inside ases | chair’s corner
A Confusion of terms
A welter of building-energy concepts calls for focused collaboration
among professional groups.
at a recent meeting of the California Association of Building Energy Consultants (CABEC; cabec. org), it became clear that while the media are abuzz
with developments in zero-net energy, net-zero energy,
energy-free, low-energy, zero-emission and hybrid buildings, these terms are baffling. Even practitioners often can’t
say precisely how these terms differ in meaning. This leaves
huge potential for confusion throughout the building supply chain, from consumers investing hard-earned dollars
into energy efficiency and renewable energy to those who
design, maintain, operate, buy and sell buildings.
A number of publications are now available, online and
in print, that help to clarify the issue.
is chair of AsEs and
at California Polytechnic state university.
Contact her at chair@
Let’s begin with definitions for the type of buildings
we are trying to describe and achieve. A seminal paper,
often cited on this subject, was published in 2006 by Paul
Torcellini et al, at the National Renewable Energy Laboratory, titled “Zero Energy Buildings: A Critical Look at the
Definition.” A few gems from the paper:
In concept, a net [zero energy building, or ZEB] is a building with greatly reduced energy needs through efficiency gains
such that the balance of the energy needs can be supplied by
The article defines several different goals for ZEBs,
depending on which element we are trying to balance out.
Is it site energy or source energy, energy cost or energy
emissions? All of these are laudable goals, and each needs its
own metric for evaluation. Each needs its own set of data!
Here’s how the authors define these goals:
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.
Net Zero Source Energy: A source ZEB produces at least
as much energy as it uses in a year, when accounted for at the
source. Source energy refers to the primary energy used to generate and deliver the energy to the site. To calculate a building’s
total source energy, imported and exported energy is multiplied
by the appropriate site-to-source conversion multipliers.
Net Zero Energy Costs: In a cost ZEB, the amount of
money the utility pays the building owner for the energy the
building exports to the grid is at least equal to the amount the
owner pays the utility for the energy services and energy used
over the year.
Net Zero Energy Emissions: A net zero emissions building
produces at least as much emissions-free renewable energy as it
uses from emissions-producing energy sources.
The paper is far too comprehensive to be summarized here,
but you can read it at nrel.gov/docs/fy06osti/39833.pdf.
cient approach to design, construction and building operation, emphasizing super insulation, ventilation/air tightness
and internal gains. Buildings around the world have been
built to this standard, with impressive results.
No discussion of ZEB would be complete without
reference to the several existing green rating systems for
buildings and their components such as the National
Association of Home Builder’s Green Building Program
( nahbgreen.org) and LEED for Homes ( usgbc.org/leed/
homes). I’ve recently been getting familiar with LEED for
Homes (LEED-H), thanks to my involvement in a student
What are we trying to save —
site energy or source energy,
energy cost or energy emissions?
design competition, which requires students to perform a
Herculean design feat: a small, green, affordable home for
New Orleans. Check out the competition web site for more
details, at openarchitecturenetwork.org. Four winners will
be announced this summer; those teams will design and
build LEED-H Platinum homes for the Salvation Army.
What impressed me about the system is the emphasis on
measurement and verification during the building process
and the incorporation of other well-established guidelines
like Energy Star.
The CABEC conference highlighted the need to engage
the entire community of professionals — students, architects, engineers, contractors and modelers — in the discussion about ZEB. Many of our professional organizations
have made a good start toward bringing these topics to the
forefront. We need more of the same. There is opportunity
and imperative for ASES to join the conversation and to
promote professional collaboration in support of the energy
and environmental benefits we seek.