Overall and thermal comfort under different temperature, noise, and vibration exposures

Public transports like the bus and subway inherently experience noise, vibration, and temperature variations that are different from building environment. Each of them can influence passengers' comfort, but little is known about their combined effects, especially how they affect thermal comfort. This paper presents experimental results from a series of human subject tests under different noises, vibrations, and temperatures. 32 subjects' subjective perception and physiological response were collected under three temperatures (22.5, 25.5, 28.5℃), five noise levels (55, 60, 65, 70, 75 dB(A)), and five vibrating accelerations (0, 0.2, 0.4, 0.6, 0.8 m/s² ). We also varied the noise and vibration spectrums to simulate the bus and subway environments. In total, 48 195-min and 192 115-min laboratory tests were conducted. By using significance tests (paired t tests and two-way ANOVA tests) and sensitivity analysis (Treed Gaussian Process), the results show that temperature, noise, and vibration exposures can significantly affect subjects' overall satisfaction. More interestingly, high noise and vibration levels can cause warmer thermal sensations. A change in the noise of 20 dB(A) or vibration of 0.6 m/s² is equivalent to an ambient temperature change of 0.6 °C. We also observed higher heart rates and metabolic heat production at higher levels of noise and vibrating accelerators. Based on the test results, regression models were developed to describe the combined effects of temperature, noise, and vibration on subjects' overall comfort perception and thermal neutral temperature. They can serve as references for the design and operation of public transport environments.