Experiments conducted in the tropical city-state of Singapore indicate that slightly raising indoor temperatures and equipping office workers with smart fans can save significantly on office building energy costs while maintaining employee comfort.
Findings from the research, by an interdisciplinary team of researchers from the University of California, Berkeley, and Stanford University in the United States and Nanyang Technological University in Singapore, can guide the design and operation of new and existing office buildings in the world's tropical regions.
The team's objective was to show that it is possible to provide the same or more comfort with less energy.
The typical set point for office building indoor temperatures has for decades been 23 degrees Celsius in Singapore, where the yearly average outdoor temperature during the day is 29 degrees. Stefano Schiavon, a principal investigator on the Singapore research and a UC Berkeley assistant architecture professor in sustainability, energy and environment, wanted to see what would happen when they turned up the thermostat.
Schiavon and his team conducted five experiments in the summer of 2014, with 56 participants dressed in typical Singaporean office attire, and assembled in a room at Nanyang Technological University featuring an open-office layout, with no cubicles.
During the 90-minute tests, participants were asked to gauge their comfort levels when temperatures were adjusted to 23 degrees, 26 degrees or 29 degrees. Relative humidity was controlled at 60 percent, a typical indoor level in Singapore. At 26 degrees and 29 degrees, subjects were allowed to control air movement with personal electric fans if they wished.
The tests used smart, energy-efficient desk fans that run on more efficient, direct-current (DC) motors using between 3 and 17 watts, rather than alternative-current (AC) motors that use around 100 watts.
Key findings reported by the researchers in the latest issue of Indoor Air include:
-- Thermal comfort, perceived air quality and symptoms of sick building syndrome are reported to be equal or better at 26 degrees Celsius and at 29 degrees, rather than at the common "set point" of 23 degrees, if a personally controlled fan is used.
-- The best cognitive performance, as indicated by task speed, was recorded at 26 degrees; at 29 degrees, the availability of an occupant-controlled fan partially mitigated the negative effect of the elevated temperature. The typical Singaporean indoor air temperature set point of 23 degrees yielded the lowest cognitive performance.
Increasing the indoor temperature set point to the range of 26-29 degrees and providing occupants with personally controllable fans could be a cost-effective, sustainable and energy-efficient option for providing thermal comfort in new and existing buildings in the tropics, said Schiavon.
"If applied to commercial building in Singapore, we could save up to 35 percent of the energy for air conditioning," he said, adding that "we are now working on smart fans that can adapt to the environmental conditions and provide the needed comfort."
"In 2050, most of the world population will live in the tropics, and the use of air conditioning is already exploding in tropical countries. Forecasts for an even hotter, more densely populated and wealthier planet just add to the significance of our research," Schiavon was quoted as saying in a news release from UC Berkeley.