Experimental study on dynamic thermal responses and comfortable evaluations under bathing conditions.

This study investigated the dynamic thermal responses and comfortable boundaries under different bathing conditions through a series of human subject experiments. Eleven subjects' subjective questionnaires and physiological parameters were collected. During the 40-min 40 °C bath, subjects' whole-body thermal sensation, sweating sensation, and fatigue relieving vote increased from 0 (neutral) to 2.6 (near 'hot' sensation), 3.5 (near 'very sweaty' sensation), and 1.6 (near 'relieved' vote), respectively. Thermal comfort vote firstly increased to 1.5 (near 'comfortable' sensation) in the first 10 min, then decreased to -0.5 (between 'neutral and slightly uncomfortable' sensation), and eventually remained around 1.1 ('slightly comfortable' sensation) after the bath. After the 40-min bath, the skin temperature and core temperature rose by 2.0 °C and 0.9 °C respectively. The mean heart rate increased by 45% and blood pressure decreased in most subjects. The percentage of β brain wave (representing concentration emotion) decreased while that of δ brain wave (representing relaxing emotion) increased, indicating that the bathed subjects tended to be more relaxed and sleeping emotionally. Based on these observations, we inferred that bathing thermal comfort can be influenced by multiple factors simultaneously but effective evaluation tools quantifying bathing thermal comfort are yet to be produced. Compared with showering, bathing usually induces more intensive thermal stress to the body, causing similar changing patterns but stronger amplitudes in subjective and physiological responses. These results can provide references for more comfortable and healthier bathroom environment design and relevant environmental conditioning products.