YORK INTERNATIONAL
58
Sequence of Operation
FORM 100.50-NOM1 (604)
VARIABLE AIR VOLUME SEQUENCE OF OP ER A TION
Under Variable Air Volume Operation, the unit will be
controlled from one of two sources:
• 7-Wire Thermostat
• Space Sensor
In addition to the two control methods, a VAV con-
Þ
g ured unit can also operate “stand-alone” with the only
direct control being the Occupied/Unoccupied signal.
The method of control is as selected as described in the
following sections.
VAV Operation With a Thermostat
When “
VAV with Thermostat”
parameter is set to ON,
a Thermostat is used for SAT reset control.
If the Thermostat is not available, the Primary Unit
Controller will self-con
Þ
gure to Standalone VAV op-
eration
VAV Operation With a Space Sensor
A Space Sensor is used for control when:
• The
VAV with Thermostat
parameter is OFF, and:
◦
A Space Sensor is available and the
"Space Sensor
Enable"
parameter is ON.
• If a Space Sensor is not available, the con trol ler will
self-con
Þ
gure to Standalone VAV op er a tion.
Standalone VAV Operation
Standalone VAV operation is used by the control
when:
• The
VAV with Thermostat
parameter is OFF, and
• No Space Sensor is available.
VAV Operating Modes
VAV operating modes have the following common
functions:
• For heating, the Heating Mode Enable pa ram e ter
must be ON.
• For cooling, the Cooling Mode Enable pa ram e ter
must be ON.
◦
Cooling (compressor) stages are con trolled as
described in the following sections.
◦
The SAT control algorithm for cooling is de scribed
in the following sections.
◦
The Supply Fan is:
– Controlled as described in the Fan.
– Controlled to maintain the Duct Static Pres-
sure setpoint when cooling or heating is
ON.
– ON and controlled for heating or cool ing when
the Ther mo stat G output is ON.
– Ramped up to its operation condition using
its vari able output control when turned ON.
– OFF when heating or cooling is OFF and oc-
cu pan cy is UNOCCUPIED.
– Optionally controlled ON and OFF by a BAS
input when occupancy is UNOCCUPEID.
◦
For Economizer Operation, the
Econ o miz er In-
stalled
parameter must be ON and the
Econ o miz er
Enable
parameter must be ON. The econ o miz er
is:
– Closed for all unoccupied heating.
– At the minimum position for occupied heat-
ing.
– At minimum for occupied cooling when
econ o miz er is not available.
– Closed for unoccupied cooling when econ o -
miz er is not available.
– At the economizer algorithm de ter mined
po si tion for cooling with economizer avail-
able.
Unoccupied Heating With A Thermostat
The heating control is as described for “Occupied
Heat ing With A Thermostat” and the general op er at ing
conditions.
Occupied Cooling With A Thermostat
• The thermostat Y1 and Y2 outputs con trol SAT
to:
◦
Y1 = OFF, Y2 = OFF – No cooling
◦
Y1 = ON, Y2 = OFF - Cooling to
"VAV Cool High
Temp Setpoint".
◦
Y1 = ON, Y2 = ON - Cooling to
"VAV Cool Low
Temp Setpoint".
◦
Y1 = OFF, Y2 = ON - Cooling to
"VAV Cool Low
Temp Setpoint".
Unoccupied Cooling With A Thermostat
The cooling control is as described for Occupied
Cooling With A Thermostat and the general operating
con di tions.
Sequence of Operation