Load Calculations for Heat Strips

[bswithms]

I prepare load calculations for optional stand by generators. In South Florida most municipalities require us to match the load of the panel or service we are picking up with an automatic transfer switch. There is also not very much need for heating here so most single family homes have only supplemental type heat strips in the air handlers.

I see numerous architectural and engineered plans with these heat loads derated to 65%. NEC 220.30(C)(4) in the 2002 ed seems to back this up and most municipalities take load calculations done in this manner. However some do not and the 2005 is being adopted.

My question is two-part, first, am I correct in reading the code believing that it states that the load of AHU w/ electric heat strips may be derated to 65%? Second, it seems as if this code has been removed from the optional load calculation portion of the 2005 ed., is that true?

 

[Smart $]

I prepare load calculations for optional stand by generators. In South Florida most municipalities require us to match the load of the panel or service we are picking up with an automatic transfer switch. There is also not very much need for heating here so most single family homes have only supplemental type heat strips in the air handlers.

I see numerous architectural and engineered plans with these heat loads derated to 65%. NEC 220.30(C)(4) in the 2002 ed seems to back this up and most municipalities take load calculations done in this manner. However some do not and the 2005 is being adopted.

My question is two-part, first, am I correct in reading the code believing that it states that the load of AHU w/ electric heat strips may be derated to 65%? Second, it seems as if this code has been removed from the optional load calculation portion of the 2005 ed., is that true?

I no longer have an NEC 2002 edition for comparison, but I can tell you 220.30 does not exist in the NEC 2005 edition.

There is no "derating" permitted for Fixed Electric Space Heating under the 2005 Part III calculation. However, only the higher load of heating or air condiitoning is required to be used for service calculation (ref: 220.60), provided they are non-coincident loads.

Under a Part IV Optional calculation, HVAC falls under 220.82(C), which provides six conditions of which the largest must be used for calculation. The demand factor varies from 100 to 40% depending on the type of load.

 

[bswithms]

Upon reading your reply I read and re-read 220.82. I also read Article 424 on fixed electric space heating where it states central systems shall be included under the scope of that article. My research has led me to believe that an AHU with heat strips can be calculated at 65% if less than 4 and 40% if 4 or more. These units contain no heating other than the heat strips. I came to this belief by concluding that these units are considered "Fixed Electric Space Heating"

Does anyone have any information to support or negate this statement?