iWorx® MPU2
505-009, Effective: April 28, 2014
29
© 2014 Taco Electronic Solutions, Inc.
Dehumidification
If the Setpoint is set to zero, dehumidification is disabled. When the humidity is above the Setpoint, dehumidification
begins, and it stops when the humidity drops below Setpoint minus 3%.
Dehumidification stops when the zone demand for heating is greater than the zone demand for cooling. Dehumidifica-
tion is disabled when the unit is in heating.
During dehumidification, the operating mode will be displayed as “Dehumid,” the cooling outputs will stage on, and the
stage timer is enforced; or, modulating output or floating point valve will be set to 100%.
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.
Error
SupplyStaticPressure LoopSetpoint
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