iWorx® MPU2
505-009, Effective: April 28, 2014
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© 2014 Taco Electronic Solutions, Inc.
During periods when the operational mode is primary off or primary fan only, if the supply air temperature rises above
175
°F, the system fan is started. If the supply air temperature does not drop below 150
°F after 5 minutes, the bypass
damper closes and an alarm is sent to the zone controllers and LCI. The zone controllers react to the alarm by position-
ing their dampers to the maximum position.
During periods when the operational mode is primary cooling, if the supply air temperature does not drop below 100 °F
after 15 minutes, the cooling mode is terminated and the MPU2 enters the primary off operational mode. The primary
off logic then checks for the stuck gas valve condition.
Indoor Air Quality
An indoor air quality input is provided. If an indoor air quality alarm is indicated while the space is occupied, the supply
air fan is energized and the economizer is overridden to supply fresh air to the space. The source of an indoor air qual-
ity signal can be a digital sensor providing an on/off signal or a configurable analog sensor.
Setup of the analog sensor requires the IAQ sensor settings to be populated. A Min, Max, Setpoint, and Offset can be
specified.
When an indoor air condition is sensed by the controller, the economizer is opened to 100%. If the mixed air tempera-
ture drops too low, the economizer modulates in an attempt to maintain the IAQ MAT setpoint while still allowing fresh
air into the system.
The controller has a temperature reset function for IAQ alarm operation. The temperature reset function allows the
space temperature to rise above or drop below the calculated control setpoints by a configurable amount. During IAQ
Alarm operation, if the space temperature rises above or drops below the temperature reset limit, the controller
resumes normal economizer control to maintain a comfort space temperature. Once the space temperature is brought
within the calculated setpoints and an IAQ Alarm condition still exists, the controller resumes the IAQ mode of opera-
tion.
The controller has a configurable alarm delay function. This function allows the controller to attempt to clear the IAQ
condition with the economizer before triggering an alarm. If the IAQ condition is still present after the IAQ Alarm Delay,
the alarm message is sent to the LCI.
Return Air IAQ
The controller can read the status of an IAQ sensor placed in the return air duct. When the IAQ sensor indicates that
contaminants are above a preset limit, the MPU2 energizes the fan. After a preset time delay, the economizer is
enabled to supply fresh air to the zones. All of the zones are made aware of the IAQ alarm condition. Any zone config-
ured to participate in return air IAQ modulates its damper open. Heating and cooling operate as normal.
Local Zone IAQ
The MPU2 can receive the status of local IAQ sensors connected to discrete inputs of each zone controller. When the
local zone IAQ sensor indicates that contaminants are above a preset limit, the MPU2 energizes the fan. After a preset
time delay, the economizer is enabled to supply fresh air to the zones. Only the MPU2 and local zone controller partici-
pates in local zone IAQ. Heating and cooling operate as normal.
Smoke Detection
A smoke detector input is provided. If the smoke detector indicates smoke is present, then all of the stages and the fan
turn off. Once the situation has been corrected, reset the controller to clear this condition.
Mixed Air Low Limit Detection
An input is provided for a mixed air low limit detection device. If a low limit condition is detected, all of the stages and
the fan turns off. The controller returns to normal operation after a reset. After the controller switches from unoccupied
mode to occupied mode, there is a ten minute delay before it reports Mixed air Low Limit alarms. If heating and cooling
are configured as modulated or floating point, the heating valves open to 100%.
