Assessment of Thermal Stratification Impact in a Storage Tank on the Performance of PV/T and Hybrid PV/T-Heat Pump System using Computational Method
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Date
2023-07
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Addis Ababa University
Abstract
In solar thermal systems, hot water storage tanks are employed to store the heat energy extracted from multiple energy sources and to balance the supply/demand of thermal energy requirements. One of the main challenges of these systems is the mixing of hot and cold water in the storage. Though several storage utilization methods were adopted, identifying the best approach to utilize the stored heat energy effectively and efficiently is still critical. Hence, this study has focused on modelling thermal stratification in a storage tank to assess its positive impact on the performance of existing hybrid PV/T and heat pump water heating system.
One-dimensional multi-node model was simulated in MATLAB, with implicit finite-difference scheme, for evaluating temperature distribution and annual efficiencies of the system after the thermal stratification is applied. Details of the fluid flow stored in the stratified storage were studied in two dimensional CFD model using ANSYS Fluent. Both models were validated with experimental results from literature.
Compared to the system with mixed storage, the stratified storage enhanced the annual solar fraction to 0.73. Thermal and overall efficiencies were also elevated with 14.8% and 15.6% respectively. Both the collector and storage heat losses were diminished with significant figures. Performance analysis was also done on geometrical parameters like H/D ratio, insulation, inlet locations, and operational conditions such as collector flow rates, heat removal factor and hourly hot water consumption fraction.
The results of the CFD model showed that the temperature gradient differences in increasing storing time. Applying improved quality of model is still needed for simulating a better appropriate thermally stratified storage tank model in a solar thermal system technology.