Types of Tools
There are generally three approaches to generating a score or rating that would populate a home energy label: asset-based, operational, or automated. These three types of scores vary greatly. While all approaches to scoring share the goal of summarizing home energy performance into a single metric, or score, they are typically utilized for different purposes. Each approach has its benefits and drawbacks depending on the use case. The three approaches to scoring are discussed briefly below.
Asset-based building energy labels provide information about how a home is likely to perform based on a set of standard testing criteria. Just as an automobile’s actual performance varies based on maintenance, driver behavior, or weight of cargo (i.e., "your mileage may vary"), a home's energy performance will vary based on maintenance, occupant behavior, the number of residents, and actual weather as opposed to average weather.
Home Energy Score and Home Energy Rating System (HERS) produce asset scores. Asset scores evaluate only the physical assets of the home -- insulation, HVAC and water heating equipment, home envelope, duct sealing, etc. They do not evaluate the operational aspects of the home -- i.e. whether a home has two residents or four, if the thermostat is set to 70 or 75 in the summer, etc. Asset scores apply the same set of behavioral assumptions to the home regardless of the current occupants. Applying a common set of assumptions and evaluating only the physical assets protects resident privacy, allows comparison of different homes, and produces a durable score that remains valid through a change of ownership of the home. The only way to change a home’s asset-based score is to change the home's energy-related systems (HVAC, hot water, envelope, etc.).
The DOE Home Energy Score may be produced directly by the Home Energy Scoring Tool, available on-line for Qualified Assessors working with DOE Partners[1]. Alternatively, third-party software providers may license the Home Energy Score application programming interface (API) and provide a home energy score directly through their software[2]. This approach is particularly useful in cases where an existing program utilizing an energy auditing software wants to integrate the Home Energy Score into their program. By contrast, HERS ratings are produced by multiple software tools that have been accredited by RESNET. Software providers must go through an accreditation process with RESNET before their software is approved to generate ratings[3]. Whether the DOE Home Energy Score Tool or a RESNET accredited software is generating the data for a home energy label, some programs have found it beneficial to develop a simple app to collect data in the field that can then connect to the scoring tool and produce a label. Due to the nature of the software utilized to produce a DOE Home Energy Score or a RESNET HERS Rating, new and existing homes are typically better served by different scoring systems. The Home Energy Score is better suited to existing homes, as it requires fewer data inputs and is less costly. HERS ratings are more often used for new homes, as the software requires a larger number of data inputs, including some that cannot be obtained if the sheetrock in a home has been hung. A HERS rating is also eligible for use as a compliance path for building energy codes in some jurisdictions through the Energy Rating Index (ERI) pathway, leading to increasing uptake in the new home market.
"Operational scores" are derived from actual energy consumption data through utility bills and/or delivered fuel records. These can be beneficial for encouraging efficient behavior by occupants of a home. By evaluating actual energy use, these scores can support the adjustment or continuation of energy-use habits over time. However, this type of score is less useful for comparing homes, as the actual energy use of a home will vary by occupants (e.g. a family of four with young children uses energy differently from the same home occupied by family of four with teenage children or occupied by a retired couple) and by weather (e.g. if the prior winter was exceptionally cold, or the summer exceptionally warm, it will have a large impact on the operational score). Examples of operational scores include the ENERGY STAR® Home Energy Yardstick[4] and ENERGY STAR® Portfolio Manager[5]. These tools are commonly used for benchmarking, where a baseline for energy consumption is established and then monitored for improvement over time. Operational scores are likely to be most beneficial for homeowners who want to understand and improve their current home energy performance. Since this guidance document is focused on policies and programs to support residential home comparisons and the use of energy information in the real estate market, operational scores are not discussed further.
"Automated scores" are another type of score that has been gaining traction in some real estate markets. These scores can utilize regulated utility data and public record data about a home to automatically generate a score for the home. Automated scores are typically not part of a home energy label, but may be utilized by on-line real estate portals to provide a 'first pass' assessment of home energy performance. They offer a mechanism to provide a high volume of data at low cost compared to on-site verified asset-based scores and may offer a path to raising awareness of energy performance among home owners, buyers and sellers. When utilized in real estate portals, automated scores are often published as 'unverified' and provide a home buyer or seller with an opportunity to connect with a third-party provider to verify or update their score. This is typically accomplished by certified asset-based providers. Rocky Mountain Institute has recently published a report, An MPG for Homes[6] , that describes recent efforts around this automated scoring approach.
The authors of this guidance document believe that asset-based scores, which rate home energy performance independent of individual occupant behavior, normalize for weather, and are transferable with homes, are more apt to support policy goals of increased residential energy efficiency upgrades. Additionally, the authors believe asset-based scores, provided by qualified professionals, are most likely to gain credibility with homeowners, buyers, and sellers.
Existing Tools
To view a list of currently available building energy software tools visit: www.buildingenergysoftwaretools.com. Please note that this list is not exhaustive and further research is recommended to determine if other tools are available in your jurisdiction.
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