Subject to strict regulations and to stringent requirements, the distribution of temperature-sensitive health products is experiencing strong growth and considerable progress. The field players look for the most optimised solutions in terms of performance and cost to secure the cold chain. Depending on the transportation means, logistical constraints and costs, several systems are used to ship temperature-sensitive products:
- Dynamic system (actif), equipped with a refrigeration unit requiring a power source during transport
- Static system (passive) in the form of insulated containers equipped with eutectic plates or other phase change material, or dry ice
- Other systems: thermo-chemical refrigeration, semi-dynamic refrigeration using dry ice and a fan operates with a power source.
The temperature-controlled container ‘Pallet Shipper Frizbox’ presented in this article is a static solution suitable for all transportation means. It allows to ship a full pallet of products between +2 and +8°C or between +15 and + 25°C or also below -35°C.
Description of the Pallet Shipper Frizbox
Insulating material
The walls of the container are made from closed cell, high density, rigid polyurethane panels (32 kg.m-3), without CFC and HCFC. With low thermal conductivity (less than 0.023 W.m-1) and good mechanical strength, the panels offer good insulation, a sufficient strength and an optimised weight/volume ratio. Both faces of the panels are coated with a multilayer aluminium coating constituting an effective radiation and a vapour barrier. The outer face of the coating can be aluminised or kraft paper. The wall thickness varies according between 40 and 80 mm. The good assembly of the container allows avoiding of thermal bridges.
Internal arrangements
Internal compartments are arranged on the lateral sides and on the top to insert the gel or PCM trays (the cold source) before or after loading the product palette (Figure 1). These arrangements allow to maintain the location of the cold source and to ensure the temperature homogeneity. To prevent that the product pallet damages the walls, the floor is completely covered with wood and the sides are also partially covered. The box is equipped with internal straps to attach the product pallet. For dry ice application, the inside of the container is equipped with a double wooden structure, completely covering the polyurethane. This structure protects the insulation and forms compartments to insert dry ice trays (Figure 1).
Outer packaging & opening of the container
The outer packaging is a double corrugated cardboard. The container is provided with a door allowing a full frontal opening. This ergonomic design facilitates operations and reduces loading times.
Pallet and external dimensions
The container is fixed on a specific pallet and it is designed to be shipped by air or truck. The external dimensions are 1520 x 1200 x 1600 mm (±5 mm). With an internal volume of more than 1900 litres, it can carry an entire Europe or US pallet. It simplifies the loading procedure and the logistics management. It can also be tailor-made.
Cold source
The cold source is suited and adjusted according to the required temperature of the products to be transported. For the same insulated container, 0°C eutectic gel, +5°C and +21°C Phase Change Materials (PCM) and dry ice can be used.
+2/+8°C temperature range
To maintain products between +2 and +8°C, eutectic gel packs ‘Rigid Snowgam’ with 0°C melting temperature are used. The composition of the eutectic gel provides a melting duration 33% higher than water. The gel packs are distributed on trays and inserted in specific compartments to ensure the homogeneity of the temperature and to avoid cold shock. The trays of gel packs are inserted frozen for hot external temperature profiles and inserted liquid stabilised at +5°C for cold external temperature profiles. The location of gel packs ensures reproducible thermal performance. Trays of PCM with a melting temperature of +5°C can be used alone or in combination with 0°C gel packs for mixed hot/cold external temperature profiles.
+15/+25°C temperature range
To maintain products between +15 and +25°C, PCM packs, Rigid Snowgam with a melting temperature of +21°C are used. As in the previous case, the PCM packs are distributed on identical trays and inserted in the same compartments. They are inserted frozen at +15°C for hot external temperature profiles and inserted liquid at +25°C for cold external temperature profiles.
Working principle
As with all refrigerating equipment, the container is sized on the basis of a heat balance. The insulation thickness and the gel/PCM packs are determined according to the heat exchange with the surrounding environment and inside the container. The thermal performance tests allow the validation of the configuration for the required conditions. The principal design parameters are:
- Product requirements: The product temperature range is the primary factor to define the need. The container is designed to transport an entire pallet of products, for the most requested temperature ranges: + 2/+8°C, +15/+25°C and below -35°C.
- Logistics constraints: The logistics circuit is a series of open and closed environments. Each segment is characterised by its temperature and its duration. The required performance of the container corresponds to the total time from the loading of the box to arrival at its destination. The duration is calculated for the worst case of the shipment.
