Sound attenuating shield for an electric heater

A sound-abating flow disruptor quiets a PTAC refrigerant system by disturbing the airflow between an energized electric heater and an adjacent fan wheel. In some embodiments, the flow disruptor is a perforated metal plate that attenuates a whistle, which appears to be caused by vortex shedding in the confined area between the energized heater and the fan. In some cases, the heater comprises selectively energizable heating elements of various wattage. The heating elements closest to the fan wheel are the lower wattage ones to minimize the heat near the fan.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject invention generally pertains to PTAC refrigerant systems that include an electric heater and a blower. The invention more specifically pertains to a way of attenuating the whistle that tends to emanate from an area near the electric heater.

2. Description of Related Art

Packaged Terminal Air Conditioners/Heat Pumps or PTACs, as they are known in the HVAC industry, are self-contained refrigerant systems with an electric heater for selective heating and cooling modes. Although PTACs are often used for cooling and heating hotel rooms, they are also used in a wide variety of other commercial and residential applications such as apartments, hospitals, nursing homes, schools, and government buildings. PTACs are usually installed in an opening of a building's outer wall, so an exterior-facing refrigerant coil can exchange heat with the outside air. In some cases, the refrigerant side of the system is a heat pump that not only provides cooling, but also provides heat during milder conditions or contributes heat when the electric heater is operating.

Because PTACs protrude into the living space of a room, they need to be as compact and quiet as possible. The electric heater, refrigerant circuit, fans, and other components of the system are all tightly packaged within a minimally sized housing. This presents a number of challenging problems, particularly with the electric heater.

The heater, of course, can get quite hot, so it needs to be safely spaced apart from the exterior walls of the PTAC's housing. To avoid wasting heat, the heater should also be isolated from the exterior-facing refrigerant coil, which is cold during the heating mode for absorbing heat from the outside air. Consequently, the electric heater is typically installed immediately upstream of the indoor fan, which circulates the room air and/or some ventilating outside air through the PTAC.

With the electric heater at this location, the current inventors have discovered that a “whistling” noise seems to emanate from the heater. Supporting the heating elements or other components more firmly or less firmly failed to eliminate the whistle. Since the noise disappears when the heater is de-energized (while the indoor fan is still running) the true source of the noise was a mystery. After closely studying the problem, however, the current inventors have discovered the true source of the noise and now propose a solution.

SUMMARY OF THE INVENTION

It is an object of the invention to reduce the tonal noise resulting from the proximity of an electric heater and a fan wheel.

Another object of some embodiments is to reduce the tonal noise by minimally disrupting the airflow between the electric heater and the fan wheel.

Another object of some embodiments is to reduce the tonal noise by positioning higher wattage heating elements farther away from the fan wheel.

Another object of some embodiments is to provide a flow obstruction at some heating elements that are spaced within one fan diameter of the fan wheel and leave other heating elements that are at least half of fan diameter away substantially unobstructed.

Another object of some embodiments is to reduce the height of an electric heater to where the heater is shorter than an adjacent refrigerant heat exchanger.

Another object of some embodiments is to horizontally stagger a plurality of heating elements to help reduce the tonal noise.

Another object of some embodiments is to provide a noise-abating flow obstructer with no moving parts.

Another object of some embodiments is to reduce the tonal noise at a certain peak frequency between 500 and 1,500 Hz.

Another object of some embodiments is to provide a noise-abating flow disruptor that is primarily open to minimize the obstruction of flow therethrough.

Another object of some embodiments is to selectively energize heating elements to avoid energizing, whenever possible, those elements that are closest to the fan wheel.

Another object of some embodiments is to selectively energize heating elements of various wattage to provide different levels of total heat output.

One or more of these and/or other objects of the invention are provided by a refrigerant system that includes a noise-abating flow disruptor interposed between an upper heating element and a fan wheel.

