Patent Application
20210302062
The specification relates to the provision of chilled or heated air into commercial office space. In particular, the specification describes an induction unit having low-noise and low pressure drop characteristics.
Induction air conditioning entered wide-spread use in commercial buildings in the 1950s. At that time, office workers were thankful to have air conditioning, and were, therefore, less inclined to complain about the noise generated by air conditioning units. While induction air conditioning units are still in use, attitudes have changed, and the most common complaint about induction units is that they generate an unacceptable level of noise. The technology mostly died out by the 1980s, with many manufactures discontinuing the production of their induction units.
Modern air conditioning typically requires supply and return air ducts to be run throughout a building in which such air conditioning is deployed. By contrast, induction units may be fed with high-pressure air from a single fan in a central plant room. As a result, the ductwork for buildings fitted with induction units requires considerably less space than is needed for modern air conditioning.
Through the early 2000s, older buildings fitted with induction units progressively reached the end of their working life. In most cities, these older buildings where demolished and new buildings erected. However, in New York and some other cities, demolishing and rebuilding is sufficiently challenging that stripping a building back to its frame and refurbishing is often favored. In this instance, it may not be possible to fit modern air conditioning into the building as there is not the space for the required air ducts. Hence, there is a re-emerging market for induction units.
The re-emerging market for induction units is energy conscious, less tolerant of induction unit nose, and requires local room temperature controls rather than a single building temperature control. Previous induction unit designs are not able to adequately meet these demands.
Technologies are described for reducing noise and increasing the energy efficiency of induction chillers.
In one embodiment, an induction air handling apparatus includes a radiator section and an elongate air mixing chamber having an air outlet at one end of the air mixing chamber and a return air inlet configured to permit return air to flow over the radiator section and into the air mixing chamber. The apparatus further includes an air plenum extending along one end of the air mixing chamber and having a first wall forming a partition between the air plenum and the air mixing chamber, the air plenum being formed by extrusion, and having an air inlet disposed at one end thereof and numerous openings machined through the first wall. The induction air handling apparatus also includes air nozzles extending into the air mixing chamber, each nozzle having an inlet in fluid communication with the air plenum through a corresponding opening in the first wall of the air plenum, and an outlet opening into the air mixing chamber. The air nozzles are formed by machining and are rigidly connected to the first wall, to reduce audible noise when pressurized air passes from the air plenum into the air mixing chamber through the air nozzles.
In another embodiment, a method of reducing audible noise in an induction air handling unit includes forming an air plenum by extrusion and machining numerous openings through a first wall of the air plenum. The method further includes machining numerous air nozzles, each nozzle having an inlet configured to open into the air plenum through a corresponding opening in the first wall of the air plenum, and an outlet. The method also includes rigidly connecting the air nozzles to the first wall such that the inlet of each nozzle engages with a corresponding opening in the first wall of the air plenum and configuring the induction air handling unit such that the first wall forms a partition between the air plenum and an air mixing chamber, and the air nozzles are configured such that the outlet of each nozzle extends into the air mixing chamber to permit pressurized air to pass from the air plenum into the air mixing chamber through the air nozzles.
In the following detailed description, reference is made to the accompanying drawings that form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. Additionally, while the disclosure may refer to the induction units as “chillers” or as “air conditioning” units, it will be understood that the same or similar units could easily be adapted for use in heating applications, or could combine both heating and cooling functions.
Disclosed herein is an induction air conditioning (and/or heating) unit that meets modern standards for low noise and efficiency. The low-noise characteristics of the induction units described herein make them acceptable for use in refurbishing older buildings that lack space for the ductwork required by modern air conditioning while meeting the demands of tenants who need a quiet working environment. Additionally, the induction unit of the disclosure is more efficient than previous designs, resulting in lower energy consumption and operating cost. The disclosed induction unit can also be fitted with local controls so that temperature may be separately adjusted in each room, rather than at the whole-building level, as was the historical norm. As a further feature of the disclosed induction unit, noise is reduced to low-level broadband noise, which may resemble the output of a white noise generator. This low-level broadband noise may provide a benefit in a commercial office setting, as it helps to mask the sound of traffic.
