American Standard UV05 Proportional Integral PI Control Loops, Discharge Air Temperature Control

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

	PI loops	PI loop type	Set point	Feedback	Output
				(controlled
				variable)
PI-1	Space Temperature		Effective Heating or Cooling	Space Temperature	Calculated Discharge Air
			Temperature Setpoint		Temperature Setpoint Output
PI-2	Primary Cooling (Economizer)		Calculated Discharge Air Temperature	Discharge Air	Position the OA Damper
			Setpoint Output	Temperature
		Cascading
PI-3	Secondary Cooling		Calculated Discharge Air Temperature	Discharge Air	Operate the Compressor
			Setpoint Output	Temperature
PI-4	Primary Heating		Calculated Discharge Air Temperature	Discharge Air	Position the Wet Heat Valve or
			Setpoint Output	Temperature	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	Discharge Air	Position the OA Damper
			Setpoint	Temperature

Figure 17: PI loop graphic for CO2

Effective	+ -
CO2 set point

Space CO2

sensor

PI - 5

Position the OA damper

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)

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