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Marine Refrigeration and Cargo Cooling

Marine refrigeration systems on ships serve four distinct functions: provision cold rooms (galley meat, fish, dairy, vegetable storage typically at 0 to -25 degrees Celsius); accommodation HVAC (air conditioning of cabins, public spaces, bridge); cargo refrigeration (purpose-built reefer ships, fishing vessel holds, container ship reefer plug-in systems); and specialised cargo refrigeration such as LNG cargo refrigeration on LNG carriers and ammonia refrigeration on ammonia carriers. The dominant refrigerant systems use vapour compression cycles with refrigerants including R134a, R407C, R410A, R404A historically, transitioning to lower-GWP options such as R407F, R449A, R448A, R32 and CO2 (R744) under F-gas regulations and the Kigali Amendment to the Montreal Protocol. Cargo reefer ships maintain controlled-atmosphere conditions for fruit, vegetables, meat, fish and pharmaceuticals; container ship reefer integration provides electrical power and monitoring for plug-in reefer containers. Operational considerations include refrigerant charge management, leak detection, condenser performance under variable seawater temperature, evaporator defrost cycles, oil return management, and the comprehensive maintenance regime required for continuous operation over a typical 25-year ship life. ShipCalculators.com hosts the principal computational tools for marine refrigeration: the refrigeration COP calculator, the refrigeration cooling COP calculator, the refrigerant charge calculator, the condenser heat rejection calculator, the pull-down calculator, the reefer power calculator, the reefer socket count calculator, the HVAC cooling load calculator, and the HVAC accommodation cooling load calculator.

Contents

Background

Refrigeration applications on ships

Ships use refrigeration for diverse purposes:

  • Provision storage: galley cold rooms, freezer rooms, and ice machines for crew and passenger food.
  • Air conditioning: accommodation, bridge, public spaces.
  • Cargo refrigeration: dedicated reefer ships, container reefer integration, fishing vessel holds.
  • Specialised cargo: LNG carriers (boil-off gas reliquefaction), ammonia carriers (cargo refrigeration), ethylene carriers, fruit-specific atmosphere-controlled holds.
  • Process cooling: lubricating oil cooling, fresh water generator cooling, electronic equipment cooling.

The total refrigeration load on a typical commercial ship is 50 to 500 kW (cargo), 200 to 2,000 kW (cruise ship HVAC), and up to 20+ MW on dedicated reefer ships and large container ships with full reefer slots.

Vapour compression cycle

Marine refrigeration uses the vapour compression cycle:

  1. Compression: low-pressure gas compressed to high pressure (and high temperature).
  2. Condensation: high-pressure gas condenses to liquid in condenser, rejecting heat to seawater.
  3. Expansion: liquid expands through expansion valve, dropping pressure and temperature.
  4. Evaporation: liquid absorbs heat from cooled space and evaporates back to gas.
  5. Cycle repeats.

The cycle is typified by the Coefficient of Performance (COP): ratio of cooling effect to compressor work input. Marine systems typically achieve COP of 2 to 5 depending on operating conditions. The refrigeration COP calculator and refrigeration cooling COP calculator compute COP for various conditions.

Refrigerants and environmental impact

Marine refrigerants have evolved significantly:

  • CFCs (R12, R22, etc.): phased out under Montreal Protocol due to ozone depletion. R22 still in service on older ships pending replacement.
  • HCFCs (R22): phased out for new equipment; allowed for service on existing.
  • HFCs (R134a, R404A, R407C, R410A): ozone-friendly but high Global Warming Potential (GWP). Subject to phase-down under Kigali Amendment and EU F-gas Regulation.
  • HFO blends (R449A, R448A, R407F): lower-GWP HFC alternatives, increasingly common in new installations.
  • Natural refrigerants: CO2 (R744), ammonia (R717), hydrocarbons (R290 propane, R600a isobutane). CO2 is increasingly used in new container reefer and cargo refrigeration.

The transition is driven by:

  • Kigali Amendment to Montreal Protocol (2016, in force 2019): global phase-down of HFCs.
  • EU F-gas Regulation (2014): phase-down of high-GWP HFCs in EU.
  • Class society guidelines: increasingly requiring lower-GWP alternatives.

System types

Provision plant

Provision refrigeration:

  • Cold rooms: meat (-2 to +2 C), fish (-25 to -18 C), dairy (+2 to +5 C), vegetables (0 to +5 C), beverages (+5 to +10 C).
  • Compressor: typically scroll or reciprocating, 5 to 50 kW.
  • Refrigerant: typically R134a, R407C, R449A or CO2.
  • Capacity: sized for galley demand of typical 30 to 100 days provisions.

Accommodation HVAC

Air conditioning:

  • Chilled water plant: typically central plant cooling chilled water for distribution to fan coil units throughout accommodation.
  • Compressor type: typically screw compressors (10 to 1000 kW range).
  • Refrigerant: R134a or R407C historically, transitioning to R513A, R450A, R1234ze.
  • Cooling load: typically 200 to 2000 kW depending on ship type.

The HVAC cooling load calculator and HVAC accommodation cooling load calculator address sizing.

