Thermal perception of infrared radiation applied at different wavelengths to distal body segments in neutral and cool ambient environments

Personal Comfort Systems (PCS) hold the promise of simultaneously improving energy conservation and occupants’ thermal comfort. Locally applied thermal radiation is one of the most common PCS strategies for cool ambient environments. This study examines the subjective impacts of different infrared wavelengths applied to distal body segments of human subjects sitting quietly in cool and neutral environments. Experiment participants were exposed to three different wavelengths (near-infrared, mid-to far-infrared, and far-infrared), each of approximately equal flux density, on the backs of hands, lower arms, and lower legs, in both neutral (26.0 °C operative temperature) and cool (21.5 °C operative temperature) ambient environments within the chamber. Skin temperature, along with subjective thermal sensation and thermal pleasure votes were recorded throughout each exposure experiment. In the cool environment, similar to the neutral environment, far-infrared radiation increased skin temperature more than near-infrared and elicited warmer subjective thermal sensations and thermal pleasure responses. Of the three distal body segments examined, the back of the hands was most sensitive to the different wavelengths and was associated with the strongest and fastest pleasure response at the onset of radiant heating during the cool ambient environmental exposures. These findings have implications for PCS design, suggesting that irradiating the back of the hand with far-infrared wavelengths at the onset of PCS use may maximize thermal comfort of sedentary occupants in cool ambient conditions for a given power input. •Reveals that wavelength dependence of thermal perception in cool environments.•Back of the hand is more thermally sensitive than lower legs and arms.•Far-infrared radiation heating induces warmer and more pleasant responses.•Far-infrared radiation heating can elicit spatial alliesthesia.•Most pronounced pleasure response occurs at the onset of far-infrared irradiation.