Energy Recovery Bypass Damper Control; Return Fan Capacity Control; Direct Building Static Pressure Control - McQuay MicroTech II Operation Manual

When the exhaust fan is on, its capacity is modulated to
maintain the Bldg Press= parameter value at the Building
Static Pressure Set Point using three PID control loop param-
eters. These are the Building Static Pressure Proportional
Band, Building Static Pressure Integral Time and Building
Static Pressure Period. Although these parameters can be
adjusted, for most applications, the factory default values for
these parameters provide the best control. For detailed infor-
mation regarding tuning PID control loop parameters, refer
to "MicroTech II DDC Features" on page 99.
Direct Position Control
The energy recovery option includes a variable capacity
exhaust fan equipped with either a VFD or variable inlet
vanes. When the Energy Recovery Control Flag is set to
"Yes" and the Return/Exhaust Fan Capacity Control Flag is
set to "Position", the exhaust fan is controlled based on
Remote Return/Exhaust Fan Capacity Set Point. This set
point can be adjusted via network signal. The exhaust fan is
turned on when the outdoor air dampers are opened and the
exhaust fan capacity is commanded above the Exhaust Fan
Minimum Capacity Value for longer than the Minimum
Exhaust Fan Off Timer.
Note: The exhaust fan is not turned on when the outdoor
air dampers are closed (as in the Recirc or MWU
operating states).
The exhaust fan remains on until any of the following occur:
1. The Remote Return/Exhaust Fan Capacity Set Point is
commanded to the Exhaust Fan Minimum Capacity
Value for longer than the Minimum Exhaust Fan On
Timer.
2. The discharge fan is turned off
3. The outdoor dampers are completely closed.

Energy Recovery Bypass Damper Control

Table 52: Programmable Parameters
Keypad/Display ID
Menu Name Item Name
Eff MinOA Pos= ___%
OA Damper
The energy recovery option includes a set of bypass dampers
when the unit is equipped with a 0-100% modulating econo-
mizer. The bypass dampers are closed whenever the OA
Damper Pos= parameter in the OA Damper menu is equal to
the Effective Minimum Outdoor Damper Position Set Point.
The bypass dampers are driven fully open when the OA
Damper Pos= parameter is driven above the Effective Mini-
mum Outdoor Damper Position Set Point while the unit is in
the Econo or Cooling operating state.
88

Return Fan Capacity Control

When a unit is equipped with return fan inlet guide vanes or
a return fan VFD, there are two optional methods for con-
trolling the return fan capacity. These are "direct building
static pressure" control and "position" control. The follow-
ing sections describe the two methods.

Direct Building Static Pressure Control

Table 53: Programmable Parameters
Menu Name
Bldg Pressure
Building Static P
Unit Configuration
When the Return/Exhaust Fan Capacity Control Flag is set to
"BldgPres" and the Second Pressure Sensor Present Flag is
set to "Bldg", the controller modulates the return fan capac-
ity to maintain the Bldg Static Pressure Set Point.
Note:
To do this it uses three PID control loop parameters to modu-
late the return capacity as the building static pressure
changes. Theses are Building Static Pressure Proportional
Band, Building Static Pressure Integral Time and Building
Static Pressure Period. Although these parameters can be
adjusted, for most applications, the factory default values for
these parameters provide the best control. For detailed infor-
Parameter Name
mation regarding tuning PID control loop parameters; refer
to "MicroTech II DDC Features" on page 99.
Effective Minimum
Outdoor Damper
Building static pressure control of the return air fan airflow
Position Set Point
is overridden under two conditions.
1. The first condition is when the return fan capacity mod-
2. The second condition is when the outdoor air dampers
Keypad/Display ID
Item Name
BldgSP Spt= 1.00 "WC
BSP Db= 0.080 "WC
BSP Propbd= 0.400 "WC
Setup BSP IntTime= 2.0 sec
BSP Period= 2.0 sec
2nd P Sensor= Bldg
RF/EFCtrl= BldgPres
Note that this feature requires an optional building
static pressure sensor.
ulates down to 17% or the VFD speed is reduced to
25%. The controller does not allow the return fan capac-
ity to modulate below these fixed values.
are completely closed. In this case the return fan capac-
ity tracks the discharge fan capacity one-to-one. In the
case of a constant volume discharge fan the return fan
airflow is driven to 100%.
Parameter Name
Building Static Pres-
sure Set Point
Building Static Pres-
sure Dead Band
Building Static Pres-
sure Proportional
Band
Building Static Pres-
sure Integral Time
Building Static Pres-
sure Period
Second Pressure
Sensor Present Flag
Return/Exhaust Fan
Capacity Control Flag
OM 138