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OM 752-4
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Proportional Integral (PI) Control Loops
The MicroTech II UVC uses PI-loop control for heating, cooling and ventilation processes
within the unit ventilator. Numerous PI algorithms can be used depending upon the unit
ventilator configuration. The UVC uses “single” and “cascading” PI loops where needed.
Table 16: PI loop list
PI loops
PI loop type
Set point
Feedback (controlled
variable)
Output
PI-1
Space Temperature
Cascading
Effective Heating or Cooling Temperature
Set point
Space Temperature
Calculated Discharge Air Tem-
perature Setpoint Output
PI-2
Primary Cooling (Economizer)
Calculated Discharge Air Temperature
Setpoint Output
Discharge Air Temperature
Position the OA Damper
PI-4
Primary Heating
Calculated Discharge Air Temperature
Setpoint Output
Discharge Air Temperature
Operate Electric Heat
PI-6
CO2 (optional)
Single
Effective CO2 Setpoint
Space CO2
Position the OA Damper
PI-7
Low Limit
Single
Calculated Discharge Air Temperature
Setpoint
Discharge Air Temperature
Position the OA Damper
Figure 16: PI loop graphic for CO2
Discharge Air Temperature Control
The UVC uses two “cascading” PI loops to aid in providing very stable space tempera-
ture control. The Space Temperature PI-loop is used to calculate the Discharge Air
Temperature Setpoint Output required to meet the Effective Temperature Setpoint Out-
put. A second PI-loop (Primary Cooling, Secondary Cooling, or Primary Heating) is then
activated to control the heating or cooling device required to achieve the calculated
Discharge Air Temperature Setpoint Output. The second PI loop used is independent
upon unit mode (i.e., Heat or Cool).
Figure 17: Cascading PI loop graphic 1 (primary heat)
Figure 18: Cascading PI loop graphic 2 (primary cool—economizer)
Summary of Contents for MicroTech II
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