A newly published document from ASHRAE and IES gives users of their energy efficiency standard immediate access to an optional third path for compliance in ASHRAE Standard 90.1, providing more flexibility for the industry.

Michael Rosenberg, PNNL, energy efficiency standards
Michael Rosenberg, Pacific Northwest National Laboratory


ASHRAE Standard 90.1 is the model energy standard upon which most non-residential energy codes in the United States are based. The standard includes two paths for compliance.

The prescriptive path establishes criteria for energy-related characteristics of individual commercial building components such as minimum R-values of insulation, maximum lighting power allowance, occupancy sensor requirements for lighting control, and economizer requirements for HVAC systems.

The performance path, known as the Energy Cost Budget (ECB) method, provides additional flexibility by allowing a designer to “trade-off” compliance by not meeting some prescriptive requirements if the impact on energy cost can be offset by exceeding other prescriptive requirements, as demonstrated through energy simulation modeling.

In addition to the ECB method, Standard 90.1 includes a second simulation based performance approach, Appendix G, the Performance Rating Method. While similar to ECB, Appendix G is more flexible than ECB but, up to now, has not been allowed for demonstrating compliance.

Instead, Appendix G has been used to rate the performance of buildings that exceed the requirements of Standard 90.1 for “beyond code” programs including USGBC’s LEED Rating System, ASHRAE’s Green Building Standard 189.1, and the International Green Construction Code (IgCC).

Each of the two performance paths in Standard 90.1 get updated every three years to keep up with prescriptive changes when a new version of the standard is released. Because state energy codes and various beyond-code programs reference different versions of Standard 90.1, the landscape can get a little confusing. Figure 1 shows various uses for different vintages of the two performance paths in Standard 90.1.

Because of this, a single project that needed to achieve code compliance, LEED certification, and a federal tax incentive would need three separate building models, leading to confusion and unnecessary expense.


Figure 1. Uses of the Performance Paths in ASHRAE Standard 90.1.
Figure 1. Uses of the Performance Paths in ASHRAE Standard 90.1. Sixteen states have codes that reference the 2007 ver­sion of the ECB method, fifteen states reference the 2010 ECB, and six states reference the 2013 ECB.  LEED Version 2009 references the 2007 version of the Appendix G while LEED Version 4 references the 2010 version. The Federal Energy Management Program (FEMP) requires use of either the 2010 version or the 2013 version of Appendix G depending on the date construction began. The recently expired federal energy efficiency tax incentive program required the use of Appendix G 2004 and ASHRAE Standard 189.1 and the IgCC reference Appendix G 2013.

THAT IS CHANGING. A recent modification (Addendum bm) to Standard 90.1 makes two significant changes for the 2016 version that will be published in October of 2016.

First, it allows Appendix G to be used as a third path for code compliance in addition to rating “beyond code” building performance.

This change will prevent energy modelers from having to develop separate baseline building models for code compliance and beyond code programs. Using this new version of Appendix G to show compliance with ASHRAE Standard 90.1-2016, the proposed building design needs to have a performance cost index (PCI) less than targets shown in a new table based on building type and climate zone.

The second change is that the baseline design is now fixed at a stable level of performance set approximately equal to 90.1-2004. The stringency of the baseline is not meant to change with subsequent versions of the standard. Instead, compliance with new versions of the standard will simply require a reduced PCI (a PCI of 0 is a net-zero energy cost building).

Using this approach, buildings of any era can be rated using the same method. The intent is that any building energy code or beyond code program can use this methodology and merely set the appropriate PCI for their needs.

The multiple uses and stable baseline will encourage the development of software tools that automatically create the baseline building, which will help the market grow and extend the useful life of the software. This will lead to reduced cost and more accurate building energy models. Figure 2 shows the potential impact on programs that rely on the performance paths of Standard 90.1.

Appendix G provides another advantage over the ECB performance path. The baseline in ECB, to which a proposed building design is compared, is in essence a clone of proposed design, with each parameter set at exactly the prescriptive code energy efficiency level. Appendix G on the other hand, uses a more independent baseline where many the parameters are set to standard practice, thus allowing credit for design features that go beyond standard practice.

For example, Appendix G provides credit for appropriate HVAC equipment type selection, “right sizing” of HVAC equipment, optimized building orientation, efficient use of building thermal mass, and optimized window area. This helps to encourage integrated design resulting in lower energy consumption in buildings.


Figure 2. Potential Uses of the Appendix G Performance Path in ASHRAE Standard 90.1-2016.
Figure 2. Potential Uses of the Appendix G Performance Path in ASHRAE Standard 90.1-2016.

IN SUMMARY, the 2016 edition of Standard 90.1 will include a new compliance path that leads to increased flexibility for designers, lower energy modeling costs for building owners, and better recognition of energy efficient design strategies.



Michael Rosenberg’s participation on the ASHRAE Standard 90.1 committee is funded by the U.S. Department of Energy’s Building Energy Codes Program.


Contributor Michael Rosenberg is a Senior Research Scientist and member of the Building Energy Regulatory Analysis Group at Pacific Northwest National Laboratory. He has worked for over 20 years upgrading building energy codes, providing training to code officials and design professionals, designing high performance buildings, analyzing complex building systems, and developing and administering beyond-code energy programs. He is a member of the ASHRAE Standard 90.1 Energy Cost Budget Subcommittee and a former member of the LEED Energy and Atmosphere Technical Advisory Group.