The ‘Pallet Shipper Frizbox’ is qualified to maintain the products between +2 and +8°C and between +15 and +25°C for 100 to 120 hours, under standard temperature profiles required by the ‘NF S 99-700’ standard. It is also qualified to maintain the products below -30°C for at least 120 hours under a specific profile.
Performance Qualification Tests
The ‘Pallet Shipper Frizbox’ has successfully passed the mechanical and the thermal performance tests.
Mechanical tests
The mechanical tests are performed according to ASTM D4169 and ISTA 3E, for loads of 500 kg and 1000 kg. Simulating impacts during handling and transport, these tests consist of the following sequences:
- Thermal pre-conditioning test (temperature and humidity): The container is tested with only dry ice and with dry ice and the product pallet. This test lasts 2 hours and precedes the other mechanical tests sequences.
- Shock tests and impact on an inclined plane: They are performed to simulate the impact on various sides during handling of the container.
- Drop rotational tests on various edges of the container.
- Random vibration tests.
The results of these tests showed that the container provides a sufficient level of mechanical security for products at air or road transport.
Thermal performance tests de between +2 and +8°C
To maintain health products between +2 and +8°C, the container is equipped with 15 trays of eutectic plates ‘Rigid Snowgam’, inserted in the lateral compartments and on the top. The thermal performance tests are performed according to the NF S 99-700 standards, for ST-96-b and ST-96-d the temperature profiles. The eutectic plates are inserted frozen at à -20°C for the hot profile and inserted stabilized at +5°C for the cold profile. The figures 2 and 3 show that the ‘Pallet Shipper Frizbox’ keep products between +2 and +8°C for 102 hours under the ST-96-b hot profile and for minimum 120 hours under the ST-96-d cold profile.
Thermal performance tests de between +15 and +25°C
The container is equipped with 15 trays of +21°C PCM ‘Rigid Snowgam’ to maintain health products between +15 and +25°C under the hot profiles. The trays are inserted solidified at +15°C, in the lateral compartments and on the top. For the cold profiles, 19 trays of +21°C PCM are inserted with liquid at +25°C, in the lateral compartments, in the bottom under the products and on the top. The thermal performance tests are performed according to the NF S 99-700 standards, for ST-96-b and ST-96-d the temperature profiles. The figures 4 and 5 show that the “Pallet Shipper ‘keep products between +15 and +25°C for 120 hours under the ST-96-b hot profile and for 100 hours under the ST-96-d cold profile.’
Thermal performance test below -35°C
The test below -35°C is performed with 200 kg of dry ice, which corresponds to the maximum weight allowed in air transport. This test simulates the extreme conditions expected during the transportation of frozen health products between Europe and the United States. The container is first loaded with dry ice trays and then transported in freezer truck to warehouse where the products are loaded. The qualification test is performed for a specific 120 hours temperature profile, variable between +5 and +40°C. This profile starts after the loading of the product pallet. The cool products and then keep them below -35°C. It should not present any physical damage at the end. Thermal and mechanical acceptance criteria are determined. Figure 6 shows the results of thermal performance.
Logistics advantages
The container ‘Pallet Shipper’ offers logistics, economic & ecological advantages.
Economic aspect: Compared to the dynamic and semi-dynamic systems, it is an energy independent solution and does not require complicated logistics. Compared to small boxes, it offers more space and a better ratio between the payload and the external volume. It is a cost-effective compromise reducing the overall logistics cost including the price of the container and the cost of use, especially for air transport.
Ergonomic aspect: the loading an entire product pallet avoids the repackage of products and minimises the handling operations. It reduces the preparation space & facilitates the logistics organisation.
Ecological aspect: The high volume of the container reduces the consumption of energy and materials needed for the manufacture and the use of the solution, which is part of an eco-design approach.
Conclusion
The temperature-controlled container ‘Pallet Shipper Frizbox’ can carry a full pallet (Europe or US) of products. It is an ergonomic, cost-effective and ecological solution. It facilitates the logistics management and reduces the preparation time, the total logistics cost and the impact on the environment. The high thermal inertia of the load increases the thermal performance. The ‘Pallet Shipper Frizbox’ is also a versatile solution suited for air or road transport. Depending on the configuration, it is used to ship health products between +2 and +8°C or between +15 to +25°C or also below -35°C, for up to 120 hours. It also maintains the physical integrity of the products.