Referring now to
The air plenum section 102 forms an elongate, box-shaped air plenum chamber 108. As shown, the induction unit is configured to be mounted near the ceiling of a room, so that the air plenum section 102 runs along an upper end of the induction unit 100. As will be apparent to one of ordinary skill in the art, the induction unit 100 could be inverted for mounting near the floor of a room, in which case the air plenum section 102 would run along a lower end of the induction unit 100.
One or more rows of air nozzles 110 extend from a side 112 of the air plenum section 102 into an air mixing chamber 114. Each air nozzle 110 has an inlet end that is open to the air plenum chamber 108, and an outlet end that opens into the air mixing chamber 114. It will be understood that the size, shape, and number of air nozzles 110 in the induction unit 100 can be varied to meet the air handling requirements of a particular building. Further, the air nozzles in one induction unit can be different from the air nozzles in other induction units to provide different airflows.
A radiator section 120 forms a front wall of the air mixing chamber 114. The radiator section 120 includes a return air inlet 122, and a heat exchange coil. The heat exchange coil may include a series of coolant pipes 126, containing a heat transfer fluid, and heat exchange fins 128 that are connected to the coolant pipes 126 to increase heat transfer between the coolant pipes and return air flowing through the radiator section 120.
A rear wall 130 forms a back surface of the air mixing chamber 114. The rear wall may include a variety of features (not shown), such as mounting hardware (e.g., mounting connectors).
An air outlet 136 runs along a bottom edge of the air mixing chamber 114. The air outlet 136 provides an outlet into the room for mixed air passing through the air nozzles 110 from the air plenum section 102, and through the radiator section 120.
In use, pressurized air, supplied through ductwork (not shown—typically 4″ high-pressure ducting) from a central fan unit (not shown) enters the air plenum chamber 108 through the primary air inlet 104. The pressurized air is exhausted from the air plenum chamber 108 through the air nozzles 110 at a relatively high velocity. It should also be noted that several such induction units may be arranged in series, so that pressurized air may pass through or bypass the air plenum chamber 108. For example, in a system in which four induction units are connected in series, 75% of the air may pass through or bypass the air plenum chamber 108, with only 25% being exhausted through the air nozzles 110.
In use, the static pressure in the air plenum chamber 108 is higher than the static pressure in the air mixing chamber 114. Following Bernoulli's principle, that difference in pressure manifests itself as air velocity out of the nozzle. Bernoulli's principle states that an increase in the speed of a fluid coincides with a decrease in static pressure. Bernoulli's principle can be expressed as:
P
t
=P
s+0.5ρV2
Where:
In the air plenum chamber 108, we may assume velocity V is close to zero and, therefore, Pt=Ps. At the tip of each nozzle 110, Ps is lower than the pressure in the air plenum chamber 114, with the difference in pressure calculated from the 0.5ρV2 term in the equation. Thus, in the mixing chamber 114, there will be a jet of air coming out of each nozzle 110.
Entrainment is the transport of fluid across an interface between two bodies of fluid by a shear-induced turbulent flux. Air is entrained at the interface between the nozzle jets and the fluid through which those jets pass. As air is entrained into the wake of the nozzle jets, it is transported through the mixing chamber 114 and then ejected through the air outlet 136. The entrainment of air into the nozzle jets results in a mass-flow out of the mixing chamber 114, with an associated diminishing of static pressure within the mixing chamber. This diminishing of pressure within the mixing chamber 114 results in differential pressure across the radiator section 120. This differential pressure results in a flow of air from the room within which the induction unit is located, though the radiator section 120 and into the mixing chamber 114. The migration of air through the radiator section 120 results in that air being cooled (or heated) as a consequence of heat transfer from (or to) air to the chilled (or heated) water circulated through the radiator section.
