Heat Exchanger Assembly and Method for Hvac System

This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the presently described embodiments. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present embodiments. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

Modern residential and industrial customers expect indoor spaces to be climate controlled. In general, heating, ventilation, and air conditioning (“HVAC”) systems circulate an indoor space's air over low-temperature (for cooling) or high-temperature (for heating) sources, thereby adjusting the indoor space's ambient air temperature. HVAC systems generate these low-and high-temperature sources by, among other techniques, taking advantage of a well-known physical principle: a fluid transitioning from gas to liquid releases heat, while a fluid transitioning from liquid to gas absorbs heat. Within a typical HVAC system, a fluid refrigerant circulates through a closed loop of tubing that uses a compressor and other flow-control devices to manipulate the refrigerant's flow and pressure, causing the refrigerant to cycle between the liquid and gas phases. Generally, these phase transitions occur within the HVAC's heat exchangers, which are part of the closed loop and designed to transfer heat between the circulating refrigerant and flowing ambient air.

In some instances, a HVAC system is a split system having indoor and outdoor units, each having a heat exchanger, connected in fluid communication. As would be expected in such cases, the heat exchanger providing heating or cooling to the climate-controlled space or structure is described adjectivally as being “indoors,” and the heat exchanger transferring heat with the surrounding outdoor environment is described as being “outdoors.” The refrigerant circulating between the indoor and outdoor heat exchangers—transitioning between phases along the way—absorbs heat from one location and releases it to the other. Those in the HVAC industry describe this cycle of absorbing and releasing heat as “pumping.” To cool the climate-controlled indoor space, heat is “pumped” from the indoor side to the outdoor side. And the indoor space is heated by doing the opposite, pumping heat from the outdoors to the indoors.

In some other instances, a packaged HVAC system is a self-contained unit including two heat exchangers (e.g., an evaporator coil and a condenser coil), a blower, a compressor, and a refrigerant circuit installed in a shared cabinet. A packaged HVAC system can be installed at any suitable location but is often installed outside, such as on the ground or on the roof of a building. Heated or cooled air is provided from the packaged HVAC system to the indoor space of a building, such as through a supply duct, and air is drawn from the indoor space to the packaged HVAC system, such as through a return duct.

Certain aspects of some embodiments disclosed herein are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below.

Certain embodiments of the present disclosure generally relate to heat exchangers for HVAC systems. More specifically, some embodiments relate to a microchannel heat exchanger having an array of tubes arranged between a first manifold and a second manifold. Refrigerant may be routed between the first and second manifolds via tubes of the array. But in at least some instances, the array of tubes includes at least one “dead” tube that is not in fluid communication with the first and second manifold and does not convey the refrigerant between these manifolds. In the case of a multi-pass heat exchanger, so-called dead tubes may be provided in the array to reduce thermal cross-conduction between tubes of two different passes. Dead tubes may also or instead be provided in the array to reduce corrosion and increase reliability of the heat exchanger. Still further, dead tubes may also or instead be provided in the array to reduce thermal stress in the heat exchanger. If the dead tubes are positioned at the microchannel heat exchanger ends, they provide mechanical protection to the live tubes caring refrigerant. Therefore, the dead tubes are strategically positioned within the microchannel heat exchanger array. The heat exchangers may be installed in a packaged system, a split system, or any other suitable HVAC system.

Various refinements of the features noted above may exist in relation to

various aspects of the present embodiments. Further features may also be incorporated in these various aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to one or more of the illustrated embodiments may be incorporated into any of the above-described aspects of the present disclosure alone or in any combination. Again, the brief summary presented above is intended only to familiarize the reader with certain aspects and contexts of some embodiments without limitation to the claimed subject matter.

Specific embodiments of the present disclosure are described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

As noted above, some embodiments of the present disclosure relate to heat exchangers with an array of tubes in which some of the tubes convey refrigerant but one or more of the tubes are dead tubes that do not convey refrigerant. In some instances, such a heat exchanger is a microchannel heat exchanger having microchannels in the tubes for conveying refrigerant. The heat exchanger can be installed in a split system, a packaged system, or some other HVAC system.

