Air principle · displacement

The air comes in low and lets the heat do the work.

In displacement ventilation, cool air leaves a large outlet so slowly that it does not mix. It spreads as a thin layer across the floor and creeps through the room. At every heat source, a person, a machine, it rises and carries heat and contaminants up to the ceiling, where it is extracted.

See it in motion: the airflow of the Q-R →

What the air does

Low, slow, creeping.

At the outlet

Discharge velocity usually 0.2 m/s at most, with little turbulence, from an outlet with a large face. (DS 4069 E p. 2)

Across the floor

Beyond the zone near the outlet, the air flows in a very thin layer, usually less than 200 mm. Most of it glides on to the opposite wall. (DS 4069 E p. 8)

At the heat source

People, lighting and equipment lift the air. Without internal heat sources, displacement does not work. (DS 4069 E p. 2)

With height

The temperature rises gradually towards the ceiling. The lower zone stays virtually clean: that is where you draw your breathing air. (DS 4069 E p. 2–3)

Character

Low turbulence: a turbulence intensity of 25 % at most (DS 4069 E p. 3); TB 69 uses 20 % (p. 3).

When to choose displacement

Many people, clean air.

Auditoria, theatres, lecture halls. Many heat sources close together, and the air enters right next to the audience: from the steps, the seat pedestal or the floor.
Museums and foyers. Calm air, little air movement, outlets along walls or columns.
Industrial halls. Contaminants rise with the heat and are extracted above the working zone. For halls without chillers there are hybrid types that add air movement in hot weather (VA-ZH, VA-LH).

When not: With a high cooling load per m², or if heating is the main task. Heating is only possible with displacement outlets designed for it (DS 4069 E p. 2). Otherwise, look at mixing →.

Design limits: comfort

The rules from DS 4069 and TB 69.

category A to EN ISO 7730

(DS 4069 E p. 4)

Supply air at most 3 K below room air
Air just above the floor at least 21 °C
Difference room – floor at most 2 K

gradient and cooling load

(TB 69 p. 4)

Temperature difference between 0.1 and 1.1 m: A < 2 K · B < 3 K · C < 4 K
Rule of thumb for displacement: at most 45 W/m² (A) and 55 W/m² (B)

air velocity in the occupied zone at 26 °C

(TB 69 table 2)

A 0.18 · B 0.32 · C 0.45 m/s

air volume

(DS 4069 E p. 4)

In offices usually at most 20 m³/(h·m²)

The near zone

Close to the outlet, the air can move faster than is comfortable. At about half a metre to one and a half metres it reaches its highest velocity, then slows again (DS 4069 E p. 2). That zone should stay free of fixed workstations. Krantz specifies it as the distance at which the velocity has dropped to 0.2 m/s (p. 4).

Position	Near zone (indicative)	Source
Floor outlet	approx. 1 m	DS 4069 E p. 7
Outlet at ceiling level or in the corridor wall (≤ 0.25 m/s)	approx. 2 m	DS 4069 E p. 7
Rectangular outlet > 500 mm high, as a continuous band	keep the first 2 m unoccupied	DS 4069 E p. 6

Penetration depth

In the standard case the cool layer reaches the far side of the room (DS 4069 E p. 8).

The supply air must not be warmer than the room, or it will not penetrate far enough (DS 4069 E p. 8).

Step displacement

Air from the step.

In a hall with raked seating, the air comes from the riser of the step, directly behind the seats. It is fed from a pressure plenum below the steps and leaves through a finely perforated face plate. A flow straightener lifts the flow just off the floor. The cool layer rises around the audience to the breathing zone. (DS 4054 E p. 2, p. 4, p. 8)

Q-SL

(DS 4054 E)

Discharge velocity · 0.18 m/s · p. 5
At the feet up to 0.17 m/s; above 0.3 m < 0.10 m/s · p. 4
ΔT supply – room up to −4 K; supply – exhaust up to −12 K; supply 19 °C · p. 5
Temperature gradient up to 2 K/m · p. 4

Q-SR

· DN 80 max. 36 m³/h for one person; DN 100 max. 59 m³/h for two (DS 4054 E p. 4)

Types: Q-SL (linear, continuous band) · Q-SR (round, per seat) · Q-ST (in the seat pedestal) · SD-L (linear step swirl outlet)

Design limits: industry

Halls, from 3 to 30 m.