It should be noted that the high-pressure air delivered to the air plenum chamber 108 may be pre-chilled or pre-heated in a central plant (not shown in
Induction units of the type shown in
The air nozzles 110 are shown as being arranged in two rows along the length of the induction unit 100. For example, an induction unit may have a 2″ header on each end of the induction unit, with pairs of nozzles every 2″ for the remaining length. Hence, a 24″ induction unit would have ten rows of nozzles, while a 40″ unit would have 18 rows, and so forth. Of course, it will be understood that other arrangements of the nozzles are also possible.
Induction units of the type shown in
In some embodiments, the plant room 202 may also include a heating unit 212, which heats the fluid that is circulated through the heat exchange coils of induction units 208 to heat return air.
Air passing over the radiator sections (and, therefore, the heat exchange coils) of the induction units 208 is the primary method by which the induction units 208 cool or heat air within the rooms in which they are located. On most days, this is sufficient to cool or heat the air in the rooms to a comfortable level, and the primary air delivered from the plant room 202 is not cooled or heated. In some buildings, on particularly hot days, an air chiller 214 may chill the primary air that is distributed by the fan unit 204 to the induction units 208. When cooling demand is particularly high, providing chilled air to the induction units 208 increases their cooling capacity. Similarly, in some buildings, on particularly cold days, an air heater 216 may heat the primary air that is distributed by the fan unit 204 to the induction units 208.
Thus, the system may effectively have four modes of operation:
For purposes of illustration,
The use of induction units configured as shown in
As was noted above, induction units became popular in the 1950s, and the technology mostly died out by the 1980s. Historically, induction units have been fabricated from relatively thin steel sheet that is bent, welded, or screwed together. The resulting induction unit is prone to leak along edges and at joints, causing noise and inefficiency.
While the traditional manufacturing techniques are still used for producing induction units for buildings that require induction chillers, modern manufacturing techniques have opened up additional possibilities. In particular, reduction in the cost of aluminum extrusion and advances in automated control of machining tools (i.e. “computer numerical control” or “CNC” technology) now provide possibilities for the design and manufacturing of induction chillers that are less costly to manufacture and more aesthetically pleasing than previous induction units. Additionally, the use of these modern manufacturing techniques has also, unexpectedly, resulted in an induction unit that produces substantially less noise than previous designs.
Reduction in the cost of aluminum extrusion tooling has resulted in the use of aluminum extrusions for many parts of an induction unit. By contrast, the required extruded sections would either have been beyond 1950s extrusion technology capability or too expensive to produce at that time.
Historically, induction unit nozzles have been made via a mass production technique. Typically, nylon nozzles would be injection molded, or metal nozzles would have been pressed or spun. Any mass production technique involves a significant lead time to develop, manufacture, and commission. It is then necessary to make tens of thousands of nozzles of the same design to recoup the setup cost. The idea that individual nozzles could be machined from a solid bar would have been unthinkable in the 1950s.
This manufacturing situation, however, has changed significantly in the past several years, in particular with the ready availability of computer-controlled Swiss lathes. In a conventional lathe that has a fixed headstock, the workpiece is held in a chuck or collet and extends into the machine enclosure as a cantilever. Alternatively, the workpiece can be supported on the end by the tailstock. What distinguishes a Swiss lathe from other types of lathes is that its headstock moves. Bar stock passes through a chucking collet in the headstock, which clamps onto it. The bar emerges into the tooling area through a guide bushing, which locates the bar radially during machining. The headstock moves back and forth, taking the bar with it. Hence, a conventional lathe rotates the material but otherwise does not move it. Cutting of metal is achieved by moving the cutting tool relative to the part. However, a Swiss lathe both rotates the material and moves it back and forth. The cutting tools do not move back and forth, only radially toward or away from the material.
The above difference between a conventional and Swiss lathe is significant in that it facilitates the machining of long thin parts. Swiss lathes were initially developed in 19th century Switzerland to facilitate mass production of the miniature screws needed to support the growing watch industry.
