High Ambient Heating Lockout; Discharge Air Low Limit Control - McQuay MicroTech II Operation Manual

tion, the Effective Heating Enable Set Point is set
by the controller equal to the Heating Enable Set
Point.
The MWU operating state is similar to the Heating operating
state; the only difference is that the Eff Min OA Pos= param-
eter is set to 0% during MWU. The unit remains in the
MWU operating state until either the Ctrl Temp= value is
equal to or greater than the Effective Heating Enable Set
Point or the duration of the MWU operating state exceeds
the Maximum Morning Warm-up Timer setting. In either
case, since the Ctrl Temp= value has not risen above the
Effective Heating Enable Set Point by more than half the
Heating Enable Dead Band when this occurs, the controller
enters the Heating operating state.
The Maximum Morning Warm-up Timer parameter is pro-
vided to ensure that the required minimum ventilation air is
being supplied after a known time regardless of the space
temperature condition. For example, if actual occupancy is at
8:00 a.m. and unit startup is scheduled for 6:30 a.m., a Maxi-
mum Morning Warm-up Timer setting of 90 minutes would
ensure that the outdoor air dampers open to minimum posi-
tion when building occupancy occurs.
Note: The morning warm-up function does not occur on
units equipped with 100% OA hoods.

High Ambient Heating Lockout

Table 47: Programmable Parameters
Keypad/Display ID
Menu Name Item Name
OATHtg Lock= 55.0 ºF
Zone Heating
OATLock Diff= 1.0 °F
Heating is disabled whenever the outdoor air temperature is
greater than the High Ambient Heating Lockout Set Point.
When this occurs, the Htg Status= parameter in the System
and Zone Heating menu indicates "Off Amb" if heating is
not disabled for some other reason. When the outdoor air
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temperature drops below the High Ambient Heating Lockout
Set Point by more than the High Ambient Heating Lockout
Differential, heating operation is re-enabled.

Discharge Air Low Limit Control

Table 48: Programmable Parameters
If heating is enabled and there is no heating load (normally
Fan Only operating state), the controller can activate the unit
heating equipment as required to prevent the discharge air
temperature from becoming too cool. It accomplishes this by
entering the Min DAT operating state when necessary.
Entering Min DAT Operating State
When the Min DAT Control Flag is set to "Yes" and if the
Disch Temp= parameter falls below the Minimum Discharge
Temperature Limit by more than half the Discharge Heating
Dead Band, the unit operating state changes from Fan Only
to Min DAT. When in the Min DAT operating state, heating
capacity is increased if the Disch Temp= parameter is below
the Minimum Discharge Temperature Limit by more than
Parameter Name half the Discharge Heating Dead Band. Heating capacity is
decreased if the Disch Temp= parameter rises above the
High Ambient Heating
Minimum Discharge Temperature Limit by more than half
Lockout Set Point
the Discharge Heating Dead Band.
High Ambient Heating
Leaving Min DAT Operating State
Lockout Differential
When the heating capacity has be 0% for one Heat Interstage
Time period and the Disch Temp= parameter is above the
Minimum Discharge Temperature Limit by more than half
the Discharge Heating Dead Band, the unit leaves the Min
DAT operating state and re-enters the Fan Only operating
state.
Keypad/Display ID
Menu Name Item Name
Eff Clg Spt= 55.0 ºF
Discharge Cooling
Clg Db= 1.0 ºF
Discharge Heating Min DAT Ctrl= Yes
Parameter Name
Effective Discharge
Cooling Set Point
Discharge Cooling
Dead Band
Min DAT Control Flag
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