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YORK INTERNATIONAL
62
Sequence of Operation
FORM 100.50-NOM1 (604)
TABLE 17 – VAV MODES OF OPERATION
Sequence of Operation
Control
Heating
Cooling
Occupied
Unoccupied
Occupied
Unoccupied
Thermostat
‘stat uses its programmed
occupied htg. Setpoint,
controls SAT to “no
heating” (W1=OFF), or
“full heating (W1=ON).
During heating, supply
fan meets duct static
requirements. If hydronic
heat, SAT controlled to
2nd stage hydronic heat
setpoint.
Same as occupied
heating, except ‘stat
uses its programmed
unoccupied heating
setpoint, ‘stat generates
“unoccupied” output that
overrides ODA damper
min. position to 0%.
During heating, supply
fan at 100%.
‘stat uses its programmed
occupied clg. setpoint,
‘stat Y1, Y2 outputs
control SAT to “no
cooling” (Y1=OFF),
cooling to “VAV Cool
High Temp SAT setpoint”
(Y1=ON) and cooling
to “VAV Cool Low
Temp SAT setpoint”
(Y1=ON, Y2=ON). ODA
damper at min. position
(damper may modulate
open if free cooling is
being used) Supply fan
controlled during cooling
by supply duct static,
supply fan uses a “soft
start.”
Same as occupied
cooling, except ‘stat
uses its programmed
unoccupied cooling
setpoint, ‘stat generates
“unoccupied” output that
overrides ODA damper
min. position to 0%
(damper may modulate
open if free cooling is
being used). Supply fan
controlled during cooling
by supply duct static.
Network
Communicated
Sensor
Similar to thermostat
operation above, ‘stat W1
signal is replaced by a
network command.
Similar to thermostat
operation above, ‘stat
W1 signal is replaced
by a network command.
Network supplies an
“unoccupied” command.
Similar to thermostat
operation above, ‘stat
signals are replaced
by network commands
requesting cooling to
High SAT setpoint (Stage
1), or to Low SAT setpoint
(Stage 2).
Similar to thermostat
operation above, ‘stat
signals are replaced
by network commands
requesting cooling to
High SAT setpoint (Stage
1), or to Low SAT setpoint
(Stage 2), network
supplies an “unoccupied”
command.
Space Sensor
Control algorithm is same
as for Morning WarmUp
cycle. RAT is controlled
to a programmed setpoint
w/ 2°F deadband when
space temperature drops
2°F below “VAV setpoint
for SAT reset”. During
heating, supply fan meets
duct static requirements.
If hydronic heat, SAT
controlled to 2nd stage
hydro heat setpoint. Both
space and RAT must be
below setpoints.
An external “unoccupied”
signal initiates this mode.
Space temperature
is controlled to a
programmed unoccupied
htg. Setpoint by cycling
unit On/Off. Full heating
(all stages) is ON when
space temperature drops
0.3°F below the setpoint,
OFF when temperature
is 0.1°F or less below
the setpoint for at least
60 sec.
During heating, supply
fan at 100%. If hydronic
heat, SAT controlled to
2nd stage hydronic heat
setpoint.
Cooling SAT setpoint
is reset by space
temperature vs. “VAV
setpoint for SAT reset”.
“VAV Cool Low Temp”
setpoint used if space
temperature 2°F above
the reset setpoint, “VAV
Cool High Temp” setpoint
if space temperature
0.5°F below the reset
setpoint. ODA damper
at min. position (damper
may modulate open if
free cooling is being
used) Supply fan
controlled during cooling
by supply duct static,
supply fan uses a “soft
start”.
An external “unoccupied”
signal initiates this
mode, overrides ODA
damper min. position
to 0% (damper may
modulate open if free
cooling is being used).
Space temperature is
controlled to programmed
unoccupied clg. Setpoint
by cycling unit On/Off.
When space temperature
increases 0.3°F above
the setpoint, cooling
runs at programmed
High SAT setpoint, when
temperature is 0.1°F or
less above the setpoint
for at least 60 sec,
unit turns OFF. During
cooling, supply fan is
controlled by supply duct
static, supply fan uses a
“soft start”.
None
(standalone)
RAT must be below
setpoint for 10 minutes.
An external “unoccupied”
signal initiates this mode,
unit shuts down.
SAT is controlled to the
“VAV Cool High Temp”. if
the economizer is active
or to the “VAV Cool Low
Temp” if the economizer
is not active. Supply fan
is always running and
controlled by the duct
static.
An external “unoccupied”
signal initiates this mode,
unit shuts down.