Honeywell W7340 - Manual (Page 9)

W7340, W7345 COMMUNICATING ECONOMIZER LOGIC MODULES
9 63-2569—04
Limit On Minimum Damper Position
On the W7340A and B models, the logic module as shipped
from the factory, limits the minimum position setpoint to 50%.
The logic module will not allow a minimum position greater
than 50% open (from fully closed).
NOTE: This setpoint limit can only be changed using a
Modbus command.
Equation 1. Formula to aid in minimum position adjustment.
or
Where:
T
O
= Outdoor air temperature
OA = Percent of outdoor air
T
R
= Return air temperature
RA = Percent of return air
T
M
= Resulting mixed air temperature
NOTE: The following sample calculation uses only
Fahrenheit temperature.
EXAMPLE: Assume local codes require 10% outdoor air
during occupied conditions, outdoor air is 60° F
and return air is 75° F. Under these conditions,
what is the temperature of the mixed air?
or
Mixed air will be 73.5° F when OA is 60° F and RA is 75° F with
10 percent outdoor air entering the building.
NOTE: The W7340C model min position and DCV min must
be set in the field by the installer. See Section DCV
Min and Min Position Damper Set up.
Enthalpy Changeover (W7340 only)
Outdoor Enthalpy Changeover Setpoint (Single
Enthalpy Changeover)
The outdoor enthalpy changeover setpoint returns the outdoor
air damper to minimum position when enthalpy rises above its
setpoint. Enthalpy setpoint scale markings, located on the
device, are A, B, C, D and E. See Fig. 10 for the corresponding
control point.
Differential Enthalpy Changeover Setting
Differential enthalpy control uses:
— W7340A and B use two C7400A Enthalpy Sensors
connected to one logic module, or
— Two 10K NTC temperature sensors and two C7600C
Humidity Sensors connected to one logic module.
— W7340C uses C7400C Enthalpy Sensor(s) or
— Two 10K NTC temperature sensors and two C7600C
Humidity Sensors connected to one logic module.
With outdoor and return air sensors, the logic module
compares outdoor air to return air instead of to a setpoint as it
does for single enthalpy. The logic module selects the lower
enthalpy air (return or outdoor) for cooling; for example, when
outdoor air has lower enthalpy than return air, the outdoor air
damper opens to bring in outdoor air for free cooling.
NOTE: When using the W7340 for differential enthalpy, keep
the setpoint potentiometer set at D.
Exhaust Setpoint (W7340 only)
The exhaust setpoint determines when the exhaust fan will run
based on the damper position.
The logic module, as shipped from the factory, uses an
exhaust setpoint of 25%. When the damper position is greater
than 25% open (from fully closed), relay contact for the
exhaust fan is closed. When the damper position is below 22%
open, the relay is de-energized.
Control Configuration (W7340 only)
The W7340 can be configured for humidity or enthalpy
sensors. Configuration can be performed manually or over the
Modbus.
IMPORTANT
If only a temperature sensor is connected to the
W7340, the device will operate using dry bulb
changeover control.
To configure the W7340 manually:
1. Within the first three minutes after powering the device,
short the external minimum damper position terminals
(P-P1).
NOTE: The LED will go solid within five seconds of
shorting these terminals.
2. Maintaining the short for another five seconds causes
the LED to flash quick pulses (between off periods)
indicating the sensor configuration type:
a. Two quick pulses: Humidity.
b. Three quick pulses: Enthalpy.
3. To toggle the sensor configuration type:
a. Remove the short until the LED goes solid again.
b. Reapply the short for another five seconds.
NOTE: Once the short is removed for over 10 seconds,
the device saves the most recent configuration.
T
O
OA × ( ) T
R
RA × ( ) + T
M
=
T
O
T
R
– ( ) OA T
R
+ × T
M
=
0.1x6° F ( ) 0.9x75° F ( ) + 6.0° F 67.5° F + 73.5° F = =
60° F 75° F – ( ) 0.1 75° F + × 1.5 – 75° F + 73.5° F = =