March 15, 2016

HPXML: A Common Language Structure for Home Energy Efficiency

By Don Knapp

One of the next big leaps in home energy efficiency and market transformation hinges not on some new energy-saving gadget, but on our ability to share data about homes. Specifically, the ability to share standardized data on an individual home’s performance and on the energy upgrades that it received.

To do that, it's most helpful if everyone is able share information via the same format—and the emerging national data standard for residential energy efficiency that will facilitate this is called Home Performance Extensible Markup Language, or HPXML. If you haven’t yet heard of it, take a moment to get up to speed.

“In California, Build It Green and Pacific Gas and Electric Company (PG&E) are leading the drive to adopt HPXML for utility rebate programs. We’re collaborating with the U.S. Department of Energy (DOE) and other national and California-based partners on refining and implementing the new standard,” says Torsten Glidden, Senior Technical Manager at Build It Green (BIG).

(BTW, thanks to the DOE for the recent shout-out on BIG's industry-leading efforts.)


HPXML's Big-Picture Benefits

The Home Performance with ENERGY STAR website sums up the purpose of HPXML best: “HPXML was created to achieve some basic goals that are critical to a growing industry.” These goals are outlined below: 

  • Standardize terminology and facilitate the collection of higher quality data as a means to track and quantify the work being completed across the residential energy-efficiency industry.

  • Create interoperability -- and foster innovation -- between software systems to allow the transfer of home performance data across a diverse set of market actors.

  • Improve industry efficiency by reducing the costs of data collection and exchange between market actors.

California's Home Upgrade Program adopted HPXML as part of a larger goal of fostering innovation among energy software solutions by creating a competitive marketplace based on transparent data transfer standards.

HPXML Connected Market
[Source: Home Performance with ENERGY STAR website]


HPXML's Real-World Benefits

Imagine talking with ease to someone who speaks a different language. Just think of the possibilities if standardized information on a home’s characteristics, energy performance, and energy upgrades could be captured digitally by contractors and shared via databases with utility programs, market researchers, insurers, lenders, real estate MLS systems, and others:

  • A lender, appraiser, or potential homebuyer would be able to see what energy upgrades, green certifications or energy scores have been achieved (including the estimated energy savings of those upgrades) and factor that into a home’s valuation, sale price, or eligibility for financing.

  • Contractors would save time and reduce paperwork by using HPXML-based mobile apps to collect data in the field—from energy modeling inputs like duct leakage to rebate program application forms. BIG developed an online contractor portal for just this purpose, and in 2015 we rolled it out to participating contractors in the Energy Upgrade California® Home Upgrade Program in PG&E service territory.

  • Utilities and other program providers could analyze higher quality data for more accurate program evaluation and more easily report their program impacts to regulators and industry, as well as other governmental and community stakeholders. Standardized data via HPXML would also improve and streamline quality assurance (QA) processes for these programs.

HPXML data flow
[Source: Home Performance with ENERGY STAR website]

A Closer Look at HPXML Data Standards

The foundation of HPXML is the data standards pioneered for it by the Build Performance Institute (BPI). BPI developed two primary HPXML standards that can be thought of as a common language to represent, define, and organize data on home performance:

  • BPI-2100-S-2013: Standard for Home Performance-Related Data Transfer—Provides requirements for an extensible mark-up language (XML) standard data transfer protocol that can be used to transfer home performance-related data.

  • BPI-2200-S-2013: Standard for Home Performance-Related Data Collection—Provides a standard vocabulary for describing terms related to buildings, energy consumption, and energy conservation measures, in alignment with DOE’s Building Energy Data Exchange Specification (BEDES), Home Energy Score (HES) and Standard Energy Efficiency Data (SEED) platform..

BPI is developing these additional draft standards:

  • Standard Requirements for a Certificate of Completion for Residential Energy Efficiency Upgrades

  • Standard for Home Energy Auditing Data Collection with Energy Modeling Tools

  • Standard for Home Energy Job Completion Data Collection with Energy Modeling Tools

“HPXML makes home performance data more transparent, and for energy rebate programs, it can improve their cost-effectiveness and save time and money for everyone from contractors to program implementers and administrators,” says Glidden. “PG&E’s Home Upgrade Program led the way in California, but other programs here and in other states are transitioning to HPXML as well.”

Energy Upgrade California® Home Upgrade is funded by California utility Customers and administered by Pacific Gas and Electric Company (PG&E) under the auspices of the California Public Utilities Commission. In PG&E territory the program is implemented by Build It Green.