Passive pre-cooling potential for reducing building air-conditioning loads in hot climates

Abstract

A major source of energy consumption in the building sector is the extensive use of Heating, Ventilation and Air-Conditioning (HVAC) systems to meet the rising demands for indoor comfort. Advancements in reducing cooling loads will have a direct impact on energy consumption in the built environment. The present study investigated the thermal performance of a heat pipe heat exchanger in transferring sensible heat from high-temperature natural air streams. In order to ensure the system's sustainable operation, water was used as the working fluid and heat is transferred using its indirect evaporation phenomenon. The physical domain comprised of 19 cylindrical copper heat pipes measuring 800mm in length and 15.9mm in internal diameter, assembled in a systematic arrangement at an angle of 90° with respect to ground. The heat pipes were divided by a separator plate to segregate the evaporator and condenser ends from each other. Hot air at 41°C was delivered to the evaporator end while a temperature of 15°C was maintained in control volume at the condenser end. Computational Fluid Dynamics (CFD) was used in order to analyze the heat pipe model at fixed inlet velocities of 1m/s and 2.3m/s. The results showed a maximum temperature reduction of 3.8°C at an external air velocity of 1m/s, delivering an internal air temperature of 37.2°C. A cooling load of 976W was achieved indicating a heat pipe effectiveness of 6.4% when the velocity was increased to 2.3m/s. The numerical values predicted at the measurement locations were compared against experimental results for the purpose of validation. Good correlation was observed between the two techniques with error variations of 10% for air velocity and 28% for air temperature. The present study identified the potential of sustainable pre-cooling using a heat pipe heat exchanger in natural ventilation air streams for regions incorporating hot and dry climatic conditions.