EP3362759B1

EP3362759B1 - Heat exchanger for residential hvac applications

Info

Publication number: EP3362759B1
Application number: EP15804581.5A
Authority: EP
Inventors: Charbel RAHHAL; Kazuo Saito; Michael F. Taras; Tobias H. Sienel; Arindom Joardar; Lee G. Tetu; Jackie S. ANDERSON
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 2015-10-12
Filing date: 2015-10-12
Publication date: 2022-07-27
Anticipated expiration: 2035-10-12
Also published as: EP3362759A1; US20180299205A1; WO2017064531A1

Description

This disclosure relates generally to heat exchangers and, more particularly, to a heat exchanger configured for use as an outdoor heat exchanger in residential air conditioning and heat pump applications.
In recent years, much interest and design effort has been focused on the efficient operation of heat exchangers of refrigerant systems, particularly condensers and evaporators. A relatively recent advancement in heat exchanger technology includes the development and application of parallel flow (such as microchannel, minichannel, brazed-plate, plate-fin, or plate- and frame) heat exchangers as condensers and evaporators.
JP 2013-139971 , disclosing a heat exchanger according to the preamble of claim 1, US 5695004 and EP 0855567 disclose heat exchangers having headers with bends.
According to a first aspect of the invention, a heat exchanger is provided including a first header, a second header, and a plurality of heat exchange tubes arranged in a spaced parallel relationship and fluidly coupling the first and second headers. Both of the first header and second header include a bend. The heat exchanger has an aspect ratio between about 2 and 6 after formation of the bend, where the aspect ratio is a ratio of a length of the heat exchanger to a height of the heat exchanger. An inner diameter of the first header and the second header is equal to a width of one the plurality of heat exchanger tubes plus 1-4 mm
The plurality of heat exchange tubes may have a tube depth between about 8 mm and about 20 mm.
When the heat exchanger is configured for use in a refrigerant system having a capacity less than three tons, the depth of the plurality of heat exchange tubes may be about 10 mm.
When the heat exchanger is configured for use in an refrigerant system having a capacity less than three tons, the depth of the plurality of heat exchange tubes may be about 12 mm.
When the heat exchanger is configured for use in a refrigerant system having a capacity of at least three tons, the depth of the plurality of heat exchange tubes may be about 16 mm.
The plurality of heat exchange tubes may have a height of about 1.3 mm ± .3 mm.
The plurality of heat exchange tubes may have a tube pitch between about 8.9 mm and about 15.5. mm.
The plurality of heat exchange tubes may have a tube pitch of about 9.3 mm.
The heat exchanger may be configured for use in an air conditioning system.
The heat exchanger may be configured with a first pass and a second pass. In this case, as first portion of the plurality of heat exchange tubes is configured for the first pass, and a second portion of the plurality of heat exchange tubes is configured for the second pass, and a ratio of a number of heat exchange tubes within the first portion and the second portion is about 2.5 to 6.
The heat exchanger may be configured for use in a heat pump system.
The first header and the second header may be oriented generally horizontally with the plurality of heat exchange tubes extending generally vertically there between.
The first header and the second header may be bent to form a C or U-shape.
The heat exchanger may be configured with a first pass and a second pass, wherein a first portion of the plurality of heat exchange tubes is configured for the first pass, and a second portion of the plurality of heat exchange tubes is configured for the second pass, and a ratio of a number of heat exchange tubes within the first portion and the second portion is about 0.3 to about 3.
A plurality of fins may be disposed in thermal communication with the plurality of heat exchange tubes.
The plurality of fins may have a louver length between about 80% and 90 % of a fin height.
The plurality of fins may have a louver pitch between about 1 mm and 1.7 mm.
The plurality of fins may have a louver angle between about 28 degrees and about 45 degrees.
When the heat exchanger is configured for use in an air conditioning system, the plurality of fins may have a louver angle of about 32 degrees.
When the heat exchanger is configured for use in a heat pump system, the plurality of fins may have a louver angle of about 43 degrees.
The plurality of fins may have a fin density between about 10 fins per inch and about 25 fins per inch.
The plurality of fins may have a fin thickness between about .07 mm and about .1 mm.
The heat exchanger optionally is configured for use in an air conditioning system, with the plurality of fins having a fin density of 23 fins per inch.
When the heat exchanger is configured for use in a heat pump system, the plurality of fins may have a fin density of 16 fins per inch.
The bend may comprise a ratio of bend radius divided by a total thickness of the heat exchanger. The ratio of the bend radius to the total thickness of the heat exchanger may be greater than 4.
The bend may comprise a ratio of bend radius divided by a total thickness of the heat exchanger, with the ratio of the bend radius to the total thickness of the heat exchanger is greater than 10.
The heat exchanger may be part of an air management system, wherein the air management system is in fluid communication with the heat exchanger and is configured to impart an airflow having an average face velocity of greater than or equal to 200 feet per minute over an outer surface of the heat exchanger when the system is operating.
The air management system may comprise a fan.
A noise level of the air management system at a measurement distance of 1 meter from the system may be less than or equal to 65 dBa.
The subject matter, which is regarded as the present disclosure, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the present disclosure are apparent from the following detailed description of example embodiments taken in conjunction with the accompanying drawings in which:

