Air shield (an air curtain) is a device that creates a continuously moving sheet of air right at a doorway, keeping outside air out of the temperature-controlled space inside. In industrial refrigeration it is an ancillary device whose role is to maintain energy efficiency and protect the store temperature.
An air curtain works by blowing air at 6 m/s to 12 m/s (about 20–39 ft/s), vertically or horizontally, across the door opening. That airflow creates an invisible barrier between two zones at very different temperatures — a freezer room at −18°C (0°F) and a corridor outside at +25°C (77°F), for example. The heat entering through the doorway each time it opens falls substantially, so the compressor does not have to keep making it up.
Tân Long has advised on and installed air curtains for many cold storage and food plant projects in Vietnam. This article brings together the practical technical information you need to choose the right unit for each application.
What is an air curtain and how is it built?
Air shield (also known as an air curtain) is an important electromechanical device in solutions that prevent heat loss from cold stores and industrial buildings. It has three core parts: a centrifugal or axial fan, an air distribution plenum, and an adjustable discharge angle.
On Tân Long’s professional cold storage projects, the fan type is carefully selected for the particular building:
- Centrifugal fans: the preferred choice for doorways 2.5 m to 4 m high. Their advantage is high static pressure, giving an air stream strong enough to cut off heat exchange between the two environments.
- Axial fans: typically used on wide openings that need a high air volume but do not demand high downward pressure.
Shell of fan shield are usually made from powder-coated galvanised steel or premium aluminium alloy, operating reliably from −10°C to +50°C. For industrial cold storage down to −40°C, Tân Long recommends purpose-made units with integrated insulation and cold-rated components to prevent surface icing.
On operating specifications, the rating of an fan shield commonly ranges from 150W to 1,500W depending on the door it covers. For a door 1.5 m wide and 3 m high, for example, the unit needs at least 250W. The technical target is to keep air velocity at the bottom edge of the doorway above 0.5 m/s. That is the minimum velocity for the unit to work effectively alongside the insulated door in keeping warm air, dust and insects out of the storage space.
How does an air curtain work?
Air shield works by producing a continuous sheet of air moving fast enough to overcome the pressure difference between the two sides of the doorway. How well it separates the two depends on three key technical factors: the air velocity at the discharge nozzle, the angle of the airflow relative to the plane of the doorway, and how completely it covers the width of the opening.
Based on international standards and hands-on installation experience, Tân Long applies strict technical criteria:
- International standards: Under AMCA (Air Movement and Control Association) guidance, the air sheet has to reach a minimum velocity of 0.5 m/s at the lowest point of the opening for effective thermal separation.
- Tan Long Standard: In practice on projects in Vietnam, Tân Long always designs for 0.8 to 1.2 m/s at the bottom edge. That allows for cross-draughts and pressure fluctuations when the door opens suddenly.
The energy savings from an fan shield are clear. When a industrial cold storage door stays open for 10 seconds with nothing to stop the exchange, the heat entering can reach 2 to 5 kJ/m² depending on the temperature difference. With a standard Tân Long fan shield installed, that falls to 0.5 to 1.2 kJ/m². That is a 60% to 75% reduction in the heat load lost through the doorway, easing the duty on the refrigeration compressor and extending equipment life.
Air curtain types by application
Classification fan shield is currently based on three core technical criteria: discharge direction, the installation environment, and the expected operating temperature range.
- By discharge direction, there are two common types. Vertical blow-down units mount above the door frame and suit openings 2 m to 5 m high (6.5–16.5 ft). They take up no floor space and are easy to fit on standard cold store entrances. Horizontal blow-through units mount to one side of the doorway and suit wide but low openings, or spaces where nothing can be hung above.
- By installation environment, air curtains fall into three groups. Commercial units (supermarkets, restaurants, retail) operate from 0°C to +50°C. Food industry units operate from −10°C to +30°C and usually have an antibacterial coating and can be washed down. Deep-freeze units operate from −40°C to 0°C, with a casing and motor that withstand condensation and abrasion from ice.
- By additional function, some models include an electric heating element or hot coil, allowing warm air to be blown in winter for better thermal separation when the outside temperature drops below 15°C (59°F).
