Update: On September 26, 2014, the U.S. Department of Energy (DOE) named the ASHRAE/IES 90.1-2013 energy standard as the new national energy reference standard, superseding the 2010 version in effect until then. Within two years, all states in the United States must put into effect a commercial building energy code at least as stringent as the 2013 version of 90.1, or justify why they cannot comply.
ASHRAE/IES Standard 90.1 provides a model commercial building energy code that can be adopted by states and other jurisdictions. The standard, which applies to new construction and major renovations (including requirements for lamp-ballast retrofits), is updated every three years. ASHRAE published the latest version in October 2013. The lighting section of ASHRAE/IES 90.1 has become increasingly sophisticated over the past 14 years, particularly in regard to lighting controls. The 2013 standard attempts to go even further while simplifying understanding and application.
What’s new? The major changes to ASHRAE/IES 90.1 2013’s Section 9 (lighting) include:
• adjusted lighting power densities (LPD)
• more stringent lighting control requirements
• a new table format for determining lighting power and control requirements in individual spaces
First, let’s look at LPD values, most of which were adjusted. For example, Building Area Method LPDs were adjusted for hospitals (down from 1.21W/ft2 to 1.05), office (up from 0.9W/ft2 to 1.01), retail (down from 1.4W/ft2 to 0.9), schools/universities (up from 0.99W/ft2 to 1.05), and warehouse buildings (up from 0.66W/ft2 to 1.01).
These adjustments save power where possible according to new light level recommendations published by the Illuminating Engineering Society (IES).
Lighting controls got a significant makeover in the 2013 standard:
• Occupancy sensors must be set to turn the lights off within 20 minutes (instead of 30 minutes) after a space is vacated.
• Automatic independent control is now required in secondary sidelighted daylight zones (covering additional luminaires farther from the windows) rather than just incentivized with a control credit.
• Daylight harvesting step-dimming control now requires two control points between off and full-on—one dim level between 50–70 percent of design power and one between 20–40 percent—to provide greater flexibility.
• A second automatic lighting shutoff option is required for certain occupancy sensor installations—partial-off to 50 percent of design power within 20 minutes of the space being vacated—spaces where the lights are periodically not needed but must remain ON.
• More detailed functional testing requirements are imposed.
The primary change in ASHRAE/IES 90.1-2013 is a new table (Table 9.6.1) format for determining LPD allowances using the space by space method and minimum mandatory control requirements using either the space by space method or building area method.
The table was developed to simplify reading and reference of LPD and control requirements in each space, but, at first glance, it may appear confusing. One must read the accompanying text as separate requirements and options applicable to the table, not a consecutive list of actual requirements. Otherwise, proper use of the table is in the fine print. For example, two tables actually list space types, but the first represents space types commonly found in multiple building types, while the second covers space types typically found in a single building type.
For open offices, the LPD is 0.98 if using the space by space method. The room cavity ratio (RCR) threshold is 4, meaning an additional lighting power allowance of 20 percent is available if the actual RCR (2.5 × room cavity height × room perimeter length ÷ room area) exceeds the threshold. Various controls are then required, and some choices are available. For example, in open offices, space controls are required to give users control over their lighting. All lighting must be capable of bilevel control. If daylight is present, lighting in the daylight zones must be separately and automatically controlled. The lights may be manual-on (“ADD1”) or partial-automatic-on (“ADD1”), and they must be turned off automatically based on occupancy (“ADD2”) or a schedule (“ADD2”).