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