Abstract:
In recent years, population growth and industrial developments have resulted in a dramatic increase in energy consumption and greenhouse gas emissions. Energy consumption in buildings accounts for one-third of the total energy consumption worldwide, of which 50% is responsible for space heating and cooling. This raises the need for sustainable technologies and materials to reduce energy consumption with less environmental impact. The incorporation of thermal energy storage systems using phase change materials (PCMs) is a promising approach. PCM increases buildings' thermal mass and hence improves their overall energy efficiency and reliability whilst providing thermal comfort and interior temperature stabilization. The high cost of PCM makes the use of a control strategy mandatory to optimize the PCM quantity used. This research aims to investigate the potential of an active PCM storage system in combination with a smart control strategy to reduce the electrical energy consumption of a building. To this end, an air-PCM heat exchanger/storage unit was designed using mathematical modeling developed in this work and was fabricated at the University of Auckland. Two identical experimental huts, located at the University of Auckland, were used to examine the heating/cooling energy-saving of an office-size building in the presence of the designed PCM storage unit. The experiments were conducted under real environmental conditions of the city of Auckland, New Zealand. A control method was implemented to store solar energy in PCM for use in winter during the following cooler hours. The PCM storage could also store free cooling available at night in summer for later and hence reduce the cooling demand of the building. The results showed an energy-saving of 40% in May and 10.3% in June/July for space heating, and an energy-saving of 30% in March/April and 10% in January, for space cooling. Further, the use of the active PCM system in conjunction with a price-based control could contribute to peak load shifting and cost-saving, consequently. Indeed, low-rate energy, powered by an electric heater in winter or an air conditioning unit in summer, was utilized to charge the PCM during the off-peak period. The energy was then released during peak hours. Up to 47% of daily energy-saving with a corresponding 65% of electricity cost-saving, in winter and up to 23% daily energy saving with a relevant 42% of cost-saving, in summer, were achieved. The performance of the designed active PCM system was then compared with that of a passive PCM system. Results showed that the active system consumed 20% less energy with a corresponding less cost to provide comfort when the same energy storage capacity was used. Next, a model predictive control strategy, which integrates weather data and electricity cost predictions, was implemented to improve the thermal efficiency of the storage system while minimizing electricity cost. This numerical study showed a potential of 11.46% cost-saving in services buildings, 57% in domestic buildings, and 49.4% in offices. Finally, through cost analysis, a payback time of six years was achieved for the implementation of the PCM storage system in combination with solar heater and control system.