Continuous frost protection with the discharge air temperature
If a coil discharge (coil off) air temperature sensor is available, the minimum setpoint can be calculated. This setpoint is outside air temperature compensated between the values, defined by the parameters OAT-01 and OAT-02, in order to override the valve output to open, as shown in the next figure.
Depending on the P-band (DAT-04), the I-time (DAT-05) and the calculated setpoint of the discharge air temperature, the control signal varies from 0...100%, as shown in the next figure. The calculated discharge air temperature setpoint is a display value.
The parameter DAT-01 selects if this discharge air temperature control function is enabled "always" or only during the "plant on" or "plant off" condition.
If the parameter DAT-01 is set to "2" the discharge air temperature control is only active during unoccupied periods when outside air temperature is below the value of the parameter OAT-03.
If parameter SYS-01 is set to "2" (re-heater), the discharge air temperature control function is disabled.
If the return water temperature- and the discharge air temperature sensors are present, then the temperature control with the highest demand controls the valve.
Description |
Default value |
SYS-01: define heating coil type 0 = heater 1 = pre-heater 2 = re-heater |
0 |
DAT-01: discharge air temperature control 0 = always 1 = only plant on 2 = only plant off |
0 |
DAT-02: discharge air temperature low setpoint |
5 °C |
DAT-03: discharge air temperature high setpoint |
15 °C |
DAT-04: discharge air temperature P-band |
10 K |
DAT-05: discharge air temperature I-time |
0 sec |
OAT-01: outside air temperature minimum limit |
-10 °C |
OAT-02: outside air temperature maximum limit |
10 °C |
OAT-03: low limit frost protection |
6 °C |
DISP-03: calculated discharge air temperature setpoint |