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.
The present work aims to investigate the load-following capability of a tower-based CSP plant assumed to cover a high fraction (90%) of the power demand of a mid-size remote community. The design of a CRS requires the determination of several variables (number of heliostats, layout arrangement, tower height, receiver dimensions) depending on the solar field size and the site location. In this paper, a two-step optimization procedure is presented. A preliminary optimization is carried out to define the solar field configurations minimizing the budget costs for a range of receiver thermal design powers (from 300 MWth to 1000 MWth). The second optimization, based on annual simulation, selects the storage tank volume, the steam turbine rated power, and the actual reflective area (number of mirrors) capable to cover 90% of the power demand at minimum cost. The analysis is carried out for two load profile and two locations in Egypt. The load profile, compared to the solar radiation availability, determines the relationship between tank capacity and turbine size. The level of radiation has the strongest impact on the oversizing of the solar field and levelized cost of electricity.
The paper presents a complete solar cooling comparison. A detailed model of a tertiary sector building has been evaluated in three locations (Riyadh, Abu Dhabi, and Palermo) and coupled with four solar cooling systems: two solar thermal cooling systems (Li-Br absorption chiller and adsorption chiller), a solar Desiccant Evaporative Cooling system and a solar electric cooling (Photovoltaic coupled with Compression chiller). A multi-variable optimization procedure selects the optimal size of each component. The results show that the solar cooling system based on absorption chiller satisfied the cooling demand regardless of the site location whilst the performance of the Desiccant Evaporative Cooling system is dramatically affected by ambient conditions. The electric solar cooling option shows the best overall efficiency and appears a costeffective solution despite the high cost of the storage system.
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