Friday, November 12, 2010
Cool Technology of the Week
Part of this dream is live off grid and achieve a minimal carbon footprint through Green Engineering principles.
Recently, my second in command of IT at BIDMC, John Powers, went to a Green Engineering seminar, since he's pursuing the Green construction dream too.
Here are his lessons learned:
"The conference was an educational session for builders, architects and others on the new NH building code based on the International Energy Conservation Codes for 2009 (IECC 2009).
It was not a LEED or Energy Star course. These are far more comprehensive and cover building standards plus many other “green living” topics such as sustainable landscaping, pest control alternatives, water re-use, green appliances and so forth.
ARRA incentivized States such as NH to more aggressively adopt stringent energy conservation codes. My goal was to become a more educated consumer in preparation for building our “cabin” on a farm we purchased in northern NH.
Among lessons learned was green building was THE topic at the annual NH Builder’s Conference. This year’s banner was “Energy Efficient, Sustainable Building”. See the “Building NH Show Guide” a
Other States have similar organizations into which home owners can tap. Unfortunately, I had only time to attend the day long session on the new code. Looking over the Show Guide made me realize how much learning is still ahead. It emphasized the need to work with a builder and architect who understand the topic well.
The good news is there is an abundance of free material on the topic. Among the sites that have relevant content are
A refresher in basic building science, especially types of heat transfer. Radiation and conduction are important, but convection (heat transfer through air motion) is most important. Air leakage is the focus of many parts of the energy code. To drive home the point, the instructor provided an example. A 4’x8’ sheet of wall board will diffuse 1/3 of a quart of water a year. Punch a one square inch hole in it and it will exfiltrate (air leakage) 30 quarts of water a year.
The code refers to a “thermal envelope”. It’s the space you heat and/or cool. The envelope needs to be surrounded by a very, very tight thermal and air barrier. These barriers need to be next to one another (as in touching) and contiguous (no gaps). Use of strapping, odd structures such as dormers, stairs, rim joists, chases, shafts, penetrations, and the like require special attention.
With common use of 2”x6” for outside walls, it may no longer be necessary to use 16” on center studding for structural soundness. A typical outside wall may be 20 percent wood using routine construction standards. The “R” value of wood is 1 for every 1 inch thickness. Compare that to R22 for high density spray foam. Reducing outside wood surface, if structural soundness is not sacrificed, promotes a better thermal barrier.
Heat moves from areas of high temp to low temp. Heat does not always rise. Warm air rises, but heat can move in any direction. If you intend to heat your basement, it needs to be insulated and included in the thermal envelope.
You cannot average “R” values. For example, an attic insulated with one-half R-50 insulation and one-half R-10 insulation is not equivalent to (50+10)/2 or R-30. It’s far less or the equivalent of R-17.
There is a home energy rating system (HERS) that was developed by the Residential Energy Services Network (www.resnet.us). It rates the energy efficiency of a building relative to one built using the IECC 2006 codes. The latter would have a value of 100. A “zero energy” home would be rated “0”. The lower the score the better. For every point drop, there is a 1 percent reduction in energy compared to the index house.
The Department of Energy has issued a builders’ challenge to have, by 2030, cost-neutral, net-zero (NZEH) energy houses available in every location in the US."
Green Engineering is exciting stuff and I'm looking forward to the sheer geekiness of re-learning my thermodynamics and participating in the engineering of an energy efficient cabin in the woods. For now, I'll live vicariously through John Powers' project, but in another 10-15 years, I'll pursue my own. Green Engineering to save the planet - that's cool!
Posted by John Halamka at 3:00 AM