70 AGZ 035A through 065A IOMM AGZ-3
Figure 28, Delta-T Setpoints for Chillers
Menu #15: Softload Set Points—The controller can limit the number of available stages when the
unit is initially started to prevent excessive power consumption and help control overshoot of the
water temperature set point. The maximum number of stages will equal the Soft Load Maximum
Stages for the time period defined in the softload timer set point. If the softload timer is set to zero, no
soft loading will take place. Any time remaining in the softload timer will be displayed when the soft
load option is enabled. During morning start-up, the controller will run the chilled water pump and
sample the loop water temperature for a time equal to the Load Delay set point. If cooling or heating
is required at the end of this time delay, the first compressor will be started.
Menu #16: Compressor Set Points—This menu is used to set the lead-lag order of the refrigerant
circuits. The lead compressor can be manually set to circuit #1 or circuit #2 or the Automatic mode
can be enabled. In Automatic mode, the MicroTech controller will select the refrigerant circuit with
the lowest number starts as the lead. The interstage timer set point sets the delay time between the
current cooling stage and the next stage up request. The stage down request time delay is a fixed ratio
of the stage up delay.
The minimum Start/Start and Stop/Start timers provide protection against compressor short cycling.
During normal operation the Compressor Interstage Timers provide a time delay between cooling or
heating stages.
Menu #17: Head Pressure Set Points—The set points for head pressure control are adjusted from
within this menu. The Minimum Lift Pressure is the minimum differential pressure to be maintained
across the expansion valve. The dead band defines the pressure differential range within which no fan
staging will occur. If the head pressure moves outside of the deadband, the controller will integrate
the pressure error over time. When the Pound/Second exceeds the Stage Up Error or Stage Down
Error set point, the controller will adjust the fan staging up or down to bring the head pressure back
within the deadband. Refer to the section on head pressure control in this manual for details.
Menu #18: Demand Limit—The Demand Limit set point defines the maximum number of cooling
stages allowed by an external demand limit signal. The actual remote demand limit signal level in
milliamps is also displayed here.
In place of demand limit input, a 0 or 5 volts signal from a unit switch open or cool (5 volts - switch
closed) modes.
Menu #19: Time/Date—The MicroTech controller uses an internal calendar and clock to provide
automatic operation for each day of the year. Provision is made for Manual Override to accommodate
unscheduled building occupancy. Press the Control key to enter the control area of the menu structure
then press the Next Menu key until the display shows Menu Item #24, Set Date/Time. If the date is
incorrect, press the Incr or Decr key and the controller will prompt you for your password. When you
have entered the correct password, the controller will return to the Set Date/ Time display. Press the
Incr or Decr keys to scroll the month up or down. Press the Enter key when the display shows the
correct month. The cursor will advance to the Date position on the display that can be set in the same
manner. After pressing the Enter key to set the Date, the cursor will advance to the Year position on
the display. Use the Incr, Decr, and Enter keys to set the correct Year.
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