You probably have seen refrigerated van trailers on the road transporting food. Do you wonder how this type of trailer manages to transport this food safely under well-controlled temperatures while still in motion?
Well, the answer is very simple. It is a simple refrigeration process through the use of modern equipment. Here, we will explain this fundamental principle using physics but it is nothing to worry about.
You don’t need to be scientist to understand this. Many people think that refrigerators work by way of creating cold. The fact is, it is not possible to create cold. Basically, cold is the lack of heat energy.
Therefore, cold conditions are achieved by removing heat energy with the surrounding. This is the main underlying specifications of a refrigerated van system.
All you need to do is to have a self-contained atmosphere and then get rid of as much heat as you can from such an environment.
Table of Contents
- Refrigerated Van Specs for reference
- One. How It Keeps the Temperature
- Two. Working Principle
- Three: Different Types of Outer Surface of a Van
- Four: Different Types of Material of Heat Insulating Layer
- Five: Different Types of Refrigerator
- Six: Different Types of Refrigerating Method
- Seven: Things to Check When buying a Refrigerated Trailer
Refrigerated Van Specs for reference
Learn the refrigerated van trailer specs, material, dimensions.
|Refrigerated Van Trailer|
|Term||Refrigerated truck body|
|Standard thickness||Front/rear/side panel: 83 mm|
|roof/floor panel: 103 mm|
|The thickness can be changed according to customer’s requirements.|
|Refrigerator brand||Thermo king, origin USA|
|Carrier, origin USA|
|Temperature||-18 Celsius -20 Celsius -22 Celsius -24 Celsius|
|Dimension of panel||Length 0-15000 mm|
|Width 0-3100 mm|
|Height 0-3100 mm|
|Main characters insulated body||Thickness 33, 43, 63, 83, 103 mm|
|1. Light in weight: 40% lighter than metal body.|
|2. Better insulation: K value less than 0.3w/m2k.|
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One. How It Keeps the Temperature
Now that you have understood the principle, here is detailed information of how this self-contained atmosphere is created and the heat energy removed.
The first step is by creating this self-contained atmosphere by insulating the truck trailer compartment. The insulation is normally made of high-density polymer foam.
This type of foam is quite the same as polystyrene foam even though it is usually of a higher density. Additionally, it is a more durable polymer than for polystyrene.
The insulation, coupled together with a seal all around the door forms an atmosphere that is somewhat heat-tight. The next step is to remove the heat that is left inside as well as any heat that goes in after the door is opened.
This is achieved through the use of a refrigeration system with a simple operation mode. Three different mechanisms work together to accomplish this: a condenser, a compressor and lastly, an evaporator.
Two. Working Principle
The condenser has a metal piece of pipe work normally twisted perfectly into a convoluted shape. The pipework is then filled with an unbelievably high-tech coolant liquid.
This coolant has been in use for a long time but new modifications are coming up with the advent of new technology. The efficiency of this liquid is determined in its ability to absorb heat.
During the cooling process, the liquid is usually circulated all through the pipe work to suck up all the heat contained in the freezer chamber. The coolant fluid changes into a gas as it sucks up the heat.
The already heated coolant fluid in gaseous state goes to the condenser. This mechanism tightly compresses the gas. Extreme pressure applied on the gas forces all its molecules together.
The condense gas is then held at a high pressure and then allowed into the evaporator. This element then sucks air from the outside environment and pushes it via the high-pressure coolant gas.
The coolant fluid then gets cooled down, instantaneously converting it back into a gas and getting rid of the heat into the atmosphere. The gas then gets reintroduced into the condensing unit to start the process all over again.
As this process gets repeated continually, the atmosphere contained in the reefer van trailer gets colder and colder.
To facilitate a smooth process, you need to make a good choice of all part surfaces and elements needed for the construction of a refrigerated truck trailer. In this section, you will get to learn the following:
- Different Types of Outer Surface of a Van
- Different Types of Material of Heat Insulating Layer
- Different Types of Refrigerator
- Different Types of Refrigerating Methods
Three: Different Types of Outer Surface of a Van
3.1 Aluminum alloy
First, aluminum alloy for the outer surface are good because of their light weight and malleability making them easy to work with. Again, it gives you the ability to increase the cargo weight each time during transportation.
