ECONOMIZER
Ventilation Air
Outdoor Air for Free Cooling
Mixes Outdoor Air and Return Air
ECONOMIZER
Two sets of dampers, connected to an actuator, are opened and
closed to provide more or less outside air, based on the
demand for cooling, and the condition of the air with respect
to it’s heat content.
COMPONENTS
W7459 LOGIC MODULE
Responds to single
or dual enthalpy
sensors
Discharge air sensor
Used on “standard”
economizers
Does not have IAQ
features
W7212 IAQ LOGIC MODULE
The W7212 control will
modulate the
economizer actuator in
response to a variety of
inputs. Not all terminals
shown are used when
this module is applied
to all units.
ENTHALPY SENSOR
HONEYWELL C7400
Enthalpy is a measure
of total heat.
It’s output is 4-20
milliamps.
Two are used when the
application calls for
dual enthalpy.
C7650 AMBIENT SENSOR
DRY BULB AMBIENT
TEMPERATURE SENSOR
Responds only to
temperature (no humidity)
Can be used for “dual”
temp control with 1 in
return and 1 in outside air
4-20 milliamps output
Mounted in
outdoor
hood
Slide 105
ACTUATOR
HONEYWELL M7415
TR –TR1 = 24vac
power
T-T1 = Mixed air
sensor
P1-P – Minimum
position
90 degree travel
IAQ CO2 SENSOR
model 2AQ04700324.
Room sensor for CO2
monitoring
If the unit has a W7459
Economizer Control, install a
Honeywell Q769C Potentiometer
signal converter
0-10 VDC Potentiometer
Signal Converter (Honeywell
Q769C)Q769C BOX
.
IAQ CO SENSOR WIRING
WITH W7459 MODULE
Q769C
Converter
SEQUENCE OF OPERATION
SEQUENCE OF OPERATION
Economizers should
always be installed
with a 2-stage
thermostat
Provides both
economizer cooling
and mechanical
cooling as needed
LOGIC MODULES
W7459 LOGIC MODULE
CONNECTIONS
TR – TR1 = 24 vac power supply
So - +o = Outside Air Enthalpy
Sensor
Sr - +r = Return Air Enthalpy
Sensor. Not used in single
enthalpy applications (620 ohm
resister is put in it’s place)
N = 24vac input to force the
actuator to minimum position
1 = 1st stage cooling input
2 = 1st stage mechanical cooling
output
3 = 2nd stage cooling input
4 = 2nd stage mech. Cooling output
T & T1 = Mixed Air Sensor
P & P1 = Remote Min Position
W7459 MODULE ADJUSTMENTS
Enthalpy set point
• Sets where
economizer will open
in relation to
temperature &
Humidity
Minimum position
potentiometer
• Used to set % of
outside air for
ventilation
W7459 LOGIC MODULE LED
LED
• Lit whenever unit is in
“free cooling” mode
W7212 LOGIC MODULE INPUTS
TR & TR1 - Provides 24vac to the control.
Nothing happens unless these terminals are
powered
N - 24vac at this terminal indicates occupied
mode. When TR & TR1 are powered, 24vac at
this terminal will force the actuator to move
to its minimum position
P1 & P - This circuit is jumpered at the
factory, but can be used with an optional
minimum position potentiometer. When
these terminals are jumpered, the module will
control the minimum position of the outdoor
air damper using the on-board adjustment.
T1 & T - These terminals are used for the
discharge air sensor. If the free cool LED is
lit and a call for stage 1 cooling has been
initiated, then the module will vary the 210vdc output to the actuator to maintain the
discharge air temperature to between 50º and
56º.
W7212 ADJUSTMENTS
Min Pos - This setting is adjustable
from 2 to 10 vdc. When the module
has voltage at Tr1, Tr and N, this pot
will control the output voltage
supplied to the actuator for minimum
position.
DCV Max & DCV Set - These two pots
are used to position the dampers in
response to an input from an
optional CO2 sensor placed across
the AQ1 & AQ terminals.
Enthalpy Setpoint - This adjustment
pot, marked by letters A B C D, is
used to by the module to determine
under what conditions the module
should allow free cooling.
