Does the NEC allow for the application of a Diversity Factor in sizing the service to an office building or any building for that matter? I am re-sizing the service (now that I know the load for one tenant) to a moderate size office building with multiple tenants. Given that the space for each of the tenants is the same size and each of the tenants have their own distribution panels that are fed from a common Main Switchboard I was curious as to whether I could apply a diversity factor (maybe 1.5) to the feeders to determine the size of the building Main Switchboard / Service.
Service Sizing and Diversity Factor
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- Lockport, IL
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- Retired Electrical Engineer
I am a bit confused by your description. This appears to be an existing building with an existing service and with one or more existing tenants. What is your present project? Is either the service equipment or the conductors from the utility in need of replacement? Are you trying to determine what size the service needs to be? Is there reason to believe it is too small to handle the present or projected requirements?
Also, I don't think you are using the term "diversity factor" in the proper manner. What do you think that factor would do for you? My old college textbook defines it as a ratio of the sum of the maximum demands for the individual parts of a distribution system to the maximum demand of the system as a whole. The NEC does not ever use that phrase. It uses something that sounds similar, "load diversity," but that is not the same thing.
Welcome to the forum. I think we can help you, but I for one will need a bit more information first.
Also, I don't think you are using the term "diversity factor" in the proper manner. What do you think that factor would do for you? My old college textbook defines it as a ratio of the sum of the maximum demands for the individual parts of a distribution system to the maximum demand of the system as a whole. The NEC does not ever use that phrase. It uses something that sounds similar, "load diversity," but that is not the same thing.
Welcome to the forum. I think we can help you, but I for one will need a bit more information first.
This may give you some guidance but for the most part you won't be able to use a load factor for commercial building. The lighting and A/C is usually 100%.
http://www.necplus.org/Features/Pages/CommercialandIndustrialCalculations.aspx?sso=0
http://www.necplus.org/Features/Pages/CommercialandIndustrialCalculations.aspx?sso=0
I believe I understand the meaning and application of diversity factor. I suppose the answer to my question lies within NEC Article 220.40 (and others) in that there is no reference to diversity factor and therefore it does not apply in building service sizing as required by the NEC.
The particular application that I am referencing is a new office building for which I generated an initial estimate of the service size without any real data and now I have all the loads for the first of what is to be a somewhat typical build-out (4 total) and the HVAC loads seem a bit high. I estimated about 13.5 W/sqft as an initial total estimate but it turns out that the HVAC loads (8 AHU & HP split units) alone amount to about 12.2 W/sqft. I still have time to change the building service size if necessary.
The maximum building demand is sure to be much less than the sum of the demands on the many feeders from the main switchgear as calculated per NEC; due to non-coincidental loads. Further, in discussion with the utility company I understand that existing buildings of the same type have actual recorded demands of 5.3 to 8.1 W/sqft.
Maybe I?m not properly accounting for the HVAC loads as the paired HP and AHU?s should not be coincidentally at full capacity. Is there a rule to follow in this regard? In the past I?ve always included both HP and AHU?s at full capacity in the loads.
Thanks for your help.
The particular application that I am referencing is a new office building for which I generated an initial estimate of the service size without any real data and now I have all the loads for the first of what is to be a somewhat typical build-out (4 total) and the HVAC loads seem a bit high. I estimated about 13.5 W/sqft as an initial total estimate but it turns out that the HVAC loads (8 AHU & HP split units) alone amount to about 12.2 W/sqft. I still have time to change the building service size if necessary.
The maximum building demand is sure to be much less than the sum of the demands on the many feeders from the main switchgear as calculated per NEC; due to non-coincidental loads. Further, in discussion with the utility company I understand that existing buildings of the same type have actual recorded demands of 5.3 to 8.1 W/sqft.
Maybe I?m not properly accounting for the HVAC loads as the paired HP and AHU?s should not be coincidentally at full capacity. Is there a rule to follow in this regard? In the past I?ve always included both HP and AHU?s at full capacity in the loads.
Thanks for your help.
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