Patent Publication Number: US-2022221203-A1

Title: Interlaced microchannel heat exchanger systems and methods thereto

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit, under 35 U.S.C. § 119, of U.S. Provisional Patent Application No. 63/136,440, filed 12 Jan. 2021, the entire contents and substance of which is incorporated herein by reference as if fully set forth below. 
    
    
     FIELD OF DISCLOSURE 
     The present disclosure relates generally to heat exchanger systems and methods and, in particular, to heat exchanger systems and methods that include multiple interlaced microchannel heat exchangers (iMCHXs) (e.g., a first iMCHX configured to function as an evaporator and a second iMCHX configured to function as a condenser). 
     BACKGROUND 
     Commercial buildings, homes, or other structures can commonly be equipped with one or more air systems for heating and/or cooling, such as a heat pump system or an air conditioner system. These air systems can include an indoor unit and an outdoor unit in fluid communication via a refrigerant circuit. For example, referring to  FIG. 1 , air conditioner systems can include a refrigerant circuit that includes a compressor, a condenser, an expansion valve, and an evaporator, which can operate to provide a cooling effect in an indoor space by transferring heat from the indoor space to the refrigerant via the evaporator and transferring heat from the refrigerant to an outdoor space via the condenser. As another example, heat pump systems can include a refrigerant circuit similar to the one shown in  FIG. 1  but also including a reversing valve or another component or system configured to selectively change the direction of refrigerant flow through the refrigerant circuit. Thus, the heat pump system can have a cooling mode in which the indoor heat exchanger operates as an evaporator and the outdoor unit operates as a condenser (i.e., operating as an air conditioner system), and the heat pump system can have a heating mode in which the indoor heat exchanger operators as a condenser and the outdoor heat exchanger operates as an evaporator (i.e., operating as a heating system). 
     To improve the efficiency and performance of air systems, the microchannel heat exchanger was designed. Referring to the partial cross-sectional view shown in  FIG. 2 , microchannel heat exchangers are heat exchangers that direct the flow of refrigerant through ports that are smaller in internal diameter than conventional finned heat exchanger tubes (e.g., less than or equal to approximately 1 mm in diameter). Microchannel heat exchangers can provide a variety of advantages over conventional finned heat exchanger tubes including higher heat transfer ratios, reduced refrigerant charge, smaller and more compact design, lower weight, and higher energy efficiency of the overall system. 
     SUMMARY 
     Despite the various air systems presently available, there are opportunities to further increase the efficiency and performance of air systems. Moreover, there are opportunities to provide air systems having increased efficiency and performance while also limiting associated manufacturing costs. These and other problems can be addressed by the technologies described herein. 
     The disclosed technology includes a system comprising a first interlaced microchannel heat exchanger and a second interlaced microchannel heat exchanger. The system can include a first refrigerant circuit comprising a first compressor, the first interlaced microchannel heat exchanger, a first thermal expansion valve, and the second interlaced microchannel heat exchanger. The system can include a second refrigerant circuit fluidly separated from the first refrigerant circuit, the second refrigerant circuit comprising a second compressor, the first interlaced microchannel heat exchanger, a second thermal expansion valve, and the second interlaced microchannel heat exchanger. 
     The first compressor and the second compressor can be the same size. Alternatively, the first compressor and the second compressor can be different sizes. 
     The first refrigerant circuit and the second refrigerant circuit can include the same refrigerant. Alternatively, the first refrigerant circuit can include a first refrigerant, and the second refrigerant circuit can include a second refrigerant that is different from the first refrigerant. 
     The first refrigerant circuit can include a refrigerant charge quantity that is the same as a refrigerant charge quantity of the second refrigerant circuit. Alternatively, the first refrigerant circuit can include a first refrigerant charge quantity, and the second refrigerant circuit can include a second refrigerant charge quantity that is different from the first refrigerant charge quantity. 