FIG. 1 is an example of a conventional heat exchanger;
FIG. 2 is a perspective, partly sectioned view of an example of a parallel flow heat exchanger;
FIG. 3 is a cross-sectional view of a portion of the parallel flow heat exchanger of FIG. 2;
FIG. 4 is a perspective view of a heat exchanger configured for use in an air conditioning system and being outside the scope of the claims;
FIG. 5 is a perspective view of a heat exchanger configured for use in a heat pump system according to an example of the claimed invention; and
FIG. 6 is a schematic diagram of various configurations of a heat exchanger having multiple heat exchanger slabs.

The detailed description explains embodiments of the present disclosure, together with advantages and features, by way of example with reference to the drawings.
Microchannel heat exchangers as outdoor coils entered residential cooling only air conditioning applications and are being considered for the residential heat pump applications as well. Due to regulatory efficiency requirements, sound constraints, and a non-optimized heat exchanger design, the size of the outdoor heat exchanger is typically large. As a result, the heat pump and air conditioning systems incur higher costs and have a higher refrigerant charge. Current legislation limits the amount of charge of refrigerant systems, and heat exchangers in particular, containing most low global warming potential refrigerants (currently classified as A2L substances).
Microchannel heat exchangers have a small internal volume and therefore store less refrigerant charge than conventional round tube plate fin heat exchangers. Although a lower refrigerant charge is generally beneficial, the smaller internal volume of microchannel heat exchangers makes them extremely sensitive to overcharge or undercharge situations, which could result in refrigerant charge imbalance, degrade refrigerant system performance, and cause nuisance shutdowns. In addition, the refrigerant charge contained in the manifolds of the microchannel heat exchanger, particularly when the heat exchanger operates as a condenser, is significant, such as about half of the total heat exchanger charge. As a result, the refrigerant charge reduction potential of the heat exchanger is limited.
Referring now to FIG. 1, an example of a known parallel flow, microchannel heat exchanger is illustrated. The heat exchanger 20 includes a first manifold or header 30, a second manifold or header 40 spaced apart from the first manifold 30, and a plurality of heat exchange tubes 50 extending in a spaced parallel relationship between and fluidly connecting the first manifold 30 and the second manifold 40. In the illustrated, non-limiting embodiments, the first header 30 and the second header 40 are oriented generally horizontally and the heat exchange tubes 50 extend generally vertically between the two headers 30, 40. By arranging the tubes 50 vertically, water condensate collected on the tubes 50 is more easily drained from the heat exchanger 30. In the non-limiting embodiments illustrated in the FIGS., the headers 30, 40 comprise hollow, closed end cylinders having a circular cross-section. However, headers 30, 40 having other configurations, such as a semi-elliptical, square, rectangular, hexagonal, octagonal, or other cross-sections for example, are within the scope of the disclosure. The heat exchanger 20 may be used as either a condenser or an evaporator in a vapor compression system, such as a heat pump for example.
Referring now to FIGS. 2 and 3, each heat exchange tube 50 comprises a flattened heat exchange tube having a leading edge 52, a trailing edge 54, a first surface 56, and a second surface 58. The leading edge 52 of each heat exchanger tube 50 is upstream of its respective trailing edge 52 with respect to an airflow A through the heat exchanger 20. The interior flow passage of each heat exchange tube 50 may be divided by interior walls into a plurality of discrete flow channels 60 that extend over the length of the tubes 50 from an inlet end 62 to an outlet end 64 and establish fluid communication between the respective first and second manifolds 30, 40. The flow channels 60 may have a circular cross-section, a rectangular cross-section, a trapezoidal cross-section, a triangular cross-section, or another non-circular cross-section (e.g. elliptical, star shaped, closed polygon having straight or curved sides). The heat exchange tubes 50 including the discrete flow channels 60 may be formed using known techniques and materials, including, but not limited to, extrusion or folding.
