Trane RT-DS-10 - Manual (Page 14)

14
Application
Considerations
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
close to or over 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.
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 as shown 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.