General technical information: fans

An external rotor motor is essentially constructed like a normal non-synchronous motor, with one difference: the stator and the rotor have
swapped places. The stator with its windings is at the centre of the
motor, while the rotor is located in the casing itself. The motor shaft
(connected to the rotor) turns on sealed ball bearings inside the stator,
and the impeller or fan blades are fitted to the rotor casing. With this
design, the motor and fan form a compact unit at the centre of the air
stream.
Because the external rotor motor's unique construction allows it to be
cooled by the transported air, the motor speed can be controlled by
voltage regulation.

Casing
Most of the fans have an outer casing made
of hot-rolled galvanised sheet steel complying with EN 10 142/10 147. The sheet steel
has a layer of 20 m zinc which provides
excellent protection against corrosion. The
galvanised sheet-metal parts are either spotwelded, screwed or riveted together.
Fans with powder-coated surfaces are
well protected against corrosion. The powder
coating is at least 40 m thick and produces
a hard and impact-resistant surface. To avoid
environmental pollution, no solvents are
used at the Systemair powder-coating plant.

Insulation
The material used in our insulated fans is
water-repellent, non-capillary mineral wool
whose stability is unaffected by steam and
moisture. The insulation is classified as noncombustible material which tolerates 200C.

Motors and impellers

The direction of rotation for three-phase fans
is indicated by an arrow on the motor housing.
Fans with forward-curved impellers are manufactured from galvanised sheet steel.
Backward-curved impellers have polyamid
or galvanised steel plate blades. These blades
are mounted on a galvanised steel plate. The
impellers are press-fitted directly onto the
rotor of the external rotor motor. The motor
(complete with impeller) is balanced dynamically in two planes in accordance with DIN
ISO 1940.
Bearings
The motor's ball bearings are completely
maintenance-free and can be used in any
installation position at the maximum indicated temperature for transported air. At a 40C
ambient temperature for transported air, the
life expectancy of the bearings is at least
40.000 hours (L10). NB! Low ambient temperature is not a problem for the motor ball
bearings if the fan is operating. The reason
is the 60- to 90 K temperature increase inside
the motor during operation.
Motor protection
Most fans have an integral thermal protection
relay which provides the motors with better
protection against overheating than an overcurrent protection relay. This is especially

important if the fan is speed-controlled by

means of voltage reduction, as it is then
impossible to stipulate the precise overcurrent.
The thermal contacts are fitted in the motor
winding. It will open and disconnect the power
supply to the fan when the critical temperature is reached. This is 130C for motors with
insulation class B and 155C for motors with
insulation class F.
Integral thermal contact
Fans with integral thermal contacts are reset
either automatically or manually by switching
off the current and then wait for up to an hour
before the fan can be started again.
External leads from thermal contact
Fans with external leads from the thermal
contact are supplied with two leads connected to the integral thermal contact (marked TK
in wiring diagrams). These leads must always
be connected to a motor-protection relay. The
S-ET 10 is suitable for single-phase fans (or
the AWE-SK if the current is below 0.45 A)
and the STDT-16 is suitable for three-phase
fans. If the thermal contact has opened, the
protection relay must be reset manually.
Thermal contacts that can be reset electrically
If a fan is fitted with a thermal contact that
can be reset electrically, one must first switch
off the current and then wait for up to an hour
before the fan can be started again. KVKF
and small KD fans are among those models
which require electrical resetting.

Rating
Rated voltage/ Frequency
Maximum permitted voltage variation: +6%, 10% in accordance with DIN IEC 38, plus
maximum permitted frequency.
Power rating
Maximum power used by the fan from the
mains supply.
Rated current
Rated current means the maximum current
used by the fan from the mains supply at
nominal mains voltage. When the fan speed
is controlled by lowering the voltage, the current in the motor may exceed the specified
rated current when the voltage is low. (The
recommended speed controllers are

designed with this in mind.) The increased

current in the motor requires a reduction of
the maximum permitted temperature for
transported air. In the technical tables, the
highest permitted temperature for transported air is shown for both the rated current
and for speed control.
Airflow
The air flow is shown for free-blowing conditions (at zero back pressure). Air flow is
measured in accordance with DIN 24 163
and BSA BS 848. Assumed air density is 1.2
kg/m3 at 20C.
Pressure
The static pressure is shown in the fan diagrams as ps (Pa).
R.p.m.
The tables show the fan's nominal r.p.m. at
the rated current.
Capacitor
A capacitor is connected to the single-phase
motors. The relevant capacitance is shown in
the table for each fan.

Sound pressure and sound

power level
The sound pressure level emitted by duct
fans to the surroundings is measured while
operating at optimal efficiency in a 20 m2
equivalent room absorption area (Sabine) at
a distance of 3 m.
The sound pressure level emitted by roof
fans to the surroundings is measured while
operating at optimal efficiency in a free field
and at a distance of 4/10 m.

Room volume
Room's equiv.
absorption area
Distance from fan (r)
Direction factor (Q)

Duct fan Roof fan

Free field
80 m3
20 m2
3m
1

Difference between -7 dB
sound power (LW) and
sound pressure (Lp)

4/10 m
1
23/-31 dB

The relationship between the sound pressure level and sound power level is
described in the Theory Section on page 509.

General technical information: fans

Adjusted sound values
In this catalogue, all the sound values for
fans (both sound power levels and sound
pressure levels) have been adjusted to the
ear's sensitivity with an A filter.
The sound power levels shown in the diagram are measured at the fan's inlet. Octave
band apportioning of the sound pressure
level is made at the fan's maximum operating efficiency. The tables show the inlet, outlet and ambient sound.

Speed control
Choosing a speed control method
Both economical and technical aspects should
be taken into consideration when selecting
speed control. When assessing the most
economical option, both the investment cost
and the operating cost should be included in
the calculations. The most important technical aspects that need to be considered are
noise and life-expectancy.
Most of the electrical means for varying a
motor's speed cause some degree of noise
in the motor, with the exception of transformercontrolled speed. Power dissipation increases when running at lower speeds. This dissipation is transformed into heat in the motor.
If the power dissipation is substantial, the operating temperature for the bearings will alter
significantly, which will reduce their lifeexpectancy.
Suitable operating conditions and characteristics of the different speed control methods:
Transformers
No increased motor noise when the speed is
regulated. Life-expectancy of the motor bearings can be shortened when operating at low
voltages for long periods (voltage steps 1 and
2). Suitable range for speed control: steps 1-5.
Several fans can be run via the same transformer without special procedures.
The five curves in the fan diagram show
the different voltage outputs from our transformers.
Step (curve) 1
Voltage, 1~
80
Voltage, 3~
95

2
105
145

3
4
130 160
190 240

5
230
400

Single-phase stepless speed control

Can cause noise problems when reducing
speed. Should be avoided in noise-sensitive
installations. The life-expectancy of the motor
bearings will be reduced by operating at lower
voltages. Suitable range of adjustment: 60100% of the rated voltage. Using the same
speed control to run several fans increases
the levels of noise and electromagnetic interference. Shielded motor cables are recommended for installations with several fans
connected to one speed control unit.
Three-phase speed control
There are normally no noise problems associated with speed-controlled operation. The
life-expectancy of the motor bearings will be
somewhat reduced by operating at lower
voltages. Suitable range for speed control:
40-100% of rated voltage. Suitable when
using one speed-control unit for several fans.
In order to minimise noise and electromagnetic interference, we recommend sound fil-

10

ters and also the use of shielded motor

cables when several fans are connected to
one speed-control unit.

Explosion-proof fans
The owner of the property and the installation
engineer are responsible for ensuring that all
equipment that is installed in explosive areas
is approved by a recognised testing laboratory and installed correctly. Fans must be
installed and protected so that no foreign
object can come into contact with the impeller
or cause hazardous sparking. Both the motorprotection relay and the transformer must be
positioned outside the risk area.
EX series
These fans are fitted with specially-made EX
motors. Single-phase fans use a special EXapproved motor capacitor encased in sand
which complies with the requirements for
Fire Class T5.
The fans casings are cast in silumin alloy,
and the impeller is made of aluminium. The
certificate of compliance refers to explosionproof versions in accordance with EN 50014,
EN 50017, EN 50019, EN 1127-1 and
EN13463-1. Improved safety versions comply with EEx e II T3.
This series must always be connected to
an over-current relay which protects the motor
against overheating or short-circuiting (for
instance with a seized rotor). The motor protection must break the circuit within 15 seconds of a short circuit. The current must be
disconnected definitively. This means that the
motor-protection relay must require manual
resetting. Fans in the EX series are not
speed-controllable.
The DKEX and KTEX series
These fans are supplied as 400 V threephase models. Permissible ambient temperature range: from -20C to +40C. The fan
casing and impeller are manufactured in galvanised steel plate and the inlet cone is made
of copper. The certificate of compliance refers
to explosion-proof versions in accordance
with EN 50014, EN 50019, EN 1127-1 and
EN13463-1. Improved safety versions comply with EEx e II T3.
The fans are fitted with specially-made
external rotor motors which allow their speeds
to be adjusted from 100% to 15% by lowering the voltage. These motors must be connected to the U-EK230E thermistor motor
protection unit.
Step (curve)
Voltage, 3~

1
90

2
3
140 180

4
5
230 400

The fan motors have six series-connected

thermistors (two per phase winding) whose
resistance is determined by the motor temperature. When the motor temperature
exceeds the permitted limit, the resistance
rises sharply and the connected motor protector is triggered to break the circuit.

