Tang Yau Hoong

Today, we are in the midst of an era of regulated efficiency. And as a major consumer of electric energy in commercial buildings, lighting is subject to a large host of design restrictions and control requirements. Various product standards are affecting the availability of lighting equipment, while municipal lighting ordinances are setting boundaries on outdoor lighting design, and energy codes are dictating building design efficiency. Case in point: Within the next two years, tighter lighting-power allowances and more intensive use of automatic lighting controls will become required practice as commercial building energy codes, which will have to be at least as stringent as the ASHRAE/IES 90.1-2010 standard, are adopted across the United States.

As energy codes grow more complex, it becomes more difficult to provide good lighting while complying with them, which makes any lighting designer who can do that well highly valuable.

The 90.1 Standard

Produced by ASHRAE and the Illuminating Engineering Society (IES), 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings, provides a template for legal jurisdictions to regulate commercial building energy efficiency to a model design standard. First published in 1975, the standard was republished in 1980, 1989, 1999, 2001, 2004, 2007, and 2010; the intent is to update it every three years. (The process for developing the 2013 version has already begun.) Today, most states have either adopted 90.1 or the International Energy Conservation Code (IECC) as their commercial energy code, created a code based on one of them, or built a state-specific code with similar requirements. The IECC references 90.1 as an alternative compliance standard, although the 2009 version requires that the building be designed to either 90.1 or IECC in whole, not selectively. While this can simplify code inspection, it can also reduce lighting-design flexibility if the design team chooses the IECC—as this model code does not offer the Space-by-Space compliance method.

The Energy Policy Act of 1992 established ASHRAE/IES 90.1-1989 as the national reference standard, and gave the Department of Energy (DOE) the legal authority to update it. In 2002, the DOE recognized the 1999 standard, which went into effect in 2004; in 2008, the DOE recognized the 2004 standard, which went into effect in 2010. So, by Dec. 30, 2010, all states had to institute a commercial building energy code at least as stringent as ASHRAE/IES 90.1-2004. If they didn't, they had to justify why they could not comply.

In July 2011, the DOE recognized the 2007 standard, and the department issued a rule requiring ASHRAE/IES 90.1-2007 compliance for all new federal buildings for which construction begins on or after Oct. 11 of this year. Then, in October 2011, the DOE recognized the 2010 standard as the new national reference standard, which will go into effect Oct. 18, 2013. At the time of that announcement, more than half of the states had a code in place that was at least as stringent as ASHRAE/IES 90.1-2007, according to information available at the DOE's Building Energy Codes Program website (energycodes.gov).

If history is any guide, about 37 states will comply with the new standard, while the other 13 likely will not for various reasons, such as home-rule state constitutions (although there may be significant adoption at the level of local governments). Initial adoption is expected in energy-progressive states, typically those in the Pacific Northwest and the Northeast, and local jurisdictions, such as Seattle and New York City, which often implement even stricter codes than those required at the national level. ASHRAE/IES 90.1-2010 is more comprehensive, more stringent and more complicated than its predecessors, representing the most dramatic revision of the standard since 1999.

Lighting Aspects

ASHRAE/IES 90.1 contains both prescriptive and mandatory provisions. The prescriptive provisions establish maximum-allowed lighting power density (LPD, in watts per square foot), broken down by building and space type. Designers may then choose to comply with the LPD cap on the basis of either building area by building type (Building Area Method), space-by-space basis by space type (Space-by-Space Method), or total building (Energy Cost Budget Method).

The Space-by-Space Method provides more design flexibility than the Building Area Method because it allows the total installed lighting wattage in the building to be calculated by assessing individual spaces, with additional tradable power allowances. It is more precise because the total lighting power allowance is not calculated as a one-size-fits-all value based on a building type, but as the sum of a series of space power allowances, some of which have higher allowances.

