6.3
Return air temperature limit
The temperature range within which the return air temperature may vary is determined by
the parameters
Return air temperature minimum limit and Return air temperature maximum
limit. If the return air temperature moves towards these limits, the set point is corrected (for
the cascade control, the set point of the exhaust air or room temperature). In the range
Re-
turn air temperature minimum limit, the set point is directly raised by the amount x multiplied
by the
Return air temperature limit factor for every amount x that the return air temperature
falls below. In the range
Return air temperature maximum limit, the set point is directly low-
ered by the amount x multiplied by the
Return air temperature limit factor for every amount x
that the return air temperature exceeds.
Return air temperature falls below limit:
4
x =
Return air temperature minimum limit – Actual return air temperature
4
Supply air temperature set point
calculated
=
Supply air temperature set point + x · Return air temperature limit factor
Return air temperature exceeds limit:
4
x =
Actual return air temperature – Return air temperature maximum limit
4
Supply air temperature set point
calculated
=
Supply air temperature set point – x · Return air temperature limit factor
The supply air temperature limit function has priority.
Functions
WE
Configuration
Sensor F4,
Return air temperature, heating coil
Fb4 = ON
Parameters
WE
Range of values
Return air temperature minimum limit
20 °C
0 °C up to return air temperature maximum limit
Return air temperature maximum limit
70 °C
Return air temperature minimum limit up to 100 °C
Return air temperature limit factor
1
0 to 10
6.4
Variable return air temperature maximum limit
If an outdoor temperature sensor exists, it is possible to vary return air temperature limit. The
following parameters apply for the upper variable limit of the return air temperature:
Return
air temperature maximum limit coordinate 1, Outdoor temperature coordinate 1, Return air
temperature maximum limit coordinate 2, Outdoor temperature coordinate 2.
The gray shaded area in Fig. indicates the permissible return air temperatures.
54
EB 5477 EN
Control functions