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Table 3 -- EconoMi$er IV Sensor Usage

APPLICATION

ECONOMI$ER IV WITH OUTDOOR AIR

DRY BULB SENSOR

Accessories Required

None. The outdoor air dry bulb

sensor is factory installed.

CRTEMPSN002A00*

Differential Enthalpy

CO2 for DCV Control using a

wall-mounted CO2 sensor

CO2 for DCV Control using a

ECONOMI$ER IV WITH SINGLE

ENTHALPY SENSOR

Accessories Required

Outdoor Air Dry Bulb CRTEMPSN002A00*

Differential Dry Bulb (2) CRTEMPSN002A00*

Single Enthalpy HH57AC078 None. The single enthalpy sensor is

factory installed.

HH57AC078

and CRENTDIF004A00*

CRENTDIF004A00*

33ZCSENCO2

33ZCSENCO21-

and CRCBDIOX005A001-1-

33ZCASPCO2**

duct-mounted CO2 sensor

33ZCSENCO2

33ZCSENCO21- _)

and CRCBDIOX005A001-1-

33ZCASPCO2**

*CRENTDIF004A00 and CRTEMPSN002A00 accessories are used on many different base units. As such, these kits may contain parts that will

not be needed for installation.

1-33ZCSENCO2 is an accessory CO2 sensor.

_*33ZCASPCO2 is an accessory aspirator box required for duct-mounted applications.

1-1-CRCBDIOX005A00 is an accessory that contains both 33ZCSENCO2 and 33ZCASPCO2 accessories.

Demand Controlled Ventilation (DCV) -- When using the

EconoMi$er IV for demand control ventilation, there are some

equipment selection criteria which should be considered. When

selecting the heat capacity and cool capacity of the equipment,

the maximum ventilation rate must be evaluated for design

conditions. The maximum damper position must be calculated

to provide the desired fiesh air.

Typically file maximum ventilation rate will be about 5 to

10% more than the typical cfm required per pelion, using

normal outside air design criteria.

A proportional anticipatory strategy should be taken with

the following conditions: a zone with a large area, varied

occupancy, find equipment that cannot exceed the required

ventilation rate fit design conditions. Exceeding the required

ventilation rote means the equipment can condition air at a

maximum ventilation rate that is greater than the required

ventilation rate for maximum occupancy. A proportional-

anticipatory strategy will cause the fi'esh air supplied to

increase as the room CO2 level increases even though the CO2

set point has not been reached. By the time the CO2 level

reaches the set point, the damper will be at maximum ventila-

tion and should maintain the set point.

In order to have the CO2 sensor control the economizer

dmnper in this manner, first determine the damper voltage out-

put for minimum or base ventilation. Base ventilation is the

ventilation required to remove contaminants during unoccu-

pied periods. The following equation may be used to determine

the percent of outside air entering the building for a given

damper position. For best results them should be at least a

10 degree difference in outside and return-air temperatures.

(To x OA) + (TR x RA) = TM

To = Outdoor-Air Temperature

OA = Percent of Outdoor Air

TR = Return-Air Temperature

RA = Percent of Return Air

TM = Mixed-Air Temperature

Once base ventilation has been determined, set the mini-

mum damper position potentiometer to the correct position.

The same equation cfm be used to determine the occupied or

maximum ventilation rote to the building. For example, an output

of 3.6 volts to the actuator provides a base ventilation rote of 5%

and an output of 6.7 volts provides the maximum ventilation rate

of 20% (or base plus 15 cfin per pelion). Use Fig. 19 to deter-

mine the maximum setting of the CO2 sensol: For example, a

1100 ppm set point relates to a 15 cfln per pelion design. Use the

1100 ppm curve on Fig. 19 to lind the point when the CO2 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 for

the CO2 sensor should be 1800 ppm. The EconoMi$er IV con-

troller will output the 6.7 volts from file COo sensor to the actua-

tor when the CO2 concentration in the space is at 1100 ppm. The

DCV set point may be left fit 2 volts since the CO2 sensor voltage

will be ignored by the EconoMiSer IV controller until it rises

above the 3.6 volt setting of the minimum position potentiometel:

1 2 ... 21 22 23 24 25 26 27 28 29 30 31 ... 48 49

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