The need to insulate the container with very thick walls to the side necessitates the choice of a light weight material such as aluminum.
On such grounds, steel which is commonly used in the construction of refrigerated van would make the container very heavy hence reduce your cargo carrying capacity.
In that case, an aluminum container is a more logical way of transporting temperature sensitive products.
Additionally, the thermal efficiency and ability to ensure minimum air leakage are the other good aspects why aluminum becomes a favorable option.
Looking at these advantages, the moment the serviceable refrigerated trailers are retired and the cooling machinery gets out of service, you can use them to carry any cargo type whether dry or frozen.
Well, aluminum is the best option when you want to transport refrigerated products.
One important caution to take with aluminum alloys is during maintenance and their lifespan. Aluminum containers have high repair costs since the welding process is quite demanding.
Some of the seams require riveting making it a costly affair. However, in a severe environment with temperature sensitive products to transport, the option of an aluminum container is the best.
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Fiberglass is the other alternative for aluminum alloys for this application. This material is good for heat insulation – the primary reason why it used here.
Again, it is cheap and widely used. Here are other reasons why fiberglass has found major applications in this industry:
- The fiberglass material deflects moisture, provides an easy-to-clean surface and is capable of keeping a smooth, attractive look for many years.
- Fiberglass outer surface for your trailer resists dents and scratches that would damage other materials and ruin the professional look you always want to keep.
- It is also perfect for doing great graphics as you would please hence enhancing the quality of your trailer.
- With fiberglass, you are assured of seamless glass board interior walls that are easy to maintain and clean. This gives you a professional work environment for your products and one that works for your team as well.
Four: Different Types of Material of Heat Insulating Layer
4.1 Sandwich Plate
The structure is simple and easy to produce. The middle layer is polyurethane and the outer layer is fiberglass. The polyurethane material is sandwiched in between these fiberglass walls and pressed together.
The trailer is usually constructed of 3/8-inch plywood for the wall construction that offers a rugged protection from rigorous use. The plywood is usually wrapped in polyester resin and then reinforced with the woven fiberglass.
This provides great protection from the outside elements. The polyurethane foam ensures consistent density and uniform insulation through the entire floor.
Thermal breaks at the door and the threshold also help in the minimization of infiltration and in keeping an even temperature all through the cargo section.
Fully insulated walls, floors and ceiling helps to minimize any passive heat transfers and leaks that normally occur at joints and seams.
This helps a lot in the reducing significant temperature differences inside the cargo section. Well, the insulation effect created is inferior to the vacuum insulating plate as will be discussed below.
4.2 Vacuum Insulating Plate
The middle layer is no-Freon polyurethane. The van plate is formed by pressing a machine with high temperature and high pressure and make the inner side a vacuum.
Ideally, this is a vacuum heat insulating body made of a superfine glass fiber. An aluminum foil obstruction bag is carefully arranged outside the vacuum plate body offering insulation against the heat.
Sealing ports are then created to one side of the obstruction bag.
The vacuum heat insulating plate is done in a way that the sealing ports consist of two sealing ports where one is positioned outside the other.
This set up offers an insulation film with a small thickness that comes with a lot of many other advantages such as:
- Its Light weight with a high sealing property
- It offers long heat insulation spans
- There is enhanced effective volume
- Decreased costs of transportation and increased distance of transportation
- Evident economic effect of great technical and economic impact
- It is most appropriate for a product that requires high energy conservation
Five: Different Types of Refrigerator
5.1 Independent Type
Ideally, this is a small refrigerator type and is suitable for 4-30m³ small refrigerated vehicles. It is convenient and quick to install and maintain. These are the kind you will find connected to a vehicle’s alternator unit.
You can choose to have your vehicle engine crankshaft drive an advanced single-5 alternator and a 70 Ah battery. The work of the alternator is to charge the battery of the vehicle which then feeds a small refrigerator using a 12V DC supply.
