A Net-Zero Energy Home Grows Up: Lessons and Puzzles from 10 Years of Data

Bethany Sparn, Lieko Earle, Paul Norton, Craig Christensen

Research output: Contribution to conferencePaper


In 2005, Habitat for Humanity of Metro Denver, with support from NREL and other partners, built one of the first homes in the US to achieve net-zero energy based on monitored data. A family of three moved into the house when it was completed and lives there still. The home has been monitored continuously for the past ten years. Although PV production has remained steady, net energy performance has varied each year. The home was a net producer of energy annually in each of the first three years and in the ninth year, but not in years four through eight. Over the years, the PV system provided between 124% and 64% of the home source energy use. Electricity use in the home increased steadily during the first eight years, even though no significant new appliance was introduced into the house, such as a window air conditioner. Miscellaneous electric loads and space heating, both strongly dependent on occupant behavior, appear to be primarily responsible for the observed increase in energy use. An interesting aspect of this case study is how, even within a single family, natural changes in occupant lifestyles over time (e.g., kids growing up, schedules changing) can substantially impact the overall energy intensity of a home. Data from the last ten years will be explored for lessons learned that can improve the way we design low-load homes without sacrificing comfort or convenience for the occupants, and how we can make realistic predictions of long-term energy performance.
Original languageAmerican English
Number of pages12
StatePublished - 2016
Event2016 ACEEE Summer Study on Energy Efficiency in Buildings - Pacific Grove, California
Duration: 21 Aug 201626 Aug 2016


Conference2016 ACEEE Summer Study on Energy Efficiency in Buildings
CityPacific Grove, California

Bibliographical note

Available from ACEEE: see http://aceee.org/files/proceedings/2016/data/index.htm; see NREL/CP-5500-66122 for preprint

NREL Publication Number

  • NREL/CP-5500-67079


  • miscellaneous electric loads (MELs)
  • net energy performance
  • net-zero energy
  • NZE


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