HEAT EXCHANGER ASSEMBLY

Abstract

Described herein is a heat exchanger assembly that comprises a first heat exchanger comprising a first inlet header, a first outlet header, and a plurality of first heat exchange tubes fluidically connected to and extending between the first inlet header and the first outlet header. The heat exchanger assembly further comprises a second heat exchanger comprising a second inlet header, a second outlet header, and a plurality of second heat exchange tubes fluidically connected to and extending between the second inlet header and the second outlet header. Further, the heat exchanger assembly comprises a first outlet connector connected to a first end of the first outlet header, and a second outlet connector connected to a first end of the second outlet header, wherein a second end, opposite to the first end, of the respective first outlet header and the second outlet header are adjacent to each other.

Claims

1. A heat exchanger assembly comprising: a first heat exchanger comprising a first inlet header, a first outlet header, and a plurality of first heat exchange tubes fluidically connected to and extending between the first inlet header and the first outlet header; a second heat exchanger comprising a second inlet header, a second outlet header, and a plurality of second heat exchange tubes fluidically connected to and extending between the second inlet header and the second outlet header; a first outlet connector connected to a first end of the first outlet header; and a second outlet connector connected to a first end of the second outlet header, wherein a second end, opposite to the first end, of the respective first outlet header and the second outlet header are adjacent to each other.

2. The assembly of claim 1, wherein the first heat exchanger and the second heat exchanger are arranged adjacent to each other along a same plane such that the first inlet header and the second inlet header remain in line, and the first outlet header and the second outlet header remain in line.

3. The assembly of claim 1, wherein the assembly is configured to receive a fluid within the first inlet header and the second inlet header through a non-adjacent end of the first inlet header and the second inlet header, respectively.

4. The assembly of claim 3, wherein the assembly further comprises: a first inlet connector connected to a first end of the first inlet header; and a second inlet connector connected to a first end of the second inlet header, wherein a second end of the respective first inlet header and the second inlet header remain adjacent to each other.

5. The assembly of claim 4, wherein the assembly further comprises: a first expansion valve fluidically connecting the first inlet connector to a refrigerant line, the first expansion valve configured to regulate a supply of the fluid within the first inlet header; and a second expansion valve fluidically connecting the second inlet connector to a refrigerant line, the second expansion valve configured to regulate the supply of the fluid within the second inlet header.

6. The assembly of claim 1, wherein the assembly is configured to allow extraction of a fluid, received in the first outlet header and the second outlet header, through a non-adjacent end of the first outlet header and the second outlet header, respectively.

7. The assembly of claim 1, wherein the first heat exchanger and the second heat exchanger are mirror images of each other.

8. The assembly of claim 4, wherein the assembly further comprises a common fluid collector fluidically connecting the first outlet connector and the second outlet connector of the assembly to a compressor.

9. The assembly of claim 1, wherein the first and second heat exchangers are arranged adjacent to each other such that a gap remains between adjacent sides of the first heat exchanger and the second heat exchanger.

10. The assembly of claim 9, wherein the assembly further comprises a support pad configured in the gap between the adjacent sides of the first heat exchanger and the second heat exchanger, and wherein the support pad is made of a thermally insulative material.

11. The assembly of claim 9, wherein the gap is less than or equal to 2 millimeters.

12. The assembly of claim 1, wherein the first heat exchanger and the second heat exchanger are supported on one or more mounting fixtures.

13. The assembly of claim 1, wherein the first heat exchanger and the second heat exchanger are supported on separate mounting fixtures.

14. The assembly of claim 1, wherein the first heat exchanger and the second heat exchanger are identical.

15. The assembly of claim 1, wherein the first heat exchanger and the second heat exchanger are non-identical.

16. The assembly of claim 1, wherein the plurality of first heat exchange tubes and the plurality of second heat exchange tubes of the respective the first heat exchanger and the second heat exchanger are in any one of: a single slab configuration, a multi-slab configuration, a one full slab and a fractional-slab configuration, and a two full slab configuration.

