Adjustable Helical Swirl Diffuser

Smartemp HSC-AD

High airflow, variable air pattern swirl diffuser for high ceiling, large volume spaces. Installation flush with ceiling or free-hanging. Substantially constant pressure air direction adjustment (manually, thermally or electrically) via adjustable blades affixed to adjustable guide-ring that slide helically over visible fixed swirl vanes flush with diffuser face.

The SMARTEMP Adjustable Helical Swirl Diffuser, type HSC-AD, produces highly inductive swirl discharge of the supply air, diffusing the swirling air stream with adjustable horizontal-to-vertical discharge direction and strong mixing characteristics into the space. High levels of draught-free cooling and efficient heating from elevated discharge heights to floor level are achieved from the patent pending design.

The cambered leading edges of the twenty off-set radial vanes reduce both the sound power level and pressure drop, improving aural comfort and saving fan energy. The geometric twist of the helical vane tips provides increased downward penetration when heating and reduces the minimum permissible airflow rate of the diffuser when cooling.

The pressure drop of the diffuser is substantially constant across the full range of airflow direction adjustment, ensuring stable HVAC system operation regardless of discharge direction.


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.

Adjustable direction
Constant pressure variable air pattern modulation from horizontal to vertical via adjustable blades attached to a helically adjustable guide-ring. Horizontal discharge pattern provides draught-free cooling; vertical discharge pattern provides effective heating from elevated discharge heights.

Manual adjustment
Air pattern direction adjustment is manual.

Circular face shape
Face diameter = 1.4 x DN. Suitable for plaster board ceilings or freely suspended applications.

Radial face pattern
20 substantially radially aligned swirl vanes provide high induction swirl discharge. Helical twist (patents pending) extend airflow operating range. Cambered leading edges reduce pressure drop and noise.

Metal Face
Powder coated metal finish.

Airflow rate 

  • 70 – 4000 L/s (250 – 14,400 m³/h)

Discharge height

  • 2.5 – 15 m

Nominal neck sizes

  • DN250
  • DN355
  • DN500
  • DN710
  • DN1000 (in selected markets)


  • High capacity variable air pattern swirl diffuser for large volume spaces with high ceilings.
  • Substantially constant pressure manual, thermal or electric air pattern adjustment from horizontal to vertically downwards.
  • Air pattern adjustment via adjustable swirl vanes affixed to helically adjustable guide-ring – patents pending.
  • Helical twist of swirl vanes reduces vane pitch towards the periphery for increased airflow operating range.
  • Steep central swirl vane pitch increases airflow capacity and reduces pressure drop.
  • Four nominal neck sizes, each available with an optional reducer for reduced airflow.
  • Airflow rate range reduces by approximately 30% with each reduction in effective neck size.
  • Circular face shape standard for all sizes.
  • Optional square face for sizes DN250 – DN500, suitable for ceiling grids from 300 mm up to 600 mm, depending on diffuser neck size.
  • Installation freely suspended or flush with closed ceiling.
  • Substantially flush face with 20 radially off-set swirl vanes.
  • Similar aesthetic to HSC-FD.


International patent applications and granted patents are listed at


The SMARTEMP Adjustable Helical Swirl Diffuser, type HSC-AD, includes discharge pattern adjustment to vary airflow direction from a radially projecting horizontal swirl pattern, for draught-free cooling, to a downward penetrating swirl cone, for effective heating from large heights. Constant pressure variable air pattern adjustment is achieved via a helically adjustable guide-ring with 20 off-set adjustable radial vanes. The adjustable vanes and guide-ring are substantially hidden from view and slide over 20 visible off-set fixed vanes that form the flush diffuser face. All discharge direction settings produce a highly inductive swirling airflow pattern.

Air pattern control may be manual (all sizes), or via thermally or electrically operated actuator kits (DN250-DN500), or via integrated electrical adjustment (DN710 and DN1000).

Thermal and electrical actuator kits are interchangeable. The thermal or electrical actuator kit is suitable for diffusers equipped with a base module (available for sizes DN250 to DN500 only) affixed to the rear of the diffuser hub.

Each thermally operated actuator kit (DN250-DN500) includes a self-acting thermal wax-bulb that alters discharge direction in response to supply air temperature. No external power source or controls are required. Thermal wax-bulb bias may be pre-set or altered on site to suit the discharge height, airflow rate and temperature range on hand. Thermal kit bias adjustment includes fixed vertical discharge and fixed horizontal discharge end stops.

