Flawed sensor readings doom efficient HVAC systems

Thermometers misread temperature to affect HVAC system design
As shown by a thermal camera, the person is cool when standing in front of a radiant cooling system. (Eric Teitelbaum)

Researchers have found that standard comfort measurements used to design buildings' heating and cooling systems fail to account for convection air flow, due to the instruments used to measure temperature.

According to findings in the journal Scientific Reports, the researchers said the use of the globe thermometer, and associated formulas used to calculate comfort based on the sensor's readings, do not properly account for air flow called free convection. In experiments, the failure led to temperature errors of more than two degrees Celsius, the researchers said.

Forrest Meggers, an assistant professor at Princeton University's Andlinger Center for Energy and the Environment and one of the lead researchers, said the team found problems with traditional measurements while building an outdoor exhibit in Singapore. While the team had no issues keeping the exhibit participants comfortable using a radiant cooling system, using standard measurement techniques, they had difficulty demonstrating these cooling effects.

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Meggers, also an assistant professor of architecture, explained that while the participants remained comfortable and the system was able to keep them feeling cool, the calculations showed the system was not working and that the environment should feel uncomfortable.

"That's when we realized the formula was wrong. We had a hard time accepting it," Meggers said.

The notion of using radiative heat exchange cooling or heating walls and surfaces to keep people nearby comfortable has been identified as an energy efficient design feature, but air conditioning is still the primary solution for keeping people comfortable in buildings in the United States and other places. The researchers noted that understanding and effectively capturing the impact of radiant systems on comfort can have a major impact on energy savings. Letting the air reach five degrees warmer while cooling surfaces, the researchers said, can lower cooling demand by up to 40% and maintain occupant comfort.

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