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What’s New for Lighting in ASHRAE 90.1-2007

State and local governments adopt commercial energy codes to establish minimum energy efficiency standards for the design and construction of buildings.

Most energy codes in the United States are based on ASHRAE 90.1 or IECC. Four out of five states, in fact, have adopted ASHRAE 90.1-1999/2001/2004 or IECC 2001/2003/2006, either verbatim or amended, as their energy code.

ASHRAE 90.1, Energy-Efficient Design of New Buildings Except Low-Rise Residential Buildings became the reference national energy standard in 2002. IECC and the NFPA’s 5000 Building Construction and Safety Code reference ASHRAE 90.1 as an alternative compliance standard. The Energy Policy Act of 2005 also requires all new nonresidential federal buildings to exceed Standard 90.1-2004 by 30 percent.

Developed jointly by American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) and the Illuminating Engineering Society of North America (IESNA), Standard 90.1 was first published in 1975 and was subsequently updated in 1980, 1989, 1999, 2001 and 2004. After 2001, the intention is to update the Standard every three years. In January 2008, ASHRAE published 90.1-2007, enabling states to adopt it or an amended version of it as their energy code.

In terms of lighting, ASHRAE 90.1-2007 clarifies the Standard’s intent and enacts several refinements but otherwise doesn’t revise the lighting power density (W/sq.ft.) limits from the 2004 version, which itself was 20-25 percent more stringent than the 1991/2001 versions.

So what’s new in 90.1-2007?

Code Intent

First, it might be helpful to have a short recap of how the Standard is structured.

The lighting portion of ASHRAE 90.1 includes both mandatory and prescriptive provisions.

Mandatory provisions cover automatic shutoff controls, space controls, additional controls, tandem wiring, exit signs and outdoor building grounds lighting.

The intent is not to dictate design, however, so the Standard is largely prescriptive. Regarding indoor lighting, it establishes maximum allowed lighting power for spaces and buildings, expressed in watts per square foot. The installed lighting power—the aggregate of power used by all of the light fixtures and controls—cannot exceed this allowance.

Section 9.1.4. Luminaire Wattage (b)

Luminaire, or light fixture, wattage is an important consideration because it contributes to the installed lighting power, which cannot exceed the power allowance. Standard 90.1-2007 provides two clarifications to this section.

Standard 90.1-2004 says the wattage of light fixtures with permanently installed or remote ballasts or transformers is the input watts of the maximum lamp/ballast or lamp/transformer combination. The 2007 version also allows the wattage of the fixture to be the input watts of the maximum labeled wattage of the light fixture, which recognizes fluorescent lamp-ballast systems with a multi-tap or multi-level type ballast.

As a result, light fixtures can be specifically labeled to indicate the maximum lamp wattage, and this value can be used for compliance.

Section 9.1.4. Luminaire Wattage (c)

Standard 90.1-2007 also clarifies the criteria for determining the installed lighting power for line-voltage track lighting in Section 9.1.4.

In previous versions, the track lighting must be counted as contributing at least 30W/linear foot of track to the installed lighting power. This was to try to offset a loophole in previous codes that could not account for unlimited track heads added after installation. Unfortunately, this penalizes installations with an actual wattage below 30W.

Various manufacturers began offering devices that limit the current available for the track section to a load closer to the actual lighting design, but acceptance by code inspectors was not guaranteed. Standard 90.1-2007 now officially recognizes these methods, stating that the input watts for line-voltage track fixtures contributing to the installed lighting power can be 30W/linear foot or the wattage limit of either 1) the system’s circuit breaker or 2) another permanent current-limiting device on the system.

Solutions include sub-panels with current-limiting breakers and current-limiter track connectors with a re-settable breaker that trips if the connected load exceeds the current limit.

Section Interior Lighting Power

A number of non-general, separately controlled types of lighting do not have to be counted as part of the installed interior lighting power, such as lighting in casino gaming areas, advertising sign lighting and other listed types.

ASHRAE 90.1-2007 adds to this list furniture-mounted task lighting that is 1) controlled by automatic shutoff and 2) has an integral or nearby wall-mounted switch to the list of exceptions.

