iWorx® MPU2
30
505-009, Effective: June 30, 2015
© 2015 Taco Electronic Solutions, Inc.
MPU2 and VAVD Communications
The MPU2 and its associated VAVD controllers transfer information, depending on the number of VAVD controllers
configured. The MPU2 polls a VAVD controller every 5 seconds to transfer information necessary for control. The fol-
lowing information is transferred from the MPU2 to the VAVD controller:
• Operational Mode: primary cool, primary heat, and primary off
• Occupancy Mode: occupied, unoccupied, and bypass
• Alarm Conditions: IAQ Mode and Heat Failed On
The following information is transferred from the VAVD to the MPU2 controller:
• Zone temperature
• Calculated Heating Setpoint
• Calculated Cooling Setpoint
• IAQ Sensor Status (safe, alarm)
• Local Alarm (VAVD shutdown)
• Occupancy Mode: occupied, unoccupied, and occupied extension)
• Supplemental heat status: on, off
Associating VAVDs
In order for the MPU2 and VAVDs to share information, the controllers need to be associated. To associate the VAVDs
to the MPU2, you first need to select the MPU2 from the LCI's list of controllers. Once the MPU2 has been selected,
depress the
HVAC Setup
button followed by the
Zone Members
button. You will see a list of all VAVDs on the net-
work, with the designation “Included” or “Excluded” showing on each line. To include a VAVD, simply depress the
desired VAVD in the list and it will show “Included” and the color will change to Red. After all the desired associations
are complete, depress the
Save
button so the information will be sent to all associated controllers.
Supply Air Temperature Monitoring
The MPU2 monitors the supply air temperature to determine if the heating and cooling stages are operating properly.
During heating mode, if the supply air temperature does not rise above the heat mode alarm setpoint after a 10-minute
delay, a heat mode alarm is generated. During cooling mode, if the supply air temperature does not drop below the cool
mode alarm setpoint after a 10-minute delay, a cool mode alarm is generated.
The MPU2 has provisions for detecting a gas valve that has been become stuck in the open position. The stuck gas
valve sequence helps to prevent overheating the HVAC unit.
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.