     The system can include a first reversing valve in fluid communication with the first refrigerant circuit and a second reversing valve in fluid communication with the second refrigerant circuit. The system can include a controller configured to independently control the first compressor, the second compressor, the first reversing valve, and the second reversing valve. The controller can be configured to output instructions to the first compressor, the second compressor, the first reversing valve, and the second reversing valve for operating in a defrost mode. The instructions for operating in a defrost mode can cause (i) the first reversing valve to direct refrigerant through the first refrigerant circuit in a first flow direction and (ii) the second reversing valve to direct refrigerant through the second refrigerant circuit in a second flow direction that is opposite the first flow direction. 
     The first interlaced microchannel heat exchanger can be located at an indoor location and the second interlaced microchannel heat exchanger is located at an outdoor location. 
     The first interlaced microchannel heat exchanger can include an inlet header and a plurality of heat exchanger tubes. Each of the plurality of heat exchanger tubes can include a plurality of microchannels configured to flow refrigerant therethrough. The first interlaced microchannel heat exchanger can include a distributor tube located within the inlet header, and the distributor tube can include a plurality of apertures. Each aperture can be aligned with at least one corresponding microchannel of the plurality of microchannels such that the aperture can thereby permit the refrigerant to flow through the at least one corresponding microchannel of the plurality of microchannels. 
     A portion of the distributor tube can prevent or limit the refrigerant from flowing through at least one of the plurality of microchannels. The portion of the distributor tube can prevent or limit the refrigerant from flowing through at least one of the plurality of heat exchanger tubes. 
     A portion of the distributor tube can increase an amount or flow rate of refrigerant flowing through at least one of the plurality of microchannels, and/or a portion of the distributor tube can increase an amount or flow rate of the refrigerant flowing through at least one of the plurality of heat exchanger tubes. 
     At least one of the plurality of apertures can have a size that is approximately equal to a size of at least one corresponding microchannel of the plurality of microchannels. Alternatively or in addition, at least one of the plurality of apertures can have a size that is smaller than a size of at least one corresponding microchannel of the plurality of microchannels. 
     The plurality of apertures of the distributor tube can include a first aperture having a first size and a second aperture having a second size that is smaller than the first size. The first size can be smaller than a size of a microchannel of the plurality of microchannels. The second size can be smaller than the size of the microchannel of the plurality of microchannels. 
     The first interlaced microchannel heat exchanger can include one or more baffles, and each of the one or more baffles can be configured to inhibit airflow through a portion of the first interlaced microchannel heat exchanger. 
     Various aspects of the present disclosure are expressly described in the Detailed Description below and the accompanying figures. Other aspects and features of the present disclosure will become apparent to those of ordinary skill in the art upon reviewing the following description of specific examples of the present disclosure in concert with the figures. While features of the present disclosure may be discussed relative to certain examples and figures, all examples of the present disclosure can include one or more of the features discussed herein. Further, while one or more examples may be discussed as having certain advantageous features, one or more of such features may also be used with the various other examples of the disclosure discussed herein. In similar fashion, while examples may be discussed below as devices, systems, or methods, it is to be understood that such examples can be implemented in various devices, systems, and methods of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Reference will now be made to the accompanying figures, which are not necessarily drawn to scale, and wherein: 
         FIG. 1  illustrates a schematic view of an example prior art refrigerant circuit; 
         FIG. 2  illustrates a partial cross-sectional view of an example prior art microchannel heat exchanger; 
         FIG. 3A  illustrates a schematic view of an example air system, in accordance with the disclosed technology; 
         FIG. 3B  illustrates a schematic view of another example air system, in accordance with the disclosed technology; 
         FIG. 4  illustrates a schematic diagram of an example controller for an air system, in accordance with the disclosed technology; 
         FIGS. 5A-5C  illustrate schematic view of an example air system operating in a heating mode, a cooling mode, and a defrost mode, respectively, in accordance with the disclosed technology; 
         FIG. 6A  illustrates a schematic view of a refrigerant circuit in an example heat exchanger, in accordance with the disclosed technology; 
