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46
DAMPER MOVEMENT — Damper movement from full open to
full closed (or vice versa) takes 2 1/2 minut es.
THERMOSTATS — TheEconomizer control works with conven-
tionalthermostatsthathaveaY1 (coolstage1),Y2 (coolstage2),W1
(heatstage1),W2(heatstage2),andG(fan).TheEconomizercontrol
doesnotsupportspacetemperaturesensors.Connectionsaremadeat
the thermostat terminal connection board located inthe main control
box.
OCCUPANCY CONTROL — The factory default configuration
for the Economizer control is occupied mode. Occupied status is
provided bytheblack jumper fromterminal TR to terminal N.When
unoccupied mode is desired, install a field supplied time clock
functioninplaceofthejumperbetweenTR and N.SeeFig.45.When
the timeclock contacts are closed, the Economizer control will be in
occupiedmode.When thetimeclockcontactsareopen(removingthe
24--v signalfrom terminalN),the Economizer willbe in unoccupied
mode.
DEMAND CONTROLLED VENTILATION (DCV)—When
using the Economizer for demand controlled ventilation, there are
someequipmentselectioncriteriawhich shouldbeconsidered.When
selecting the heat capacity and cool capacity of the equi pment, the
maximum ventilation rate must be evaluated for design conditions.
The maximum damper position must be calculated to provide the
desired freshair.Typically themaximumventilationratewill beabout
5 to 10% more than the typical CFM required per person, using
normal outside air design criteria. An exponential anticipatory
strategy should be taken with the following conditions: a zone with
alargearea,variedoccupancy,and equipment thatcannotexceed the
requi redventilation rateat design condition s.Exceeding therequired
ventilation rate means the equipment canconditionair ata maximum
ventilation rate that is greater than the required ventilation rate for
maximum occupancy. An exponential--anticipatory strategy will
causethefreshairsuppliedtoincreaseastheroomCO
2
levelinc reases
even though the CO
2
set point has not been reached. By the time the
CO
2
level reaches the set poi nt, the damper will be at maximum
ventilationandshould maintainthesetpoint.InordertohavetheCO
2
sensorcontroltheeconomizer damper in thismanner, firstdetermine
the damper voltage output for minimum or base ventilation. Base
ventilation is t he ventilationrequired to removecontaminantsduring
unoccupied periods. The following equation may be used to
determinethepercentof outside--airentering thebuilding fora given
damper position. For best results there should be at least a 10_F
(12.2_C) difference in outside and return--air temperatures.
(T
o
x OA/100) + (T
R
x RA/100) = T
M
T
O
= Outdoor-- Air Temperature
OA = Percent of Outdoor Air
T
R
= Return--Air Te mperature
RA = Percent of Return Air
T
M
= Mixed--Air Temperature
Oncebase ventilation has been determined, settheminimum damper
positionpotentiometer t othecorrectposition. The sameequationcan
be used to determinetheoccup ied ormaxi mum ven tilation rateto the
building.For example,anoutput of3.6 voltsto the actuatorprovides
a base ventilation rate of 5% and an output of 6.7 volts provides the
maximum ventilationrate of 20% (or baseplus 15 CFM per person) .
Use Fig. 43 to determinethemaximum setting oftheCO
2
sensor.For
example,a1100ppm setpointrelatesto a15 CFMper person design.
Use the 1100 ppm curve on Fig. 43 to find the point when the CO
2
sensor output will be 6.7 volts. Line up the point on the graph with
the left side of the chart to determine that the range configuration f or
the CO
2
sensorshould be1800 ppm.TheEconomizer controllerwill
outputthe6.7voltsfromtheCO
2
sensortotheactuatorwhen theCO
2
concentration in the space is at 1100 ppm.
The DCV set point may b e left at 2 volts since the CO
2
sensor
voltage will be ignored by the Economizer controller until it rises
above the 3.6 volt setting of the minimum position potentiometer.
Once the fully occupied da mper pos ition has been determined, set
the maximum damper demand control ventilation pot entiometer to
this po sition. Do not set to the maxi mum position as t his can result
in ove r ventilation t o the space and potential high--humidity levels.
CO
2
SENSOR CONFIGURATION — The CO
2
sensor has preset
standa rd voltagesettingsthatcan beselected any time a fterthesensor
is powered up. Use setting 1 or 2 for equipment. See Table 16.
1. Press Clear and Mode buttons. Hold at least 5 seconds until
the sensor enters the Edit mode.
2. Press Mode twice. The STDSET Menu will appear.
3. Use the Up/Down button to select the preset number. See
Table 16.
4. Press Enter to lock in the selection.
5. Press Mode to exit and resume normal operation.
The custom settings of the CO
2
sensor can be changed anytime
after the sensor is energized. Follow the steps below to change the
nonstandard settings:
1. Press Clear and Mode buttons. Hold at least 5 seconds until
the sensor enters the Edit mode.
2. Press Mode twice. The STDSET Menu will appear.
3. Use the Up/Down button to toggle to the NONSTD menu
and press Enter.
4. Use the Up/Down button to toggle through each of the nine
variables, starting with Altitude, until the desired setting is
reached.
5. Press Mode to move through the variables.
6. Press Enter to lock in the selection, then press Mod e to
continue to the next variable.
DEHUMIDIFICATION OF FRESH AIR WITH DCV
CONTROL—Inform ation from ASHRAE i ndicates that the largest
humidity load on any zone is the fresh air introduced. For some
applications, an energy recovery unit can be added to reduce the
moisturecontentofthefresh airbeingbroughtintothebuildingwhen
the enthalpy is high. In most cases, the normal heating and cooling
processes are more than adequate to remove the humidity loads for
most comm ercial app lications.
If normal rooftop heating and cooling operation is not adequate for
the outdoor humidity level, an energy recovery unit and/or a
dehumidification option should be considered.
607C-- --A