Emerson Liebert Prop Fan Condensing Unit Manual de instalación descargar pdf (Pagina 41)

Microprocessor Control

3.9.3 Humidity Control Method

The operator may select either relative (direct) or absolute (predictive) humidity control. If “relative”

is selected, the RH control is taken directly from the RH sensor. If “absolute” is selected, the RH con-

trol is automatically adjusted whenever return air temperature deviates from the desired tempera-

ture setpoint (i.e., predictive humidity control). The LCD display will indicate percentage relative

humidity for both methods of control. If the “absolute” feature is selected, the adjusted humidity read-

ing will also be shown. When utilizing the predictive humidity control feature, the humidity level is

automatically adjusted ~2% RH for each degree difference between the return air temperature and

the temperature setpoint.

Unnecessary dehumidification can result when overcooling occurs during a dehumidification cycle.

This is due to a higher than normal RH reading caused by overcooling the room (about 2% RH for

each degree of overcooling). This drop in temperature extends the dehumidification cycle. Later, when

the dehumidification ends and the temperature rises to the setpoint, the RH reading falls. The final

RH reading will then be lower than actually desired. If the temperature drop was significant enough,

the percentage RH could be low enough to activate the humidifier.

If the absolute humidity control is selected, over-dehumidification may be avoided. When overcooling

occurs (i.e., causing an increase in the RH reading) the humidity control program estimates what the

RH will be when the dehumidification cycle ends and temperature returns to the setpoint. This allows

the dehumidification cycle to end at the proper time. Predictive humidity control can greatly reduce

energy consumption by minimizing both compressor/reheat operation. Use the UP or DOWN arrow

key to select the desired humidity control method.

3.9.4 Show DIP switch

This function shows the position of the DIP switches, which are located on the control board in the

unit; 1 = Switch is “ON” and 0 = Switch is “OFF.” For more information on the DIP switches and their

functions, see Table 15.

3.9.5 Valve Time (for Systems With a Modulating Chilled Water Valve)

This function shows the full valve travel time of the modulating valve on a chilled water system. This

is the time it takes for the valve to travel from full closed to full open. It is programmable from 50 to

250 seconds; factory default time is 165 seconds and should not be changed. The full valve travel time

is used by the control to determine the appropriate valve position. For example, if the valve travel

time is 165 seconds and 50% cooling is being called for, the valve will open for 83 seconds to achieve

50% open.

3.9.6 CW Flush (for systems with a modulating chilled water valve)

This function shows the interval time at which the system will perform a modulating chilled water

valve system flush cycle. The factory default is 24 (hours) and is programmable from 0 (hours) which

signifies to never flush, to 99 (hours) which signifies to flush after every 99 hours of valve non-use. If

the valve is called on by the control to open within the programmed interval time, the timer will be

reset to 0. The flush cycle is active even when the fan is turned off, but power is applied to the unit.

When the interval timer reaches the programmed time, the valve will be opened for 3 minutes to flush

any contaminants that may have collected in the system.

Table 13 Setup functions, default values and allowable ranges

Function Default Range

Restart Time

Delay

0.1 0 to 9.9 min

(0 = manual restart)

C/F Degrees

°F °C or °F

Humidity Control Rel Relative or Absolute

Valve Time 165 50 to 250 sec(s)

CW Flush 24 0 to 99 hours

1 2 ... 36 37 38 39 40 41 42 43 44 45 46 ... 67 68

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Emerson Liebert Prop Fan Condensing Unit Manual de instalación Pagina 41

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