         FIGS. 6B and 6C  illustrate schematic views of a refrigerant circuit in an example heat exchanger having a distributor tube, in accordance with the disclosed technology; 
         FIG. 7A  illustrates an end view of tube of an example microchannel heat exchanger, in accordance with the disclosed technology; 
         FIGS. 7B-7F  illustrate various configurations of an example distributor tube interfacing with a microchannel heat exchanger, in accordance with the disclosed technology; 
         FIG. 8A  illustrates a schematic view of an example heat exchanger, in accordance with the disclosed technology; and 
         FIG. 8B  illustrates a schematic view of the example heat exchanger of  FIG. 8A  further including baffles, in accordance with the disclosed technology. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosed technology relates to a multi-circuit air system that includes a plurality of fluidly separated refrigerant circuits, and each of the refrigerant circuits can flow through a single indoor heat exchanger (e.g., evaporator) and a single outdoor heat exchanger (e.g., condenser). As will be described more fully herein, refrigerant can be selectively flowed through each individual refrigerant circuit. This can enable the air system to provide a full-load efficiency comparable to existing air systems while also providing increased part-load efficiency. That is, at part-load, the disclosed technology can be configured to selectively operate fewer than the total number of the refrigerant circuits. In addition to providing an increased part-load efficiency, the disclosed technology can provide air systems having lower cost (e.g., manufacturing cost, installation cost, operating cost), increased reliability, and compactness (e.g., of the indoor heat exchanger). 
     The disclosed technology will be described more fully hereinafter with reference to the accompanying drawings. This disclosed technology can, however, be embodied in many different forms and should not be construed as limited to the examples set forth herein. The components described hereinafter as making up various elements of the disclosed technology are intended to be illustrative and not restrictive. Such other components not described herein may include, but are not limited to, for example, components developed after development of the disclosed technology. 
     In the following description, numerous specific details are set forth. But it is to be understood that examples of the disclosed technology can be practiced without these specific details. In other instances, well-known methods, structures, and techniques have not been shown in detail in order not to obscure an understanding of this description. References to “one embodiment,” “an embodiment,” “example embodiment,” “some embodiments,” “certain embodiments,” “various embodiments,” “one example,’ “an example,” “some examples,” “certain examples,” “various examples,” etc., indicate that the embodiment(s) and/or example(s) of the disclosed technology so described may include a particular feature, structure, or characteristic, but not every embodiment necessarily includes the particular feature, structure, or characteristic. Further, repeated use of the phrase “in one embodiment” or the like does not necessarily refer to the same embodiment, example, or implementation, although it may. 
     Throughout the specification and the claims, the following terms take at least the meanings explicitly associated herein, unless the context clearly dictates otherwise. The term “or” is intended to mean an inclusive “or.” Further, the terms “a,” “an,” and “the” are intended to mean one or more unless specified otherwise or clear from the context to be directed to a singular form. 
     Unless otherwise specified, the use of the ordinal adjectives “first,” “second,” “third,” etc., to describe a common object, merely indicate that different instances of like objects are being referenced and are not intended to imply that the objects so described should be in a given sequence, either temporally, spatially, in ranking, or in any other manner. 
     Throughout this disclosure, reference is made to the accompanying drawings in which like numerals represent like elements. Certain groups of elements and/or components are referenced generally using a common numeral, while specific instances of the element and/or component are referenced using the numeral followed by a corresponding alphanumeric reference. For example, this disclosure references refrigerant circuits of the disclosed technology generally using reference numeral  110 , whereas reference to specific refrigerant circuits is made herein using reference numerals  110   a ,  110   b , and/or  110   c . The same convention is applied to certain other elements and/or components (e.g., compressors, thermal expansion valves, reversing valves). 
     Unless otherwise specified, all ranges disclosed herein are inclusive of stated end points, as well as all intermediate values. By way of example, a range described as being “between approximately 2 and approximately 4” includes the values 2 and 4 and all intermediate values within the range. Likewise, the expression that a property “can be in a range from approximately 2 to approximately 4” (or “can be in a range from 2 to 4”) means that the property can be approximately 2, can be approximately 4, or can be any value therebetween. 
