| Refrigerated and insulated containers | [German version] |
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Description |
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Figures |
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Dimensions/weights |
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Use |
Description
Refrigerated and insulated containers are mainly available as 20′ and 40′ containers. A distinction may be drawn between two different systems:
1. Integral Unit (Integral Reefer Container, Integrated Unit):
This type of refrigerated container has an integral refrigeration unit for controlling the temperature inside the container. The refrigeration unit is arranged in such a way that the external dimensions of the container meet ISO standards and thus fit into the container ship cell guides, for example. The presence of an integral refrigeration unit entails a loss of internal volume and payload.
 Figure 1 |
When being transported by ship, integral units have to be connected to the on-board power supply system. The number of refrigerated containers which may be connected depends on the capacity of the ship’s power supply system. If the aforesaid capacity is too low for the refrigerated containers to be transported, "power packs" may be used, which are equipped with relatively large diesel generators and satisfy ISO requirements with regard to the dimensions of a 20′ container. When at the terminal, the containers are connected to the terminal’s power supply system. For transport by road and rail, most integral unit refrigeration units are operated by a generator set (genset). This may either be a component of the refrigeration unit or connected to the refrigeration unit.
 Figure 2 |
 Figure 3 |
Air flows through the container from bottom to top. In general, the "warm" air is drawn off from the inside of the container, cooled in the refrigeration unit and then blown back in the container as cold air.
 Figure 4 |
To ensure adequate circulation of the cold air, the floor is provided with gratings. Pallets form an additional space between container floor and cargo, so also forming a satisfactory air flow channel. In addition, the side walls of the container are "corrugated", which ensures satisfactory air flow there too.
 Figure 5 |
 Figure 6 |
 Figure 7 |
In the upper area of the container, adequate space (at least 12 cm) must likewise be provided for air flow. For this purpose, during packing of the container adequate free space must be left above the cargo. The maximum load height is marked on the side walls.
 Figure 8 |
 Figure 9 |
To ensure vertical air flow from bottom to top, packaging must also be appropriately designed and the cargo must be sensibly stowed.
In addition to temperature regulation, integral units also allow a controlled fresh air exchange, for example for the removal of metabolic products such as CO2 and ethylene in the case of the transport of fruits.
In the refrigeration units, both the supply and return air temperatures are measured and, depending on the operating mode, one of these values is used to control the cold air. Temperature measurement may be performed in various ways. The Partlow recorder generally records return air temperature, since this provides an indication of the state or temperature of the cargo. Data loggers are increasingly used, which detect temperature digitally and indicate it on a display. Once transferred to a PC, the data may then be evaluated.
The temperature display is attached to the outside of the refrigeration unit, so that operation of the unit may be checked at any time.
Digital or analog recorders may also be positioned directly in the cargo, so as to measure temperatures inside the container. The recorder should be accommodated in such a way that it records the temperatures at risk points in the container (inside the packaging, top layer at door end).
 Figure 10 |
 Figure 11 |
Integral units may be stowed both above and below deck on a ship. Above deck stowage has the advantage that the heat from return air may be more readily dissipated. However, the containers are often exposed to strong solar radiation, leading to increased refrigeration capacity requirements.
2. Porthole containers:
This type of container is often referred to not as a refrigerated container but as an insulated container, as it has no integral refrigeration unit. The lack of a refrigeration unit allows such containers to have a larger internal volume and payload than integral units. On board, the inside of the container is supplied with cold air via the ship’s central cooling plant. The air flows through the container in the same way as in integral units. Cold air is blown in at the bottom and the "warm" air is removed at the top.
 Figure 12 |
 Figure 13 |
| Portholes (sealable openings) at the end of a porthole container. | |
 Figure 14 |
 Figure 15 |
 Figure 16 |
 Figure 17 |
Off the ship, the temperature is controlled by a terminal refrigeration system or "clip-on units". After completion of transport, the "clip-on units" may be returned using special frameworks, dimensions of which match those of a 20′ container.
 Figure 18 |
 Figure 19 |
On the opposite end wall from the door, the containers are provided with openings for supply and return air. In general, supply air is blown into the lower opening, distributed by means of the gratings in the container floor, conveyed upwards through the cargo and discharged via the return air opening. This type of container also requires adequate air flow. For this purpose, appropriate air ducts must be provided in the floor and the ceiling and the cargo must be sensibly packaged and stowed.
Porthole containers do not have an integral temperature display. Either such a display is installed in the terminal refrigeration systems or the "clip-on units" or the temperature values may be obtained from the ship’s central cooling plant.
If the porthole-containers are provided with "clip-on units" when ashore, they no longer fulfill ISO requirements with regard to dimensions.
3. General:
The doors constitute a weak point in both integral units and porthole containers. Wear to rubber door gaskets or improper handling may result in the doors no longer closing correctly, so that they are no longer sealed against rainwater and the like. During transport of chilled goods and frozen goods, water ingress may lead to cargo spoilage or to ice formation in the door area. In addition, refrigeration capacity has to be increased to compensate for losses due to cold air leakage.