Factories follow different air velocities, to VDI 3802, depending on activity and clothing. At 26 °C, moderate standing work (2 met) and standard work clothing (0.9 clo), up to 0.41 m/s is allowable; at 28 °C up to 0.45 m/s. Because activity varies per workstation, Krantz recommends adjustable displacement outlets. (TB 69 p. 7)

Type	Position	Height	Max. ΔT	Key point	Source
VA-PV	high above the occupied zone	4–8 m	−6 K cooling; heating +10 K (p. 8)	vertically down, support jet for heating	DS 4061 E p. 2
VA-K	ceiling, very high halls	6–30 m	−5 K / +8 K	coverage radius approx. 3–5 m	DS 4011 E p. 3–4
VA-ZD	approx. 3 m or on the floor	—	±10 K above the occupied zone	supply depth up to approx. 20 m	DS 4059 E p. 11
VA-ZH	approx. 3 m above the floor	—	—	switchable jet nozzles	DS 4203 E p. 2–3
VA-LH	wall or column	3–5 m	—	linear, hybrid	DS 4202 E p. 2–3
VA-RV · VA-RN	floor, along the wall	—	−8 K / +6 K (VA-RV)	cooling reach up to 20 m	DS 4009 E p. 2, p. 5
VA-S	on the supply duct	3–5 m	±8 K	swivelling front	DS 1276 E p. 3
VA-T · VA-TH	below the duct, or in front of wall or column	3–4 m	−3 to −8 K (VA-T)	permanent cooling	DS 4010 E p. 7

Typical mistakes

Where it goes wrong.

A fixed workstation in the near zone. The air is faster than comfortable there. Keep the zone clear, or choose an outlet with a smaller near zone.
Supply too cold. More than 3 K below room temperature in category A means cold feet and too steep a gradient (DS 4069 E p. 4).
Too much cooling load. Above 45 W/m² (A) or 55 W/m² (B) the gradient between feet and head increases (TB 69 p. 4). Combine with a chilled ceiling, or choose mixing.
Warm supply air. Warmer than the room, the air does not penetrate far enough (DS 4069 E p. 8). Heat with a type made for it, such as the VA-PV or VA-K with support jet.
A room without heat sources. Nothing rises, so the principle does not work (DS 4069 E p. 2).
The displacement pattern disturbed by mixing. An additional outlet blowing with high momentum breaks up the cool layer.

The types in the collection

Comfort, floor and wall: Q-R · Q-Z · Q-ZH · Q-W · Q-S (skirting)

Comfort, floor outlets: Q-B · Q-B-DN 215 · Q-BR · BA-V (switches between swirl and displacement)

Comfort, ceiling: Q-DN · Q-DV

Step and seat: Q-SL · Q-SR · Q-ST · SD-L

Industry: VA-PV · VA-K · VA-ZD · VA-ZD-L · VA-ZH · VA-LH · VA-RV · VA-RN · VA-S · VA-T · VA-TH

Façade: IG-Q-SB (induction unit for displacement)

All displacement outlets →

Where you’ll find it

Krantz displacement outlets in Dutch projects, according to the old Peek website: Rijksmuseum, Amsterdam (VA-PV and Q-R); Amphion Theater, Doetinchem (Q-SL); TivoliVredenburg, Utrecht (Q-SR); Heineken, ‘s-Hertogenbosch (VA-PV); Lakhal 14, Schiphol (VA-K).

All references →

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