W6215, W7215, W7460 ECONOMIZER LOGIC MODULES
7
63-2544—3
Fig. 5. Potentiometer and LED locations.
Adjusting Minimum and Maximum Positions
The minimum position potentiometer maintains the minimum
outdoor air flow into the building during occupied period. The
maximum position potentiometer allows the installer to limit
the amount of outdoor air flow into the building, when the ISI
overrides the mixed air sensor. Setting the maximum position
of the damper prevents the introduction of large amounts of
hot or cold air into the space.
IMPORTANT
With the maximum position set below the minimum
position, the minimum position overrides the
maximum position (negating most functions of the
logic module, as the damper cannot move).
NOTES:
—
When the mixed air sensor takes control, it
overrides the maximum position potentiometer.
—
If mixed air temperature drops to 40°F, the mixed
air sensor overrides the ISI and closes the damper
to minimum position to protect from freezing the
hot or chilled water coils. Control returns to normal
once the mixed air temperature rises to 43°F.
Minimum Position Adjustment
For detailed assistance in minimum position selection
reference the Economizer Application Guide (form 63-8594)
Ventilation section. The following provides basic guidelines for
minimum position selection and adjustment:
IMPORTANT
Adjust the minimum position potentiometer to allow
the minimum amount of outdoor air, as required by
local codes, to enter the building.
NOTE: Make minimum position adjustments with at least a
10°F [6°C] temperature difference between outdoor
and return air.
1.
Calculate the appropriate mixed air temperature, see
Equation 1.
2.
Disconnect mixed air sensor from terminals T and T1.
3.
Ensure that either the factory-installed jumper is in
place across terminals P and P1 or, of remote damper
position is required, that it is wired according to Fig. 4
and turned fully clockwise.
4.
Connect 24 Vac across terminals TR and TR1.
5.
Carefully adjust the potentiometer on the face of the
device with a small screwdriver until the mixed air
temperature reaches the calculated value.
NOTE: Ensure that the sensed air is well mixed.
Equation 1. Formula to aid in minimum position
adjustment.
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
IMPORTANT
This procedure requires use of a quality thermometer
capable of reading to 0.5°F [0.25°C].
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?
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.
Maximum Position Adjustment
1.
Disconnect mixed air sensor from terminals T and T1
and short terminals T and T1.
2.
Make sure either the factory-installed jumper is in place
across terminals Q and Q1 or, if remote damper position
is required, that it is wired according to Fig. 4 and turned
fully clockwise.
3.
Connect 24 Vac across terminals TR and TR1.
4.
Adjust the potentiometer on the face of the device with a
screwdriver for desired maximum position.
Enthalpy Changeover
Outdoor Enthalpy Changeover Setpoint
The outdoor enthalpy changeover setpoint returns the outdoor
air damper to minimum position when enthalpy rises above its
setpoint. Enthalpy setpoint scale markings, located in the
device, are A, B, C, and D. See Fig. 7 for the corresponding
control point. The factory-installed 620-ohm jumper must be in
place across terminals S
R
and +.
24VAC
TR Hot
24VAC
Com
24VAC
Hot
2-10V
OUT
Free
Cool
Unit
Control
Exhaust
Fan
Indoor
Fan
Mininum
Position
Maximum
Position
Open
Free Cool
Closed
ISI
Exhaust
Exhaust
Set Pt
0%
100%
50%
2
6
10
ISI
Set Pt
A
B
C
D
TR1
Com
+
+
5
2
4
3
1
T1
T
P1
P
Q1
Q
AQ1
AQ
SD1
SD
AC1
AC
PG1
PG
So
Sr
W7215A
+
–
ENTHALPY
CHANGEOVER
SETPOINT
MINIMUM
DAMPER
POSITION
SETTING
MAXIMUM
DAMPER
POSITION
SETTING
LED LIGHTS
WHEN
OUTDOOR
AIR IS
SUITABLE
FOR FREE
COOLING
INDOOR AIR
SENSOR
SETPOINT
LED LIGHTS
WHEN INDOOR
SENSOR INPUT
IS ABOVE
SETPOINT
EXHAUST
FAN
SETPOINT
LED LIGHTS WHEN EXHAUST IS ON
Q
Q
Q
M11787A
+
–
T
O
OA
×
(
)
T
R
RA
×
(
)
+
T
M
=
0.1 60°F
×
(
)
0.9 75°F
×
(
)
+
6.0°F 67.5°F
+
73.5°F
=
=