ASHRAE 90.1-2007

Section: 9.6.2 - Additional Interior Lighting Power

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When using the Space-by-Space Method, an increase in the interior lighting power allowance is allowed for specific lighting functions. Additional power shall be allowed only if the specified lighting is installed and automatically controlled, separately from the general lighting, to be turned off during non-business hours. This additional power shall be used only for the specified luminaires and shall not be used for any other purpose.

An increase in the interior lighting power allowance is permitted in the following cases:

1. For spaces in which lighting is specified to be installed in addition to the general lighting for the purpose of decorative appearance, such as chandelier-type luminaries or sconces or for highlighting art or exhibits, provided that the additional lighting power shall not exceed 1.0 W/ft² of such spaces.

2. For lighting equipment installed in retail spaces and specifically designed and directed to highlight merchandise, calculate the additional lighting power as follows:

   Additional Interior Lighting Power Allowance = 1000 watts +

   (Retail Area 1 × 1.0 W/ft2) +

   (Retail Area 2 × 1.7 W/ft²) +

   (Retail Area 3 × 2.6 W/ft²) +

   (Retail Area 4 × 4.2 W/ft²) ,

   where

   Retail Area 1 = the floor area for all products not listed in Retail Areas 2, 3, or 4;

   Retail Area 2 = the floor area used for the sale of vehicles, sporting goods, and small electronics;

   Retail Area 3 = the floor area used for the sale of furniture, clothing, cosmetics, and artwork; and

   Retail Area 4 = the floor area used for the sale of jewelry, crystal, and china.

   Exception: Other merchandise categories may be included in Retail Areas 2 through 4 above, provided that justification documenting the need for additional lighting power based on visual inspection, contrast, or other critical display is approved by the authority having jurisdiction.