Compact air handling unit with integral silencing

A compact air handling system includes an inlet channel which defines an inlet flow path in a first direction along a flow axis and a discharge channel which defines a discharge flow path in a second direction, opposite to the first direction along the flow axis. Air enters the air handling system through an inlet port and is discharged via an discharge port. The inlet channel is provided with acoustical buffering to attenuate inlet noise. The discharge channel is also provided with acoustical buffering in the form of a discharge silencer to attenuate noise in the discharge channel. An acoustical inlet plenum couples the inlet channel to the discharge channel. The cross-sectional area of the discharge channel adjacent the discharge port is larger than the cross-sectional area of the discharge channel adjacent the acoustical inlet plenum. If the inlet ports are not substantially equally distributed about the air handling system, a transfer passage can be provided between the inlet ports and the inlet channel to provide equalization of the air flow.

BACKGROUND OF THE INVENTION 
This invention relates to heating, ventilating and air conditioning systems 
and, more particularly, to a noise reducing air handling system which is 
compact and efficient. 
Air handling systems are used to provide large volumes of air, typically to 
commercial environments. One of the problems common to conventional air 
handling systems that are designed to move large volumes of air is the 
undesirable level of noise that is generated. To reduce the noise in prior 
art systems, additional noise reduction and attenuation components are 
added resulting in large or bulky and generally inefficient air handling 
systems. 
Accordingly, it is an object of this invention to provide an improved air 
handling system. 
It is another object of this invention to provide a compact, quiet and 
efficient air handling system. 
SUMMARY OF THE INVENTION 
An air handling system includes an acoustically lined plenum box having at 
least one inlet port and defining an inlet channel. The inlet channel 
extends from the inlet port to an acoustical inlet plenum and defines an 
inlet flow path in a first direction along a flow axis. The air handling 
system also includes a fan and an acoustically attenuating discharge 
silencer defining a discharge channel which extends from the acoustical 
inlet plenum to a discharge port. The discharge channel defines a 
discharge flow path in a second direction opposite to the first direction. 
The discharge silencer and discharge channel can be located substantially 
concentrically with respect to the plenum box and the inlet channel. The 
fan produces inlet airflow that enters the inlet port, travels in the 
first direction along the inlet flow path into the acoustic inlet plenum 
and produces the discharge airflow that draws air from the acoustic inlet 
plenum into the discharge channel and out the discharge port. 
The inlet port can extend substantially continuously along the perimeter of 
the plenum box. Alternatively, a plurality of discrete inlet ports can be 
disposed about the perimeter of the plenum box. Where multiple discrete 
inlet ports are used, a transfer passage can be provided between the inlet 
ports and the inlet channel in order to equalize the airflow into the 
inlet channel. 
The cross-sectional area of the discharge channel can transition from the 
fan diameter at a first end to a larger cross-sectional area at a second 
end adjacent the discharge port. The cross-sectional shape of the 
discharge channel can also transition to a round or polygonal shaped 
discharge opening in order to facilitate connection with commercial or 
residential duct work. 
The fan can be adapted for rotating about a fan axis that extends 
substantially parallel to the discharge channel. The discharge channel can 
further include a central sound absorbing pod which extends from the fan 
along the fan axis. The central sound absorbing pod serves to reduce the 
impact noises behind the fan motor and to improve fan efficiency. 
Both the inlet channel and the discharge channel can be provided with 
acoustic baffles to further attenuate sound generated by or carried with 
the inlet and/or discharge airflow. Optionally, the channel enclosing the 
fan can be lined with removable panels which provide further acoustical 
attenuation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows an air handling system 10 according to the present invention. 
The air handling system 10 is constructed from an acoustically attenuating 
plenum box 20 having one or more air inlet ports 12 and one or more air 
discharge ports 14. Filters or coil boxes 16 can be disposed about the 
plenum inlet openings 12. Element 16, which is adjacent to inlet port 12, 
is a fluid (e.g., air) conditioner, which, for example, is capable of 
changing at least one characteristic (e.g., temperature or humidity) of an 
inlet fluid along an inlet flow path, such as characteristics of an air 
flow 72 entering inlet port 12. As shown in FIGS. 2 and 3, the plenum box 
20 can have a round cross section or a polygonal (such as a square or 
rectangular) cross-section. In the case where the inlet port 12 does not 
extend continuously around the plenum box 20 or inlet ports 12 are not 
provided on all sides around the plenum box 20, a transfer passage 22 
surrounding the outlet duct 50 is provided to equalize the air flow to the 
inlet channel 24. Inlet channel 24 can include intermediate baffles 62 to 
provide additional acoustical attenuation and/or to stabilize the inlet 
airflow. Alternatively, inlet channel 24 can include intermediate baffles 
(not shown) which divide the inlet channel 24 into a plurality of 
circumferentially spaced inlet channels. Inlet channel 24 feeds air to an 
acoustical inlet plenum 26. 
