An intelligent defrost control strategy that initiates heating cycles based on measured evaporator conditions—actual ice accumulation, pressure differential, or coil temperature—rather than arbitrary fixed time intervals, reducing defrost energy consumption by 20-30% while improving temperature stability.
How Demand Defrost Works
Demand-based systems use sensors to detect when defrosting is actually needed. Common approaches include pressure differential sensing (measuring airflow restriction across the evaporator), coil temperature monitoring, optical ice detection, or artificial intelligence algorithms combining multiple inputs. The system initiates defrost only when ice accumulation genuinely impairs cooling performance, then terminates immediately when the coil is clear—not after a fixed duration regardless of actual conditions.
Why This Matters for Courier Operations
In multi-stop frozen delivery, evaporator ice accumulation varies dramatically based on door opening frequency, ambient humidity, and cargo moisture content. A route with 40 door openings on a humid Johannesburg summer day accumulates ice far faster than a 10-stop route in dry winter conditions. Timer-based defrost systems ignore these variables entirely, defrosting on schedule whether coils are heavily iced or completely clean.
Research from Oak Ridge National Laboratory found that time-based defrost often supplies significantly more heating than required, while sometimes proving insufficient to remove all accumulated frost. This double failure—wasting energy when unnecessary while leaving ice when defrost is actually needed—represents the fundamental problem with timer-based approaches.
Quantified Energy Savings
Demand defrost systems consistently deliver 20-30% reduction in defrost-related energy consumption compared to fixed-timer systems. For transport refrigeration operating 2,500 hours annually, this translates to meaningful fuel savings. Our calculations in the Technical Formulas Reference show timer-based systems waste approximately 60% of defrost energy through inappropriate scheduling.
South African Humidity Challenges
Research confirms that ambient humidity is the primary factor influencing frost formation rates. South African coastal operations in Durban or Cape Town face different accumulation patterns than the drier Gauteng highveld. Demand defrost adapts automatically to these regional differences; timer defrost ignores them entirely.
Industry Resistance
Despite proven savings, most transport refrigeration units still use timer-based defrost because it’s simpler for manufacturers, generates higher fuel consumption (benefiting diesel TRU economics), and creates more maintenance events from excessive thermal cycling. The technology exists—it just doesn’t serve supplier interests.
Related Terms: Timer-Based Defrost, Defrost Cycle, Evaporator
Related Articles: Technical Formulas Reference – Defrost Cycle Energy Waste