The advent of CNC machining technology in the latter part of the 20th century and early 21st century has resulted in the rapid development of all forms of CNC technology, including the Swiss lathe. However, because of the characteristics of a Swiss lathe, the application of CNC technology fundamentally changes the capability of a Swiss lathe. As discussed above, the difference between a conventional lathe and a Swiss lathe is that a Swiss lathe moves the material back and forth. In combination with CNC technology, this allows one end of a part to be machined, and then that part moved forward, griped by a second chuck, following which the part may be cut from the bar stock from which it is being machined. Once cut, the CNC controller can withdraw the bar stock to allow the other end of the part to be machined.
In combination with an automatic feeder, multiple lengths of bar stock may be loaded into the Swiss lathe. In the case of a typical Swiss lathe, bar stock may be 12 feet long, with a single nozzle for an induction chiller requiring typically about 4″ of bar stock. Hence, 36 nozzles may be machined from a single 12-foot length of bar stock. The process of machining a typical nozzle takes approximately 45 seconds, so one 12-foot length of bar stock is consumed in approximately 30 minutes. A typical automatic feeder would be able to hold fifty lengths of bar stock, and in so doing, facilitates the operation of the CNC machine continuously for approximately 24 hours.
Once set up and running, the CNC-controlled Swiss lathe requires minimal supervision. It can convert bar stock into machined nozzles for little more than the cost of the material used in the manufacture of each nozzle. Hence, a Swiss lathe, in combination with CNC technology, facilitates the machining of nozzles for induction units from solid metal bar stock.
Using a conventional lathe in the 1950s, 60s or 70s to manually machine individual nozzles would have been economically infeasible, and hence was never seriously considered. However, the advent of CNC-controlled Swiss lathes means that it is not only possible but practical. A single Swiss lathe running continuously can manufacture the 80,000 nozzles needed for a typical order of 2,000 induction units in approximately 6 weeks. Induction units are typically manufactured to order on a 12-week lead time. Hence, the nozzle manufacturing time on a Swiss lathe is consistent with the delivery time of induction units.
While manufacturing cost and lead-time are important, as is shown below, switching to extruded aluminum manufacturing of many components of an induction unit, in combination with the use of machined metal nozzles, has also reduced the noise and increased the efficiency of the induction unit described herein.
The described extruded embodiments effectively eliminate or minimize almost every noise source associated with an induction unit, except for the nozzle. Hence, the nozzle is the dominant noise source, and optimization of the nozzle to reduce nozzle-induced noise effectively reduces induction unit noise. The flexibility to adapt nozzle geometry as a consequence of machining the nozzles allows nozzle geometry to be optimized, reducing or minimizing induction unit noise.
The net result of what started as production engineering work relating to how the induction unit could be manufactured quickly and at a lower cost has unexpectedly also resulted in an induction unit that is inherently quieter and more efficient than conventional forms of construction. The use of nozzles that are readily optimized and then securely screwed into the induction unit plenum has also contributed significantly to reduced noise. In combination, the result is a significantly quieter induction unit. It will be understood that in addition to improving the nozzles themselves it is also possible to mix various sizes and configurations of nozzles within a single induction unit to further improve sound performance.
In
Manufacturing at least the extruded air plenum section 302 of a metal, such as aluminum, using an extrusion process results in a solid (i.e., seamless) and substantially rigid extruded air plenum section 302. Because there are no seams in the metal, significant sources of pressurized air loss and noise are eliminated. The rigidity of the extruded material, as well as the additional structural elements such as ridges that can be readily incorporated into an extruded design, creates a plenum with higher stiffness. Due to the increased stiffness of the plenum, noise is reduced, and/or the frequencies associated with vibration are shifted to higher frequencies, which are more easily attenuated. It will be understood that although the extruded air plenum section 302 is described as being made of aluminum, other metals or non-metal materials could be used to form the extruded air plenum section 302.