This change reinforces the intent that all lighting, including task lighting, should comply with the energy code as long as it’s part of the original lighting design. It also encourages automatic shutoff, which would usually be a fixture-mounted or nearby occupancy sensor.

Section Exterior Lighting Control

All exterior lighting not specifically exempted by the Standard must have automatic shutoff either when sufficient daylight is available or the lighting is no longer required to be operating during the night. Lighting designated for dusk-to-dawn operation therefore must be controlled by a photosensor (daylight) or astronomical time switch (scheduling).

The previous version of ASHRAE 90.1 says that non-dusk-to-dawn outdoor lighting must be controlled by an astronomical time switch. The 2007 version amended this to specify that non-dusk-to-dawn fixtures can be controlled by either a time switch or a combination of 1) an astronomical time switch and 2) a photosensor.

Allowing light fixtures with combined control increases flexibility by allowing the user to decide which is best for the application.

Section 9.6.2. Additional Lighting Power

ASHRAE 90.1 basically offers two compliance paths: Building Area Method and the Space-by-Space Method.

The Building Area Method requires adding up the installed interior lighting power in an entire building and ensuring it’s not greater than the single interior lighting power allowance for the given building type.

The Space-by-Space Method also compares the total installed lighting wattage in the building but allows the user to develop the lighting power allowance based on the specific space types in the building. Each space type has its own power density value and the total allowance is calculated as a space-weighted average of these.

The Space-by-Space Method is more involved but is also more flexible. It also enables claiming additional interior lighting power for certain decorative and retail applications.

First, 90.1-2007 clarifies that additional lighting power is only allowed if the lighting is installed and controlled separately from the general lighting and automatically shut off during non-business hours. This clarification reinforces the Standard’s intent.

Next, 90.1-2007 eliminates Section (b) that is in previous versions, which enabled additional lighting power for VDT applications such as offices with computer screens—a provision introduced to 90.1 years ago, when light levels tended to be higher, fixtures didn’t control glare as well, and computer screens themselves were highly susceptible to glare. Since then, light fixture design and computer screen technology gradually eliminated the need for the allowance; this means the lighting power allowance for open and enclosed office spaces is capped at a total 1.1W/sq.ft.

Finally, the additional lighting power allowances for retail spaces were significantly revised over the previous version. Standard 90.1-2007 says that separately controlled, non-general lighting installed in sales areas and used to highlight merchandise can claim additional lighting power up to but not greater than the wattage of the specified non-general luminaires from the applicable allowance shown in Table 1. These changes were made to increase application clarity and simplicity while reducing the potential for overlighting.

Table 1. Lighting installed in sales areas and used to highlight merchandise qualify for additional lighting power in ASHRAE 90.1-2007.

Change Is in The Air

While 90.1-2007 does not include many major changes, change is in the air nevertheless. ASHRAE is already working on the 2010 version, and many changes have been proposed and approved for the lighting section, with others currently working their way through the process.

ASHRAE 90.1-2010, for example, may require lighting controls for daylighted spaces, manual-on operation for occupancy sensors, incentives for non-mandatory controls, and controls commissioning.

Meanwhile, at the time this article is being posted, ASHRAE had recently posted Standard 189.1P, Standard for the Design of High-Performance Green Buildings Except Low-Rise Residential Buildings, for a second public review.

This Standard, developed jointly by ASHRAE, IESNA and the U.S. Green Building Council, will provide minimum requirements for the design of high-performance commercial buildings, addressing energy efficiency, sustainable sites, water use, materials and resources, and indoor environmental quality.

The lighting section of 189.1 is based on 90.1 but then goes far beyond with more restrictive lighting power allowances and a number of mandatory controls requirements, some of these provisions similar to what may be in store for 90.1-2010.

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1 comment to What’s New for Lighting in ASHRAE 90.1-2007

  • J. Goetz

    I am working on a municipal boardroom in Illinois with maximum capacity of 100. Typical seated usage 60.

    This room broadcasts public hearing meetings on cable televisionso lighting for cameras is required. What is my maximum allowable watts per sq. ft. I saw something about ADP spaces ?

    Thank you

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