Tangential (Cross-Flow) Fan: Air Curtain and Fan Coil Motors

A tangential fan (cross-flow fan) uses a long cylindrical impeller that draws air in along its whole length and blows it out along that same length as a wide, flat jet; it is found in air curtains, fan coils, split air-conditioner indoor units and convectors. In most cases its motor is an integrated single-phase unit supplied with the fan, rated at tens or a few hundred watts, and it does not fit DRG Motor's three-phase induction motor range, which starts at 0.25 kW. A standard three-phase motor is really used only in large industrial air curtains where the motor drives the impeller through a belt.

This article explains when you should replace only the motor of a tangential fan and when the whole fan assembly, and how to choose the motor for large air curtains. Removing and connecting a motor must be done by a qualified electrician; air curtains may also contain an electric heater circuit next to the fan supply. All three-phase models are among the 120 models on the Buy Electric Motors Online page; for a general overview of fan applications see our Fan Motors page.

What is a tangential fan and which fan group does it belong to?

Tangential is the name of an operating principle, in the same group as axial, centrifugal and mixed-flow fans. It does not describe a casing or installation type (wall, duct) or an application (air curtain, burner). An air curtain is an application: it may contain a tangential fan or a double-inlet centrifugal fan. This distinction matters when replacing a motor, because the phrase "air curtain motor" does not yet tell you the fan type or the drive arrangement.

The impeller is what sets it apart: many short forward-curved blades arranged between two end discs, forming a cylinder of small diameter but long length. One manufacturer's catalogue gives impeller diameters of 30–65 mm and lengths up to 2×300 mm [1]. Air enters on one side, crosses the blade row twice and leaves on the opposite side through an outlet as wide as the impeller is long. A vortex inside the impeller guides the flow, so the casing and the vortex wall shape performance as much as the impeller itself.

Where it is used:

• Air curtains over shop, supermarket and cold-room doors.
• Split air-conditioner indoor units, cassette and wall-mounted fan coils.
• Trench and wall convectors, electric heaters.
• Refrigerated display cabinets and equipment cooling (oven jackets, electronics cabinets).

What sets a tangential fan apart from axial and centrifugal fans?

The strength of a tangential fan is spreading air evenly over a wide area. An axial fan gives a round jet and a centrifugal fan a concentrated stream from a narrow outlet, while a tangential fan produces a uniform air blade across the width of a door. The price is pressure: tangential fans are designed for low back pressure and are not suited to ductwork. In one manufacturer's 80 and 100 mm impeller series the maximum pressure is around 45 and 75 Pa [2].

• Pressure: low; flow drops quickly when a filter or long duct is added.
• Air flow: rises with impeller length; a wider door needs a longer impeller or several fans side by side.
• Noise: quiet thanks to low speed and a wide outlet, which is the main reason it is used in living spaces.
• Air throw: sets the mounting height of an air curtain and depends on outlet velocity.

What does the motor do here, and why is it rarely bought separately?

In small tangential fans the impeller is fitted directly on the motor shaft. The motor sits at one end of the impeller, outside the air stream, fixed to the side plate; the other end of the impeller runs in a sleeve bearing seated in the casing. Motor and impeller come from the same maker and are balanced together. One manufacturer offers shaded-pole, capacitor and electronically commutated (EC) motors for these fans [1]; all of them run on single-phase mains or low voltage.

The power level separates these motors from the standard IEC motor world. In one manufacturer's brochure the 80 mm tangential fan draws 38 W and the 100 mm one 80 W, on a 220–240 V supply [2]. In an air curtain catalogue the fan input of the tangential models is 150–240 W at 220–240 V 50 Hz [3]. The smallest 4-pole motor in our range, DRG-711-4, is a three-phase motor rated 0.25 kW, 1340 rpm and 0.66 A at 400 V. Even the smallest DRG motor is therefore three times more powerful than a typical 100 mm tangential fan motor, and it does not run from a single-phase socket.

The division of responsibility is clear. Selecting the fan, the fan curve, the impeller and casing design is the job of the fan or equipment maker, or of the mechanical design engineer on large projects. The motor supplier's job is to provide a motor that suits the given shaft power, speed, mounting and ambient conditions. In an integrated fan assembly these two jobs are combined in one product, so the spare part is ordered as a fan assembly as well.

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Can a DRG motor replace a burnt-out tangential fan motor?

The decision depends on how the motor is mounted and what its nameplate says:

In the first three rows a DRG motor is not suitable: the frame does not fit, the shaft end and connection differ and the supply is single-phase. Trying to "adapt" a three-phase motor upsets balance and bearing alignment. In the last row, if the nameplate states an IEC frame, kW, speed and 400 V, a three-phase motor with the same values is a direct replacement.

How many kW is a tangential fan or air curtain motor?

There is no fixed power for a tangential fan; it varies with impeller diameter and length, speed, number of blades, pressure loss at the outlet (grille, heater coil), required outlet velocity and belt losses. Values seen in the sources: 38–80 W for small tangential fans [2] and 150–240 W fan input for tangential air curtains [3]. A data sheet for a belt-driven industrial air curtain lists a 5–15 hp (about 3.7–11 kW) totally enclosed single-speed motor, with a 380 V 3-phase 50 Hz option [4]. That document does not state the impeller type; whether the fan inside is tangential or centrifugal, the motor is the same kind of three-phase induction motor.

