Enhancing outdoor thermal comfort in hot humid climates by forming dry cool region under canopy using desiccant-evaporative cooling system

Abstract

Increased urbanization is causing elevated ambient temperatures and when accompanied with high humidity, deterioration in outdoor thermal comfort (OTC) develops. This study proposes a novel sustainable strategy to enhance OTC in hot and humid climates by implementing a solid desiccant dehumidification and evaporative cooling system to create cool and dry air region under shaded canopy to improve OTC for a seated individual. A computational fluid dynamics model, validated experimentally, was developed to study the interaction between cold, dry jets of varying temperatures, humidity, and flow rates with the existing ambient hot humid air. The model was used to assess improvements in OTC using 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 for the desiccant system was predicted at ambient temperature and relative humidity conditions ranging from 28 to 34°C and 60 to 85% respectively, at supply temperatures of 22 and 24°C for different relative humidities and supply flow rates. Results showed that the proposed system effectively reduced temperature and humidity and enhanced airflow under the canopy, thereby lowering UTCI by up to 6.3°C. 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”. Enhancement in OTC uses lower regeneration energy at lower ambient conditions than higher ones to achieve improvements in the UTCI level.