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ASHRAE Releases 90.1-2010–Part 1: Design, Scope, Administrative Requirements

ASHRAE/IES 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings is published every three years to provide states and other jurisdictions with a model commercial building energy code. Today, most states have adopted either 90.1 or the International Energy Conservation Code (IECC), published by the International Code Council (ICC), as their energy code, have a code based on one of them, or publish a state-specific code with similar requirements.

The 2010 version, published November 2010, represents the most dramatic revision of the standard since 1999. Over the past decade, the standard has steadily become more restrictive in terms of allowed lighting power and requirements to install lighting controls. The 2010 version takes both of these trends to a new level with the goal of achieving dramatic energy savings and taking a significant step towards the ultimate goal of net-zero buildings. According to the Department of Energy, commercial buildings designed to ASHRAE/IES 90.1-2010 are expected to achieve 32.6% site energy savings and 30.1% energy cost savings compared to buildings compliant with ASHRAE/IES 90.1-2004, excluding plug loads.

In all, the new ASHRAE/IES 90.1 standard is far more comprehensive, stringent and complicated than its predecessors. Expect early adoption in states and other jurisdictions that are most progressive towards energy conservation, such as the Northeast and Pacific Northwest. To obtain a copy of the standard, visit the ASHRAE bookstore at or the IES bookstore at

“This version of the 90.1 energy standard is definitely aggressive but the developers have taken great care to develop a set of requirement that are fair, practical and effective,” says Eric Richman, LC, senior research engineer for the Pacific Northwest National Laboratory and chair of the ASHRAE 90.1 Lighting Subcommittee. “As with all energy codes, there will be conflicts for some applications and building or space types. It is hoped that when these occur, the building owner and local building officials can follow the intent of the standard and craft an energy-effective yet practical solution.”

In this two-part series of special reports by the Lighting Controls Association, we will examine the new energy standard in detail. Part one, presented here, focuses on changes to the prescriptive lighting power requirements as well as changes to scope and administrative requirements. Part two, to be published next month, will focus on the standard’s extensive list of new mandatory and optional lighting control requirements.

Lower lighting power allowances

ASHRAE/IES 90.1 imposes limits on the amount of lighting power installed in the building, expressed in watts per square foot (or W/linear ft.), to promote efficient technology and design. These lighting power densities (LPDs) apply to interior and exterior applications. It is the designer’s job to design a lighting system that satisfies the owner’s requirements within the given LPD limit.

The 90.1 standard is considered friendlier to designers than current versions of the IECC code because it provides LPDs for individual space types in addition to whole building types, which provides more flexibility (but is more cumbersome to enforce, which is why IECC, written by code officials, does not include a space by space method). In ASHRAE/IES 90.1, designers have a choice of using the Building Area Method (whole building power allowance) or Space by Space Method (individual spaces, with potential additional and tradable allowances).

In the 2010 version, the majority of whole building and space LPDs are reduced by varying amounts, based on modeling that incorporated the latest off-the-shelf energy-efficient technologies and current IES light level recommendations.

Power adjustment credit for odd room geometries. If using the Space by Space Method for designing lighting systems in interior spaces, a new adjustment credit is available for rooms with odd geometries, increasing flexibility even further.

“The 2010 Standard will now provide a room geometry-based adjustment to interior space type LPDs based on the room cavity ratio (RCR) of the empty room,” says Richman. “This is in recognition of the fact that the current LPDs simply don’t have much play in them, are based on typically expected room geometries, and that not all room geometries for a specific space type are the same.”

In review, RCR is calculated as (2.5 x room cavity height x room perimeter length)/room area, with room cavity height being the distance in feet between the light fixtures and the workplane. The adjustment is allowed when RCR for a given room can be shown to be greater than the threshold RCR that is tied to the LPD allowance as shown in a table provided in the standard. It also applies to corridor/transition spaces that are less than 8 ft. wide regardless of RCR. In these cases, the LPD allowance can be increased by the LPD for the space type x 0.20.

“It won’t be an easy adjustment to get,” says Richman. “The RCR thresholds in the standard are not particularly loose but those spaces that do need extra allowance for their odd geometries will be able to get it.”

