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11RT-PRC007-EN
4
If several units are to be placed on one
span, they should be staggered to
reduce deflection over that span.
It is impossible to totally quantify the
effect of building structure on sound
transmission, since this depends on the
response of the roof and building
members to the sound and vibration of
the unit components. However, the
guidelines listed above are experience-
proven guidelines which will help reduce
sound transmissions.
Clearance Requirements
The recommended clearances identified
with unit dimensions should be
maintained to assure adequate
serviceability, maximum capacity and
peak operating efficiency. A reduction in
unit clearance could result in condenser
coil starvation or warm condenser air
recirculation. If the clearances shown are
not possible on a particular job, consider
the following:
Do the clearances available allow for
major service work such as changing
compressors or coils?
Do the clearances available allow for
proper outside air intake, exhaust air
removal and condenser airflow?
If screening around the unit is being
used, is there a possibility of air
recirculation from the exhaust to the
outside air intake or from condenser
exhaust to condenser intake?
Actual clearances which appear
inadequate should be reviewed with a
local Trane sales engineer.
When two or more units are to be placed
side by side, the distance between the
units should be increased to 150 percent
of the recommended single unit
clearance. The units should also be
staggered for two reasons:
1
To reduce span deflection if more than
one unit is placed on a single span.
Reducing deflection discourages sound
transmission.
2
To assure proper diffusion of exhaust air
before contact with the outside air intake
of adjacent unit.
Duct Design
It is important to note that the rated
capacities of the rooftop can be met only
if the rooftop is properly installed in the
field. A well designed duct system is
essential in meeting these capacities.
The satisfactory distribution of air
throughout the system requires that
there be an unrestricted and uniform
airflow from the rooftop discharge duct.
This discharge section should be straight
for at least several duct diameters to
allow the conversion of fan energy from
velocity pressure to static pressure.
However, when job conditions dictate
elbows be installed near the rooftop
outlet, the loss of capacity and static
pressure may be reduced through the
use of guide vanes and proper direction
of the bend in the elbow. The high
velocity side of the rooftop outlet should
be directed at the outside radius of the
elbow rather than the inside.
Heat selections other than gas heat will
not be affected by altitude. Nominal gas
capacity (output) should be multiplied by
the factors given in Table PD-3 before
calculating the heating supply air
temperature.
Acoustical Considerations
Proper placement of rooftops is critical to
reducing transmitted sound levels to the
building. The ideal time to make
provisions to reduce sound
transmissions is during the design
phase. And the most economical means
of avoiding an acoustical problem is to
place the rooftop(s) away from
acoustically critical areas. If possible,
rooftops should not be located directly
above areas such as: offices, conference
rooms, executive office areas and
classrooms. Instead, ideal locations
might be over corridors, utility rooms,
toilets or other areas where higher
sound levels directly below the unit(s)
are acceptable.
Several basic guidelines for unit
placement should be followed to
minimize sound transmission through
the building structure:
1
Never cantilever the compressor end of
the unit. A structural cross member must
support this end of the unit.
2
Locate the unit’s center of gravity which
is close to, or over, a column or main
support beam.
3
If the roof structure is very light, roof
joists must be replaced by a structural
shape in the critical areas described
above.
Application
Considerations