The present invention provides a refrigerant system. The system includes a housing, a refrigerant heat exchanger disposed within the housing and a fan wheel rotating about an axis and thereby forcing air through the housing. The system also includes an electric heater upstream of the fan wheel and downstream of the refrigerant heat exchanger wherein the electric heater can be selectively energized and de-energized. The system further includes a sound at a certain peak frequency between 500 and 1,500 hertz emanating from the refrigerant system, wherein the sound at one meter from the axis is no more than 5 decibels louder when the electric heater is energized than when the electric heater is de-energized.

The present invention also provides a refrigerant system including a housing defining an inlet and an outlet, a fan wheel disposed within the housing and being rotatable about an axis to force air through the housing, a refrigerant heat exchanger disposed within the housing and an electric heater disposed within the housing. The electric heater is downstream of the refrigerant heat exchanger and upstream of the fan wheel. The system also includes a noise-abating flow disruptor located downstream of the electric heater and upstream of the fan wheel such that the air passes sequentially through the electric heater, through the noise-abating flow disruptor and across the fan wheel. The noise-abating flow disruptor creates a sufficient airflow disruption such that the refrigerant system operates more quietly with the noise-abating flow disruptor than if the noise-abating flow disruptor were omitted.

The present invention further provides a refrigerant system including a housing, a fan wheel disposed within the housing and being rotatable about an axis for forcing air through the housing, a refrigerant heat exchanger disposed within the housing, an electric heater disposed within the housing and a noise-abating flow disruptor interposed between the electric heater and the fan wheel. Air passes sequentially through the electric heater, through the noise-abating flow disruptor and across the fan wheel. The noise-abating flow disruptor creates a sufficient airflow disruption such that the refrigerant system operates more quietly with the noise-abating flow disruptor than if the noise-abating flow disruptor were omitted. More specifically, at a certain peak sound frequency within 500 to 1,000 hertz, the noise-abating flow disruptor allows the refrigerant system to generate at least 5 decibels less noise at one meter from the axis than if the noise-abating flow disruptor were omitted.

The present invention still further provides a refrigerant system which includes a housing, a refrigerant heat exchanger disposed within the housing, an electric heater disposed within the housing and a fan wheel disposed within the housing for forcing air across the refrigerant heat exchanger and the electric heater. The electric heater has a plurality of selectively energizable heating elements including a higher-wattage element and a lower-wattage element, and the fan wheel is closer to lower-wattage element than the higher-wattage element.

The present invention additionally provides a refrigerant system which includes a housing, a refrigerant heat exchanger disposed within the housing, an electric heater disposed within the housing and a fan wheel disposed within the housing for forcing air through the refrigerant heat exchanger and the electric heater. The electric heater has a plurality of selectively energizable heating elements that are vertically distributed and staggered such that at least two of the plurality of the selectively energizable heating elements are displaced out of alignment with each other.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Although PTACs come in various configurations,FIG. 1illustrates an exemplary refrigeration system10that is particularly suited as a PTAC unit. System10includes an outer housing12that can be installed in an opening14of a building's exterior wall16. In this example, housing12contains a refrigerant circuit18, an outdoor fan20, an indoor fan or centrifugal fan wheel22, and an electric heater24. To reduce or eliminate a “whistling” noise26emanating from an area near heater24, a novel noise-abating flow disruptor28can be installed between heater24and fan wheel22. Before describing details of flow disruptor28, more general information about system10will be presented.

Refrigerant circuit18of system10comprises a compressor30for compressing refrigerant, an outdoor refrigerant heat exchanger32, an expansion device34(e.g., thermal expansion valve, electronic expansion valve, orifice, capillary, etc.), and an indoor refrigerant heat exchanger36. In a cooling mode, compressor30forces refrigerant sequentially through outdoor heat exchanger32functioning as a condenser to cool the refrigerant with outdoor air38moved by fan20, through expansion device34to cool the refrigerant by expansion, and through indoor heat exchanger36functioning as an evaporator to absorb heat from indoor air40(and/or some outside air) moved by fan wheel22.

