In order to comply with federal law, specifically the Energy Policy Act of 1992, many states have recently amended their energy codes. These amendments incorporate, by reference, energy efficiency requirements for commercial and multi-family high-rise buildings that meet but do not exceed federal requirements. Accordingly, ASHRAE/IESNA 90.1 (1989) shall be the standard for the energy efficiency requirements of newly constructed commercial buildings. Buildings of Use Groups R-3, R-4 and R-2, which are three stories or less, shall continue to be subject to Standard LEM-1 (1982).
Standard 90.1 is intended to promote efficient lighting design by requiring, and in some cases by encouraging, the use of advanced lighting control. This standard is more restrictive than Standard LEM-I for buildings such as offices, hospitals and retail spaces which represent a large portion of new construction. Unlike Standard LEM-I, it requires some means of control for all lighting except for emergency and exit lights. The project complies if the total connected lighting power (CLP) of the installed system does not exceed the interior lighting power allowance (ILPA) of the building. When qualifying lighting controls are used, the connected lighting power (CLP) may be reduced by the lighting power control credits (LPCC) to account for the energy saved because of these controls. The final figure represents the adjusted lighting power (ALP) for the buildings equipped with qualifying controls.
Standard 90.1 has two approaches to calculate the interior lighting power allowance (ILPA) of a building. Out of these two, the prescriptive method is easy to use and is intended for use with speculative buildings or during the early design stages. This method is more stringent (i.e., mandates lower lighting power requirements) but is not sensitive to specific space functions or room configurations. The other method, known as the system performance method, takes into account the space functions and room geometrics of the proposed design. This method provides greater flexibility and is a more accurate and detailed calculation procedure. It is recommended for most projects. If the building type or space activity is not applicable to those mentioned in the prescriptive method, then the system performance method is recommended. In no case should the prescriptive method be the only path available to the designer.
To ensure compliance with the new Standard 90.1, the design engineer should review all the worksheets for compliance. This design engineer should also be satisfied that the proposed allowance, total connected lighting power and adjustments are reasonable, and the value of CLP/ALP does not exceed the ILPA of the project.
