Energy Performance Score

January 03, 2012
January/February 2012
A version of this article appears in the January/February 2012 issue of Home Energy Magazine.
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There are many different ways to describe a home, ranging from the optimistic prose of a real estate agent to a complex mathematical model based on the building’s structural assemblies. In the world of home performance, we definitely like numbers, such as blower door and duct testing results. We also seem to like models that result in numerical scores—HERS scores, green certification point counts, and the like.

Steve Mann
is a HERS rater, Green Point rater, LEED AP, Certified Energy Analyst, serial remodeler, and longtime software engineer.

The various home-rating systems have their strengths and, more often, their weaknesses. A major weakness is that if you reduce everything to a number, how do you explain that number to a homeowner? A HERS index between 0 and 100 is best explained with simple logic—0 is good; over 100 (or 85, or some other arbitrary threshold) is bad. As a homeowner, my first question would be, zero what? A hundred what? My second question would be, compared to what?

Another problem with some rating systems is the amount of data that must be collected in order to analyze the building. The Home Energy Saver, a consumer-friendly, web-based tool developed by a group at Lawrence Berkeley Labs, provides results with about 20 data entry points. The Passive House Planning Package, on the other hand, is a multisheet Excel model that asks specifics like the inset depth of each window from the building’s exterior.


Audit Summary
Audit Summary
Figure 1. The Audit Summary is designed to be an easy-to-digest consumer summary akin to the EPA's miles per gallon metric for vehicles, letting you compare efficiency data for multiple homes.


EPS—How It All Started

In 2008, the Earth Advantage Institute and the Conservation Services Group, with funding from the Energy Trust of Oregon, developed a pilot program designed to develop a cost-effective and accurate method for reporting home energy performance. Drawing on the U.K.’s Energy Performance Certificate, the resulting Energy Performance Score (EPS) is designed to easily communicate the energy efficiency of new and existing homes to the general public, and provide useful information to various other stakeholders, such as utility companies. The EPS is described as a miles per gallon rating for homes. It is an asset rating, meaning that occupant behavior is not factored into the calculations. Instead, normalized assumptions for occupancy and behavior are applied to all houses to guarantee consistency.

In the pilot program, the EPS team surveyed more than 100 software tools as potential candidates for the program. They selected four: REM/Rate, SIMPLE, and two versions of the Home Energy Saver. REM/Rate is a well-known HERS modeling tool from Architectural Energy Corporation. SIMPLE, developed by Michael Blasnik, is a spreadsheet-based model that requires only 32 data points to do its calculations. Home Energy Saver has three levels of complexity. The two most complicated levels were used.

Energy auditors were sent to more than 300 homes in Oregon. They used a data collection sheet that included all the values required for all four modeling tools. One hundred and ninety homes were then modeled in all four tools, and the predicted energy uses were compared to actual energy use. Surprisingly, the simplest of the four tools, SIMPLE, tuned out to be the most accurate overall. Based on the results of this pilot program, the Energy Trust of Oregon and Earth Advantage Institute decided to develop a full-blown commercial version of the EPS, based on the SIMPLE algorithms.

EPS is designed to easily communicate the energy efficiency of new and existing homes to the general public.

The Audit Process

Most whole-house programs these days never seem to address just one level of professional certification. The EPS program is no exception. It includes two different types of audit, the Diagnostic Survey and the EPS Plus Audit. A Diagnostic Survey consists of an exterior walk-around, with a building takeoff, and an interior evaluation including lighting, appliances, and mechanical inventories. You also check the attic and crawlspace, if any, and try to determine levels and quality of insulation. The survey includes a blower door test and visual duct inspection.

You collect all the information you need to enter into the software, using a standardized data collection form. For a full survey, you collect 36 data points and make judgments about ten building characteristics. For instance, you don’t test the ducts. Instead, you assign them one of five states—excellent, tight, average, leaky, or very leaky—based on a visual inspection. The survey process is well documented, and the guidelines for characterizing building elements are clear and easy to follow. The only math involved is calculating building volume and building leakage in ACH, based on the blower door test.

