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Home » Dock levellers and strip curtains: A smart solution for temperature control

Dock levellers and strip curtains: A smart solution for temperature control

Written by Eamonn Ryan

Dock levellers and strip curtains are essential to efficient cold chain warehousing.

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 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.

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.


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.


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.


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.



Hennie le Roux, sales manager: DDL Equipment. Image supplied by © Eamonn Ryan | Cold Link Africa
Hennie le Roux, sales manager: DDL Equipment. Image supplied by © Eamonn Ryan | Cold Link Africa

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 size vehicles and the application thereof. Systems used will be dictated by the type and size of the vehicles being loaded and the exterior mounting surface of the building. Sectional and high-speed doors form part of the package to control the environment. Various models available depend on the environment they will be used in and can be operated in various ways, including push buttons or radars that can be set to detect pedestrian traffic, remote controls fitted to forklifts, or loop detectors in the buildings’ floor – even biometrics can be added.”

Dock levellers and curtains are essential for preventing airborne contaminants, such as dust, pests or pollutants, from entering the cold storage area. The cold chain requires effective sealing mechanisms, including inflatable or brush seals, to create a barrier between the indoor and outdoor environments.

Le Roux adds: “DDL makes use of brush seals and PVC skirts that can be fitted to the front of a dock leveller that creates another barrier to minimise the ingress of contaminants. This also has the unintended benefit of minimising pilferage. Seals are used to  envelop the entire vehicle to keep pollutants and dust at bay. High speed doors are being more widely used to deal with temperature control, cross contamination between areas and to keep vermin from entering the building. This is achieved by rapid opening and closing which still has a host of built-in safety features. Some models can reset themselves in their tracks if collided with and will continue to operate as normal. These high-speed doors are designed for use in specific environments.”

He explains that safety is a critical concern in dock operations. Manufacturers ensure that dock levellers and curtains are designed and installed with safety features to prevent accidents and injuries. This includes features such as safety edges, photoelectric sensors and emergency stop systems. “Safety features form a big part of the design and manufacturing of docking systems. Research and development is constantly adding to the pool of new products or improvements which can be anything from simple handrails or walkways to signalling systems. For instance, our products are designed in such a way that safety sensor can be added where required.”

Dock levellers and curtains are subjected to significant wear and tear due to frequent use and exposure to harsh environments.

Manufacturers select durable materials and robust construction to ensure long-lasting performance. Regular maintenance and inspection of dock levellers and curtains are also essential to identify and address any issues promptly, minimising downtime and maximising their operational lifespan.

“For instance, DDL seals are manufactured using a double layer of hardwearing canvas and in most cases, damage is repairable – extending service life,” says Le Roux. “Canvas is also washable and holds up to being cleaned by chemicals and disinfectors used to keep docks hygienic. Aluminium is used when fixing the dock hardware because it is lightweight and does not rust when exposed to the elements. It’s advised that a dock leveller be serviced quarterly, and customers may also consider entering into an SLA (service level agreement) giving peace of mind that their dock equipment is kept in good working order and potential problems are caught and rectified timeously. In coastal or corrosive areas, some opt for fully galvanised dock levellers and pit frames.”

A DDL Combo Seal. Image supplied by DDL
A DDL Combo Seal. Image supplied by DDL

Manufacturers must adhere to relevant regulations and standards governing dock levellers and curtains. These may include safety regulations, building codes, fire safety requirements and energy efficiency guidelines. Compliance ensures the safe and efficient operation of dock facilities and avoids penalties or legal consequences.

Le Roux explains that their dock levellers are designed to BS-EN-1398 standards, which is a British and European standard that complies with local food standards. “Dock levellers are designed at DDL by in-house engineers while third-party engineering is used to do Finite Element Analysis – to analyse all the elements and to ensure each will stand the test of time. Furthermore, strength tests are carried out to determine the lifecycle of the dock leveller.”

Automation and technology are increasingly being employed in the cold chain and logistics industry. Engineers work on integrating dock levellers and curtains with automated systems, such as dock management systems, to streamline operations and improve efficiency. This may include features like automated levelling, remote control operation or integration with warehouse management systems for better inventory tracking and logistics planning.