By way of example, and turning now the figures,illustrates a split HVAC systemin accordance with one embodiment. As depicted, the systemprovides heating and cooling for a residential structure. But the concepts disclosed herein are applicable to a myriad of heating and cooling situations, including industrial and commercial settings. And while some HVAC systems provide each of heating, ventilation, and air conditioning, others do not. The term “HVAC system,” as used herein, means a system that provides one or more of heating, ventilation, air conditioning, or refrigeration. For example, an air conditioner that does not provide heating or ventilation is considered an HVAC system. The use of the term “HVAC” in describing a system, unit, component, equipment, etc., herein is not to be interpreted as a requirement that each of heating, ventilation, and air conditioning is provided.

Many North American residences employ “ducted” systems, in which a structure's ambient air is circulated over a central indoor heat exchanger and then routed back through relatively large ducts (or ductwork) to multiple climate-controlled indoor spaces. However, the use of a central heat exchanger can limit the ducted system's ability to vary the temperature of the multiple indoor spaces to meet different occupants' needs. This is often resolved by increasing the number of separate systems within the structure—with each system having its own outdoor unit that takes up space on the structure's property, which may not be available or at a premium.

Residences outside of North America often employ “ductless” systems, in which refrigerant is circulated between an outdoor unit and one or more indoor units to heat and cool specific indoor spaces. Unlike ducted systems, ductless systems route conditioned air to the indoor space directly from the indoor unit—without ductwork. Typically, ductless systems are suited for moderate climates, and are not optimal for climates where robust heating of the indoor space may be desired.

The described HVAC systemofis a split system with two primary portions: the outdoor unit, which mainly comprises components for transferring heat with the environment outside the structure; and the indoor units&, which mainly comprise components for transferring heat with the air inside the structure. In the illustrated structure, a ducted indoor unitand ductless indoor unitsprovide heating and cooling to various indoor spaces.

Focusing on the ducted indoor unit, it has an air-handler unit (or AHU)that provides airflow circulation, which in the illustrated embodiment draws ambient indoor air via a return vent, passes that air over one or more heating/cooling elements (i.e., sources of heating or cooling), and then routes that conditioned air, whether heated or cooled, back to the various climate-controlled spacesthrough supply vents. As depicted in, air between the AHU(which may also be referred to as an air handler) and the ventsandis carried by ducts or ductwork, which are relatively large pipes that may be rigid or flexible. A blowerprovides the motivational force to generate airflow and circulate the ambient air through the ventsand, AHU, and ducts.

As shown, the ducted indoor unitis a “dual-fuel” system that has multiple heating elements. A gas furnace, which may be located downstream (in terms of airflow) of the blower, combusts natural gas to produce heat in furnace tubes (not shown) that coil through the furnace. These furnace tubes act as a heating element for the ambient indoor air being pushed out of the blower, over the furnace tubes, and into supply ductsto supply vents. In other instances, the furnaceis an electric furnace, with one or more heat strips or other electric heating elements for heating air passing through the AHU, rather than a gas furnace. Whether gas or electric, the furnaceis generally operated when robust heating is desired. During conventional heating and cooling operations, air from the bloweris routed over an indoor heat exchangerand into the supply ducts.

The blower, furnace, and indoor heat exchangermay be packaged as an integrated AHU, or those components may be modular. Moreover, it is envisaged that the positions of the furnace, indoor heat exchanger, and blower can be reversed or rearranged. Internal components of the blower, the furnace, and the indoor heat exchangercan be positioned within one or more casings, cabinets, or other housings (integrated or modular).

The indoor heat exchanger—which in this embodiment for the ducted indoor unitis an A-coil(), as it known in the industry—can act as a heating or cooling element that adds or removes heat from the structure by manipulating the pressure and flow of refrigerant circulating within and between the A-coiland the outdoor unitvia refrigerant lines.

