iWorx® MPU2
505-009, Effective: June 30, 2015
29
© 2015 Taco Electronic Solutions, Inc.
Bypass Damper
Static pressure control is achieved by modulating a bypass damper between the fully open and fully closed positions
based on the measured static pressure in the supply duct. The static pressure sensor input has maximum range of
5.000" W.C. with a minimum resolution of 0.005" W.C.
The bypass damper is modulated by a P+I control loop based on the static pressure loop setpoint and the supply static
pressure measurement. The P+I control loop modulates the damper to maintain a constant static pressure within the
supply air duct. As the supply static pressure decreases 0.025" W.C. below the static pressure loop setpoint, the
bypass damper is modulated closed. The bypass damper modulates open as the supply static pressure increases to
0.025" W.C. above the static pressure loop setpoint. When the static pressure is within ±0.025” W.C. of the static pres-
sure setpoint, the damper remains at its current position.
To prevent the integral component from becoming too large, there is anti-wind up reset protection. This protection
clamps the integral value when all of the components add up to more than 100% or less than 0%. The following equa-
tions are used for P+I control:
Kp = Proportional Gain
Ki = Integral Gain
A separate static pressure setpoint is provided to increase the supply static pressure when an IAQ alarm condition
exists. The bypass damper control maintains the IAQ alarm pressure setpoint as long as an IAQ alarm condition exists.
The bypass damper modulates to the full open (bypass) position prior to the fan energizing. During operational mode
changes the bypass damper remains open until the supply air temperature has reached the programmable cooling and
heating setpoints. This prevents thermal shock in the zones.
Programmable minimum and maximum outputs are provided for the bypass damper. These settings can be reversed
for reverse-action. Overrides are provided to assist in system air balancing during commissioning.
Analog Outputs
The modulated Economizer and Bypass Damper analog outputs support normal and reverse actuation. Making the
analog output's minimum voltage scaling parameter less than the maximum enables normal actuation. Making the ana-
log output's maximum scaling parameter less than the minimum enables reverse actuation.
Fan Operation
During occupied periods, the fan may either always run or cycle off when there is no demand for heating or cooling.
The fan is interlocked with the cooling and heating stages. If there is a call for heating or cooling the fan immediately
energizes. During unoccupied period, the fan always cycles off when there is no demand for heating or cooling. During
IAQ alarm conditions the fan energizes to provide fresh air to the zones.
Fan Proof
When there is a call for heating or cooling, the fan output is energized. A fan status input is provided for monitoring the
operation of the fan. When the fan is initially turned on, there is a 30 second delay before the fan status is checked. If at
any time after the delay, the fan status indicates the fan is not running, a fan failure condition is generated. The heating
and cooling stages are interlocked with the fan. When a fan failure condition exists, the heating stages, cooling stages
and the fan immediately turn off. The controller must be reset to clear this condition.
NOTE:
If not providing a fan proof switch, the dip switch for the fan proof input must be configured with the (0-10V)
switch set to “on” and the “Vth” set to off. After a fan failure, the controller's status LED changes from green to solid red.
To return the controller to normal operation after the failure condition is resolved, you must reset the controller by
removing and reapplying power or by using the controller reset feature on the LCI.
Error
SupplyStaticPressure LoopSetpoint
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