Implications of climate change for thermal risk assessment in indoor workplaces

Dear Editor, The most important thermal comfort standards such as ISO 7730 and ASHRAE 55 were established on the Predicted Mean Vote (PMV)/Predicted Percentage of Dissatisfied “comfort index” created by Fanger,[1] which predicts the thermal sensation as a function of both individual (activity and clothing) and environmental (air temperature, mean radiant temperature, air velocity, and humidity) parameters. As the PMV model has been recommended by technical standards for thermal comfort risk assessment in buildings with heating, ventilating, and air‐conditioning (HVAC) systems, field studies in warm climates showed that in non air‐conditioned buildings, an “adaptive model” that relates the neutral temperature indoors to the monthly average temperature outdoors is more suitable. [2] Indeed, even if Fanger introduced an expectancy factor for using his model in non air‐conditioned buildings in warm climates, and many researchers have tried to improve the PMV model, thermal neutrality is not necessarily the ideal thermal condition, especially in warmer climatic contexts. The risk assessment strategy for moderate indoor climate was based on by European directives concerning health and safety at work on technical standards such as ISO 7730 and ISO 15265. However, many researchers showed their inconsistencies. According to Humphreys and Nicol,[3] the ranges of the component variables that are consistent with the valid use of PMV are much narrower than those given in ISO 7730. According to Lenzuni and Del Gaudio,[4] PMV = 2 implies temperatures >30°C and as such it is entirely outside the effective range determining the validity of the PMV method, while a PMV = 1.3 corresponds to the few available data on the maximum allowable temperature in offices, indicated by national documents. According to Levin,[5] the Fanger’s model and its application have little or no place in the buildings occupied by the vast majority of the Earth’s population because it serves the wealthier 15% who live in the advanced, industrialized economies within buildings provided with HVAC systems. Recently, due to global warming, the European Union (EU) has released the Directive 2002/91/EC (Energy Performance of Buildings Directive) to promote the improvement of the energy performance of buildings. This mandatory directive is aimed at saving buildings’ energy use, and at the same time, contributing to decrease atmospheric concentrations of some greenhouse gases. [6] As a result, on one side, many EU countries had to indicate a maximum temperature limit at indoor workplaces, and on the opposite, PMV model is still to be used as the leading model for evaluating workers’ thermal comfort within indoor workplaces. With a warming climate, cooling is becoming a great priority for people because overheating can have a huge impact on heat‐related illness and mortality within homes and other indoor environments such as offices and hospitals. Many people are aging and living in cities where temperature increases is a matter of concern. Further, energy production and use are most important sources of air pollution, which was responsible for more than three out of four premature deaths (399,000 out of 487,000) in 2014 within the 28 EU countries. [7] Therefore, the electricity consumption to support HVAC systems is being increasingly limited. For this reason, questions about which is the best cool or heat system and which are the most appropriate models for evaluating workers’ thermal comfort are urgent to face. The adaptive model is able to adjust the indoor temperature on the basis of outdoor temperature, giving a further advantage in terms of balancing between thermal comfort and energy‐saving use. Moreover, the adaptive model is relatively easy to calculate because it does not require six input parameters and iterative calculations. However, this model is applicable when there are no functioning HVAC systems and mean monthly outdoor temperatures are between 10°C and 33°C, because above 33°C, the only predictive tool available is the PMV model. I believe that, ultimately, no one model alone is always proper; however, the adaptive model could be integrated with other solutions, including engineering measures to increase energy efficiency, a climate‐sensitive design, preventive measures to address any potential factors of local discomfort, and measures for individual control;[7,8] all of them could be probably able to create an acceptable thermal indoor environment for most indoor workers.