Using EnergyPlus for California Title-24 compliance calculations

LBNL-61527 USING ENERGYPLUS FOR CALIFORNIA TITLE-24 COMPLIANCE CALCULATIONS Joe Huang 1 , Norman Bourassa 2 , Fred Buhl 1 , Ender Erdem 1 , Rob Hitchcock 1 Lawrence Berkeley National Laboratory, Berkeley CA California Energy Commission, Sacramento CA ABSTRACT For the past decade, the non-residential portion of California’s Title-24 building energy standard has relied on DOE-2.1E as the reference computer simulation program for development as well as compliance. However, starting in 2004, the California Energy Commission has been evaluating the possible use of EnergyPlus as the reference program in future revisions of Title-24. As part of this evaluation, the authors converted the Alternate Compliance Method (ACM) certification test suite of 150 DOE-2 files to EnergyPlus, and made parallel DOE-2 and EnergyPlus runs for this extensive set of test cases. A customized version of DOE-2.1E named doe2ep was developed to automate the conversion process. This paper describes this conversion process, including the difficulties in establishing an apples-to-apples comparison between the two programs, and summarizes how the DOE-2 and EnergyPlus results compare for the ACM test cases. Title-24 standards, the Commission has been evaluating the possible future replacement of DOE-2.1E by EnergyPlus as the reference building simulation program. The technical reasons for such a move are compelling. DOE-2.1E is now over 13 years old and no longer being maintained by the Department of Energy (DOE) or any other public or private entity, except for minor bug fixes. As newer technologies appear on the marketplace, there will be increasing difficulty in modeling them using DOE-2.1E. 2 EnergyPlus is a major new building-energy-simulation program under development by DOE since 1996 (Crawley et al. 2004). In support of the Commission’s interest in evaluating the use of EnergyPlus for Title-24, a previous project in 2004 compared the features and capabilities of DOE-2.1E and EnergyPlus for modeling Title-24 measures (AEC 2005). That project concluded, from an algorithmic point of view, there were numerous improvements and benefits in migrating from DOE- 2.1E to EnergyPlus, but raised concerns about the usability of EnergyPlus and suggested a measured approach towards this transition. The work described in this paper represents the first quantitative comparison of the two programs, using the ACM certification suite as a ready-made comprehensive set of tests for various changes in building shell, equipment, and operations in different California climates. The Commission has a vested interest in knowing how much the calculated energy performance of different conservation measures would change should EnergyPlus replace DOE-2.1E as the reference program. A large amount of political capital has been invested over the years in promoting Title-24 as a rational building energy standard, and both the Commission staff and the building industry are now familiar with the compliance levels and trade-off procedures. A sudden change in the calculated results, particularly a sizeable shift in the relative performance of different conservation measures, will be problematic and may damage the integrity of the building standard. BACKGROUND California has had a set of comprehensive building energy standards (Title-24) since the late 1970’s, all of which have been developed through use of computer simulations. For the non-residential portion of Title-24, the reference computer simulation program for the past decade has been DOE-2.1E (Winkelmann et al. 1993). To be certified as an Alternate Compliance Method (ACM), any commercial compliance software must be run through a rigorous suite of 150 test cases established by the California Energy Commission (hereafter referred to as the Commission) to demonstrate that the software produces results consistent with benchmark values maintained by the Commission. 1 To date, all candidate compliance programs use DOE-2 for their simulation engine, so the primary function of the certification process is to ensure that the inputs and modeling procedures are as prescribed. However, entering the latest round of revisions for 2008 In actuality, the benchmark DOE-2 files were also produced by one of the compliance software venders, so that the ACM certification is not entirely a double-blind process. Even for the 2005 standards, there are already several energy features that are being modeled outside of DOE-2.1E.