A reefer container is an enclosed unit used for transporting temperature sensitive cargo. The container requires an external power supply for its operation. The article describes everything you ever wanted to know about container refrigeration units.
When reefer containers are loaded in ships, the power supply is provided from the power generated from the D.G sets of the vessel. If the vessel’s generator capacity is not enough to support the additional power consumption of the refrigerated containers (in case of old ship or unavailability of generator due to overhauling etc.), mobile power packs are installed on the ship.
There are a different variety of refrigerated shipping containers present in the market today. A particular type is used depending upon the efficiency requirement and the cargo they need to carry.
Types of Refrigerated Shipping Containers are:
1. Closed Reefer: This is a conventional type refrigerated container. It comes in one-piece with integral front wall and an all-electric automatic cooling and heating unit for ISO sea-going containers.
2. Modified/ Controlled Atmosphere (MA/CA) reefer containers: These type of insulated shipping containers maintain a constant atmosphere by replacing consumed oxygen using an air exchange system, keeping an ideal atmosphere in equilibrium with the product’s deterioration rate.
3. Automatic Fresh Air Management Containers: Popularly known by its acronym – AFAM reefer containers uses advanced technology to regulate the air combination by automatically adjusting the scale of fresh air exchange. It works similar to Controlled Atmosphere refrigerated container, controlling the composition of oxygen, carbon dioxide and others. The controls of the AFAM refrigerated containers can be adjusted to influence and extend the shelf lives of the cargo they carry.
Some important points about container refrigeration are:
- Container Refrigeration unit is fitted in front of the container and it serves as a container front wall.
- Some units are dual voltage, designed to operate on 190/230 or 380/460 volts A.C, 3 phase, 50-60 hertz power.
- Operating control power is provided by single phase transformer which steps down the A.C supply power source to 24 volts, 1 phase control power.
Related reading: How perishable food is transported using refer ships?
Understanding the Basic Sections of Refer Unit
1. Compressor Section
- Consists of a compressor (with H.P switch) and power cable storage compartment. Power transformer may be an option where the ship supply differs.
- It also contain modulating and suction solenoid valve (for controlling the quantity of gas flow).
- Safety fittings in the section are- moisture liquid indicator, pressure relief valve, filter drier etc.
- Safety of the system is further enhanced by electronic monitoring with the help of following sensors- Compressor suction and discharge sensor, supply air temperature sensor, supply recorder sensor, ambient sensor.
Related reading: What are safety devices on a refrigeration system of a ship?
2. Condenser Section
- The condenser section contains condenser fan and its motor, an air cooled condenser coil and condenser saturation sensor.
- For air cooled condenser air is normally pulled from bottom and discharged horizontally through centre of the unit.
- Some units consists of water cooled condenser /receiver. This unit is expensive.
Related reading: Heat exchangers on ship explained
3. Evaporator Section
- This section contains temperature sensing bulb, return recorder bulb sensor and a thermostatic expansion valve (for flow of refrigerant and maintenance of inside temperature).
- Assembly consist of evaporator coil and heater, drain pan and heater, defrost and heat transmission switches.
- The evaporator fan circulates air throughout the container by pulling air in top of refrigeration unit and directing air through evaporator coil where it’s either heated or cooled and is then discharged out at the bottom of refrigeration unit into the container.
4. Fresh air Make up Vent
- Purpose of this vent is to provide ventilation for commodities that requires fresh air circulation and must be closed when transporting frozen foods.
- Air exchange depends upon static pressure differential which will vary depending upon how container is loaded.
Safety and Operating Precaution
An injury, no matter how small, should never go unattended. Always obtain first aid or medical attention immediately.
- Always wear safety gloves and glasses while working on any unit and also when charging refrigerant.
- Keep hand, tools, and clothing clear from evaporator and condenser fan.
- No work should be performed on any unit until all circuit breaker and start-stop switches are turned off and power supply disconnected.
- Do not bypass any electrical safety device.
- When performing arc welding on unit or condenser, disconnect all wire harness connection from the module in control box. Do Not remove wire harness from the module unless you are grounded to a unit frame with a static safe wrist strap.
- In case of electrical fire, open circuit switch and extinguish it with CO2 extinguisher.
- Officer and crew responsible for refrigerated shipping container must know the hazard related to refrigerant gas such as – Phosgene gas hazard (due to high temperature), Asphyxiation hazard in non-ventilated spaces etc.
- Safely handle the compressed gas bottles when charging refrigerant
Most common Problem in refrigerated shipping containers – Leakage.
The leakage of refrigerant is the most common problem faced by onboard staff during the voyage. Following tests must be carried out to detect leakages:
1. Soap water test: This is done on low-pressure line by spraying soapy water on the troubled pipe or space. If the soapy water comes in contact with leakage area, bubbles will form
2. Halide lamp test: This is used for all pressure lines
3. Electronic leak detector: It is a portable unit to carry out leak detection. It should not be used in a noisy area.
4. Permanent or fixed type leak detection unit: Some reefer containers come with fixed type leak detection unit which gives audio-visual alarm in case of leakage
*Note: All the pipes in the refrigerated container unit are insulated. Before testing the piping for leakage, make a small hole in the insulation and check the leakage near the hole (using soap/ halide lamp or electronic detector). Once the leakage is confirmed, then remove the insulation of the complete pipe section to spot the leakage area.
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