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The researchers, Mark Mendell and Anna Mirer of Berkeley Lab's Environmental Energy Technologies Division, analyzed data collected from 95 air-conditioned office buildings across the U.S. The data had been gathered by the U.S. Environmental Protection Agency in a study called BASE (Building Assessment Survey and Evaluation). The study produced data about indoor environmental conditions and the health of occupants in a representative set of U.S. office buildings.
The study collected standard measurements in each building on factors such as temperature and humidity, during one week in either summer or winter. Building occupants filled out a survey at that time with questions about building-related symptoms, defined as symptoms that were experienced in the building but improved away from the building. Symptoms assessed were related to the upper and lower respiratory tract, eyes, skin, headache, fatigue, and difficulty concentrating.
Using the data from this study, the Berkeley Labs scientists conducted what is called a cross-sectional statistical analysis of two questions:
1) How did the temperatures in the 95 buildings from the BASE study compare to the temperature comfort ranges recommended for summer and winter by ASHRAE?
2) Were there associations between the occurrence of building-related symptoms and indoor temperature or humidity?
Buildings substantially overcooled in summer
In winter, the researchers found, the buildings were kept mostly within the recommended temperature comfort range for winter, but in summer building temperatures were, on average, below the comfort range for summer. Surprisingly, buildings were, on average, kept even cooler in the summer than in the winter, by almost 1 degree F (0.5 degree C), even though people are more comfortable with warmer temperatures in summer.
These low temperatures in summer suggest that many occupants would be too cold in their offices, and this overcooling by the air conditioning systems also indicates wasted energy.
Some building temperatures associated with increased symptoms in office workers
Furthermore, in summer, a variety of building-related symptoms such as headache, fatigue, and difficulty concentrating were increased by over 50 percent in the buildings kept below 73.4F (23C). These buildings, kept too cold for comfort in summer, included almost half the buildings measured in summer. These symptoms thus might be expected to decrease if buildings were air-conditioned less and kept warmer in the summer.
In winter, buildings with higher indoor temperatures (above 73.4F, even though that is near the middle of the recommended temperature range) were associated with approximately 30 to 80 percent increases in building-related nose, eye, and skin symptoms, and also headaches. This included more than half the buildings measured in winter. These symptoms thus might decrease if buildings were kept cooler in the winter.
Simply put, avoiding overcooled buildings in the summer, and keeping buildings at the cooler end of the recommended temperature range in the winter, may result in a substantial decrease in building-related symptoms. This should still maintain thermal comfort in the buildings in winter, and should actually improve comfort in the summer.
Benefits seen for both energy efficiency and occupant health
Keeping air-conditioned buildings warmer in summer will save energy. Keeping buildings cooler in the winter will in many cases save energy through reduced heating. However, many of the buildings studied in winter, especially those with moderate outdoor temperatures at the time, may have been in cooling mode to handle internally generated heat from occupants, lights, and equipment. For these buildings, lowering indoor temperatures in the winter to decrease occupant symptoms would not be expected to provide energy savings, and in some cases it might increase energy use.
"As we look for ways to save energy, these results suggest a potential win-win situation," says Mendell. "Our findings suggest that energy efficiency and keeping buildings healthy and comfortable for the occupants are not necessarily in conflict. Less summer cooling in air-conditioned buildings and less winter heating in heated buildings might reduce energy use in buildings substantially, yet have health benefits for the occupants that we did not expect, and still keep occupants as comfortable as before or even more comfortable."
The paper, "Indoor Thermal Factors and Symptoms in Office Workers: Findings from the U.S. EPA BASE Study," by Mark Mendell and Anna Mirer, has been published online in the journal Indoor Air.