Bryant 558F Outside Air Temperature, Changeover Set Points, Return Air Temperature or Enthalpy

Differential Dry Bulb Control

For differential dry bulb control the standard outdoor dry bulb sensor is used in conjunction with an additional acces- sory dry bulb sensor (part number CRTEMPSN002A00). The accessory sensor must be mounted in the return airstream. See Fig. 30. Wiring is provided in the EconoMi$er IV wiring harness. See Fig. 23.

In this mode of operation, the outdoor-air temperature is compared to the return-air temperature and the lower tem- perature airstream is used for cooling. When using this mode of changeover control, turn the enthalpy set point potentiom- eter fully clockwise to the D setting. See Fig. 28.

Outdoor Enthalpy Changeover

For enthalpy control, accessory enthalpy sensor (part num- ber HH57AC078) is required. Replace the standard outdoor dry bulb temperature sensor with the accessory enthalpy sensor in the same mounting location. See Fig. 17. When the outdoor air enthalpy rises above the outdoor enthalpy changeover set point, the outdoor-air damper moves to its minimum position. The outdoor enthalpy changeover set point is set with the outdoor enthalpy set point potentiome- ter on the EconoMi$er IV controller. The set points are A, B, C, and D. See Fig. 31. The factory-installed 620-ohm jumper must be in place across terminals SR and SR+ on the EconoMi$er IV controller. See Fig. 17 and 32.

19

	18	LED ON
				D
	17
	16		LED OFF		LED ON
						C
	15
mA	14				LED OFF			LED ON
									B
	13
	12							LED OFF		LED ON
												A
	11
	10										LED OFF
	9												100
	40	45	50	55	60	65	70	75	80	85	90	95
					DEGREES FAHRENHEIT

Fig. 29 — Outside Air Temperature

Changeover Set Points

Differential Enthalpy Control

For differential enthalpy control, the EconoMi$er IV con- troller uses two enthalpy sensors (HH57AC078 and CRENTDIF004A00), one in the outside air and one in the return air duct. The EconoMi$er IV controller compares the outdoor air enthalpy to the return air enthalpy to determine EconoMi$er IV use. The controller selects the lower enthalpy air (return or outdoor) for cooling. For example, when the out- door air has a lower enthalpy than the return air, the EconoMi$er IV opens to bring in outdoor air for free cooling.

Replace the standard outside air dry bulb temperature sensor with the accessory enthalpy sensor in the same mounting loca- tion. See Fig. 17. Mount the return air enthalpy sensor in the return air duct. See Fig. 30. Wiring is provided in the EconoMi$er IV wiring harness. See Fig. 23. The outdoor enthalpy changeover set point is set with the outdoor enthalpy set point potentiometer on the EconoMi$er IV controller. When using this mode of changeover control, turn the enthalpy set point potentiometer fully clockwise to the D setting.

Indoor Air Quality (IAQ) Sensor Input

The IAQ input can be used for demand control ventilation control based on the level of CO2 measured in the space or return air duct.

Mount the accessory IAQ sensor according to manufacturer specifications. The IAQ sensor should be wired to the AQ and AQ1 terminals of the controller. Adjust the DCV potentiome- ters to correspond to the DCV voltage output of the indoor air quality sensor at the user-determined set point. See Fig. 33.

If a separate field-supplied transformer is used to power the IAQ sensor, the sensor must not be grounded or the EconoMi$er IV control board will be damaged.

Exhaust Set Point Adjustment

The exhaust set point will determine when the exhaust fan runs based on damper position (if accessory power exhaust is installed). The set point is modified with the Exhaust Fan Set Point (EXH SET) potentiometer. See Fig. 28. The set point represents the damper position above which the exhaust fans will be turned on. When there is a call for exhaust, the EconoMi$er IV controller provides a 45 ± 15 second delay before exhaust fan activation to allow the dampers to open. This delay allows the damper to reach the appropriate position to avoid unnecessary fan overload.

Minimum Position Control

ECONOMI$ER IV

ECONOMI$ER IV

CONTROLLER

GROMMET

RETURN AIR

SENSOR

RETURN DUCT (FIELD-PROVIDED)

There is a minimum damper position potentiometer on the EconoMi$er IV controller. See Fig. 28. The minimum damper position maintains the minimum airflow into the building during the occupied period.

When using demand ventilation, the minimum damper posi- tion represents the minimum ventilation position for VOC (volatile organic compound) ventilation requirements. The maximum demand ventilation position is used for fully occu- pied ventilation.

When demand ventilation control is not being used, the min- imum position potentiometer should be used to set the occu- pied ventilation position. The maximum demand ventilation position should be turned fully clockwise.

Adjust the minimum position potentiometer to allow the minimum amount of outdoor air, as required by local codes, to enter the building. Make minimum position adjustments with at least 10 F temperature difference between the out- door and return-air temperatures.

Fig. 30 — Return Air Temperature or Enthalpy

Sensor Mounting Location

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