TREAT complies with Home Energy Rating System Building Energy Simulation Test (HERS BESTEST). HERS BESTEST is a verification procedure developed by the National Renewable Energy Laboratory (NREL) to determine the accuracy and effectiveness of the energy load prediction capability of software tools. The validation methodology consists of comparative testing – in which results from software programs are compared to results from other software programs. The comparative approach includes both ‘sensitivity testing’ and ‘intermodal comparisons’. It uses a wide variety of building configurations and characteristics as test cases for the evaluation. The comparative procedure uses results from three widely-used and well- validated, detailed building energy simulation software programs to develop a range of reasonable results for each of the test cases. The reference programs used to generate the test case results are:


  1. BLAST 3.0, Level 215: Developed by the U.S. Department of Defense for use in analyzing energy efficiency improvements for their buildings.
  2. DOE2.1E-W54: At the time of HERS BESTEST Development, DOE2.1E was considered to be the most advanced of the programs sponsored by the U.S. Department of Energy and the technical basis for setting national building energy codes and standards in the United States.
  3. SERIRES/SUNCODE 5.7: SERIRES is a public domain program developed by NREL. SUNREL, the calculation engine behind the TREAT software, was developed as an upgrade to SERIRES.

The results from these three reference programs are then statistically analyzed to determine the 90% confidence interval for each set of test case results. These 90% confidence intervals establish the range of acceptable results for each test case. The National Association of State Energy Officers’ (NASEO) National Home Energy Rating Technical Guidelines and the Mortgage Industry’s National Accreditation Procedures for Home Energy Rating Systems require that home energy rating software tools “pass” each test for each building configuration that the rating system software intends to evaluate. HERS BESTEST procedures describe two ‘Tiers’ of software test cases – Tier 1 and Tier 2.

BESTEST Tier 1 tests consist of exercising the elements of a basic house with typical glazing and insulation. Specific Tier 1 tests are designed to test a program’s ability produce energy consumption and savings results as described below. BESTEST Tier 2 tests are more focused on testing a software program’s ability to guide passive solar design, and are not addressed in this document.

Note: Software is considered to ‘pass’ a HERS BESTEST Tier if it passes ALL tests included within the Tier.


RESNET Accreditation

TREAT v 3.4 is RESNET Accredited as an Existing Homes Tax Credit Compliance Tool

Several of TREAT’s internal calculations have been improved and validated against the RESNET accreditation suite, which includes the following tests:

  1. HERS BESTEST Tier 1 Tests
  2. RESNET DHW Tests
  3. RESNET HVAC Tests
  4. RESNET DSE (Distribution System Effectiveness) Tests
  5. RESNET Heating and Cooling TestsL125A