Analysis of Solar District Cooling systems: the Effect of Heat Rejection

The paper presents the performance assessment of a solar district cooling system with special attention to the heat rejection process. The investigation includes energetic, economic and environmental aspects. The district cooling network is driven by two-stage Li-Br absorption chillers coupled with parabolic trough solar collectors. The whole system, including solar field, storage tanks and chilled water pipeline, has been modelled in Trnsys. The focus is on the heat rejection systems, and their impact on the performance of the cooling plant. Four different types of heat rejection systems are considered: Air Cooling (AC), Evaporative Cooling Tower (ECT), Groundwater Heat Exchanger (GHE) and Geothermal Boreholes (GB). The paper presents two case studies in the Gulf region: the warm climate is compared for two condition of humidity, dry (Riyadh) and humid (Abu Dhabi). Furthermore, the work presents a multivariable optimization procedure based on GenOpt software interacting with Trnsys model under the constraint of a 70% annual solar fraction. The best option resulted to be the one based on absorption chillers coupled with Groundwater Heat Exchanger in both locations. The annual power consumption is reduced by 83% in Abu Dhabi and 82% in Riyadh compared to conventional cooling systems.