If refrigerant circuit18is a heat pump operating in a heating mode, the refrigerant's direction of flow through heat exchanger32, expansion device34and heat exchanger36is generally reversed so that indoor heat exchanger36then functions as a condenser to heat air40, and outdoor heat exchanger32functions as an evaporator to absorb heat from outdoor air38. If additional heat is needed or refrigerant circuit18is only operable in a cooling mode, heater24can be energized for heating air40.

When system10operates in a heating or cooling mode, a motor is energized to rotate fan wheel22about an axis42. Fan wheel22draws air40from within a comfort zone44through an inlet46of housing12. After air40enters housing12, fan22forces air40to pass through heat exchanger36and heater24. Fan22then discharges heated or cooled air40through an outlet47of housing12to return the air to comfort zone44. For variable capacity, fan wheel22can be run at high or low speed to adjust the flow rate of air40, and heater24may comprises a plurality of electric resistant heating elements24a,24b,24c,24d,24eand24fthat can be selectively energized in different combinations to provide various kilowatts of heat energy. In a currently preferred embodiment, heating elements24a-fare helical coils of electrically resistive wire that are supported by heat resistant electrical insulators48(FIG. 2). Electrically resistive heating elements and insulators48are well known to those of ordinary skill in the art.

Although the location of heater24provides a PTAC that is generally compact yet avoids creating dangerous hot spots within housing12, noise26needs to be addressed. Noise26is a tonal sound whose maximum sound pressure level occurs at a certain peak frequency somewhere between 500 and 1,500 hertz. The actual peak frequency may vary depending on the rotational speed of fan wheel22and other factors. At a fan speed of about 800 rpm, the peak frequency in some cases is about 630 hertz. At 1,000 rpm, the peak frequency may be about 800 hertz.

It appears that noise26is not generated by vibration of heater24, vibration of fan wheel22, or other PTAC components because noise26primarily occurs only when heater24is hot. Moreover, the heating elements closest to fan wheel22seem to have the greatest effect on the noise. It is speculated that the high pitch noise is due to vortex shedding generated in the tight space between fan wheel22and heater24. Tests indicate that the heating elements closest to fan wheel22, such as elements24aand24b,which are less than one fan diameter50away from fan wheel22have the greatest impact. The impact is less for elements spaced farther away, particularly if the heating element is more than one fan diameter50away (e.g., element24f); however, heating elements even half a fan diameter away (e.g., element24b) may have noticeably less impact.

One or more solutions implemented alone or in combination may reduce or eliminate tonal noise26. Examples of some conceivably workable solutions include, but are not limited to, installing noise-abating flow disruptor28between heater24and fan wheel22, lowering the height of heater24below that of heat exchanger36, providing heater24with lower wattage elements near the top of heater24and higher wattage elements near the bottom, and horizontally or otherwise staggering the heating elements. In a currently preferred embodiment, PTAC system10includes flow disruptor28, the top of heater24is lower than heat exchanger36, and the lower wattage heating elements of heater24are near the top.

InFIG. 1, flow disruptor28is schematically illustrated to represent various designs including, but not limited to, a perforated plate28a(FIG. 2), a series of vertical bars28b(FIG. 3), a series of horizontal bars28c(FIG. 4), and a wire mesh screen28dor expanded metal (FIG. 5). Flow disruptor28preferably has a plurality of fixed openings through which air40can flow. The openings can be of various shapes as indicated by openings52,54,56and58, which are illustrated inFIGS. 2,3,4and5, respectively.

Flow disruptor28has an outer perimeter, e.g., perimeter60ofFIG. 2or perimeter62ofFIG. 3such that the perimeter60or62surrounds an area that is mostly open to allow air40to pass. In some cases, flow disruptor28a,for example, has a set of perforations whose total area comprises about 52% of the entire area within perimeter60.