In the illustrated embodiment of, the state of the A-coil(i.e., absorbing or releasing heat) is the opposite of the outdoor heat exchanger. More specifically, if heating is desired, the illustrated indoor heat exchangeracts as a condenser, aiding transition of the refrigerant from a high-pressure gas to a high-pressure liquid and releasing heat in the process. And the outdoor heat exchangeracts as an evaporator, aiding transition of the refrigerant from a low-pressure liquid to a low-pressure gas, thereby absorbing heat from the outdoor environment. If cooling is desired, the outdoor unithas flow-control devicesthat reverse the flow of the refrigerant—such that the outdoor heat exchangeracts as a condenser and the indoor heat exchangeracts as an evaporator. The outdoor unitalso contains other equipment—like a compressor, which provides the motivation for circulating the refrigerant, and electrical control circuitry, which provides command and control signals to various components of the system.

The outdoor unitis a side-flow unit that houses, within a plastic or metal casing or housing, the various components that manage the refrigerant's flow and pressure. This outdoor unitis described as a side-flow unit because the airflow across the outdoor heat exchangeris motivated by a fan that rotates about an axis that is non-perpendicular with respect to the ground. In contrast, “up-flow” devices generate airflow by rotating a fan about an axis generally perpendicular to the ground. (As illustrated, the Y-axis is perpendicular to the ground.) In one embodiment, the side-flow outdoor unitmay have a fanthat rotates about an axis that is generally parallel to the ground. (As illustrated, the X- and Z-axes are parallel to the ground.) It is envisaged that either up-flow or side-flow units could be employed. Advantageously, the side-flow outdoor unitprovides a smaller footprint than traditional up-flow units, which are more cubic in nature.

In addition to the ducted indoor unit, the illustrated HVAC system has ductless indoor unitsthat also circulate refrigerant, via the refrigerant lines, between the outdoor heat exchangerand the ductless indoor unit's heat exchanger. The ductless indoor unitsmay work in conjunction with or independent of the ducted indoor unitto heat or cool the given indoor space. That is, the given indoor spacemay be heated or cooled with the structure's air that has been conditioned by the ductless indoor unitand by the air routed through the ductworkafter being conditioned by the A-coil, or it may be entirely conditioned by the ductless indoor unit or the ducted indoor unit working independent of one another. As another embodiment, the A-coil refrigerant loop may be operated to provide cooling or heating only—and the ductless indoor units may also be designed to provide cooling or heating only.

As is well known, the HVAC system may be in communication with a thermostatthat senses the indoor space's temperature and allows the structure occupants to “set” the desired temperature for that sensed indoor space. The thermostat may operate using a simple on/off protocol that sends 24V signals, for example, to the HVAC system to either activate or deactivate various components;

or it may be a more complex thermostat that uses a “communicating protocol,” such as ClimateTalk or P1/P2, that sends and receives data signals and can provide more complex operating instructions to the HVAC system.

provides further detail about the various components of an HVAC system and their operation. The compressordraws in gaseous refrigerant and pressurizes it, sending it into the closed refrigerant loopvia compressor outlet. (A flow metermay be used to measure the flow of refrigerant out of the compressor.) The outletis connected to a reversing valve, which may be electronic, hydraulic, or pneumatic and which controls the routing of the high-pressure gas to the indoor or outdoor heat exchangers. Moreover, the outletmay be coupled to an oil separatorthat isolates oil expelled by the compressor and, via a return line, returns the separated oil to the compressor inlet—to help prevent that expelled oil from reaching the downstream components and helping ensure the compressor maintains sufficient lubrication for operation. The oil return linemay include a valvethat reduces the pressure of the oil returning to the compressor.

To cool the structure, the high-pressure gas is routed to the outdoor heat exchangers, where airflow generated by the fansaids the transfer of heat from the refrigerant to the environment—causing the refrigerant to condense into a liquid that is at high-pressure. As shown, the outdoor unithas multiple heat exchangersand fansconnected in parallel, to aid the HVAC system's operation.

