7. Economizer
Page 25
PRODIGYT M2 UNIT CONTROLLER
7. Economizer
7.1. General
The economizer, when configured, controls
S damper position, which determines how much outdoor air is used to meet free cooling or indoor air quality (IAQ) require-
ments, and
S the optional power exhaust fans.
On a cooling demand, outdoor air is used for free cooling instead of first−stage compressor(s) when outdoor air is suitable
(OAS).
7.2. Outdoor Air Suitable (OAS) LED
A yellow LED which is labeled OAS provides economizer status. A steady yellow LED indicates that outdoor air is suitable for
free cooling. A flashing yellow OAS light indicates the IAQ sensor requires outdoor air. (A flashing yellow LED can also mean
that the economizer dampers are open to bring in fresh air while a compressor is on.) If the economizer is already operating,
a flashing yellow OAS light indicates the IAQ sensor requires more outdoor air than is suitable for free cooling (see figure 8).
STEADY YELLOW OUTDOOR
AIR SUITABLE" LED INDICATES
OUTDOOR AIR CAN BE USED
FOR COOLING
ECON DIP SWITCH
0−100% MINIMUM
POSITION
POTENTIOMETER
M2 UNIT CONTROLLER
Figure 8. Economizer controls
7.3. DIP Switch Settings
The DIP switch setting determines the mode used to enable free cooling. The DIP switch also has a mode to set the damper
minimum position and test damper operation. DIP switch is factory−set when the economizer is factory−configured.
7.4. Free Cooling Discharge Air Setpoint
When outdoor air conditions are suitable and economizer is set to provide free cooling, dampers will modulate to achieve a
discharge air temperature of 55°F (13°C) default. This setpoint is adjustable between 45° and 65°F.
The setpoint can also be automatically increased when outdoor or return air temperatures drop. See Outdoor Air Reset and
Return Air Reset in the Discharge Air Control section. The unit does not have to be operating in discharge air cooling mode to
adjust the setpoint, or to use setpoint reset.
The operating profile of the economizer damper, during free cooling when any compressors are on, can be selected as
follows:
S damper opens to its maximum position when any compressors start.
S damper continues to modulate while compressors are on, but the effect of mechanical cooling will force the damper
closed to its minimum position.
S damper modulates to its maximum position where it remains for at least 3 minutes. If the damper has been continuously
in this position for at least three minutes, then a second stage cooling demand will be allowed to turn on the first stage
of mechanical cooling. While the mechanical cooling is on, the damper is held to its maximum position, and does not
modulate until the second stage demand is satisfied.
7.5. Free Cooling Compressor Lockout Setpoint
When the outdoor air temperature falls below the free−cooling setpoint, and outdoor air is suitable, then mechanical cooling
is kept off, or is turned off if it is on.
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