     Referring now to  FIGS. 3A and 3B , an air system  100  can include a plurality of fluidly separated refrigerant circuits  110 , and all of the refrigerant circuits  110  can be configured to pass through a single, shared indoor interlaced microchannel heat exchanger (iMCHX)  112  (also referenced herein as indoor coil  112 ) and a single, shared outdoor iMCHX  114  (also referenced herein as outdoor coil  114 ). The air system can also include a blower or fan  113  configured to move air across the indoor iMCHX and a blower or fan  115  configured to move air across the outdoor iMCHX  114 . Each of the refrigerant circuits  110  can include its own compressor  116  and expansion valve  118 . For example,  FIG. 3A  illustrates an air system  100  having multiple refrigerant circuits  110  that each include a corresponding compressor  116  and a corresponding expansion valve  118 , which includes a first refrigerant circuit  110   a  that includes a first compressor  116   a  and a first expansion valve  118   a , as well as a second refrigerant circuit  110   b  that includes a second compressor  116   b  and a second expansion valve  118   b.    
     As will be appreciated by those having skill in the art, the interlaced aspect of the iMCHXs enables the system  100  to connect multiple, fluidly separated refrigerant circuits though a single indoor heat exchanger (e.g., acting as an evaporator) and a single outdoor heat exchanger (e.g., acting as a condenser). This configuration provides a high part-load efficiency compared to traditional microchannel heat exchangers by increasing the available surface area and airflow for heat transfer. One or both of the indoor iMCHX and outdoor iMCHX can have a counter-flow circuit configuration, and/or one or both of the indoor iMCHX and outdoor iMCHX can have a parallel-flow circuit configuration. 
     Each of the refrigerant circuits  110  can include the same type of refrigerant (e.g., R-410A, R-454B). Conversely, one, some, or all of the refrigerant circuits  110  can include a different type of refrigerant. 
     Each of the refrigerant circuits  110  can have the same charge quantity. Conversely, one, some, or all of the refrigerant circuits  110  can have a different charge quantity. 
     Each of the refrigerant circuits  110  can have the same type and/or size of compressor  116 . Conversely, one, some, or all of the compressors  116  can be a different type and/or a different size. A system including compressors  116  of the same size will provide a comparatively simple design, whereas a system  100  including compressors  116  of differing sizes can provide a comparatively higher efficiency, particularly under partial-load conditions. For example, referring to  FIG. 3A , the air system  100  can include two refrigerant circuits  110 , which can include a first refrigerant circuit  110   a  having a first compressor  116   a  and a second refrigerant circuit  110   b  having a second compressor  116   b . The first compressor  116   a  can be smaller than the second compressor  116   b  such that (1) the first compressor  116   a  can be operated at low partial-load conditions (e.g., based on a low amount of cooling required), (2) the larger, second compressor  116   b  can be operated at high partial-load conditions (e.g., based on a middle amount of cooling required), and (3) both of the first and second compressors  116   a ,  116   b  can be operated at full-load conditions (e.g., based on a high amount of cooling required). 
     Likewise, referring to  FIG. 3B , the air system  100  can include three refrigerant circuits  110 , which can include a first refrigerant circuit  110   a  having a first compressor  116   a , a second refrigerant circuit  110   b  having a second compressor  116   b , and a third refrigerant circuit  110   c  having a third compressor  116   c . As discussed above, some or all of the three compressors  116  can be the same size, and/or some or all of the three compressors  116  can be different sizes. For example, the first compressor  116   a  can be smaller than the second and third compressors  116   b ,  116   c , and the second and third compressors  116   b ,  116   c  can be the same size. Thus, the system  100  can be configured to operate one compressor  116  under a lower partial-load condition, operate two compressors  116  under a higher partial-load condition, and operate all three compressors  116  under a full-load condition. The air system  100  can also be configured to operate various combinations of the compressors  116  to approximately match (or match as nearly as possible) the current load condition. Optionally, the air system  100  can be configured to rotate which of the compressors  116  is operated under partial-load conditions (e.g., based on total runtime, time since last use, etc.), particularly among compressors  116  of the same or approximately the same size. 