The refrigerant leaving the heat exchangersis or is almost entirely in the liquid state and flows through or bypasses a metering device. From there, the high-pressure liquid refrigerant flows into a series of receiver check valvesthat manage the flow of refrigerant into the receiver. The receiverstores refrigerant for use by the system and provides a location where residual high-pressure gaseous refrigerant can transition into liquid form. The receiver may be located within the casingof the outdoor unit or may be external to the casingof the outdoor unit (or the system may have no receiver at all). From the receiver, the high-pressure liquid refrigerant flows to the indoor units,, specifically to metering devicesthat restrict the flow of refrigerant into each heat exchanger of the indoor units,, to reduce the refrigerant's pressure. The refrigerant leaves the indoor metering devicesas a low-pressure liquid (or mostly liquid). In the described embodiment, the metering deviceis an electronic expansion valve, but other types of metering devices—like capillaries, thermal expansion valves, reduced orifice tubing—are also envisaged. Electronic expansion valves provide precise control of refrigerant flow into the heat exchangers of the indoor units, thus allowing the indoor units—in conjunction with the compressor—to provide individualized cooling for the given indoor spacethe unit is assigned to.

Low-pressure liquid refrigerant is then routed to the indoor heat exchangers. As illustrated, the indoor heat exchangerfor the ducted indoor unitis an “A-coil” style heat exchanger. But the heat exchangercan be an “N-coil” (or “Z-coil”) style heat exchanger or a slab coil or can take any other suitable form. Airflow generated by the bloweraids in the absorption of heat from the flowing air by the refrigerant, causing the refrigerant to transition from a low-pressure liquid to a low-pressure gas as it progresses through the indoor heat exchanger. And the airflow generated by the blowerdrives the now cooled air into the ductwork(specifically the supply ducts), cooling the indoor spaces. In a similar fashion, the low-pressure liquid refrigerant is routed to the indoor heat exchangersof the ductless indoor units, where it is evaporated, causing the refrigerant to absorb heat from the environment. However, unlike the ducted indoor unit, the ductless indoor units circulate air without ductwork, using a local fan, for example.

The refrigerant leaving the indoor heat exchangers, which is now entirely or mostly a low-pressure gas, is routed to the reversing valvethat directs refrigerant to the accumulator. Any remaining liquid in the refrigerant is separated in the accumulator, ensuring that the refrigerant reaching the compressor inletis almost entirely in a gaseous state. The compressorthen repeats the cycle, by compressing the refrigerant and expelling it as a high-pressure gas.

For heating the structure, the process is reversed. High-pressure gas is still expelled from the compressor outletand through the oil separatorand flow meter. However, for heating, the reversing valvedirects the high-pressure gas to the indoor heat exchangers. There, the refrigerant—aided by airflow from the bloweror the fans—transitions from a high-pressure gas to a high-pressure liquid, rejecting heat. And that heat is driven by the airflow from the blowerinto the ductworkor by the fansin the ductless indoor units, heating the indoor spaces. If more robust heating is desired, the gas furnacemay be ignited, either supplementing or replacing the heat from the heat exchanger. That generated heat is driven into the indoor spaces by the airflow produced by the blower. In other instances, electric heating elements (e.g., of an electric furnaceof the indoor unitsor) may also or instead be used to provide heat to the indoor spaces.

The high-pressure liquid refrigerant leaving each indoor heat exchangeris routed through or past the given metering valve, which is, in this embodiment, an electronic expansion valve. But for other embodiments, the valve may be any other type of suitable expansion valve, like a thermal expansion valve or capillary tubes, for example. Using the refrigerant lines, the high-pressure liquid refrigerant is routed to the receiver check valvesand into the receiver. As described above, the receiverstores liquid refrigerant and allows any refrigerant that may remain in gaseous form to condense. From the receiver, the high-pressure liquid refrigerant is routed to an outdoor metering device, which lowers the pressure of the liquid. Just like the indoor metering device, the illustrated outdoor metering deviceis an electrical expansion valve. But it is envisaged that the outdoor metering device could be any number of devices, including capillaries, thermal expansion valves, reduced orifice tubing, for example.

The lower-pressure liquid refrigerant is then routed to the outdoor heat exchangers, which are acting as evaporators. That is, the airflow generated by the fansaids the transition of low-pressure liquid refrigerant to a low-pressure gaseous refrigerant, absorbing heat from the outdoor environment in the process. The low-pressure gaseous refrigerant exits the outdoor heat exchangerand is routed to the reversing valve, which directs the refrigerant to the accumulator. The compressorthen draws in gaseous refrigerant from accumulator, compresses it, and then expels it via the outletas high-pressure gas, for the cycle to be repeated.