17. The assembly of claim 1, wherein the assembly is in a downward-flow configuration.

18. The assembly of claim 1, wherein the assembly is in an upward-flow configuration.

19. The assembly of claim 1, wherein the assembly is associated with a rooftop unit having a heat exchanger length ranging from 40 inch to 120 inch, and a capacity ranging from 5 Ton to 50 Ton.

20. A method comprising: providing at least a first heat exchanger and a second heat exchanger, wherein the first heat exchanger comprises a first outlet header connected to a first outlet connector at a first end of the first outlet header, and wherein the second heat exchanger comprises a second outlet header connected to a second outlet connector at a first end of the second outlet header; arranging the first heat exchanger and the second heat exchanger such that a second end, opposite to the first end, of the respective first outlet header and the second outlet header are adjacent to each other.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings are included to provide a further understanding of the subject disclosure and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the subject disclosure and, together with the description, serve to explain the principles of the subject disclosure.

[0024] In the drawings, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label with a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

[0025] FIGS. 1A and 1B illustrate exemplary views of a heat exchanger assembly for a heating, ventilation, and air conditioning (HVAC) unit or rooftop units (RTU) in accordance with one or more embodiments of the subject disclosure.

[0026] FIG. 1C illustrates an exemplary view of the heat exchanger assembly having a thermally insulative support pad between the adjacent sides of the first heat exchanger and the second heat exchanger headers associated with the heat exchanger assembly in accordance with one or more embodiments of the subject disclosure.

[0027] FIG. 1D illustrates an exemplary view of a heat exchanger assembly for an HVAC unit or RTU where the first heat exchanger and the second heat exchanger are non-identical in accordance with one or more embodiments of the subject disclosure.

[0028] FIG. 1E illustrates an exemplary view of the heat exchanger assembly where the first heat exchanger and the second heat exchanger are supported on separate mounting fixtures in accordance with one or more embodiments of the subject disclosure.

[0029] FIG. 1F illustrates an exemplary view of the heat exchanger assembly where the first heat exchanger and the second heat exchanger are supported on a single mounting fixture in accordance with one or more embodiments of the subject disclosure.

DETAILED DESCRIPTION

[0030] The following is a detailed description of embodiments of the subject disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the subject disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the subject disclosure as defined by the appended claims.

[0031] Various terms are used herein. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.

[0032] In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the subject disclosure, the components described herein may be positioned in any desired orientation. Thus, the use of terms such as above, below, upper, lower, first, second or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, described herein may be oriented in any desired direction.

[0033] Construction of microchannel heat exchangers (MCHX) involves connecting several microchannel tubes between an inlet header (manifold) and an outlet header. Conventionally, these components, including the headers, the tubes, and fins, are then assembled and subjected to a brazing process in a furnace, resulting in the formation of an MCHX coil. However, the maximum size of the MCHX coil manufactured is constrained by the dimensions of the brazing oven and the length of the coil's manifold. The largest rooftop units (RTUs) or heating, ventilation, and air conditioning (HVAC) units may involve header lengths that may exceed the capacity of existing industrial brazing ovens. There is therefore a need to address this limitation, by providing an improved and efficient solution for manufacturing longer MCHX coils without compromising on the refrigerant distribution across the heat exchange tubes.

[0034] Referring to FIGS. 1A to 1D, a heat exchanger assembly 100 for HVAC units or RTUs is disclosed. The assembly 100 may include a first heat exchanger 100A that may include a first inlet header 102, a first outlet header 104, and a plurality of first heat exchange tubes 106 fluidically connected to and extending between the first inlet header 102 and the first outlet header 104. Further, the assembly 100 may include a second heat exchanger 100B that may include a second inlet header 108, a second outlet header 110, and a plurality of second heat exchange tubes 112 fluidically connected to and extending between the second inlet header 108 and the second outlet header 110. In one or more embodiments, the plurality of first heat exchange tubes 106 and the second heat exchange tubes 112 may be microchannel heat exchange (MCHX) tubes forming an MCHX coil. In one or more embodiments, the first heat exchanger 100A and the second heat exchanger 100B may be arranged adjacent to each other along the same plane P such that the first inlet header 102 and the second inlet header 108 remain in line along a first longitudinal axis (A-A), and the first outlet header 104 and the second outlet header 110 remain in line along a second longitudinal axis (B-B). This assembly 100 of the first and second heat exchangers 100A, 100B may accordingly act and operate as a single heat exchanger having longer headers and longer MCHX coils, which may be employed in an HVAC unit (not shown). In one or more embodiments, the HVAC unit may be a RTU having a heat exchanger length ranging from 40 inches to 120 inches, and a capacity ranging from 5 Ton to 50 Ton.

