Optimization and performance assessment of a solar district cooling system

Abstract

The present paper deals with the performance evaluation of a solar district cooling system for a residential compound in three different locations (Abu Dhabi, Riyadh and Palermo). A three-step procedure has been developed: 1. estimation of the cooling load; 2. performance prediction of the district cooling network; 3. optimization of the cooling production plant. The work compares four different technologies: triple, double and single-stage lithium-bromide absorption chillers driven by Parabolic Trough Collectors (PTC-3sABS, PTC-2sABS and PTC-1sABS) and 1-stage lithium-bromide absorption chillers fed by Evacuated Tube Collectors (ECT-1sABS). A multi-variable optimization has been carried out to find out the best combination of solar field area and thermal energy storage capacity. For each technology, the best solution has been selected by minimizing the primary costs under the constraint of a solar fraction target 70%. The results show that all plant configurations are strongly affected by ambient condition and cooling load characteristics. The PTC-3sABS system is potentially the most efficient configuration, but it is penalised by the high investment costs. The case ETC-1sABS is based on the components (collectors and chillers) with the lowest unit costs: nevertheless, the low chiller's COP has a detrimental impact on the required solar field area and, consequently, on the overall costs. The double-stage chillers driven by PTCs resulted to be the most cost-effective solution, mainly for site locations with high level of beam solar radiation, where the troughs perform better than ETCs.