Numerous other parts of the induction unit 300 may also be manufactured by an extrusion process. For example, the radiator cap 324, return line plate 326, and the return line plate cover 328 may all be manufactured by extrusion. The use of extrusion for these parts is both economical and results in relatively rigid parts with fewer seams and connections, which may help reduce noise.
As is discussed in greater detail below, the nozzles 330 may be manufactured using a machining process on a Swiss lathe. By manufacturing the nozzles in this way, metal nozzles can be produced in the volumes needed for a “typical” deployment of induction units. Because the nozzles are rigidly connected to the extruded air plenum section 302 using, e.g., threading, they have little or no air leakage and do not cause substantial additional noise (except, of course, for the noise associated with exhausting air through the nozzles when the induction unit is in use).
Various other parts of the induction unit 300, including the heat exchanger section 304, plenum end plate 306, plenum inlet plate 308, inlet connector 310, heat exchanger inlet pipes 312, heat exchanger outlet pipes 314, valve 316, actuator 318, and wire connectors 320 may all be manufactured using conventional techniques, and some may be purchased from any of a number of commercial suppliers. Many other parts, such as gaskets, screws, nuts, bolts, and rivets may be used in assembling the induction unit 300, and may also be purchased from commercial suppliers or manufactured using conventional techniques for manufacturing such parts.
The extruded air plenum section 302 includes numerous machined nozzle openings 404. These openings are machined after extrusion and may include threading, so that machined nozzles (described below) may be securely threaded into the extruded air plenum section 302 in a rigid manner that permits little or no unintentional air loss. The extruded air plenum section 302 also includes flow balancing plate attachment openings 406, which are elongated to permit a range of positions in which a flow balancing plate (shown below, in
In constructing a complete induction unit, a plenum endplate (not shown) and a plenum inlet plate (not shown) including an air inlet (not shown), which may either be integral to the inlet plate or may be a separate inlet adaptor (not shown), will be secured to open ends 408a and 408b of the extruded air plenum section 302. In some embodiments, a gasket (not shown) may be used with the plenum endplate and plenum inlet plate to reduce unintentional air loss and noise through the ends of the extruded air plenum section 302. In some embodiments, screws or other fasteners may be used to secure the plenum endplate and plenum inlet plate to the extruded air plenum section 302. The plenum endplate, air inlet plate, gaskets, and screws, or other fasteners may be of conventional manufacture and design.
The return line plate 326 includes an inlet pipe run 502, through which a fluid inlet pipe (not shown) for the heat exchanger section (not shown) may be run. The return line plate 326 also includes a return pipe run 504, through which a fluid return pipe (not shown) for the heat exchanger section may be run. A wire run area 506 is also included, through which wires may be run between wire connectors (not shown) mounted on the sides of the induction unit. A mounting area 508 is formed in the return line plate 326 to accommodate mounting brackets (not shown) for mounting the induction unit near the ceiling of a room. Alternatively, the induction unit may be flipped, and the mounting area 508 may be configured to accommodate mounting brackets suitable for mounting the induction unit near the floor of a room.
The return line plate cover 328 is configured to cover a portion of the return line plate (not shown) through which an inlet pipe (not shown), a return pipe (not shown), and wires (not shown) run. The return line plate cover 328 includes an inlet pipe cover portion 602, configured to cover the inlet pipe, and a return pipe cover portion 604, configured to cover the return pipe. The central portion 606 covers a portion of the return line plate through which wires may be run.
Referring now to
The threading 802 couples with threading on a nozzle opening on an outer surface of the extruded air plenum section (described above, e.g., as extruded air plenum section 302). The use of threading provides a substantially rigid and air-tight connection between the nozzle 800 and the extruded air plenum section. While threading provides a good solution for connecting the nozzle 800 to the extruded air plenum section, it will be understood that other ways of connecting these parts in a substantially rigid and air-tight manner could also be used.
In use, pressurized air from the air plenum chamber through inlet 804, through bore 808, and then through outlet 806 into the mixing chamber of the induction unit. In an induction unit such as is described herein, the extruded parts and threading on the nozzles reduce the noise produced, e.g., by escaping air or movement of the parts of the induction unit. Hence, the primary source of noise from the induction unit is the passage of air through the nozzles.