[0035] As illustrated, the first heat exchanger 100A and the second heat exchanger 100B may be arranged adjacent to each other along the same plane P such that first end 102-1, 104-1 of the first inlet header 102 and the first outlet header 104 may remain on the same side, and second end 102-2, 104-2 (opposite to the first end) of the first inlet header 102 and the first outlet header 104 may remain on the same side. Further, first end 108-1, 110-1 of the second inlet header 108 and the second outlet header 110 may remain on the same side, and second end 108-2, 110-2 (opposite to the first end) of the second inlet header 108 and the second outlet header 110 may remain on the same side. Furthermore, the second end 104-2, 110-2 of the respective first outlet header 104 and the second outlet header 110 may remain adjacent to each other, and the first end 104-1, 110-1 of the respective first outlet header 104 and the second outlet header 110 may remain opposite to each other.

[0036] In one or more embodiments, the assembly 100 may include a first inlet connector 114-1 connected to the first end 102-1 of the first inlet header 102, and a second inlet connector 114-2 connected to the first end 108-1 of the second inlet header 108. In addition, the assembly 100 may include a first outlet connector 116-1 connected to a first end 104-1 of the first outlet header 104, and a second outlet connector 116-2 connected to a first end of the second outlet header 110. Further, in one or more embodiments, the HVAC unit may include a common fluid collector 118 fluidically connecting the first outlet connector 116-1 and the second outlet connector 116-2 of the assembly 100 to a compressor 126 (shown in FIGS. 1A and 1C) associated with the HVAC unit.

[0037] In addition, in one or more embodiments, the HVAC unit may include a first expansion valve 120-1 fluidically connecting the first inlet connector 114-1 to a refrigerant line 122 or an evaporator (not shown) associated with the HVAC unit, where the first expansion valve 120-1 may be configured to regulate the supply of the fluid within the first inlet header 102. The HVAC unit may further include a second expansion valve 120-2 fluidically connecting the second inlet connector 114-2 to the refrigerant line or the evaporator associated with the HVAC unit, where the second expansion valve 120-2 may be configured to regulate the supply of the fluid within the second inlet header 108. In such embodiments, the refrigerant line extending from an outlet of the evaporator may split into separate lines 122-1, 122-2 before entering the first and second expansion valves 120-1, 120-2. However, in other embodiments, the HVAC unit may include a single expansion valve fluidically connecting the first inlet connector 114-1 as well as the second inlet connector 114-2 to the evaporator via a single refrigerant line 122. Further, a sensing unit associated with the corresponding expansion valves may be in thermal or fluidic communication with the outlets of the first and second outlet headers 104, 110, to sense the temperature of the refrigerant or fluid exiting the first and second outlet header 104, 110.

[0038] In one or more embodiments, the assembly 100 may be in an upward-flow configuration, such that the first outlet header 104 and the first heat exchange tubes 106 remain above the first inlet header 102, and the second outlet header 110 and the second heat exchange tubes 112 remain above the second inlet header 108. However, in other embodiments (not shown), the assembly 100 may also be in a downward-flow configuration, such that the first outlet header 104 and the first heat exchange tubes 106 remain below the first inlet header 102, and the second outlet header 110 and the second heat exchange tubes 112 remain below the second inlet header 108, and all such embodiments are well within the scope of the subject disclosure without any limitations.

