Air principle · swirl

The air mixes before you feel it.

A swirl diffuser gives the supply air a twist and discharges it radially along the ceiling. On its way, the jet entrains a great deal of room air. By the time the air reaches the occupied zone it is mixed, slowed down and close to room temperature. That is mixing ventilation, and the swirl diffuser is its best-known tool.

See it in motion: the airflow of the DD-N →

What the air does

Twist, spread, mix.

At the outlet

Fixed vanes give the air a twist. The curved outlet deflects the jets horizontally, along the ceiling. (DD-N, DS 1175 E p. 3) With a radial swirl diffuser such as the RA-N, the Coanda effect makes the jet attach to the ceiling. (DS 4012 E p. 3)

In the room

The swirling jets have a high induction: they entrain room air, so velocity and temperature difference drop quickly. The mixed air fills the whole room evenly. There is no fixed jet in the occupied zone. (DS 1175 E p. 3)

Character

Turbulent, with a turbulence intensity of about 40 %. (TB 69 p. 3)

When to choose swirl

Lots of air, little space.

Large temperature differences. Ceiling swirl diffusers and radial swirl diffusers accept up to −12 K between supply and room air (TB 69 table 7). Displacement stays at 3 K at most in category A (DS 4069 E p. 4). With the same air volume you remove more cooling load.
Changing layouts. The air comes from the ceiling; the floor stays free. Offices, schools and hospitals are the typical application (DS 1175 E p. 2).
High rooms with changing use. Adjustable types tilt the jet from horizontal (cooling) to vertical (heating), for discharge heights up to 15 m (RA-V2, DS 4122 E p. 2) and 28 m (DD-VG, DS 4033 E p. 2). From about 3–3.5 m, that is Peek’s standard choice.

When not: Many heat sources, a modest cooling load per m², and contaminants you want to rise away at the source: look at displacement →.

Design limits

The limits per type.

general, TB 69

Max. ΔT cooling · swirl diffuser, radial swirl diffuser · −12 K · table 7
Max. ΔT cooling · swivel jet outlet, floor swirl diffuser · −10 K · table 7
Air velocity in the occupied zone at 26 °C · A 0.15 · B 0.25 · C 0.33 m/s · table 2
Max. specific cooling capacity · follows from allowable air velocity and discharge height · fig. 7

The datasheet of the type always prevails. It is sometimes stricter than the general rule.

Type	Position	Discharge height	Max. ΔT cooling / heating	Source
DD-N	ceiling	2.2–4.5 m	−12 K / +5 K (+10 K up to 3 m room height)	DS 1175 E p. 4
RA-N	ceiling	2.2–4.5 m	−12 K / +5 K (+10 K up to 3 m)	DS 4012 E p. 3, p. 12
RL	ceiling	2.5–4.5 m (size 300/400); 2.7–4.5 m (500/600)	−12 K flush, −10 K freely suspended / +10 K up to 3 m, +5 K above	DS 4186 E p. 2
OC-Q	ceiling, modular ceiling	up to 4.5 m	±10 K up to 3 m room height; ±5 K up to 4.5 m	DS 4136 p. 2
RA-V2	ceiling, adjustable	2.8–15 m	−12 K / +12 K	DS 4122 E p. 2
DD-VG · DD-VL	ceiling or freely suspended, high halls	DD-VG 3–28 m; DD-VL 3–12 m	DD-VG −10 K / +20 K with jet straightener; DD-VL −10 K / +15 K	DS 4033 E p. 2
WL	wall	2.6–6 m (per size)	−8 K / +5 to +8 K	DS 4029e p. 3
DB-E	floor	—	±10 K supply – return	DS 1146 E p. 5

Peek rule of thumb

From a discharge height of about 3–3.5 m, choose an adjustable swirl diffuser, so you can direct the jet for cooling and for heating: horizontal when cooling, vertical when heating. Adjustable types are the RA-V2 (2.8–15 m, DS 4122 E p. 2), the DD-VG · DD-VL (3–28 m and 3–12 m, DS 4033 E p. 2) and the DD-VK (on request; 3–5 m with round outlet, 4.5–15 m with staggered outlet, DS 1256 E p. 2). The datasheets point the same way: above 3 m room height the allowable heating difference of the DD-N, RA-N and RL drops from +10 K to +5 K (DS 1175 E p. 4; DS 4012 E p. 12; DS 4186 E p. 2).

spacing

The minimum distance between two outlets follows from the air volume per outlet and the allowable air volume per m² of floor (DS 4122 E, chart 2). In that datasheet’s “supermarket” example, 790 m³/h per outlet at 61 m³/(h·m²) gives a spacing of 3.6 m.

Typical mistakes

Where it goes wrong.

An outlet that doesn’t mix. A simple grille lets the cold jet drop into the occupied zone unmixed. You feel it as draught. A swirl diffuser mixes while the air is still under the ceiling.
A fixed outlet in a high room. A DD-N or RA-N is made for 2.2 to 4.5 m, and above 3 m room height it may only heat by +5 K. Warm air from a fixed outlet stays under the ceiling. That is why a theatre ceiling takes an RA-V2, not a DD-N. Peek’s rule of thumb: from about 3–3.5 m, an adjustable swirl diffuser (RA-V2, DD-VG · DD-VL, DD-VK) that tilts the jet to vertical for heating.
Too large a temperature difference. Beyond the type’s maximum the jet is heavier than the mixing can handle and drops into the occupied zone too early.
Outlets too close together. Jets from neighbouring outlets meet and bend down together, into the occupied zone. Keep to the minimum spacing.
Freely suspended, calculated as flush. Without a ceiling the jet does not attach (Coanda). That is why the RL, freely suspended, is limited to −10 K instead of −12 K (DS 4186 E p. 2).
Too close above an open grid ceiling. A DD-N above an open ceiling sits at least 1 × DN above the grid (DS 1175 E, installation sketch p. 4).

The types in the collection

Ceiling, up to 4.5 m: DD-N · RA-N · RA-N3 · RL · RL-C · OC-Q · OC-R

Ceiling, high rooms, adjustable: RA-V2 · RA-V · OC-V · DD-VG · DD-VL · DD-VK (on request)

Wall: WL

Floor: DB-E · DB-D

All swirl diffusers and radial swirl diffusers in the collection →

Where you’ll find it

Krantz swirl diffusers and radial swirl diffusers in Dutch projects, according to the old Peek website: De Rotterdam, Rotterdam (RA-V2); De Kunsthal, Rotterdam (RA-V2); Willemswerf, Rotterdam (DD-N); Van Lanschot Bankiers, Zeist (RA-N3).

All references →

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