Is it the case that per ASHRAE/IES 90.1 the maximum possible wattage for the fixture will be applied?

The fixture wattage to be used in the power calculation depends on the type of lighting technology (see ASHRAE/IES Standard 90.1-2001, Section 9.2.5, or visit the section of this website that explains Standard 90.1-2001). Consult lighting designers and manufacturers as to what wattage would be appropriate for "lamp/auxiliary" combinations for fixtures with permanent or remote ballasts or transformers.

There was a question about the maximum lamp/ballast wattage for light fixtures that use energy-saving (25W, 28W and 30W) T8 lamps. If the ballast can operate these as well 32W lamps, would a 32W lamp have to be assumed for the energy calculations? The industry requested guidance from ASHRAE, which responded:

"The intent of section 9.1.4 (b) in ASHRAE/IESNA 90.1-2004 is to ensure that the calculation of wattage for lighting compliance includes ballast and/or transformer energy for the lighting equipment that is to be installed and used. If the actual equipment to be installed and used is not known or specified, than the maximum lamp/auxiliary combination becomes the basis for wattage calculation. However, it was never the intent of the requirement that installed lamp/auxiliary combinations drawing lower wattage than the maximum should be penalized at the maximum value. Therefore, similar to the language included for screw-based socket luminaires in 9.1.4 (a), the "maximum labeled wattage" (lamp/auxiliary combination for the maximum lamp wattage allowed by the label) of a luminaire could be used for wattage calculation of luminaires with permanently installed or remote ballasts or transformers.

Note1: a proposed change to the standard for the 2007 version will add this additional language to 9.1.4 (b)
Note2: This informal interpretation also applies to the 1999 and 2001 versions of the standard."

This indicates that the actual wattage of fluorescent systems using energy-saving T8 lamps can be used in energy calculations, not the maximum lamp-ballast wattage, for the purposes of achieving efficiency levels for the purposes of qualifying for the Commercial Buildings Deduction.

 

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