[0039] In one or more embodiments, the assembly 100 may be oriented along a vertical plane, such that the first outlet header 104, the first heat exchange tubes 106, the first inlet header 102, the second outlet header 110, the second heat exchange tubes 112, and the second inlet header 108 remain oriented along the same vertical plane. Further, in other embodiments, the assembly 100 may be in a horizontal arrangement, such that the first outlet header 104, the first heat exchange tubes 106, the first inlet header 102, the second outlet header 110, the second heat exchange tubes 112, and the second inlet header 108 remain oriented along the same horizontal plane at the same elevation. However, in some embodiments, the assembly 100 may also be oriented at an angle from the horizontal plane or the vertical plane, in any of the upward-flow configuration or downward-flow configuration, and all such embodiments are well within the scope of the subject disclosure without any limitations.

[0040] In one or more embodiments, the assembly 100 may be configured to receive the refrigerant from refrigerant line 122 within the first inlet header 102 and the second inlet header 108 through the non-adjacent end (or first end) 102-1, 108-1 of the first inlet header 102 and the second inlet header 108 via the corresponding inlet connectors 114-1, 114-2 and the expansion valves 120-1, 120-2. For instance, the first inlet header 102 may receive the refrigerant through the first end 102-1 via the first inlet connector 114-1 and the first expansion valve 120-1, and the second inlet header 108 may receive the refrigerant through the first end 108-1 via the second inlet connector 114-2 and the second expansion valve 120-2. The received refrigerant may then flow towards the adjacent ends (or second ends) 102-2, 108-2 of the first inlet header 102 and the second inlet header 108, respectively, causing the refrigerant to flow along an entire length of the respective inlet headers 102, 108 and further uniformly distribute and flow into the first and second heat exchange tubes 106, 112 associated with the first and second heat exchangers 100A, 100B.

[0041] Further, the refrigerant may flow from the first heat exchange tubes 106 and the second heat exchange tubes 112 into the first outlet header 104 and the second outlet header 110, respectively. The assembly 100 may be further configured to allow extraction of the refrigerant, received in the first outlet header 104 and the second outlet header 110, through the non-adjacent end (or first end) 104-1, 110-1 of the first outlet header 104 and the second outlet header 110. For instance, the first outlet header 104 may allow extraction of the refrigerant through the first end 104-1 via the first outlet connector 116-1, and the second outlet header 110 may allow extraction of the refrigerant through the first end 110-1 via the second outlet connector 116-2. As a result, the overall assembly 100 may allow the received refrigerant to evenly distribute and flow into the inlet ports associated with the heat exchange tubes of both the first and second heat exchangers 100A, 100B, thereby enabling uniform and efficient heat exchange between the flowing refrigerant and fluid/air flowing across the respective heat exchange tubes. Thus, the assembly 100 provides or acts as a single heat exchanger having longer headers and longer MCHX coils, which enables uniform and efficient refrigerant distribution across the heat exchange tubes or MCHX coils.

[0042] In one or more embodiments, the first heat exchanger 100A and the second heat exchanger 100B may be identical having the same dimension and size, which may be arranged adjacent to each other along the same plane P such that the first heat exchanger 100A and the second heat exchanger 100B may form mirror image to each other as shown in FIGS. 1A to 1C. However, in other embodiments, the first heat exchanger 100A and the second heat exchanger 100B may not be identical but may be arranged adjacent to each other along the same plane P as shown in FIG. 1D.

[0043] While various embodiments and drawings described herein illustrate the heat exchange tubes 106, 112 associated with the first heat exchanger 100A and the second heat exchanger 100B having a single slab configuration, however, the first heat exchanger 100A and the second heat exchanger 100B may also have multi-slab configuration, a one full slab and a fractional-slab configuration, and a two full slab configuration, and all such embodiments are well within the scope of the subject disclosure without any limitation.

