Diversity Calculations for Military Dormitory BEQ

[blvengineers]

Hello. I am trying to size main feeder and branch feeders for a 4 story military dorm. Here is the distribution. Main service on 1st floor servers 10 individual panels separated by mechanical, lighting and general receptacle loads. On the 2nd, 3rd and 4th floors, there are large distribution panels that serve the same for each floor. Where do I start with diversifying the load? There are approximately 8 dorm units served from each general receptacle panel, about 20 units served from the mechanical panel and 44 from the lighting panels. Approximately the same for each floor. I am having issues understanding how to apply the diversity. For the record, there is no fixed cooking equipment.

 

[Smart $]

Hello. I am trying to size main feeder and branch feeders for a 4 story military dorm. Here is the distribution. Main service on 1st floor servers 10 individual panels separated by mechanical, lighting and general receptacle loads. On the 2nd, 3rd and 4th floors, there are large distribution panels that serve the same for each floor. Where do I start with diversifying the load? There are approximately 8 dorm units served from each general receptacle panel, about 20 units served from the mechanical panel and 44 from the lighting panels. Approximately the same for each floor. I am having issues understanding how to apply the diversity. For the record, there is no fixed cooking equipment.

Before providing "speculations", your query leaves me with one of my own... How is it that the number of panels, type of loads, and number of units served by each panel is already set without having already determined the diversity?

 

[blvengineers]

blvengineers

blvengineers

There are 6 circuits extending from the electrical room to each unit. Microwave, Refrigerator, GFCI in restrooms, and General use receptacles. In addition there is a common lighting circuit for each two units, and one 2-pole 208, circuit for the PTAC units. We have circuited all rooms according to this protocol. Hence, the number of panels is already set. The base required that we separate the loads for LEED points w.r.t. metering.

 

[BJ Conner]

No difference it's still NEC

No difference it's still NEC

Army TM-5-683 "Electrical Interior Facilities" Chapter 1 says The National Electrical Code is what to follow [National Fire
Protection Association #70 (NFPA 70)].
That should send you to section 220.

The USACE is responsible for the builidng of such faciliteis and most of their Tech Manuals are on the web.

http://140.194.76.129/publications/armytm/tm5-683/

 

[Smart $]

There are 6 circuits extending from the electrical room to each unit. Microwave, Refrigerator, GFCI in restrooms, and General use receptacles. In addition there is a common lighting circuit for each two units, and one 2-pole 208, circuit for the PTAC units. We have circuited all rooms according to this protocol. Hence, the number of panels is already set. The base required that we separate the loads for LEED points w.r.t. metering.

Well it all starts at the unit level and adds up all the way back to the main. The hardest part I see is dividing up the lighting and GP/GFI receptacle load. Under the NEC, these load minimums are lumped together and determined by the floor area served.

Start with determining the floor area of each two units served by one lighting circuit (use the outside dim's of walls enclosing the two units floor area). Multiply this by the 3VA/ft? required minimum. Subtract the actual connected lighting load for the two units plus the ampacity of the receptacle circuits times 120V (assumed voltage since you mentioned the 2-pole 208V AC circuit) times the number of receptacles circuits for both units. If there is a positive balance, divide between lighting and receptacle panels at a ratio equal to the number of circuits. If no balance or a negative balance, use actual connected lighting load as the load on the lighting panel, and the balance as the load on the receptacle panel. Don't forget to add in your "house" area circuits too.

From there you sum up your loads per panel and apply the lighting demand factor to each lighting and respective portion of receptacle panels. For upstream equipment, the calculated load prior to applying the demand factor gets carried up, added together, then the demand factor is applied to the appropriate portion of the panel's load.

The remaining loads are all dedicated circuits and get calculated at nameplate value. I don't believe there is any applicable demand factor for these loads.

 

[skeshesh]

Smart, I don't see how you've answered your first concern... The selection of how many panels you need and what application they are dedicated to comes AFTER you've identified each load by it's magnitude and application, only then can you attempt to have panels serving each need.
I can see that the OP wants individual panels serving "mechanical", "lighting" and "receptacles". Start with separating your loads. Make a little chart with mech, ltg and rec. Each of the loads (not the panels) need to have the diversity factor as allowed per NEC (or local codes or special needs per gov't approved methods) considered. Then you take a look at the load and how many panels and at what rating you may have and try to organize it... which reminds me, another point that was not brought up is what are the sizes of your panels? I mean tbh this whole question does not seem right to me - major pieces and considerations are missing...

 

[Smart $]

Smart, I don't see how you've answered your first concern... The selection of how many panels you need and what application they are dedicated to comes AFTER you've identified each load by it's magnitude and application, only then can you attempt to have panels serving each need.
I can see that the OP wants individual panels serving "mechanical", "lighting" and "receptacles". Start with separating your loads. Make a little chart with mech, ltg and rec. Each of the loads (not the panels) need to have the diversity factor as allowed per NEC (or local codes or special needs per gov't approved methods) considered. Then you take a look at the load and how many panels and at what rating you may have and try to organize it... which reminds me, another point that was not brought up is what are the sizes of your panels? I mean tbh this whole question does not seem right to me - major pieces and considerations are missing...

Your right, I didn't answer my first concern... OP'er did. He's saying the number of circuits are predetermined. Besides, the only place diversity (demand factoring) is applicable is on panel feeder and ocpd ratings. He gave the rough circuit breakdown per unit and per panel type... to which demand does not apply.