As known, a plurality of heat transfer fins 70 (FIG. 3) may be disposed between and rigidly attached, usually by a furnace braze process, to the heat exchange tubes 50, in order to enhance external heat transfer and provide structural rigidity to the heat exchanger 20. Each folded fin 70 is formed from a plurality of connected strips or a single continuous strip of fin material tightly folded in a ribbon-like serpentine fashion thereby providing a plurality of closely spaced fins 72 that extend generally orthogonal to the flattened heat exchange tubes 50. Heat exchange between the fluid within the heat exchanger tubes 50 and the air flow A, occurs through the outside surfaces 56, 58 of the heat exchange tubes 50 collectively forming the primary heat exchange surface, and also through the heat exchange surface of the fins 72 of the folded fin 70, which form the secondary heat exchange surface.
Referring again to FIG. 1, the illustrated heat exchanger 20 has a single-pass flow configuration. For example, refrigerant is configured to flow from the first header 30 to the second header through the plurality of heat exchanger tubes 50 in the direction indicated by arrow B.
Due to the vertical orientation of the heat exchange tubes 50 in evaporator or heat pump applications, configurations of a parallel flow heat exchanger 20 having a multi-pass flow orientation have not been feasible due to refrigerant maldistribution, which is particularly challenging at high vapor qualities, such as in the intermediate manifolds for example. With reference now to FIGS. 4 and 5, two forms of optimized microchannel heat exchanger 20 having a multi-pass configuration are illustrated. Although the heat exchanger 20 is illustrated and described herein with reference to a plurality of microchannel tubes 50, embodiments including other types of tubes or conduits connecting the headers 30, 40 are also within the scope of the disclosure.
To form a multi-pass flow configuration, at least one of the first manifold 30 and the second manifold 40 includes two or more fluidly distinct sections or chambers. In an embodiment, the fluidly distinct sections are formed by coupling separate manifolds together to form the first or second manifold 30, 40. Alternatively, a baffle or divider plate (not shown) known to a person of ordinary skill in the art may be arranged within at least one of the first header 30 and the second header 40 to define a plurality of fluidly distinct sections therein.
With reference now to FIG. 4, a heat exchanger 20 configured for use in an air conditioning system (typically as a condenser) is illustrated in more detail. This heat exchange is outside the scope of the claims. As shown, the first header 30 and the second header 40 are arranged substantially vertically such that the plurality of heat exchange tubes 50 extends horizontally there between. The plurality of heat exchanger tubes 50 includes at least one bend. In the illustrated, non-limiting embodiment, the heat exchange tubes 50 form a substantial C or U-shape between the headers 30, 40. However, heat exchanger tubes 50 having any number of bends, such as to form an L, V, W, or S-shape for example, are also within the scope of the disclosure.
As shown in FIG. 4, the heat exchanger 20 has a two-pass configuration, with each of the first header 30 and second header 40 being divided into a first section and a second section. When the heat exchanger 20 is configured as a condenser, a gaseous refrigerant is provided to a first section 30a of the first header 30 via an inlet 80. From the first section 30a, the refrigerant flows through a first group 50a of heat exchange tubes 50 to the first section 40a of the second header 40. The refrigerant then passes into the second section 40b of the second header 40, through the second group 50b of heat exchange tubes 50, and into the second section 30b of the first header 30. Refrigerant within the second section 30b of the first header 30 may be provided to a downstream component of the system via an outlet 82. As the refrigerant flows sequentially through the first and second groups 50a, 50b of heat exchanger tubes 50, heat from the refrigerant is transferred to an adjacent flow of air A. As a result, a substantially liquid refrigerant is provided at the outlet 82. It should be understood that a heat exchanger having two passes illustrated and described herein is intended as an example only, and that a heat exchanger having any number of passes is also within the scope of the disclosure. For example, the number of passes of the heat exchanger 20 may be selected between 1 and 4 depending on the system capacity, refrigerant charge, and thermodynamic efficiency.