DVEX series
These fans can be speed-controlled from
100% to 15% by lowering the voltage. These
motors must be connected to the U-EK230E
thermistor motor protection unit.
The fan motors have six series-connected
thermistors (two per phase winding) whose
resistance is determined by the motor temperature. When the motor temperature
exceeds the permitted limit, the resistance
rises sharply and the connected motor protector is triggered to break the circuit.
DVEX fans are supplied as 400 V threephase models. Permissible ambient temperature range: from -20C to +40C. The casing is manufactured in galvanised steel plate
and the impeller is made of aluminium. The
inlet cone is made of copper. The certificate
of compliance refers to explosion-proof versions in accordance with EN 50014, EN
50019, EN1127-1 and EN 13463-1. Improved
safety versions comply with EEx e II T3.

Installation
All fans can be installed in any position, but
roof fans should be installed horizontally.
Smaller roof fans can be installed on the
roof pitch. To avoid the transfer of vibrations
to the duct system, we recommend that fans
are installed with mounting clips or flexible
sleeve couplings. All fans are designed for
continuous operation.
Fitting a straight duct or silencer onto the
inlet and outlet of the fan will help to prevent
pressure-drop and system efficiency losses
caused by turbulent air flow. The straight
section must have no filter or similar, and its
length must be at least 1 x the duct diamater
on the fan's inlet side and at least 3 x the
duct diameter on the fan's outlet side. (See
figure 1.)
Figure 1. Correctly installed duct fan.

For a rectangular duct, the duct diameter is

calculated as:
D = duct diameter
H = duct height
B = duct widht
Guarantee
The guarantee period is specified in the relevant terms and conditions for delivery. The
guarantee is only valid when the thermal
contact motor protector and transformer are
correctly installed.

General technical information: fans

Electrical connection
Fan type
AR/AW
AR/AW
AR/AW
AR/AW
AR/AW
AR/AW
AR/AW

Diagram

200E2-K to 450E4-K . . . . . . . . . . . . . . . . . . . . . . . . . .5
315D4-2K to 450D4-K . . . . . . . . . . . . . . . . . . . . . . . .16
630E6, 710E6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
450E4 to 560E4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
450D4 to 710D4 . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
630D6 to 1000D6 . . . . . . . . . . . . . . . . . . . . . . . . . . .18
1000D8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

Fan type

Diagram

KBR 315DV, 355DV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

KBR 315DZ, 355DZ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
KBR 355DV/K, 355DZ/K . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
KBR 355E4/K, 355E4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
KBT 160DV to 280DV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
KBT 160E4 to 250E4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

AW 355D4EX, 420D4EX . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

AW 550D6EX to 650D6EX . . . . . . . . . . . . . . . . . . . . . . . . . .19

KD 200L to 355S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
KD single phase (other models) . . . . . . . . . . . . . . . . . . . . . . .6
KD three phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

CE (other models) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
CE 200 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

KDRD 50 to 70 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
KDRE 45 to 65 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

CKS single phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

CKS three phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

KE (other models) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
KE 40-20 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

CT (other models) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
CT 200 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

KT (other models) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
KT 40-20 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

DKEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

KTEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

DVC-S
DVC-S
DVC-P
DVC-P
DVC-S
DVC-S
DVC-P

KVK 125-400 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
KVK 500 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

225 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
315-400 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
225-400 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
450K . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
450K . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
450-630 3~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
450-630 3~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25

KVKE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
KVKF 125-250L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
KVKF 315M/L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
KVKF 355-400 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

DVEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
DVN/DVNI
DVN/DVNI
DVN/DVNI
DVN/DVNI
DVN/DVNI

355DV to 630DS . . . . . . . . . . . . . . . . . . . . . . . . .17

355E4, 400E4 . . . . . . . . . . . . . . . . . . . . . . . . . . .21
630D4 to 900D8 . . . . . . . . . . . . . . . . . . . . . . . . . .17
710D6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
800D6-900D6 . . . . . . . . . . . . . . . . . . . . . . . . . . .13b

DVS/DHS/DVSI
DVS/DHS/DVSI
DVS/DHS/DVSI
DVS/DHS/DVSI
DVS/DHS/DVSI
DVS/DHS/DVSI
DVS/DHS/DVSI
DVS/DHS/DVSI
DVS/DHS/DVSI
DVV
DVV
DVV
DVV
DVV
DVV
DVV
DVV
DVV
DVV
DVV

190EZ, 225EZ, EV . . . . . . . . . . . . . . . . . . . .20

310ES, 311ES . . . . . . . . . . . . . . . . . . . . . . .20
310EV, 311EV . . . . . . . . . . . . . . . . . . . . . . .20
355DV, 450DV . . . . . . . . . . . . . . . . . . . . . . .16
355E4, 400E4 . . . . . . . . . . . . . . . . . . . . . . . .5
400DS to 710DS . . . . . . . . . . . . . . . . . . . . .18
400DV to 560DV . . . . . . . . . . . . . . . . . . . . .18
400E6 to 500E6 . . . . . . . . . . . . . . . . . . . . . . .6
450E4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

1000 D4-8-P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

1000D4-6-P, D6-8, D8-12 . . . . . . . . . . . . . . . . . . . . . . .15
1000D6, D8, D4-P, D6-P . . . . . . . . . . . . . . . . . . . . . . . .13
400D4 to 630D4, 400D6 to 630D6 . . . . . . . . . . . . . . . .13
400D4-6 to 560D4-6 . . . . . . . . . . . . . . . . . . . . . . . . . . .15
450D4-8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
630D4-6-K, D6-8-K, D4-6, D6-8 . . . . . . . . . . . . . . . . . .15
630D4-K, 630D4-K . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
800D4-6-K, D4-6-P, D6-8 . . . . . . . . . . . . . . . . . . . . . . . .15
800D4-K, D4-M, D4-P, D6-K, D8-K, D6, D8 . . . . . . . . .13
800D6-12-K . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

MUB
MUB
MUB
MUB
MUB
MUB
MUB
MUB
MUB
MUB
MUB
MUB
MUB
MUB
MUB
MUB
MUB
MUB

025
025
042
042
042
042
042
042
042
062
062
062
062
100
100
025
042
042

355DV-A2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
355E4-A2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
400E4-A2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
450DS-A2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
400DV-A2, 499DV-A2 . . . . . . . . . . . . . . . . . . . . . . .18
499E4-A2-500E4-A2 . . . . . . . . . . . . . . . . . . . . . . . .6
400DV-K2 to 500DV-K2 . . . . . . . . . . . . . . . . . . . . .17
500DS-A2 to 630DS-A2 . . . . . . . . . . . . . . . . . . . . .17
500DV-A2, 560DV-A2 . . . . . . . . . . . . . . . . . . . . . . .17
560DV-K2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
630D4-A2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
630D4-K2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
630DV-B2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
630D4-L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
710D6-A2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
315EC-A2 to 400EC-A2 . . . . . . . . . . . . . . . . . . . . .23
450EC-A2-K . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
450EC-A2 to 630EC-A2 . . . . . . . . . . . . . . . . . . . . .26

RS 30-15 to 50-25 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
RS/RSI single phase (other models) . . . . . . . . . . . . . . . . . . . .6
RS/RSI three phase 60-35 to 100-50 . . . . . . . . . . . . . . . . . . .8
RVF 100M . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
RVF 100XL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
RVK 100 E2-A1, 125 E2-A1 . . . . . . . . . . . . . . . . . . . . . . . . . . .1
RVK 125 E2L1 to 315E2-L1 . . . . . . . . . . . . . . . . . . . . . . . . . . .2
RVK 315Y4-A1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

DVV-EX 560D4 to 1000D8 . . . . . . . . . . . . . . . . . . . . . . . . . .13b

DVV-EX 560D4-6 to 800D6-8 . . . . . . . . . . . . . . . . . . . . . . .15b

TFSR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
TFSK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28

EX
EX
EX
EX
EX
EX

TOE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
TOV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

140-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
140-2C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
140-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
140-4C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
180-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
180-4C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

K/KV 100M & 125M . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

K/KV 100XL, K125XL to 315L . . . . . . . . . . . . . . . . . . . . . . . .2
KBR-F 280D2-355DZ-K . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
KBR-F 280D2-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

