EP1395786B1

EP1395786B1 - Condenser for air cooled chillers

Info

Publication number: EP1395786B1
Application number: EP02739443A
Authority: EP
Inventors: Michael L. Kraay; Paul R. Glamm
Original assignee: American Standard International Inc
Current assignee: Trane International Inc
Priority date: 2001-06-14
Filing date: 2002-05-24
Publication date: 2006-04-26
Anticipated expiration: 2022-05-24
Also published as: CN1295476C; CN1516804A; EP1395786A1; US20040134226A1; US20020195240A1; CA2450306C; CA2450306A1; WO2002103270A1

Description

Background of the Invention

The present invention is directed to air cooled condensers for heating, ventilating and air conditioning (HVAC) systems. More specifically, the present invention is directed to aluminum heat exchangers for use in large air cooled air conditioning chillers, such chillers cooling a transport fluid for use in air conditioning elsewhere. In particular the present invention applies to a condenser using microchannel tubing, also known as parallel flow tubing or multi-path tubing.
HVAC condensers presently use fin and tube coils, primarily with copper tubes and aluminum fins. A significant weight reduction of the overall unit could be accomplished if the tubes were also formed of aluminum and then brazed or glued to the fins. Small sized brazed aluminum heat exchangers as microchannel tubing are used in the automotive industry. However, the application and the sizes are distinct. Automobile radiators are not as concerned about efficiency as the HVAC industry is. Also, simply resizing an automotive heat exchanger does not provide an optimum solution.
In order to accomplish this, the design of an aluminum heat exchanger with microchannel tubing must be analyzed and optimized.
U. S. Patent 4,998,580 to Guntly et al. and U. S. Patent 5,372,188 to Dudley et al. are directed to a condenser with a small diameter hydraulic flow path where hydraulic diameter is conventionally defined as four times the cross sectional area of the flow path divided by the wetted perimeter of the flow path. The Guntly et al. patent requires hydraulic diameters of about 0.07 inches and less while the Dudley et al. patent requires a hydraulic diameter in the range of 0.015 to 0.040 inches. This technology is used in the automotive industry and is not optimum for an air cooled chiller application.
GB 2 346 680 discloses a condenser for use in an air conditioning or refrigeration system having refrigerant flowpaths extending adjacent one another and grouped such that adjacent groups carry refrigerant passes in opposed directions across the condenser. The arrangement of groups is such that the number of refrigerant passes across the condenser is five or above. The refrigerant flowpaths may comprise tubes extending across the condenser.
EP 0 990 828 discloses a flat tube containing parallel flow channels, which have oval cross sections, and/or the outer tube surfaces have a corrugated contour corresponding to the flow channels. In vertical direction, the pipe is thinner between two flow channels than in the area of a flow channel. The large axis of the flow channels are at right angles or parallel to the transverse tube direction, or are angled relative to it.
US 5 967 228 discloses a heat exchanger for an air conditioner outdoor unit including tubing of the microchannel type which is internally partitioned into separate, parallel refrigerant flow passages and a wrapping of heat conductive flexible heat transfer material, commonly known as spine fin. The heat exchanger provides for greater heat transfer and a more compact package. Further, such heat exchangers allow for a reduced refrigerant charge in the air conditioning unit in which they are used.
US 6 062 303 discloses a multiflow type condenser for an automobile air conditioner comprising: a pair of header pipes disposed in parallel with each other and arranged to have an inlet and an outlet; a plurality of flat tubes each connected to said header pipes at opposite ends thereof, each of said flat tubes having a plurality of inside fluid paths, a hydraulic diameter of said inside fluid paths being in the range of about 1 to 1.7 mm; a plurality of corrugated fins each disposed between adjacent flat tubes; at least a pair of baffles disposed in said header pipes one by one; each of said baffles having a projection inserted into a slit provided with each header pipes and dividing each header pipes into a plurality of chambers; at least one by-pass passageway formed in the baffles to route a vapor-abundant phase of said refrigerant from an upper chamber to a lower chamber within the same header pipes by providing a communication path between the adjacent chambers; a ratio of a hydraulic diameter of said by-pass passageway over said hydraulic diameter of said inside fluid paths being in the range of about 0.28 to 2.25; and an area of a pass on the inlet side is about 30% to 65% of an overall area of all of said passes.
GB 2 133 525 discloses a flat tube of an evaporator for automotive air conditioners which is formed such that the upstream end portion of the tube with respect to the air stream flowing along the flat tube has a thicker wall than that of the remaining downstream portion of the same, thereby to cope with corrosive environments. The thicker upstream end portion effectively prevents the same from being severely corroded when used in areas where the atmosphere includes relatively large amounts of salt and humidity.
US 5 067 560 discloses a condenser for an air conditioning or refrigeration system having first, second, third and fourth condenser coils arranged in a modified "W" arrangement.