ASHRAE/IES 90.1-2010 expands the scope of the standard to explicitly include existing and new construction. If a project includes lamp-plus-ballast retrofits in which more than 10 percent of the connected interior or exterior lighting load is replaced, the lighting in the affected area must comply with the standard's LPD limits and automatic shutoff requirements. If a panelboard upgrade is undertaken to achieve schedule-based shutoff function, some form of override is not explicitly required, but should be included.

Whole-building and space LPD caps are significantly reduced in ASHRAE/IES 90.1-2010, based on modeling using the latest commercially available lighting technologies and current IES light-level recommendations. The maximum lighting power allowance (in terms of energy efficiency) is reduced—by an average 17 percent—in 29 out of 32 building types, with three exceptions, which were given the same or higher power allowances: automotive facilities, hospitals, and hotels.

Two new credits for design are now available that make the Space-by-Space Method more flexible. The first is a power-adjustment credit to help designers account for room geometries that are oddly shaped. The second is a list of power-adjustment credits for using advanced lighting-control strategies in certain office, meeting, education, or retail sales areas, as well as in public spaces. Qualifying strategies range from manual dimming to automatic continuous daylight harvesting, with power-adjustment factors applied to the controlled lighting load of 5 percent to negative 30 percent.

For exterior lighting, a new zone-based system is introduced (LZ0 through LZ4), covering application environments in order of increasing population density, with accompanying higher light levels and associated power allowances. For example, lighting for sales canopies is limited to 0.6 watts per square foot in a rural area, but increases to 1.1 watts per square foot in an urban commercial district. Most applications are expected to fall in the middle categories of neighborhoods and light-industrial districts, which in general have lower power allowances than the last version of the standard

Finally, ASHRAE/IES 90.1-2010 requires that certain documents be turned over to the owner within 90 days of acceptance, including as-built drawings of the lighting and control system, a recommended relamping program, a schedule for inspecting and recalibrating controls, and a complete narrative of how each lighting-control system is supposed to operate, including recommended settings.

Control Aspects

ASHRAE/IES 90.1-2010 contains a comprehensive list of mandatory lighting-control provisions, especially as it recognizes more advanced strategies with power adjustment credits. For more detail, read the full standard.

Automatic shutoff is still a staple, but now it applies to buildings of any size, not merely those larger than 5,000 square feet. Occupancy sensors are now required for a long list of interior applications, from classrooms and lecture halls to restrooms and office spaces up to 250 square feet. Exterior lighting must be controlled by a photosensor, and building façade and landscape lighting must also be controlled by a switch that turns the lights off during the night when they are no longer required.

Interior and exterior lighting must be more flexible, using multilevel control, particularly in spaces where lighting must remain on but is intermittently used, such as stairwells, parking garages, and some exterior spaces. Manual controls must provide a step between 70 and 30 percent of full lighting power. All automatic controls must be either manual-on or must automatically turn the lighting on to not more than half of full lighting power.

Daylight harvesting is now required, and standard 90.1-2010 defines daylight zones around windows, skylights, and roof monitors. If these daylight zones exceed a certain size, the general lighting in the zones must be separately controlled using either a stepped-switching or continuous-dimming controller. More aggressive daylight-harvesting control, including secondary sidelighted daylight zones farther away from windows, is rewarded with power adjustment credits. Also, it is required that perimeter lighting in parking garages automatically lessens in response to daylight.

ASHRAE/IES 90.1-2010 also requires that all lighting controls and systems be functionally tested, and that the construction documents identify who will conduct and certify the testing. All lighting controls and associated software must be calibrated, adjusted, and programmed to operate in accordance with construction documents and manufacturer installation instructions, with specific requirements identified for occupancy sensors, programmable schedule controls, and photosensors.

Going forward, as the next round of commercial building energy codes are adopted, lighting designers will continue to be under pressure to provide lighting solutions that meet ever more strict energy parameters. And lighting practitioners will find new ways to marry design creativity with due diligence.

Craig DiLouie is a contributing editor to ECO-STRUCTURE and a lighting specialist and principal of Zing Communications. This article originally appeared in the May issue of Architectural Lighting magazine.