To gain some insight into the particulars of refrigeration systems for medium duty trucks, Fleet Maintenance visited with Tina Hickman, product manager, truck products, for Carrier Transicold (www.carrier.com/truck-trailer), Truck, Trailer, Rail Division. The company helps improve transport and shipping temperature control with a complete line of equipment and services for refrigerated transport and cold chain visibility.
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Fleet Maintenance (FM): What are the most important considerations when specifying refrigeration systems?
Hickman: The most important factors include insulation type and thickness, net box (body) size, number of door openings and the anticipated maximum outside temperature where the truck will travel. In addition, the design temperature or temperature range for the box should be determined &#; in other words, identify the anticipated temperature set points that will be required for the type of cargo.
Once these parameters have been determined, an estimated refrigeration load requirement can be calculated for the truck body. This requirement can then be compared with refrigeration systems&#; rated capacities to determine the best fit for the application.
For example, a large truck body maintaining frozen products in a hot ambient environment will require a larger refrigeration unit than a small box maintaining perishable products in a mild ambient environment.
When considering system capacities, it is also important to consider the average amount of airflow the evaporator fans provide for the product.
FM: What types of truck refrigeration technologies are available, and how can a fleet determine which is best for its needs?
Hickman: The two most common types of truck refrigeration systems are diesel and direct drive. Cold plate/eutectic systems can also be utilized and may be popular in some applications. However, they are not as widely used as diesel and direct drive technology, primarily because of the lack of application flexibility, since diesel and direct drive units provide both heating and cooling across a wide range of thermostat settings.
Direct drive units are primarily used on vans or smaller truck applications where short, local deliveries are necessary &#; for example, box sizes up to 12&#; in length for frozen products or 16&#; to 18&#; for perishable products.
Direct drive units have a compressor mounted to the vehicle&#;s engine, similar to how an automotive air conditioning system is designed. While this eliminates the diesel engine in a standard truck refrigeration unit, it does require the vehicle engine to be running to provide refrigeration.
Most truck refrigeration applications are more rigorous and require autonomy from the vehicle engine, necessitating a refrigeration unit with its own diesel engine. For these reasons, the diesel-powered unit is North America&#;s industry standard for box truck applications.
Diesel refrigeration technology produces constant cooling capacity versus direct drive technology, where capacity typically varies with the speed of the vehicle engine or cold plates, which may lose effectiveness over the course of the route.
As with direct drive units, diesel units are available in different sizes to suit the application. Multi-temperature versions can refrigerate two compartments at different temperatures with the installation of a second evaporator in the remote compartment. This enables both frozen and perishable goods to be delivered using a single truck.
FM: Is electric standby important?
Hickman: Yes, because it allows shippers to secure their loads, plus it reduces costs and the environmental impact of their operations. With electric standby technology, drivers can connect the refrigeration unit to an electric circuit during periods where the truck is stationary, such as during loading, staging or storing products on the vehicle overnight.
Electric standby allows the engine in the refrigeration unit &#; or the vehicle engine in the case of a direct drive system &#; to be shut off. This can result in significant operational savings because the cost of operating on electricity is typically less than the cost of burning fuel. In addition, utilizing electric standby reduces engine hours and allows owners to save on maintenance costs, such as oil and filter changes, as well as other engine-related costs.
Equally important is the fact that running on electric standby also reduces noise and local diesel exhaust emissions for those fleet and distribution operations located in sensitive neighborhoods.
FM: How important is &#;after sales&#; support?
Hickman: Regularly scheduled preventive maintenance is important in order to prolong the life of the equipment. Obtaining support from a dealer who understands the refrigeration unit and OEM maintenance requirements is vital, especially as equipment becomes more technically sophisticated in providing value-added benefits to refrigerated fleets.
Performing service at the proper intervals will help maximize fuel economy and reduce downtime, which can also reduce the total cost of ownership.
Extended warranty options and comprehensive maintenance and repair agreements provide a cost-effective means for owners to adhere to OEM service intervals.
