Design of a Building-Scale Space Solar Cooling System Using TRNSYS

Abstract

Research into solar absorption chillers despite their environmental benefits has been limited to date to mainly larger systems whilst ignoring smaller building-scale units, which can significantly benefit from the use of optimally designed, low concentrating, non-imaging optical reflectors. A solar absorption chiller system designed to provide year-round space cooling for a typical primary health care facility in Cairo, Egypt, was designed to match local ambient, solar, and occupancy conditions, its performance simulated and then optimized to minimize auxiliary power consumption using the TRNSYS18 software, TRNOPT. Different configurations of collector types, array areas, storage sizes and collector slopes were used to determine the optimum specifications for the system components. Non-concentrating Evacuated Tube Collectors (ETCs) were compared with the same Evacuated Tube Collectors but integrated with external Compound Parabolic Concentrators (CPCs) with a geometric concentration ratio of 1.5X for supplying thermal energy to the single-effect absorption chiller investigated. This paper describes a user-friendly methodology developed for the design of solar heat-powered absorption chillers for small buildings using TRNSYS18 employing the Hookes–Jeeves algorithm within the TRNOPT function. Clear steps to avoid convergence problems when using TRNSYS are articulated to make repeatability for different systems and locations more straightforward. Collector array areas were varied from 30 m2 to 160 m2 and the size of the water-based thermal storage from 1 m3 to 3 m3 to determine the configuration that can supply the maximum solar fraction of the building’s cooling requirements for the lowest lifetime cost. The optimum solar fraction for ETCs and CPCs was found to be 0.66 and 0.94, respectively. If the current air conditioning demand is met through adoption of the CPC-based solar absorption systems this can potentially save the emission of 3,966,247 tCO2 per annum.