Home Energy Score: Engineering Documentation

Home Energy Scoring Tool

Overview

In 2010, the U.S. Department of Energy (DOE) tasked 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. In 2015, DOE tasked Pacific Northwest National Laboratory (PNNL) to transition the initial Home Energy Scoring Tool (HEScore) into production-level system, allowing LBNL to focus on extensions to the model's building science elements. The HEScore system now resides at http://hescore.labworks.org/. A concise summary of the initial version of the tool (version 2012) is provided in this paper. An overview of the current program is here.

HEScore s a key component of DOE'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 is the first national asset rating method that allows all U.S. regions to opt into a simplified standardized energy assessment process that complements existing advanced home energy audit methods.

HEScore 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 homeowners 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 Building Performance Association.

A set of background research projects and publications have informed development of the HEScore tool:

A draft report by Newport Partners summarizes findings from 12 consumer focus groups conducted in summer 2010 concerning home energy labeling (here).
A report summarizing feedback from homeowners during the pilot projects conducted in 2011 (here)
A report summarizing feedback from professional Qualified Assessors during the pilot projects conducted in 2011 (here)
The HEScore tool's accuracy has been documented in detail by the National Renewable Energy Laboratory (here).

HEScore is designed to support the existing marketplace for energy analysis tools and services by providing a substantially lower-cost, "entry-level" assessment (not a formal work scope or cost estimate), which can help service providers 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 the HEScore analysis in under an hour, while a comprehensive follow-up assessment could take several times that long.

Application Programming Interface ("APIs") services are available with HEScore for third-party energy software developers to embed the HEScore method into their products and business processes

Asset Rating

An asset rating seeks to evaluate a home, allowing it to be compared to other homes based on differences in fixed characteristics while holding occupant-determined factors and behaviors constant. An asset rating also excludes energy by employing features that are not considered fixed components of the building. Thus, a furnace's efficiency would be regarded as an asset attribute, while 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 HEScore, space-conditioning and water-heating systems (and the associated building envelope components) are assets, while non-hardwired appliances, lighting, and other equipment (and their use) are not.

To fully reflect the value of asset-based upgrades, scores are computed based on the energy use associated with those features, essentially heating, cooling, and water-heating.

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 HEScore tool, non-asset related inputs are standardized to a nationally consistent set. The main differences between the HEScore default values and the Home Energy Saver are described on the Defaults and Dependencies - Methodology Section 2.3 page.

Required Inputs

HEScore has five simple pages of user inputs used to describe the home construction and equipment, described in detail on the HEScore User Interface page. If the home has the same window and wall types on each building side, the total number of required inputs typically is less than 50. Exact wordings along with a more detailed log of questions and required inputs are included in the checklist here.

Scoring Methodology

To develop a scoring system that could fairly compare the energy performance of existing homes, DOE accounted for many different factors and available data sources. The goal was to develop a simple system that allows consumers to understand how one 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 U.S. and Hawaii.

HEScore scores a home on a 10-point scale, where a 10 corresponds to the greatest efficiency (minimal energy use). Each point on the scale corresponds to a specific source BTU level. National average source energy factors are 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).

Recommendations

In keeping with the asset-based method, 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 HEScore include improvements to the home envelope and major equipment (the "assets") but not to lighting and appliances upgrades or use changes. HEScore applies a fixed, standardized retrofit cost (from the NREL National Residential Efficiency Measures Database) and generates recommendations, providing the highest performance level with a package of improvements that will payback in approximately 10 years or less. Energy savings are achieved by moving between the baseline home and the deemed efficiency level of the upgrade.

The following two categories and specific upgrades are currently provided:

Type 1 - Improvements Recommended Now

These upgrades can help save energy right away:

Attic insulation
Basement wall insulation
Basement/crawlspace floor insulation
Crawlspace wall insulation
Air tightness
Exterior walls
Ducts - seal
Ducts - insulate

The Type-1 incremental cost used for the cost-benefit analysis is the full cost of installation.

Type 2 - Recommendations When Equipment Must be Replaced

These recommendations will help save energy when it is time to replace or upgrade:

Central air conditioner
Boiler, furnace, or heat pump
Room air conditioner
Roof - reflectance
Roof - insulated sheathing
Skylights
Siding - insulated sheathing
Water heater
Windows

The Type-2 incremental cost used for the cost-benefit analysis is the cost differential between equipment complying with current standards and the upgrade cost (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.

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