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Study of MIT Buildings Suggests Additional Approaches to Energy Efficiency

Colleges and universities are notorious for inefficiency in energy use. A recent study by the Massachusetts Institute of Technology of two MIT buildings can assist both other educational institutions and other types of facility owners in reducing energy use through planning and scheduling. Titled “ENERNET: Studying the dynamic relationship between building occupancy and energy consumption,” the paper deals with the significant issue of matching building and equipment schedules with dynamic occupancy patterns.  

Many workplaces feature major changes in occupancy over the course of a day or throughout the week. As a result, energy use tends to be inefficient—too large or too small—in relation to the use pattern.

The MIT study reveals some data that could help designers and building managers, on campuses or in the commercial sector, optimize energy usage. It also sets the stage for more research on the subject. The study, published in the April issue of the Energy and Buildings journal, finds that while electricity use corresponds to occupancy fairly well in those spaces, the activity of heating, ventilation, and air conditioning (HVAC) systems in the buildings does not correlate closely to occupancy.

The researchers analyzed two very different kinds of buildings—one housing researchers in a combination of offices, classrooms, and labs, and the other a stand-alone classroom building with a sizable entrance atrium and a large number of offices inside. The study used data about Wi-Fi connections as a proxy for building occupancy, a method the researchers believe could be replicated elsewhere at low cost; while the data does not necessarily reveal an exact population count inside buildings, it does indicate relative occupancy levels over time.
Analyzing data from all four seasons of 2006, the researchers found that both buildings have a distinctive cyclical “signature” of electricity usage that rises and falls daily. Both buildings use more steam (for heat) in winter and spring, and more chilled water (for air conditioning) in summer and fall. But while about two-thirds of the variation in electricity levels can be accounted for by changing occupancy levels, the use of the HVAC systems correlated only weakly to occupancy. These MIT buildings tended to be heated or cooled according to the season but not in a way that optimized the use of energy.
The researchers, part of MIT’s SENSEable City Lab, noted that part of the variance between occupancy and energy use may derive from the special needs of academic buildings, which often house labs with around-the-clock heating or refrigeration demands.

There are many possible architectural or engineering solutions to this issue. Co-author of the study, Carlo Ratti, notes “You can move the people to the energy, in which case the architecture can help a lot, or you can move the energy to the people, which is more futuristic.” The larger point, he says, is that “you want to have a better match.”
The study suggested possible design-based solutions including:
  • rearranging plans so that heat from larger, less used spaces can seep into more rooms
  • using sensing based thermometers that regulate temperatures on a more granular basis within buildings,according to the number of people
  • repurposing large spaces for more intensive and improved use


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