Table 220.86.

The initial calculated load based on 220.86 is 1.5 mVA, or 1,500,000 VA.
1.15 mVA/100,000 ft2 = 11.5 VA/ft2

I think this is in error... should be 1.5mva/1000,000= 15va/ft2



First 3 VA/ft2 at 100%:
3 VA  100,000 = 300 kVA
Remaining 8.5 VA at 75%:
8.5 VA  100,000  0.75 = 637.5 kVA
Demand load for the school:
300 kVA  637.5 kVA = 937.5 kVA
937,500 VA/1,500,000 VA = 0.82
or 82% overall demand factor on entire building load obtained
using Table 220.86 demand factors.

 

[electrified1980]

this was in both books if im not mistaken 2011 handbook and the 2014. The part i was struggling with i guess is the basic math when you start off with 15 va/ft2 and use the first 3 at 100% you should have 12 va/ft2 not 8.5 at 75% unless im missing something. Im just checking because ive been struggling with this equation and cant find any other explanations on this.
My equation looks like this





First 3 VA/ft2 at 100%:
3 VA 100,000 = 300 kVA
Remaining 12 VA at 75%:
12 VA 100,000 0.75 = 900 kVA
Demand load for the school:
300 kva +900kva =1.2mva
1.2/1.5=.80

 

[Dennis Alwon]

Did you look at the error in the book that I posted. The book used 11.5 instead of 15 and that is where the difference lies.