Optimization of design and operation of solar assisted district cooling systems

Abstract

The demand for air conditioning and cooling services is rapidly increasing worldwide. As cooling demand has high coincidence to occur in countries with high solar irradiation, the combination of solar thermal energy and cooling appears to be an exciting alternative to replace traditional electricity-driven cooling systems where electricity is generated from fossil fuels. Nevertheless, solar assisted cooling is not yet widely deployed because of many barriers amongst them the presumed high investment cost of solar cooling technology. This research aims at making this technology more affordable by providing a holistic optimization design of solar assisted district cooling systems. Toward this end, a mixed-integer linear programming model (MILP) is proposed that captures the key design and operation variables of a solar-assisted district cooling system. Hence, the proposed model aims at finding the optimal system design (i.e., the system’s main components along with their optimal capacities) together with the optimal hourly policies for production and storage of hot and cold water while satisfying the expected cooling demand. The model was validated using collected real data of different case studies. The optimal system design of some cases showed that solar collectors covered about 46% of the chiller’s heat demand. Moreover, the existence of the cold-water TES in the system depends on the chosen chiller capacity and the cooling demand of the case study. Furthermore, a sensitivity analysis was carried out to study the model robustness. The sensitivity analysis shows that the chiller COP had the highest impact on the annual total system cost, where increasing COP by 20% of its initial value, will decrease the annual total system cost by 4.4%.

Keywords

• Solar assisted district cooling
• Mixed integer linear model
• Absorption chiller
• Thermal energy storage