Outdoor Microclimate Variations and Indoor Thermal Stress: Summer Field Measurements in an Elderly Care Facility

¹ Building Physics and Sustainable Design, Department of Civil Engineering, KU Leuven, Ghent, Belgium
² Faculty of Architecture and Planning, Hanoi University of Civil Engineering, Hanoi, Vietnam

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Rising temperatures driven by climate change degrade both indoor and outdoor thermal conditions in cities. This challenge is particularly critical for vulnerable populations, such as older adults in care facilities, where combined indoor and outdoor heat exposure may pose serious risks. This study presents a summer field campaign at an elderly care facility in Ghent, Belgium, where indoor and outdoor thermal environments were monitored synchronously to evaluate recent heat stress in the built environment. Four representative urban microclimate locations (canyon, courtyard, semi-shaded park, exposed park) and seven resident rooms with different neighbouring microclimate contexts were selected. Rooftop and pedestrian-level weather stations, together with HOBO loggers, were used to record outdoor and indoor environmental variables. Physiological Equivalent Temperature (PET) and Standard Effective Temperature (SET) were applied to quantify outdoor and indoor heat stress, respectively. Tukey tests were used to assess significant differences in heat stress between sites and rooms, while SHapley Additive exPlanations (SHAP) were employed to identify key driving factors. The results showed that the exposed park (EXP) experienced the highest outdoor heat stress, with Exceedance Degree-hour (ED-h) of 600-1100 °Ch, whereas the semi-shaded park (SDP) showed roughly half this value, demonstrating the effectiveness of tree cover ratio in mitigating outdoor heat stress. Canyon (CAN) and courtyard (COY) showed similar heat stress with ED-h ranging from 280 to 740 °Ch. SHAP results indicated that air temperature and solar radiation (during daytime) are two key drivers of outdoor heat stress at pedestrian levels. For indoor results, all top-floor rooms exhibited higher heat stress than ground-floor rooms, particularly those facing the canyon and courtyard, with ED-h of 136 °Ch and 75 °Ch, respectively. Moreover, rooms with same east-facing orientation but different surrounding microclimates (COY and SDP) showed a significant difference in ED-h, with maximum delta SET reaching around 1.42 °C. Beyond orientation, the surrounding microclimate may be a key driver of indoor thermal stress. These findings highlight the importance of outdoor morphology (e.g., tree and impervious cover) in shaping local temperatures and should be considered in indoor heat mitigation strategies. Future work will assess these influences using coupled building-microclimate simulations.