For a large curtain the shaft power is found with P_shaft = Q·Δp / η_fan. Example (assumptions stated): 9,000 m³/h (2.5 m³/s) of air, 400 Pa including heater coil and grille, and an assumed fan efficiency of 0.45 give a shaft power of about 2.2 kW. With a 0.95 allowance for the belt drive the motor shaft needs about 2.3 kW, and with a 15% service margin about 2.7 kW. A 3 kW 4-pole DRG-100L2-4 (1450 rpm, 6.02 A at 400 V) is then chosen. You can repeat the calculation with your own values in the Pump & Fan Motor Power calculator.

DRG range: aluminium frame 0.25–11 kW, cast iron 0.55–355 kW; 1000, 1500 and 3000 rpm; 3-phase, 230/400 V or 400/690 V; mounting B3, B5, B14 and B35 (with an order note). On the tangential fan side this range only matches large belt-driven curtains, which is why the price table below is limited to 4-pole models from 1.5 to 11 kW.

How are speed, pulleys and mounting chosen for a large air curtain?

Because a tangential impeller is long and slender, its maker sets a speed limit; that limit is met through the pulley ratio, not the motor speed. Belt-driven curtains favour 4-pole (1500 rpm class) motors: the pulley ratio stays reasonable and the motor is quiet. Example: if the impeller must turn at 950 rpm, a 1450 rpm motor needs a pulley ratio of about 1.53. A 2-pole motor needs a larger ratio and a smaller motor pulley for the same impeller speed, which raises belt force and noise. A 6-pole motor of the same power moves up to a larger frame and may not fit inside the curtain casing.

Mounting: fixing the fan above a door or on a wall is a different matter from the motor's IEC mounting type. In belt-driven curtains the motor is usually foot-mounted (B3) on a base with tensioning rails; the exact type is taken from the fan maker's drawing. The motor normally sits in a corner of the casing, outside the air stream, so a totally enclosed self-cooled motor is sufficient. Compare terminal box orientation and cable entry with the old motor before replacement.

Data needed to select the motor (checklist):

• Nameplate of the old motor: kW, rpm, voltage, connection (Δ/Y), IEC frame, mounting type.
• Shaft diameter and length (D × E), key width; bore of the existing pulley.
• Pulley diameters and belt type; impeller speed.
• Curtain supply voltage: single-phase or 400 V three-phase?
• Heated model or not; whether the motor sits on the warm-air side.
• How often the fan starts when the door opens (frequent starts affect the overload setting).
• Is speed control by inverter required?

The overload relay is set to the nameplate current; the overload, fuse and contactor selection tool helps. For a broader view of belt-driven fans see our article Electric Motor Selection for Industrial Fans and Extractors.

DRG motors for belt-driven air curtains

• DRG-90L-4 – 1.5 kW – 1445 rpm – IEC 90L cast iron
• DRG-100L1-4 – 2.2 kW – 1450 rpm – IEC 100L cast iron
• DRG-100L2-4 – 3 kW – 1450 rpm – IEC 100L cast iron
• DRG-112M-4 – 4 kW – 1450 rpm – IEC 112M cast iron
• DRG-132S-4 – 5.5 kW – 1460 rpm – IEC 132S cast iron
• DRG-132M-4 – 7.5 kW – 1460 rpm – IEC 132M cast iron
• DRG-160M-4 – 11 kW – 1465 rpm – IEC 160M cast iron

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Tangential fan and air curtain motor: FAQ

Is a tangential fan the same as a centrifugal fan?

No. Both may have forward-curved blades, but in a centrifugal fan air enters along the axis and leaves at the rim; in a tangential fan air crosses the impeller and leaves through an outlet as wide as the impeller is long.

My air curtain motor burnt out. Can I fit a three-phase motor?

Only if the curtain is already belt-driven with a three-phase IEC motor. Curtains whose impeller sits directly on a single-phase or EC motor need the maker's spare motor or fan assembly.

Can an industrial motor replace an air-conditioner indoor fan motor?

No. These motors are rated at tens of watts, have unit-specific connections and are often electronically controlled; use the unit's own spare part.

How many amps does a 3 kW 1500 rpm motor draw?

DRG-100L2-4 draws 6.02 A at 400 V and its rated speed is 1450 rpm. In a large belt-driven air curtain the overload relay is set to this value.

Send us the curtain or fan label and the old motor's nameplate, and we will confirm together whether a three-phase motor fits: phone +90 (542) 666 11 11, e-mail [email protected], contact page. For matching models and current prices see Buy Electric Motors Online.

Sources

1. ebm-papst – Tangential blowers (ürün sayfası) – impeller diameter 30–65 mm, length up to 2×300 mm; shaded-pole, capacitor and EC motor options
2. ebm-papst – Tangential blowers QL 80 / QL 100 (broşür, PDF) – 80 and 100 mm impeller models: 220–240 V, 38 W and 80 W input, 1500 min⁻¹
3. KINAIR Air Curtain Units – Product Technical Catalogue (PDF) – cross-flow air curtains: 220–240 V 50 Hz, 150–240 W input, 120 mm impeller
4. Berner – Industrial Belt Drive 20 Air Curtain Data Sheet (PDF) – belt-driven industrial air curtain: totally enclosed single-speed motor, 5–15 hp, 380 V 3-phase 50 Hz option