Summary of the Invention

The present invention is directed to solving the problem in the prior art systems.
It is desirable to provide an aluminum heat exchanger with multiple parallel flow paths for use in a large chiller for air conditioning purposes. It is a further desirable to significantly reduce the weight of a large chiller.
It is desirable to provide a heat exchanger with multiple parallel flow paths having a hydraulic diameter greater than 0.07 inches (1.8 mm) and less than 0.30 inches (7.6 mm). It is further desirable to provide a hydraulic diameter in the range greater than 0.07 inches (1.8 mm) and less than or equal to 0.26 inches (6.6mm). It is yet further desirable to provide a hydraulic diameter in the range greater than 0.07 inches (1.8 mm) and less than or equal to 0.14 inches (3.6mm). It is still further desirable to provide a hydraulic diameter in the range of 0.14 inches (3.6mm) less than or equal to 0.26 inches (6.6mm). Finally, in the preferred embodiments of the present invention the hydraulic diameter is either 0.07 inches (1.8mm) or 0.14 inches (3.6mm).
The present invention provides a heat exchanger. The heat exchanger comprises a first coil assembly including an inlet manifold, an outlet manifold parallel to and spaced from the inlet manifold; and a plurality of tubes each operably connected to and linking the inlet and the outlet manifolds. Each tube has a multiplicity of flow paths and a hydraulic diameter in the range of 0.07 ≤ to HD ≤ 0. 30 inches (1.8 ≤ HD ≤ 7.6mm).
The present invention also provides an air conditioning system including a compressor, a first heat exchanger as defined above, a fan motivating air across the first heat exchanger, an expansion device and a second heat exchanger serially linked into an air conditioning cycle by tubing.
The present invention further provides a method of manufacturing an air cooled chiller. The method comprises the steps of: forming a first heat exchanger to include a multiplicity of adjacent flow paths wherein the flow paths are sized and shaped to a preferred hydraulic diameter within the range of 0.07 ≤ the hydraulic diameter is ≤ 0.30 inches (1.8 ≤ HD ≤ 7,6 mm) where hydraulic diameter = 4 times the cross sectional area divided by the total wetted perimeter; providing a fan to move air across the multiplicity of adjacent flow paths; providing a compressor, a second heat exchanger, and an expansion device; and linking the compressor, the first heat exchanger, the expansion device, and the second heat exchanger serially into an air conditioning cycle by tubing.
Preferably, the method further comprises the step of transferring heat through a wall enclosing said flow paths and to a fluid contained therein.
Other preferred aspects are set out in the dependent claims.
In order that the present invention be more readily understood, specific embodiments thereof will now be described with reference to the accompanying drawings.

Brief Description of the Drawings

Figure 1 is a block diagram of an air cooled chiller system in accordance with an embodiment of the present invention.
Figure 2 shows a preferred embodiment of the present invention taken along lines 2-2 of Figure 1.
Figure 3 is an alternative embodiment of the multipath tubes shown in Figure 2.
Figures 4a and 4b are diagrams of fins used in the heat exchanger shown in Figure 1.
Figure 5 is a block diagram of a multiple coil assembly configuration as a preferred embodiment of Figure 1.

