The Building Energy Simulation Test for Existing Homes (BESTEST-EX) is a method for testing home energy audit software and associated calibration methods. BESTEST-EX is one of the energy analysis tools developed by NREL on behalf of the U.S. Department of Energy (DOE).
Residential buildings in the United States accounted for about 22% of national annual primary energy consumption in 2008, according to DOE's Buildings Energy Data Book. Reducing the energy use of existing homes offers significant energy-saving opportunities, which can be identified through building simulation software tools that calculate optimal packages of retrofit measures. To support the larger effort of assessing and improving the accuracy of energy analysis for residential buildings, the NREL Buildings Research team developed BESTEST-EX, a method for testing the accuracy of building energy audit software and calibration procedures.
BESTEST-EX is a test procedure that allows software developers to evaluate their audit tools' performance in modeling energy use and savings in existing homes when utility bills are available for model calibration. Similar to energy analysis tests previously developed by NREL, such as HERS BESTEST and other BESTEST suites included in ANSI/ASHRAE Standard 140, BESTEST-EX compares software simulation findings to reference results generated with state-of-the-art simulation tools such as EnergyPlus, SUNREL, and DOE2-1E.
BESTEST-EX includes two types of test cases: building physics and utility bill calibration. Learn more about these test cases by selecting the appropriate button on the right.
Through development of BESTEST-EX, NREL researchers aim to increase the quality and accuracy of energy analysis tools for the building retrofit market. The BESTEST-EX methodology:
- Tests software predictions of retrofit energy savings in existing homes
- Ensures building physics calculations and utility bill calibration procedures perform up to a minimum standard
- Quantifies impacts of uncertainties in input audit data and occupant behavior.
BESTEST-EX is targeted primarily to developers of energy audit tools who want to evaluate their software's ability to predict energy use and savings. In addition, retrofit building managers and utility program managers may find the BESTEST-EX methodology useful in comparing their building simulation tools to "state-of-the-art" analysis software.
BESTEST-EX currently addresses retrofit measures related to the building envelope such as air tightness, attic and wall insulation, windows, thermostat control, reflective (cool) roofs, and external shading. Additional retrofit measures are being considered for future versions of BESTEST-EX. Supplemental test cases for comparing software tools to empirical data are also being considered.
The first generation of this multi-generational software test suite is complete and existing cases are continually being refined.
To help formulate and vet the test procedures, NREL formed the BESTEST-EX Working Group. Participants include audit software developers, NREL researchers, and DOE program managers. Please contact the NREL research team if you would like more information about the Working Group.
The following documents are available as Adobe Acrobat PDFs.
Overview and Methodology
- Overview of BESTEST-EX
- Building Energy Simulation Test for Existing Homes (BESTEST-EX) Methodology
- Technical Highlight: NREL Improves Building Energy Simulation Programs Through Diagnostic Testing
Test Suite Documents
- Building Energy Simulation Test for Existing Homes (BESTEST-EX): Instructions for Implementing the Test Procedure, Calibration Test Reference Results, and Example Acceptance-Range Criteria
- Building Energy Simulation Test for Existing Homes (BESTEST-EX)
- Example Procedures for Developing Acceptance Range Criteria for BESTEST-EX
Additional Background Materials
- What Did They Do in IEA 34/43? Or How to Diagnose and Repair Bugs in 500,000 Lines of Code
- Model Validation and Testing: The Methodological Foundation of ASHRAE Standard 140
- A Comparative Validation Based Certification Test for Home Rating System Software
- Assessing and Improving the Accuracy of Energy Analysis for Residential Buildings
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