Flow disruptor28does not necessarily have to extend fully down to the bottom of heater24because the lower heating elements, such as elements24eand24f,may be sufficiently distant from fan wheel22that those elements do not cause a problem. Thus, in some cases, flow disruptor28provides more of an obstruction at the upper heating elements than at the lower ones.

Ultimately, flow disruptor28preferably creates a sufficient airflow disruption such that PTAC system10operates more quietly with flow disruptor28than if flow disruptor28were omitted (FIG. 6). To measure the noise emanating from system10, the noise can be sensed at one meter64from axis42. With flow disruptor28and/or with other aforementioned ways for reducing noise26, the sound or tonal noise26at a certain peak frequency between 500 and 1,500 hertz is no more than 5 decibels, and in some cases less than 2 decibels, louder when electric heater24is energized than when heater24is de-energized (i.e., with fan22running and the sound sensed at one meter from axis42).

In one particular embodiment, the addition of noise-abating flow disruptor28areduced noise26about 12 db (as measured at one meter from axis42) when fan wheel22was rotating at about 800 rpm. In this case, noise26occurred at a peak frequency of about 630 Hz. When the fan speed of this same unit was increased to 1,000 rpm, the addition of flow disruptor28areduced noise26about 7 db, wherein the peak frequency occurred at about 800 Hz.

To further minimize the tonal noise caused by the proximity of heater24relative to fan wheel22, the two upper heating elements24aand24b,which are closest to fan wheel22, are each only 0.5-kw heaters, while the rest of the heating elements24c-fare 1-kw heaters. This not only minimizes the localized heating near fan wheel22, the heating elements can be selectively energized for adjusting the heat output. Only heaters24eand24fare energized for 2-kw of heat, heaters24a,24b,24eand24fare energized for 3-kw, and all of the heating elements24a-fare energized for 5-kw of heat.

Although placing the lower-wattage heating elements closest to fan wheel22may alone reduce the tonal noise to an acceptable level, better results may be achieved by also installing flow disruptor28such that flow disruptor28provides more of an airflow obstruction at lower-wattage element24athan at the higher wattage element24f.

In another embodiment, heaters24a,24b,24c,24d,24eand24fare 0.25-kw, 0.25-kw, 0.75-kw, 0.75-kw, 1.75-kw and 1.75-kw respectively. In this case, heaters24a-dare energized for 2-kw of heat, heaters24eand24fare energized for 3.5-kw, and heaters24c-fare energized for 5-kw. It should be appreciated by those of ordinary skill in the art that there are infinite combinations of the quantity of heating elements, their individual kilowatt ratings, and how they are selectively energized.

FIG. 7illustrates yet another way that might reduce the tonal noise down to an acceptable level. In this example, electric heater66comprises a plurality of selectively energizable heating elements68that are horizontally staggered. The staggered arrangement places the uppermost heating element farther away from fan wheel22than it might be otherwise. Moreover, the positions of the heating elements68could perhaps be such that the noise or vortex shedding at each heating element68may help cancel each other. Although the heating elements are shown in a horizontally staggered and symmetrical arrangement, other arrangements, such as an asymmetrical staggered arrangement, are contemplated where the heating elements68are located so that noise generated by any particular heating element68either interferes with or cancels noise generated by one or more of the other heating elements68. An asymmetrical staggered arrangement can occur by horizontally staggering the heater elements at different distances from an arbitrary vertical line, or, as shown inFIG. 8, can occur by staggering heating elements68such that at least one heating element68ais displaced from a first adjacent heating element68bby a first distance69and is displaced from a second adjacent heating element68cby a second distance20where the first distance differs from the second distance. Asymmetrical staggering can also occur through the use of a combination of horizontal and vertical staggering as described above.

Although the invention is described with respect to a preferred embodiment, modifications thereto will be apparent to those of ordinary skill in the art. Therefore, the scope of the invention is to be determined by reference to the following claims.