Detailed Description of the Drawings

Figure 1 shows an air conditioning system 10 including a compressor 12, a first heat exchanger 14 fimctioning as a condenser, an expansion device 16 such as an expansion valve, and a second heat exchanger 18 functioning as an evaporator. The compressor 12, the first heat exchanger 14, the expansion device 16, and the second heat exchanger 18 are serially linked in an air conditioning cycle by tubing 20. The first heat exchanger 14 functions as a condenser in releasing heat from the system, while the second heat exchanger 18 functions as an evaporator in cooling a fluid transported to and from the heat exchanger 18 by means of conduit 22. Such systems are generally well known and are sold by The Trane Company, a Division of American Standard Inc., under the registered trademarks CenTraVac and Series R
The condenser 14 is preferably formed of aluminum and has an inlet manifold 30 receiving hot gaseous refrigerant from the conduit 20 and the compressor 12. This hot gaseous refrigerant is distributed by the inlet manifold 30 to a plurality of tubes 32. These tubes 32 conduct the hot gaseous refrigerant from the inlet manifold 30 through the tubes 32 to an outlet manifold 34. In the process, the hot gaseous refrigerant is condensed and returns to the conduit 20 as a liquid where it is modulated through the expansion device 16 to the second heat exchanger 18. The tubes 32 are preferably microchannel or parallel flow tubing. Microchannel tubing is shown by U. S. 5,967,228.
Air is moved over the tubes 32 by an air moving device 36 such as a fan either to or away from the fan 36 as indicated by arrow 38. To enhance heat transfer from the tubes 32, fins 40 are provided to enhance the heat transfer. These fins 40 will be subsequently described with reference to Figure 4.
The preferred embodiment of the tubes 32 is shown in Figure 2 and an alternative embodiment is shown in Figure 3. The heat transfer tube 32 shown in Figure 2 includes a multiplicity of adjacent flow paths 40, 42, 44, 46 and 48 throughout the length of the tube 32 and surrounded by a common tube wall 50. The adjacent flow paths 40 through 48 are separated by barrier walls 52,54,56 and 58 respectively.
In Figure 2, the flow paths 40 and 48 are of similar shape and cross sectional area and the flow paths 42, 44 and 46 are of similar shape and cross sectional area. The flow paths 40,42,44,46 and 48 are sized and shaped to form a preferred hydraulic diameter HD within the range of: $0.07 < HD \leq 0.30 inches (1.8 < HD \leq 7.6 mm) .$
Hydraulic diameter is conventionally calculated according to the following formula: $Hydraulic Diameter (HD) = \frac{cross sectional area X 4}{total wetted perimeter}$
Empirical study shows that a 100 ton air cooled chiller should have a hydraulic diameter of at least 0.07 inches (1.8mm) whereas a 240 ton air cooled chiller should have a hydraulic diameter of about 0.14 inches (3.6mm). Linear extrapolation shows that a 480 ton air cooled chiller should have a hydraulic diameter of about 0.26 inches (6.6mm). Thus, the preferred range of hydraulic diameters is 0.07 < HD < 0.30 inches (1.8 < HD < 3.6 mm) with an intermediate range of 0.07 < HD ≤ 0.26 inches (1.8 < HD ≤ 6.6 mm). An optimum range appears to be 0.07 < HD < 0.14 inches (1.8 < HD < 3.6 mm), with preferred hydraulic diameter of 0.14 inches (3.6mm).
In determining the hydraulic diameter, the total cross sectional area of the flow paths 40, 42, 44, 46 and 48 is either measured or calculated, and the total wetted perimeter for those same flow paths is determined in a similar manner.
Figure 4a shows a first fin embodiment where a corrugated fin 40a is used. Similarly, Figure 4b shows the use of a sinusoidal fin 40b.
Figure 5 is directed to a multiple coil assembly embodiment of the invention in contrast to Figure 1 which shows a single coil assembly 70. In practice, multiple coil assemblies 70,72,74 and 76 might be used. The arrangement shown in Figure 5 is described in U.S. 5,067,560. The control of such a condenser is described in U.S. 5,138,844.
In Figure 5, the first coil assembly 70 is basically perpendicular to ground and a second coil assembly 76 is spaced from the first coil assembly 70 and is generally arranged in a parallel plane. A third coil assembly 72 is positioned between the first and second coil assembly 70,76 and lying in a plane which is not parallel to the planes of first and second coil assemblies 70,76. A fourth coil assembly 74 also lies between the first and second coil assembly 70,76 at a line in a plane which is not parallel to the planes of the first and second coil assembly 70,76. The fourth coil assembly 74 preferably is at a complimentary angle to the third coil assembly 72. The potential airflow paths are shown by arrows 80.
What has been described is a condenser for use in the large air cooled chiller. It will be apparent to a person of ordinary skill in the art that many alterations and modifications are readily apparent. Such modifications include varying the material from aluminum to other light weight materials having a good heat transfer coefficient as well as modifying the number and shape of the multiple flow paths within each tube. All such modifications and alterations are contemplated to fall within the scope of the following claims.