How are air curtains used in industrial refrigeration?
In industrial refrigeration systems, fan shield is a mandatory ancillary at high-traffic doorways such as loading bays, anteroom doors and openings between rooms at different temperatures. At the seafood and food processing plants Tân Long has built, fitting an fan shield at the cold store door noticeably shortens the pull-down time after each shift, keeping the storage process stable.
The economic benefit shows clearly in actual operating figures:
- Dealing with lost heat: When an industrial cold store runs at −18°C to −22°C with the door opening 50 times a day on average, the total heat entering without an fan shield is estimated at 1,500 to 2,500 kJ.
- Energy saving: That loss is equivalent to the refrigeration compressor using an extra 0.4 to 0.7 kWh a day purely to deal with heat coming through the doorway. With the help of an fan shield, that extra consumption falls substantially, giving the business a net energy gain.
Beyond keeping heat out, an fan shield also plays an important part in humidity control. High humidity entering a freezer room causes frost build-up on the condenser, reducing heat exchange efficiency and forcing the compressor to run harder. Fitting an fan shield to the correct specification extends the defrost interval from every 8 hours to every 12 or 16 hours in the hot, humid climate of southern Vietnam, improving the efficiency of the whole refrigeration system.
Common air curtain brands in the Vietnamese market
The Vietnamese market offers many air curtain brands, from commercial to heavy industrial ranges. The table below summarises the common brands by origin, application segment and typical specifications:
| Trademark | Origin | Band | Coverage width | Warranty |
|---|---|---|---|---|
| Nedfon | China | Commercial, light industrial | 0.6 m – 2.0 m | 12 months |
| Jinling | China (founded 1974) | Supermarkets, offices, warehouses | 0.9 m – 1.8 m | 12 months |
| Nanyoo | China | Retail, F&B | 0.9 m – 1.5 m | 12 months |
| Kyungjin | South Korea | Industrial, commercial | 0.9 m – 1.5 m | 24 months |
| Panasonic | Japan | Premium commercial | 0.9 m – 1.2 m | 12–18 months |
| Oulai | China | Retail, small supermarkets | 0.9 m – 1.5 m | 12 months |
Nedfon holds cULus, KC, SASO, CE, RoHS and CCC certification, meeting export and FDI project requirements. Ratings run from 165 W to 1,100 W, suiting both commercial doorways and industrial store doors up to 3.5 m (11.5 ft) high.
Kyungjin is a South Korean brand imported fully assembled, with strong mechanical durability and after-sales service. Its 24-month warranty sets it apart from Chinese brands in the same segment. Kyungjin’s industrial range withstands wet environments and food-grade cleaning chemicals.
Panasonic is optimised for quiet running (under 45 dB at 1 m) and a compact design, suiting commercial spaces where appearance matters, such as showrooms, restaurants and office lobbies.
How to choose the right air curtain for each application
The choice fan shield to the correct specification is what determines how well it actually keeps heat out. For the system to work at its best, the investor needs to establish the following four core specifications.
- Door opening width: The unit’s discharge nozzle has to be as long as, or longer than, the actual door width. For a 1.2 m wide door, for example, you need a unit with a nozzle at least 1.2 m long. For large store doors over 2.5 m wide, Tân Long usually recommends two units side by side so the air sheet covers the whole opening and keeps dust and outside heat out completely.
- Actual mounting height: Each line fan shield all have a specified maximum mounting height, typically 2.5 m to 4 m. Fitted higher than designed, the air velocity at the bottom edge of the doorway falls below the effective threshold and the air sheet stops protecting the industrial cold store.
- Operating ambient temperature: Ordinary commercial units cannot run reliably at cold store doors below −5°C. For deep-freeze environments, the unit has to meet demanding technical criteria: a motor rated at least IP54, heat-resistant windings, and purpose-made casing material that will not become brittle at low temperature.
