Refrigerated Cargo Containers

Refrigerated cargo containers, commonly called reefers, provide mobile cold chain capability for intermodal transport of temperature-sensitive products across ship, rail, and truck modes. These self-contained units integrate refrigeration machinery, insulation, and structural framing within ISO standard container dimensions.

Container Construction Standards

Refrigerated containers conform to ISO 1496-2 specifications, which define dimensional tolerances, structural strength, and thermal performance requirements for international shipping. Standard lengths include 20-foot (6.1 m) and 40-foot (12.2 m) high-cube configurations, with internal volumes of 28 m³ and 67 m³ respectively.

Insulated panel construction utilizes polyurethane foam with thermal conductivity of 0.019-0.022 W/(m·K), achieving overall U-values of 0.35-0.45 W/(m²·K). Wall thickness ranges from 80-120 mm depending on temperature requirements. Stainless steel or aluminum interior linings provide corrosion resistance and cleanability for food-grade applications.

The T-floor design incorporates longitudinal channels beneath cargo that distribute airflow uniformly across the container length. This engineered air delivery system maintains temperature uniformity within ±0.5°C throughout the cargo space when properly loaded.

Refrigeration Unit Specifications

Container refrigeration units mount on the front wall, creating an integrated system that draws return air from the rear, conditions it, and delivers supply air through the T-floor channels. These units must operate reliably under extreme ambient conditions from -40°C to +50°C.

Vapor compression systems employ hermetic scroll or reciprocating compressors with capacities ranging from 5-12 kW depending on container size and temperature requirements. R-404A and R-452A refrigerants remain common, though R-134a and CO₂ systems are gaining adoption for lower global warming potential.

Microprocessor controllers maintain setpoint temperatures from -35°C to +30°C with ±0.3°C precision. Multi-stage cooling provides:

• Deep-frozen cargo: -35°C to -18°C
• Frozen products: -18°C to -10°C
• Chilled products: -2°C to +2°C
• Fresh produce: +2°C to +14°C

Heat rejection occurs through condenser coils located in the machinery compartment with forced air circulation. Condensers must handle thermal loads in direct sunlight with ambient temperatures exceeding 50°C during desert crossings or tropical port operations.

Power Supply Systems

Refrigerated containers operate on 380-460V, 3-phase, 50/60 Hz electrical power. Power connection methods vary by transport mode:

Vessel Operations: Ships provide standardized electrical service through deck-mounted power sockets. Reefer vessels dedicate 20-40% of generator capacity to container refrigeration, with individual containers drawing 5-15 kW depending on ambient conditions and cargo requirements.

Terminal Operations: Container yards install power pedestals at regular intervals, supplying shore power during loading, unloading, and temporary storage. These pedestals include circuit breakers, metering, and monitoring systems for fleet management.

Clip-On Generator Sets: For inland transport and locations without grid power, diesel-powered gensets mount directly to container frames. These units produce 12-20 kVA at 400V, operating continuously for 24-48 hours on integrated fuel tanks. Gensets add 400-600 kg to total container weight and produce 65-75 dB(A) noise levels at 7 meters.

Rail Transport: Electrified rail routes provide power through standardized connectors on flatcar platforms. Non-electrified routes require clip-on gensets or battery systems for journey segments without shore power access.

Controlled Atmosphere Technology

Advanced reefer containers incorporate controlled atmosphere (CA) capability for extending produce shelf life during long-distance shipments. CA systems modify the internal gas composition by controlling oxygen, carbon dioxide, and nitrogen concentrations.

Nitrogen generators using pressure swing adsorption (PSA) or membrane separation reduce oxygen levels from atmospheric 21% to 1-5% depending on commodity requirements. Carbon dioxide scrubbers employ activated carbon or chemical absorption to maintain CO₂ within 0.5-10% ranges.

Fresh air exchange systems precisely regulate air changes per hour, balancing respiratory gas production from living cargo against target atmosphere composition. Typical exchange rates range from 0.5-5 air changes per hour based on produce type and metabolic activity.

CA-equipped containers include:

• Gas-tight door seals and panel joints
• Oxygen and CO₂ sensors with ±0.1% accuracy
• Automated gas injection and venting valves
• Ethylene removal filters for climacteric fruits
• Independent humidification systems maintaining 85-95% RH

Temperature Monitoring and Data Logging

Modern refrigeration units integrate comprehensive monitoring systems that continuously record operational parameters for cold chain validation and regulatory compliance.

Data Logger Capabilities:

• Temperature recording at 1-15 minute intervals
• Supply and return air temperature differential
• Compressor runtime hours and cycle counts
• Defrost cycle frequency and duration
• Alarm event timestamps and durations
• Ambient temperature conditions
• Power interruption events

Data retrieval methods include USB downloads, wireless telemetry, and cellular communication systems. Remote monitoring platforms provide real-time visibility of container status during transit, enabling proactive intervention for temperature excursions.

Alarm Systems: Controllers monitor multiple fault conditions including:

• Temperature deviation beyond ±2°C from setpoint
• Low or high discharge pressure
• Insufficient airflow across evaporator
• Phase loss or power quality issues
• Defrost termination failures
• Door open sensors (when equipped)

ISO Container Standards

ISO 1496-2 establishes structural and thermal requirements, while additional standards govern operational aspects:

ISO 10368: Container remote condition monitoring specifications define data protocols and communication interfaces for telematics systems.

ISO 7225: Specifies dimensions and ratings for air-cooled container refrigeration units, ensuring interchangeability across manufacturers.

CSC Plate Requirements: Convention for Safe Containers mandates inspection plates documenting maximum gross weight (30,480 kg for standard 40’ reefers), construction date, and certification authority.

ATP Agreement: European Agreement on International Carriage of Perishable Foodstuffs defines testing procedures for thermal efficiency classification. Containers meeting standards receive FRC (Mechanically Refrigerated Container) certification.

Airflow and Load Configuration

Proper cargo loading maintains airflow channels that enable uniform temperature distribution. Blocking T-floor channels or stacking cargo against walls creates dead zones with inadequate air circulation.

Loading Principles:

• Maintain 25-75 mm clearance at walls and ceiling
• Avoid blocking return air inlet at rear door
• Pre-cool cargo before loading when possible
• Use load-securing systems that preserve airflow paths
• Stack palletized cargo with ventilation gaps

Air delivery rates of 90-150 m³/min at the supply plenum create sufficient velocity to reach the container rear while overcoming resistance from stacked cargo. Return air paths must allow unobstructed flow to the evaporator inlet.

Maintenance and Service

Refrigerated containers require regular inspection and maintenance for reliable operation across multi-year service lives. Pre-trip inspections verify refrigerant charge, electrical connections, drain line patency, and controller function.

Scheduled Maintenance Intervals:

• Monthly: Clean condenser and evaporator coils, inspect door gaskets
• Quarterly: Test alarm functions, verify sensor calibration
• Annual: Refrigerant system pressure test, electrical connection inspection
• Biennial: Thermal efficiency verification per ATP standards

Modular component design enables field replacement of compressors, fans, and control boards without specialized tools. Service networks at major ports provide 24-hour repair capability for minimizing cargo disruption.

Container tracking systems monitor cumulative operating hours and maintenance due dates, triggering service notifications before failures occur. This predictive approach maintains fleet reliability above 99% for major shipping lines.

File Reference: /Users/evgenygantman/Documents/github/gantmane/hvac/content/refrigeration-systems/applications/transport-refrigeration/cargo-containers-refrigerated/_index.md

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