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Home Energy Score Research and Background

With the goal of addressing the significant, and yet untapped, potential for saving energy in existing homes, the U.S. Department of Energy, in collaboration with the Lawrence Berkeley National Laboratory and the National Renewable Energy Laboratory, developed the Home Energy Score as a low cost and reliable method for estimating the energy use of a home and motivating investment in efficiency improvements. The Home Energy Score uses a systematic approach to provide a reliable and scientifically–based analysis of a home’s energy characteristics and overall energy efficiency. The Home Energy Score uses standard calculations, formulas, and scoring methods; compares a building to a clearly defined baseline; requires qualified professionals to conduct the assessment; and provides a label displaying how efficient a home is on a 10-point scale.

The Home Energy Score applies a transparent and thoroughly tested calculation methodology to estimate a home’s energy use. This calculation methodology takes into account local climate and applies standard assumptions regarding occupant behavior, providing a consistent, national, standardized approach that allows an “apples-to-apples” comparison of homes both locally and nationally. The calculations of the Home Energy Score are based on the Lawrence Berkeley National Laboratory’s DOE-2 model, the same calculation engine used by other computer tools approved by RESNET.

The Home Energy Score uses a 10-point scale with a “1” applying to homes likely to use a lot of energy and a “10” corresponding to the most efficient homes. A home’s estimated energy use is translated into a score on the 10-point scale, where the value of a “1” corresponds to the amount of energy used by the 20% highest energy consuming homes and a “10” corresponds to the amount of energy used by the 12% lowest energy consuming homes.1

The Home Energy Score relies on weather data from approximately 1,000 weather stations across the United States to adjust the energy values underlying the 10-point scales and thereby account for climate variations. An individual home is linked to the appropriate 10-point scale by its zip code. This weather data also informs the energy load calculations used to estimate the home’s energy use.

To generate an official DOE recognized Home Energy Score, a qualified energy assessor must collect and submit a standard set of data inputs regarding the energy related features of a home, including but not limited to its envelope, heating, cooling and hot water systems. Those who provide the Home Energy Score are required to hold an industry accepted qualification before they are approved as a potential candidate. Once they meet that requirement, they are required to pass a two-part proctored test to verify their knowledge of building science and how to generate a Home Energy Score. Only then are they provided access to the Home Energy Score software and allowed to provide Home Energy Scores to customers.

As part of the Home Energy Score oversight, DOE reviews all of the data provided by the assessors for every home scored. Local and national Partners are required to carry out additional quality assurance through on-site reassessment of 5% of homes scored using qualified energy professionals who are skilled in energy efficiency, energy rating, and evaluation methods. DOE reviews these assessments as well to ensure consistent scoring across assessors. The results of these reviews are used to provide direct feedback to individual assessors and programs and to improve DOE’s training modules for assessors.

 

1Home Energy Score uses the 2009 Residential Energy Consumption Survey (RECS) dataset to determine the end points of its scale. RECS as well as the Commercial Building Energy Consumption Survey (CBECS) – conducted by the U.S. Energy Information Administration – are widely used data sources and serve as benchmarks for a number of national tools including the U.S. Environmental Protection Agency’s Home Energy Yardstick and ENERGY STAR Portfolio Manager.

Scoring Tool v.2014

In January 2014, the U.S. Department of Energy (DOE) released the first major update to the Home Energy Scoring Tool. After more than a year of implementation and feedback from program Partners, DOE made significant improvements to the scoring tool's calculation methodology and user interface. A newly refined scoring system will allow inefficient homes to more easily move up the scale with investments in efficiency improvements. This enhanced mobility is expected to help motivate greater action among homeowners.

The Energy Department's National Renewable Energy Laboratory (NREL) performed a variety of analyses to test the updated scoring tool. Analysis included comparisons of the scoring tool's energy estimates with actual utility bills for about 1,000 homes. Data from previously scored homes as well as data from prototypical homes were run through the new scoring tool to ensure appropriate ranking of homes on the 10-point scale.

What's New?

Calculation Methodology

  • The Score is now calculated based on a home's "asset energy" only, i.e. the estimated energy use of the heating, cooling and hot water systems. By removing the base load, larger homes that are relatively energy efficient will generally receive a higher score than was possible with the previous version of the Scoring Tool.
  • The new tool is more sensitive to local climate— reflecting data from more than 1,000 weather stations nationwide compared to 250 stations used previously. Energy calculations are therefore more accurate, reflecting more localized weather data as well as more recent weather data.
  • An updated infiltration model is used for calculating energy use when a blower door leakage value is not provided. Initial testing indicates that this will calculate lower energy use.
  • A more accurate model for calculating heat transfer in buffer spaces is used. This tends to lower the estimated energy use.
  • The tool will use new assumed thermostat settings that more accurately reflect most homeowner's actual settings. The prior settings included much more aggressive setbacks.

User Interface

  • Townhouses and duplexes can be easily characterized with options to denote middle or end units and number of exterior walls.
  • Qualified Assessors will be able to characterize up to three duct locations and identify roof absorptance by color rather than a number.
  • The Scoring Tool will accept ground source heat pumps, heat pump water heaters and evaporative coolers as heating and cooling system types.
  • There is better interactive data entry control to help guide the assessor to provide the most appropriate information.

Mobility

  • Base loads were removed from the Scoring Tool inputs to increase the opportunities for large homes to improve their scores.
  • The 10-point scale remains linear in that each jump along the scale corresponds to a specific reduction in energy use. However, the end points of the scale now better reflect the current housing stock based on analysis of data from the Residential Energy Consumption Survey.

Background

In Fall 2009, the Vice President and the White House Council on Environmental Quality called upon the Department of Energy (DOE) to create a system that enabled homeowners to easily and affordably find out how their homes' energy performance compare with other homes nationwide. After a year of consumer and expert research and development, DOE launched a pilot program, which ran from November 2010 to July 2011. Using the results of the pilots and other research, as well as considering industry factors and homeowner motivations, DOE created the Home Energy Score.

Learn more about the Home Energy Score: