Bryant 580J*08--14D, F appendix Differential Enthalpy Control, Return Air Enthalpy Sensor

The enthalpy control receives the outdoor air enthalpy from the outdoor air enthalpy sensor and provides a dry contact switch input to the RTU-MP controller. A closed contact indicates that outside air is preferred to the return air. An open contact indicates that the economizer should remain at minimum position.

Differential Enthalpy Control

Differential enthalpy control is provided by sensing and comparing the outside air and return air enthalpy conditions. Install the outdoor air enthalpy control as described above. Add and install a return air enthalpy sensor.

Return Air Enthalpy Sensor

Mount the return-air enthalpy sensor (HH57AC078) in the return-air duct. The return air sensor is wired to the enthalpy controller (HH57AC077). (See Fig. 51.)

ENTHALPY CONTROLLER				RED		S (OUTDOOR
						+	AIR
				BRN
	B C	TR	TR1		BLK		ENTHALPY
A							SENSOR)
	D	SO	+		RED
		SR	+			S (RETURN AIR
						+	ENTHALPY
		2	3				SENSOR)
			1		GRAY/ORN
	LED					WIRE HARNESS
					GRAY/RED	IN UNIT

NOTES:

1.Remove factory-installed jumper across SR and + before connecting wires from return air sensor.

2.Switches shown in high outdoor air enthalpy state. Terminals 2 and 3 close on low outdoor air enthalpy relative to indoor air enthalpy.

3.Remove sensor mounted on back of control and locate in outside air- stream.

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Fig. 51 - Outside and Return Air Enthalpy

Sensor Wiring

To wire the return air enthalpy sensor, perform the following:

1.Use a 2-conductor, 18 or 20 AWG, twisted pair cable to connect the return air enthalpy sensor to the enthalpy controller.

2.At the enthalpy control remove the factory-installed resistor from the (SR) and (+) terminals.

3.Connect the field-supplied RED wire to (+) spade connector on the return air enthalpy sensor and the (SR+) terminal on the enthalpy controller. Connect the BLK wire to (S) spade connector on the return air enthalpy sensor and the (SR) terminal on the enthalpy controller.

NOTE: The enthalpy control must be set to the “D” setting for differential enthalpy control to work properly.

The enthalpy control receives the indoor and return enthalpy from the outdoor and return air enthalpy sensors and provides a dry contact switch input to the RTU-MP controller. A closed contact indicates that outside air is preferred to the return air. An open contact indicates that the economizer should remain at minimum position.

Indoor Air Quality (CO2 Sensor)

The indoor air quality sensor accessory monitors space carbon dioxide (CO2) levels. This information is used to monitor IAQ levels. Several types of sensors are available, for wall mounting in the space or in return duct, with and without LCD display, and in combination with space temperature sensors. Sensors use infrared technology to measure the levels of CO2 present in the space air.

The CO2 sensors are all factory set for a range of 0 to 2000 ppm and a linear mA output of 4 to 20. Refer to the instructions supplied with the CO2 sensor for electrical requirements and terminal locations. See Fig. 52 for typical CO2 sensor wiring schematic.

580J

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Fig. 52 - Indoor/Outdoor Air Quality (CO2) Sensor

(33ZCSENCO2) - Typical Wiring Diagram

To accurately monitor the quality of the air in the conditioned air space, locate the sensor near a return-air grille (if present) so it senses the concentration of CO2 leaving the space. The sensor should be mounted in a location to avoid direct breath contact.

Do not mount the IAQ sensor in drafty areas such as near supply ducts, open windows, fans, or over heat sources. Allow at least 3 ft (0.9 m) between the sensor and any corner. Avoid mounting the sensor where it is influenced by the supply air; the sensor gives inaccurate readings if the supply air is blown directly onto the sensor or if the supply air does not have a chance to mix with the room air before it is drawn into the return airstream.

Wiring the Indoor Air Quality Sensor

For each sensor, use two 2-conductor 18 AWG (American Wire Gauge) twisted-pair cables (unshielded) to connect the separate isolated 24 vac power source to the sensor and to connect the sensor to the control board terminals.

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