W7212 LED’S
ExH - If this LED is energized, it
indicates the module is in exhaust
mode. Contacts EF & EF1 will be
closed.
DCV - If this LED is energized, it
indicates the module is in demand
ventilation mode. The IAQ sensor is
providing a dc voltage higher than
the DVC Setpoint.
Free Cool - If this LED is energized,
it indicates the module is in free
cooling mode. When using a single
outdoor enthalpy sensor, this
indicates the enthalpy sensor is
measuring an enthalpy level below
the corresponding A, B, C, D setpoint
W7212 EXHAUST MODE
This mode of operation is used when an optional power
exhaust is installed on the unit.
If the voltage output to the actuator exceeds the adjustable
setpoint, the ExH LED is energized and the normally open
contacts between terminals EF & EF1 are closed. At this
point, two things will happen:
• The coil for relay CR is energized. Its normally closed
contacts open, locking out the second stage compressor
• The coil for relay ER is energized. Its normally open
contacts close, energizing the power exhaust motor.
NOTE: The 45 (+/- 15) second delay in closing the EF &
EF1 contacts allows the actuator to drive to the exhaust fan
setpoint.
W7212 COOLING MODE
In a single enthalpy application, when the logic module
senses 24 vac at terminal 1, it compares its enthalpy
setpoint (A, B, C or D) to the milliampere signal being sent
by the C7400 sensor to terminals So+ & So.
If the enthalpy of the air passing over the sensor is below
the setpoint, the free cooling LED is energized and the
voltage output to the actuator is now determined by the
discharge air sensor.
As the discharge air sensor resistance goes up (an
indication the air temperature is dropping) the voltage
output to the actuator goes down. As the sensor
resistance goes down (indicating the air temperature is
rising), the voltage output to the actuator goes up.
W7212 DEMAND VENTILATION
This mode of operation allows the logic module to
respond to a 2 -10 vdc input on terminals AQ1 & AQ. There
are a variety of sensors available, depending on which
contaminant you want to control. The most frequently used
sensor controls carbon dioxide (CO2) so we’ll use that to
illustrate an example.
If the carbon dioxide level, in the space where the sensor is
located, begins to increase, the sensor sends a 2 -10 vdc
signal to the AQ1 & AQ terminals on the logic module.
If the output voltage from the CO2 sensor is higher than the
DCV setpoint, then the demand ventilation mode will begin
to drive the actuator open. However the voltage output to
the actuator is limited by the DCV Max pot setpoint.
W7212 FREEZE PROTECTION
During demand ventilation mode, if the discharge air
temperature drops below 45º, the voltage output to the actuator is
reduced to the minimum position pot setpoint. This was
designed into the W7212 to protect the coil and building from
freezing. .
ECONOMIZER SETTINGS
Minimum Position Adjustment
CORRECT MINIMUM POSITION
SETPOINT
Measure the temperature of the outside air. Multiply it by
the percentage of outside air required. Measure the
temperature of the return air, then multiply it by the
percentage of return air required. Add the two remainders.
That sum is the temperature of the mixed air.
CORRECT MINIMUM POSITION
SETPOINT
(OAT X OA%) + (RAT X RA%) = MAT
WHERE:
OAT = Outdoor Air Temperature
OA% = Percentage of Outdoor Air Required
RAT – Return Air Temperature
RA% = Percentage of Return Air Required
MAT = Mixed Air Temperature
CORRECT MINIMUM POSITION
SETPOINT
(OAT X OA%) + (RAT X RA%) = MAT
EXAMPLE: The building requires 15% of outside air. The
outdoor air is 50º and the return air is 78º.
50º outside air x 15% = 7.5º
78º return air x 85% = 66.3º
7.5º + 66.3º = 73.9º
Therefore, our mixed air temperature, when the minimum
position damper is set for 15%, will be 74º.
Note: For greatest accuracy, this method requires a minimum
temperature difference between OA & RA of 15 degrees
TROUBLE SHOOTING
SAFETY
You've carefully thought out all the
angles.
You've done it a thousand times.
It comes naturally to you.
You know what you're doing.
Its what you've been trained to do.
Nothing could possibly go wrong,
Right?