 Figure 20 |
In the case of frozen cargo and cargo containing non-respiring goods (goods other than fruit and vegetables), the goods are usually packed using the block stowage method. The cold air only flows around the goods and does not circulate between the boxes. Here it is important for the cargo to be pre-chilled to the required temperature before it is loaded into the container. If a load which is too warm is loaded into a refrigerated container, the heat is passed to the air and the cooling effect of the refrigeration unit is not passed to the cargo. If the air cannot pass the available cooling capacity to the cargo, it is cooled rapidly by the high cooling capacity of the refrigeration unit, and the actual cargo requires a considerably longer period for refrigeration.
Two examples of how not to do it:
A consignment of frozen goods is to be transported from Izmir to East Asia with transshipment in Egypt. Required temperature = -18°C. The cargo is too warm. The refrigerated container is not able to cool the cargo by more than 13°C within 15 days (see Figure 21).
 Figure 21 |
The same consignment:
The temperature chart (see Figure 22) of a further container shows that at -10°C this cargo was too warm when it was loaded into the container. After 12 days, the temperature even rose by one degree. The daily variation of the external air temperature can be seen clearly. The reason: The supply air opening was not completely closed. Warm external air was drawn into the reefer. This was warmer during the day than by night. Despite automatic, 3-hour defrosting phases, the refrigeration unit starts to ice up. After the supply air openings are closed and an additional manual defrosting operation has been carried out, the temperature is stabilized and automatic defrosting only occurs every 12 hours. The required temperature is reached after 19 days.
 Figure 22 |
Respiring goods (e.g. fruit, vegetables, plants) require the supply of a certain amount of fresh air and cooling air, depending on their metabolic activity. This restricts metabolic processes and draws off the gases produced such as ethylene and carbon dioxide. Suitable packaging such as crates, perforated plastic containers or perforated boxes must be used to allow the mixture of cooling air and fresh air to penetrate directly to the goods. Fresh air is supplied through the fresh air flaps. To allow the supply air to circulate through the cargo from bottom to top, it is necessary for the perforations in the packaging to be aligned. If the cargo is loaded on pallets, steps must be taken to ensure that the containers are arranged in such a way that the circulation of supply air is not interrupted by the base of the pallet. Steps should also be taken to avoid spaces on the floor to prevent the supply air from taking the path of least resistance (circulation bypass), thus threatening correct cooling of the goods in some areas. Circulation bypass can also be caused by slippage of the load, which means that any spaces should be filled to prevent the load from slipping. Spaces between the last row of pallets and the container door can often not be avoided. In this case, a plastic sheet can be jammed between the stack of pallets and the container door. This returns the cold air under the pallets, allowing it to reach the goods.
 Figure 23 |
Ultra-low temperature refrigerated containers are capable of transporting goods at a temperature of -60°C. At temperatures of -62°C, the "eutectic point" (EP) is reached Only once the EP is reached is all the water in the cells of the product completely frozen and all microbial decomposition brought to a standstill. This means that at temperatures of below -62°C it is possible to transport or store foodstuffs for an "infinite" period without loss of quality.
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Figures
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Dimensions/weights
The following are some of the most important details relating to refrigerated container types. The data was taken from Hapag-Lloyd, Hamburg [68].
| Insulated container: 20′ long and 8′ high, with steel frame, walls of sandwich construction | ||||||||
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| Internal dimensions | Door openings | Weights | Volume [m³] |
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| Length [mm] |
Width [mm] |
Max. load height [mm] |
Width [mm] |
Height [mm] |
Gross [kg] |
Tare [kg] |
Net [kg] |
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| 5724 | 2286 | 2014 | 2286 | 2067 | 24000 | 2550 | 21450 | 26,4 |
| 5770 | 2260 | 2110 | 2260 | 2090 | 24000 | 2900 | 21100 | 27,5 |
| 5770 | 2260 | 2110 | 2260 | 2090 | 27000 | 2900 | 24100 | 27,5 |
| Insulated container: 40′ long and 8’6" high, with steel frame, walls of sandwich construction | ||||||||
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| Internal dimensions | Door openings | Weights | Volume [m³] |
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| Length [mm] |
Width [mm] |
Max. load height [mm] |
Width [mm] |
Height [mm] |
Gross [kg] |
Tare [kg] |
