Temperature Control | Emerson DE, VH, VE, DH instruction

Response by Control Type—Advanced Microprocessor Controls

5.0RESPONSE BY CONTROL TYPE—ADVANCED MICROPROCESSOR CONTROLS

This section describes how your Advanced Microprocessor Controls respond depending on the algo- rithm/control type selected in setting up the controls.

5.1Temperature Control

5.1.1Cooling/Heating Required, in Percent (%)

The temperature control program for the advanced microprocessor is based on a calculated percent requirement for cooling/ heating, but the response varies according to the control algorithm or type.

5.1.2Response to Control Types Proportional Control

If Proportional Control is selected, the % requirement is determined by the difference between the return air temperature and the temperature setpoint. As the return air temperature rises above the temperature setpoint, the % cooling required increases proportionally (from 0 to 100%) over a temper- ature band equal to the temperature sensitivity +1°F. The % heating requirement is determined the same way as the temperature decreases below the setpoint. With this type of control the temperature at which the room is controlled increases as the room cooling load increases. At full cooling load, the room would be controlled at a temperature equal to the setpoint plus the sensitivity.

PID Control

If PID Control is selected, the return air temperature is controlled at or near the temperature set- point independent of the room load. The % cooling/heating requirement is calculated by adding together three individual terms - proportional, integral, and derivative.

The proportional term is figured in a manner similar to the previously described Proportional Con- trol. The integral term (sometimes called “reset action”) is figured by measuring how much and for how long the temperature has been above or below the setpoint. If the temperature is above the set- point, the % cooling requirement is slowly but continuously increased until the total is sufficient to bring the temperature back to the setpoint. The derivative term provides an anticipation control for rapid changes in temperature. If the temperature is rising, the % cooling is increased temporarily until the temperature begins to stabilize. The % heating requirement is increased if temperature is falling.

The proportional, integral, and derivative terms are all adjustable through the control selection menu and should be set or “tuned” to the characteristics of the room being controlled (see 5.3 - Load Con- trol Features).

Intelligent Control

If Intelligent Control is selected, the return air temperature is controlled at or near the temperature setpoint. The % cooling/heating required is calculated based on a set of logical “rules” that are pro- grammed into the control. These “rules” basically simulate the actions that an expert human operator would take if manually controlling the system (see Intelligent Control on page 35).

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