This function does not occur during normal operation in occupied periods. It can happen only during total cool down or un-occupied periods in winter times below the prost protection outdoor temperature.
In this case the minimum mixed water temperature control setpoint is defined by the parameter MWT-01. It protects the heating circuit against freezing, as long as the heating circuit system has not been shut down by the electronic caretaker. This minimum water temperature controller is a proportional controller with a P-band, as defined in the parameter MWT-07.
The internal control signal varies from 0-100% as shown in the next figure:
Fig. 11. Minimum mixed water temperature protection
If the filtered outside air temperature is below the value of parameter OAT-03, the minimum water temperature protection will control the heating valve. As soon as the valve position is greater than 3%, the pump will start. This way the heating circuit frost protection is achieved. Only at low outside air temperatures (below the OAT-03), the minimum water temperature protection will generate a calculated heating demand.
Table 14. Parameter List
Description |
Value Range |
Default Value |
Unit |
|
MWT-01: minimum MWT temperature protection |
5…20 |
10 |
°C |
|
MWT-07: P-band minimum MWT protection |
1…50 |
10 |
K |
|
OAT-03: low limit frost protection |
50…150 |
2 |
°C |