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Energy Consumption Getting to and From Buildings Exceeds Energy Use for Operations

Brattleboro, VT (September 05, 2007)

An examination of the “transportation energy intensity” of buildings has found that getting people to and from buildings uses more energy than the buildings themselves consume. The lead article in the September 2007 issue of Environmental Building News shows that for an average office building in the United States, 30 percent more energy is expended by office workers commuting to and from the building than is consumed by the building itself for heating, cooling, lighting, and other energy uses. For an office building built to modern energy codes (ASHRAE 90.1-2004), more than twice as much energy is used by commuters than by the building.

“This was a huge surprise,” says Environmental Building News (EBN) executive editor Alex Wilson, author of the article. “I knew that transportation energy requirements were significant, but I was amazed at the differences.” For the article, Wilson collected average U.S. data for commute distance, vehicle fuel economy, the split among different commuting options, and the number of square feet of building per office worker to normalize transportation energy intensity in Btu/square foot per year. He was then able to compare that transportation energy intensity to the average building energy use (also in Btu/ft2-yr) for average existing office buildings and energy code-compliant buildings (see table below).

Comparing Transportation and Operating Energy Use for an Office Building

 

U.S. Units

Metric Units

Average U.S. commute distance – one way (1)

12.2 mi

19.6 km

U.S. average vehicle fuel economy – 2006  (2)

21.0 mi/gal

 8.9 km/liter

Work days

235 days/yr

Annual fuel consumption

273 gal/year

1033 liters/year

Annual fuel consumption per automobile commuter  (3)

33,900 kBtu/yr

9,890 kWh/yr

Transportation energy use per employee (4)

27,700 kBtu/yr

8,100 kWh/yr

Average office building occupancy (5)

230 ft2/person

21.3 m2/person

Transportation energy use for average office building

121 kBtu/ft2

381.2 kWh/m2

Operating energy use for average office building (6)

92.9 kBtu/ft2-yr

292.7 kWh/m2-yr

Operating energy use for code-compliant office building (6, 7)

51.0 kBtu/ft2-yr

160.7 kWh/m2-yr

Percent transportation energy use exceeds operation energy use for an average office building

30.2%

Percent transportation energy use exceeds operation energy use for an office building built to ASHRAE 90.1-2004 code

137%

1. U.S. Department of Transportation, Transportation Energy Data Book 26th Edition, 2007, Table 8.6 

2. U.S. EPA Light-Duty Automotive Technology and Fuel Economy Trends: 1975 Through 2006 

3. Assumes 124,000 Btu/gallon of gasoline, DOE Energy Information Administration data 

4. Assumes 76.3% commute in single-occupancy vehicle, 11.2% carpool (2 per car) and no other energy use (commuting transportation modes from U.S. DOT Transportation Energy Data Book 26th Edition, 2007, Table 8.14. 

5. U.S. General Services Administration 

6. This includes site energy only, not source energy. U.S. DOE Energy Information Administration Commercial Building Energy Consumption Survey (CBECS) data for 2003, published June 2006. 

7. Bruce Hunn, ASHRAE, personal communication 

Source: Environmental Building News, September 2007

“The green building community has expended tremendous effort to reduce the operating energy use of buildings,” notes Wilson, “but very little effort to reduce the transportation energy use of those buildings.” He would like to see this change. “To achieve widely shared goals for dealing with climate change,” says Wilson, “we simply can’t ignore the energy consumption getting to and from our buildings.”

Many of the strategies for reducing the transportation energy intensity of buildings relate to location. The September EBN article, “Driving to Green Buildings: The Transportation Energy Intensity of Buildings,” reviews a wide range of strategies for reducing vehicle use. Such strategies are often lumped under the heading “transit-oriented development” and include increasing development density, creating mixed-use development, providing various forms of public transit, restricting parking, and creating more pedestrian-friendly streetscapes. “Although progressive urban planners have been advocating for such development features for years,” says Wilson, “the building industry has only recently begun paying attention to these issues.”

In an editorial in the same issue of EBN, Wilson calls for changes to the LEED Rating System to make the credits relating to location and transportation performance-based, rather than prescriptive. “While the prescriptive approach in LEED to site and transportation issues has served an important role,” Wilson says in the editorial, “it’s time to provide a more rigorous basis for these credits.”

The full article on transportation energy intensity and the accompanying editorial can be accessed at www.BuildingGreen.com. These articles are part of BuildingGreen Suite, a leading online resource on green building. While this is a paid-access site (with members paying $199 per year) these articles are provided free as a sampling of content. Environment Building News is the oldest and one of the most respected sources of green building information in North America. Celebrating its 15th year of publication in 2007, EBN has never carried advertising and is supported entirely by subscription revenue. For information, visit www.BuildingGreen.com, or call 800-861-0954 (outside the U.S. and Canada, call 802-257-7300). BuildingGreen is an independent, socially responsible, 20-person company based in Brattleboro, Vermont.

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