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Where You Build May Matter More Than What You Build

The transportation-energy intensity—how much energy is used by people who commute to a building—can often be more energy than the building uses itself

Posted on Sep 2 2009 by Alex Wilson

One of the things I like most about my seven-mile bicycle commute into work is the chance it affords me to just think about stuff in an unfocused way. When I drive to work (more often than I’d like) I usually have the radio on, letting the “Morning Edition” reporters direct my thoughts.

Sometimes, on these half-hour meditations along Route 30, I actually come up with interesting ideas. A few years ago, one of those was a realization that I needed to dig into—and publicize—the significance of “where we build” as a new measure of the energy intensity of buildings. I had been writing about and consulting on energy consumption of buildings for nearly 30 years, but had said very little about the significance of energy use getting to and from those buildings.

My interest in this issue had been piqued a few years earlier when a New York City colleague, Dan Nall, who is both a registered architect and engineer, mentioned in a lecture that he had done some back-of-the-envelope calculations showing that a typical office building required as much energy getting workers to and from the building as the building itself used. Could that really be the case? I resolved, on that bike ride, to figure that out.

I spent several weeks digging into this question, then published my findings in the September, 2007 issue of Environmental Buildings News (EBN), the national newsletter our company puts out from its Brattleboro, Vermont office. That article, I think, is one of the two or three most significant that we’ve ever published.

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.

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 (kBtu1,000 Btus/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 (ASHRAEAmerican Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). International organization dedicated to the advancement of heating, ventilation, air conditioning, and refrigeration through research, standards writing, publishing, and continuing education. Membership is open to anyone in the HVAC&R field; the organization has about 50,000 members. 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!

This is really significant, because in the past few decades tremendous effort has gone into making buildings more energy efficient, but very little attention has been paid to where we put those buildings. Building location, it turns out, has a huge impact on the total energy use of those buildings.

This understanding argues strongly for considering in our planning: access to public transit; the walkability of our communities; access to safe pathways for walking and biking; and zoning regulations that permit mixed-use development (combining residential and commercial development in an area). While I used office buildings to make this argument, it would also hold true, to varying degrees, for other building types, such as schools, retail stores, and houses. The most energy-efficient, “greenest” house won’t be all that green if its owners have to drive twenty miles to work or to pick up a quart of milk.

The EBN article came out at an opportune time. The LEEDLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. Rating System (a way to measure the “greenness” of buildings developed by the U.S. Green Building Council) was undergoing significant change in late 2007, and based in part on my findings, the relative weighting of points relating to location and alternative means of transportation was significantly boosted. The Center for Neighborhood Technology in Chicago is currently working to advance this idea of “transportation energy intensity,” and I recently had a conversation with someone from the U.S. General Services Administration (GSA) about how to address this concept in siting new federal buildings.

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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  1. Alex Wilson

1.
Sep 2, 2009 3:28 PM ET

Special Neighborhoods
by John Brooks

We recently built in a Historic Neighborhood.
They encourage people to work at home....
Two Blocks from the light rail station ...walking distance to the park, downtown, restaraunts and a produce market.

Very pleased that we did not have to tear down an existing home.... ours is a very small lot that was part of a larger estate that "vanished" over fifty years ago.


2.
Sep 3, 2009 3:35 PM ET

You May Have Missed Something:
by Steve A.

With all due respect, I see a possible flaw in your calculations.

You should calculate the total from source energy intensity, not site energy intensity. The efficiency losses of electrical generation production and distribution is on par to being 50% - which is not being calculated in this equation.

There is energy consumed with drilling, refining and transporting oil, but I don't believe it nears the 50% range. Most of oil based energy is lost at the point of use (in the form of waste heat) during combustion. This is why your energy use calcs are so high for autos and so low for buildings.

I have a feeling if he were to calculate his numbers from *source* Btu intensity, it would put the burden largely on the building.

I manage a very efficient office facility, with a site intensity of 42 kBtu/ft2/year. Not bad. But If you do the same numbers from *source* intensity (according to the EPA energystar building calc), that jumps by nearly a factor of 3, to 123 kBtu/ft2/year.

If the average office building consumes 93 kBtu/sf/yr, their source energy needs are on the range of 280 kBtu/sf/year - which is much higher than automobile needs.

You should adjust your calcs accordingly.


3.
Sep 7, 2009 12:15 PM ET

good eye on the source energy
by Brennan Less

Steve, you make a very good point. Here's how I interpret your point: Alex calculates transportation energy as 56.5% (121kBtu/(121kBtu + 93kBtu)) of total building energy intensity, and your source-adjusted figures put transportation energy as 30.2% (121kBtu/(121kBtu + 280kBtu)) of total building energy intensity. There is a difference of 26.3% between these two figures--not insignificant. But let's not lose sight of the real issue here. If any other building element were responsible for 30.2% of total energy intensity, then engineers would target it directly for aggressive load reductions (for example, lighting in commercial buildings). I think Alex is simply pointing out that targeting transportation energy reduction in green design may be more effective than targeting building elements with respectively lower percentages of total energy intensity. I think there is potentially a very interesting economic/green house gas argument to be made here. Enjoy your holiday.


4.
Mar 3, 2010 7:56 AM ET

hayaloglunakliyat
by hayaloglunakliyat

The program’s next challenge is to help push national leaders around the world to consider transportation when putting together Nationally Appropriate Mitigation Actions (NAMAs), the low-carbon, sustainable development plans written by developing nations to receive funding under the United Nations Framework Convention on Climate Change (UNFCCC).


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