WVA/WVI
WVA/WVI
WVA/WVI
WVA/WVI
WVA/WVI
WVA/WVI
WVA/WVI
WVA/WVI
WVA/WVI
WVA/WVI

400D4 to 630D4 . . . . . . . . . . . . . . . . . . . . . . . . . .13

400D4-6 to 630D4-6 . . . . . . . . . . . . . . . . . . . . . . .15
400D6-8 to 1000D6-8 . . . . . . . . . . . . . . . . . . . . . .15
630D4-6-K . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
630D4-8, 630D6-12, 1000D6-12 . . . . . . . . . . . . . .14
630D4-8-K, 630D6-12-K . . . . . . . . . . . . . . . . . . . .14
630D4-K . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
800D6, 800D6-K, 1000D6 . . . . . . . . . . . . . . . . . . .13
800D6-12, 800D6-12-K . . . . . . . . . . . . . . . . . . . . .14
800D6-8-K . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

11

blue

brown

12

3
7
11

10

230V3~ (D)
(white)

yellow/green

black

brown
blue

yellow/green

(white)

yellow/green

black

yellow/green

black

brown

blue

black

blue

General technical information: fans

8

General technical information: fans

12

14

13a

15a

Low speed connection

Delta connection

Star connection

High speed connection

15b

13b

Low speed connection

Delta connection

Star connection
High speed connection

13

General technical information: fans

19

16

Delta connection

Delta connection

Star connection
Star connection

20

17

High speed
Delta connection
High speed connection

U1 = blue
U2 = black
Z = brown

Star connection
Low speed connection

18

Delta connection

Star connection

14

21

Low speed

General technical information: fans

22

23

Net voltage

Black

Blue

Green-yellow

1-200-277V PE

Net voltage

Black

Blue

Green-yellow

1-200-277V PE

PE

White

NC

White
White
Red
+

Yellow

0-10V -

P1

External signal

10k

Blue

Potentiometer

Tacho

COM

Red

+10V Exit

0-10V Inlet
GND

0-10V External signal

Motor

Alarm

+10V Exit
0-10V Inlet

Yellow
P1

PE

Blue

GND

10k
Potentiometer

Motor

24

Fan, ECmotor

PE
N
L

Alarm relay

1
2
1
2

PE
N
L

EC-motor

Alarm relay
Normally
closed contact

1
2
3
1
2
3

Mains

Mains 1
100-177 VAC
50/60 Hz

Input

Operatione
mode

Pressure control
GND 10

Night 9
GND 8
Day 7
GND 6
0-10V in 5
+10V 4
GND 3
0-10V out 2
Tacho in 1
3
2
1
GND 2
+20V in 1

Fan (EC-motor)
074/084

Red
Blue
Yellow
White 1
White 2
Blue
Black
Green/yellow

+10V
GND
0-10V
NC
COM
L
N
PE

15

General technical information: fans

25

Alarm relay
Normally
closed contact

Fan, ECmotor

Alarm relay

1
2
1
2

Fan, ECmotor

PE
N
L
PE
N
L

Mains

1
2
3
1
2
3

Input

Operatione
mode

Pressure control
GND 10

Fan (EC-motor)

Night 9

GND 8
7
GND 6
0-10V in 5
+10V 4
GND 3
0-10V out 2
Tacho in 1

112/150

Day

3
2
1

26

Kl. 3 / class 3

+
P1
10k

Potentiometer

12

RS A

Interface RS485 for ebmBUS

11

RS B

Interface RS485 for ebmBUS

10

RS A

Interface RS485 for ebmBUS

RS B

Interface RS485 for ebmBUS

GND

GND

0-10V

Control- / Actual value inlet

6 4-20mA

Control- / Actual value inlet

+20V

Supply ext. sensor 50mA

+10V

Supply ext. potentiometer 10mA

0-10V

Control- / Actual value inlet

GND

GND

OUT

Master exit 0-10V max. 3mA

NO

Error signal relay, closer in the case of error

Kl. 2 / class 2 2

Kl. 1 / class 1

COM

Error signal relay, COMMON

NC

Error signal relay, opener in the case of error

L1

Net, L1

L2

Net, L2

L3

Net, L3

PE

Protective conductor

Art.-Nr.: 305332

16

RS B
RS A
RS B
GND
0-10V
4-20mA

KL.3

+20V
+10V
0-10V
GND
OUT

3 NO
2 COM KL.2
1 NC
2 L
1 N
PE

PE

External signal

RS A

GND 2

+20V in 1

L
N

0-10V -

12
11
10
9
8
7
6
5
4
3
2
1

KL.1

General technical information: fans

27

Kl. 3 / class 3

+
0-10V -

External signal

P1
10k

Potentiometer

12

RS A

Interface RS485 for ebmBUS

11

RS B

Interface RS485 for ebmBUS

10

RS A

Interface RS485 for ebmBUS

RS B

Interface RS485 for ebmBUS

GND

GND

0-10V

Control- / Actual value inlet

6 4-20mA

Control- / Actual value inlet

+20V

Supply ext. sensor 50mA

+10V

Supply ext. potentiometer 10mA

0-10V

Control- / Actual value inlet

GND

GND

OUT

Master exit 0-10V max. 3mA

NO

Error signal relay, closer in the case of error

Kl. 2 / class 2 2

COM

Kl. 1 / class 1

NC

Error signal relay, COMMON

Error signal relay, opener in the case of error

Net, L

Net, N

PE

Protective conductor

Art.-Nr.: 305386

28

YellowGreen
( )

(L)
(N)
Black (L)
Blue (N)
Brown

17

Theory
THEORY SECTION
The intention of this Theory Section is to explain the basic principles
of acoustics and ventilation.
The theory section concludes with a description of the parts which
are integral to a ventilation unit or an air-handling unit, i.e. fans,
heaters, heat exchangers and filters.
Explanatory texts and further information are provided in the margin.
Some diagrams and formula also feature in the margins, together with
examples of their application.
Contents
Fans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page
Heat recovery units, heaters and filters . . . . . . . . . . . . . .page
Acoustics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page
Air terminal devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . .page

500
506
509
515

499

Theory
Fans
Blade profiles for radial fans
The arrow indicates the impeller's direction of
rotation.

Fans are used in ventilating units to transport the air from various air intakes
through the duct system to the room which is to be ventilated. Every fan must
overcome the resistance created by having to force the air through ducts, bends
and other ventilation equipment. This resistance causes a fall in pressure, and
the size of this fall is a decisive factor when choosing the dimensions of each
individual fan.
Fans can be divided into a number of main groups determined by the
impeller's shape and its operating principle: radial fans, axial fans, semi-axial
fans and cross-flow fans.
Radial fan
Radial fans are used when a high total pressure is required. The particular
characteristics of a radial fan are essentially determined by the shape of the
impeller and blades.

Backward curved

Figure 24: The air stream through a radial fan with forward-curved blades
Backward-curved blades (B impeller): The air volume which can be delivered
by backward-curved blades varies considerably according to the pressure conditions. The blade form makes it less suitable for contaminated air. This type of
fan is most efficient in a narrow range to the far left of the fan diagram. Up to
80% efficiency is achievable while keeping the fan's sound levels low.
Backward-angled straight blades (P impeller): Fans with this blade shape are
well suited for contaminated air. Up to 70% efficiency can be achieved.
Straight radial blades (R impeller): The blade shape prevents contaminants
from sticking to the impeller even more effectively than with the P impeller. No
more than 55% efficiency can be achieved with this type of fan.
Straight radial

Forward-curved blades (F impeller): The air volume delivered by radial fans

with forward-curved blades is affected very little by changes in air pressure.
The impeller is smaller than the B impeller, for example, and the fan unit consequently requires less space. Compared with the B impeller, this type of fan's
optimal efficiency is further to the right on the diagram. This means that one
can select a fan with smaller dimensions by choosing a radial fan with an F
impeller rather than a B impeller. An efficiency of approximately 60% can be
achieved.
Axial fan
The simplest type of axial fan is a propeller fan. A freely-rotating axial fan of
this type has a very poor efficiency rating, so most axial fans are built into a
cylindrical housing. Efficiency can also be increased by fitting directional vanes
immediately behind the impeller to direct the air more accurately. The efficiency
rating in a cylindrical housing can be 75% without directional vanes and up to
85% with them.

Forward curved

Figure 25. The air flow through an axial fan

500

Theory
Mixed flow fan
Radial impellers produce a static pressure increase because of the centrifugal
force acting in a radial direction. There is no equivalent pressure increase with
axial impellers because the air flow is normally axial. The mixed flow fan is a
mixture between radial and axial fans. The air flows in an axial direction but
then is deflected 45 in the impeller. The radial velocity factor which is gained
by this deflection causes a certain increase in pressure by means of the centrifugal force. Efficiency of up to 80% can be achieved.

Figure 26. The air flow through a mixed flow fan

Cross-flow fan
In a cross-flow fan the air flows straight across the impeller, and both the in
and out flow are in the periphery of the impeller. In spite of its small diameter,
the impeller can supply large volumes of air and is therefore suitable for building into small ventilation units, such as air curtains for example. Efficiency of
up to 65% can be achieved.

Figure 27. The air flow through a cross-flow fan

501

Theory

Theoretical calculation of the system line

Fan curves
The fan diagram indicates the fan's capacity at different pressures. Each pressure corresponds to a certain air flow, which is illustrated by a fan curve.