DDL has developed a docking bay communication system that integrates all the docking equipment: dock leveller, sectional door, traffic lights system and sealing system. “The PLC (programmable logic controllers) system can be linked to wireless communication if need be. Sensors along the floor that detect where in the docking stage the vehicle is, are generally used in conjunction with truck wheel guides. The latter are used to guide the truck into the docking bay to ensure it contacts the seal in exactly the right place to get the best seal between truck and building.

“The HMI (human machine interface) screen inside the building guides the operator through the steps. Sensors are triggered as the truck’s wheels pass through the beams – turning on different coloured lights at the various stages during docking. The last sensor is installed on the dock sealing system and a red light is illuminated once the truck has reached the optimum seal and before the truck contacts the building or docking structure. This helps to protect the building and the seals, ensuring the vehicle contacts the seals without compressing them too far and causing damage to the seals. Trip switches on doors are also used and linked to the dock leveller. This will prevent the dock leveller from being operated before the door in the fully open position and vice versa, for closing the door before the dock leveller is returned to its rest position,” he says.

The industry often requires flexibility in dock operations, accommodating various types of vehicles, container sizes or load configurations. Dock levellers and curtains are designed so that they can adapt to different loading scenarios. This may involve adjustable or modular systems that can accommodate varying dock heights, different door sizes, or specialised loading equipment.

At DDL, Le Roux says the company offers a design service to meet any special needs that clients might have. “This includes custom-made seals to accommodate different vehicles or to deal with space constraints in loading yards. Mini-dock levellers are also used, but are best suited to uniform vehicles. Where loading docks aren’t available, elevating dock levellers or scissor lifts are an option, as they are relatively compact which is useful where space may be an issue. Freestanding dock levellers are used in conjunction with ISO panel enclosures to which seals can be fitted.”


A DDL air powered dock leveller. Image supplied by © Eamonn Ryan | Cold Link Africa
A DDL air powered dock leveller. Image supplied by © Eamonn Ryan | Cold Link Africa


In most modern loading bays, goods are transported directly from a cold-room facility onto a truck. Loading bays can either be designed to be inside of the building, situated outside on a loading platform or mounted on a free-standing frame. There are many benefits to having the loading bays outside of the building. These include saving valuable space inside the warehouse and creating more energy efficient loading bays incorporating dock levellers, dock shelter and load house.

There are two main types of dock levellers available: air-powered and hydraulic.

When a new facility is built, the inclusion of a loading dock is a fundamental consideration. Their presence becomes particularly necessary when lifting heavy objects using specialised equipment such as lift trolleys and forklifts. In such cases, dock levellers are required to ensure the safety of workers during the docking process by creating a bridge between the loading bay and the truck floor. Docks require a minimum height of 1.2m from the floor to effectively carry out their duties, whether it involves the loading from a forklift or a pallet-jack.

Ideally, appropriate dock bays should be included in the design and construction of a warehouse to meet these requirements, but many older facilities may lack them and can still be retrofitted. The latter requires an assessment of the layout and functionality of the space to determine the optimal placement of equipment. It may require the construction of ramps or modifications to existing structures to accommodate the 1.2m height requirement of docks.

There are also a number of accessories that accompany the dock leveller: bumpers to prevent damage to the dock or door, a dock shelter – which prevents cold air escaping in the cold chain for improved energy saving and working conditions – and others.

One notable innovation in dock leveller design is the development of telescopic dock levellers, which allow the doors to open within the sheltered area. Telescopic dock levellers are designed to extend outwards, allowing for greater reach and flexibility. With telescopic dock levellers, it becomes easier to access trucks or containers that are positioned farther away from the dock, streamlining the loading and unloading process. This advancement is particularly useful in cold regions where sheltered access and tight temperature control are crucial, and these innovations prevent any loss of temperature in or out.

