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NOTE: The W7620 VAV Box Controllers have their own
method of determining if morning warmup is required.
The VAV Box Open Output does not have to be config-
ured when using the W7620 VAV Box Controller.
A programmable variable (AUTO_CHANGEOVER)
can be set to either allow heat mode only for morning
warm-up when the occupied mode changes or to allow heat
mode anytime. In the later case, the control places the
system into the heat mode whenever the input temperature
falls below the warm-up setpoint and the system is in the
occupied mode.
NOTE: If the HEAT_MODE digital input is configured, it is
the sole determinator of the AHU heat/cool mode.
In the night setback mode, heating is provided based on
an unoccupied setpoint. The system allows up to six stages
of heat with programmable minimum heat time delay be-
tween stages from 0 to 63 minutes. Heating safeties and
limits include a heat fail input for alarm and a heat mode
input to enable or disable heat function.
OUTDOOR AIR PREHEAT
An Outdoor Air Preheat control function is available to
control the preheating of outside air introduced into the air
handling system when the outside air temperature is low.
Setpoint, Control Band, Analog Output and Digital Output,
and Preheat Lockout are configurable.
ECONOMIZER OPERATION
The economizer operation can be selected to use out-
door air or condenser water for free cooling depending on
the specific system design. The ECON_SELECT param-
eter is used to configure the economizer operation for this
purpose.
0 = Disable economizer.
1 = Use enthalpy high digital input.
2 = Use condenser water temperature and setpoint.
3 = Use difference between two analog input sensors.
(Enable when: sensor 1 < sensor 2—economizer
offset.)
If this variable is programmed to 1, the digital input
OD_ENT must be configured. If this variable is programmed
to 2, the analog input CNDTMP must be configured. If this
variable is programmed to 3, the two configuration vari-
ables
ECON_SENS1
ECON_SENS2 must be programmed.
The ECONO_TYPE Configuration Parameter is used to
set up the system to use modulating or floating actuators for
the economizer.
Mechanical cooling can be locked out automatically, if
desired, in both economizer options using the
LOCKOUT_SENS parameter. It is important to configure
the parameters to complement each other; for example, if
the outdoor air temperature is used for economizer opera-
tion, this parameter should also be selected for mechanical
cooling lockout when mechanical cooling lockout is de-
sired.
An optional method of economizer operation allows the
use of an external control to open the free cooling valve for
and
ECON_SENS1
and
the economizer. When this method is used, a bypass valve
should be installed around the free cooling coil; an end
switch installed on the free cooling valve; and the digital
input for proof of free cooling (FRE_CL 159) must be
configured. When free cooling is available, the free cooling
valve opens, making the end switch, allowing water to flow
to the economizer and closing the bypass valve around the
economizer coil.
If free cooling is operating but is not sufficient and
mechanical cooling is required, the W7600 checks for the
proof of free cooling digital input from the free cooling
valve end switch before the compressor is enabled. In this
situation, a time delay is programmed to allow the bypass
valve to open and the free cooling valve to close. If the free
cooling valve is not open when mechanical cooling is
required, the W7600 opens the bypass valve, allowing
water to flow to the condenser. See Fig. 3.
Fig. 3—Use of condensor water for econo-
mizer cycle.
COOLING
TOWER
FREE COOL
VALVE
END SWITCH TO INDICATE
"FREE-COOLING" IS AVAILABLE.
CONNECT TO DIGITAL
INPUT "FREE_COOL" (CTRL # 159)
An Economizer override function is available on input
of an IAQ Digital Input Signal. If an IAQ Digital Input
signal is received from an IAQ Sensor, indicating insuffi-
cient ventilation, the Economizer Minimum position is
changed (usually increased) to a configurable % Open
position. This IAQ Economizer Minimum position is
configrable from 0 to 100% Open.
SYSTEM RESET AND ALARM SILENCE
A system switch input is selectable via hardware or
software to cycle the W7600 on and off. When cycled off,
all digital outputs are in the off condition and analog
outputs cycle to the fully closed position. The only excep-
tions are floating close and unload outputs, which are
energized to close valves and dampers. A system reset
input, also selectable via hardware or software, clears the
VAV control algorithm and restarts the W7600. The W7600
system safety input monitors normally closed input(s). On
system failure, the VAV system is de-energized until ser-
vice has occurred and the W7600 is reset. The W7600
system also provides an alarm silence function via integral
membrane touch key to silence the alarm output. When an
alarm occurs, the alarm output is silenced until the condi-
tion is resolved, until a new alarm occurs, or until the
system is reset.
The W7600/S7600 system must resolve alarm condi-
tions. When an alarm occurs, the alarm output is turned on
35
OPERATION
CONDENSER
BYPASS
VALVE
THE BYPASS VALVE
IS CLOSED WHEN
FREE_COOL - "ON"
FREE
COOLING
COIL
63-4309—2
PM7600B
M4139
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