Experimental analysis of R454B charge optimization in a variable-speed brine-to-water heat pump: Performance comparison with R410A

The transition to refrigerants with low-GWP in residential heat pumps is driven by global regulations to reduce greenhouse gas emissions. R454B stands out as a promising alternative to R410A, due to its moderate GWP (531) and similar thermodynamic properties, making it ideal for compact brine-to-water heat pumps designed for indoor installation. However, R454B is mildly flammable (A2L), so its charge should be minimized without compromising performance. This aspect is particularly relevant in modern heat pumps equipped with variable speed compressors, which are increasingly used to meet stringent energy efficiency requirements. Despite numerous studies on R454B drop-in tests, research on the combined effect of refrigerant charge and variable-speed operation remains scarce. This paper investigates a brine-to-water heat pump originally designed for R410A and tested with R454B as a drop-in replacement. Experiments were conducted under EN 14511 and EN 14825 rating conditions for low- and intermediate-temperature space heating applications. The effects of refrigerant charge and compressor speed on heating capacity, COP, discharge temperature, and seasonal performance were analyzed. Results reveal that improper charge significantly affects the unit performance and operating limits, identifying an optimal charge range for maximizing COP and SCOP. Compared to R410A, R454B achieves slightly higher COP and requires less charge, though at the expense of lower heating capacities and higher discharge temperatures. A SCOP evaluation showed better performance with R454B at equal design heating load. These findings provide practical guidelines for optimizing R454B charge in variable-speed heat pumps, supporting its adoption as a lower-GWP alternative in residential applications. • The R454B charge impact in a domestic heat pump designed for R410A is analyzed. • Heat pumps without a liquid receiver are highly sensitive to the refrigerant charge. • Improper charge affects efficiency and operating limits in variable-speed systems. • An optimum refrigerant charge that maximizes the system COP or capacity was found. • R454B needs less charge than R410A and can achieve a higher SCOP.