Development of Revised Intercept Equations to Update the ASHRAE Standard 90.2-2001 Envelope Criteria PDF

In order to update the envelope criteria in ANSI/ASHRAE Standard 90.2-2001, the Standard 90.2 Standing Standard Project Committee decided to make five major changes so the resulting standard would be acceptable in the code arena. This paper presents the development of the revised intercept equations that are used to determine the envelope criteria and addresses three of those changes. The economic analysis was changed from incremental life-cycle costs to simple payback periods. The ability to account for reductions in the first costs of the HVAC systems with improvements in the envelope was added. Finally, the climatic variable used for cooling was changed from CDH74 (CDH23) to CDD50 (CDD10) in order to be consistent with the U.S. Department of Energy proposal on climate simplification. The intercept equations presented in this paper were used to develop a proposal that updates the ASHRAE Standard 90.2-2001 envelope criteria.