TESTING THE MOD MOTOR
With the module
removed
• Apply 24 VAC to TR &
TR1
• Jump T & T1
• Jump P & P1
Motor should drive open
If not, remove the
linkage and try again
TESTING THE ENTHALPY SENSOR
12.30
Normal reading
between 4 and 20
milliamps
+
-
TESTING
C7400 ENTHALPY
SENSOR
Determine the dry bulb temperature and relative humidity of the air in the
area where the sensor in located.
Insert a dc amp meter in series with the So or Sr (whichever sensor is being
tested), and compare with the mA output current shown on the attached
chart.
TESTING THE ENTHALPY
SENSOR
Jumper R to G on the unit control board. This will provide 24
volts to TR & TR1 on the logic module
Insert a DC ammeter in series with either SO or SR,
depending on which sensor is being checked
Make sure to connect the positive lead from the meter to S on
the sensor and the negative lear to either the wire or S on the
control
Meter should indicate a reading between 4 to 20 mA if the
sensor is operating properly
If the meter indicates “0”, the sensor may be wired
backwards.
If the reading is out of the 4 to 20 mA range --- replace the
sensor.
TESTING THE ECONOMIZER LOGIC
MODULE
Apply 24
VAC Power
Supply
•Jumper TR to 1
•Jumper T to T1
•Jumper P to P1
•Apply 24 VAC to TR and TR1
•Remove enthalpy sensor and
leave resistor in place
L.E.D. is off, motor to minimum position
TESTING THE ECONOMIZER LOGIC
MODULE
Apply 24
VAC Power
Supply
•Jumper TR to 1
•Jumper T to T1
•Jumper P to P1
•Apply 24 VAC to TR and
TR1
•Remove resistor from SR
&+
•Jumper So & +
L.E.D. is on, motor drives open
TESTING THE LOGIC
MODULE
Disconnect power at TR & TR1. Remove the jumper across P & P1.
Jumper TR to terminal 1 on the logic module
Jumper T & T1
Remove leads from outdoor sensor at SO and +. Leave the factory
installed 620 ohm resistor across SR & +.
Apply 24 volts to TR & TR1 by energizing the blower circuit
When power is applied, the L.E.D. should be OFF on the
module and the dampers should be in the CLOSED position.
Next, shut off power to the unit. Disconnect the 620 ohm
resistor across SR & +.
When power is reapplied, the L.E.D. should be ON and the
dampers should drive to the FULL OPEN position
ELECTRICAL
TROUBLESHOOTING
To electrically check the “staging relays” in the
module, perform the ELECTRICAL
TROUBLESHOOTING PROCEDURE as outlined on
the following slide.
To check out the sensors and L.E.D. on the
module, use the chart marked “QUICK CHECK OUT
CHART”.
To BY-PASS the economizer, refer to the wiring
diagram slide in this section
Single Enthalpy Economizer Checkout
T - T1
SO - +
SR - +
L.E.D.
Outside Air Damper Position
Jumper
Jumper
620 ohm R
On
Full Open
Jumper
Open
620 ohm R
Off
Closes to Minimum Setting
Open
Open
620 ohm R
Off
Closes to Minimum Setting
Open
Jumper
620 ohm R
On
Closes to Minimum Setting
Dual Enthalpy Economizer Checkout
T - T1
SO - +
SR - +
L.E.D.
Outside Air Damper Position
Jumper
Jumper
Jumper
On
Full Open
Jumper
Jumper
Open
Off
Closes to Minimum Setting
Jumper
Open
Jumper
Off
Closes to Minimum Setting
Open
Jumper
Open
Off
Closes to Minimum Setting
Open
Jumper
Jumper
Off
Closes to Minimum Setting
SIMULATING LOW ENTHALPY
•Reconnect 620 ohm
resistor to SR & +
•Connect 1.2K ohm
checkout resistor to SO
&+
•Turn enthalpy setpoint
pot to “A”.
L.E.D. turns on,
motor drives open
SIMULATING HIGH ENTHALPY
•Turn enthalpy setpoint
pot to “D”.
L.E.D. turns off, motor
drives to minimum
DISCHARGE AIR SENSOR
A negative coefficient
resister.
3K at 77 Degrees F
DISCHARGE AIR SENSOR