Assessment of cool thermal storage strategies in Kuwait

Abstract

The extensive use of air conditioning for indoor cooling in offices and large commercial buildings in Kuwait represents a major part of the power and electricity consumption in that country. The main objective of this research was to investigate ice and chilled water cool thermal storage technologies and operating strategies for air conditioning. This was motivated by the extreme climatic conditions in Kuwait and the necessity to reduce both maximum power demand and energy consumption whilst being economically feasible. This work represents the first such study undertaken. In Kuwait approximately 45% of the total annual exported electrical energy is consumed solely by air conditioning systems as a result of the very high ambient temperatures occurring between March and October. Furthermore, it was estimated air conditioning systems represent about 62% of the peak electrical load. To assess the potential of cool thermal storage, the air conditioning system for an existing clinic building, representing a typical medium size building in Kuwait, was designed with and without a cool thermal storage system. The results demonstrate that internal ice-on-coil and chilled water storage systems are suitable storage technologies that can be implemented in Kuwait. The cooling demand of the clinic building was first estimated using the ESP-r building energy simulation program, following which the different components in the air conditioning systems were sized including chiller, storage tanks, pumps, air handling units for conventional, ice and chilled water storage air conditioning systems operating with load levelling, 50% demand limiting and full storage strategies. The heat gains by different auxiliary components in the air conditioning systems were estimated and the final cooling demand profiles were developed. For each air conditioning design, the power and energy consumption for the design day condition and over the whole year were calculated and analysed. Furthermore, the life cycle costs were determined based on the estimated capital, maintenance, operating costs and a financial analysis was carried out. For the Kuwaiti climate, the results demonstrate ice and chilled water storage systems can reduced the maximum power consumption during the day time when the electricity demand is high and largest reduction in the maximum power achieved full storage strategy. However, the energy consumption of ice storage system operating with 50% demand limiting and full strategies were found were found to be higher than the conventional air conditioning system. Nevertheless, the energy consumption in the ice storage system with a load levelling operating strategy was slightly lower. Chilled water storage system was found to be unlike ice storage system, the energy consumption in all operating strategies improved over the conventional system. Based on the estimated life cycle cost using the actual operating costs for both the government and user, it was established that for the government, ice storage operating with load levelling strategy and all other strategies of the chilled water storage systems would be more economical than conventional systems. However, for the user, load levelling ice storage, load levelling chilled water storage, and 50% demand limiting chilled water storage systems would be more cost effective. Out of all alternatives, chilled water storage system with a load levelling strategy was found to be the most cost effective for the climate of Kuwait and for similar climates of Kuwait. Although, the outcome from this research work can not be generalised however, the method of sizing and energy and economic analysis, which was discussed in this thesis can be generalised and followed to evaluate the impact of cool thermal storage systems on energy performance and economy of the air conditioning systems.