Sound Attenuator for a Fan Coil

Background of the Invention

[0001] This invention relates generally to air conditioning systems and, more particularly, to a method and apparatus for reducing sound emanating from the return air opening of a fan coil unit.

[0002] Fan coils are commonly provided in air conditioning systems to provide a heat exchange relationship between air that is being returned to the unit from a space to be conditioned, and a medium, in a liquid, vapor or gaseous form, which has been "conditioned" in a closed loop air conditioning system. The fan coil therefore includes a heat exchanger coil through which the medium is circulated and over which the return air is circulated by way of the fan.

[0003] As the fan draws the return air into the fan coil unit and over the heat exchanger coil, it necessarily produces a good amount of noise which then tends to emanate in the direction of the space from which the return air is flowing. The fan coil may be connected to the space by way of a duct, in which case the sound may be somewhat attenuated by the air in the duct, but the fan coil may connect directly to the space without an attached duct, in which case, there tends to be no attenuation of the emitted sound. In either case, it is desirable to reduce the amount of sound that is transmitted to the space to be conditioned.

[0004] In ducted systems, there is room to install various types of sound attenuating devices, some of which are quite sophisticated and effective, but not without significant expense. In non-ducted systems, however, there has traditionally been no treatment of the sound emanating from the inlet duct of a fan coil. [0005] Another consideration in providing attenuation is that of a pressure drop that may be associated with any sound attenuation system. That is, generally there is a pressure drop that is associated with any type of attenuation system, and it is preferable to obtain as low as a pressure drop as possible while still obtaining the desired degree of sound attenuation.

Summary of the Invention

[0006] Briefly, in accordance with one aspect of the invention, one or more sound attenuating elements are placed in the return air inlet duct of the fan coil unit such that they absorb sound as it emanates from the fan toward the inlet opening.

[0007] In accordance with another aspect of the invention, the sound absorbing elements are so placed within the duct that there are portions thereof between the entire fan and the entire inlet opening, as seen along axially extending lines.

[0008] In accordance with another aspect of the invention, the sound absorbing elements include a central element extending across a central portion of the inlet duct and a pair of spaced peripheral elements located on opposite walls thereof.

[0009] By yet another aspect of the invention, the inlet duct is rectangular, the centrally located element is cylindrical in form, and the peripheral elements include elements which are triangular in form.

[0010] In the drawings as hereinafter described, a preferred embodiment is depicted; however, various other modifications and alternate constructions can be made thereto without departing from the spirit and scope of the invention.

Brief Description of the Drawings

[0011] FIG. 1 is an exploded perspective view of a fan coil unit in accordance with the prior art.

[0012] FIG. 2 is a perspective view of ducted fan coil unit in accordance with the prior art.

[0013] FIG. 3 is a fan coil unit with the present invention incorporated therein.

[0014] FIG. 4 is a front perspective view thereof.

[0015] FIG. 5 is a side view thereof.

[0016] FIG. 6 is a perspective view of the internal components thereof.

[0017] FIG. 7 is a longitudinal side view of a fan coil unit with the present invention incorporated therein.

Detailed Description of the Invention

[0018] Shown in Fig. 1 is a typical ducted fan coil unit 11 in accordance with the prior art. The fan coil unit 11 includes an outer casing 12 in which there is disposed a heat exchanger (not shown) through which refrigerant is circulated and over which air is circulated by way of one or more fan assemblies 13 disposed within the casing 12 as shown. A filter 14 is preferably placed on the upstream side of the fan assemblies 13 to filter out any solid impurities that may be in the air stream. On the upstream side of the casing 12 is a return air plenum 16 having a plurality of openings 17 which are fluidly connected to return air ducts (not shown). [0019] On the downstream side of the casing 12 is a supply air plenum 18 with openings 19 which are fluidly connected to supply air ducts (not shown) from supplying conditioned air to spaces within a building.

