Johnson Controls
5513350-JTG-1018
The rooftop units enable installation flexibility with the
option of either exhaust or return fan to control the
building static pressure. Return ductwork with short
-
er runs and lower static requirements usually only
need an exhaust fan. The return fan is available to
overcome the static imposed by longer return ducts.
Refer to the
Variable Air Volume for Rooftop Units
Application Guide (Form 5515844-JAD).
7
The unit controller has sequences of operation for
standalone applications. These sequences cover
simple applications such as single zone variable air
volume (SZVAV) control of the supply fan and com
-
pressors in accordance with
ASHRAE 90.1-2016,
as well as demand control ventilation (DCV) that
ensures adequate fresh air to the building. Complex
applications are also supported, like the twinning of
multiple rooftops on a common supply and return
duct shaft for the ultimate in redundancy for critical
spaces, such as Medical Office Buildings (MOBs).
7.
Blank Section
)
Blank sections can be provided for field installed ac
-
cessories or to accommodate the installation of spe-
cific factory components including an air blender, fi-
nal filters, humidifier, or sound attenuator.
LD27638
Figure 6:
OLED Display
Final Filters
Blank Section
LD26881
Figure 7:
Final Filter Section
The rooftop unit can be equipped with a final filter
before the conditioned air is delivered from the roof-
top into the supply duct. Various final filter options
are available to meet critical needs including high ef-
ficiency particulate air (HEPA) filtration. Differential
pressure measuring options can be supplied to meet
the requirements for ASHRAE 170-2017.
For cold northern climates where heat tends to dry
out the supply air, a humidifier option with a stainless
steel drain pan is also available.
In order to mitigate sound originating in the rooftop unit
from reaching the conditioned space, optional sound
attenuators in the rooftop unit can be factory-installed.
8. Exhaust/Return Fan
(
Item 13 in Figure 3
Features and Benefits (Continued)
Optional airflow measurement is available for units
equipped with a return fan. This makes it possible
to precisely understand and log the different airflows
through the rooftop unit.
9. Hot Gas Reheat (HGRH)
(Figure 9)
Occupant comfort can be a challenge during shoul-
der months when low loads and high humidity occur.
In many cases, the combined efforts of refrigeration
system compressor multistep control, an interlaced
evaporator coil, and the supply fan modulation of SZ
-
VAV control are sufficient. The rooftop unit provides
an optional modulating hot gas reheat (HGRH) coil
to further reduce the humidity level within the space.
10.
Indoor Air Quality (IAQ)
To meet the critical needs of IAQ, the rooftop unit
provides a stainless steel evaporator drain pan for
longevity and to facilitate cleanability. The drain pan
can be optionally equipped with an overflow switch to
warn of improper drainage and minimize the potential
for damage to the conditioned space. Ultraviolet (UV)
light banks are also an available option that minimize
mold and bacteria growth and assists in keeping the
evaporator coil clean.
