Desiccant dehumidification and evaporative cooling conditioning of canopy shaded space for improved outdoor thermal comfort in hot humid climates

Abstract

Climate change and increased urbanization are resulting in elevated outdoor ambient temperatures. When combined with high humidity levels and intense solar radiation in outdoor spaces, a major deterioration in outdoor thermal comfort (OTC) is happening. This study proposes a novel strategy to enhance OTC in hot and humid climates by integrating sustainable technologies, such as desiccant dehumidification and evaporative cooling, which can operate on solar energy. These technologies are used to condition hot, humid ambient air and supply it as cool, dry air under a shaded canopy, providing localized thermal comfort in semi-outdoor settings for a seated individual. A computational fluid dynamics (CFD) model, validated experimentally, was created to study the interaction between cold, dry jets of varying temperatures, humidity, and flow rates with the existing ambient air. This model was used to assess improvements in thermal comfort through a thermal comfort assessment tool, the universal thermal climatic index (UTCI). To design and size the air conditioning system, mathematical models for the dehumidification and evaporative cooling processes were implemented. Regeneration energy requirements for system operation at different supply and ambient conditions were calculated. Then, ANN was combined with GA to optimize the operation of the system in terms of energy consumption. To make the study more comprehensive, a case study was conducted to assess the impact of supply angle on OTC under the canopy. Results showed that the proposed system effectively reduced temperature and humidity levels and enhanced airflow under the canopy across all ambient conditions studied, thereby lowering UTCI by up to 6.3 ℃. This reduction in UTCI led to decreases in heat stress, shifting conditions from "very strong" and "strong" to "moderate" and, under certain supply conditions, even to "no thermal stress”. The implemented optimization allows for achieving the lowest possible heat stress levels for all ambient combinations at optimal thermal energy requirement where the reduction in thermal energy required for operation reached a maximum of almost 67%.