Features:
Components of a Truck Refrigeration System
A truck refrigeration system consists of 8 key components that work together to provide cooling or refrigeration for the transported goods. The main components include:
: The compressor is responsible for compressing the refrigerant gas, raising its temperature and pressure. It is typically powered by a separate engine or motor.
Condenser
: The condenser is a heat exchanger where the high-pressure and high-temperature refrigerant gas from the compressor releases heat and condenses into a liquid state. The condenser is usually located on the outside of the truck or trailer and uses either air or water to cool the refrigerant.
Expansion Valve or Orifice Tube
: The expansion valve or orifice tube is a metering device that regulates the flow of refrigerant into the evaporator. It reduces the pressure and temperature of the refrigerant, allowing it to evaporate in the evaporator coils.
Evaporator
: The evaporator is another heat exchanger typically located inside the cargo area of the truck or trailer. As the low-pressure and low-temperature refrigerant enters the evaporator, it absorbs heat from the air circulating over the evaporator coils. This cools down the air, which is then distributed back into the cargo area.
Refrigerant
: The refrigerant is a specialized fluid that undergoes phase changes (from gas to liquid and vice versa) within the refrigeration system. It is responsible for transferring heat and enabling the cooling process.
Control System
: The control system includes sensors, thermostats, and electronic controls that allow the operator to set and monitor the temperature inside the cargo area. The control system maintains the desired temperature by regulating the operation of the compressor, fans, and other components.
: Fans are used to circulate air over the condenser and evaporator coils. They help in heat transfer and ensure efficient cooling throughout the system.
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Power Source
: The power source provides the necessary energy to operate the truck refrigeration unit. It can be a separate diesel engine, an electric motor, or a combination of both, depending on the type of unit.
These components work in a coordinated manner to remove heat from the cargo area and maintain the desired temperature, ensuring the freshness and quality of perishable goods during transportation.
A truck refrigeration unit works by utilizing the principles of refrigeration to remove heat from the cargo area and maintain the desired temperature.
Compression: The process starts with the compressor, which is powered by a separate engine or motor. The compressor takes in low-pressure refrigerant gas and compresses it, increasing its temperature and pressure.
Condensation: The high-pressure and high-temperature refrigerant gas then flows into the condenser, which is usually located on the exterior of the truck or trailer. In the condenser, the refrigerant releases heat to the surrounding environment, usually through air or water cooling. As a result, the refrigerant undergoes a phase change and condenses into a high-pressure liquid.
Expansion: From the condenser, the high-pressure liquid refrigerant passes through an expansion valve or orifice tube. These devices act as throttling devices, reducing the pressure and temperature of the refrigerant.
Evaporation: The now low-pressure and low-temperature refrigerant enters the evaporator, which is typically situated inside the cargo area. As air from the cargo area passes over the evaporator coils, the refrigerant absorbs heat from the air, causing the refrigerant to evaporate. This evaporation process cools down the air circulating in the cargo area.
Circulation: Fans or blowers circulate the cooled air from the evaporator back into the cargo area, maintaining the desired temperature. The fans also help distribute the cool air evenly throughout the cargo area.
Refrigerant Cycle: The refrigerant, in its gaseous state after absorbing heat in the evaporator, returns to the compressor to restart the cycle. It is then compressed again, initiating another round of heat absorption, condensation, expansion, and evaporation.
Control and Monitoring: The truck refrigeration unit is equipped with a control system that allows the operator to set and monitor the desired temperature inside the cargo area. The control system regulates the operation of the compressor, fans, and other components to maintain the set temperature.
By continuously cycling refrigerant through the compressor, condenser, expansion valve, and evaporator, the truck refrigeration unit effectively removes heat from the cargo area, ensuring the preservation of perishable goods during transportation.
Truck refrigeration units typically use a variety of refrigerants, but the choice of refrigerant depends on several factors including the specific unit model, regulations, environmental considerations, and efficiency requirements.
R-134a: R-134a is a hydrofluorocarbon (HFC) refrigerant that has been widely used in truck refrigeration systems. It has low ozone depletion potential (ODP) but is considered a high global warming potential (GWP) refrigerant. R-134a has good thermodynamic properties and is compatible with many existing systems.
