jismart2024072: Performance Comparison of Transcritical CO2 and Subcritical Refrigerants in Air-Source Heat Pumps for Clean Heating in Rural Shandong

Abstract

Rural heating in northern China, particularly in Shandong Province, is heavily reliant on coal, which contributes significantly to greenhouse gas emissions and air pollution. This study evaluates low-temperature air-source heat pumps (ASHPs) as a clean heating alternative, comparing transcritical CO₂ (R744) systems with subcritical refrigerants R22, R32, R410A, and HFOs R1234yf and R1234ze across physical properties, economic factors, and performance simulations. While Shandong is used as an example of a cold region, it is important to note that other northern regions may experience different climatic conditions, which could influence the performance of ASHPs. CO₂ stands out for its low critical temperature (31.1°C), high critical pressure (7.38 MPa), and excellent thermal conductivity (0.16 W/m·K), enabling efficient transcritical operation in cold climates. Environmentally, CO₂ is superior with a GWP of 1 and ODP of 0. Economically, CO₂ achieves the lowest total cost due to its natural abundance, zero compliance costs, and competitive operating expenses, despite moderate equipment investment. Simulations show CO₂ maintains a Coefficient of Performance (COP) of 4.1 to 10.4 across ambient temperatures of -15°C to 10°C and supply water temperatures of 35°C to 75°C, outperforming subcritical refrigerants in colder climates and at higher temperature outputs. However, while these results are useful, further analysis is needed to account for practical factors such as environmental fluctuations, system optimization, and maintenance needs that could impact real-world performance. In conclusion, CO₂ is a sustainable, cost-effective refrigerant for rural ASHPs, offering efficiency and environmental benefits. Its adoption in cold regions like Shandong is highly recommended, though real-world implementation will require optimization based on local conditions and operational considerations.