Dock levellers and strip curtains are essential to efficient cold chain warehousing .
FEATURE
INCORPORATING COLD CHAIN
DDL © Eamonn Ryan | Cold Link Africa
Dock levellers and strip curtains :
A smart solution for temperature control
Both are key to moving goods in and out of trailers and trucks , and for maintaining optimal temperature levels . Cold chain warehousing has witnessed considerable technological advancement over the years . Two elements which have gained significant importance are the dock leveller , mainly because it is crucial for unloading and loading trailers and trucks , and strip curtains .
With an increasing number of businesses loading containers or trucks , the need for efficient loading and unloading systems has grown . Dock levellers provide a safe and convenient bridge between the loading bay and the truck .
Docking bays – and the accompanying guides , shelters , seals and levelers , doors , curtains , supports and rails – all impact the function of the cold chain , from the packhouses on the farm all the way to the retail outlets ( and transportation in-between ). There are several designs and technologies to choose from today as well . The available solutions add value , mitigate risks and aid in better efficiency in holistic operations – while also contributing or transferring
DDL installation .
A high-speed door .
Dock levellers and strip curtains are essential to efficient cold chain warehousing .
benefits to other facility components such as their impact or integration on refrigeration and storage systems respectively .
Dock levellers and strip curtains specifically play a crucial role in maintaining temperature control during loading and unloading operations . Maintaining an unbroken cold chain demands a focus on ensuring the proper sealing and insulation of dock levellers and curtains to minimise air leakage and heat transfer .
When a door is left open for an extended period , air flow – according to scientific principles – will naturally attempt to reach an energy equilibrium by mixing with hot or ambient air . This is of course a problem when a controlled environment is in use – the more heat that enters a space , the harder a refrigeration system needs to work . This is also potentially a bigger problem when high levels of humidity are present outside a space – mixing with cold air can produce condensation , water vapour or ice that can affect insulation over time and affect products , as well as expose a facility to dangerous mold growth or conditions where some bacteria can thrive .
Written by Eamonn Ryan
Different techniques and systems have been developed over the years , for instance to reduce the amount of temperature loss at these entry and exit points – using different materials , combined products , air curtains , strip curtains , solid plastic curtains and naturally speed of operation , remote control ( or system integration ), motion sensing and even as part of airlock-type systems . Furthermore , the type of system selected allows for different scenarios in traffic flows and of course caters to several health and safety aspects .
Improper door selection can result in high energy costs , higher maintenance costs , lower productivity , wasted man-hours and lower product lifespan . When considering a facility design and specifications , energy conservation in the cold storage facility begins with the unwanted ingress of heat , which can be transferred in three different ways : convection , conduction and infiltration .
• Convection : In a refrigerated warehouse , products could be moved in and out of storage thousands of times a day . With each opening of a door , two air streams are set in motion at the doorway . Cold , dry air escapes from the storage area along the floor into the dock or holding area ( depending on facility setup ) and warm , moist air from the dock or holding area enters the cold storage area through the upper part of the door opening . This creates ice crystals on the walls , ceiling and the door itself . Conversely , cold air streams out of the door along the floor , mixing with the warm , moist dock air , forms fog and even ice and snow on the floor in front of the door . How fast this frost build-up occurs depends largely upon the frequency and duration of door openings . With each opening of the door , more moisture enters the cold storage room , and the frost / ice layer grows , acting as an insulator on the walls and evaporator coils . As a result , system efficiency drops , ultimately causing the refrigeration units to become ineffective or inoperative . With decreased system efficiency through frost build up , the warm air entering the cold storage room requires the refrigeration system to run longer and use more energy to compensate . Preventing or minimising the ability of the air streams to reach laminar flow stage requires reducing open door time . Basic powered doors give you a better chance of minimising infiltration by reducing open door time , but high-speed doors offer the greatest reduction in open time .
• Conduction : The transfer of heat or cold through a door itself can also be a substantial operational
cost to a facility . Conduction losses occur when heat is transmitted through one medium to another of different density , such as heat transmission through a closed door . Solid panel insulated doors have been the traditional choice to handle conduction problems in coolers and freezers where there is a large temperature differential . These applications tend to be door openings which are cycled less and spend substantial periods of time in the ‘ closed position .’ In those applications , insulation value becomes a paramount issue to stop the transfer of heat and cold . Inadequate insulation values can contribute significantly – not only to the cost of operations but also to the amount of frost , ice and moisture build-up on the door and floor surfaces . Low insulation values can create slippery floor conditions due to condensation formation and thus contribute to safety hazards .
• Infiltration : Air passage created by an inability to provide tight seals around door surfaces can be the cause of substantial refrigeration loss and heat gain . The air creeping in through damaged or missing gaskets , through cracks in strip curtains , or under door panels is a constant daily operational cost . This is a common problem with doors in which the seals are not in good working condition or the sealing surface for the door is not level . Aside from energy loss , the infiltrated moisture will also turn the doorway into a hazard area . The frost becomes ice on the floor and fog around the threshold , making unsafe , slippery conditions and poor visibility for personnel . Material handling speed suffers as the operators slow down in response to the hazardous conditions . Scraping away frost from floors , walls , product , racks and other areas of the cold storage room also means higher maintenance related costs and functional time losses .
SYSTEMS EMPLOYED ARE DICTATED BY APPLICATION
To prevent air leaks and ensure a tight seal between the dock and the vehicle , it is important to choose the right dock sealing system for a cold chain warehouse . One of the leading suppliers of such systems in South Africa is DDL Equipment , which offers a range of solutions to suit different needs and specifications .
Hennie le Roux , sales manager of DDL Equipment , explains : “ To minimise heat transfer , DDL has three dock sealing systems – namely Contact Curtain Seals ( CCS ), Dock Cushion Seals ( DCS ) and Combo shelters – to accommodate different
14 www . coldlinkafrica . co . za COLD LINK AFRICA • October 2023