How ASHRAE Standard 90.1 contributes to integrated design

ASHRAE Standard 90.1 is under continuous maintenance. This article focuses on the recent evolution of this standard, the impact on energy and performance, the design process, and how human interaction can improve energy efficiency.


This article has been peer-reviewed.
ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings
has been the benchmark for defining energy-efficiency and simulation procedures in the built environment since its inception in 1975. It is a fluid document, designed to define the minimum level of energy efficiency while being mindful of the limits of technology and value proposition of lifecycle cost.

As of the 2001 version, this standard is published in its entirety every 3 years. The period between publishing cycles allows for review, comment, and approval of new content. It is also common for addenda to be issued between the formal updates. The evolution from the 2010 to the 2013 edition helps engineers and designers understand how an integrated design process provides the most efficient means of planning for, and applying, the principles held within.

ASHRAE Standard 90.1 provides the minimum benchmark for energy-efficient design practices for building envelope, HVAC systems, water heating systems, power, and lighting. This standard also provides one of the most recognized procedures for energy simulations of facilities.

Figure 1: The new Library and Student Resource Center at the Los Angeles Community College District’s Harbor College is designed to achieve U.S. Green Building Council LEED Platinum certification. Its signature design element is a bold southern facade with exterior louvers that reduce solar heat gain. All graphics courtesy: DLR Group

Although Standard 90.1 is respected by many jurisdictions, it is not necessarily recognized as a code for all jurisdictions in the United States. Therefore, the requirements of Standard 90.1 can be followed by the design professional, but enforcement by the local authority having jurisdiction (AHJ) is generally limited to the applicable building or energy conservation code.

This standard does influence many other building codes. Building envelope (sometimes called building enclosure) is a good example of how this works. In the 2007 version, the requirement for continuous insulation started to appear in many building types for most climate zones. These requirements appear in the 2009 version of the International Energy Conservation Code (IECC). These codes began to be adopted in 2010, and projects started hitting the streets in 2011. There are numerous examples of other technical features and model building codes. Many jurisdictions recognize ASHRAE 90.1 as an acceptable compliance path for energy performance.

Changes to note


The significant changes in the 2013 version include: building envelope, HVAC, energy simulation procedures, and lighting. As the design professional might expect, the modifications generally impose stricter requirements on design elements. This standard also gives more details and requirements for computer room environments. Major changes in the 2013 version include more clarifications and provisions for optimizing natural daylighting and artificial lighting control. The Dept. of Energy, in an announcement in the Federal Register on Sept. 26, 2014, estimated that the ASHRAE 90.1- 2013 energy efficiency standard contains 8.5% source energy savings and 7.6% site energy savings compared to the 2010 version.

Figure 2: The Elk Grove Center in Elk Grove, Calif, is a satellite campus of the Cosumnes River College. The design combines exterior screens and a light shelf to optimize views to outside, solar gain, and natural daylight.

The changes in the 2013 version that affect building envelope modify the requirements for opaque elements and fenestrations. 

These include a simplification of skylight requirements, requirement of double pane glazing in most climate zones, and the additional requirement of a minimum visible transmission (VT)/solar heat gain coefficient (SHGC) ratio. The point of this ratio is to balance daylighting capabilities with heat gain through fenestrations.

The HVAC equipment performance requirements are stricter in the 2013 version. Fan efficiency requirements have been added to the standard for the first time. There also are increasing coverage and strategies for systems required to be controlled by building automation systems (BAS). An example of the impact of these changes can be found in the stricter performance requirements for heat pumps. ASHRAE Standard 90.1 Table 6.8.1-2 shows performance improvements required for ground-source, water to air heat pumps (see Table 1).

Table 1: This provides a summary of the data taken from various versions of ASHRAE 90.1. Data from ASHRAE Standard 90.1-2010 and 2013. Courtesy: DLR Group

The requirements for building simulation procedures continue to evolve in the 2013 version. Significant changes in simulation procedures include: new data tables for applying glazing areas; envelope infiltration calculations; modifications to calculation procedures for assembly areas; heat rejection equipment, such as cooling towers; more provisions for dealing with computer room environments; and additional information to improve the simulation of natural daylighting to predict energy conservation opportunities.

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