Note: A concise summary of the initial version of the tool (version 2012) is provided in this paper.
In 2010, the U.S. Department of Energy (Department) tasked the Lawrence Berkeley National Laboratory (LBNL) to develop a new tool within the Home Energy Saver suite to provide an "asset-based" analysis of single-family residential buildings. The primary goal is to provide improved and standardized energy information for home buyers and sellers. The resulting Home Energy Scoring Tool (Scoring Tool) resides at http://homeenergyscore.lbl.gov.
The Scoring Tool is a key component of the U.S. Department of Energy's residential building energy label initiative to support the American Recovery and Reinvestment Act of 2009 (Recovery Act) funded Recovery Through Retrofit plan. The Home Energy Score Program will be the first national asset rating method that allows all USA regions to opt into a simplified and standardized energy assessment process that complements existing advanced home energy audit methods.
The Home Energy Score is designed to provide a rapid low-cost opportunity assessment of a home's fixed energy systems (also known as an "asset rating") and provide the home owner with general feedback on the systems that potentially need more detailed attention from certified home performance diagnostics and weatherization professionals (such as those engaged with RESNET, Building Performance Institute, and the Affordable Comfort Institute).
A set of background research projects and publications informed development of the tool:
The Scoring Tool has been designed to support the existing marketplace for energy analysis tools and services by providing a substantially lower-cost "entry level" assessment (but not a formal work scope or cost estimate), which can help the service provider establish the potential for energy savings and the value of a more comprehensive investigation and retrofit recommendation report. For a typical home, an experienced assessor can complete a Scoring Tool analysis in under an hour, while a comprehensive follow-up assessment could take several times that long.
Also developed within the Scoring Tool are Application Programming Interface ("APIs") services, which third-party energy software developers can use to embed the Home Energy Score methodology into their products and business processes.
An asset rating seeks to evaluate a home and allow it to be compared to others based on differences in fixed characteristics, while holding occupant-determined factors and behaviors constant. An asset rating also excludes energy using features that are not considered fixed components of the building. Thus, the efficiency of a furnace would be regarded as an asset attribute while the operation of the thermostat controlling that furnace would be deemed a behavioral (non-asset) attribute. There is some subjectivity in determining which energy-using components of a home are "assets". For the purposes of the Scoring Tool, space conditioning and water-heating systems (and the associated building envelope components) are assets, while non-hardwired appliances, lighting, and other equipment (and their utilization) are not.
To ensure that users proactively define asset characteristics, no input values are defaulted and all questions must be answered. For those systems not considered fixed assets, attributes are not adjustable by the user and are set consistent with those used in the Home Energy Saver software suite (documented elsewhere in this Wiki).The Scoring Tool provides an asset calculation and thus has limited application for informing home occupants how to optimally operate their home. For that reason any Scoring Tool session input may be automatically imported into Home Energy Saver (hes.lbl.gov) or Home Energy Saver Pro (hespro.lbl.gov) -- feature coming soon. These tools allow the homeowner or contracted energy professional to consider the operational/behavioral aspects of the home as well as evaluate ancillary energy-using devices (such as pools, wells, second refrigerators) that are not included in the standardized asset score.
Fixed Assumptions and Default Values
For an asset rating to have meaning in the marketplace, one home must be comparable to another. For home characteristics NOT individually recorded and entered into the Scoring Tool, non-asset related inputs are standardized to a nationally consistent set.
In keeping with the standardized nature of the assessment, predicted energy costs and savings assume state-average energy prices. The Scoring Tool applies a standardized retrofit cost from the NREL National Residential Efficiency Measures Database (http://www.nrel.gov/ap/retrofits/) and limits recommendations to those achieving a payback time of 10 years or less. As a result, predicted energy use may be different from actual utility bills. The extent of these variations will depend on additional factors such as how the occupant maintains their home, appliance ownership and use, actual number of occupants, and year-to-year weather variations.
The Scoring Tool has five simple pages of user inputs used to describe the home construction and equipment (Figure 2). The total number of required inputs is typically less than 50 if the home has the same window and wall types on each building side. Required inputs are listed below, and exact wordings plus a more detailed log of questions and required inputs are included in the checklist here.
About this Home
Heating, Cooling & Hot Water
The Department took into account many different factors as well as available sources of data in an effort to develop a scoring system that could fairly compare the energy performance of existing homes. The Department sought to develop a simple system that allows consumers to understand how a home compares to other homes regardless of location and weather patterns. The current methodology is applicable to single-family homes and townhouses in the continental US and Hawaii.
The tool scores a home on a 10-point scale, where a 10 corresponds to greatest efficiency (minimal energy use). Each point on the scale corresponds to a specific source BTU level. National average source energy factors were used to calculate a total energy value for electricity, natural gas, liquified propane gas and distillate fuel oil energy sources delivered to the home. The source energy factors are from the Energy Star Portfolio Manager Technical Reference (US EPA, 2013).
Also in keeping with the asset-based methodology, a
consistent set of upgrade recommendations must be considered for each home
(variations in which are recommended as a function of home
characteristics, cost-effectiveness, etc.). Upgrades considered in the Scoring Tool include improvements to the home envelope and major equipment (the "assets"), but not to upgrades
of lighting and appliances or usage changes. Unlike the other Home Energy Saver tools, the Scoring Tool applies a fixed, standardized retrofit cost (from the NREL National Residential Efficiency Measures Database) and generates recommendations providing the highest performance level with a payback time of 10 years or less. Energy savings are those achieved by moving
between the baseline home and the level of the deemed efficiency level of the
upgrade. General information on "non-asset" upgrades is provided in a "Tips" sheet, attached to the Home Energy Score Label.
The following two categories and specific upgrades are currently provided by the Scoring Tool:
The Type-1 incremental cost used for the cost-benefit analysis is the full cost of installation.
The Type-2 incremental cost used for the cost-benefit analysis is the cost differential between equipment complying with current standards and cost of the upgrade (Energy Star, where applicable).
It is important to note that the sum of the savings from the individual measures of the recommendations report may not equal the total savings for the package of selected upgrades (the number shown on the label). This difference is due to interactive effects of individual energy improvements. When improvements reduce energy consumption within the same end-use (e.g., a window upgrade plus an air conditioner upgrade), the resulting dollar savings is less than the sum of the savings shown for the individual improvements.