Power adjustment credit for advanced lighting controls. Although controls will be covered in more detail in next month’s whitepaper, it is important to point out here that ASHRAE/IES 90.1-2010 offers lighting power adjustment credits based on use of advanced lighting control strategies. Qualifying applications include certain offices, meeting spaces, education spaces, retail sales areas and public spaces. Qualifying technologies range from manual dimming control to automatic continuous daylight harvesting dimming, with power adjustment factors, which are applied to the controlled lighting load, of 5-30%.

“When a lighting control system is installed that is more advanced—higher energy-saving capability—than the controls required in the standard, an incentive in the form of additional lighting power is allowed,” says Richman. “Because the 2010 version of the standard is aggressive in terms of controls, users will find that the controls needed to go beyond the requirements and enable getting the additional allowance will be advanced and more complicated but will also provide additional energy savings.”

Exterior lighting power allowance section expanded for lighting zones. In recent versions of 90.1, the exterior lighting section has evolved to impose lighting power allowances similarly to the way interior lighting power allowances are treated, effectively creating a Space by Space Method addressing outdoor lighting. A large number of outdoor lighting applications are identified covering virtually all possible applications from building façade to parking lot, with some applications considered “tradable” (you can take wattage savings in one applications and give those watts to another applications) and some “nontradable.”

In ASHRAE/IES 90.1-2010, the evolution continues with the introduction of Lighting Zones 0-4 covering application environments in order of increasing population density (and increasing light level requirements due to assumed higher level of ambient light from other sources in the surrounding environment), from undeveloped areas through high-activity commercial districts. The result is a matrix crossing outdoor application with these lighting zones, resulting in customized power allowances by zone.

“This change is based on the current lighting community understanding that exterior lighting needs are partially based on the level of surrounding light,” Richman explains. “Exterior applications in areas with bright surrounding night need higher light levels to provide appropriate contrast and eye adaptation. The table of allowances has been split into zone sections and the allowances increased or decreased accordingly. With this version of the standard, the exterior allowances will be applied based on the exterior zone type.”

For example, lighting for sales canopies is limited to 0.6W/sq.ft. in developed areas of national and state parks, forest land and rural areas, but this is increased to 1W/sq.ft. in high-activity commercial districts in major metropolitan areas.

“It is expected that most exterior environments will fall in the middle categories of neighborhood districts and light industrial,” Richman adds. “These categories have generally lower allowances than the previous single category, which included major metropolitan high-activity commercial districts and was therefore set high to cover these areas. The expected impact is that each site will have more specific and appropriate allowance with a general reduction in exterior lighting energy use across the country.”

Table 1. ASHRAE/IES 90.1 lighting power allowances using the Building Area Method.

Building Type Maximum Lighting Power Density (W/sq.ft.) Allowed Per Version of the ASHRAE/IES 90.1 Standard
1989 1999/2001 2004/2007 2010
Automotive Facility 0.96 1.5 0.9 0.982
Convention Center 2.07 1.4 1.2 1.08
Court House 1.44 1.4 1.2 1.05
Dining: Bar Lounge/Leisure 1.37 1.5 1.3 0.99
Dining: Cafeteria/Fast Food 1.37 1.8 1.4 0.90
Dining: Family 1.37 1.9 1.6 0.89
Dormitory 1.15 1.5 1.0 0.61
Exercise Center 2.07 1.4 1.0 0.88
Gymnasium 2.07 1.7 1.1 1.00
Healthcare Clinic 1.44 1.6 1.0 0.87
Hospital 1.44 1.6 1.2 1.21
Hotel 1.15 1.7 1.0 1.00
Library 1.29 1.5 1.3 1.18
Manufacturing Facility 0.96 2.2 1.3 1.11
Motel 1.15 2.0 1.0 0.88
Motion Picture Theater 2.07 1.6 1.2 0.83
Multi-Family 1.15 1.0 0.7 0.60
Museum 2.07 1.6 1.1 1.06
Office 1.26 1.3 1.0 0.90
Parking Garage 1.03 0.3 0.3 0.25
Penitentiary 1.44 1.2 1.0 0.97
Performing Arts Theatre 2.07 1.5 1.6 1.39
Police/Fire Station 1.44 1.3 1.0 0.96
Post Office 1.44 1.6 1.1 0.87
Religious Building 2.07 2.2 1.3 1.05
Retail 2.25 1.9 1.5 1.40
School/University 1.29 1.5 1.2 0.99
Sports Arena 2.07 1.5 1.1 0.78
Town Hall 1.44 1.4 1.1 0.92
Transportation 2.07 1.2 1.0 0.77
Warehouse 1.03 1.2 0.8 0.66
Workshop 0.96 1.7 1.4 1.20

Tandem wiring

The mandatory requirement related to tandem wiring in previous versions of the standard is now eliminated. “This requirement was aimed directly at eliminating the use of older standard magnetic ballasts that are designed to drive two T12 lamps and have unnecessary losses when only driving one lamp,” explains Richman. “The current reality is that this older technology is simply not an option anymore for new or retrofit projects, so the language was removed.”