[0044] In one or more embodiments, the first and second heat exchangers 100A, 100B may be arranged adjacent to each other such that a gap (G) remains between adjacent sides of the first heat exchanger 100A and the second heat exchanger 100B as shown in FIGS. 1A, 1B, and 1D, such that substantially no air may flow between the adjacent ends of the headers associated with the assembly 100 or through the middle area of the assembly 100. More particularly, the gap (G) may be between adjacent end 102-2, 108-2 of the first inlet header 102 and the second inlet header 108. Similarly, the gap (G) may be between adjacent end 104-2, 110-2 of the first outlet header 104 and the second outlet header 110. In one or more embodiments, the gap (G) may be less than or equal to 2 mm, however, in other embodiments, the gap (G) may also be more than 2 mm.

[0045] Further, in one or more embodiments, the assembly 100 may include a support pad 124 made of thermally insulative material being configured in the gap between the adjacent sides of the first heat exchanger 100A and the second heat exchanger 100B as shown in FIG. 1C to prevent heat exchange between the headers of the first and second heat exchangers 100A, 100B, and further provide structural support and stability to the headers and the overall assembly 100. More particularly, the support pad 124 may be between adjacent end 102-2, 108-2 of the first inlet header 102 and the second inlet header 108. Similarly, the support pad 124 may be between adjacent end 104-2, 110-2 of the first outlet header 104 and the second outlet header 110.

[0046] In one or more embodiments, the first heat exchanger 100A and the second heat exchanger 100B may be supported on one or more mounting fixtures installed on a rigid surface. Further, in one or more embodiments, the first heat exchanger 100A and the second heat exchanger 100B may be supported on separate mounting fixtures 128-1, 128-2 as shown in FIG. 1E. However, the heat exchangers 100A, 110B may also be supported on a common mounting fixture 130 as shown in FIG. 1F. The mounting fixtures may include a set of rods or brackets forming a frame that may be secured on the rigid surface using fasteners.

[0047] In one or more embodiments, the assembly 100 in the upward-flow configuration may include a first mounting fixture configured to support the first inlet header 102 of the first heat exchanger 100A thereon such that the corresponding first outlet header 104 and the first heat exchange tubes 106 remain above and in non-contact with the first mounting fixture. The assembly 100 may further include a second mounting fixture configured to support the second inlet header 108 of the second heat exchanger 100B thereon such that the corresponding second outlet header 110 and the second heat exchange tubes 112 remain above and in non-contact with the second mounting fixture. However, in some embodiments, the first and second mounting fixtures in contact with the first inlet header 102 and the second inlet header 108, may also support the MCHX coils associated with the assembly 100.

[0048] In one or more embodiments, the assembly 100 in the upward-flow configuration may include a first mounting fixture configured to support the first outlet header 104 of the first heat exchanger 100A thereon such that the corresponding first inlet header 102 and the first heat exchange tubes 106 remain below and in non-contact with the first mounting fixture. The assembly 100 may further include a second mounting fixture configured to support the second outlet header 110 of the second heat exchanger 100B thereon such that the corresponding second inlet header 108 and the second heat exchange tubes 112 remain above and in non-contact with the second mounting fixture. However, in some embodiments, the first and second mounting fixtures in contact with the first outlet header 104 and the second outlet header 110, may also support the MCHX coils associated with the assembly 100.

[0049] In one or more embodiments, the assembly 100 in the downward-flow configuration may include a first mounting fixture configured to support the first outlet header 104 of the first heat exchanger 100A thereon such that the corresponding first inlet header 102 and the first heat exchange tubes 106 remain above and in non-contact with the first mounting fixture. The assembly 100 may further include a second mounting fixture configured to support the second outlet header 110 of the second heat exchanger 100B thereon such that the corresponding second inlet header 108 and the second heat exchange tubes 112 remain above and in non-contact with the second mounting fixture. However, in some embodiments, the first and second mounting fixtures in contact with the first outlet header 104 and the second outlet header 110, may also support the MCHX coils associated with the assembly 100.