Sys
tem
line

Pressure

where
P = the fan's total pressure (Pa)
qv = air flow (m3/h or l/s)
k = constant
Example
A certain fan produces an air flow of 5000 m3/h
at a pressure of 250 Pa.

Fa
n

Working point

cu
rv
e

A. How does one produce a system line in the

diagram?

Pressure

Sy
ste
m

c) Do the same thing for 350 Pa and mark

point (3) in the diagram.

Each change of pressure in the ventilation system gives rise to a new system
line. If the pressure increases, the system line will be the same as line B. If the
pressure reduces, the system line will be the same as line C instead. (This only
applies if the rotational speed of the impeller, i.e. the revolution count, remains
constant).

d) Now draw a curve that indicates the system

line.

lin
eC

b) Select an arbitrary pressure reduction, for

example 100 Pa, calculate the air flow and
mark point (2) in the diagram.

System lines
The duct system's pressure requirement for various air flows is represented by
the system line. The fan's working point is indicated by the intersection between
the system line and the fan curve. This shows the air flow which the duct system
will produce.

Sy
ste
m

Enter the same value in the formula above to

obtain a value for the constant k.
k = P/qv2 = 250/50002 = 0.00001

line
B

a) Mark the point on the fan curve (1) where

the pressure is 250 Pa and the air flow is
5000 m3/h.

Flow

Figure 28. Curves in a typical fan diagram

Flow

Figure 29. Changes in pressure give rise to new system lines

If the ventilation system's actual pressure requirement is the same as system

line B, the working point will move from 1 to 2. This will also entail a weaker air
flow. In the same way, the air flow will increase if the system's pressure
requirement corresponds instead to line C.

502

Theory
Pressure

B. What will happen if the pressure in the system increases by 100 Pa, (for example
because of a clogged filter)?

m
ste
Sy

eC
lin

n)
rve tio
cu rota
n)
n
io
e
Fa ster
rv tat
cu r ro
(fa
n
e
Fa low
(s

em
st
Sy

e
lin

a) Calculate the constant for the new system

line: k = 350/50002 = 0,000014
b) Select two other pressure reductions, for
example 150 and 250 Pa, and calculate the
air flow for them.

Flow

Figure 30. Increase or reduction of the fan speed

To obtain the same air flow as calculated, one can in the first case (where the
system line corresponds to B) quite simply increase the fan speed. The working point (4) will then be at the intersection of system line B and the fan curve
for a higher rotational speed. In the same way, the fan speed can be reduced if
the actual system line corresponds to line C.

c) Plot in the two new points (2 and 3) and

draw in the new system line.

Pressure

Flow

Figure 31. Pressure differences at different rotational speeds

The new working point (4) is located at the

intersection between the fan curve and the new
system line.
This diagram also indicates that the pressure increase causes a reduction of the air flow
to approximately 4500 m3/h.

In both cases, there will be a certain difference in pressure from that of the system for which the dimensioning has been calculated, and this is shown as DP1
and DP2 respectively in the figure. This means that if the working point for the
calculated system has been chosen so as to give the maximum degree of efficiency, any such increase or decrease of the fan's rotational speed will reduce
the fan's efficiency.

503

Theory

Definition of the system line

Efficiency and system lines

To facilitate the selection of a fan, one can plot in a number of considered system lines in a fan diagram and then see between which lines a particular type
of fan should operate. If the lines are numbered 0 to 10, the fan will be completely free-blowing (maximum air flow) at line 10 and will be completely choked
(no air flow at all) at line 0. This then means that the fan at system line 4 produces 40% of its free-blowing air flow.

Pressure

where
L = the fan's system line
pd = dynamic pressure (Pa)
pt = total pressure (Pa)

Flow

Figure 32. System lines (0-10) in a fan diagram

Each fan's efficiency remains constant along one and the same system line.
Fans with backward-curved blades frequently have a greater efficiency than fans
with forward-curved blades. But these higher levels of efficiency are only achievable within a limited area where the system line represents a weaker air flow at
a given pressure than is the case with fans with forward-curved blades.
To achieve the same air flow as for a fan with forward-curved blades, while
at the same time maintaining a high level of efficiency, a fan with backwardcurving blades in a larger size would have to be selected.

Efficiency ()
max (backward-curved)
max (forward-curved)

System line

Figure 33. Efficiency values for the same size of radial fan with backwardcurved and forward-curved blades respectively

504

Theory
Fan application
It is assumed in the fan diagram that the fan's connections to the inlet and outlet are designed in a specific way. There must be at least 1 x the duct diameter
on the suction side (inlet) and 3 x the duct diameter on the pressure side (outlet).

Efficiency of a fan

where
Pt = total pressure change (Pa)
q = air flow (m3/s)
P = power (W)
Figure 34. Correctly installed duct fan

If the connections are different from this, there could be a greater pressure
reduction. This extra pressure drop is called the system effect or system dissipation, and can cause the fan to produce a smaller volume of air than indicated in the fan diagram. The following factors must be considered in order to avoid
system dissipation:
At the inlet

The distance to the nearest wall must be more than 0.75 x the inlet's diameter

The inlet duct's cross-section must not be greater than 112% or less than
92% of the fan inlet

The inlet duct's length must be at least 1 x the duct diameter

The inlet duct must not have any obstacles to the air flow (dampers,
branching or similar)

At the outlet

The angle at the reduction of the duct cross-section must be less than 15

The angle at the enlargement of the duct cross-section must be less than 7

A straight length of at least 3 x the duct diameter is required after a duct fan

Avoid 90 bends (use 45)

Bends must be shaped so that they follow the air stream after the fan

Specific Fan Power

There are now stringent requirements to ensure that power consumption in a
building is as efficient as possible so as to minimise energy costs. The Svenska
Inneklimatinstitutet [Swedish Inner Climate Institute] has introduced a special
concept known as the Specific Fan Power (SFPE) as a measurement of a ventilation system's energy efficiency.
The Specific Fan Power for an entire building can be defined as the total
energy efficiency of all the fans in the ventilation system divided by the total air
flow through the building. The lower the value, the more efficient the system is
at transferring the air.
The recommendations for public sector purchasing and similar are that the
maximum SFPE should be 2.0 when maintaining and repairing ventilating units,
and 1.5 for new installations.

Specific Fan Power

The Specific fan power for an entire building

SFPE =

Ptf + Pff
(kW/m3/s)
qf

where
Ptf = total power for air supply fans (kW)
Pff = total power for air exhaust fans (kW)
qf = dimensioned air flow (m3/s)

Theoretical calculation of a fan's power

consumption

where
P = the fan's consumption of electric power
from the network (kW)
pt = the fan's total pressure (Pa)
q = air flow (m3/s)
fan = the fan's efficiency
belt = efficiency of the transmission
motor = efficiency of the fan motor

505

Theory
Heat recovery units
Thermal efficiency

In a ventilating unit, it is often economical to attempt to recover the heat which

is contained in the exhaust air and use it to warm the supply air. There are several
methods for achieving this type of heat recovery.

where
tu = outside air temperature

Plate heat recovery units

The exhaust air and supply air pass on each side of a number of plates or lamellae. The exhaust- and supply air are not in contact with each other which results
in low leakage. There may be some condensation in a plate heat recovery unit,
so they need to be fitted with condensation drains. The drains should have a water
seal to prevent the fans from sending the water back into the unit. Because of this
condensation there is also a serious risk of ice formation, so some type of defrosting system is also needed. Heat recovery can be regulated by means of a bypass
valve which controls the intake of exhaust air. Plate heat recovery units have no
moving parts. High efficiency (50-90%).

tf = exhaust air temp. (no heat recovery)

ti = supply air temp. (after heat recovery)

Used air

Supply air

Exhaust air

Fresh air

Counterflow plate heat recovery units

The air streams (exhaust and supply air) pass
in opposite directions through the entire heat
recovery unit, which results in an efficient
recovery of heat.

Rotary heat recovery units

Heat is transferred by a rotating wheel between exhaust and supply air. This system is open and there is a risk that impurities and odours will be transferred
from the exhaust to the supply air. This can be avoided to some extent by correct designed ventilation system with the right pressure conditions or by positioning the fans in a preventing way. The degree of heat recovery can be regulated by increasing or decreasing the rotational speed. There is little risk of freezing in the heat recovery unit. Rotary heat exchange units contain moving parts.
High efficiency (75-85%).
Battery heat recovery units
Water, or water mixed with glycol, circulates between a water battery in the
exhaust air duct and a water battery in the supply air duct. The liquid in the exhaust
air duct is heated so that it can transfer the heat to the air in the supply air duct.
The liquid circulates in a closed system and there is no risk of transferring impurities from exhaust air to supply air. Heat recovery can be regulated by increasing or decreasing the water flow. Battery heat recovery units have no moving
parts. Low efficiency (45-60%).
Chamber heat exchangers
A chamber is divided into two parts by a damper valve. The exhaust air first
heats one part of the chamber, then the damper valve changes the air stream
so that the supply air is heated by the warmed-up part of the chamber.
Impurities and odours can be transferred from exhaust air to supply air. The
only moving part in a chamber heat exchanger is the damper valve. High efficiency (80-90%).
Heat pipe
This heat recovery unit consists of a closed system of pipes filled with a liquid
that vaporises when heated by the exhaust air. When the supply air passes the
pipes, the vapour condenses back into liquid again. There can be no transfer of
impurities, and the heat recovery unit has no moving parts. Low efficiency (5070%).