The heat exchanger 20 is generally optimized to minimize size and cost while similarly reducing refrigerant charge for a variety of air management systems and airflow configurations. Regardless of the pass configuration, , the heat exchanger 20 may have a face area between about 30% and about 60% of a baseline round tube plate fin heat exchanger. In addition, an air management system including a fan is configured to move air over an outer surface of the heat exchanger 20 with a face velocity of up to three times that of a baseline conventional propeller fan. For example, when the air management system is configured as an air conditioning system, the minimum face velocity is about 270 ft/min and when the air management system is configured as a heat pump syste,, the minimum face velocity is about 220 ft/min. The heat exchanger 20 may also be configured such that a ratio of the heat exchange tubes 50a in the first pass to the heat exchange tubes 50b in the second pass is about 2.5 to 6. In another embodiment, a ratio of the length of the heat exchanger 20 to the height of the heat exchanger 20 measured in a plane coinciding with the face area of the heat exchanger 20 (e.g. a plane perpendicular to the dimension along which the tube depth is measured) when folded in the bent configuration, also referred to as the aspect ratio, is between about 2 and 6.
With reference now to FIG. 5, a heat exchanger 20 configured for use in a heat pump system also has a shape including at least one bend. For example, the illustrated heat exchanger 20 has a C or U-shape similar to the heat exchanger 20 of FIG. 4. However, in this embodiment, the at least one bend is formed in the first header 30 and the second header 40, not the tubes 50. Each of the first header 30 and the second header 40 is generally divided into a first, second, and third section, respectively. A first group 50a of heat exchanger tubes 50 extends vertically between the first sections 30a, 40a of the first and second header 30, 40, a second group 50b of heat exchanger tubes 50 extends vertically between the second sections 30b, 40b of the first and second header 30, 40, and a third group 50c of heat exchanger tubes 50 extends vertically between the third sections 30c, 40c of the first and second header 30, 40. In an embodiment, a length of the first and third sections of the headers 30, 40 and the number of tubes 50 within the first and third groups 50a, 50c are substantially identical.
Although the heat exchanger 20 of FIG. 5 has a two-pass flow configuration, a configuration including any number of passes, for example between 2 and 5 passes is within the scope of the disclosure. The direction of fluid through the heat exchanger 20 may depend on the mode in which the heat pump is being operated. For example, when the heat exchanger 20 is configured to operate as an evaporator and heat the fluid therein, a two-phase refrigerant mixture is provided via an inlet (not shown) to the second section 30b of the first header 30. Within the second section 30b, the refrigerant is configured to flow through the second group 50b of tubes 50 to the second section 40b of the second header 40. From the second section 40b of the second header 40, the fluid flow is configured to divide such that a portion of the fluid flows into the first section 40a of the second header 40 and a portion of the fluid flows into the third section 40c of the second header 40, and through the first and third groups of tubes 50a, 50c, simultaneously. Once received within the first section 30a of the first header 30 and the third section 30c of the first header 30, the fluid is provided via outlets 80 to a conduit (not shown) where the fluid is rejoined and provided to a downstream component of a vapor compression system.
As the refrigerant flows sequentially through the second and first groups 50b, 50a of heat exchanger tubes 50, or alternatively, through the second and third groups 50b, 50c of heat exchanger tubes 50, heat from an adjacent flow of air A, is transferred to the refrigerant. As a result, a substantially vaporized refrigerant is provided at the outlets 80. Alternatively, refrigerant is configured to flow in a reverse direction through the heat exchanger 20 when operated as a condenser.
The face area of the heat exchanger 20 configured for use in a heat pump is between about 30% and about 70% of the baseline round tube plate fin heat exchanger with a higher face velocity of up to three times a baseline conventional propeller fan. This increased face velocity occurs as a result of the combination of increased air flow and the smaller face area of the heat exchanger 20. In addition, the noise generated by the heat exchanger 20 may be reduced compared to conventional heat exchangers. As a result, the noise of a system containing by the heat exchanger 20 is at or below an allowable noise level for residential applications. For example, the noise level of a refrigerant system measured at a distance of 1 meter from the system is less than or equal to 65dBa.