As illustrated in, the system is a “two-pipe” variable refrigerant flow system, in which the HVAC system's refrigerant is circulated between the outdoor and indoor units via two refrigerant lines, one of which is a line that carries predominantly liquid refrigerant (a liquid line) and one of which is a line that carries predominately gas refrigerant (a gas line). However, it is also envisaged that, in other embodiments, aspects described herein could be applied to a three-pipe variable refrigerant flow system, in which in addition to the gas and liquid lines a third discharge line aids in the circulation of refrigerant.

In many instances, the structuremay have had a previous HVAC system with pre-existing refrigerant piping at least partially built into the structure's interior walls. For example, the pre-existing system may be a traditional HVAC unit that uses circulating refrigerant for cooling only and a gas furnace for heating, with all of the conditioned air delivered to the interior spaces via the ductwork. And the pre-existing refrigerant lines—which are built into the walls of the structure—may have a gas line with a 6/8-inch, ⅞-inch, or 9/8-inch outer diameter gas line. However, in certain embodiments, the outdoor unitmay have more modern refrigerant piping, which tends to be smaller in outer diameter. For example, the outdoor unitmay be 2-, 3-, or 4-Ton unit that has a gas line diameter of ⅝inch. It would be laborious and cost ineffective to replace the pre-existing gas line in the structure with ⅝-inch diameter tubing. Accordingly, the illustrated HVAC system includes a couplerthat helps couple the varying diameter gas lines to one another. For example, the couplermay facilitate coupling of the outdoor unit's ⅝-inch diameter gas line to the structure's pre-existing 6/8-inch, ⅞-inch, or 9/8-inch diameter gas line. In another embodiment, the outdoor unitmay be a 5-Ton unit with a gas line having a diameter of 6/8inch. The coupler could facilitate coupling of this outdoor unit with a pre-existing gas line of ⅞-inch or 9/8-inch diameter.

In another embodiment depicted in, a packaged HVAC systemincludes various components housed in a shared cabinet. The packaged systemcan output conditioned air (e.g., heated or cooled air) from a supply duct openingand draw air into the cabinetvia a return duct opening. Ductwork can be connected between a structure and the openingsandto circulate air between the systemand the structure. Heat exchangersandwithin the cabinetfacilitate heat transfer and allow ambient air received through the return duct openingto be treated (e.g., heated or cooled) and supplied to the structure via the supply duct opening. The heat exchangeris an evaporator coil and the heat exchangeris a condenser coil in at least some instances. Like described above with respect to the split system, fluid refrigerant is circulated through and between the heat exchangersandto cause the refrigerant to cycle between the liquid and gas phases and transfer heat with ambient air. It will be appreciated that other components are also installed within the cabinet, such as a blower, a compressor, and tubing for routing the refrigerant between the compressor and the heat exchangersand.

The heat exchangers,,, andcan be provided in any suitable form. In certain embodiments, for instance, some or all of the heat exchangers,,andare microchannel heat exchangers. An example of a microchannel heat exchangeris generally provided in. In this depicted example, the microchannel heat exchangerincludes an arrayof tubes arranged between manifoldsand. Refrigerant is conveyed between the manifoldsandby the tube array. More specifically, at least some tubes of the arrayconnect the manifoldin fluid communication with the manifold.

In the embodiment depicted in, the microchannel heat exchangeris a closed refrigerant circuit including connectionsandfor receiving refrigerant and then outputting refrigerant after passing through tubes of the array. The connectionis an inlet and the connectionis an outlet in some embodiments, but this is reversed in others, with the connectionas the inlet and the connectionas the outlet. As shown, the microchannel heat exchangeris a multi-pass heat exchanger in which refrigerant passes from the manifoldto the manifoldand is then returned from the manifoldto the manifold. That is, refrigerant received through the inlet (e.g., connection) passes from the manifoldto the manifoldthrough some of the tubes of the array. This refrigerant is then returned from the manifoldto the manifoldthrough other tubes of the array.

