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MIXIT may be set into frost protection state via the following methods:
1.
Via external digital input at DI4
2.
Via BACnet/Modbus at BO,4/00101.7
3.
Via internal detection
The options 1 to 3 for setting MIXIT into frost protection state can be used in any combination. They have
equal priority.
4.3.1.1.1
When is a frost risk detected by the build in function?
When the internal frost protection is enabled (this is the default for MIXIT’s heating coil application), a frost
risk is registered if the supply air temperature or the return temperature, or both drops below their
respective threshold values. The configuration of the threshold values needs to be done by Grundfos GO. It
cannot be done by fieldbus, e.g. see Figure 10.
Figure 10: Configuration of frost protection by Grundfos GO.
4.3.1.2
The build in preheat function
The preheat function will warm up the coil until the water return temperature is above a certain threshold.
The threshold can only be set from Grundfos GO, e.g. see Figure 10.
The preheat function makes sure there is a flow in the shunt, such that the return temperature sensor can
be trusted. That is, it exists into the
“
TEMPERATURE CONTROL
”
state shown in Figure 9 when the mixed
water temperature is 85% or less of the water supply temperature, while the return temperature is above
the preheat threshold.
Preheating will be done at every start after MIXIT has been stopped e.g. again see Figure 9.
The preheat function cannot be disabled from the fieldbus, disabling the feature must be done from
Grundfos GO. The default setting i
n MIXIT’s heating coil application is “enabled”.
4.3.1.2.1
Exit of preheat by time out
If the coil could not be preheated inside a predefined time limit MIXIT will switch to TEMPERATURE
CONTROL anyway by one of the two conditions:
