C11 -- Near Zero Cooling Residential Building Using Hot and Cold Phase Change Material Thermal Storages-Lebanon Case Study

The present paper investigates the performance of a solar cooling system using hot and cold phase change material as thermal storage to reach near-zero cooling energy building. The system consists of evacuated tube solar collectors, hot water Lithium Bromide absorption chiller, hot and cold phase change material storage tanks. A residential building (3000m2 (32291.73ft2) total occupied area) in Lebanon was taken as a case study. A baseline conventional cooling system was modeled using the "Design Builder" simulation program and the hourly cooling load year-round was calculated (the annual chilled water load is 200.96 MWh, (685.7 MBtu)). Since chillers work the best at their full load capacity, two operating strategies were compared: Load Shifting and Load Leveling. In the "Load Shifting" strategy, the absorption chiller will work only when solar irradiances are available. While in the "Load Leveling" strategy, the absorption chiller will work 24hours per day. Both hot and cold phase change materials were introduced to meet the hourly fluctuations in solar irradiance and needed cooling load. A mathematical model for the solar cooling system was coded using "Visual Basic" for the different components. Using the "Hooke and Jeeves" optimization algorithm, the sizing of the different components in the two strategies was found. Finally, the life cycle assessment performed shows that adopting the load-leveling strategy was capable of providing the cooling energy year-round without the use of any auxiliary source of energy. The optimal combination was as follows: 457.6 m2 (4925.56 ft2) evacuated tube solar collectors, 124.425 kW (424.538 kBtu/h) absorption chiller, 24m3 (32757.33 gals) cold phase change material thermal storage, and 98m3 (25888.86 gals) hot phase change material thermal storage. The energy consumption reduction percentage reached up to 92.6% and a feasibility study shows that the payback period is around 9 years.