As a commercial estimator, when calculating the lighting load I generally use 3.5 watts per square foot. Since all of the changes in the last few years have drastically lowered the lighting loads, am I able to adjust the watts per square foot to match my known installation? I have a project that involves local utility rebate structure and I am required to have the installation come in under 1 watt per square foot. I would think that I could go back and adjust my service calculations to match?
Calculating Lighting Service Load?
- Thread starter mwh1023
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Table 220.12 gives the minimum volt-amperes per square foot required to be included in your load calculations. For most of the occupancies listed, the number to use is less than the 3.5 watts that you have been using. There is nothing wrong with using a larger number, but you are not required to.
But this brings up an interesting situation. I believe more and more jurisdictions are adopting some energy code. The International Energy Conservation Code for example, lists the maximum amount of lighting that may be provided in watts/sq. ft. for various occupancies. In most cases, the maximum amount of lighting that may be provided is less than the minimum amount that the NEC requires to be used in the load calculation. IMO, the way these codes are currently written, the larger figure from the NEC is the number that must be used for load calculation purposes, but when actually providing the light fixtures, the smaller amount allowed by the energy code is the limit to what can actually be provided. This may be an area where a code amendment proposal may be in order.
But this brings up an interesting situation. I believe more and more jurisdictions are adopting some energy code. The International Energy Conservation Code for example, lists the maximum amount of lighting that may be provided in watts/sq. ft. for various occupancies. In most cases, the maximum amount of lighting that may be provided is less than the minimum amount that the NEC requires to be used in the load calculation. IMO, the way these codes are currently written, the larger figure from the NEC is the number that must be used for load calculation purposes, but when actually providing the light fixtures, the smaller amount allowed by the energy code is the limit to what can actually be provided. This may be an area where a code amendment proposal may be in order.
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