Outside air enthalpy — EconoMi$erIV will be enabled based on the outside air enthalpy curves as shown in the EconoMi$erIV Changeover diagram below. The A, B, C, and D curves shown have been in use for many years and have been included as part of the latest ASHRAE 90.1 energy efficiency code. The curves are designed to take into consideration both outdoor temperature and humidity. These curves are used to set up the EconoMi$erIV control- ler to use the EconoMi$erIV for free cooling when the condi- tions to the left of the curve exist. When the conditions are to the right of the curve, then outdoor air cooling will not be used and the outdoor air damper position will be set at the minimum position.

Deciding which curve is used is a function of the outdoor cli- mate and the type of economizer utilized. Since EconoMi$erIV is a fully integrated economizer, the range where outdoor air can be utilized for free cooling is expanded and the A and B curves may be used. The con- trol point table in the EconoMi$erIV Changeover diagram below provides assistance for whether the A and B curves

will be suitable. In general terms, a hot and humid climate may be a reason not to use the A curve, while a cooler cli- mate might be more applicable for using the A or B curve.

The EconoMi$erIV has expanded outdoor air capability. For a changeover economizer which cannot utilize simulta- neous economizer and compression, both A and B curves would potentially be undesirable since the temperature and humidity levels are too high without compression assistance to provide effective cooling. Therefore, most changeover economizers utilize the D curve.

Differential enthalpy — The EconoMi$erIV will be enabled based on the comparison of the enthalpy of the return air and outside air. When the outside air enthalpy is lower than the return side, the unit will be in economizer mode.

Using the EconoMi$erIV controller for implementing differ- ent control changeover strategies requires the use of differ- ent combinations of dry bulb and humidity sensors as outlined in the EconoMi$erIV Sensor Usage table.

ECONOMI$ERIV SENSOR USAGE

 

ECONOMI$ERIV WITH OUTDOOR AIR

ECONOMI$ERIV WITH SINGLE

APPLICATION

DRY BULB SENSOR

ENTHALPY SENSOR

 

Accessories Required

Accessories Required

Outdoor Air Dry Bulb

None. The outdoor air dry bulb sensor is factory installed.

CRTEMPSN002A00*

Differential Dry Bulb

CRTEMPSN002A00*

(2) CRTEMPSN002A00*

Single Enthalpy

HH57AC078

None. The single enthalpy sensor is factory installed.

Differential Enthalpy

HH57AC078

CRENTDIF004A00*

and

 

CRENTDIF004A00*

 

CO2 for DCV Control using a

CGCDXSEN004A00

Wall-Mounted CO2 Sensor

 

 

CO2 for DCV Control using a

CGCDXSEN004A00†

and

 

Duct-Mounted CO2 Sensor

 

CGCDXASP001A00**

 

*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.

†CGCDXSEN004A00 is an accessory CO2 sensor.

**CGCDXASP001A00 is an accessory aspirator box required for duct-mounted applications.

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Bryant 549C manual ECONOMI$ERIV Sensor Usage, Differential Dry Bulb