page 6
4
MIXIT WITH AIR HANDLING UNITS
The objectives of using an air handling unit (AHU) are multiple:
•
Supplying fresh air to a building zone.
•
Discharging dirty air from a building zone.
•
Pressurizing the building zone.
•
Heating and cooling the fresh air supplied to the zone.
•
Dehumidification and humidification of the fresh air supplied to the zone.
The heating and cooling of the fresh air happens by a combination of heat recovery and use of a heating
coil or a cooling coil. The AHU controller manages the local setpoints, sequencing and safety functions of
the AHU.
When MIXIT is used with AHUs it shall run a temperature control loop for either the discharge air
temperature from the coil or the fluid temperature flowing towards the coil. It is up to the integrator to
choose between these two options as follows:
•
The selected MIXIT application is the
Heating coil
application: MIXIT controls the discharge
air
temperature
leaving the coil.
•
The selected MIXIT application is the
Radiator heating
application: MIXIT controls the
fluid
temperature
flowing towards the coil.
The difference between the two are briefly described below. In either case local setpoints, sequencing and
safety functions can be managed by the AHU controller.
The application selection is done via the Grundfos GO app.
4.1
MIXIT AHU control of discharge air temperature (heating coil application)
Figure 4 shows the simplified cascaded control loops associated with the AHU. The control loop for the air
temperature which MIXIT runs when the heating coil application is selected is highlighted by the green box.
Figure 4: Simplified AHU control loops with MIXIT.
The air temperature needs to be feed to MIXIT via an analogue signal. The air temperature is also used by
the AHU and the signal can be shared as shown in figure 3.
By method 1 the signal is shared via a signal splitter, all signals are analogue. By method 2 the analogue
signal is fed to MIXIT and the AHU controller reads the air t
emperature value from MIXIT’s fieldbus profile.
By method 3 the sensor is connected to the AHU controller which feeds the signal to MIXIT via the field bus.
In the current release of MIXIT there is no datapoint for this in the fieldbus profile it will be available in a
future release.