Another option would be driving the refrigeration compressor unit directly using a belt from the vehicle engine.
5.2 Non-Independent Type
This is for a much bigger application basically for a 20 – 55 m³ large refrigerated vehicles. It uses a power pack to provide power with the refrigeration and heating integrated in one.
With this type of a refrigerator, the cooling effect is good. Again, it offers a more safe and reliable operation of the refrigeration unit and most importantly, it provides a wide range of temperature control.
A type of this unit is one with an auxiliary diesel power pack. The system usually has an engine attached to the refrigeration unit that can be powered either using red or white diesel due to cost and environmental impact advantages respectively.
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Six: Different Types of Refrigerating Method
6.1 Cold-blast Air
This is a widely used refrigeration method. It is a low-cost process that is suitable in most applications and is highly suitable for common goods such as vegetables or any an assortment of cold foods.
However, it has a limitation – it can’t ensure the temperature balance in the van. This method uses fiercely drive cold air in order to rapidly cool down the temperature of hot products to store it in a frozen condition for re-heating in the future.
Here are important things to note:
- Allowing foods to cool down without refrigeration can be a dangerous effort because dangerous bacteria can develop in the course of the process.
- Again, cooling hot food products inside your fridge that has already chilled food substances is also harmful as it will increase the temperature of the rest of the food in it, this compromises the safety of your food. Therefore, cold-blast air offers a solution in that sense.
The air is normally throttled at very high pressure into a low pressure in the valve. This causes the temperature to reduce instantly as its enthalpy remains unchanged.
This is how refrigeration is achieved in this arrangement. In this gas refrigeration cycle, there are no phase changes of the refrigeration gas as observed with other liquid refrigerants.
A cold-plate refrigeration method is a type that can ensure that there is a temperature balance in the van. This is the idea choice for the high-end cold food.
If you are looking for a system of refrigeration that offers a reliable and affordable way of refrigerating cargo that needs accurate temperature control, this is what to go for.
The cold plate is electrically powered and this saves a lot of energy costs when compared to engine-driven refrigeration systems.
Combined with the insulation characteristics of the materials used in the construction of a reefer trailer,
the plate system together with its blower is designed to keep products cold throughout the day in an un-opened cargo section even in devastating conditions without power supply.
Here are important advantages with this kind of approach:
- The refrigeration unit does not rely on engine uptime
- It saves on fuel
- You will not need idling during stops
- There is proper and efficient means of maintaining body temperature
- There are low costs of maintenance and minimum moving sections making its operation simple
- You can easily access all parts and clean them
- It provides a simple hot gas defrost procedure. All you need is to plug it during the night
Seven: Things to Check When buying a Refrigerated Trailer
There you have it: how refrigerated truck trailers work to maintain temperatures, different materials for their construction and the characteristic properties that make them the best option in such an application.
The most important thing to note in all this is that, refrigerated trailers serve the same function regardless of whether you want to preserve, meat, flowers, seafood, ice cream and other perishable products.
The concept is to keep these products at the desired temperature that is predetermined and acceptable for the end user. Anything short of this will be a disastrous engagement.
In a fast food restaurant, for instance, the signature chicken patties should be maintained at about 42oF. Should they reach the store at 45oF, the manager might reject them.
There are dire consequences to that effect: wasted products, unsatisfied customers and additional trips to the main store. All these lead to increased costs of operation.
These are some of the main consequences that will befall you should you make a wrong choice of a refrigerated truck trailer. In that case, be keen on the following:
- The Rear Door Selection
Choosing the wrong type of rear door for your refrigeration trailer may prove to be costly. You may opt for roll-up doors instead of hinged doors for ease of use.
However, it is important to look at the loss of insulation value that may be experienced over time with the choice of roll-up rear doors.
This would definitely lead to increased temperature control issues and increased operation costs should the refrigeration unit be improperly sized to cater for the insulation value loss.
