Bryant 581A operation manual XII. Operating Sequence, Cooling, Units Without Economizer

The same equation can be used to determine the occupied or maximum ventilation rate to the building. For example, an output of 3.6 volts to the actuator provides a base ventilation rate of 5% and an output of 6.7 volts provides the maximum ventilation rate of 20% (or base plus 15 cfm per person). Use Fig. 29 to determine the maximum setting of the CO2 sensor. For example, a 1100 ppm set point relates to a 15 cfm per person design. Use the 1100 ppm curve on Fig. 29 to find 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 deter- mine that the range configuration for the CO2 sensor should be 1800 ppm. The EconoMi$er IV controller will output the

6.7volts from the CO2 sensor to the actuator when the CO2 concentration in the space is at 1100 ppm. The DCV set point may be left at 2 volts since the CO2 sensor voltage will be ignored by the EconoMi$er IV controller until it rises above the 3.6 volt setting of the minimum position potentiometer.

Once the fully occupied damper position has been deter- mined, set the maximum damper demand control ventilation potentiometer to this position. Do not set to the maximum position as this can result in over-ventilation to the space and potential high-humidity levels.

CO2 Sensor Configuration

The CO2 sensor has preset standard voltage settings that can be selected anytime after the sensor is powered up. See Table 29.

Use setting 1 or 2 for Bryant equipment. See Table 29.

1.Press Clear and Mode buttons. Hold at least 5 sec- onds 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 29.

4.Press Enter to lock in the selection.

5.Press Mode to exit and resume normal operation.

The custom settings of the CO2 sensor can be changed any- time after the sensor is energized. Follow the steps below to change the non-standard settings:

1.Press Clear and Mode buttons. Hold at least 5 sec- onds 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 Mode to continue to the next variable.

Dehumidification of Fresh Air with DCV Control

Information from ASHRAE (American Society of Heating, Refrigeration, and Air Conditioning Engineers) indicates 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 moisture content of the fresh air being brought into the building when the enthalpy is high. In most cases, the normal heating and cooling processes are more than adequate to remove the humidity loads for most commercial applications.

If normal rooftop heating and cooling operation is not adequate for the outdoor humidity level, an energy recovery and/or a dehumidification option should be considered.

XII. OPERATING SEQUENCE

A. Cooling, Units Without Economizer

When the thermostat calls for one stage of cooling, Y1 and G are energized. The indoor-fan contactor (IFC) and compres- sor contactor(s) (C.A1 and C.B1 on three-compressor units or C.A1 only on two-compressor units), and outdoor-fan contac- tors (OFC1 and OFC2 when outdoor temperature is above FCS [fan cycling switch] setting) are energized and the indoor-fan motor, compressor(s) (A1 and B1 on three- compressor units or A1 only on two-compressor units), and outdoor fans controlled by OFC1 are started. If the outdoor temperature is above the setting of the low temperature switch, the outdoor fans controlled by OFC2 are also started.

If more cooling is required, the thermostat will call for a sec- ond stage of cooling, energizing Y2. This will allow relay CR1 to energize, which in turn energizes the compressor contactor (C.C1 on three-compressor units or C.B1 on two-compressor units). The second stage compressor (C1 on three-compressor units or B1 on two-compressor units) is then started.

Table 29 — CO2 Sensor Standard Settings

			VENTILATION	ANALOG	CO2	OPTIONAL	RELAY
SETTING	EQUIPMENT	OUTPUT	RATE		CONTROL RANGE	RELAY SETPOINT	HYSTERESIS
				OUTPUT
			(cfm/Person)		(ppm)	(ppm)	(ppm)
1		Proportional	Any	0-10V	0-2000	1000	50
				4-20 mA
2	Interface w/Standard	Proportional	Any	2-10V	0-2000	1000	50
	Building Control System			7-20 mA
3		Exponential	Any	0-10V	0-2000	1100	50
				4-20 mA
4		Proportional	15	0-10V	0-1100	1100	50
				4-20 mA
5		Proportional	20	0-10V	0- 900	900	50
				4-20 mA
	Economizer
6		Exponential	15	0-10V	0-1100	1100	50
				4-20 mA
7		Exponential	20	0-10V	0- 900	900	50
				4-20 mA
8	Health & Safety	Proportional	—	0-10V	0-9999	5000	500
				4-20 mA
9	Parking/Air Intakes/	Proportional	—	0-10V	0-2000	700	50
	Loading Docks			4-20 mA

LEGEND

ppm — Parts Per Million

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