506

Theory
Heating batteries
In most cases the outside air is colder than the required temperature for the
supply air, so it is often necessary to warm the air before it enters the building.
The air can be warmed in a heating battery, by using either a hot water, or an
electric heating battery.
Electric-heating battery
An electric-heating battery consists of a number of enclosed metal filaments or
wire spirals. They create an electrical resistance which converts the energy to
heat. The advantages of the electric battery are: it has a small pressure drop, it
is easy to calculate the power and it is inexpensive to install. The disadvantage
is that the metal filaments have a considerable heat inertia so the electric battery has to be fitted with overheating protection.
Water-heating battery
Crossflow water-heating batteries are the most common type of water-heating
batteries in ventilation units. The water flows at right angles and in the opposite
direction to the air stream. The water is conducted from below and flows upwards
through the battery, and this allows any air bubbles to collect at the highest point
where they can be easily drawn off via a ventilating pipe.
Water-heating batteries have to be protected against ice formation to ensure
they do not crack as the result of freezing. The greatest risk of this happening
is actually when the air temperature is immediately below 0C. Most water batteries therefore have a frost guard which stops the intake of fresh air when there
is a risk of freezing. Because still water freezes faster than flowing water, it is
also usual to fit an internal pump which keeps the water flowing through the
battery.
The air velocity through the battery, calculated for the entire front area, should
be dimensioned to 2-5 m/s. The water velocity should not be below 0.2 m/s, as
this could cause difficulties with venting. Nor should the water velocity be higher
than 1.5 m/s in copper pipes or 3 m/s in steel pipes, as this could lead to erosion
of the metal pipes.
Filters
There are two reasons for using filters in an air-handling unit: to prevent impurities in the outside air from entering the building and to protect the unit's components from contamination.
An analysis of the impurities in the air indicates that among other things the
air contains soot particles, smoke, metallic dust, pollen, viruses and bacteria.
The particles vary in size from less than 1 m to whole fibres, leaves and insects.
It is thought that these pollutants are a significant contributing factor in the cause
of many asthmatic and allergic conditions, and it is therefore important for people
to protect themselves against them.
Since as much as 99.99% of all particles in the air are smaller than 1 m, it
is necessary to use filters in a ventilation system that are adequately fine-meshed.
The filter's capacity to trap particles is called its Dust Holding Capacity and filters are often divided into three classes depending on this capacity: coarse filters, fine filters and absolute filters.
Filter classes
Coarse filter
Fine filter
Absolute filter

Water-heating battery
The power input (kW) to a water-heating battery
in a ventilating unit is:

where
L = the air flow (m3/h)
ti = required supply air temperature (C)
tu = dimensioned outside temperature (C)
= the efficiency of the heat recovery unit

Water battery
The hot water should be conducted in the
opposite direction to the air, otherwise it will
cool too quickly and the water battery's warming of the air will not be as efficient.

Air

Water

Dust Holding Capacity for different filter

classes

EU1 to EU4
EU5 to EU9
EU10 to EU14

The coarse filter essentially only traps particles larger than 5 m, and has virtually no effect at all on particles smaller than 2 m. This means, therefore, that
it does not trap soot particles, which are the most prevalent impurities in the outside air. Fine filters should be fitted in a ventilation unit instead. The best fine
filters work effectively with particles larger than 0.1 m, and therefore trap the
most important impurities in the outside air.

507

Theory
Pressure drop
The pressure drop caused by a completely clean filter is called the start pressure drop, and this is somewhere between 80 and 120 Pa for fine filters. After
impurities have been trapped by the filter, the pressure drop will increase and
the air flow will be reduced. Eventually there will be a pressure drop which makes
the filter no longer usable. For fine filters this will be between 200 and 250 Pa.
It is usual for filters in a unit to be fitted with some kind of filter monitor which
constantly measures the pressure drop caused by the filter. This can give a signal
when a pre-set pressure drop has been reached and it is time to replace the
filter. In any event it is advisable to replace the filter twice a year, irrespective of
whether or not the final pressure drop has been reached, so as to prevent the
dirt in the filter becoming a breeding ground for bacteria.
Suppliers of filters have been debating for a long time as to whether glass fibre
or synthetic fibre provides the best filter material. Some research has been carried out, but without any clear results. It appears, however, that glass fibre filters maintain a better Dust Holding Capacity throughout their working life.
Just as important as the selection of the filter material is the need to ensure
that there is a good seal around the filter to prevent dirt and dust passing around
the edge. The filter housing should be designed so that repeated filter replacements can be made without any space developing between the filter and the
housing. It is also important to protect the filter from moisture as this can alter
the characteristics of the filter fibres and impair its Dust Holding Capacity. Glass
fibre filters are more susceptible to the effects of moisture than synthetic filters.

508

Theory
ACOUSTICS
Basic principles of sound
Before we discuss the connection between the sound power level and the sound
pressure level, we must define certain basic concepts such as sound pressure,
sound power and frequency.
Sound pressure
Sound pressure is the pressure waves with which the sound moves in a medium,
for instance air. The ear interprets these pressure waves as sound. They are
measured in Pascal (Pa).
The weakest sound pressure that the ear can interpret is 0.00002 Pa, which is
the threshold of hearing. The strongest sound pressure which the ear can tolerate without damage is 20 Pa, referred to as the upper threshold of hearing.
The large difference in pressure, as measured in Pa, between the threshold of
hearing and the upper threshold of hearing, makes the figures difficult to handle. So a logarithmic scale is used instead, which is based on the difference
between the actual sound pressure level and the sound pressure at the threshold of hearing. This scale uses the decibel (dB) unit of measurement, where
the threshold of hearing is equal to 0 dB and the upper threshold of hearing is
120 dB.
The sound pressure reduces as the distance from the sound source increases, and is affected by the room's characteristics and the location of the sound
source.
Sound power
Sound power is the energy per time unit (Watt) which the sound source emits.
The sound power is not measured, but it is calculated from the sound pressure.
There is a logarithmic scale for sound power similar to the scale for sound
pressure.
The sound power is not dependent on the position of the sound source or
the room's sound properties, and it is therefore easier to compare between different objects.

Frequency
Frequency is a measurement of the sound source's periodic oscillations.
Frequency is measured as the number of oscillations per second, where one
oscillation per second equals 1 Hertz (Hz). More oscillations per second, i.e. a
higher frequency, produces a higher tone.
Frequencies are often divided into 8 groups, known as octave bands: 63 Hz,
125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz and 8000 Hz.

Calculation of equivalent absorption area Aeqv

where
2

Sound power level and sound pressure level

There is a link between a sound source's sound power level and the sound
pressure level. If a sound source emits a certain sound power level, the following factors will affect the sound pressure level:
The position of the sound source in the room, including the direction factor
(1), the distance from the sound source (2) and the room's sound-absorbing
properties, referred to as the room's equivalent absorption area (3).
1) Direction factor, Q
The direction factor indicates the sound's distribution around the sound source.
A distribution in all directions, spherical, is measured as Q = 1. Distribution
from a diffuser positioned in the middle of a wall is hespherical, measured as
Q = 2.

S = Size of surface (m )
a = Absorption factor, depending
on the material
n = Number of surfaces

Calculation of sound pressure level

Estimate based on figures 1, 2 and 3 together
with table 1.
A normally damped room in a nursing home,
measuring 30 m3, is to be ventilated. According
to the information in the catalogue, the directional supply-air terminal device fitted in the ceiling
has a sound pressure level (LpA) of 33 dB(A).
This applies to a room with a space damping
equivalent to 10 m2 Sabine, or 4 dB(A).
A) What will the sound pressure level be in this
room, 1 m from the diffuser?
The sound pressure level depends on the
room's acoustic properties, so first of all it is
necessary to convert the value in the catalogue
to a sound power level (LWA).

Q
Q
Q
Q

=
=
=
=

1
2
4
8

In centre of room
On wall or ceiling
Between wall or ceiling
In a corner

Fig.3 shows that L (space damping) = LpA - LWA

LWA = LpA + L
LWA = 33 + 4 = 37 dB(A)

Figure 1. The distribution of sound around the sound source

509

Theory
With the following values
r=1
Q = 2 (fig.1)
and information about the room's dimensions,
you can calculate the equivalent absorption area
with the help of figure 2.

2) Distance from sound source, r

Where r indicates the distance from the sound source in metres.
3) The room's equivalent absorption area, Aeqv
A material's ability to absorb sound is indicated as absorption factor a. The
absorption factor can have a value between '0' and '1', where the value '1' corresponds to a fully absorbent surface and the value '0' to a fully reflective surface. The absorption factor depends on the qualities of the material, and tables
are available which indicate the value for different materials.
2

A room's equivalent absorption area is measured in m and is obtained by

adding together all the different surfaces of the room multiplied by their respective absorption factors.
In many instances it can be simpler to use the mean value for sound absorption in different types of rooms, together with an estimate of the equivalent
absorption area (see figure 2 ).

