Refer to the ASHRAE 90.1-2007 standard for lighting power density allowances. The prerequisite requires your project’s lighting power density (in watts/ft2) to be 10% lower than the standard. ASHRAE lists allowable LPDs in the reference standard of Section 9.5.1 for building types, and in Section 9.6.1 for individual space uses.

Lighting Power Density Reduction of 10% 

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. So, if the hot water boiler is owned by the base building, and the tenant is installing a pipe and pumps to deliver hot water to the bathrooms, the prerequisite covers only the delivery method. So the pipe and the pumps must meet ASHRAE requirements for minimum pipe insulation and pump efficiency—the efficiency of the hot water boiler need not be accounted for. 

In addition to meeting the mandatory requirements, the project must demonstrate that the energy use of the project is equivalent to ASHRAE 90.1-2007. This can be demonstrated by complying with the prescriptive checklist or simulating whole-building energy use with an energy model, also known as the performance option.

ASHRAE 90.1-2007 – Prescriptive Option or Performance Option 

The mandatory provisions (Section x.4) are separate from and in addition to the prescriptive requirements (Sections x.6) of ASHRAE 90.1. The two are commonly but incorrectly used interchangeably. None of the mandatory provisions can be compromised; prescriptive requirements, however, provide a way to meet the minimum efficiency requirements of this prerequisite and offer multiple options for doing so. 

Non-compliance with any of the requirements disqualifies the project from LEED certification. All projects, including remodeling projects, must meet the requirements for all components and systems within the scope of the fit-out. Exemptions include buildings designated “historically significant” by a recognized authority (such as the U.S. Dept. of the Interior), 24-hour facilities, equipment and portions of building systems that use energy primarily to provide for industrial, manufacturing, or commercial processes.