Experimental testing has shown that nozzles with straight bores may produce undesirable tonal noise or “whistling.” This is because the induction units work over a range of plenum pressures. As plenum pressure is varied, velocity through the nozzles is also varied, so there is likely to be a critical plenum pressure/nozzle velocity that has a wavelength (or fraction of a wavelength) that matches the nozzle length. This results in tonal noise that is perceived by the observer as whistling.
To reduce this noise, the bore 808 is a tapered bore, in which the diameter of the bore 808 at the inlet 804 is wider than the diameter of the bore 808 at the outlet 806. The bore 800 is tapered by approximately 3°, but it will be understood that other angles, ranging from approximately 1° to approximately 10°, could also be used to reduce undesired tonal noise.
The height of the nozzle is effectively limited by the diameter of the base, and the degree of tapering, with greater tapering leading to a shorter possible height given a fixed base diameter. The maximum diameter of the base of the nozzles generally depends on the spacing between nozzle openings in the induction unit. For example, in the induction unit described above with reference to
There is an “optimal” height for the nozzles, at which the flow induced through the heat exchange coil can be maximized. However, increasing the nozzle height to be closer to this “optimal” height may necessitate decreasing the degree of tapering, which could lead to audible whistling. Additionally, increased nozzle height may increase the manufacturing cost of the nozzles, since more bar stock would be used for each nozzle. Even a minor increase in manufacturing cost for a nozzle may be significant, since a “typical” order may use 80,000 nozzles.
To further reduce noise and manufacturing costs, a short nozzle may be used.
While these short nozzles are below the “optimal” height for maximizing flow through the heat exchange coil, as is discussed below, induction units according to a “new design” that uses them are still substantially more efficient than conventional induction units. In some embodiments, the reduction in noise and reduction in manufacturing cost may outweigh the efficiency difference. In other embodiments, it may be more desirable to use a taller tapered nozzle, such as is shown in
As can be seen, the nozzle 900 has a wide inlet, which will reduce air velocity at the inlet, and reduce noise. Additionally, the channel 906 has no straight bore, which may be useful in eliminating the undesirable tonal noise or “whistling” that can occur when air passes through a nozzle having a straight bore. The shape used for the channel 906 conforms to a contraction design used in wind tunnels and follows the contours of a Bell-Mehta fifth-order polynomial function.
As can be seen, the nozzle 950 has a wide inlet, which will reduce air velocity at the inlet, and reduce noise. Additionally, the channel 956 has no straight bore, which may be useful in eliminating the undesirable tonal noise or “whistling” that can occur when air passes through a nozzle having a straight bore. The shape used for the channel 956 conforms to a Vitoshinsky profile, and the inlet 952 is even wider than the inlet 902 of
It has been found in testing that a short nozzle using the Vitoshinsky profile produces less noise than either the angled bore nozzle described above with reference to
The conventional induction unit had a design similar to that shown in
Acoustic measurements were made in accordance with the International Organization for Standardization (ISO) standard 3741:2010, “Acoustics—Determination of sound power levels and sound energy levels of noise sources using sound pressure Precision methods for reverberation test rooms.” Reverberant room background noise was measured with no induction unit installed in the reverberant room. Additionally, a test was run with the air supply to the induction unit running, supplying air as it would if an induction unit were fitted. However, no induction unit was installed. The resulting measurements in the reverberant room were the same as those without the air supply running. Thus, background noise was measured to be the same, both with and without the air supply running. It is, therefore, reasonable to conclude that for these tests, the air supply-borne noise is lower than the reverberant room background noise. Therefore, any noise measured with the induction unit in the reverberant room may be attributed to the induction unit and not to noise carried into the induction unit by the air supply.
