Thermodynamic Investigation of Solar-Assisted Heat Pumps for Water Heating Applications in Cold Climatic Conditions
Date
2023-12-14
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Abstract
In this thesis, the annual energy use, exergy, environmental, and economic performance of a direct-expansion solar-assisted heat pump (DX-SAHP) and a dual-source (solar/air) indirect-expansion solar-assisted heat pump (IDX-SAHP) for water heating under cold climatic conditions of Calgary, Alberta, is investigated. Also, the thermodynamic performance of the DX-SAHP system operating with various low global warming potential (GWP) refrigerants is evaluated. A mathematical model based on the fundamentals of thermodynamics and heat transfer is developed, validated, and implemented in MATLAB®. CoolProp®, a MATLAB® addon, was used to determine the required refrigerant properties. Besides, a series of experiments were performed on a prototype DX-SAHP water heater in Calgary, Alberta. The results show that a DX-SAHP can supply domestic hot water for a typical Canadian household in Calgary throughout the year with the maximum and minimum monthly average COPs of 3.94 and 2.4, respectively. Compared to a conventional ASHP and an electric water heater, the energy consumption of the system was reduced by 25% and 62%, respectively. Moreover, using SAHP lowers CO2 emissions by 1283 kg/year when switching from gas water heaters to SAHPs, while the payback period of these systems is more than a decade. Among the investigated low GWP refrigerants, R1233zd achieves the highest COPs, whereas R32 shows the lowest COPs. The second-law analysis results indicate that the exergy efficiency of the heat pump water heaters reduces in summer. The ASHP obtained the highest monthly average exergy efficiencies, followed by the DX-SAHP and the dual-source IDX-SAHP. The test results of a 2.3 m2 DX-SAHP prototype in Calgary show that the system can heat 178 L of water on sunny days in winter and sunny and cloudy days in summer in 4.5, 3, and 3.5 hours, respectively. The average COP of the system varied from 3.0 to 3.44. However, the system showed a considerable degree of superheat during operation, which resulted in inefficient performance. The imperfect bonding between the collector plate and the serpentine tube is identified as the leading cause of this issue. This collector is being replaced with a professionally fabricated one in the next design.
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Keywords
Solar-assisted heat pump, Water heater, Exergy analysis, Economic analysis, Environmental analysis
Citation
Abbasi, B. (2023). Thermodynamic investigation of solar-assisted heat pumps for water heating applications in cold climatic conditions (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.