Fixed Helical Swirl Diffuser

Smartemp HSC-FD

The world’s highest performing fixed vane VAV swirl diffuser.

High capacity swirl diffuser with high induction, fixed horizontal discharge from swirl vanes flush with diffuser face, optionally screened by perforated cover plate. Suitable for low temperature supply air (≥ 5°C) and CAV or VAV systems with extended turndown. May be mounted flush with ceiling or free-hanging.

The SMARTEMP Fixed Helical Swirl Diffuser, type HSC-FD, produces highly inductive swirl discharge, diffusing the supply air stream radially with fixed horizontal discharge and strong mixing characteristics into the space. The patent pending design delivers high levels of draught-free comfort well suited to both constant volume or VAV applications, inclusive of low temperature or cold air supply air systems with a minimum supply-to-room temperature differential of -16 K including turndown to approximately 25%.


Mixed flow discharge
High induction swirl discharge intensely mixes supply air with room air. Strong supply air dilution with rapid discharge velocity decay produces draught-free, high momentum supply air motion with uniform temperature distribution over short or long throws. Ideal for enhanced thermal comfort (ADPI ≥ 90%).

Return air
Also suitable for use as a return air inlet.

Ceiling location
Air supply from above the space, integrated flush with a closed ceiling or freely suspended.

Low temperature supply
May be used for low temperature (cold air) supply systems (Tsupply ≥ 5°C), where ∆Tsupply-room ≥ -16 K.

VAV dependent throw
Throw dependent upon airflow rate. Minimum airflow dependent upon ∆Tsupply-room (eg turndown to 25-28%, neck reducer dependent, and down to ≈1 L/s/m2 @ ∆Tsupply-room ≈ -16 K).

Fixed direction
360° radial pattern (4-way blow), horizontal discharge.

Square face shape
Lay-in tile, suitable for standard ceiling grids of up to 600 mm or 24″.

Radial face pattern
20 substantially radially aligned vanes provide highly inductive swirl discharge. Vanes with helical twist (patents pending) extend VAV operating range. Cambered leading edges reduce pressure drop and noise.

Metal Face
Powder coated metal finish.

Airflow rate

  • 10 – 440 L/s (36 – 1584 m³/h)

Supply temperature

  • ≥ 5°C

Nominal neck sizes

  • DN250
  • DN355
  • DN500

Discharge height

  • 2.4 – 4.5 m


  • Flush face swirl diffuser with 20 off-set radial vanes.
  • High airflow capacity.
  • Suitable for CAV or VAV with large range (eg turndown to 25%-28% @ Tsupply-room = -16 K).
  • Suitable for low temperature supply air (≥ 5°C and ∆Tsupply-room ≥ -16 K).
  • Swirl vanes with helical twist (flatter peripheral vane angle) extend VAV operating range – patents pending.
  • Swirl vanes with cambered leading edges reduce noise & pressure loss.
  • Bell-mouth extends VAV operating range.
  • Optional neck reducers for reduced airflow rates.
  • Optional blanking segments for 3-way blow (270°) and 2-way blow (2×90° or 180°) discharge.
  • Square (standard) or round face (optional).
  • Installation freely suspended or flush with closed ceiling.
  • Similar aesthetic to HSC-AD.
  • Optional CleanScreen™ smudge minimser and sweat inhibitor – patents pending.
  • Optional perforated face screen (down to 36% open area).


International patent applications and granted patents are listed at


The SMARTEMP Fixed Helical Swirl Diffuser, type HSC-FD, discharges the supply air with high induction swirl, radially, producing fixed horizontal discharge direction into the space.

The patent pending 20 off-set radial swirl vanes with helical twist and cambered leading edges increase both the maximum airflow rate and the VAV operating range, whilst reducing noise and minimum permissible supply air temperature.

The SMARTEMP HSC-FD is the highest performing, fixed vane VAV swirl diffuser.

The diffuser is made of powder coated galvanised steel and may be flush mounted in a ceiling or freely suspended (ie no Coanda attachment to the ceiling required). The swirl vanes form a flush surface with the surrounding diffuser face, which can be round or square, and may be optionally screened by a perforated face (down to 36% open area).

Optional neck reducers may be inserted from behind (not affecting the aesthetics of the diffuser face) to reduce the diffuser neck size to suit reduced airflow rates, in particular in VAV applications. Segment covers are available to reduce the discharge pattern from 360° to 270°, 180° or 2 x 90° (ie from four-way to three-way or two-way blow).

The high induction of swirl diffusers offers many advantages. Intense mixing at the diffuser discharge surface strongly dilutes the swirling supply air stream with large quantities of room air. Rapid temperature equalisation of the supply air with room air is achieved, preventing cold air dumping and producing uniform temperature distribution with high comfort levels in the space. Supply air stream temperature dilution also improves heating performance by reducing the bouyancy of the supply air stream. High induction produces a strong increase in the mass flow rate of the supply air stream, due to induced room air, as well as rapid discharge velocity decay. At any given airflow rate, the SMARTEMP HSC-FD swirl diffuser is suitable both for long throws (due to the high momentum of the swirling supply air stream) as well as short throws (due to its low velocity).

The SMARTEMP HSC-FD swirl diffuser is available with a round or square face and may be used in CAV systems, as well as VAV systems. Extended VAV turndown is possible. VAV system turndown is dependent upon ΔTsupply-room (eg to approximately 25-28% at ΔTsupply-room = -16 K). Draught-free comfort is enhanced, achieving air diffusion performance index (ADPI) in excess of 90% even at specific airflow rates as low as ≈1 L/s/m2. Due to the rapid discharge decay characteristics of the swirl discharge, a high maximum specific airflow rate of ≈15 L/s/m2 may be achieved at 90% ADPI.

Optional CleanScreen™ includes a perforated hub that discharges clean, dehumidified supply air to screen the diffuser face from soiling and condensation due to humid air and air borne contaminants in the space. CleanScreen™ enhances hygiene, maintains clean aesthetics, and effectively eliminates on-going cleaning costs. CleanScreen™ is well suited to applications with a high concentration of pollutants (such as restaurants or near busy streets), in places of high humidity (such as the tropics or the coast) or where high infiltration may occur (such as lobbies and public spaces).

The SMARTEMP HSC-FD Fixed Helical Swirl Diffuser is available in selected markets as the LTG Helix-Deckendrallauslass ILH.

Smudge minimiser:
CleanScreen™ air supply through optional perforated hub washes diffuser face with clean supply air, minimising diffuser face soiling due to air borne contaminants from the room. Patents pending.

Sweat inhibitor:
CleanScreen™ (patents pending) air supply through optional perforated hub washes diffuser face with dehumidified supply air, eliminating diffuser face condensation due to humid room air.

Circular face shape:
Face diameter = 1.4 x DN.  Well suited to plaster board ceilings or freely suspended applications.

Perforated face pattern:
Square perforated face panel (down to 36% open area) to screen diffuser face.

Neck reducers:
Reduce airflow duty. Blanking segments: Provide 2-way or 3-way discharge patterns. May be combined with neck reducers.

Side-entry foam connection boxes with threaded rod or magnetic edge strip fastenings.


Product Type


Supply Temperature


Airflow Direction

Face Pattern


Face Shape


Face Material


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