Exposure to slowly drifting warm thermal environments inside greenhouses

An adaptation of the PHS method to slowly drifting thermal environments has been developed. The generalized PHS code has been used to predict the daily evolution of physiological responses and the maximum allowable exposure, given the detailed daily indoor evolution of temperature and humidity. Results indicate a strong dependence on outdoor meteorological conditions. Despite allowing an early morning start (7 am), the core temperature increase is usually quite fast, and exposures longer than 2.5 hours should be ruled out under most of the investigated circumstances. Exposure duration is always limited by the excessive core temperature, whereas water loss is largely inconsequential. Results obtained using our generalized PHS model differ significantly from those of the standard (static) PHS model (i.e. using daily averages for air/radiant temperatures and humidity). A constant monitoring of the greenhouse thermo-hygrometric quantities, with time resolution not exceeding a few minutes, is a mandatory pre-requisite for reliable thermal risk assessment.