Another significant development in dock leveller technology is the introduction of insulated dock levellers. These levellers feature a completely sealed underside and insulation materials to minimise temperature gaps, reduce energy loss and prevent the influx of cold air. Insulated dock levellers are particularly popular in European countries where energy efficiency regulations are stringent. By maintaining temperature control, businesses can minimise energy consumption and, consequently, reduce operational costs. These are new to South Africa but already have a long history in Europe.


Dock levellers are not the only way to improve energy efficiency in the cold chain. Another solution that many businesses use is strip curtains.

Strip curtains are flexible plastic sheets that hang from a doorway or an opening, creating a barrier between two different environments. They can help reduce heat loss, maintain temperature control and prevent contamination. Businesses in the cold chain typically use strip curtains to separate two areas in a space from one another. Here are some of the ways that strip curtains can benefit the cold chain:

  • Keeping two different areas of a warehouse separate from one another
  • Keeping a cold area and a room temperature area separate in a food production facility
  • Using them almost like a door at a loading dock to keep the cool air inside and the bugs outside
  • Using them in factories instead of doors to allow forklifts and other vehicles easy passage from one room to another.

While these are just a few of the most common applications of strip curtains, there are many more. They are extremely versatile, and because of their many benefits, there are a lot of reasons why many businesses choose to use strip curtains instead of having wide open spaces or installing multiple doors. They offer a lot of helpful benefits, such as:

Protecting workers and inventory from dirt and insects: Loading docks are known to be dirty, and bugs can easily find their way inside warehouses from your dock doors. Strip curtains protect the area from bugs, and because they are made of heavy-duty PVC, dirt has a harder time finding its way through.

Temperature control: Cold chain warehouses or storage facilities often need a way to separate room temperature products from those that need to be kept cold or even frozen. PVC strip curtains can transform any storage space into a temperature-controlled area. This can also dramatically lower energy bills.

Greater visibility than walls or doors: PVC strip curtains can be either clear (where visibility is desired), or not (where visibility isn’t required such as a butchery). Facilities can therefore obtain the level of separation that they wish  for while not obstructing anyone else’s vision. This can help workers find what they are looking for more easily while they still get to enjoy the other benefits of having strip curtains.


As strip curtains have been in use for over forty years, there has been a vast amount of development in the flexible PVC material used to make them. There are now many different grades of material on the market, but when looking for quality, it is advisable to source material that is formulated with non-phthalate plasticiser, which is more environmentally friendly than some cheaper materials available.

Maxiflex offers various materials made for different environments and applications. For freezers, there is the Polar material, which can withstand temperatures ranging from -25°C to +30°C, and the Super Polar material for blast freezers is suitable for temperatures as low as -60°C. As these materials are especially made for cold environments they do not go hard and brittle which often results in them cracking and breaking. It is therefore important to order the correct material for your application.

Other specialised materials available are the Anti-Insect formulated with citronella, which acts as a repellant for flying insects, as well as the Stop Bac with antibacterial properties. Flexible PVC is available as standard clear, transparent or opaque coloured material.

Strip curtains have become a popular solution for controlling various factors in different environments. They are used to control temperature, dust, pests and even wind for areas that need to be enclosed, such as retailers for food manufacturers, where they don’t want to spend money on a high-speed door – or use it in conjunction with a freezer door from which the cold air flows out as soon as it opens. The curtain presents an additional barrier and improves energy efficiency.

When national retailers perform an audit of their food suppliers, they typically will – at a minimum – want to see the use of strip curtains. These are also commonly used in conjunction with freezer doors in hospitals or cold storage facilities where they act as barriers to prevent cold air from flowing out when the doors are opened. This makes them an essential component in maintaining the desired temperature and hygiene in such facilities.

In conclusion, dock levellers and strip curtains are two effective solutions for improving energy efficiency in the cold chain. They can help businesses save money, reduce their environmental impact and ensure the quality and safety of their
products. By choosing the right dock leveller and strip curtain for their needs, businesses can optimise their operations and enhance their performance in the cold chain.


  • ASHRAE Fundamentals
  • Assa Abloy
  • CB Engineering Company
  • Dock Design Layout
  • Maxiflex
  • Stab-A-Load