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APPENDIX D — MODE SELECTION PROCESS
The following section is to be used in conjunction with
Fig. 4 on page 34. To help determine why the unit controls are
in a certain mode, the programming logic is provided below.
The software will proceed, step by step, until a mode is
reached. If an “If” statement is true, then that mode will be en-
tered. The “Else” statement refers to other possible choices.
If the System Mode is OFF:
{ If the fire shut down input (Inputs
FIRE
FSD)
is in “alarm”:
HVAC mode: ("Fire Shut Down ") OFF
Else
HVAC mode: ("Disabled ") OFF}
Else If: The rooftop is not in “factory test” and a fire
smoke-control mode is “alarming”:
{ If the pressurization input (Inputs
FIRE
PRES)
is in “alarm”:
HVAC mode: ("Pressurization ")
Else If the evacuation input (Inputs
FIRE
EVAC)
is in “alarm”:
HVAC mode: ("Evacuation ")
Else If the smoke purge input (Inputs
FIRE
PURG)
is in “alarm”:
HVAC mode: ("Smoke Purge ")}
Else If: Someone changed the machine’s
control type (Configuration
UNIT
C.TYP) during
run time, a 15 second delay is called out:
{ HVAC mode: ("Disabled ") OFF}
Else If: The System Mode is TEST:
{ HVAC mode: ("Test ")}
Else If: The “soft stop” command (Service Test
S.STP)
is forced to YES:
{ HVAC mode: ("SoftStop Request")}
Else If: The remote switch config (Configuration
UNIT
RM.CF)=2; “start/stop”, and the remote
input state (Inputs
GEN.I
REMT)=ON:
{ HVAC mode: ("Rem. Sw. Disable") OFF}
Else If: Configured for static pressure control
(Configuration
SP
SP.CF = 1,2) and the static
pressure sensor (Pressures
AIR.P
SP) fails:
{ HVAC mode: ("Static Pres.Fail") OFF}
Else If: Configured for supply fan status monitoring
(Configuration
UNIT
SFS.M = 1,2) and
configured to shut the unit down on fan status fail
(Configuration
UNIT
SFS.S = YES)
{ HVAC mode: ("Fan Status Fail ") OFF}
Else If: The unit is just waking up from a power reset
{ HVAC mode: ("Starting Up ") OFF}
Else If: A compressor is diagnosed as being “Stuck On”
{ HVAC mode: ("Comp. Stuck On ")
Else The control is free to select the normal heating/
cooling HVAC modes:
{ HVAC mode: ("Off ")
— The unit is off and no operating modes are active.
HVAC mode: ("Tempering Vent ")
— The economizer is at minimum vent position but
the supply air temperature has dropped below the
tempering vent set point. Gas heat is used to
temper the ventilation air.
HVAC mode: ("Tempering LoCool")
— The economizer is at minimum vent position but
the combination of the outside-air temperature and
the economizer position has dropped the supply-air
temperature below the tempering cool set point.
Gas heat is used to temper the ventilation air.
HVAC mode: ("Tempering HiCool")
— The economizer is at minimum vent position but
the combination of the outside air temperature and
the economizer position has dropped the supply air
temperature below the tempering cool set point.
Gas heat is used to temper the ventilation air.
HVAC mode: (“Re-Heat”)
— The unit is operating in reheat mode.
HVAC mode: (“Dehumidification”)
— The unit is operating in dehumidification mode.
HVAC mode: ("Vent ")
— This is a normal operation mode where no heating
or cooling is required and outside air is being
delivered to the space to control IAQ levels.
HVAC mode: ("Low Cool ")
— This is a normal cooling mode when a low cooling
demand exists.
HVAC mode: ("High Cool ")
— This is a normal cooling mode when a high
cooling demand exists.
HVAC mode: ("Low Heat ")
— This is a normal heating mode when a low
heating demand exists.
HVAC mode: ("High Heat ")
— This is a normal heating mode when a high
heating demand exists.
HVAC mode: ("Unocc. Free Cool")
— In this mode the unit will operate in cooling but
will be using the economizer for free cooling.
Entering this mode will depend on the status of the
outside air. The unit can be configured for outside
air changeover, differential dry bulb changeover,
outside air enthalpy changeover, differential
enthalpy changeover, or a custom arrangement
of enthalpy/dewpoint and dry bulb. See the
Economizer section for further details.}
NOTE: There is also a transitional mode whereby the machine
may be waiting for relay timeguards to expire before shutting
the machine completely down:
HVAC mode: ("Shutting Down ")