Jargon Watch: "Transportation Energy Intensity" of Buildings


Image via: Cycling.com

A few years ago, Alex Wilson of Green Building Advisor wondered how much energy was being used commuting to offices, versus the actual energy consumed by the offices. After all, we going to all of this effort and expense to make our buildings more energy efficient, but is it meaningful in the face of all the travelling people do to get there? Wilson did the math.

I started by collecting a bunch of data from government sources: the average commuting distance by U.S. workers; the breakdown of commuting by modes of transportation (76% is in single-occupancy vehicles); the average fuel economy of our vehicles (21 mpg); and building occupancy in square feet per office worker. Given this information, I was able to calculate the average energy use for transportation for an office building per square foot of space.

Sorry for the long quote, but the process is important:

I wanted to come up with a metric for the transportation energy use associated with buildings that was parallel to the metric used to measure the energy intensity of a building--for heating, cooling, lighting, computers and other uses. This is commonly reported in thousands of British Thermal Units, or Btus, of energy per square foot per year (kBtu/sf-yr). The U.S. Department of Energy reports that the average energy intensity of office buildings in the U.S. is 93 kBtu/sf-yr. If I could calculate the average energy consumption for commuting using this same metric, I'd be able to show how the commuting energy use compared with the direct building energy use. I called this value "transportation energy intensity."

The results were really interesting. Using these admittedly crude assumptions, I found that office building energy use for commuting averages 121 kBtu/sf-yr. That's 30% more energy than an average office building uses itself. So it takes more energy to get to and from our office buildings than those buildings use directly!

Even more significantly, if we make the same comparison using a new office building that is built according to modern energy codes (ASHRAE 90.1-2004), we find that the transportation energy use is nearly 2.4 times as great as the direct energy use of the building!

So the more efficient we make our buildings, the worse the transportation efficiency looks relative to the building. It is a real lesson in the importance of planning, of designing our cities right so that one can walk or take transit or bike to work in safety and comfort, that all the green building in the world isn't going to make that much difference if we don't fix these things first.

LEED now takes this into account and has points for location and transit; so should the building code and planning bylaws- Transportation Energy Efficiency is clearly as important as building efficiency.

And one can learn from Alex Wilson's closing sentence:

For me, even though I live in a rural area, seven miles from my office, this understanding of transportation energy intensity inspires me to get on my bike and enjoy that invigorating (and sometimes mentally productive) ride to work.

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Tags: Green Building

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