Emerson VH, DE, VE, DH manual Dual Cooling Source Dehumidification, Chilled Water Dehumidification

Response by Control Type—Advanced Microprocessor Controls

Dual Cooling Source Dehumidification

When dual cooling is available, the humidity control will calculate a total dehumidification require- ment of 200% rather than 100%. The cooling valve opens proportionally as the requirement for dehu- midification rises from 0 to 100%. If more than 100% dehumidification is required, then the compressors are activated at 150% and 200% respectively. Dual cooling is available if the entering chilled water temperature is 14°F (50% capacity) below the return air temperature. If dual cooling is not available, the humidity control will operate the compressors in the same manner as a 2-stage dehumidification system.

Chilled Water Dehumidification

The chilled water control valve is adjusted proportionally as the humidity control varies the require- ment for dehumidification from 0 to 100%.

5.2.4Humidification Operation System Activation

The humidifier (infrared or steam) is activated when the humidity control calculates a requirement of 100% humidification, and deactivated when the requirement falls below 50%.

5.2.5Control Types Proportional Control

This is a standard control method that maintains the room at a temperature proportional to the load. The temperature maintained increases as the room load increases. At full load the room would be con- trolled at a temperature equal to the temperature setpoint plus the temperature sensitivity. If Pro- portional Control is selected, the gain is factory set and cannot be adjusted by the user. Operator inputs are the usual setpoint and sensitivity adjustments.

PID Control

The PID Control combines three individual terms to determine the control output for a given set of conditions. Note that PID Control is used only for temperature. If PID Control is selected, humidity will continue to use Proportional Control.

The proportional (P term) is determined by the difference between the current temperature and the control setpoint. This term is expressed in % cooling (heating) desired for each degree above (below) the setpoint. It is adjustable from 0% to 100% per degree. The purpose of this term is to adjust the control output for any deviation between the current temperature and the control setpoint.

The integral (I term) is determined by two things: the difference between the temperature and control setpoint and the amount of time this difference has existed. This term is expressed in % cooling (heat- ing) desired for each minute and degree above (below) the setpoint. It is adjustable from 0% to 100% per degree-minute. The purpose of this term is to force the control to maintain the temperature around the setpoint by slowly but continuously adding (subtracting) a small amount of cooling (heat- ing) to the total control output until the temperature is at the setpoint.

The derivative (D term) is determined by the rate of change of temperature. This term is expressed in % cooling (heating) desired for each degree per minute rise (fall) in temperature. It is adjustable from 0% to 100% per degree/min. The purpose of this term is to adjust the control output for quickly chang- ing temperatures, thus providing an anticipation control.

All three types are adjusted in the Select Control Type menu, a submenu of the Setup System menu. If PID Control is selected, the temperature sensitivity setting is not used by the control.

For optimum performance, a PID Control must be adjusted or tuned according to the characteristics of the particular space and load to be controlled. Improper tuning can cause the control to exhibit poor response and/or hunting. The characteristics of the space and load may change seasonally, so occa- sional retuning is required for optimum performance.

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