Instruction manual

McQuay OM 920 27
Keypad/Display Menu Structure
Min DAT Limit is a status only item which indicates the discharge air low limit temperature
on CAV zone control units. Heating will be activated to maintain this setting when the
discharge temperature falls below it during the Fan Only operating state. On VAV or CAV
discharge control units, the minimum discharge temperature limit is the DAT Clg Spt.
Occ Heating is an adjustable item which enables and disables the “daytime” heating mode of
operation. If the Occ Heating parameter is set to No, the unit will only go into heating during
the initial morning warm-up cycle. If the Occ Heating parameter is set to Yes, the unit can go
into the heating mode of operation any time during the day.
Energy Recovery
The Energy Recovery menu contains parameters that relate to or are used to control the
enthalpy wheel and exhaust fan when a unit is equipped with an optional energy recovery
wheel system.
Energy Rvcy is an adjustable item which turns the optional energy recovery system on /off.
Wheel Speed a status only item that indicates the energy wheel VFD speed.
Wheel Spd Cmd is a status only item that indicates the current energy wheel VFD
commanded speed.
ER DAT is status only item which displays the current discharge air temperature leaving the
optional energy recovery wheel.
ER Exh T is status only item which displays the current exhaust air temperature leaving the
optional energy recovery wheel. Note: This sensor is present only when the unit is equipped
with the energy recovery wheel frost protection option
Min Exh T Diff is an adjustable item that sets a differential below the calculated potential
energy recovery exhaust air frosting point. When the ER Exh T falls below the calculated
frosting point by more that this value the energy wheel will be driven to its minimum speed to
prevent frosting.
Max Exh T Diff is an adjustable item that sets a differential above the calculated potential
energy recovery exhaust air frosting point. Once the wheel is drive to minimum speed to
prevent frosting it driven back to maximum speed only when ER Exh T rises back above the
calculated frosting point by more that this value.
Stage Time is an adjustable item used to set a minimum time period for operating at either the
minimum or maximum speed before action is taken to change speed during the frost protect
mode of operation.
Min Off Time is an adjustable item used to set the minimum amount of time the energy wheel
will remain off after being turned off due to a frosting/condensation condition.
Rel Humidity is a status only item that indicates the current relative humidity reading of the
sensor.
Table 16: Energy Recovery
Menu Display Name Item Display Name Default Setting Range Password Level
Energy Recovery Energy Rec= Yes No 6
Yes
Wheel Speed= - 0-100% 6
Whl Spd Cmd= - 0-100% 6
ER DAT= - -50.0-200.0°F 6
ER ExhT= - -50.0-200.0°F 6
Min ExhT Diff= 2.0°F 1.0-10.0°F 6
Max ExhT Diff= 6.0°F 1.0-10.0°F 6
Stage Time= 5min 1-100min 6
Min Off Time= 20min 1-100min 6
Rel Humidity= - 0-100% 6