Monday, December 29, 2014

Odds 'N Ends - Carbon-Phobic Homes Come In Many Stripes

The "Energy" Component in Green Building
The best summary I have seen on levels of energy independence is found in the introduction to Johnson and Gibson's "Toward a Zero Energy Home - a Complete Guide to Energy Self-Sufficiency at Home". The book is a good read for anyone interested in sustainability--it is full of success stories for both new construction and remodeling.  They differentiate between net zero energy homes, off-the-grid homes and carbon neutral homes

Net Zero Energy Homes
These homes produce as much energy as they consume.  They are tied to the utility grid with net-metering, have photovoltaic arrays or wind turbines and store any excess production on the grid rather than in batteries.  The utility typically pays a fair price for the energy it gets when the house is producing more than it is using.  However, some utilities drop the price to a pittance once net-metering reaches zero.

Off-the-Grid Homes
These homes live on an energy budget.  When production exceeds usage, the excess goes into on-site batteries that have a limited storage capacity.  If the sun isn't shining or the wind isn't blowing and the batteries are running low, there's a problem.  The solution is lifestyle adaptations that ration or manage energy usage.  Toasting bread for breakfast and taking a hot shower simultaneously might not be possible.

Carbon Neutral Homes
A carbon neutral home carries zero energy to another level.  It produces enough energy, not just to handle its daily needs, but to cover the costs of building the home in the first place.  This means covering the embodied energy in extracting, manufacturing and transporting the building materials to the home site (which, according to Johnson and Gibson, is 8% of the home's energy use).  Only the most principled and ethical home owners go there (which is hard to do anyway if the utility refuses to pay a fair price after net-metering reaches zero).

Passive House Movement
According to the authors, the Passive House Movement began in Germany in 1990 based upon passive solar research in the '70's by the U S Dept of Energy, spread rapidly across Europe and finally made its way back to this country in '03.  The first net zero energy Passive House was built in Urbana, IL where the Passive House Institute U.S. is located. According to the Institute, the standards for Passive Houses are as follows:
  • Use of the Passive House Institute software to model the house
  • Super-insulate
  • Eliminate thermal bridges
  • Make the house airtight
  • Use heat-recovery ventilation
  • Optimize passive solar design
  • Use high-performance windows and doors
  • Use internal heat gain (people, appliances, electronic equipment)
  • Zero out energy needs with renewable energy (my addendum, based on the authors' discussion following the list in the text)
Can We Call Our Project "Net Zero"?
With exception of the first standard listed above (we did a DIY design without software), our home will exceed the Passive Home I guess it's safe to use the term "net zero" energy, or at least "near zero" energy to describe it once it's finished and the photovoltaics have been added.  And we will take great pride in achieving net-zero at a fraction of the cost of typical new construction -- green or otherwise.