To comply with ASHRAE's energy conservation standard, users must test energy analysis computer programs with the society's Standard 140. ANSI/ASHRAE Standard 140-2004, Standard Method of Test for the Evaluation of Building Energy Analysis Computer Programs, specifies test procedures for evaluating the technical capabilities and ranges of applicability of computer programs that calculate the thermal performance of buildings and their HVAC systems.

"A state-of-the-art whole building energy simulation computer program may have on the order of 100,000 lines of computer code," Ron Judkoff, director of the Buildings and Thermal Systems Center at the National Renewable Energy Laboratory, Golden, CO, and chair of the committee that wrote the standard, said. "Even a minor typo in a single line of code can have significant and not easily knowable negative consequences for the results produced by the program. Many consultants use computer simulation in their professional practice for the design of building HVAC systems. For these reasons, ASHRAE Standard 90.1 requires that whole building energy computer simulation software be tested with Standard 140."

Standard 140 is referenced by ANSI/ASHRAE/IESNA Standard 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings. Software to be used to show compliance with the 90.1 performance path is now required to be tested in accordance with Standard 140.

The standard now contains a test suite for the modeling of air-conditioning equipment. An initial test suite in the 2001 standard emphasized fundamental heat and mass transfer mechanisms of the building fabric or envelope. However, the standard also defined a theory and framework for creating and adding additional test suites on other aspects of building energy performance, such as the modeling of air-conditioning equipment.

An added benefit of the standard's method of test is the diagnostic power of the procedure, which helps program authors debug and correct software errors.