A Non-Invasive Assessment of Thermal Comfort in a University Library Using Infrared Thermography

Thermally comfortable conditions in university libraries support occupant productivity and academic performance. Conventional assessment depends on contact physiological sensors and self-administered questionnaires, which raise ethical concerns, cause participant discomfort, and lose accuracy in busy, variably occupied educational settings. This study evaluates thermal comfort in the Kashim Ibrahim Library (KIL) at Ahmadu Bello University, Zaria, using a hybrid non-invasive approach combining infrared thermography (IRT), structured questionnaires and indoor environmental measurements. The contribution is the first field calibration of IRT against subjective thermal sensation in a sub-Saharan university library, and the first pairing of an IRT- derived forehead temperature band with a locally derived adaptive neutral temperature for a heat-acclimatised tropical population. A quantitative cross-sectional design was applied to 100 library users selected by systematic random sampling. Individual indoor air temperature readings across four zones and repeated measurement sessions spanned 22.0–37.0°C, with zone means of 22.0–27.0°C and relative humidity of 75–81%. Forehead skin temperatures were captured without contact using a calibrated infrared imager, and thermal perception was recorded on the ASHRAE Standard 55 sensation scale and the Bedford comfort scale. Regression of thermal sensation vote on indoor air temperature returned a neutral temperature of 28.8°C, within the measured range and 2.8°C above the ASHRAE Standard 55 upper comfort boundary, which quantifies the adaptive margin of this population. Forehead temperatures of 30.50–33.49°C corresponded with neutral votes (r = 0.61, p < 0.001), confirming IRT as a valid non-contact indicator of thermal state. The study establishes IRT as an ethically compliant substitute for contact measurement in occupied educational buildings and supports hybrid ventilation targeted at a 26–30°C adaptive band in comparable tropical facilities.