On/off operational pattern of fixed-speed refrigeration compressors responding to temperature demand, characterized by full-speed operation until setpoint reached, complete shutdown until temperature rises, then restart – creating thermal stress, energy inefficiency, and temperature instability. Why It Matters: Compressor cycling represents massive energy waste baked into fixed-speed TRU design. Each startup draws 5-7x normal running current (locked rotor amperage), generates heat without useful cooling, and stresses mechanical components. In variable-load courier operations with frequent door openings, compressors may cycle 20-40 times daily, each cycle wasting energy and degrading equipment. The fundamental problem: fixed-speed compressors must run at 100% capacity or 0%, unable to modulate output to match actual load. When cargo space needs 40% cooling capacity, fixed-speed compressor delivers 100% briefly, then shuts off completely, then restarts – instead of simply running at 40% speed continuously like modern variable-speed systems do.
The Efficiency Loss:
- Startup Surge: 5-7x current draw for 2-5 seconds = wasted electrical energy
- Short Cycling: System never reaches steady-state efficiency
- Temperature Overshoot: Cools below setpoint, then drifts above, repeat
- Mechanical Wear: Start/stop stress reduces compressor life 30-50%
- Oil Return Issues: Cycling disrupts oil circulation in refrigeration circuit
Variable Speed Alternative: DC compressors modulate speed 20-100% matching actual thermal load, eliminating cycling waste. Instead of 40 daily on/off cycles, variable-speed compressor runs continuously at varying speeds, reducing energy 25-35% while improving temperature stability and extending equipment life.
Related Terms: Variable Speed Compressor, Fixed-Speed Compressor, Energy Efficiency (Cold Chain), Total Cost of Ownership (TCO), Compressor Displacement