[BLDG-SIM] Net Zero and Nearly Net Zero

Brian Thornton thorntonenergy at comcast.net
Sat Mar 4 07:22:50 PST 2006

Thanks for all the many great replies to my query on Net Zero, and use of
bio-mass CHP in addition to PV and wind in this context.


To me, Net Zero is a very powerful term, and there are some important strict
definitions and also a lot of support for interpreting the term on a project
by project basis.  Net zero takes us out of achieving some percent of energy
reduction in to the realm of true sustainability.  Net Zero has been applied
primarily to homes, but would be a potent tool for commercial and
institutional buildings as well. At the strictest level Net Zero energy
refers to a building that generates annually on-site from on-site available
renewable sources enough energy to equal the annual building energy usage.
This goal is a subset of the goal that buildings meet all of their energy
needs from renewable sources in some way.  To me the Net Zero concept
provides several benefits. 


*	Benchmark for measuring achievement of a very aggressive energy
*	A target that can shape any design and orient design towards a truly
sustainable energy endpoint
*	A "sexy" marketing tool/concept to really help promote a step up
from LEED and other energy % reduction targets (which are great, but not


Several people provided the link to a good summary article from
BuildingGreen.com, in the October 2005 edition, that covers four NREL
definitions related to Net Zero  http://www.buildinggreen.com/articles/
(Need to subscribe on line to download article) The first of these is the
strictest version noted above. 


Zero-net annual site-energy

Zero-net annual source energy

Zero-net annual energy cost

Zero-net annual emissions


Another resource is a NAHB study on a net zero home model, which also
provides these definitions, and other useful references, and is available
for free.  http://www.toolbase.org/tertiaryT.asp?TrackID=
777> &CategoryID=1979&DocumentID=4777


Another way to consider this is in terms of what type of renewables are in
the project.  Perhaps there is a hierarchy:


0)  Conservation/Efficiency

1)  True off-grid on-site generation from solar and wind only

2)  Net zero, utility connected, meeting annual average energy usage from
solar and wind only

3)  Add other renewables with off-site fuel supply to 2), such as bio-mass,
wood and wood pellets, bio-diesel, ideally with combined heat and power

4)  Purchased renewables


Achieving 1 and 2 for commercial buildings above a story or two in an urban
setting is going to be very difficult, because the area available for PV
compared to square footage of the building is so small.  (one person
suggested the vertical axis wind turbines may be worth a closer look) Yet
these commercial buildings are critical to push towards a sustainable energy
design building stock.  


There may be value in preserving "Net Zero Energy"to refer strictly to 1)
and 2), with on-site solar and wind only.  The concept is so powerful and
useful in marketing and pushing the ideas with the people who will pay for
it and design to it, that I think we need to find a way to use the terms
more broadly.  As some pointed out, this is already being done with Zero
Energy Homes, that may actually be 60% from renewables not 100%.  I plan to
use the term "Nearly Net Zero", or perhaps "Net Zero with PV and Off-site
Wood", and define if this is Nearly Net Zero for a. Energy, b. Source
Energy, c. Energy Cost, and/or d. Emissions.  It may be reasonable or
possible to assign a number description to this to help make comparisons.
For example, the project I am working on is getting to Nearly Net Zero
Energy using conservation, PV, and a wood pellet CHP unit.


Conservation (below ASHRAE 90.1 or other baseline):                70%

PV (or wind) on-site (true net zero generation):

Other renewables generated on-site (possible off-site fuel):         15%

Purchased Renewables:
0%       (not needed to offset usage for my project, but also will be buying
green power) 


Nearly Net Zero: 70/15/15/0


Here are some possible ways to carry the ideas forward. Many commentators on
this string, and the Building Green article promote using the concept of Net
Zero to push us into another level of energy achievement.  I would
appreciate any additional comments on this.  


Brian Thornton, PE


Thornton Energy Consulting

p. 503-231-6600 f. 503-231-3555

thorntonenergy at comcast.net


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