Net [kg] |
|
| 11840 | 2286 | 2120 | 2286 | 2195 | 30480 | 3850 | 26630 | 60,6 |
| 11810 | 2286 | 2210 | 2286 | 2300 | 30480 | 3650 | 26830 | 59,8 |
| Integral Unit: 20′ long and 8’6" high, with steel frame, walls of sandwich construction | ||||||||||
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| Internal dimensions | Door openings | Weights | Volume [m³] |
Footnote | ||||||
| Length [mm] |
Width [mm] |
Height [mm] |
Max. load height [mm] |
Width [mm] |
Height [mm] |
Gross [kg] |
Tare [kg] |
Net [kg] |
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| 5479 | 2286 | 2257 | 2157 | 2286 | 2220 | 30480 | 3160 | 27320 | 28,3 | 1) |
| 5459 | 2295 | 2268 | 2168 | 2291 | 2259 | 30480 | 3050 | 27430 | 28,4 | 2) |
| 5448 | 2290 | 2264 | 2164 | 2286 | 2260 | 30480 | 3060 | 27420 | 28,3 | 2) |
| 5534 | 2316 | 2331 | 2231 | 2316 | 2290 | 30480 | 3030 | 27450 | 29,9 | 2) |
| 5529 | 2316 | 2331 | 2290 | 2316 | 2290 | 30480 | 2960 | 27520 | 29,9 | 2) |
| 5535 | 2284 | 2270 | 2224 | 2290 | 2264 | 30480 | 2942 | 27538 | 28,7 | 2) |
1) Not suitable for transporting foodstuffs
2) Suitable for clip-on generators
| Integral Unit: 40′ long and 8’6" high, with steel frame, walls of sandwich construction, not suitable for transporting foodstuffs | |||||||||
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| Internal dimensions | Door openings | Weights | Volume [m³] |
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| Length [mm] |
Width [mm] |
Height [mm] |
Max. load height [mm] |
Width [mm] |
Height [mm] |
Gross [kg] |
Tare [kg] |
Net [kg] |
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| 11563 | 2294 | 2261 | 2161 | 2288 | 2188 | 34000 | 4600 | 29400 | 60,0 |
| Integral Unit: 40′ long and 9’6" high, with steel frame, walls of sandwich construction | |||||||||
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| Internal dimensions | Door openings | Weights | Volume [m³] |
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| Length [mm] |
Width [mm] |
Height [mm] |
Max. load height [mm] |
Width [mm] |
Height [mm] |
Gross [kg] |
Tare [kg] |
Net [kg] |
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| 11643 | 2288 | 2498 | 2378 | 2288 | 2517 | 30480 | 4180 | 26300 | 66,5 |
| 11575 | 2294 | 2560 | 2440 | 2286 | 2570 | 32500 | 4300 | 28200 | 68,0 |
| 11568 | 2290 | 2509 | 2389 | 2290 | 2473 | 32480 | 4240 | 28240 | 66,4 |
| 11580 | 2288 | 2498 | 2378 | 2288 | 2517 | 30480 | 4180 | 26300 | 66,2 |
| 11580 | 2290 | 2513 | 2393 | 2290 | 2522 | 30480 | 4180 | 26300 | 67,0 |
| 11580 | 2286 | 2528 | 2408 | 2286 | 2545 | 30480 | 4000 | 26480 | 67,0 |
| 11580 | 2286 | 2515 | 2395 | 2286 | 2535 | 30480 | 4150 | 26330 | 67,0 |
| 11578 | 2295 | 2550 | 2425 | 2290 | 2560 | 30480 | 4640 | 25840 | 67,8 |
| 11585 | 2290 | 2525 | 2405 | 2290 | 2490 | 34000 | 4190 | 29810 | 67,0 |
| 11577 | 2286 | 2525 | 2400 | 2286 | 2490 | 34000 | 4110 | 28890 | 66,8 |
| 11577 | 2286 | 2532 | 2407 | 2294 | 2550 | 34000 | 4190 | 29810 | 67,0 |
| 11583 | 2286 | 2532 | 2412 | 2294 | 2550 | 34000 | 4120 | 29880 | 67,0 |
| 11595 | 2296 | 2542 | 2402 | 2294 | 2550 | 34000 | 4190 | 29810 | 67,7 |
| 11578 | 2280 | 2525 | 2400 | 2276 | 2471 | 34000 | 4150 | 29850 | 66,8 |
| 11578 | 2280 | 2525 | 2400 | 2276 | 2471 | 34000 | 4240 | 29760 | 66,8 |
| 11578 | 2296 | 2542 | 2402 | 2294 | 2550 | 34000 | 4300 | 29700 | 66,7 |
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Use
Refrigerated containers are used for goods which need to be transported at a constant temperature above or below freezing point. These goods are divided into chilled goods and frozen goods, depending on the specified transport temperature. They principally include fruit, vegetables, meat and dairy products, such as butter and cheese.
High-cube integral units are used in particular for voluminous and light goods (e.g. fruit, flowers).
Nowadays, goods requiring refrigeration are mostly transported in integral units, which have a markedly higher market share than porthole containers.
Chilled meat is sometimes also transported hanging, for which purpose the ceilings of refrigerated containers are equipped with special hook rails.
 Figure 29 |
Special controlled atmosphere refrigerated containers are available for transporting fruit and vegetables which may be stored for a longer period in a controlled or modified atmosphere.
The atmosphere is usually established by flushing the container with nitrogen and CO2. During transport, the atmosphere is regulated by nitrogen flushing or CO2 and ethylene scrubbers. Controlled atmosphere containers must be as gastight as possible to prevent ambient air (oxygen) from penetrating.
A number of manufacturers supply the refrigerated container market with controlled atmosphere systems which may be installed in integral refrigerated containers. Controlled atmosphere systems for porthole containers are also available. In recent years, the large refrigeration unit manufacturers have acquired an increasing share of the market for standalone controlled atmosphere containers.
 Figure 30 |
 Figure 31 |
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