[BLDG-SIM] Net Zero and Nearly Net Zero

John Porterfield john_m_porterfield at yahoo.com
Mon Mar 6 21:01:07 PST 2006


Brian,
Wind is a less costly technology to expand grid generation capacity in many locations.  I'm curious how much renewable energy is created, and how much carbon/nuclear generation capacity avoided, by placing renewables on houses (i.e., scaling down to capacity of a residence).  Consider the amount of renewable energy created, and conventional capacity avoided, if one invested the, say, $20,000 or so (for a rooftop-scale system), in a company that develops renewable energy to compete head-to-head with conventional generating capacity addition.   
An interesting comparison of generating capacity addition, by technology, accounting for the health and environmental cost of power production:  www.tellus.org  search for publication "Coal . . . "
Opportunities to displace conventional generating capacity addition with renewable energy, based on renewable energy applied at the most promising locations and where a capacity addition choice is present, perhaps merit our attention (and enthusiasm!) more than the 'net zero' house.   
John Porterfield
john at energydetectives.com


Brian Thornton <thorntonenergy at comcast.net> wrote:          st1\:*{behavior:url(#default#ieooui) }                     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 design   
   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 enough) 
   
  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=&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):                            15%
  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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