Design and optimization of a hybrid air conditioning system with thermal energy storage using phase change composite

• Published in: Energy conversion and management 2018-08, Vol.169, p.404-418
• Main Authors: Aljehani, Ahmed, Razack, Siddique Ali K., Nitsche, Ludwig, Al-Hallaj, Said
• Format: Article
• Language: English
• Subjects: Air conditioners; Air conditioning; Air conditioning equipment; Air cooling; Carbon dioxide; Carbon dioxide emissions; Cold storage; Composite materials; Compression; Compressor efficiency; Computer simulation; Cooling water; Design optimization; Electric power demand; Electric power distribution; Electric power generation; Electricity; Electricity consumption; Electricity’s demand side management; Emissions; Energy storage; FORTRAN; Heat transfer; HVAC; Hybrid systems; Integration; Latent heat storage; Mathematical models; Paraffin; Paraffin wax; Phase change; Phase change material; Phase transitions; Power plants; Refrigeration; Simulation; Solidification; Tetradecane; Thermal energy; Thermal energy storage
• ISSN: 0196-8904; 1879-2227
• DOI: 10.1016/j.enconman.2018.05.040

•High thermal conductivity phase change composite for thermal energy storage.•Hybrid HVAC/thermal energy storage with high-conductivity phase change composite.•Hybrid HVAC-TES for flexible resource to shave/shift on-peak power demand.•HVAC efficiency and optimized control strategies for smart grid applications.•HVAC-thermal storage system level modeling and simulation study using Aspen Plus®. This paper evaluates the use of a phase change composite (PCC) material consisting of paraffin wax (n-Tetradecane) and expanded graphite as a potential storage medium for cold thermal energy storage (TES) systems to support air conditioning applications. The PCC-TES system is proposed to be integrated with the vapor compression refrigeration cycle of an air conditioning (AC) system. The use of this PCC material is novel because of its unique material and thermal characteristics as compared to ice or chilled water that are predominantly used in commercial TES systems for air cooling applications. The work of this paper proposed and tested a hypothesis, which suggests that integrating a conventional AC with a PCC-TES would result in significant benefits concerning compressor size, compressor efficiency, electricity consumed and CO2 emissions. The proposed integration would also contribute to reduce electricity demand during peak hours and reduce necessity to build more expensive power plants and distribution lines. To test the hypothesis, a simulation model in Aspen Plus® software was prepared. However, Aspen Plus® does not have a built-in library to predict PCC’s melting and solidification behaviors. Therefore, an analytical heat transfer model was written as a system of equations in Fortran code into Aspen Plus® calculation block to simulate the phase change behavior and associated characteristics. The overall simulation model, which was designed specifically for this research work, consists of two main parts that communicate with each other. The first part simulates the AC’s refrigeration loop using the built-in Aspen Plus® components and the second part implements the PCC heat transfer model written within the calculation block of Aspen Plus®. The simulation model was validated by crosschecking the calculated results with actual experimental data from an actual 4 kWh PCC-TES benchtop thermal storage system. Very good agreement was observed between the simulations and laboratory data. Simulated performance of the proposed integration between the AC and the PCC-TES in