American Standard UV05 User's Manual | Page 29

American Standard Air Conditioners User's Manual - UV05.
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McQuay OM 751

29

Description of Operation

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

Figure 17: PI loop graphic for CO2

Discharge Air Temperature Control

The UVC uses two “cascading” PI loops to aid in providing very stable space temperature 
control. The Space Temperature PI-loop is used to calculate the Discharge Air Temperature 
Setpoint Output required to meet the Effective Temperature Setpoint Output. 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. 

Figure 18: Cascading PI loop graphic 1 (primary heat)

Figure 19: Cascading PI loop graphic 2 (primary cool—economizer)

PI loops

PI loop type

Set point

Feedback

(controlled 

variable)

Output

PI-1

Space Temperature

Cascading

Effective Heating or Cooling 

Temperature Setpoint

Space Temperature

Calculated Discharge Air 

Temperature Setpoint Output

PI-2 Primary Cooling (Economizer)

Calculated Discharge Air Temperature 

Setpoint Output

Discharge Air 

Temperature

Position the OA Damper

PI-3

Secondary Cooling

Calculated Discharge Air Temperature 

Setpoint Output

Discharge Air 

Temperature

Operate the Compressor

PI-4

Primary Heating

Calculated Discharge Air Temperature 

Setpoint Output

Discharge Air 

Temperature

Position the Wet Heat Valve or 

F&BP Damper

PI-5

 CO2 (optional)

Single

Effective CO2 Setpoint

Space

 CO2

Position the OA Damper

PI-6

Low Limit

Single

Calculated Discharge Air Temperature 

Setpoint

Discharge Air 

Temperature

Position the OA Damper

+

-

Space CO2

sensor

Effective

CO2 set point

PI - 5

Position the

OA damper

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