An alternative to this would be going for hinged doors that will be in a position to keep the insulation performance with time.
In your choice of a refrigerated van trailer, look at the delivery type by considering such things as multiple stops, reducing load all through the day against full capacity load/unload delivery when spacing the back door.
Not all door types are suitable for the kind of application you want. For instance, a roll-up door would be the wrong choice for ice cream delivery.
It becomes difficult to maintain these temperatures in between the stops. The only situation in which a roll-up door could work is when offloading the entire ice cream at one destination.
As you give specifications for the liftgate, consider the type of rear door to choose. If your operations would require a lot of dock loading, a tuck-away liftgate would be what you need.
If you go for the rail-style type, which moves up and down along the outer rails of the back door-frame, it would not function well with swing doors. In the end, you could get stuck with the roll-up type for the rear door.
- Power Interrupt Switches
The moment the rear door of your refrigerated box opens up, the blow will force cold air out. At the same time, it sucks humid air into the body from the surrounding environment.
This creates a lot of inefficiencies that adds extra stress on the refrigeration system and also puts the product in the danger of not staying in the right temperature.
This will definitely occur unless you have gotten a specification for a power interrupt switch. In the absence of a blower interrupt switch on the van door, the entire compartment will be filled up with moist air each time that door opens up.
The coils for the refrigeration system once hit by the humid air will start to frost hence forcing the unit to go to a defrost mode. This heats the coils in order to get rid of the frost.
Should you get to the next stop while the refrigeration unit has not fully defrosted the coils, you could think that the refrigeration system isn’t working properly.
However with an interrupt switch, the blower will shut down once you open the door. The cold air then stays inside the compartment as the warm air stays out. This makes it easier to keep the desired temperature inside all through the day.
- Matching the Chassis Specs to the trailer chassis Requirements
Prior to ordering the trailer chassis, make sure that you have verified the frame height at the back of the trailer frame. A problem might arise because of failing to do so.
The van body vendor will not be able to install the body because the box with the original specifications and constructions exceeds the overall height requirements for the trailer.
Therefore, it is always recommended to work with the body manufacturer and the chassis representatives to make sure that there is compatibility with the specifications prior to signing off the order for the vehicle.
- Airflow Considerations
Specifying a box that does not have sufficient airflow once loaded can lead to uneven cooling hence damage your cargo.
Therefore, it is crucial to provide specifications of the body to guarantee proper airflow around your cargo for uniform cooling. Getting a proper airflow condition is highly determined by the choice of your floor.
Other factors that may count include how the product is loaded whether in boxes, on pallets, in milk-type crates and so on. These should be considered when choosing the most suitable floor.
Liaise with the manufacturer of the body to establish the optimal floor specification that you will need for your application.
- Compromising Specifications due to Costs
Some people get caught up with how much to spend to a point of under-specifying the equipment and the body. A lower up-front payment may lead to an inappropriately specified body.
This is not the time to be stingy with your money. Make proper investment to get a well-insulated box. Failure to do so will attract high operation costs and increased lifecycle costs by the time the life of the body expires.
Don’t bother so much with the initial cost. Don’t compromise the insulation with reduced costs. You will end up spending a lot to operate the refrigerated van trailer.
Enough said! To avoid these mistakes, keep increasing your knowledge continually on the full range of options that exist in the market concerning refrigerated bodies.
Based on this, you can challenge the existing specifications of these trailers. The process of buying refrigerated / reefer van trailer should not be an annual event.
Rather, it is a continuous process of gathering information throughout the year. Ask yourself if something has changed in your operations from the last time you bought a refrigerated trailer.
If it has, see the adjustments that you can make to your specifications in order to cater for these changes.
Still, you will need to consider the developments that might have taken place in the market in every area including the body, the impact chassis, or in the refrigeration unit specifications.
Consider whether these developments could be of any value to your operations. When making a decision on the specifications of a refrigeration trailer, make sure that you are doing it from a well-informed point of view.
It is important to have sufficient knowledge of what exists in the market and choose the most appropriate one for your budget and most importantly, the application.