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Figure 5: Ways of sharing the air temperature signal with MIXIT.
Integrating MIXIT where it controls the air temperature has the following benefits for heating coil control:
•
MIXIT has a build in algorithm that can detect a frost risk at the coil and protect against coil
damage.
•
MIXIT can run a coil preheat routine when the AHU is started op.
This way of integrating is described in section 4.3 together with the setpoint configuration in section 3.
4.2
MIXIT AHU control of hot water temperature (radiator heating application)
Figure 6 shows an alternative way of cascading the control loops when MIXIT is integrated with the AHU. In
that figure, the AHU controller gives the setpoint for the water temperature that is supplied to the coil.
MIXIT controls therefore the water temperature (T
F
) out of the mixing loop according to the setpoint. The
AHU controller is responsible for setting the appropriate water temperature setpoint, such that the air
temperature leaving the coil is at its appropriate setpoint for T
A
.
Figure 6: Alternative AHU control loops with MIXIT.
The drawbacks of this way of integration are, since MIXIT does not have access to the air temperature at
the coil:
•
AHU controller needs to handle frost protection of the coil via the water temperature setpoint for
MIXIT.
•
AHU controller needs to control coil preheat via the water temperature setpoint for MIXIT.
m et hod 2
m et hod 3
( in fut ure MI XI T release)
m et hod 1
an
al
og
ue
MI XI T
AHU
cont roller
Signal
split t er
Air t em p
sensor
an
alo
gu
e
field bus
Air t em p
sensor
MI XI T
AHU
cont roller
field bus
MI XI T
Air t em p
sensor
AHU
cont roller
