Bryant LEGACY 558J - Manual (Page 18)

18
APPLICATION DATA
Min operating ambient temp (cooling):
In mechanical cooling mode, your Bryant rooftop can
safely operate down to an outdoor ambient temperature of
25_F (--4_C), with an accessory winter start kit. It is
possible to provide cooling at lower outdoor ambient
temperatures by using less outside air, economizers,
and/or accessory low ambient kits.
Max operating ambient temp (cooling):
The maximum operating ambient temperature for cooling
mode is 115_F (46_C). While cooling operation above
115_F (46_C) may be possible, it could cause either a
reduction in performance, reliability, or a protective action
by the unit’s internal safety devices.
Min and max airflow (cooling mode):
To maintain safe and reliable operation of your rooftop,
operate within the cooling airflow limits. Operating above
the max may cause blow--off, undesired airflow noise, or
airflow related problems with the rooftop unit. Operating
below the min may cause problems with coil freeze--up.
Airflow:
All units are draw--though in cooling mode.
Outdoor air application strategies:
Economizers reduce operating expenses and compressor
run time by providing a free source of cooling and a
means of ventilation to match application changing needs.
In fact, they should be considered for most applications.
Also, consider the various economizer control methods
and their benefits, as well as sensors required to
accomplish your application goals. Please contact your
local Bryant representative for assistance.
Motor limits, break horsepower (BHP):
Due to Bryant’s internal unit design, air path, and
specially designed motors, the full horsepower (maximum
continuous BHP) band, as listed in Table 5, can be used
with the utmost confidence. There is no need for extra
safety factors, as Bryant’s motors are designed and
rigorously tested to use the entire, listed BHP range
without either nuisance tripping or premature motor
failure.
Sizing a rooftop
Bigger isn’t necessarily better. While an air conditioner
needs to have enough capacity to meet the load, it doesn’t
need excess capacity. In fact, having excess capacity is
often bad.
Using higher design temperatures than ASHRAE
recommends for your location, adding “safety factors” to
the calculated load, and rounding up to the next largest
unit, are all signs of oversizing air conditioners.
Oversizing can cause short--cycling, and short cycling
leads to poor humidity control, reduced efficiency, higher
utility bills, drastic indoor temperature swings, excessive
noise, and increased wear and tear on the air conditioner.
Rather than oversizing an air conditioner, wise contractors
and engineers “right--size” or even slightly undersize air
conditioners. Correctly sizing an air conditioner controls
humidity better; promotes efficiency; reduces utility bills;
extends equipment life, and maintains even, comfortable
temperatures.
Low ambient applications
When equipped with a Bryant economizer, your rooftop
unit can cool your space by bringing in fresh, cool outside
air. In fact, when so equipped, accessory low--ambient kit
may not be necessary. In low ambient conditions, unless
the outdoor air is excessively humid or contaminated,
economizer--based “free cooling” is the preferred less
costly and energy conscious method.
In low ambient applications where outside air might not
be desired (such as contaminated or excessively humid
outdoor environments), your Bryant rooftop can operate to
ambient temperatures down to --40_F (--40_C) using the
recommended accessory Motormaster low ambient
controller.
Winter start
Bryant’s winter start kit extends the low ambient limit of
your rooftop to 25_F (--4_C). The kit bypasses the low
pressure switch, preventing nuisance tripping of the low
pressure switch. Other low ambient precautions may still
be prudent.
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