Applying 90.1 in lighting design

ASHRAE Standard 90.1 requires lighting designers and engineers to include power allowances, daylighting controls, functional testing, and submittals in their lighting designs.


This article is peer-reviewed.Learning Objectives:

  • Explain the lighting designer's compliance-path options for ASHRAE Standard 90.1. 
  • Analyze the differences between ASHRAE Standard 90.1-2010 and 90.1-2013.
  • Recall how controls play a role in lighting design.

On Oct. 18, 2013, all states were required by the U.S. Department of Energy (DOE) to put in place a commercial-building energy code at least as stringent as the 2010 version of ASHRAE Standard 90.1. Eight states are in compliance as of October 2013. Most states are expected to adopt ASHRAE 90.1-2010 in whole or in part, adopt the 2012 version of the International Energy Conservation Code (IECC) that references Standard 90.1 as an alternate compliance standard, or develop their own unique code, such as California Title 24. Thirty-seven states are expected to comply based on similar past rulings. The exception is Colorado, which follows home rule.

Figure 1: The lighting design for this DSW retail store met ASHRAE Standard 90.1 requirements. Courtesy: Metro CD Engineering

ASHRAE Standard 90.1 requires lighting designers to include power allowances, daylighting controls, functional testing, and submittals in their lighting designs. Both the 2010 and 2013 versions of ASHRAE 90.1 have changes, including tables, definitions, and sections, with the 2013 version being the most stringent. Energy-savings calculations compared to ASHRAE 90.1-2004 were improved by approximately 25%, including plug loads, and approximately 31% for lighting alone. The DOE liked these improvements, endorsed them, and notified the states that they should adopt Standard 90.1-2010 (or a code that DOE sees as equivalent) by October 2013.

The 2010 standard is much more detailed and stringent than previous versions, with much stronger mandatory lighting control requirements. Commissioning elements including design documentation, and commissioning are now requirements. Projects that are retrofitting light fixtures for which 10% or more of connected lighting load is replaced must satisfy the lighting-power density (LPD) requirements and automatic-shutoff provisions.

LPD values dropped slightly on average from the previous version. Requirements for daylighting and associated lighting controls were added. Many other lighting control requirements were added including independent functional testing of lighting controls, occupancy, vacancy controls, exterior lighting, and whole-building shutoff controls. The most important of the 30 total addenda to the 2010 version are:

  • Exterior LPD requirements expansion (exterior zones)
  • Detailed daylighting control and skylight requirements
  • Occupancy-sensor control (more spaces; vacancy)
  • Exterior-lighting control (after-hours requirements)
  • Parking-garage lighting control (daylighting/after hours)
  • Emergency (night light) shutoff and stairwell control
  • Control incentives for advanced controls
  • Guest room bathroom lighting control
  • Receptacle shutoff control (50% auto-off)
  • Testing (commissioning).

Compliance options

There are two routes for a designer's compliance with ASHRAE 90.1:

  • Prescriptive path: All components of the building meet the minimum standards specified by ASHRAE 90.1.
  • Performance path: A proposed building design is demonstrated (by doing a building energy simulation) to use less energy than a baseline building built to ASHRAE 90.1 specifications. Within the sections of the standard, there are some variations to this. Some sections have mandatory provisions, simplified approaches, and trade-offs.

When using the prescriptive path, ASHRAE 90.1 includes prescriptive requirements for:

  • Section 5, building envelope: minimum wall insulation, minimum roof insulation, roof reflectance, minimum glazing performance
  • Section 6, HVAC: minimum equipment efficiency, minimum system features, limitation on reheat, limitation on fan power
  • Section 7, domestic hot water: minimum equipment efficiency, minimum system features
  • Section 8, power: transformer efficiency, automatic receptacle controls, energy monitoring
  • Section 9, lighting: maximum indoor LPD (expressed in watts per square foot), minimum lighting controls, exterior lighting, parking garage lighting
  • Section 10, other equipment: electric motors, potable-water-booster pumps, elevators and escalators.

In the performance approach, a baseline energy-cost budget (ECB) is established, based on the building size and program. This baseline ECB is established using building energy simulation to model a building with the same size and program as the project building, built according to the prescriptive requirements of ASHRAE 90.1 (Sections 5-10). The ECB is expressed in dollars to calculate savings.

A building energy simulation is then performed on the proposed building design. The ECB proposed must be less than or equal to the baseline energy-cost budget to achieve compliance. The performance approach also is used to demonstrate design energy efficiency, often expressed as a percentage better than a specific version of ASHRAE Standard 90.1. (i.e., "40% better than ASHRAE 90.1-2007). For ASHRAE 90.1-2010 and 2013, there are two methods to achieve the compliance-path/calculation methods.

  • The space-by-space method is about flexibility. Each "space" must be enclosed, and can be broken into smaller pieces. Areas are calculated to the centerline of the wall (interior) or outside surface (exterior). This allows for additional interior-lighting power and room-cavity ratio (RCR) correction.
  • The building-area method is much simpler. To determine the gross lighted-floor area for each area type, multiply by appropriate LPD. Interior LPD = sum of LPDs for various areas of a building and trade-offs among areas are permitted.

Lighting controls

There are significant changes to both the 2010 and the 2013 lighting control requirements. These are separated to help clarify the requirements for each version.

2010: Daylighting control additions

Several changes require control of electric lighting when top- or side-daylight is available as well as installation of skylights where applicable. 2010: Occupancy-based control additions Occupancy sensors control lighting generally required in more spaces. These include but are not limited to conference/meeting rooms and training rooms; classrooms and lecture halls; employee lunch and break rooms; storage/supply rooms of 50 to 1,000 sq ft; rooms used for document copying and printing; dressing, locker, and fitting rooms; office spaces up to 250 sq ft; and restrooms.

2010: Occupancy manual-on control requirement

Automatic control devices shall not be set to automatically turn on lights. This mode of operation requires manual-on or 50% auto-on function for automatic controls. This is commonly known as "vacancy" sensor type of controls. Exceptions (i.e., where automatic-on is allowed) include public corridors and stairways, restrooms, primary building entrances and lobbies, and areas where manual-on operation would endanger safety or security of the space or building occupants.

2010: Bi-level space lighting control

This requires that manually controlled lighting has at least one control step between 30% and 70% (inclusive) of full lighting power in addition to all off. Exceptions: lights in corridors, electrical/mechanical rooms, public lobbies, restrooms, stairways, storage rooms, spaces with only one fixture with rated input power less than 100 W (like a common janitor closet), and space types with a lighting-power allowance of less than 0.6 W/sq ft.

2010: Stairwell 50% reduction control

Stairwell lighting must have automatic control. This applies to lighting in enclosed stairwells, which must have control to automatically reduce lighting power in any control zone by at least 50% within 30 minutes of all occupants leaving the zone.

2010: Receptacle control (2013: now in Section 8, "Power")

Requires that 50% of receptacles in a space have auto-shutoff control and at least 25% of branch-circuit feeders installed for modular furniture were not shown on construction documents (2013 addition). Applies to 125 V, 15- and 20-amp receptacles, private offices, open offices, and computer classrooms. It requires automatic control using time-of-day (TOD) schedule. Also required: occupancy sensors or other automatic control based on occupancy. Exceptions: spaces where automatic shutoff would be a safety/security issue and/or where all loads require 24/7 operation.

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