Cargo refrigeration on reefer ships

Dedicated reefer ships:

  • Cargo holds with insulated structure: thick insulation to maintain temperatures against external heat.
  • Air circulation systems: distributing cold air throughout the cargo space.
  • Multi-temperature zones: different holds at different temperatures for various cargoes.
  • Compressor stations: typically multiple parallel compressors for redundancy.
  • Refrigerant: typically R134a, R404A historically, transitioning to lower-GWP options.

Reefer ship cargoes include bananas, citrus, deciduous fruit, meat, fish, dairy, pharmaceutical products.

Container ship reefer integration

Container ships provide infrastructure for plug-in reefer containers:

  • Reefer sockets: 380V/440V/600V three-phase electrical sockets at each reefer slot.
  • Reefer container plugs: standardised electrical connections.
  • Monitoring: bridge-side monitoring of each container’s temperature, alarm, power.
  • Power generation: substantial electrical demand on auxiliary plant for reefer load.

The reefer power calculator and reefer socket count calculator address container ship reefer planning.

LNG carrier reliquefaction

LNG carriers may use:

  • No reliquefaction: BOG (boil-off gas) is used as fuel on dual-fuel vessels.
  • Reliquefaction plant: refrigerating BOG back to liquid for return to cargo tanks. Energy-intensive but preserves cargo.
  • Hybrid: BOG used as fuel with reliquefaction available for surplus.

Reliquefaction is associated with steam-turbine LNG carriers and modern dual-fuel vessels with high cargo retention requirements.

Operational considerations

Refrigerant management

Refrigerant management:

  • Charge tracking: documented quantity in each system.
  • Leak detection: continuous monitoring with alarms on substantial loss.
  • Recovery during maintenance: refrigerant recovered to recovery cylinders, not vented.
  • Documentation: records under EU F-gas Regulation and equivalent flag-state rules.

The refrigerant charge calculator addresses charge sizing.

Condenser performance

Condenser performance under variable seawater temperature:

  • Tropical waters (28-30 C SW): condenser pressure higher, COP lower, capacity reduced.
  • Polar waters (0-5 C SW): condenser pressure lower, COP higher, capacity higher.
  • Sizing: typically based on tropical conditions with reserve for fouling.

The condenser heat rejection calculator addresses condenser sizing.

Evaporator defrost

Evaporator defrost cycles:

  • Hot gas defrost: redirecting hot compressor discharge through evaporator.
  • Electric defrost: heaters on evaporator.
  • Frequency: typically 1 to 4 times per day depending on operating temperature and humidity.
  • Duration: 15 to 30 minutes per cycle.

Inadequate defrost causes evaporator capacity loss and energy waste.

Pull-down

Pull-down (initial cooling of warm cargo to operating temperature):

  • Time-critical: cargo quality depends on rapid pull-down to inhibit microbial growth and ripening.
  • Power demand: typically 2 to 3 times steady-state during pull-down.
  • Multi-stage: large cargoes loaded in sections allow staged pull-down.

The pull-down calculator addresses pull-down operations.

Maintenance and surveys

Routine maintenance

Routine refrigeration maintenance:

  • Daily: visual inspection, pressure/temperature monitoring, alarm verification.
  • Weekly: oil sight glass inspection, filter pressure differential check.
  • Monthly: leak check (visual and electronic), oil sample analysis.
  • Quarterly: more detailed inspection of compressor, controls.
  • Annual: comprehensive inspection, refrigerant-charge verification.

Class society oversight

Class society oversight:

  • Initial certification: at delivery for cargo refrigeration on reefer ships and LNG carriers.
  • Annual surveys: verification of operational and safety systems.
  • Periodic surveys: detailed inspection.
  • Refrigerant management: increasing class society attention as F-gas regulations tighten.

Crew training under STCW

Crew training:

  • STCW Section A-III/1, A-III/2: covering general engineering including refrigeration.
  • F-gas certification: required in EU and increasingly other states for handling fluorinated refrigerants.
  • Specific equipment training: for actual refrigerant systems installed.

Future developments

Lower-GWP refrigerants

Continued transition to lower-GWP refrigerants:

  • CO2 systems: increasing in container reefer and provision plant.
  • Ammonia systems: limited maritime use due to safety concerns but used in some applications.
  • HFO refrigerants: R513A, R450A, R1234ze, R1234yf increasingly common.
  • Hydrocarbon refrigerants: limited maritime use due to flammability concerns.

The lower-GWP transition will continue through the 2030s.

Energy efficiency

Energy efficiency improvements:

  • Variable-speed compressors: matching capacity to demand.
  • Heat recovery: from condenser for hot water generation.
  • Thermal storage: ice or chilled water storage shifting peak demand.
  • Free cooling: using cold seawater directly when conditions permit.

These improvements support CII rating compliance.

Digital monitoring

Digital monitoring:

  • Cloud-based monitoring: of cargo refrigeration container by container.
  • Predictive maintenance: based on operating data analysis.
  • Manufacturer remote support: with diagnostic data exchange.

See also

Additional calculators:

Additional formula references:

Additional related wiki articles:

References

  • Montreal Protocol on Substances that Deplete the Ozone Layer.
  • Kigali Amendment to the Montreal Protocol (2016).
  • EU F-gas Regulation 517/2014.
  • IACS Common Structural Rules.
  • Class society marine refrigeration rules.
  • ASHRAE Handbook (Refrigeration).