The heat exchanger 20 may also be configured such that when operated as a condenser, a ratio of the heat exchange tubes 50 in the first pass (50a and 50c) to the second pass (50b) is about .3 to 3. In another embodiment, the aspect ratio of the heat exchanger 20 is between about 2 and 6.
To further optimize the heat exchanger 20, for example a heat exchanger 20 configured for use in any heat transfer application and having any tube depth, the size of the headers 30, 40 is such that the headers 30, 40 have an inner diameter equal to a width of one of the heat exchange tubes 50 plus 1-4 mm (millimeters). In addition, the tubes 50 of the heat exchangers 20 may have a depth between about 8 mm and 16 mm, and in an embodiment between about 10 to 12 mm, or 10 mm. Further, in embodiments where the heat exchanger 20 is configured for use in a system having a capacity between about three tons and five tons, the tubes 50 may have a depth between about 12 mm and 22 mm, more specifically 14 to 16 mm. In another embodiment, the tubes 50 may have a height of about 1.3 mm ± .3 mm. The tubes of the heat exchanger 20 may additionally have a tube pitch between about 8.9 mm and 15.5 mm, e.g., 9.3 mm.
With respect to the fins 70, the fins 70 mounted to each of the plurality of tubes 50 may have a louver length between about 80%-90% of the fin height, a louver pitch between about 0.8 mm and 1.7 mm, e.g., 1.3 mm, and a louver angle between 28 degrees and 47 degrees. In an embodiment, the louver angle of the fins 70 in a heat exchanger 20 configured for use in an air conditioning system is about 30 degrees and the louver angle in a heat exchanger configured for use in a heat pump is about 45 degrees. The fin density in a heat exchanger 20 for use in an air conditioning system may be between about 18-25 fins/inch, e.g., 23 fins per inch. Alternatively, the fin density of a heat exchanger 20 configured for use in a heat pump may be between about 12-18 fins/inch, e.g., about 16 fins per inch.
The heat exchangers 20 provided herein result in a substantial size and therefore cost reduction, between 30 and 70% compared to other heat exchangers. Further, this reduced size can allow for refrigerant charge of the system to be reduced from 50-70% compared to the baseline heat exchanger. The heat exchangers 20 additionally have a higher performance due to improvements in both refrigerant and air distribution, along with the optimal heat transfer and hydraulic resistance balance by optimizing the number of refrigerant passes and airflow.
In an embodiment, the heat exchanger 20 has a multi-slab configuration such that the heat exchanger 20 includes at least a first slab 80 and a second, substantially identical slab 82 arranged downstream from the first slab 80 relative to an airflow A. In an embodiment, the plurality of heat exchange tubes 50, or alternatively, the headers 30, 40 include at least one bend to form the first heat exchanger slab 80 and the second heat exchanger slab 82. However, in alternate embodiments, the first slab 80 and the second slab 82 may be distinct. Various configurations of a heat exchanger 20 having a first and second heat exchanger slab 80, 82 are illustrated in FIG. 6. It should be understood that embodiments including more than two heat exchanger slabs are also within the scope of the disclosure.
A total thickness of the heat exchanger 20 is measured between an exterior surface of a first heat exchanger slab and an exterior surface of the furthest heat exchanger slab of the heat exchanger 20. In embodiments where the plurality of tubes 50 are bent, the ratio of the bend radius (measured to a centerline of the heat exchanger 20) to the total thickness of the heat exchanger 20 at the bend is greater than 10, and in an embodiment is equal to about 15 ± 4. In embodiments where the headers 30, 40 of the heat exchanger 20 are bent to define a plurality of heat exchanger slabs, the ratio of the bend radius to the total thickness of the heat exchanger at the bend is greater than 4, and in an embodiment is equal to about 7 ± 2.5. In addition, when the header 30, 40 is bent about 180 degrees, a spacer may be positioned on opposing sides of the bend to prevent the adjacent portions from contacting one another. By forming the one or more bends of the heat exchanger tubes 50 or the headers 30, 40 with a minimum bend radius, the formation of sharp bends that may constrict the flow of a fluid there through are eliminated. → Page 18
It is intended that the present invention not be limited to the particular embodiment(s) disclosed as, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

