Unit installation
46 OMRCPMICRO
Control menus
Menus 13 through 23 are the set point menus. All adjustable control parameters and set points, time
schedules, control options, and alarm thresholds are accessed through these menus.
CAUTION
Any changes to these parameters must be determined and implemented by qualified
personnel with a thorough understanding of how these parameters affect the operation of
the unit. Negligent or improper adjustment of these controls may result in damage to the unit
or personal injury.
Menu # 13: Control Mode
—One of several automatic and manual operating modes may be selected from within this menu. Typically, the
selected control mode will be Automatic which will allow the MicroTech controller to handle all compressor
and condenser fan staging. Refrigerant circuit #2 may be locked off while still allowing circuit #1 to stage
automatically by selecting AutoCir#1-Off#2 as the operating mode. OffCirc#1-Auto#2 allows the normal
staging of refrigerant circuit #2 but circuit #1 is locked off. Select Manual Staging if manual control is desired.
In this operating mode, the condenser fans are controlled by the MicroTech but the number of stages is
determined manually via the keypad. If manual staging is selected, the second item under this menu indicates
the number of active cooling or heating stages. Use the INCR or DECR keys to increase or decrease the
number of active stages.
CAUTION:
Do not leave the controller in the manual staging mode unattended.
This mode overrides stage up timers and should be used for testing only.
Menu # 14: Leaving Water Set Points
—The leaving water set points, control band, maximum pull down rate and water reset options are adjusted
from this menu. The first menu item is The Active Set Point ("Active Spt"). The current control temperature—
leaving evaporator or leaving condenser water—is displayed here. The Leaving Chilled Water Set Point ("Lvg
Evap") for chillers and the Leaving Heated Water Set Point ("Lvg Cond") for THRs appear towards the top of
this menu. These are the set points that will be maintained for chillers and Templifiers, respectively, if no reset
options are in effect. Most reset options apply to leaving chilled water only—ALRs, WHRs and THRs
operated in chiller mode. For THRs operated in heating mode (controlled off of leaving condenser water), the
None, 4-20mA and Network reset options only are applicable. The Active Control Set Point " ("Active Spt")
will display the calculated chilled or heated water temperature to be maintained when one of the reset options
is enabled.
If the 4-20 milliamp reset option is enabled, the controller will reset the leaving chilled water temperature to a
higher value based on a percentage of the Maximum Chilled Water Reset set point ("MaxChWRst"). At 4mA
or less, no reset will occur. At 20mA, the chilled water set point will be reset to a value equaling the Leaving
Evaporator Water Set Point (" Lvg Evap") plus the value stored in the "MaxChWRst". Any milliamp value
between 4 and 20mA will cause a proportional value of the Maximum Chilled Water Reset to be added to the
Leaving Chilled Water Set Point. The reset schedule is linear and may be calculated using Figure 7. The
external 4-20 milliamp control signal and current reset set point will be displayed under "Reset Sig" and
"Active Spt", respectively, on Menu 14. For specific information, see the Reset Options portion of this
manual. For THRs operated in heating mode, the "Active Spt" reflects the degree of heating reset. Based on
the reset signal, a proportional value of the "MaxChWRst" will be subtracted from the "Lvg Cond" set point
and displayed under "Active Spt".
By selecting Return as the reset mode, the leaving chilled water temperature will be reset by the controller as
required to maintain a constant return water temperature. The user must select the "Return" option under
"ResetOpt" and select the return set point to be maintained under "ResetSpt". The current leaving chilled
water reset set point will be displayed under "Active Spt".
If the chiller is to be used for ice storage, select the "Ice" option in Menu 14 "LvgWater Spt", "ResetOpt=". To
calculate the leaving chilled water set point, the control band (Menu 14 "CntrlBand=") and shut down delta-T
(Menu 14 ShutDn D-T=") must first be selected. The equation to determine leaving chilled water temperature
is: