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The advantage is that MIXIT does not need connection of additional sensor signals. This way of integrating
is described in section 4.4 together with the setpoint configuration in section 3.
4.3
Integration of MIXIT in AHU control with MIXIT configured for the heating coil
application
Here some basic topics of interfacing MIXIT with AHU control are covered. It is a prerequisite that MIXIT is
configured for heating coil application to follow the below guides.
Notice!
When MIXIT is configured with the heating coil application, it will assume control of the air
temperature leaving the heating coil, and it needs an air temperature sensor connected, e.g. see Figure 5 in
section 4.1.
4.3.1
AHU sequencing with safety functions for heating coil
This section describes the start and control sequence when MIXIT is integrated with the AHU controller.
Figure 7 shows the state diagram of MIXIT with the integrated coil preheat and frost protection functions
enabled. The shown states are as follows:
READY
: If a start signal is not given MIXIT is in the READY state. The pump is stopped, and the valve is
closed.
PREHEAT:
When a start signal is given the PREHEAT state is entered, e.g. see section 4.3.1.2.
TEMPERATURE CONTROL:
When the coil has been preheated the air temperature after the coil is
controlled according to the setpoint. MIXIT signals this at the fieldbus by setting BI,1=1.
FROST:
The frost state is entered if a frost risk at the coil is signaled or it is detected by the integrated frost
protection function. Both conditions have to be false for MIXIT to enter the TEMPERATURE CONTROL state
again, e.g. see section 4.3.1.1.
STOP:
When the start signal is removed MIXIT initializes for next start via the STOP state. After the STOP
state MIXIT always enters READY.
Figure 7: State machine for MIXIT heating coil application.
The data points associated with the state transitions are listed in Table 3.