The microchannel heat exchangercan have any suitable number of passes in which refrigerant flows from one of the manifoldsorto the other. For instance, the microchannel heat exchangercan be a two-pass heat exchanger in which the refrigerant received in the manifoldvia the inlet flows in one direction (a first pass) from the manifoldto the manifoldthrough some of the tubes of the arrayand then flows in an opposite direction (a second pass) from the manifoldto the manifoldthrough other tubes of the arraybefore exiting the heat exchangerthrough the outlet. In other embodiments, the heat exchangerwith the inlet and outlet provided on the manifoldcould have four, six, eight, ten, or even more passes. In still other instances, the inlet and outlet could be provided on opposite sides (e.g., the inlet on the manifoldand the outlet on the manifold) and the heat exchangermay have an odd number of passes, such as one pass, three passes, five passes, seven passes, nine passes, and so forth.

Additional details of the microchannel heat exchangerare depicted in. In this example, the arrayincludes tubeswith heat transfer fins. The tubesinclude microchannelsfor conveying refrigerant between the manifoldsand. Opposite endsof at least some tubesof the arrayare connected to the manifoldsandto enable refrigerant to flow between the manifoldsandvia those tubes. As described in greater detail below, however, in at least some embodiments one or more other tubesof the arraydo not connect the manifoldsandin fluid communication with each other and do not convey refrigerant between the manifoldsand. The tubesthat are connected to convey refrigerant between the manifoldsandmay be considered live tubes, while the tubesthat are not connected to convey refrigerant between the manifoldsandmay be considered dead tubes.

Each tubeis shown inas having ten microchannels, but the tubesmay have some other number of microchannels. In certain other embodiments, the heat exchangeris not a microchannel heat exchanger and the tubesdo not include microchannels. And while the tubesare shown inas flat tubes, in other embodiments the tubescould have some other shape, such as round tubes.

Ambient air is treated by flowing the ambient air through the array, between the tubesand past the fins, and transferring heat between the refrigerant circulated through the tubesand the ambient air. Although the heat exchangeris depicted inas having triangular fins, these finscan take various other shapes and forms. In some embodiments, for instance, the finscan also or instead include plain fins, wavy fins, perforated pins, louvered fins, serrated fins, rectangular fins, or curved fins.

The heat exchangercan be made of any suitable material. In some embodiments, the heat exchangeris an aluminum heat exchanger having each of the manifoldsand, the tubes, and the finsmade of aluminum or an aluminum alloy. Each of the components could be made of the same aluminum alloy, for instance, or multiple aluminum materials (pure aluminum or aluminum alloys) could be used for the different components. Other materials, such as stainless steel, copper, or polymer, may also or instead be used.

By way of further example, the heat exchangeris shown as a six-pass microchannel heat exchanger in. As depicted, the heat exchangerincludes an arrayof flat tubes, which include an outer flat tubeat the upper end of the array, an outer flat tubeat the lower end of the array, and additional flat tubes(inner flat tubes) positioned between the outer tubesand. The tubes(including the inner tubes, the outer tube, and the outer tube) can be arranged in parallel within the array. Although shown in the shape of a slab coil in, the heat exchangermay be constructed in any other suitable shape, such as an A-shape or a C-shape.

Refrigerant may be received through the connectioninto a boreof the manifold. A baffle(e.g., a separator plate) within the boreblocks flow of the refrigerant down the boreand causes the refrigerant received through the connectionto flow from the manifoldthrough a first subsetof tubes(which includes the outer flat tube) into a boreof the manifold. This transit of refrigerant from the manifoldto the manifoldthrough the first subsetof tubesis the first pass in the heat exchanger. A bafflein the borecauses the refrigerant received from the first subsetof tubesto then flow through a second subsetof tubesfrom the manifoldto the manifold(i.e., the second pass). In similar fashion, a bafflecauses this refrigerant to flow back to the manifoldthrough a third subsetof the tubes(i.e., the third pass), and a bafflethen causes the refrigerant to flow from the manifoldback to the manifoldthough a fourth subsetof tubes(i.e., the fourth pass). Another bafflecauses refrigerant received in the manifoldfrom the fourth subsetof tubesto flow to the manifoldthrough a fifth subsetof tubes(i.e., the fifth pass), and the refrigerant flows back to the manifoldfrom the manifoldthrough a sixth subsetof tubes(i.e., the sixth pass) and exits the heat exchangerthrough the connection.