The equivalent absorption area is therefore 4 m2.

Equivalent absorption area (m2)

It is now possible to use figure 3 to establish the

difference between the sound pressure and the
sound power.

3) Equivalent absorption area based on estimates

If values are not available for the absorption factors of all the surfaces, and a
more approximate value of the room's total absorption factor is quite adequate,
an estimate can be calculated in accordance with the diagram below. The diagram is valid for rooms with normal proportions, for example 1:1 or 5:2.
Use the diagram as follows to estimate the equivalent absorption area: calculate the room's volume and read off the equivalent absorption area with the correct mean absorption factor, determined by the type of room, see also table 1.

LpA - LWA = 0
LpA = 0 + LWA
Enter the LWA value which has already been
calculated.
LpA = 0 + 37 = 37 dB(A)

Room volume (m3)

room with high attenuation factor

A) The sound pressure level (LpA) one metre

from the diffuser in this particular nursing
home room is therefore 37 dB(A).

room with damping

normal room
less hard room
hard room

This calculation has to be made for all rooms not

corresponding to the information in the catalogue
which assumes a standard 10 m2 Sabine.
The less damped (harder) the room is, the
higher the actual sound pressure level will be in
comparison with the value indicated in the catalogue.

Figure 2. Estimate of equivalent absorption area.

Type of room
Radio studios, music rooms

Mean absorption factor

0.30 - 0.45

TV studios, department stores,

reading rooms

0.15 - 0.25

Domestic housing, offices, hotel

rooms, conference rooms, theatres

0.10 - 0.15

School halls, nursing homes, small

churches

0.05 - 0.10

Industrial premises, swimming pools,

large churches

0.03 - 0.05

Table 1. Mean absorption factors for different types of rooms

510

Theory
Calculation of sound pressure level
With the help of the factors previously described, it is now possible to calculate
the sound pressure level if the sound power level is known. The sound pressure level can be calculated by means of a formula incorporating these factors,
but this equation can also be reproduced in the form of a diagram.
When the diagram is used for calculating the sound pressure level, you must
start with the distance in metres from the sound source (r), apply the appropriate directional factor (Q), and then read off the difference between the sound
power level and the sound pressure level next to the relevant equivalent
absorption area (Aeqv). This result is then added to the previously calculated

L = LpA-LWA

sound power (see also the example on page 509).

Calculation of sound pressure level

where
LpA = sound pressure level (dB)
LwA= sound power level (dB)
Q = direction factor
r = distance from sound source (m)
Aeqv = equivalent absorption area (m2 Sabine)

The room's equivalent absorption area

Distance from sound source, r

Figure 3. Diagram for estimating the sound pressure level

Near field and reverberation field

Near field is the term used for the area where the sound from the sound
source dominates the sound level. The reverberation field is the area where the
reflected sound is dominant, and it is no longer possible to determine where
the original sound comes from.
The direct sound diminishes as the distance from the sound source increases, while the reflected sound has approximately the same value in all parts of
the room.

Calculation of reverberation time

If a room is not too effectively damped (i.e. with
a mean absorption factor of less than 0.25), the
room's reverberation time can be calculated
with the help of Sabine's formula:

where
T= Reverberation time (s). Time for a 60 dB
reduction of the sound pressure value
V= Room volume (m3)
Aeqv=The room's equivalent absorption area, m2

Figure 4. Direct and reflected sound

The reverberation time indicates the time it takes for the sound level to reduce
by 60 dB from the initial value. This is the echo effect one hears in a quiet
room when a powerful sound source is switched off. If the reverberation time is
measured precisely enough, the equivalent absorption area can be calculated.

511

Theory
Example of addition
There are two sound sources, 40 dB and 38 dB
respectively.

Several sound sources

To establish the total sound level in a room, all the sound sources must be
added together logarithmically. It is, however, often more practicable to use a
diagram to calculate the addition or subtraction of two dB values.

1) What is the value of the total sound level?

Addition
The input value for the diagram is the difference in dB between the two sound
levels which are to be added. The dB value to be added to the highest sound
level can then be read off they scale.

The difference between the sound levels is 2

dB and, according to the diagram, 2 dB must
be added to the highest level.

To add to the higher level, (dB)

1) The total sound level is therefore 42 dB.

Example of subtraction
The total sound level is 34 dB in a room fitted
with both supply and exhaust ventilation systems.
It is known that the supply system produces 32
dB, but the value for the exhaust system is not
known.

Difference between the levels to be added, (dB)

2) What is the sound level produced by the

exhaust system?

Figure 5. Logarithmic addition

Subtraction
The input value for the diagram is the difference in dB between the total sound
level and the known sound source. The y scale then shows the number of dB
that have to be deducted from the total sound level to obtain the value for the
unknown sound source.
To deduct from the total level (dB)a

The difference between the total sound level and

the sound level of the supply system is 2 dB.
The diagram indicates that 4 dB must be deducted from the total level.
2) Therefore the exhaust system produces 30 dB.

Difference between the total level and sound source

Figure 6. Logarithmic subtraction

512

Theory
Adjustment to the ear
Because of the ear's varying sensitivity at different frequencies, the same
sound level in both low and high frequencies can be perceived as two different
sound levels. As a rule, we perceive sounds at higher frequencies more easily
than at lower frequencies.

NR curves

Sound pressure level

A filter
The sensitivity of the ear also varies in response to the sound's strength. A
number of so called weighting filters have been introduced to compensate for
the ear's variable sensitivity across the octave band. A weighting filter A is
used for sound pressure levels below 55 dB. Filter B is used for levels between
55 and 85 dB, and filter C is used for levels above 85 dB.

Attenuation (dB)

Medium frequency (Hz)

Medium frequency for octave band (Hz)

Figure 7. Damping with different filters

The A filter, which is commonly used in connection with ventilation systems,

has a damping effect on each octave band as shown in table 2. The resultant
value is measured in dB(A) units.
Hz
dB

63
-26,2

125
-16.1

250
-8.6

500
-3.2

1k
0

2k
+1.2

4k
+1.2

8k
-1.1

Table 2. Damping with the A filter

There are also other ways of compensating for the ear's sensitivity to different
sound levels, apart from these filters. A diagram with NR curves (Noise Rating)
shows sound pressure and frequency (per octave band). Points on the same
NR curve are perceived as having the same sound levels, meaning that 43 dB
at 4000 Hz is perceived as being as loud as 65 dB at 125 Hz.

513

Theory
Sound attenuation
Sound attenuation is principally achieved in two ways: either by absorption or
by reflection of the sound.
Attenuation by absorption is achieved by internal insulation in ducts, by special silencers or by means of the room's own sound absorption. Attenuation by
reflection is achieved by forking or bending, or when the sound bounces back
from a supply-air device into the duct, which is referred to as end reflection.
The degree of sound attenuation can be calculated by using tables and diagrams presented in the relevant suppliers technical documentation.

514

Theory
Air terminal devices
There are essentially two ways of ventilating a building: ventilation by
displacement and ventilation by diffusion.
Ventilation by diffusion is the preferable method for supplying air in situations
requiring what is known as comfort ventilation. This is based on the principle of
supplying air outside the occupied zone which then circulates the air in the entire
room. The ventilation system must be dimensioned so that the air which circulates in the occupied zone is comfortable enough, in other words the velocity must
not be too high and the temperature must be more or less the same throughout the zone.
Ventilation by displacement is chiefly used to ventilate large industrial premises, as it can remove large volumes of impurities and heat if properly dimensioned. The air is supplied at low velocity directly into the occupied zone. This
method provides excellent air quality, but is less suitable for offices and other
smaller premises because the directional supply-air terminal device takes up a
considerable space and it is often difficult to avoid some amount of draught in
occupied areas.

Ventilation by diffusion
The air is blown in from one or more
air streams outside the occupied
zone.

The theory section which follows will discuss what happens to the air in rooms
ventilated by diffusion, how to calculate air velocity and displacement in the
room, and also how to select and position a directional supply-air terminal
device correctly in the premises.

Ventilation by diffusion
An air stream which is injected into a room will attract, and mix together with,
large volumes of ambient air. As a result, the air stream's volume increases
while at the same time the air velocity is reduced the further into the room it
travels. The mixing of the surrounding air into the air stream is termed 'induction'.

Ventilation by displacement
Air which is somewhat cooler than
the ambient air flows at low velocity
into the occupied zone.

Figure 8. Induction of the surrounding air into the air stream.

The air movements caused by the air stream very soon mix all the air in the
room thoroughly. Impurities in the air are not only attenuated but also evenly
distributed. The temperatures in the different parts of the room are also evened
out.
When dimensioning for ventilation by diffusion, the most important consideration is to ensure that the air velocity in the occupied zone will not be too high,
as this will be experienced as a draught.