[0050] In one or more embodiments, the assembly 100 in the downward-flow configuration may include a first mounting fixture configured to support the first inlet header 102 of the first heat exchanger 100A thereon such that the corresponding first outlet header 104 and the first heat exchange tubes 106 remain below and in non-contact with the first mounting fixture. The assembly 100 may further include a second mounting fixture configured to support the second inlet header 108 of the second heat exchanger 100B thereon such that the corresponding second outlet header 110 and the second heat exchange tubes 112 remain below and in non-contact with the second mounting fixture. However, in some embodiments, the first and second mounting fixtures in contact with the first inlet header 102 and the second inlet header 108, may also support the MCHX coils associated with the assembly 100.

[0051] In one or more embodiments, the assembly 100 may be in any of a single slab configuration, a multi-slab configuration, a one full slab and a fractional-slab configuration, and a two full slab configuration.

[0052] While various embodiments herein have been described for the assembly having a pair of heat exchangers 100A, 110B configured adjacent to each other, however, the number of heat exchangers in the assembly 100 may be more than two also, as long as these heat exchangers are configured adjacent to each other along the same plane P, without any limitations, and all such embodiments are well within the scope of this disclosure.

[0053] It is to be appreciated that the use of two adjacently configured shorter heat exchangers (first and second heat exchangers) along the same plane in this disclosure compared to a conventional single large heat exchanger (having substantially the same combined length of the first and second heat exchangers) are easier and cost-effective to manufacture due to limited size of brazing ovens available in the industry, thereby making the overall HVAC unit cost-effective, and easier to be manufactured. In addition, the use of shorter headers makes the overall assembly and HVAC unit modular, allowing easier and quicker variation in the length of the MCHX coils as per the cooling demand. Moreover, shorter-length inlet headers may also facilitate improved refrigerant distribution across the MCHX coils compared to the longer inlet headers.

[0054] While various embodiments and drawings have been described herein for the heat exchanger assembly having a single slab configuration, however, the heat exchanger assembly may also be of a multi-slab configuration, a one full slab and a fractional-slab configuration, or a two full slab configuration, without any limitations, and all such embodiments are well within the scope of this disclosure.

[0055] Additionally, as the refrigerant inlets and refrigerant outlets of the headers associated with the two heat exchangers in this disclosure are on the opposite (extreme) ends and not at the adjacent ends, a minimal gap (less than 2 mm) may be kept between the headers, which may allow the assembly to function as a single longer heat exchanger assembly with improved refrigerant distribution. This minimal gap between the headers may also prevent air from flowing between the adjacent headers or through the middle area of the assembly, thereby preventing air bypass. Moreover, the use of a thermally insulative support pad in the gap between the adjacent ends of the headers may prevent air bypass and provide structural support and stability to the headers as well as the overall assembly.

[0056] Another aspect of the subject disclosure relates to a method for making a heat exchanger assembly, such as assembly 100 of FIGS. 1A to 1E.

[0057] In one or more embodiments, the method includes providing at least a first heat exchanger and a second heat exchanger (such as first and second heat exchangers 100A and 100B of FIG. 1, respectively), where the first heat exchanger includes a first outlet header connected to a first outlet connector at a first end of the first outlet header, and the second heat exchanger includes a second outlet header connected to a second outlet connector at a first end of the second outlet header. In one or more embodiments, the first and the second heat exchangers may be brazed with corresponding tubes, fins, and/or headers (and/or MCHX coils) separately.

[0058] In one or more embodiments, the method includes arranging the first heat exchanger and the second heat exchanger such that a second end, opposite to the first end, of the respective first outlet header and the second outlet header are adjacent to each other.

[0059] Thus, this disclosure provides an improved, efficient, and modular solution for manufacturing longer MCHX coils without compromising on refrigerant distribution across the heat exchange tubes.

[0060] While the subject disclosure has been described with reference to exemplary 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 subject disclosure as defined by the appended claims. Modifications may be made to adopt a particular situation or material to the teachings of the subject disclosure without departing from the scope thereof. Therefore, it is intended that the subject disclosure not be limited to the particular embodiment disclosed, but that the subject disclosure includes all embodiments falling within the scope of the subject disclosure as defined by the appended claims.

[0061] In interpreting the specification, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms comprises and comprising should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refer to at least one of something selected from the group consisting of A, B, C . . . and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.