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 |