Bryant 549B - Manual (Page 3)

3
INTEGRATED ECONOMIZERS AND OUTDOOR-AIR
DAMPERS
Available as options or accessories, economizers and manual
outdoor-air dampers introduce outdoor air which mixes with the
conditioned air, improving indoor-air quality and often reducing
energy consumption.
During a first stage call for cooling, if the outdoor-air tempera-
ture is below the economizer control changeover set point, the
mixed-air sensor modulates the economizer outdoor-air damper
open to take advantage of free cooling provided by the outside
air. When second-stage cooling is called for, the compressor is
energized in addition to the economizer. If the outdoor-air tem-
perature is above the changeover set point, the first stage of
compression is activated and the economizer damper stays at
minimum position.
Accessory upgrade kits allow for control by differential dry-bulb
temperature (outdoor vs return), outdoor air enthalpy
changeover, or more precise differential enthalpy control.
Units can be equipped with different economizer options to
meet specific controls applications. The factory-installed or
field-installed EconoMi$erIV and EconoMi$er2 are available.
The EconoMi$erIV is used with the standard rooftop unit
controls and includes an industry standard, stand-alone, solid-
state control. The control can be used with a CO
2
sensor for
DCV (demand control ventilation) operation. For direct digital
control (DDC) applications, the EconoMi$er2 can be operated
using a third party controller. The EconoMi$er2 includes 4 to
20 mA actuator capability for demand control ventilation
applications.
All economizers incorporate a parallel blade, gear driven
damper system for efficient air mixing and reliable control. In
addition, the standard damper actuator includes a spring return
to provide reliable closure on power loss. The economizers for
sizes 024-120 are equipped with up to 100% barometric relief
capability for high outdoor airflow operations. Economizers for
unit sizes 024-120 are available, factory-installed, for vertical
return only. Economizers for unit sizes 150 and 180 are compat-
ible for vertical or horizontal return. An optional field-installed
barometric relief package is available for 150 and 180 size
units.
In addition, single-stage power exhaust is available as a field-
installed accessory for EconoMi$erIV to help maintain proper
building pressure.
For units without economizer, year-round ventilation is
enhanced by a manual outdoor-air damper. On size 024-120
units, a 25% or 50% manual damper is available as a field-
installed accessory. Unit sizes 150 and 180 are equipped with a
manual 25% damper.
SERVICE OPTIONS
Servicing a rooftop unit has never been easier with the new
factory-installed service options for these rooftop units. These
options include the following:
• Hinged access panels (549B, 549C and 542J only) are pro-
vided for the filter/indoor-fan motor, compressors, indoor fan,
and control box areas. Quick access to major components is
accomplished by simply unlatching and swinging open the
various panels. Each hinged panel is permanently mounted to
the unit, thereby eliminating the concern of a dropped or wind-
blown panel puncturing delicate roof materials. The
4 extended access panels are also equipped with ‘‘tie back’’
retaining devices to hold the door in the open position while
servicing the unit.
• An external, covered, 115-v Ground Fault Interrupt (GFI)
receptacle is provided as a convenient power source for drills,
lights, refrigerant recovery units, or other electrical service
tools. Simply connect the outlet to a field-supplied and prop-
erly fused branch circuit power supply.
• An integral non-fused disconnect switch within the rooftop unit
reduces installation time, labor and material costs. Safety is
assured by an interlock which prevents access to the control
box unless the switch is in the OFF position. In addition, the
externally mounted handle incorporates power lockout capa-
bility to further protect service personnel.
INDOOR-AIR QUALITY BEGINS WITH BRYANT ROOFTOPS
Sloped condensate pans minimize biological growth in rooftop
units in accordance with ASHRAE Standard 62. Two-inch filters
with optional dirty filter indicator switch provide for greater parti-
cle reduction in the return air. The face-split evaporator coils
improve the dehumidification capability of standard units, maxi-
mize building humidity control.
Optional proportional reacting CO
2
sensor is available with the
EconoMi$erIV outdoor air damper option/accessory to aid the
IAQ benefits.