Because they control flow through the manifolds and direct refrigerant into tubes, the baffles,,,, andmay be said to divide the passes through the heat exchanger. That is, the baffledivides the first pass from the second pass, the baffledivides the second pass from the third pass, the baffledivides the third pass from the fourth pass, the baffledivides the fourth pass from the fifth pass, and the baffledivides the fifth pass from the sixth pass.

Each pass can use any suitable number of tubes. The number of passes and the number of tubes used in each pass may be selected to optimize heat transfer and pressure drop through the heat exchanger. In at least some instances, the first pass uses more tubesthan the last pass. As depicted in, the heat exchangeris provided in a top in-bottom out arrangement, in which the connectionis the inlet, the connectionis the outlet, the first pass is at the top end of the array, each subsequent pass is below the previous pass, and the earlier passes (i.e., the first, second, and third passes) use more tubesthan the later passes (i.e., the fourth, fifth, and sixth passes). In other embodiments, the heat exchangermay be provided in a bottom in-top out arrangement, in which the connectionis the inlet, the connectionis the outlet, the first pass is at the bottom end of the array, and each subsequent pass is above the previous pass. In such a bottom in-top out arrangement, the earlier passes may still use more tubesthan the later passes, but with the passes having more tubes located below those with fewer tubes. Baffles (e.g., baffles,,,, and) may be provided at any desired locations within the manifoldsandto control flow of refrigerant through the heat exchanger, set the number of passes, and determine the number of tubesused for each pass.

While the tubesof the arraycollectively enable refrigerant to flow between the manifoldsand, one or more of the tubescan be provided as dead tubes that do not convey refrigerant between the manifoldsand. In some embodiments, the arrayincludes dead tubes to reduce thermal cross-conduction between tubes of two different passes. As depicted in, for instance, the baffledivides two adjacent passes, with one pass above lineconveying refrigerant between the manifoldsandin one direction (e.g., from left to right) and another pass below lineconveying refrigerant between the manifoldsandin an opposite direction (e.g., from right to left). The temperature of the refrigerant changes as it is routed through the heat exchanger, and the temperature of the refrigerant may differ significantly between these two passes. Rather than having the two passes directly adjacent one another (with live tubesof one pass immediately followed in the arrayby live tubesof the next pass), in the example ofthe two flat tubesof the arrayclosest to line(i.e., tubesand) are provided as dead tubes that separate the two passes within the arrayand do not convey refrigerant. That is, the dead tubesandare interposed directly between the two passes within the array. This increases the distance between the live tubes of the two passes and reduces thermal cross-conduction between the two passes, which may increase efficiency of the heat exchanger.

In some instances, dead tubes may also or instead be provided in the arrayto reduce thermal stress along a manifoldorof the heat exchanger. In, for example, a temperature difference between refrigerant on either side of the bafflein the manifoldcan cause thermal stress across and around the baffle. Having the dead tubesandphysically unconnected with the manifoldmay reduce the thermal stress on the microchannel tubes at that location.

As shown in, and in contrast to the live tubes, the dead tubesandhave bent endsthat are not connected to the manifold. The opposite endsof the dead tubesandcan be similarly bent and not connected to the manifold. But any other suitable technique may be used to prevent flow through dead tubes between manifoldsand. The dead tubes, for instance, may be shortened or crimped (e.g., at ends), plugged, or otherwise sealed to prevent refrigerant flow between the manifolds. And while the bent endsof the dead tubes may be spaced apart from the manifoldsand, in other instances the endsof the dead tubes may be physically connected to the manifoldsandwhile still blocking flow of refrigerant through the dead tubes.

Although two dead tubes are depicted in, any suitable number of dead tubes may be provided to reduce thermal cross-conduction between two adjacent passes or to reduce thermal stress on these tubes along the manifoldor. In, for example, the tubeis instead a live tube (of the pass below the line) and a single dead tube (i.e., tube) separates the two adjacent passes. In other instances, three or more dead tubes may be used to separate two adjacent passes within the array.