Abstract: The promotion of heat pumps is of significant importance for global carbon peak and carbon neutrality goals. Reliable operation across a wide temperature range is both a market demand and an industry challenge. Among the key factors affecting the reliability of heat pump systems under ultra-low temperature conditions is the compressor oil return issue. Experimentally analyzes the cold-start dynamic characteristics of compressors under ultra-low temperature conditions. It was found that during cold start, the compressor experiences a period of oil starvation under a ramp-up frequency control strategy. The study quantitatively investigates the effects of compressor operating frequency and system standby time before cold start on oil starvation time. The results indicate that as the frequency increases, the oil starvation time exhibits a trend of rapid initial decrease, followed by a slight rebound, and then continued decrease. Conversely, as standby time increases, the compressor oil starvation time shows a gradual reduction. These findings provide guidance for the design and use of heat pumps, particularly in ultra-low temperature environments.

Key words: Ultra-low temperature heating, Compressor cold start, R454B, Oil starvation time, Experimental study