Energy afficiency and air curtains

Training led by: Eng. Wojciech Gawlas (HVAC expert with over 10 years of industry experience) Content partners: Archispace Portal & Reventon Group

In the modern design of commercial buildings and industrial halls, energy efficiency and the optimization of operating costs have ceased to be mere recommendations and have become an absolute economic and legal requirement. One of the key elements protecting the internal microclimate of buildings is the air curtain. Its primary task is to create an effective air barrier (a pneumatic barrier) that protects an air-conditioned or heated space from the uncontrolled inflow of outside air masses—including cold in winter and heat in summer. In addition, air curtains effectively shield interiors from exhaust fumes, dust, smoke, smog, and unwanted odors (for example, separating the kitchen zone from the customer dining area in food-service establishments).

The scale of savings in numbers—what’s at stake?

According to engineering calculations performed using the Reventon Group selection calculator, fitting a properly selected air curtain to a single 5 × 4 m industrial gate that remains open for just 2 hours a day (e.g., during logistics and unloading operations) makes it possible to save as much as 21 kW of energy! Across the entire facility, this translates into a reduction in the building’s heat load of approximately 15%. A properly designed and installed air curtain is able to reduce air loss through the opening by nearly 70%.

However, for these theoretical savings to become reality, the design must be free of errors. In engineering practice, the same eight failings are nonetheless repeated time and again. Below, we discuss each of them in detail.

1. Undersizing and confusing the housing dimensions with the discharge slot

According to basic design principles, the length of the air stream generated by the curtain must be equal to or greater than the width (for horizontal installation) or height (for vertical installation) of the protected opening. A common and extremely costly mistake is selecting the unit based solely on the overall external dimensions of its housing.

Designers often forget that the total length of the curtain’s housing is not the same as the length of its discharge slot. Inside the unit’s housing, room must be found for the electric motor, the impeller, and the control electronics, which means the effective outlet slot is always shorter than the unit itself. Selecting a curtain whose housing length equals the door width results in so-called “dead zones” at the door jambs, through which outside air freely penetrates the building. The dimensions of the discharge slot itself should always be verified in the manufacturer’s technical documentation.

2. Insufficient air-jet reach (the ISO standard criterion)

The length of the unit alone is only half the battle—the critical parameter is the reach of the jet down into the opening. According to the international standard ISO 27327-1, an effective air barrier is achieved only when the velocity of the airflow reaching the far end of the opening (most often at floor level) is at least 2 m/s.

If the designer selects a curtain with too short a reach, gusts of wind from outside will easily “undercut” the curtain’s jet and make their way inside along the floor. Although minimal deviations are permissible in smaller commercial buildings (where the velocity at the floor drops to about 1.5 m/s), in large industrial projects with multiple gates the cumulative energy losses caused by insufficient reach become drastic. One should always check the limiting velocity for which the manufacturer declares the stated reach.

3. Oversizing the unit (“More does not mean better”)

Designing with excessive, unjustified parameter margins also generates serious problems. Using a curtain with a reach of, say, 4 meters on an opening only 2.5 meters high carries three negative consequences:

Capital and operating costs: Higher-powered units are considerably more expensive to purchase, and more powerful motors generate a constant, high consumption of electricity.

Acoustic problem: Oversized airflows are accompanied by a drastic increase in the level of noise generated, which—in the case of commercial buildings (shops, restaurants, public offices)—is unacceptable for human comfort.

User discomfort: Too strong an air stream (the sensation of a gale) striking people as they enter causes a strong feeling of discomfort and customer complaints.

Solution: The unit should be selected precisely for the installation height, or modern curtains should be used that are equipped with multi-speed motors (AC) or motors with smooth modulation via a 0–10 V signal (EC), allowing the jet output to be precisely fine-tuned during commissioning of the installation.

4. Treating the air curtain as a heater

This is one of the most common and most damaging mistakes. An air curtain is not a heating device and is not intended to heat the volume of a room. Its heating function (provided by water heating coils or electric heating elements) is purely auxiliary and serves to ensure the thermal comfort of people passing through the barrier. Air in intense motion (forced convection) is perceived by human skin as much colder than it actually is. Heating the jet eliminates this unpleasant sensation of a draft.

Attempting to use the curtain to raise the temperature in a hall leads to an energy paradox. Because the unit is installed directly against the external partition (the door/gate), the intense discharge of hot air in this zone drastically increases the temperature difference at the interface and intensifies the escape of energy out of the building. Buildings are heated using unit heaters and destratification fans—not air curtains.

5. Ignoring the minimum installation clearances from building partitions

Every manufacturer of air curtains precisely specifies in its technical documentation the minimum distances that must be maintained between the unit’s housing (especially on the air intake/suction side) and the ceiling or side walls. In industrial halls, where the space above the gate is often severely limited, designers frequently install units “flush,” with no clearance.

