Johnson Controls
5513350-JTG-1018
The 25–50 ton packaged rooftop platform is designed with
all the flexibility needed for today’s applications but with
tomorrow's requirements in mind. Realizing that efficiency
requirements are continuously pushing the envelope of
technology, the NexusPremier
™
delivers today the energy
efficiency levels exceeding those mandated by the U.S.
Department of Energy for 2023. All cooling only and elec-
tric heat units have an integrated energy efficiency ratio
(IEER) in excess of 13.2. All units with gas or hydronic heat
have an IEER in excess of 13. For these particular rooftop
units, when equipped with a variable speed drive compres
-
sor, they deliver efficiency levels in excess of those sug-
gested by the highest tier of the Consortium of Energy Ef-
ficiency (CEE) for 2019.
The NexusPremier is also designed for serviceability. With
small details—such as a maintenance safety tie-off (
Item 5 in
) on the roof of the condenser section that complies
with OSHA requirements, along with a single handle latching
mechanism for doors—the unit was designed for easy ser
-
vice. Options to make the unit serviceable include a conve
-
nience outlet to power lights and tools; internal lights in the air
handler section; viewports in doors of serviceable compart
-
ments to enable easier unit inspection; and extended grease
lines to simplify fan bearing lubrication for belt-driven fans.
Standard direct drive supply fan (
) do not
require lubricating fan bearings or changing belts. Numerous
refrigeration options are also available, including replaceable
core filter driers, liquid and suction isolation valves, as well as
high and low pressure transducers in each circuit that enable
easier sub-cooling and superheat measurements.
5
Features and Benefits
General
This packaged rooftop product is a sophisticated, highly
configurable rooftop unit. A controller is standard on each
unit with specific sequences of operation correlated to the
options selected. The Selection Navigator provides the
specific sequences of operation for the unit options select-
ed, eliminating confusion of the unit's capability.
Although the many options make customizing unlikely, it is
possible to have custom mechanical and sequences of op-
erations designed into the unit from the factory for ultimate
convenience and reliability.
1. Economizer
(
Item 1 in Figure 3
In order to deliver maximum efficiency, rooftop units
need an efficient economizer. The rooftop unit offers
various options for economizer control and fault de-
tection, as well as damper leakage rates and cycle
life to meet different regulatory requirements.
The amount of fresh air can also be optionally mea-
sured to ensure and record appropriate fresh air to
the conditioned space. An air blender option is also
available to deliver optimal comfort to the conditioned
space.
2.
Refrigeration System
(
Items 2, 6, and 7 in Figure 3
The refrigeration system is built to reliably deliver
cooling through a variety of loads. Two independent
refrigeration circuits ensure that in the unlikely event
of a compressor failure, the second circuit can still de-
liver cooling to the space. An interlaced tube and fin
evaporator provide maximum cooling performance
even at part loads. The microchannel condenser re-
duces the risk of refrigerant leaks and minimizes the
amount of refrigerant in the unit.
Standard fixed speed scroll compressors of differ-
ent sizes deliver excellent part-load efficiency and
control, which eliminates the need for inefficient hot
gas bypass valves at low load conditions. Optional
variable speed drive scroll compressor configura-
tions are available for stable and efficient discharge
air temperature (DAT) control regardless of the load.
For application flexibility, optional corrosion protec-
tion is available for the evaporator and condenser, as
well as intrusion protection options for the condenser.
Realizing that the refrigeration system is the heart
of the rooftop, when optionally equipped with trans
-
ducers, the unit controller can display sub-cooling or
superheat. Additionally, low ambient operation is an
available option with a variable speed condenser fan.
Besides options, there are also standard features to ensure
straightforward and safe servicing of the units, including
coil cleaning hatches (
) in the condenser
section to make cleaning condenser coils effortless, and
door safety latches to keep doors safe when opened in a
pressurized compartment. A discrete high and low voltage
compartment minimizes the amount of safety equipment re-
quired when only the low voltage compartment is accessed.
Selection Navigator is an online program available to as-
sist in providing unit selections, performance reports, and
outputs to assist in design of the unit. Certain options may
require the assistance of the local sales office.
In order to facilitate its application, Selection Navigator
also provides building information modeling (BIM) files of
the specific unit selected. This aids in modeling placement
and integration of the rooftop unit into the overall building
design.
