Application Considerations
cannot be used due to the location of the unit control
Panel. SXHG rooftop air conditioners do not have a panel configuration like the 20 through
75 ton rooftops. To achieve maximum airflow, vertical support can be removed after the
unit has been placed on the roof curb. It is secured by four screws. (See Note 1) For
horizontal discharge on SLHG and SSHG units, only the Panel A next to the condenser fan
section can be removed. The other Panel A next to the supply fan cannot be used due to the
location of the heating coils.
To return air horizontally, the exhaust fan access door
(Panel B) can be removed and used as a return opening.
High Capacity Evaporator Coil
Rooftops are popular because of their "packaged"
nature. Everything needed is contained in one box; mix-matching is neither necessary nor
available. With this convenience comes some disadvantages; one is the rooftop’s
cooling capacity may not exactly match the building load. It is conceivable that a 50 ton
rooftop would need to be used on an application that is 41 tons, simply because the 40 ton
rooftop does not meet capacity.
In order to avoid such occurrences, and to more closely
match the rooftop’s capacity to the building load, a high capacity evaporator coil
option is available on all IntelliPak® Rooftops20 through 105 tons. These high capacity
coils have an increased number of evaporator coil rows as compared to standard and
enhanced evaporator tube surfaces, resulting in a higher capacity. Capacity tables for
both standard and high capacity coils are available in the cooling data section of this
catalog. See Table 57-1 for the pressure drops associated with the high capacity coil
option. This pressure drop should be added to the total static pressure used to size the
supply fan motor.
Low Ambient Operation — Human
Interface Recommendations
Who wants to be on a roof at sub-zero temperatures? We can
understand a service technician’s reluctance to do this; that’s why we recommend
using a remote mounted Human Interface Panel. The service technician can troubleshoot and
diagnose in the comfort of a mechanical room.
Corrosive Atmospheres
Trane’s IntelliPak® Rooftops are designed and built
to industrial standards and will perform to those standards for an extended period
depending on the hours of use, the quality of maintenance performed, and the regularity of
that maintenance. One factor that can have an adverse effect on unit life is its operation
in a corrosive environment.
When rooftops are operated in corrosive environments, Trane
recommends that copper fins be utilized on the condenser and/or evaporator coil. Because
copper is more resistant to corrosion than aluminum, coil life expectancy is greatly
increased. Some industry applications expose equipment to corrosive agents that even
copper cannot fully resist. For those special applications, a baked phenolic resin coating
(i.e. Heresite) is highly desirable. Baked phenolic coatings or copper fins on the
condenser and/or evaporator coils are available on Trane’s IntelliPak Rooftops.
Ventilation Override Sequences
One of the benefits of using an exhaust fan rather than a
return fan, in addition to the benefits of lower energy usage and improved building
pressurization control, is that the rooftop can be used as part of a ventilation override
system. Several types of sequences can be easily done when exhaust fans are a part of the
rooftop system.
What would initiate the ventilation override control
sequence? Typically, a manual switch is used and located near the fire protection control
panel. This enables the fire department access to the control for use during or after a
fire. It is also possible to initiate the sequence from a field-installed automatic smoke
detector. In either case, a contact closure begins the ventilation override control
sequence.
CAUTION!: The ventilation override system should not be
used to signal the presence of smoke caused by a fire.
Trane can provide five (5) different ventilation
override sequences on both CV and VAV IntelliPak® Rooftops. For your convenience the
sequences can be factory preset or fully field editable from the Human Interface Panel or
Tracer®. Any or all five sequences may be "locked" in by the user at the Human
Interface Panel.
The user can customize up to five (5) different override
sequences for purposes such as smoke control. The following parameters within the unit can
be defined for each of the five sequences:
- Supply Fan — on/off
- Inlet Guide Vanes — open/closed/controlling
- Variable Frequency Drives — on (60Hz)/off (0
Hz)/controlling
- Exhaust Fan — on/off
- Exhaust Dampers — open/closed
- Economizer dampers — open/closed
- Heat — off/controlling (output for) VAV Boxes —
open/controlling
Compressors and condenser fans are shut down for any
Ventilation Override sequence. Factory preset sequences include unit Off, Exhaust, Purge,
Purge with duct pressure control, and Pressurization. Any of the user-defined Ventilation
Override sequences can be initiated by closing a field supplied switch or contacts
connected to an input on the Ventilation Override Module. If more than one ventilation
override sequence is being requested, the sequence with the highest priority is initiated.
Refer to the Sequence of Operation provided in the Control section of this catalog for
more details on each override sequence.
Natural Gas Heating Considerations
The IntelliPak standard, or limited modulation, gas
heat exchangers are not recommended for applications with mixed air conditions entering
the heat exchanger below 50°F. Mixed air temperatures below 50°F can cause condensation
to form on the heat exchanger, leading to premature failure. For increased reliability,
the recommendation in these applications is full modulation gas heat. For airflow
limitations and temperature rise across the heat exchanger information, see Table 34-1, 2
and RT-EB-104.
Acoustical Considerations
The ideal time to make provisions to reduce sound
transmission to the space is during the project design phase. Proper placement of rooftop
equipment is critical to reducing transmitted sound levels to the building. The most
economical means |
