ASHRAE 90.1-2007

Section: 9.5 - Building Area Method

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Building Area Method of Calculating Interior Lighting Power Allowance.

Use the following steps to determine the interior lighting power allowance by the building area method:

1. Determine the appropriate building area type from Table 9.5.1 and the allowed lighting power density (watts per unit area) from the building area method column. For building area types not listed, selection of a reasonably equivalent type shall be permitted.
2. Determine the gross lighted floor area (square feet) of the building area type.
3. Multiply the gross lighted floor areas of the building area type(s) times the lighting power density.
4. The interior lighting power allowance for the building is the sum of the lighting power allowances of all building area types. Trade-offs among building area types are permitted provided that the total installed interior lighting power does not exceed the interior lighting power allowance.

Shell Buildings: If a permit applicant wishes to install some lighting in a shell building before the building's use is known, the lowest lighting power density should be used.

Garages and Parking Areas: a covered garage is treated as an interior space while open parking lots and roof top parking are treated as exterior.

Speculative Buildings: tenant improvements in a core-and-shell buildings are considered new construction and are subject to the version of 90.1 in place at the time.