An EPS Plus Audit includes a Diagnostic Survey plus CAZ testing, plus a set of upgrade recommendations. It may include duct testing at the discretion of the auditor. An EPS Plus Audit is similar to what a BPI Building Analyst might do for a Home Performance with Energy Star audit.

Carbon Emissions Summary
Carbon Emissions Summary
Figure 3. The Carbon Emissions summary highlights the same type of information as the Energy Use summary but shows current and reduced carbon emissions.
Energy Use Summary
Energy Use Summary
Figure 2. The Energy Use summary highlights the home's current energy usage, and compares it to both consumption after upgrades and certain state metrics.

The Score

Whether you do a Diagnostic Survey or an EPS Plus Audit, the end result is the same—an Energy Performance Score (see Figure 1). It is a simple, one-page analysis that is easy to understand. It shows some basic audit information, energy use in kWh per year, carbon emissions in tons per year (factoring in source energy), and a breakdown of current and projected use in four categories—heating, cooling, water heating, and appliances. The Energy Use and Carbon Emissions graphs contain additional details (see Figures 2 and 3). They show total before and after use, state average energy use, and state legislative targets, if any. There are also some printed reports that contain much the same information as the graphs. They are watermarked as DRAFT reports until you finalize the audit, at which point you pay the EPS audit fee, currently $45.

Since the EPS auditing software is a web-based tool, all your audit results, reports, and data are maintained for you, simplifying record keeping and maintenance. Homeowners are able to review their audit results online as well.

The evaluators of the pilot program thought carefully about which results they’d use to come to a useful conclusion. They decided against using individual consumption numbers, which can make oversized houses appear as energy efficient as small houses. Instead, they decided to use total consumption per property, which makes it possible to compare dissimilar properties, answering the basic question: Which of a group of properties uses the least energy? The evaluators also discovered that homeowners are actually interested in learning about their carbon footprint, so they broke that out as a separately reported item.

Auditor Training

In order to be able to use the EPS software for evaluating homes, you have to undergo training. The training, which currently costs $199, includes a self-paced online course consisting of eight modules, and a protocol exam. After you pass the exam, you are provided with photographs, a floor plan, and a brief narrative about a sample home. You have to take this information and successfully complete an audit using the EPS Auditor software. You are successful if you correctly determine the home’s annual energy consumption and carbon footprint based on the information provided. Finally, you must participate in a 30-minute webinar on the software, followed by a second exam. If you pass the exam, you are certified as an EPS Auditor, entitled to use the software in the field for a fixed fee per audit.

In order to enroll in the training, you must be certified as a BPI Building Analyst. This is because the EPS audit protocols require blower door testing, whole-house analysis, and the ability to identify potential combustion safety issues. Anyone who has passed the BPI BA written and field exams should have no trouble with the EPS curriculum. The online course work consists of videos, PDF reading material, and online quizzes that can be taken more than once. It can be completed in no more than a day, probably less. The EPS training is not the most professionally developed online course work I’ve ever seen, but it does the job.

learn more

For more information about the EPS, go to
programs/ homes/energy-performance-score

For more information about REM/Rate, go to products/remrate.

The State of the Program

Earth Advantage Institute in Portland, Oregon, is currently offering the EPS program. The online training can be taken at any time. The schedule for the webinar required to complete the training is sketchy. In addition to auditor training, there is also a quality assurance component that currently doesn’t seem to be well defined. Overall, the program feels like a pilot program. That doesn’t make it bad—just rough around the edges with, hopefully, a bright future.

The EPS Auditor software is being used in a large-scale program in Seattle and several pilot programs on the East Coast, according to telephone messages I received from Earth Advantage. Unfortunately, as of this writing, I have been unable to get details on any of these programs. I hope to provide more details in the future.

There are quite a few regional sustainability and certification programs scattered around the country. There are also many software products designed for the existing home-auditing and retrofit market. EPS Auditor’s simplicity for both the auditor and the consumer make it a strong contender for widespread adoption once it matures a bit.

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