- Door opening frequency and duty: Where a door opens more than 100 times a day, an fan shield with industrial bearings is essential for a long maintenance interval. Units designed for commercial use typically handle only 50 to 80 openings a day and will suffer bearing failure if fitted at a high-traffic loading bay. Choosing the right rating protects the goods and significantly eases the duty on the central refrigeration compressor system.
Advantages and limitations of air curtains in practice
Application fan shield brings three clear technical and financial benefits. First, it cuts the heat load through the doorway by 60% to 75% compared with a door with nothing fitted, based on actual measurements at industrial cold storage projects Tân Long has delivered in southern Vietnam. Second, the air sheet keeps insects and dust out, helping businesses meet the demanding hygiene requirements of HACCP and ISO 22000 in food plants. Finally, fitting one extends the life of the door gasket and the insulated door system by reducing the constant temperature swings at the door frame junction.
For all its advantages, the investor should note the electricity the fan shielditself uses. A 500W unit running continuously uses about 4.4 kWh a day. In professional installations, however, Tân Long always integrates the unit with a PLC control system or a limit switch sensor. That lets the fan shield run only while the door is actually open, optimising the overall energy balance and reducing the compressor’s running costs.
In general, fan shield is a technically valuable ancillary, particularly at store doors that open frequently. Choosing the right brand, rating and operating temperature protects the goods and improves the performance of the whole cold chain.
Tân Long is ready to provide technical advice and installation of fan shield for every type of project, from processing plants to large-scale refrigeration systems. Contact Tân Long’s engineers directly for a solution document and the optimum installation specification for your project.
Frequently asked questions about air curtains
Do air curtains need routine maintenance?
Yes. An air curtain needs its bearings checked and its impeller cleaned every 6 months in a normal environment, and every 3 months in a freezer room or a wet processing plant. Worn bearings increase noise and reduce air velocity, directly affecting how well the unit keeps heat out. Replacement bearings typically cost 50,000 to 200,000 VND each, depending on the size of the unit.
Which type of air curtain suits a −18°C cold room door?
A low-temperature air curtain rated IP54 or better, with an operating temperature down to −30°C (−22°F), is the right choice. Kyungjin and some Nedfon models meet this. Do not use an ordinary commercial unit below −5°C, because of the risk of motor failure and casing cracking from thermal shock.
Is an air curtain needed if the store already has an anteroom?
An anteroom and an air curtain serve two different purposes. The anteroom reduces the volume of air exchanged each time the door opens. The air curtain reduces the rate of air exchange and blocks immediate ingress while the door is open. In a cold store with heavy goods traffic, combining both gives the best result for both temperature control and energy consumption.
Frequently asked questions about air curtains
What is an air curtain?
It is a device producing a strong vertical air stream across a doorway, forming an air sheet that separates the air inside from the air outside while still letting people and goods pass freely.
What does an air curtain do for a cold store?
It limits how much warm, humid outside air pours into the store each time the door opens, which reduces the load on the refrigeration system, cuts electricity consumption, and limits frost on the evaporator and water around the doorway.
How does an air curtain differ from a PVC strip curtain?
A strip curtain is a physical barrier — highly effective, but it obstructs forklifts and picks up dirt. An air curtain leaves the opening clear, suiting high-traffic doorways, but it uses electricity and has to be positioned correctly to form a complete air sheet.
What should the choice of air curtain be based on?
The width and height of the doorway, the air velocity needed at floor level, the temperature difference across the doorway, how often it is used, and the noise requirements of the area.
What should be considered when fitting an air curtain?
Mount it tight above the door covering the full width, angle the discharge slightly outwards, interlock it with the door so it runs only when the door is open, and clean the intake grille regularly.
Related pages
- What is AHU? Structure, operating principle, AHU parameters
- What is HVAC? Principles, structure and research documents of HVAC
- What is COP? The energy efficiency coefficient in refrigeration engineering
- What is a refrigeration system? Current types of industrial refrigeration systems
- industrial refrigeration systems designed and built by Tan Long
Engineer Nguyen Toan Thinh (Technical Director)
With over 18 years of practical experience in directing, consulting, designing, and constructing heavy industrial refrigeration systems, ASRS automated warehouses, and IQF freezing systems across more than 29 major national projects.
