Impact of integrating desiccant dehumidification processes to conventional AC system on urban microclimate and energy use in Beirut city -

Abstract

This study investigates the anthropogenic heating of the urban environment of Beirut city due to air conditioning (AC) when integrating a desiccant dehumidification wheel into the conventional vapor compression (VC) system to reduce the high electricity consumption during the summer. Two hybrid system configurations with integrated heat exchanger (HE) and an indirect evaporative cooler (IEC) are studied. Numerical simulations of the urban microclimate for the hot humid weather of Beirut were performed. The simulation results were validated by comparing measured and predicted air temperatures in four locations of the city assuming the use of conventional VC systems. Simulations were then performed using the proposed interventions of the two hybrid systems. The results showed that the conventional AC systems cause an average increase in the urban ambient temperature in Beirut city of 1.3 °C in day-time and 2.2 °C in night-time when compared with the case with no AC. The electrical power consumption of IEC and HE systems was lower by 53percent and 38percent than conventional VC systems, respectively. Compared to the conventional VC system, the sensible waste heat of Hybrid AC with IEC and Hybrid AC with HE were higher by about 2percent and 10percent respectively due to the regeneration process. The latent waste heat of Hybrid systems with IEC and HE were higher by 7.9 and 5.7 times the latent waste of the conventional VC system. As a result, the hybrid systems with IEC produced a lower increase in temperature by about 0.1 °C to 0.3 °C in day-time and night-time while the hybrid systems with HE produced a higher increase in temperature by about 0.1 °C to 0.3 °C in day-time and night-time, due to the higher release of sensible waste heat than conventional system. The relative humidity in the cases of HE and IEC were higher by a maximum of about 3percent and 5percent compared to VC case, respectively. The IEC system is therefore recommended due to its high potential for electricity savings and lower impact on the ur