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Variable air volume controllers
Room pressure ratio
In a master / slave connection, any changes in the air
system of the master (supply pressure too low, e.g. due to
a pressure control fault) are detected and reported to the
slave. This guarantees an equal percentage ratio of supply
air to exhaust air.
In a master / slave configuration, only one controller can
act as master. However, one master controller can control
several parallel slave controllers.
When are master / slave connections used?
y
y
In systems with air volume controllers in the supply
and exhaust air that are required to work sequentially
y
y
When an equal percentage ratio of supply air to ex-
haust air is specified.
Operating volumetric flow settings
The max- and min values used for the required volu-
metric flow are set on the master and transferred to the
slave by means of a reference signal.
CAV application
In constant air volume applications, operating mode con-
trol (CLOSED /
min etc.) is only set on the master controller.
Slave setting if the room pressure ratio is balanced
The min setting on the slave is always 0%. If the room
pressure ratio is 1:1 and all controllers are the same size,
the slave controller is set to max 100% / min 0%.
Slave setting if the room pressure ratio is unbalanced
The min setting on the slave is always 0%.
Setting with % scale on the ZTH-GEN hand-operated
device
The ratio of slave volume to master volume is set as fol-
lows with the max value on the slave controller:
max S% =
max S •
nom M
•100
max M •
nom S
max S% = max value that must be set on the controller in %
nom M = Nominal volume of the master unit in m 3 /h
max M = Maximum volume of the master unit in m 3 /h
nom S = Nominal volume of the slave unit in m 3 /h
max S = Maximum volume of the slave unit in m 3 /h
Example
Required:
Positive pressure in the room with 20% excess air
– Supply air unit:
nom 1600 m 3 /h / max 1500 m 3 /h
– Exhaust air unit:
nom 2400 m 3 /h / max 1200 m 3 /h
Find: max setting of the slave controller
Setting with PC-Tool / ZTH-GEN
These two setting tools can be used to enter the volumetric flow ratio
directly in m 3 / h, ll/s or cfm, i.e. there is no need to calculate the setting
ratio.
53% =
1200 • 1600
•100
1500 • 2400
Determination of the master controller
If both units have:
y
y
Non-identical
nom
settings, the controller with the
lower
nom
.
y
y
Identical
nom
settings, the controller with the higher
air olume setting acts as master
y
y
Positive pressure in the room
Master: Supply air unit
Slave: Exhaust air unit
y
y
Negative pressure in the room
Master: Exhaust air unit Slave: Supply air unit
Principle:
1. A reference signal, e.g. from a room temperature con-
troller, is connected to the master input.
min
and
max
are set on the master controller.
2. The volumetric flow actual value signal from the
master acts as a reference signal for the slave control-
ler. The master is installed on the supply or exhaust air
side, depending on the application. See “Determination
of the master controller“.
For connection diagram, see page 39-42
0
100
20
40
60
80
[V]
nom
10
0
2
4
6
8
max
max
min
Reference signal Y
Example with
mode: 0 … 10 V
The ratio is set with the max
parameter on the slave
Volumetric flow
[% nom ]
The slave min setting «0%» forms the pivot and intersection point
Equal percentage
ratio
Slave
Master
VAV-Compact
Functions
T
M
S
1
2
SUPPLY
EXHAUST
Room
Master / slave connection