Reducing this gap (e.g., installing at a clearance of 30 cm where 50 cm is required) drastically increases the resistance to airflow on the suction side. The unit becomes “choked”—it begins to operate at a different point on its performance curve, its airflow output and jet reach drop drastically, and the noise level rises. Crucially from the investor’s point of view: an unauthorized failure to maintain the installation clearances results in the manufacturer’s outright rejection of any warranty claims. Where there is no other option, written approval for a compromise installation should always be obtained from the manufacturer’s technical department.

6. Failing to account for the mechanics and kinematics of the gate

Designing the curtain in isolation from the construction and door/window-joinery shop drawings is a straight road to disaster. The way in which the gate opens is critical.

Roller (roll-up) doors are a classic example. When the door is closed, its slatted leaf poses no obstacle. Once fully open, however, the coil of material rolled up above the opening takes on considerable thickness. If the curtain is installed horizontally directly above the reveal, the massive coil of the open door will completely block and cut off the air stream supplied from above. Similar interferences occur with sectional doors that have vertical or inclined tracks. In such situations, the only correct solution is to change the concept and install the curtains in a vertical (side-mounted) configuration, provided the spatial conditions allow it.

7. Overlooking “secondary” parameters (Power supply, Acoustics, IP)

Dimensions and reach are the primary parameters that everyone looks at. But the devil is in the technical details, which can paralyze the project at the execution stage:

Electrical load: Curtains with electric modules are characterized by enormous power consumption—the heating elements for large gates can draw over 20 kW. Single-phase versions with such ratings are available on the market, where the operating current exceeds 60 A! If the designer fails to verify the building’s power balance and designs the unit for standard protective devices (e.g., 32 A), starting the curtain will end in the overcurrent circuit breakers tripping immediately. For high power ratings, a three-phase supply must absolutely be the goal.

Environmental conditions (IP class): In commercial buildings, an IP20 protection class is sufficient. However, in harsh industrial conditions—in the presence of dust, moisture, or the risk of water splashing—industrial curtains must absolutely have a protection rating of at least IP54. Ignoring this parameter leads to rapid motor damage and the risk of electric shock.

Mounting structure: It is important to check the mounting accessories—the presence of factory-made threaded holes for mounting studs, dedicated brackets, or consoles—as this determines the installer’s labor costs and the safety of installation at height.

8. Faulty control logic and the lack of priority for the door sensor

The curtain’s control system determines its real energy efficiency. In HVAC practice there is one overriding principle: the absolutely top-priority input for the curtain is the signal from the door-opening sensor (a magnetic or mechanical limit switch).

It is a mistake to base the curtain’s operation solely on the readings of wall-mounted room thermostats. The curtain must respond immediately to the gate opening (modern Reventon controls provide a reaction time and full activation within 0.5 seconds). For automatic gates, the curtain’s control should be integrated directly with the gate’s control unit by means of dedicated relays, which eliminates the need to duplicate sensors. Importantly: the curtain motors are fully suited to cyclic operation, and frequent switching on and off poses no operational limitation for them whatsoever.

Expert Q&A (A valuable bonus from the webinar discussion)

Question: How do you solve the problem of mounting a curtain on a tall glass façade, where there is no physical way to anchor a wall-mounting panel to it?

Expert’s answer: In such cases, the optimal solution is to use the factory-made threaded holes in the housing and suspend the curtain from above (ceiling mounting) using steel mounting studs. If the ceiling is too high, the installer must prepare a dedicated, independent support structure.

Question: Is it possible to order commercial or industrial curtains in a custom RAL color to match them to the building’s design?

Expert’s answer: Yes, absolutely. Both commercial curtains (where aesthetics and design play a key role in shopping centers or restaurants) and industrial ones can be painted in any color from the RAL palette specified by the investor, as a custom project order.

Question: What should be done when a self-closer is installed above a service door and conflicts with a horizontal curtain?

Expert’s answer: The protruding closer makes a proper horizontal installation just above the opening impossible—offsetting the curtain forward to clear the closer moves the jet too far from the plane of the door, destroying the tightness of the barrier. In this situation, the only correct solution is to abandon the over-door (lintel) mounting and use the curtain in a vertical configuration to the side of the door.

Summary: Design holistically

Effective, energy-efficient design using air curtains requires a fully holistic approach from the engineer. Selecting units “by shortcuts,” relying solely on the geometric width of the opening, is unacceptable. The success of the installation depends on a precise analysis of the installation conditions, the type and kinematics of the gate, the building’s electrical power balance, and rigorous adherence to the manufacturers’ guidelines on minimum clearances from building partitions. Applying these principles guarantees the investor real, long-term operating savings and trouble-free operation of the system for many years.