Heat Stress on the Balcony: Investigating the Effects of Facade Heat and External AC Units

Abstract

Balconies serve as vital semi-outdoor spaces in tropical residential architecture, yet they are often exposed to extreme heat stress that limits their usability. This study investigates the combined impact of facade surface temperature and air conditioning external units on outdoor Thermal Comfort (OTC) on residential balconies in Cau Ong Lanh Ward and Ban Co Ward, Ho Chi Minh City, Vietnam. In-situ climatic measurements were conducted in August, focusing on air temperature, surface temperature of adjacent walls, and radiant heat emissions from active AC outdoor units of 296 houses. Observations were paired with behavioral data indicating residents’ willingness to use the balcony under different thermal conditions. Results reveal that balcony environments frequently exceed strong heat stress thresholds during daytime hours, driven by direct solar gain on facades and waste heat from outdoor units. Facade orientation and proximity to mechanical units were found to significantly influence the microclimate at occu-pant level. Most residents avoided using balconies during peak hours, identifying heat from outdoor units as a major discomfort factor. The findings highlight the need to reconsider mechanical unit placement, facade material choices, and shading strategies in balcony design. This study contributes to a growing body of knowledge on climate-responsive residential architecture in tropical regions, emphasizing the integration of mechanical systems and passive design to restore balcony usability and improve occupant well-being.