MSAT 102-122-142-162-182-202-242

COIL FAN CONTROLLER
In the MSAT units, as standard the fan speed is controlled according to the temperature, with pressure-based control
available upon request; the latter configuration is supplied in a kit. The operating principle described below is the same
for both type of control.
- FAN CONTROL IN COOLING
The following graph shows operation in cooling mode, Fig. 6.
EXTERNAL FAN IN COOL OPERATION
Speed
Prop. Cooling band F09
Figure 6
Temperature
Pressure
When the compressor is started, the fans are forced on, that is, the fans are not managed directly by the controller but
rather are switched on for a set time at maximum speed, according to the value of a parameter, unless the temperature is
below the CUT-OFF value; in this case, the fans are started at minimum speed for the same period. That being stated,
we will now describe the operation of the controller.
The first parameter to be defined is the CUT-OFF, which corresponds to a special condensing temperature value below
which the fans are off. The CUT-OFF HYSTERESIS is a parameter that defines the field within which the fans switch
from operation at minimum speed to off, and vice-versa. In summary, the fans start operating at minimum speed when
the temperature is equal to the CUT-OFF + CUT-OFF HYSTERESIS, while they stop based on the difference between
the COOLING set point and the CUT-OFF DELTA. When the condensing temperature exceeds the COOLING FAN SET
POINT, the controller starts to control the speed of the fans proportionally to the condensing temperature. In the case of
Clivet units, contrary to the operation described in the graph, the control functions are maintained until the MAX
COOLING FAN SET POINT is reached. For completion, the description of the parameters MAX SILENT SPEED and
COOLING PROPORTIONAL BAND are also described. The first defines a maximum fan speed threshold corresponding
to a certain condensing temperature, below which the speed is controlled, while the PROPORTIONAL BAND defines the
gradient of the straight line corresponding to the speed control function. The CLIVET units are designed to control the
fans up to the maximum speed.
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