Each electrical actuator kit (DN250-DN500) or integrated electrical adjustment (DN710 and DN1000) includes a 24 V AC/DC actuator with 2-10 V analogue control input. (Other actuator types are available on request.)  Diffuser electrical discharge direction adjustment is typically modulated by an output from the BMS (by others) in response to the supply-to-room air temperature differential. Electrical discharge direction adjustment is recommended in preference to thermal wax-bulb adjustment where significant room temperature fluctuations are likely (eg heating from a low night setback room temperature) and/or where discharge height is extremely high (eg where the supply-to-room heating temperature differential is low).

Thermal insulation of the diffuser hub is optionally available to minimise the risk of room air condensation in humid or high infiltration applications.

The diffuser may be flush mounted in a ceiling or freely suspended (ie no Coanda effect attachment to the ceiling required).

Each consecutive reduction in diffuser neck size reduces the diffuser airflow duty by approximately 50%. Additionally, each neck size is optionally available with a neck reducer and reduced guid ring, which reduce the diffuser airflow duty by approximately 30%. Consequently, diffuser duty reduces consecutively across the entire range in compound airflow steps of approximately 30%.

The SMARTEMP HSC-AD is made of powder coated galvanised steel. The flat central hub and 20 off-set radial swirl vanes form a substantially flush surface with the surrounding diffuser face. The patent pending helical twist design of the swirl vanes, whereby the pitch of the swirl vanes steepens towards the centre, allows increased airflow rates to be discharged (providing high capacity) and reduces the minimum permissible airflow rate (for low noise applications).  Adjustable swirl blades attached to a guide-ring that traverses a helical path slide over fixed swirl vanes, providing stable, constant pressure, air pattern adjustment. This unique adjustable discharge direction design ensures constant pressure characteristics regardless of diffuser discharge direction pattern, and enhances heating penetration when the air pattern is directed downwards.

High induction swirl discharge is achieved for all discharge patterns. This provides many advantages, including the provision of enhanced draught-free comfort with uniform temperature distribution in both cooling and heating applications. Intense mixing at the diffuser discharge surface strongly dilutes the supply air stream, mixing in large quantities of room air. Highly inductive swirl discharge provides rapid temperature equalisation of the supply air stream with room air.

In cooling mode, high induction prevents cold supply air from dumping. Uniform temperature distribution and high comfort levels are achieved (no cold and draughty or hot and stagnant spots). High induction also produces a strong increase in the supply air stream mass flow rate, as well as rapid discharge velocity decay, making the SMARTEMP HSC-AD swirl diffuser well suited to both long throws (due to the high momentum of the supply air stream) as well as short throws (due to its low velocity).

In heating mode, high induction produces low velocity downward projection of the strongly diluted, gently swirling warm supply air stream over considerable discharge heights. The supply of warmth to the space is gust-free, providing uniform temperature distribution and avoiding draughty spots interspersed by zones of stagnation.

Constant pressure discharge direction adjustment ensures that changes to the airflow direction setting do not disturb air balancing and do not cause fan surging.

The SMARTEMP HSC-AD diffuser is suitable for substantially CAV systems in which ΔTsupply-room ≥ ‑13 K in cooling mode and ≤ +15 K when heating. This large volume flow rate, high induction, variable air pattern swirl diffuser is well suited to large volume spaces with high ceilings or large discharge heights. Enhanced levels of draught-free comfort are achieved in which the air diffusion performance index (ADPI) typically in exceeds 90%.

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

Electric adjustment:
Air pattern direction adjustment by means of electric actuator with 24V AC/DC power supply and 2-10 V analogue control input. Well suited to supply-to-room temperature differential control for demanding heating applications or substantial room air temperature variations.

Thermal adjustment:
Air pattern direction adjustment by means of a self-acting, thermally powered, wax-bulb actuator in the supply air stream (no controls or wiring required). Manually adjustable bias with temperature scale and horizontal and vertical discharge end-stops.

Sweat Inhibitor:
Thermal insulation behind face hub to prevent condensation of room air in cooling mode.

Square face shape:
Lay-in tile (sizes DN250 to DN500 only) suitable for standard ceiling grids of up to 600 mm or 24″.

Neck reducers:
Reduce airflow duty for each neck size by approximately 30%.


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Airflow Direction

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