Continuous frost protection return water temperature

Minimum temperature control
Optionally the coil can be equipped with a coil return water temperature sensor to protect against undesired low temperatures. If this sensor is available, a minimum return water temperature 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.

The parameter RWT-01 defines the setpoint shift during un-occupied periods.


 

Note: this minimum return water temperature control is only active when the outside air temperature is lower than the value of parameter OAT-03.

Depending on the calculated setpoint and the P-band, defined by the parameter RWT-04, the control output varies from 0...100% as shown in the next figure. The calculated return water temperature setpoint is available as a display value.

   


The parameter RWT-05 selects if this return water temperature control function is enabled "always" or only during the "plant on" or "plant off" condition.
If the parameter RWT-05 is set to "2" the return water temperature control is only active during unoccupied periods when outside air temperature is below the value of the parameter OAT-03.


Description

Default value

RWT-01: return water temp SP shift un-occupied period

5 K

RWT-02: return water temperature low setpoint

10 °C

RWT-03: return water temperature high setpoint

25 °C

RWT-04: return water temperature P-band

10 K

RWT-05: return water temperature control

0 = always

1 = only plant on

2 = only plant off

2

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