It is noteworthy that when installed in buildings, one reason why induction units may “fail” to meet their noise specification is air supply-borne noise. Air supply-borne noise is a known contributor to apparent induction unit noise, as it is known to propagate through the induction unit and out into the room in which the induction unit is installed.
Knowing whether noise originates in the induction unit or the air supply is significant. It constitutes the difference between the contractor paying to replace supply ducting with acoustically treated supply ducting, and the induction unit manufacturer replacing the induction units with new units that meet their acoustic specification. For a building with 2,000 induction units, this cost may run into millions of dollars. Of course, this tends to provoke strong feelings among induction unit manufacturers who are asked to pay for a problem that they did not create and cannot solve, since it does not originate in the induction units.
The conventional/“classic” induction unit was tested with a plenum supply pressure of 1.5″ water. The new design induction unit prototype was also tested with a plenum supply pressure of 1.5″ water. This supply pressure was selected because induction units are generally used with a plenum pressure of between 1″ and 2″ water. Thus, a plenum pressure of 1.5″ water was chosen for testing as being a representative average plenum pressure for an induction unit when installed.
As can be seen, the new design induction unit narrow band acoustic data (black line) is typically approximately 5 dB below the conventional induction unit. Further, the new design induction unit narrow band acoustic data has a relatively smooth profile compared to the conventional induction unit. The absence of tonal peaks results in a noise-profile close to white noise, which is generally acceptable to the human ear. Finally, it is noteworthy that above 6,000 Hz, the new design induction unit noise reduces to the reverberant room background noise, and therefore reaches a limit below which further reductions in induction unit noise can't be measured using standard measurement techniques.
In should be noted that there is one potentially significant tonal peak 1002 in the narrow band acoustic data. However, this tonal peak appears to be present in the background noise as well as the conventional and new design induction unit narrow band acoustic data. This is likely to indicate that the tonal noise is a resonance within the reverberant room itself and not a feature of either the conventional or new design induction unit.
Specifications for acceptable noise levels from air conditioning systems are commonly expressed in terms of an “NC rating.” The Noise Criteria (or NC) are commonly used in the U.S. for rating noise in an indoor space (in Europe, a Noise Rating Curve, or “NR” is more commonly used). This standard way of measuring noise is based on measuring sound pressure levels against a set of criteria curves. The criteria curves set maximum limits for the noise level in each octave band of noise to meet that particular NC level. To determine the NC rating for an air conditioning system, the octave band levels for the measured noise spectrum of the air conditioning system are plotted against this set of criterion curves. The NC rating for the system is determined by the lowest criterion curve that is not exceeded by any of the octave band noise levels of the noise spectrum for the air conditioning system.
As shown in
For the new design induction unit, when the narrowband data were processed into NC levels for each octave band, the NC levels peak between 15 and 20 at 2,000 Hz and 4,000 Hz. The calculated NC rating for the new design induction unit is NC-21.
Thus, as shown in
In addition to the noise levels, the primary flow into the plenum and the total flow out of the induction unit were measured for both the conventional induction unit and the new design induction unit. This measurement determined that the new design induction unit was generating more outlet flow than the conventional induction unit. The ratio of inlet-to-outlet flow was assumed to be constant and was used to correct the inlet flow down, such that the new design induction unit was generating the same induced flow over the heat exchange section as the conventional induction unit.
Induction unit energy can be determined by multiplying inlet flow by inlet pressure. When this was calculated, it was found that the new design induction unit required approximately 30% less energy than the conventional induction unit to generate the same induced flow over the heat exchange section. Thus, in addition to substantially lower noise, the new design induction unit is substantially more energy-efficient than a conventional induction unit. This difference in efficiency was also well beyond expectations.
