| Abstract | Climate change is a global concern and currently confronting all lives in the world due to the effect of greenhouse gas (GHG) emissions. The combustion of fossil fuels to serve the human needs (e.g., lighting, space comfort, transportation) is the principal cause of these emissions, especially CO2. A rapid growth in CO2 emissions is contributing to the increase in the global temperature. The world’s electricity consumption is about 16,816 TWh, of which over 56% is consumed by residential and commercial sectors. Air conditioning system accounts for more than 60% of the energy used in residential and commercial buildings. In hot and humid climates, the ambient air temperature and humidity are two significant parameters affecting the thermal comfort in a living space. Increasing awareness of the environmental impacts of CO2 emissions has triggered interest in renewable (solar) technologies, especially using liquid desiccant system driven by solar thermal heat to control the air humidity coupled with dew point evaporative cooling system to handle for the sensible load of the ventilation air by water. Earlier studies that investigated the performance of liquid desiccant system showed that it required lower solar hot water temperature, compared to absorption chiller and solid desiccant system, ranging from 40 to 80oC to run the system. For sensible load, indirect evaporative cooling system can sensibly cool the process air without any moisture addition. Earlier works also showed that the cooling effectiveness was generally low around 40–60% and theoretically limited at wet bulb temperature. Recently, dew point evaporative cooling using Maisotsenko cycle (M-cycle) has been an area of research. Previous studies indicated that it could reduce the inlet air temperature to below its wet bulb temperature and approach theoretically the dew point of its intake air. The enhancement of cooling effectiveness is thus an interesting option. Thus, this dissertation is aimed to investigate theoretically and experimentally the performance of a novel M-cycle dew point evaporative cooling system assisted by liquid desiccant system driven by solar thermal heat to provide comfort ventilation air in hot and humid climate condition. The research methodology involved the development of theoretical models and experimental investigations on the major components (i.e. dew point evaporative cooling device and liquid desiccant system) as well as the overall system. Simulation and experimental study of this novel configuration for dew point evaporative cooling component indicated that operating under different climate (covering dry, moderate and humid climate), the wet bulb effectiveness ranged between 92-114%, whereas, the dew point effectiveness varied between 58-84%. The study suggested that the system should be designed and operated at an intake air velocity below 2.5 m/s, channel gap less than 5 mm, channel height larger than 1 m and ratio of working air to intake around 35-60%, to obtain the wet bulb effectiveness greater than 100% for all typical inlet air conditions. Simulation and experimental studies of LiCl liquid desiccant packed bed tower filled with 35 mm Pall rings (packing media) using counter flow arrangement were carried out as dehumidifier and regenerator. In the experiments, moisture removal rate (minus sign for evaporation rate) was in the range of -0.60 g/s to 0.24 g/s and humidity effectiveness varied between 0.82–0.99. The results suggested that when the inlet desiccant temperature was higher than about 50°C, regeneration process was initiated iv(for 40°C of inlet air temperature, 20 g/kg of humidity ratio and 38.5% of solution concentration). The results of parametric study showed good agreement and trend with other works using different operating parameters and configurations. The air flow rate, desiccant flow rate, concentration, desiccant temperature, and inlet air humidity affected significantly the moisture removal rate. Humidity effectiveness is mainly dependent on air flow rate, desiccant flow rate, and desiccant temperature. Simulation and parametric studies of dew point evaporative cooling system integrated solar liquid desiccant system were carried out to investigate the performance covering day and night time operation. The weather data obtained from AIT meteorological were used as the input data. The results showed that average outlet air temperature leaving dehumidifier and leaving the dew point evaporative cooling system are 28.7°C and 18.0°C (8.8 g/kg of outlet humidity ratio), respectively. The results indicated that the system can supply the comfort outlet ventilation air within the upper limits of ASHRAE comfort zone. The parametric study suggested that the outlet air condition depends mainly on inlet air temperature, humidity and dehumidifier air flow rate. Dynamic experimental studies were conducted to observe the actual performances operating under real conditions. In experiments, the inlet (ambient) conditions ranged between 23.5°C to 36.3°C of air temperature and 9.6 g/kg to 22 g/kg of humidity ratio (covering summer and winter case). The results showed that the dew point evaporative cooling device (stand-alone system) could not provide the comfort condition of the outlet ventilation air when the (ambient) humidity was high. With the assistance of solar liquid desiccant system, the outlet air conditions leaving the system were within the upper limit of ASHRAE comfort zone, ranging between 17.5-19.62°C and 7.9-9.4 g/kg (62-69%RH) for the summer case, and between 11.5-16.2°C and 4.6-6.4 g/kg (52-57%RH) for the winter case. This indicated that the comfort condition of the outlet ventilation air can be provided by this system operating in hot and humid climate. The experimental results were also used to assess the accuracy of the models developed for the major components (i.e. dew point evaporative cooling device and liquid desiccant system) and for the overall system. The results showed good agreement between simulation and experimental findings. This study shows a significant step to illustrate a sustainable alternative air conditioning system, a dew point evaporative cooling system integrated with solar liquid desiccant system, using solar energy and water for cooling process of ventilation air. This would thus help our efforts in promoting renewable energy technologies and addressing the global concerns of climate change and greenhouse gas emissions. |