Five steps to success with ASHRAE 90.1

ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings is one of the main drivers used in any building design. Read the top five best practices for engineers to understand the key elements of this standard.


This article is peer-reviewed.Learning Objectives

  • Define ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings.
  • Demonstrate how ASHRAE 90.1 and other codes and standards influence the design of building systems.
  • Compare the prescriptive and performance paths to meeting code and standard requirements.

Energy codes are adopted and enforced differently in every state. Some have statewide energy codes, while others have exempt jurisdictions with their own local code departments. ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings does a lot to influence the design of buildings, but it is not always a direct influence.

Most jurisdictions adopt a version of the International Energy Conservation Code (IECC), which is often viewed as a codified version of ASHRAE Standard 90.1 even though they are developed independently. A few jurisdictions do adopt Standard 90.1 as their energy code, but the application of 90.1 to projects is largely through above code programs, such as U.S. Green Building Council's LEED program, and as an alternate compliance path to the parallel edition of the IECC.

The 2015 IECC and ASHRAE 90.1-2013 are considered to be parallel standards because Standard 90.1-2013 is an alternate compliance path. If the 2015 IECC has been adopted, either standard may be used for compliance (unless a local amendment doesn't allow it). Generally, ASHRAE 90.1-2013 is seen as more stringent than the 2015 IECC (see Figure 2). They have some requirements that are very similar, such as prescriptive window-to-wall ratio (WWR) limits, and others that are different, like the prescriptive "additional efficiency" packages. They even have different mandatory requirements. For instance, automatic receptacle controls have been a mandatory requirement for certain space types because ASHRAE 90.1-2010, but they still haven't appeared as a requirement in any of the currently published versions of the IECC.

For this reason, design teams should weigh which would be the most appropriate standard on a project-by-project basis. Requirements between the two standards cannot by mixed and matched.

Figure 1: The University of Florida Joseph Hernandez Hall is a chemistry and chemical biology lab designed to achieve U.S. Green Building Council LEED NC v2009 Gold. The design incorporates exhaust system heat recovery, daylight harvesting, occupancy sensASHRAE 90.1-2013 should be considered more often as a path to compliance. If a project can incorporate the more stringent mandatory requirements of ASHRAE 90.1-2013, then a project can take advantage of the lack of additional efficiency packages in the prescriptive path or the lower compliance threshold in the performance path. The 2015 IECC requires the design energy cost to be less than or equal to 85% of the standard reference design (baseline) rather than just being less than or equal to as in ASHRAE 90.1-2013. Here are five steps to move a project to compliance with ASHRAE 90.1-2013:

  1. Review mandatory requirements
  2. Assess the prescriptive path
  3. Evaluate the performance path
  4. Decide on the compliance path
  5. Perform compliance calculations and documentation.

Standard 90.1-2013 has two paths to compliance: the prescriptive path and the performance path. Both paths require that all mandatory requirements be met. The prescriptive path is a straightforward recipe for compliance but is restrictive in that all items must be met. The performance path is more flexible in that nearly any component's performance can be traded off for something else, but it requires energy modeling-and more effort on the part of the design team. That effort typically involves collaboration between the architect and engineer on an integrated design and can result in a much higher quality end product. For example, the energy model could be used to show how glass with a lower solar-heat-gain coefficient (SHGC) reduces peak cooling loads.

Review the mandatory requirements

Mandatory requirements are exactly what the term implies: There is no alternate path around them. The entire project team needs to review the mandatory requirements to ensure every discipline includes them in their design. Not including a mandatory requirement causes the entire project to be noncompliant.

Minimum mechanical equipment efficiencies have been mandatory since the first edition of Standard 90 was published in 1975. For the first time, minimum efficiency requirements have been added for commercial refrigeration equipment and commercial refrigerators and freezers. The space types that are required to have automatic receptacle control have been expanded to include conference rooms, print/copy rooms, break rooms, and classrooms. Previously, they were only required in private offices, open offices, and computer classrooms.

A requirement also was added in the power section for separate electrical-energy monitoring for total electrical energy, HVAC systems, interior lighting, exterior lighting, and receptacle circuits. Significant changes have been made to the interior lighting controls. The space-by-space lighting-power density (LPD) table has been revised to include the minimum lighting control requirements per space type using the nine types of lighting controls introduced in ASHRAE 90.1-2013, section The possible lighting control functions from section are:

  • Local control
  • Restricted to manual on
  • Restricted to partial automatic on
  • Bi-level lighting control
  • Automatic daylight responsive controls for sidelighting
  • Automatic daylight responsive controls for toplighting
  • Automatic partial off
  • Automatic full off
  • Scheduled shutoff.

Table 9.6.1 divides the lighting control functions into columns and the space types into rows. All lighting control functions with REQ in their column for a space type are required. When ADD 1 or ADD 2 appears in the row for a space type, at least one of the ADD1 functions and one of the ADD2 functions must be used for that space type.

There are exceptions to the lighting control function requirements, though. For example, enclosed offices less than 250 sq ft are required to have automatic daylight responsive controls for sidelighting, but exception 2 says it is not required if the total glazing area in that space is less than 20 sq ft.This is why it's important to start with the lighting control functions in the table and cross-check the specifics of their requirement and exceptions in the text of section

Another important distinction is that if ASHRAE 90.1-2013 is chosen as a compliance path to the IECC, only the mandatory requirements of Standard 90.1 must be met. This distinction is especially important if a project is also seeking certification with an above code program in addition to meeting minimum code compliance, which does not provide a certification. If an IECC compliance path was chosen, then the mandatory requirements of both the IECC and the above code program standard must be met.

For example, if a project is pursuing certification under LEED v4 and the energy code is the 2015 IECC, the project would have to meet the mandatory requirements of ASHRAE 90.1-2010 and the 2015 IECC.

To further complicate things, if Standard 90.1-2013 is chosen as the compliance path for the 2015 IECC, then the mandatory requirements of both standards 90.1-2010 and 90.1-2013 would have to be met.

No requirements from the 2015 IECC would need to be included even though it is the adopted code. It is important to talk to the authority having jurisdiction (AHJ) in advance to ensure they understand how you intend to comply with the adopted code when using a compliance path with which they may not be as familiar.

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