Occupied zone
The occupied zone is that part of the
room normally occupied by people.
This is usually defined as being a
space 50 cm from an outer wall with
windows, 20 cm from other walls,
and up to 180 cm above the floor.

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Theory
Air stream theory
= the discharge angle
The discharge angle
According to ASHRAEs Handbook (AHRAE
[The American Society of Heating, Refrigerating
and Air-Conditioning Engineers], 1996) the distribution of an air stream has a constant angle
of 20-24 (22 on average).
The shape of the vent, the geometry of the
room and also the number of vents all have an
effect on the discharge angle. Diffusers and
valves with plates or other details which spread
the air can produce a wider discharge angle,
but even after a relatively short distance from
the valve opening, these air streams have a distribution of between 20 and 24.

The figure below shows an air stream that is formed when air is forced into a
room through an opening in the wall. The result is a free air stream. If it also has
the same temperature as the rest of the room, it is referred to as a free isotherm
stream. To begin with, this section will only deal with streams of this type.

Distribution and shape

The air stream actually consists of several zones with different flow conditions
and air velocities. The area which is of most practical interest is the main section. The centre velocity, the velocity around the centre axis, is in inverse proportion to the distance from the diffuser or valve, i.e. the further away from the
diffuser the slower the air velocity.
The air stream is fully developed in the main section, and the prevailing conditions here are the ones that will principally affect the flow conditions in the
room as a whole.

Main section, with a

cross section (darker)
Calculation of air velocity
For a conical or radial air stream:
Figure 9. The main section of the air stream, the centre
velocity vx and discharge angle.

x = distance from the diffuser or valve (m)

vx = centre velocity at distance x (m/s)
v0 =velocity at the diffuser/valve outlet (m/s)
K = the diffuser coefficient
Aeff = the diffuser/valve's effective outlet area
(m2)
q = air volume through the vent (m3/s)

The shape of the diffuser or valve opening determines the shape of the air stream.
Circular or rectangular openings produce a conic (axial) stream, and this also
applies to very long and narrow openings.
To produce a completely flat air stream, the opening must be more than ten
times as wide as it is high, or nearly as wide as the room so that the walls prevent the stream widening out laterally.
Radial air streams are produced by completely circular openings where the
air can spread in all directions, as is the case with a supply-air diffuser.

For a flat air stream

x = distance from the diffuser/valve (m)

vx = velocity at distance x (m/s)
v0 = velocity at the diffuser/valve outlet (m/s)

Conical

K = the diffuser coefficient

h = the height of the slot (m)
Radial
The velocity at the cross section of the air
stream will be:

Flat

Figure 10. Different kinds of air stream

y = vertical distance from the central axis (m)

x = distance from the diffuser/valve (m)
v = velocity at distance y (m)
vx = centre velocity at distance x (m/s)

516

Theory
Velocity profile
It is possible to calculate mathematically the air velocity in each part of the
stream. To calculate the velocity at a particular distance from the diffuser or
valve, it is necessary to know the air velocity at the diffuser/valve outlet, the
shape of the diffuser/valve and the type of air stream produced by it. In the
same way, it is also possible to see how the velocities vary in every cross section of the stream.
Using these calculations as the starting point, velocity curves for the entire
stream can be drawn up. This enables one to determine the areas which have
the same velocity. These areas are called isovels. By checking that the isovel
corresponding to 0.2 m/s is outside the occupied zone, one can ensure that
the air velocity will not exceed this level in the normally occupied areas.

Theoretical calculation of the diffuser

coefficient

i = impulse factor indicating impulse dissipation

at point where air is blown in (i<1)
e = contraction factor
Cb = turbulence constant (0.2-0.3 depending on
type of diffuser or valve)
Practical calculation of the diffuser coefficient
The measurement values (vx/v0) and (x/ Aeff)
are plotted into the diagram.

Figure 11. The different isovels of an air stream

Using the values obtained from the main section of the air stream, a tangent (angle coefficient) is drawn at an angle of -1 (45).
The diffuser coefficient
The diffuser coefficient is a constant which depends on how the diffuser or valve
is shaped. It can be calculated theoretically by using the following factors: the
impulse dissipation and contraction of the air stream at the point where it is
blown into the room, together with the degree of turbulence created by the diffuser or valve.
In practice, the constant is simply determined by taking measurements on each
type of diffuser or valve. The air velocity is measured at a minimum of eight different distances from the diffuser/valve, with at least 30 cm between each measuring point. These values are then plotted into a logarithmic diagram, which indicates the measurement value for the main section of the air stream, and this in
turn provides a value for the constant.
The diffuser coefficient enables one to calculate air velocities and to predict
an air stream's distribution and path. It must not be confused with the K-factor
which is used for such tasks as entering the correct air volume from a directional
supply-air terminal device or iris damper.

The formula for the velocity profile

shows that
The K factor is described on page 389.
when

vx
v0

A line should now be drawn from the intersection of the angle coefficient and 1 on the y scale
to produce a value for the diffuser coefficient K.

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Theory
The diffuser coefficient when the Coanda effect
is influencing the air stream:

Coanda effect
If a directional supply-air terminal device is fitted close enough to a flat surface,
usually the ceiling, the air stream will cling to the surface. This is due to the fact
that the ambient air will be drawn into the stream, but close to the flat surface,
where no new air can flow from above, an underpressure forms instead, and
this causes the stream to be sucked to the surface. This is known as the Coanda
effect.

The horizontal discharge angle also increases

to 30 when the stream is sucked towards the
ceiling, while the vertical angle remains
unchanged (20-24).

Deflection
The deflection from the ceiling to the central
axis of the air stream (Y) can be calculated
using
Figure 12. The Coanda effect

where
t0 = the temperature difference between the
air stream and the ambient air
x = distance from the diffuser/valve (m)
vx = centre velocity at distance x (m/s)
v0 = velocity at the diffuser/valve outlet (m/s)
K = the diffuser coefficient
Aeff = the diffuser or valve's effective outlet
area (m2)

Point of separation
The point where a conical air stream leaves the
ceiling (xm) will be:

Practical experiments have shown that the distance between the diffuser or
valve's upper edge and the ceiling ('a' in figure12) must not be greater than 30 cm
if there is to be any suction effect.
The Coanda effect can be used to make a cold air stream stick to the ceiling and
travel further into the room before it reaches the occupied zone.
The diffuser coefficient will be somewhat greater in conjunction with the suction effect than for a free air stream. It is also important to know how the diffuser
or valve is mounted when using the diffuser coefficient for different calculations.
Non-isothermal air
The flow picture becomes more complex when the air that is blown in is nonisothermal air, in other words warmer or colder than the ambient air. A thermal
energy, caused by differences in the air's density at different temperatures, will
force a cooler air stream downwards and a warmer air stream upwards.
This means that two different forces affect a cooler stream that is sticking close
to the ceiling: both the Coanda effect which attempts to adhere it to the ceiling
and the thermal energy which attempts to force it towards the floor. At a given
distance from the diffuser or valve's outlet, the thermal energy will dominate and
the air stream will eventually be dragged down from the ceiling.
The stream's deflection and point of separation can be calculated using formulae which are based on the temperature differentials, the type of diffuser or
valve and the size of its outlet, together with air velocities etc.

and for a radial air stream will be

where
t0 = the temperature difference between the
air stream and the ambient air
v0 = velocity at the diffuser/valve outlet (m/s)
K = the diffuser coefficient
Aeff = the diffuser or valve's effective outlet area
(m2)
After the stream has left the ceiling, a new path
can be calculated with the aid of the formula for
deflection (above). The distance x is then calculated as the distance from the point of separation.

518

Figure 13. The air stream's point of separation (Xm) and deflection (Y)

Theory
Important considerations when dimensioning air supply
It is important to select and position the directional supply-air terminal device
correctly. It is also important that the air temperature and velocity are as
required for producing acceptable conditions in the occupied zone.

Correct air velocity in the occupied zone

A specification called 'throw' is indicated for most supply-air equipment in the
manufacturer's product catalogue. 'Throw' is defined as the distance from the
diffuser or valve opening to the point in the air stream where the centre velocity
has been reduced to a particular value, generally 0.2 m/s. A throw of this type
is designated by l0.2 and is measured in metres.

Effective penetration
The most common method for selecting the
correct directional supply-air terminal device is
to consider the throw l0,2. But since the desired
end velocity in the air stream depends on both
the room's geometry and the required air velocity in the occupied zone, this can sometimes be
rather misleading. Therefore the concept of the
air stream's effective penetration has been
introduced instead.
The effective penetration is the distance to
the point where an end velocity is to be calculated. This can be the distance along the centre
of the air stream from the diffuser itself to the
furthest point in the room where the supply air
is required. For wall-mounted diffusers, this
means that the effective penetration is the
same as the room's depth, while for ceiling diffusers the penetration is half the room's depth.
The velocity of the return air stream is
approximately 30% slower than the air stream's
velocity when it meets the wall. If the maximum
air velocity in the occupied zone is to be 0.18
m/s, this means that the air stream must have a
maximum velocity of 0.26 m/s when it meets
the wall.