The air handling system 10 also includes an externally lined discharge 
silencer 40 which includes a fan 30 and defines a discharge channel 42 
extending from the acoustical inlet plenum 26 to the discharge port 14. As 
is shown in the cross-sectional views of FIGS. 2 and 3, viewing in the 
direction of arrows 2A and 2B, the discharge silencer 40 and the discharge 
channel 42 are disposed in substantially concentric relation with the 
plenum box 20 and the inlet channel 24. The exterior of the discharge 
silencer 40 and the interior walls of the plenum box 20 define the inlet 
channel 24 which approximates a hollow cylinder which is substantially 
concentrically arranged about the discharge silencer 40. The resulting 
airflow through the system 10 provides for an inlet airflow 72 through the 
inlet channel 24 that is in the opposite direction with respect to the 
discharge airflow 74 through the discharge channel 42 which flows in a 
direction substantially parallel to the central axis 70 of the discharge 
silencer 40 and the fan 30. 
The acoustical inlet plenum 26 provides proper air flow to the fan inlet 
bell 34 of the discharge silencer 40. The fan 30 can be surrounded by 
acoustical baffles 38 to increase acoustical attenuation adjacent the 
inlet bell 34. Preferably, the discharge channel 42 transitions from a 
first diameter adjacent the fan to a larger diameter adjacent the 
discharge port 14, recovering by the Bernoulli effect most of the decrease 
in dynamic pressure as an increase in static pressure at the discharge 
port 14. A central sound absorbing pod 46, extending along the rotational 
axis of the fan 70 and extending from the fan motor 32, can be provided to 
reduce the impact losses behind the fan motor 32 and effectively improve 
fan 30 efficiency. Discharge channel 42 can include intermediate baffles 
64 to provide additional sound attenuation and/or to stabilize the 
expanding airflow. Alternatively, discharge channel 42 can include 
intermediate baffles (not shown) which divide the discharge channel 42 
into a plurality of circumferentially spaced discharge channels. 
The air handling system 10 can be provided with one or more inlet ports 12. 
As shown in the cross-sectional view of FIG. 2, the air handling system 10 
can include an inlet port 12 that extends continuously around the 
circumference of the system 10. Alternatively, as shown in the 
cross-sectional view of FIG. 3, the air handling system can include an 
inlet port 12 having a polygonal cross-section. Regardless of whether the 
air handling system has a round or polygonal cross-section, the system 10 
can be provided with a plurality of discrete inlet ports 12 that are 
distributed around the perimeter of the plenum box 20 and separated by 
areas that do not permit air to enter the plenum box 20. As one of 
ordinary skill will appreciate, it is not necessary for each side to be 
provided with an inlet port 12. A transfer passage 22 can be provided 
between the inlet ports 12 and the inlet channel 24 in order to equalize 
the airflow into the inlet channel 24. 
The dimensions of the plenum box 20 are determined so that the space 
between the discharge silencer lining 44 and lined plenum walls, together 
with the inlet plenum 26 volume provide the required inlet acoustical 
attenuation and permit proper airflow to the fan. As one of ordinary skill 
will appreciate, the relative volumes of the inlet channel 24, the 
acoustical inlet plenum 26 and the discharge channel 42 are selected to 
provide the necessary volume, velocity and acoustical attenuation as a 
function of the intended use of the system 10. In one preferred 
embodiment, the plenum box 20 is approximately 48 inches in diameter (or 
78 in. by 78 in., if square) and approximately 108 in. high; the discharge 
channel transitions from approximately 32 in. in diameter at fan 30 to 
approximately 36 in. by 36 in. square at the discharge port; and the width 
of the inlet channel (i.e. the space between the discharge silencer and 
the acoustically lined plenum box walls) is approximately 5 in. If needed, 
the transfer passage surrounds the outlet duct 50 and extends 
approximately 5 in. above the discharge silencer. 
Preferably, the fan 30 and motor 32 are selected to permit the air handling 
system to move 20,000 cubic feet per minute (cfm) of air flow with a 
pressure loss through the system that are less than 10% of conventional 
air handling systems. Not only is the air handling system of the present 
invention compact, one half to one quarter of the length of a conventional 
system, but also the air handling system of the present invention is more 
efficient than the prior art system by providing more cfm per unit energy 
consumed. 
The acoustical buffering provides sound and/or noise attenuation to reduce 
noise associated with airflow as well as fan noise. Methods of attenuating 
sound in airflow channels are well known. In the preferred embodiment, the 
plenum box 20 can be lined with sound absorbing material 18 and the 
discharge silencer 40 is lined with sound absorbing material 48. 
Preferably, the sound absorbing material 18 and/or 48 is 21/2 to 3 lb. 
density fiberglass duct-liner or batts. 
The description discloses an example of an embodiment of the invention that 
is effective for use in air handling systems, however as a person having 
ordinary skill in the art will appreciate, the invention can be embodied 
in systems for use in other fluid handling systems such as systems which 
handle other gases or liquids. 
The invention may be embodied in other specific forms without departing 
from the spirit or essential characteristics thereof. The present 
embodiments are therefore to be considered in respects as illustrative and 
not restrictive, the scope of the invention being indicated by the 
appended claims rather than by the foregoing description, and all changes 
which come within the meaning and range of the equivalency of the claims 
are therefore intended to be embraced therein.