Bryant 551C, 551B Adjust Evaporator-Fan Speed, Dehumidification of Fresh Air with DCV Control

Dehumidification of Fresh Air with DCV Control

Information from ASHRAE indicates that the largest humidity load on any zone is the fresh air introduced. For some applications, a device such as 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 unit and/or a dehumidification option should be considered.

Step 7 —Adjust Evaporator-Fan Speed

Adjust evaporator-fan speed to meet jobsite conditions.

Tables 8 and 9 show fan rpm at motor pulley settings for the 551C 024-060 and 551B 036-072 units. Tables 10 and 13 show maximum amp draw of belt-drive motor. Table 12 shows sound data. Refer to Tables 14-33 for performance data. See Table 34 for accessory static pressure drop. See Fig. 39 for the Perfect Humidity™ system static pressure drops.

For units with electric heating, required minimum cfm is 900 for 551B/C 036; 1200 for 551B/C 048; 1500 for 551B/C 060 and 1800 for 551B 072 and 600 for 551C 024.

Belt Drive Motors

Fan motor pulleys are factory set for speed shown in Table 1. Check pulley alignment and belt tension prior to start-up.

To change fan speed:

1.Shut off the unit power supply and tag disconnect.

2.Loosen the belt by loosening the fan motor mounting nuts. (See Fig. 40.)

3.Loosen movable pulley flange setscrew (See Fig. 41).

4.Screw movable flange toward fixed flange to increase speed and away from fixed flange to decrease speed. Increasing fan speed increases load on motor. Do not exceed maximum speed specified in Table 1.

5.Set movable flange at nearest keyway of pulley hub and tighten setscrew. (See Table 1 for speed change for each full turn of pulley flange.)

6.Adjust belt tension and align fan and motor pulleys per guidance below.

NOTE: Once the required flange position is determined for the correct blower rpm, it is recommended (but not required) that the variable pitch pulley be replaced with a corresponding size fixed sheave pulley.

To align fan and motor pulleys:

1.Loosen fan pulley setscrews.

2.Slide fan pulley along fan shaft.

3.Make angular alignment by loosening motor from mount- ing.

To adjust belt tension:

1.Loosen fan motor mounting nuts.

2.Slide motor mounting plate away from fan scroll for

proper belt tension (1/2-in. deflection with 7 to 10 lb of force).

3.Tighten motor mounting nuts.

4.Adjust bolt and tighten nut to secure motor in fixed position.

551B,C

Table 7—CO2Sensor Standard Settings

SETTING	EQUIPMENT	OUTPUT	VENTILATION	ANALOG	CO2	OPTIONAL	RELAY
			RATE	OUTPUT	CONTROL RANGE	RELAY SETPOINT	HYSTERESIS
			(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

5

6

7

	Proportional	15	0-10V	0-1100	1100	50
			4-20 mA
	Proportional	20	0-10V	0- 900	900	50
			4-20 mA
Economizer
	Exponential	15	0-10V	0-1100	1100	50
			4-20 mA
	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

31