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, the return water temperature setpoint will be defined as follows:


input RetSetpointSelect

input PlantMode

return temperature setpoint

1

doesn't care

RetTmpSpUnOcc, no valve control

2

RetTmpSpUnOcc

3

RetTmpSpOcc

4

0, 3, 11, 21, 23

RetTmpSpUnOcc, no valve control

1, 2, 20, 30

RetTmpSpUnOcc

4, 5, 6, 22

RetTmpSpOcc


The return water setpoint will always be ramped up and down with the change rate as defined in parameter RWT-05: return water temperature setpoint ramp.


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.

   

Maximum temperature control
This function is required in case of district heating applications.
The coil return water temperature is also limited by a maximum setpoint, as defined by the parameter RWT-04, in order to override the heating valve output to close if the return water temperature becomes too high.


Description

Default value

RWT-03: return water temperature maximum setpoint

85 °C

RWT-04: return water temperature P-band

10 K

RWT-05: return water temperature setpoint ramp

10 K/min

OAT-03: low limit frost protection

6 °C