The building area method is simple and it is an easy one for projects that include only a few space types and can be easily classified as one of the building types listed in ASHRAE, Table 9.5.1. The table refers to a single lighting power allowance for each building type.
The calculation addresses total lighting power use, although it can be determined in two different ways: the building area method or the space-by-space method. Review the ASHRAE LPD allowances and space-type definitions. Consider which approach is most appropriate for your project to demonstrate compliance.
Selecting a performance-based approach using an energy model solely for LEED compliance is not recommended. Equal opportunities are available with either the prescriptive or performance approaches for LEED compliance.
Most CI projects find it cost-effective to pursue the prescriptive option because of a limited design scope in HVAC systems and the building envelope, making the energy model of limited use as a design tool.
Developing a simulation model is an added expense and you may need it to provide a demonstrable payback if you’re going to use it as part of your compliance path. It can be well worth the cost, however, especially on larger projects with greater scope. If the scope of the project is larger (>100,000 ft2) and includes a central plant in addition to HVAC distribution and lighting, it can make sense to develop an energy model to assist in system selection and lighting design.
The four components of energy use under this prerequisite—envelope, lighting, HVAC and hot water—include only those components that are within the scope of CI work.