Claims

A heat exchanger (14) comprising:
a first coil assembly including

an inlet manifold (30);

an outlet manifold (34) parallel to and spaced from the inlet manifold; and

a plurality of tubes (32) each operably connected to and linking the inlet (30) and the outlet (34) manifolds, each tube (32) having a multiplicity of flow paths in a parallel arrangement characterized by each of the multiplicity of flow paths having at least first and second cross-sectional shapes and a hydraulic diameter HD in the range of 0.07 < HD < 0.30 inches (1.8mm < HD < 7.6mm).
The heat exchanger (14) of claim 1 wherein the multiplicity of flow paths (40 - 48) are in a parallel arrangement
The heat exchanger (14) of claim 2 further including fins (40) arranged in heat transfer relation between adjacent tubes of the plurality of tubes.
The heat exchanger (14) of claim 3 wherein the fins (40) have a sinusoidal shape.
The heat exchanger of claim 3 wherein the fins (40) have a corrugated shape.
The heat exchanger (14) of claim 3 further including a device (36) moving air across the first coil assembly and the heat exchanger (14) is primarily formed of aluminum.
The heat exchanger (14) of claim 3 further including a second coil assembly parallel to and spaced from the first coil assembly, each coil assembly lying in first and second respective planes which are substantially parallel to each other.
The heat exchanger (14) of claim 7 including a third coil assembly located between the first and second coil assemblies and lying in a third plane not parallel to the first and second planes.
The heat exchanger of claim 8 further including a fourth coil assembly between the first and second coil assemblies and lying in a fourth plane not parallel to the first and second planes wherein the angle of the fourth plane is complementary to the angle of the third plane.
An air conditioning system comprising:
a compressor (12),

a first heat exchanger (14) according to any of claims 1 to 11,

a fan (36) motivating air across the first heat exchanger (14),

an expansion device (16) and a second heat (18) exchanger serially linked into an air conditioning cycle by tubing.
The system of claim 10 wherein the multiplicity of adjacent flow paths in the first heat exchanger (14) are formed of aluminum.
The system of claim 10 or 11 wherein the first heat exchanger (14) includes first, second, third and fourth coil assemblies, each coil assembly including the multiplicity of flow paths, and said first, second, third and fourth coil assemblies each having a planar dimension such that the coil assemblies form a W shape when viewed in a direction perpendicular to a common plane to first, second, third and fourth coil assemblies.
The system of claims 10 to 12 wherein the multiplicity of flow paths are in first and second differing shapes.
The system of claims 10 to 13 wherein the first shape is rectangular and the second shape includes an arced surface.
A method of manufacturing an air cooled chiller comprising the steps of:
forming a first heat exchanger (14) to include a multiplicity of adjacent flow paths having at least first and second cross-sectional shapes, wherein the flow paths are sized and shaped to a preferred hydraulic diameter HD within the range of 0.07 < HD < 0.30 inches (1.8 < HD < 7.6 mm);

providing a fan (36) to move air across the multiplicity of adjacent flow paths (40-48);

providing a compressor (12), a second heat exchanger (18), and an expansion device (16); and

linking the compressor (12), the first heat exchanger (14), the expansion device (16), and the second heat exchanger (18) serially into an air conditioning cycle by tubing.
The method of claim 15 including the further step of:
adaptively configuring the second heat exchanger (18) to chill the temperature of a liquid.
The method of claim 15 including the further step of:
forming the first heat exchanger (14) from aluminum.
The method of claim 17 including the further step of interconnecting adjacent ones of the multiplicity of flow paths with a corrugated or sinusoidal fin (40).
The method of claim 18 including the step of arranging the multiplicity of flow paths in a common plane.
A method according to any of claims 15 to 19 further comprising the step of transferring heat through a wall enclosing said flow paths and to a fluid contained therein.
The method of claim 20 including forming the wall from aluminum.
The method of claims 15 to 21 including forming the flow paths into first and second distinct cross-sectional shapes.