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Maintaining RESNET as the Gold Standard for Measuring and Labeling of a Home’s Energy Performance Enhancing the Consistency of the Calculation of HERS® Index Scores

Jun 4, 2018


What RESNET has Accomplished To Date and What is Planned for the Future

A key to ensuring the quality of HERS® ratings is to enhance the consistency which the various accredited HERS® software programs calculate HERS® Index scores. Too often in the past, the same home could receive a different score based upon the software program being used.

For the past four years, the RESNET Board has strived to enhance the consistency of the calculation of HERS® Index Scores. It is important to remember the steps that RESNET has taken to date to have more consistency in the calculation of HERS® Index Scores.

What Has RESNET Accomplished To Date

  • Adoption of the RESNET Publication No. 002, “Procedures for Verification of RESNET Accredited HERS® Software Tools”. The publication sets a suite of tests that HERS® software programs must pass in order to be accredited by RESNET. The suite of tests are:
    • The HERS® Method Tests – verify whether the software tools can accurately calculate the HERS® Index Score.
    • ANSI/ASHRAE Standard 140-2011, Class II, Tier 1 Test tests the accuracy of the software to model the base loads of a home
    • HERS® Reference Home Auto-Generation Tests – verify the ability of the software tool to automatically generate the HERS® Reference Home.
    • HVAC Tests – verify the accuracy and consistency with which software tools predict the performance of HVAC equipment, including furnaces, air conditioners, and air source heat pumps.
    • Duct Distribution System Efficiency Tests – verify the accuracy with which software tools calculate air distribution system losses. ASHRAE Standard 152 results are used as the basis for the test suite acceptance criteria.
    • Hot Water System Performance Tests – determine the ability of the software to accurately predict hot water system energy use.
  • Established limits on input variables for whole-house ventilation systems
  • Incorporated bounds checks into software to limit or warn HERS® raters when input values are beyond reasonable limits
  • Established QAD flags for internal inconsistencies that should be checked prior to entering a building file into RESNET registry
  • Adoption of RESNET/ICC ANSI Standard 301


Improvements Planned for 2018

While important strives has been accomplished over the past few years RESNET believes that there is still much to be done.  The following are planned for 2018:

  • Development of a RESNET Building Input Common Schema. A common schema would be a file format with a standardized set of building input fields that facilitates the exchange of data/information between the accredited HERS® software tools.  This will lead to greater consistency in the input of data and calculation of HERS® Index scores.
  • Formation of a Continuous Improvement HERS® Software Collaborative Modelling Process.  On April 19, 2018, the RESNET Board took another giant step forward with the adoption of a HERS® Software Consistency Collaborative Modeling Process. This process will allow RESNET to improve consistency of HERS® Index scores and modeled energy consumption among RESNET accredited software tools and enhance accreditation testing parameters. This is intended to be a continuous, ongoing process to improve consistency.

The key feature of the process is the formation of a formal RESNET Board standing committee, the Software Consistency Committee (SCC). The SCC will have one primary purpose – to hear, evaluate, and respond to software modeling consistency inquires put forth by RESNET members. However, the SCC will also have the ability to proactively promote consistency through group discussion, updates to the RESNET Modeling Guidelines, recommended updates to Publication 002 test boundaries, and requests for Standards interpretations.

To support the SCC, RESNET will recruit a technical consultant with extensive knowledge of building energy software modeling, who will serve as the RESNET Energy Modeling Director.

  • Tightening of the Boundaries of the Suite of HERS® Software Program Tests.  RESNET will begin work on increasing the rigor of its software tests.  The most critical is updating the ANSI/ASHRAE Standard 140-2011, Class II, Tier 1 Test.  This test suite was developed a number of years ago by the National Renewable Energy Laboratory.  Since the test was developed more there is greater sophistication in energy modeling.  Using these advancements the requirements that a software must meet can get much tighter, increasing the consistency among software programs.

What is in Store for the Future

It is expected when fully implemented the above activities will lead to a greater consistency in the calculations of the HERS® Index scores.

Throughout all these processes, RESNET will conduct periodic evaluation of the progress toward consistency of index scores among all the software providers.  If it becomes clear that all these efforts will not achieve an acceptable level of consistency, RESNET will proceed to moving to a single engine for calculation of the HERS® index scores.