Figure 14. The 'throw' concept

One of the first considerations when dimensioning an air supply system is usually to avoid velocities in the occupied zone that are too high, but as a rule it is
not the air stream itself that reaches us there.
In the occupied zone we are more likely to be exposed to high velocities in
the return air stream: see the figure below.

Effective penetration calculation

The velocity at the effective penetration depth
of a diffuser can be calculated theoretically by
using the formula for calculating air velocity.

where
vx = velocity at the effective penetration (m/s)
v0 = velocity at the diffuser outlet (m/s)
Return air stream

K = the diffuser coefficient

Aeff = the vent's effective outlet area (m2)
xv = the effective penetration (m)

Figure 15. Return air stream with a wall-mounted diffuser

It has been shown that the velocity of the return air stream is approximately
70% of the velocity it had when it reached the wall. This means that a diffuser
or valve fitted on the rear wall, with an end velocity of 0.2 m/s, will cause an air
velocity of 0.14 m/s in the return air stream. This is within the limits for comfort
ventilation, which is understood to mean that the velocity should not exceed
0.15 m/s in the occupied zone.
The throw for the diffuser or valve described above is the same as the length of
the room, and in this instance is an excellent choice. A suitable throw for wallmounted ventilation is somewhere between 70% and 100% of the room's length.

This method enables one to dimension the ventilation system more precisely than is possible
when only using the throw data, and is therefore frequently used in different diffuser selection programmes.

Throw data for isothermal air

Rear-wall diffuser and wall-mounted diffuser:
0.7 to 1.0 x room depth.
Ceiling diffuser (supply air blown horizontally):
0.5 x room depth
(with rectangular rooms, the distance is calculated to the nearest wall).

519

Theory
The penetration of the air stream
The shape of the room can affect the flow picture. If the cross section of the air
stream is more than 40% of the cross section of the room, all induction of air in
the room will stop. As a result, the air stream will deflect and start to suck in the
induction air itself. In such a situation it does not help to increase the velocity
of the supply air, as the penetration will remain the same while the velocity of
both the air stream and the ambient air will increase.
Other air streams, secondary vortices, will start to appear further into the room
where the main air stream does not reach. However, if the room is less than three
times as long as it is high, it can be assumed that the air stream will reach all
the way in.

Figure 16. Secondary vortices are formed at the furthest point in the room,
where the air stream does not reach.

Avoid obstacles
Unfortunately, it is very common for the air stream to be obstructed by light fittings on a ceiling. If these are too close to the diffuser and hang down too far,
the air stream will deflect and descend into the occupied zone. It is therefore
necessary to know what distance (A in the diagram) is required between an air
supply device and an obstacle for the air stream to remain unimpeded.

Distance to an obstacle (estimate)

The diagram shows the minimum distance to
the obstacle as a function of the obstacle's
height (h in figure 17) and the air stream's temperature at the lowest point.

Height of the obstacle

Figure 17. Minimum distance to an obstacle

Minimum distance to obstacle/throw

520

Theory
Installing several directional supply-air terminal devices
If a single ceiling diffuser is intended to service an entire room, it should be
positioned as close to the centre of the ceiling as possible, and the total surface should not exceed the dimensions indicated in Figure 18 below.

Dimensioning with several ceiling diffusers

A large room has to be divided into several
zones. The maximum dimension for each zone
is 1.5 x the room's length (A), as long as this
does not exceed 3xH (see figure 18).
The appropriate throw is 0.5 x C, where C = the
distance between two diffusers, (see figure 19).
Example
A large room (see figure 19) has the following
dimensions:
H=3m
A=4m
B = 16 m

Figure 18. A small room ventilated by a single ceiling diffuser

If the room is larger than this, it usually has to be divided into several zones,
with each zone ventilated by its own diffuser.

1) How many zones should the room be divided

into?
2) What will be distance be between the diffusers?
1) The maximum size for each zone is 1.5 x A
= 6 m, which means that the room should
be divided into three zones, each 5.33 m
long.
2) If the diffuser is placed in the centre of each
zone, the distance (C) will be 5.33 m.

Figure 19. A large room ventilated by several ceiling diffusers

A room which is ventilated by several wall-mounted diffusers must also be divided

into several zones. The number of zones is determined by the requirement to
ensure sufficient distance between the diffusers to prevent the air streams affecting each other. If two air streams mix together, the result will be one stream with a
longer throw.

Dimensioning with several wall diffusers

The smallest distance between two wall-mounted valves or diffusers (D in figure 20) is 0.2 x l0.2.
The appropriate throw is between 0.7 and 1.0 x
A, where A = the depth of the room.
Example
A room which is 5 m deep is ventilated from the
rear wall by means of diffusers with a throw of 4
m.
1) What distance should there be between two
diffusers?
0.2 x l0.2 = 0.2 x 4 = 0.8 m

Figure 20. A large room ventilated by several wall diffusers

1) There should be 80 cm between two diffusers.

521

Theory
Blowing in warm air
Blowing supply air horizontally from the ceiling works excellently for most rooms,
including those with very high ceilings. If the supply air is above ambient temperature and also used to heat the premises, practical experiments have shown
that this works well in rooms with ceiling heights of no more than 3.5 metres.
This assumes that the maximum temperature difference is 10-15C.

Figure 21. Blowing supply air horizontally from a ceiling diffuser

In very high rooms, however, the supply air has to be jetted vertically if it is also
used for heating. If the temperature difference is no more than 10C, the air
stream should flow down to approximately 1 metre above the floor in order to
produce a satisfactory evenness of temperature in the occupied zone.

Figure 22. Supply air blowing vertically from a ceiling diffuser

522

Theory
Blowing in cold air
When supplying air that is colder than the ambient air, it is particularly important to make use of the Coanda effect to prevent the air stream from falling
down into the occupied zone too early. The ambient air will then be sucked in
and mixed more effectively, and the temperature of the air stream will have a
better chance to increase before it reaches the occupied zone.
If the sub-ambient-temperature air is directed along the ceiling in this way, it
is also important that the air stream velocity is high enough to ensure that
there is sufficient adherence to the ceiling. If the velocity is too low there is
also a risk that the thermal energy will push the air stream down towards the
floor too early.
At a certain distance from the supply-air diffuser, the air stream will in any
case separate from the ceiling and deflect downwards. This deflection occurs
more rapidly in an air stream that is below the ambient temperature, and therefore in such cases the throw will be shorter.

(non-isothermal)

Correction of throw (estimate)

This diagram can be used to obtain an approximate value for the throw of non-isothermal air.

l0.2 (corrected) = k l0.2 (isothermal air)

(isothermal)

Maximum acceptable cooling effect

A rule of thumb for the maximum acceptable
cooling effect (Qmax) is:
Figure 23. The difference between the throws of isothermal and
non-isothermal air streams.
The air stream should have flowed through at least 60% of the room's depth
before separating from the ceiling. The maximum velocity of the air in the occupied zone will thus be almost the same as when the air supply is isothermal.
The method for calculating where the air stream will separate from the ceiling is explained in the paragraph headed 'Non-isothermal air' on page 518.
When the supply air is below ambient temperature, the ambient air in the room
will be cooled to some extent. The acceptable degree of cooling (known as the
maximal cooling effect) depends on the air velocity requirements in the occupied
zone, the distance from the diffuser at which the air stream separates from the
ceiling, and also on the type of diffuser and its location.
In general a greater degree of cooling is accepted from a ceiling diffuser than
a wall-mounted diffuser. This is because the air from a ceiling diffuser spreads
in all directions, and therefore takes less time to mix together with the ambient
air and to even out the temperature.

Supply air blown from rear wall

Qmax = 20-40 W per m2 floor surface at t 8K
Supply air blown from ceiling
Qmax = 60-100 W per m2 floor surface at t 12K

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Theory
Selecting the correct supply-air terminal device
A supply-air terminal device for ventilation by diffusion can be fitted on either
the ceiling or the wall. Diffusers are often equipped with nozzles or perforations
which facilitate the admixture of ambient air in the air stream.
Nozzle diffusers are the most flexible devices because they allow individual
fitting of each nozzle. They are ideal for supplying air that is well below ambient temperature, particularly if they are fitted in the ceiling. The throw pattern
can be altered by turning the nozzles in different directions.
Perforated diffusers have a positive effect where the air stream temperature
is significantly below that of the ambient air. They are not as flexible as nozzle
diffusers, but by shielding off the air supply in different directions it is still possible to change the distribution pattern.
Wall-mounted grilles have a long throw. They have limited possibilities for
altering the distribution pattern, and they are not particularly suitable for the
supply of air that is below ambient air temperature.

The nozzles on the new Sinus series have

been specially designed to provide the fastest
possible mixing of supply air with ambient.

Ceiling

Nozzle
diffuser

Wall

Perforated
diffuser

Short throw

Long throw

Flexible distribution pattern

(x)

Sub ambient temperature air

(x)

Conical air
distributor
(x)

Perforated
diffuser

x
(x)

Table 3. Comparison of the different types of directional supply-air terminal device.

524

Nozzle
diffuser

x
x

Grille

(x)