Application of Gagge’s Two-Node Model to Evaluate Sleeping Thermal Environments

Sleeping thermal environment plays a significant role in human sleep quality, and in recent years people’s demand for a comfortable sleeping environment has increased dramatically. However, studies about evaluation methods for the sleeping thermal environment are still rare. This study aims at developing a method for evaluating the sleeping thermal environment. Gagge’s two-node model has been adapted to sleep environmental evaluations through three phases of work; modifications to the model’s inputs, its conversion to a transient model, and identification of a sleeping comfort zone. The “clo” input variable in the two-node model refers to an intrinsic insulation Icl,bed (i.e. insulation attributable to the bedding with boundary-layer air insulation removed). A calculation method for Icl,bed was developed and a matrix of thermal manikin experiments measured the Icl,bed for a sample of typical bedding in Sydney. The two-node model’s algorithm was adapted from its default, steady-state solution to a transient, time-series approach, to accommodate transients in both room environmental and physiological (metabolic) parameters through the course of the night. A sleeping environmental comfort zone, expressed in terms of the two-node model’s output (SET*) was identified from a pre-existing Sydney field survey database. Results of the intrinsic bedding insulation (Icl,bed) measurements for nine different combinations of bedding systems ranged between 1.40 clo and 3.33 clo. Nocturnal time-series of skin temperatures simulated by the modified two-node model under these clo values were validated published physiological data in the literature. Application of the modified two-node model to previously published Sydney field-study results suggested an optimal bedroom SET* range for sleeping persons in the range of 29-30.9oC. The optimum range of operative temperatures and the optimum air-conditioner control strategy were later proposed for the nine commonly used bedding systems. The developed evaluation method can serve as a valid tool for evaluating the whole-night bedroom thermal environments. It can provide reliable predictions for the sleep thermal conditions, instruct better sleep air-conditioner control strategies and lead to better sleep thermal experience