There is thus disclosed an induction air handling apparatus includes a radiator section and an elongate air mixing chamber having an air outlet at one end of the air mixing chamber and a return air inlet configured to permit return air to flow over the radiator section and into the air mixing chamber. The apparatus further includes an air plenum extending along one end of the air mixing chamber and having a first wall forming a partition between the air plenum and the air mixing chamber, the air plenum being formed by extrusion, and having an air inlet disposed at one end thereof and numerous openings machined through the first wall. The induction air handling apparatus also includes air nozzles extending into the air mixing chamber, each nozzle having an inlet in fluid communication with the air plenum through a corresponding opening in the first wall of the air plenum, and an outlet opening into the air mixing chamber. The air nozzles are formed by machining and are rigidly connected to the first wall, to reduce audible noise when pressurized air passes from the air plenum into the air mixing chamber through the air nozzles.
In some embodiments, each opening has internal threads formed on a surface thereof, and each nozzle has external threads formed adjacent to the inlet thereof and configured to engage with the internal threads. The nozzles are rigidly connected to the first wall by engaging the external threads with the internal threads.
In some embodiments, each nozzle has a tapered bore extending between the inlet and the outlet thereof. In some embodiments, the tapered bore is tapered by between 1° and 10°. In some embodiments, the tapered bore is tapered by 3°.
In some embodiments, each nozzle has a channel extending between the inlet and the outlet thereof, the inlet is wider than the outlet, and the channel includes no straight bore. In some embodiments, the channel conforms to a Vitoshinsky profile. In some embodiments, the channel conforms to the contours of a Bell-Mehta fifth-order polynomial function.
In some embodiments, the air plenum is formed of an extruded metal. In some embodiments, the metal includes aluminum.
Some embodiments further include at least one of a return line plate, a return line plate cover, or a radiator cap formed by extrusion.
In some embodiments, the air plenum further comprises a flow balancing plate configured to optionally block at least a portion of at least one of the openings.
There is further disclosed a method of reducing audible noise in an induction air handling unit includes forming an air plenum by extrusion and machining numerous openings through a first wall of the air plenum. The method further includes machining numerous air nozzles, each nozzle having an inlet configured to open into the air plenum through a corresponding opening in the first wall of the air plenum, and an outlet. The method also includes rigidly connecting the air nozzles to the first wall such that the inlet of each nozzle engages with a corresponding opening in the first wall of the air plenum and configuring the induction air handling unit such that the first wall forms a partition between the air plenum and an air mixing chamber, and the air nozzles are configured such that the outlet of each nozzle extends into the air mixing chamber to permit pressurized air to pass from the air plenum into the air mixing chamber through the air nozzles.
In some embodiments, forming an air plenum by extrusion includes forming the air plenum from an extruded metal. In some embodiments, the metal includes aluminum.
In some embodiments, machining the air nozzles includes using a CNC Swiss lathe to machine the air nozzles. In some embodiments, machining the air nozzles includes machining the air nozzles from metal. In some embodiments, machining the air nozzles includes machining a tapered bore through each air nozzle, the tapered bore connecting the inlet to the outlet. In some embodiments, machining the air nozzles includes machining a channel through each air nozzle extending between the inlet and the outlet thereof, such that the inlet is wider than the outlet, and the channel includes no straight bore. In some embodiments, machining the air nozzles includes machining threads on an outer surface of each nozzle near the inlet.
Various other components may be included and called upon for providing for aspects of the teachings herein. For example, additional materials, combinations of materials, and/or omission of materials may be used to provide for added embodiments that are within the scope of the teachings herein.
Standards for performance, selection of materials, functionality, and other discretionary aspects are to be determined by a user, designer, manufacturer, or other similarly interested parties. Any standards expressed herein are merely illustrative and are not limiting of the teachings herein.
When introducing elements of the present invention or the embodiment(s) thereof, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. Similarly, the adjective “another,” when used to introduce an element, is intended to mean one or more elements. The terms “including” and “having” are intended to be inclusive such that there may be additional elements other than the listed elements.
While the invention has been described with reference to illustrative embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. Although the title of the invention is “INDUCTION UNIT,” this title is not intended to be limiting and instead refers to particular examples described herein. Similarly, the field of the invention and description of related art are not intended to be limiting. In addition, many modifications will be appreciated by those skilled in the art to adapt a particular instrument, situation, or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