[0020] By operation of the fan assemblies 13, return air is drawn in through the return air ducts to the return air plenum 16, through the filter 14 and the heat exchanger where the air is conditioned (i.e. either cooled or warmed) after which the conditioned air passes into the supply air plenum 18 and through the openings 19 to supply conditioned air to the supply air ducts. Because of the return air plenum 16 and the return air ducts, any noise emanating from the fan assemblies 13 is substantially muffled by the time it reaches the space from which the return airflow is originating. The same is true for the supply end where the supply air plenum 18 and the supply air ducts provide an attenuation effect to any noise emanating from the supply side of the fan coil unit 11.

[0021] Referring now to Fig. 2, the same type of fan coil in 11 is shown but without the return air plenum 16. That is, there is no return air plenum 16 nor any return air ducts. Rather, the filter 14 at the upstream end of the casing interfaces directly with the space from which the return air is flowing. Thus, there is no attenuation of the sound which tends to emanate upstream from the fan assembly 13, and directly into the space from which the return air is flowing. [0022] There is shown in Fig. 3 a similar fan coil unit without a return air plenum 16 or return air ducts. However, at the upstream end of the fan coil unit 11 a sound attenuator assembly 21 is connected thereto for purposes of attenuating the sound that would otherwise would emanate toward the origin of the return air flow.

The sound attenuator assembly 21 is connected directly to the upstream end of the fan coil unit such that all air passing into the fan coil unit 11 passes first through the sound attenuator assembly 21.

[0023] The sound attenuator assembly 21 is more fully shown in Figs. 4-6.

The assembly includes a rectangular casing 22 having an inlet opening 23 leading to an inlet duct 25 and having an outlet 24 at its end. It includes an upper wall 26 and a lower wall 27. As will be seen in Fig. 4, there is disposed within the casing 22 a centrally located, transversely extending, acoustical insulation member 28. Also disposed within the casing 22 are upper and lower wall peripheral acoustical insulation members 29 and 31. These members are shown in greater detail in Figs. 5 and 6.

[0024] The acoustical insulation member 28 is cylindrical in form and extends transversely across a central portion of the casing 22 with its ends being secured to the sides of the casing. The peripheral acoustical insulation members 29 and 31 are generally triangular in shape and are mounted in an upstream position with respect to the insulation member 28 as shown. They may me mounted directly to the respective upper wall 26 and lower wall 27 or may be attached to the respective acoustical insulation members 32 and 33, which, in turn, are connected directly to the respective upper wall 26 and lower wall 27. The respective positions of the various acoustical insulation members will be more fully described hereinafter.

[0025] A filter 34 may be placed on the upstream end of the sound attenuator assembly 21 to either augment or replace the filter 14 that is provided at the inlet end of the fan coil unit 11 as shown in Fig. 3.

[0026] Shown in Fig. 7 is a longitudinal profile of a fan coil unit 11 having a sound attenuator assembly 21 attached to its upstream end thereof. A centrifugal fan or blower 36 is positioned with the casing 12 to draw air in through the sound attenuator assembly 21 and pass the air through a heat exchanger coil 37 after which it flows to a supply air plenum 18, through the supply air ducts, and finally to a spaced to be conditioned.

[0027] During operation of the fan 36 noise is produced both by the operation of the drive motor 38 and of the movement of the air as caused by the fan

39. Unless otherwise attenuated, this noise is likely to travel in both the downstream and upstream directions. To prevent or attenuate the sound from traveling in the upstream direction (i.e. out through the inlet duct 25), the sound attenuator assembly 21 with its elements 28, 29 and 31 are provided. The relative positioning of those elements, and to some extent their shape, are designed to absorb, deflect, or attenuate the sound waves which are traveling along an axial direction as indicated by the dashed lines. That is, the sound absorbing elements 28, 29 and 31 are so placed within the duct that there are portions thereof between the entire fan and the entire inlet opening as seen along the axially extending lines. At the same time, however, this arrangement results in a relatively low pressure drop through the assembly 21.

[0028] It should be understood that the various shapes, positions and numbers of the acoustical insulation members 28, 29 and 31 can be varied as desired to meet the requirements of a particular installation. Further, although the invention has been described in terms of use with a non-ducted fan coil unit, it may, as well, be used with a ducted unit.

[0029] While the present invention has been particularly shown and described with reference to a preferred mode as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.