R-404A: R-404A is a hydrofluorocarbon blend commonly used as a replacement for older refrigerants, such as R-22 and R-502. It is a non-ozone-depleting refrigerant but has a high GWP. R-404A is known for its efficiency and is commonly used in truck refrigeration systems for both cooling and freezing applications.
R-407C: R-407C is another hydrofluorocarbon blend used in truck refrigeration units. It is a non-ozone-depleting refrigerant with a moderate GWP. R-407C offers similar performance characteristics to R-22 but is more environmentally friendly.
R-410A: R-410A is a hydrofluorocarbon refrigerant commonly used in air conditioning and heat pump systems. It has become popular due to its high energy efficiency and low impact on the ozone layer. While it is less commonly used in truck refrigeration units, it may be employed in certain specialized systems.
R-452A (Opteon&#; XP44): R-452A, sold under the brand name Opteon&#; XP44, is a hydrofluoroolefin (HFO) refrigerant designed as a low-GWP alternative to R-404A. It offers similar performance and efficiency but with a significantly lower GWP. R-452A is gaining acceptance as a more environmentally friendly option in truck refrigeration applications.
Guchen pays attention to the concept of environmental protection and sustainable development, and provides users with the choice of two refrigerants, R134A and R404A, and chooses the refrigerant according to your specific needs. It is worth noting that the field of refrigerants is constantly evolving due to environmental concerns and regulations. With the advent of newer refrigerants with lower GWP and improved environmental profile, R404A refrigerant is now becoming more common in truck refrigeration systems.
Features of Guchen Thermo Quality Transport Refrigeration Unit
1. Adopts hydrophilic aluminum foil with internal ridge copper tube in evaporator
We all know that copper has the high quality of anti-corrosion, better heat transmission, so adopts copper tube as the refrigerant line in HVAC systems can be prolonged the product service life a lot. Besides that, the hydrophilic aluminum foil materials will not make the water gather together and block tube, and it can improve heat exchange rate by 30%, which improve the refrigerating effect a lot.
2. Adopts aluminum micro-channel parallel flow coils in condenser
In the condenser, we adopt micro-channel parallel flow coils; it has the advantages of smaller in size, lighter in weight and compact in structure, so it is commonly used for HVAC systems. Employ parallel flow structure, the refrigerant can flow evenly, if refrigerant cannot flow evenly, it will compact evaporator&#;s heat exchange, which can lead to the refrigerating effect bad. So adopts aluminum micro-channel parallel flow coils in condenser also can improve the evaporator heat exchange rate and give a better cooling performance.
3. Add another heat exchange device in Evaporator
In order to increase the heat exchange and improve cooling effect, we add a heat exchange device in evaporator, so the heat exchange rate can be increased by 20%.
4. Adopts worldwide famous brands spare parts
The spare parts take a very important role in the whole refrigeration units, so Guchen Thermo always pay more attention on the spare parts, even the mini parts, we also choose the best quality for customers. The main spare parts include in:&#; QP compressor from TCCI: High quality and easy to maintain&#; Spal Fans: - hours service life, high quality.&#; Danfoss filter drier, expansion valve, receiver and visual liquid length: Famous brands, easy to maintain, stable performance.&#; Castel solenoid valve: Imported from Italy, has a high quality.&#; Codan Pipeline: High quality and easy to maintain
5. Adding 2 valves: CPR valve and liquid injection valve
In the very hot areas, if compressors work some time, its ambient temperature will be high, so adding CPR valve and liquid injection valve can help to switch the compressor temperature, and protect compressor from broken, prolong the units&#; service life.
6. Equip with standby system according to demands
All of Guchen Thermo refrigeration units can equip with standby system according to customers&#; demands. Standby system is very helpful if transporters need to deliver cargoes from day to night, when at night, transporters only need to turn on standby system to refrigerate cargoes continuously. So it really help to save a lot of fuel and transportation cost.
All ofcan equip with standby system according to customers&#; demands. Standby system is very helpful if transporters need to deliver cargoes from day to night, when at night, transporters only need to turn on standby system to refrigerate cargoes continuously. So it really help to save a lot of fuel and transportation cost.
7. Equip with heating system according to demands
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