Coverage of lamp/ballast retrofits

Traditionally, 90.1 and IECC have covered new construction and major renovations. Lamp and ballast replacement is typically considered maintenance and not an alteration or repair, resulting in retrofits being traditionally ignored by code officials.

ASHRAE/IES 90.1-2010 now explicitly covers “maintenance-like” lamp plus ballast (lamp/ballast) retrofits in both indoor and outdoor applications. Specifically, if a building owner replaces lamp/ballast systems representing 10% or more of the connected lighting load in an indoor space or outdoor area, the owner must comply with the standard’s lighting power density limits and also its automatic shutoff requirements.

First, the proposed retrofit lighting power will have to be no greater than the maximum allowable lighting power density (LPD, expressed in watts per square foot) for the given building or space. Next, the lighting will have to be turned OFF automatically when it is not being used. Recognized methods include a schedule (e.g., programmable low-voltage relay control system), occupancy sensors that turn the lights OFF within 30 minutes of the space being vacated, and a signal from another control or alarm system that indicates the area is unoccupied (e.g., security or building automation system). Exceptions include lighting that must operate continuously, lighting where care is given to patients, and lighting where automatic shutoff would endanger occupants. (The retrofit does not further trigger the space controls section of the standard, but if a panelboard upgrade were to be undertaken to gain lighting automation capability, some type of manual override control should be provided as a common sense measure ensuring occupant safety.)

The result is some regulation for lamp/ballast retrofits that previously were typically considered not covered by code. Projects may require inspection depending on the authority having jurisdiction. Half-measures will no longer be acceptable for retrofits due to the requirement to achieve lower LPD levels. Again, the retrofit must be lamps plus ballasts, so lamp-only retrofits can presumably still be performed without having to satisfy the code. Requiring controls in retrofits may change the economics of some retrofit projects while requiring that practitioners achieve a high level of proficiency with lighting control application, installation and functional testing.

“This is a major change but is considered important because a majority of lighting efficiency opportunities are found in the large fraction of projects that are retrofit rather than new construction,” says Richman. “These requirements will likely force more thought behind the lamp and ballast retrofit to ensure the right equipment is used to meet the LPD limits. The additional control requirement may seem intrusive, but this is only the simple shutoff requirement that can be met with a whole building system or individual low-cost occupancy sensors or some other system. As with all requirements, there are some exemptions and allowances that will provide relief in appropriate situations.”


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

“This documentation requirement is intended to ensure that the new owner and/or operator of the lighting systems has the information needed to understand their operation, plan for future maintenance, and address any configuration concerns,” says Richman. “The requirements are fairly straightforward encompassing the need to provide drawings, operation and maintenance manuals on equipment, and narratives on the operation of each control system. Most of these are standard items that these requirements now ensure will be completed and provided.”

Next month: Part 2 of this article, where we will talk about ASHRAE/IES 90.1-2010’s dramatically expanded requirements for lighting controls.

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1 comment to ASHRAE Releases 90.1-2010–Part 1: Design, Scope, Administrative Requirements

  • Joseph Dableh

    Congratulations on a job well done. This is a fantastic development that could not have come to the lighting industry a day too soon.

    I say, this is very timely because today we have the technology to achieve and exceed all of these new requirements and to do so at an economically compelling price. The economical case for all of these new measure is made not only for new construction, but also for retrofit applications.

    I am doubly delighted with this driving force to adopt new lighting control technologies because with wide spread adoption of these new control technologies the prices will inherently drop as a function of volume and as such these new disruptive technology will become the mainstay of the industry.

    Great stuff and a well timed requirement to realize a very low hanging fruit of energy savings in all indoor and outdoors lighting system.

    Best regrad.

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