Although daylight and occupancy sensors help to keep energy costs low, they cannot be used in calculations for lighting power density. However, if your project develops an energy model to demonstrate HVAC and lighting compliance, occupancy and daylight sensors can be used to reduce design-case energy use, per ASHRAE 90.1-2007, Appendix G, Table G3.1, Section 6. 

Check Section 9.6.2 for potential additional allowances for decorative or display lighting. This additional power density is a function of the type of merchandise and the space area. 

If your project develops an energy model, you can use it not only to optimize the lighting design but also to demonstrate that lighting power density is 10% less than the ASHRAE baseline case, per Appendix G.

The prerequisite is dependent on the baseline allowance of lighting watts/ft2. Run preliminary calculations, using the building area method or space-by-space method, and determine which option provides the greater allowance for your project. 

Lighting Power Density Reduction of 10% 

The documentation for the performance approach is the same as for EAc1.3: Optimize Energy Performance—HVAC, Option 2 – Energy Cost Reduction, 15-30%. 

The energy model can also demonstrate potential savings on the whole building level. While the base building may have existing energy constraints, take the opportunity to encourage future upgrades such as a new central plant, more controls in the base system, end-user ability to set temperatures and reduce energy use, a more efficient air-distribution system—improvements that will benefit the whole building.

The model is a great design tool that should be utilized to its full potential during design development. Use it to assist in design development for interior mechanical fit-out spaces, comparison of alternative systems, determination of lighting loads, and selection of fixtures. Simulate alternative strategies or designs to provide a true cost-benefit analysis of energy-saving features, along with long-term energy savings and lower maintenance costs for the tenant and building owner. 

Work on an energy model typically takes three to four weeks before it can provide reasonable results and recommendations, so be sure to start this early in design development. 

The energy modeler should begin the modeling now, and continue to update it whenever design changes are made to ensure that the project maintains the prerequisite requirements.