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What is a Zero Energy House?

National Renewable Energy Labs (NREL) in the United States of America defines a zero energy building: 

"A zero energy building (ZEB) is a residential or commercial building with greatly reduced energy needs through efficiency gains such that the balance of energy needs can be supplied with renewable technologies.1"

A NREL research paper1, "Zero Energy Buildings : A critical look at the definition" identifies four common definitions of how zero energy is measured. The definition that we have chosen is net-zero site energy, which is defined as:

"Net Zero Site Energy:  A site ZEB produces at least as much energy as it uses in a year, when accounted for at the site."

In practical terms this means that we will generate the same amount of energy onsite using renewable energy systems (in our case photovoltaics) as that which we import from the grid (electricity will be the only imported energy source used in our house).  So, if an electricity meter measuring the electricity supply to the house ran backwards when energy was being fed back to the grid, i.e. when site generation was more than used, then it would read zero at the end of the year for a net-zero site energy building.  For more information on calculating and balancing your energy use and onsite renewable energy generation see the Systems section.

During the project we plan to calculate the embodied energy of the house and, if practical, offset this energy through onsite generation over the life of the house.

There are a number of examples of Governments internationally moving towards ZEBs. The UK government requires all homes to be carbon neutral by 2016 and has introduced a mandatory rating scheme, "The Code for Sustainable Homes3". In Germany the Passivhaus standard4 is commonly used. There are currently over 15,0005 Passivhaus certified homes internationally.

For us the project encompases more than just energy, it is also about:

  • Heath, comfort and lifestyle
  • Resilience to increased energy costs/shortages
  • Wide effects on the environment including resources, climate change and pollution
  • Low embodied energy

Footnotes

  1. Zero Energy Buildings : A critical look at the definition, NREL
  2. Wikipedia : Zero Energy Building
  3. UK Code for Sustainable Homes, UK Government
  4. Passivhaus
  5. The number of Passivhaus buildings that had been built in late 2008 was between 15,000 and 20,000, Passivhaus : Wikipedia
  6. Vale, Brenda and Robert (1975). The Autonomous House. New York, N.Y.: Universe Books. ISBN 0-876-63254-1.
  7. Vale, Brenda and Robert (2000). The New Autonomous House. New York, N.Y.: Thames & Hudson Ltd.. ISBN 0-500-34176-1.