A heat exchanger, comprising:
a first header (30);

a second header (40);

a plurality of heat exchange tubes (50) arranged in spaced parallel relationship and fluidly coupling the first header and second header;

wherein the first header and the second header each include a bend, the heat exchanger having an aspect ratio between 2 and 6 after formation of the bend, where the aspect ratio is a ratio of a length of the heat exchanger to a height of the heat exchanger; and

characterized in that an inner diameter of the first header and the second header is equal to a width of one the plurality of heat exchanger tubes plus 1-4 mm.
The heat exchanger according to claim 1, wherein the plurality of heat exchange tubes (50) have a tube depth between 8 mm and 20 mm
The heat exchanger according to claim 2, wherein when the heat exchanger is configured for use in a refrigerant system having a capacity less than three tons, the depth of the plurality of heat exchange tubes (50) is about 10 mm, about 12 mm or about 16 mm
The heat exchanger according to any of the preceding claims, wherein the plurality of heat exchange tubes (50) have a height of 1.3 mm ± .3 mm
The heat exchanger according to any of the preceding claims, wherein the plurality of heat exchange tubes (50) have a tube pitch between 8.9 mm and 15.5. mm, such as about 9.3 mm
The heat exchanger according to any of the preceding claims, wherein the heat exchanger is configured for use in an air conditioning system.
The heat exchanger according to any of the preceding claims, wherein the heat exchanger is configured for use in a heat pump system.
The heat exchanger according to claim 7, wherein the first header (30) and the second header (40) are oriented generally horizontally and the plurality of heat exchange tubes (50) extend generally vertically there between, preferably wherein the first header (30) and the second header (40) are bent to form a C or U-shape.
The heat exchanger according to claim 7 or 8, wherein the heat exchanger is configured with a first pass and a second pass, a first portion of the plurality of heat exchange tubes being configured for the first pass, and a second portion of the plurality of heat exchange tubes being configured for the second pass, wherein a ratio of a number of heat exchange tubes within the first portion and the second portion is 0.3 to 3.
The heat exchanger according to any of the preceding claims, wherein a plurality of fins is disposed in thermal communication with the plurality of heat exchange tubes; optionally; wherein the plurality of fins have a louver length between 80% and 90 % of a fin height; and/or optionally wherein the plurality of fins have a louver pitch between 1 mm and 1.7 mm; and/or optionally wherein the plurality of fins have a louver angle between 28 degrees and 45 degrees such as 32 degrees or 43 degrees, when the heat exchanger is configured for use in an air conditioning system or a heat pump system respectively.
The heat exchanger according to claim 10, wherein the plurality of fins have a fin density between 10 fins per inch and 25 fins per inch.
The heat exchanger according to claim 10 or 11, wherein the plurality of fins have a fin thickness between 07 mm and .1 mm, optionally wherein when the heat exchanger is configured for use in an air conditioning system, the plurality of fins have a fin density of 23 fins per inch, or wherein when the heat exchanger is configured for use in a heat pump system, the plurality of fins have a fin density of 16 fins per inch.
The heat exchanger of any of the preceding claims, wherein the bend further comprises a ratio of bend radius divided by a total thickness of the heat exchanger, wherein the ratio is greater than 4.
The heat exchanger of any of the preceding claims, wherein the bend further comprises a ratio of bend radius divided by a total thickness of the heat exchanger, wherein the ratio is greater than 10.
A system comprising:
the heat exchanger according to any of the preceding claims; and

an air management system in fluid communication with the heat exchanger and configured to impart on an airflow having an average face velocity of greater than or equal to 200 feet per minute over an outer surface of the heat exchanger when the system is operating.