     As another example, the first compressor  116   a  can be smaller than the second compressor  116   b , and the second compressor  116   b  can be smaller than the third compressor  116   c . Thus, the system  100  can be configured to operate (1) the first compressor  116   a  under a first partial-load condition, (2) the second compressor  116   b  under a second partial-load condition, (3) and the third compressor  116   c  under a third partial-load condition, (4) both the first and second compressors  116   a ,  116   b  under a fourth partial-load condition, (5) both the first and third compressors  116   a ,  116   c  under a fifth partial-load condition, (6) both the second and third compressors  116   b ,  116   c  under a sixth partial-load condition, and (7) operate all three compressors  116  under a full-load condition. Each of these partial-load conditions can be a different partial load condition (e.g., a different amount of cooling required). 
     Although  FIGS. 3A and 3B  illustrate the possibilities of either dual-circuit or tri-circuit configurations, the air system  100  can include any number of refrigerant circuits  110 . For example, the disclosed technology includes any number of refrigerant circuits  110 , such as four, five, or more. As will be appreciated, a higher number of refrigerant circuits  110  will increase the granularity by which the system  100  can address partial-load conditions, but increasing the number of refrigerant circuits  110  also increases the number of components (e.g., compressors  116 ) required, which can, at some point, become unnecessarily or undesirably costly. 
     Regardless of the number of refrigerant circuits  110 , the air system  100  can be configured such that each partial-load condition corresponds to the operation of one or more compressors  116  at its individualized full capacity. And because compressors  116  are typically most efficient during full-load operation, the overall efficiency of the air system  100  can be greater than that of traditional systems. 
     Alternatively or in addition, one or more of the compressors  116  can be a two-step compressor. Alternatively or in addition, one or more of the compressors can be configured to utilize a variable frequency drive (VFD) (e.g., at partial-load only, at all loads). 
     Moreover, while  FIGS. 3A and 3B  illustrate example air heating systems, the disclosed technology can be included in air cooling systems and/or heat pump systems, which can operate in a heating mode to provide air heating to the indoor space or in a cooling mode to provide air cooling to the indoor space. In addition, the disclosed technology can be included in a heat pump system that is configured to provide both heating and cooling to the indoor space. For example, each refrigerant circuit  110  of the air system  100  can include a reversing valve or another device or system configured to enabling reversing of the refrigerant flow through the refrigerant circuit  110 . In such a configuration, the air system  100  can provide efficient heating under both full- and partial-load heating conditions and can provide efficient cooling under both full- and partial-load cooling conditions. Moreover, the air system  100  can operate in a defrost mode to prevent or remove ice from the outdoor coil, which can accumulate on the outdoor coil when it is acting as an evaporator (i.e., when the air system  100  is operating in the heating mode). For simplicity&#39;s sake, the defrost mode is discussed herein with respect to the outdoor coil  114 , but it is possible that the indoor coil  114  may accumulate frost or ice and need to be defrosted. As such, the various methods discussed herein can, alternatively or in addition, be applied to the indoor coil  114 . 
     The air system  100  can include one or more sensors to determine in which mode the air system should operate and/or to determine whether a buildup of frost or ice on the outdoor coil  114  (or the indoor coil) has occurred or is likely to occur. For example, the air system  100  can include a coil temperature sensor, which can be configured to measure the temperature of the refrigerant in or near the outdoor coil  114  and output the measured temperature to the controller  400 . The coil temperature sensor can be configured to measure the temperature of the outdoor coil  114  continuously or periodically when the air system  100  is shut down, while the air system  100  is operating, or both. The coil temperature sensor can be installed directly on the surface of the outdoor coil  114 , inside of the outdoor coil  114 , partially inside of the outdoor coil  114 , or near the outdoor coil  114 . Additionally, the coil temperature sensor can be configured to measure the surface temperature, the core temperature, a temperature of a portion of the outdoor coil  114 , or any other method of measuring as would be suitable for the particular application and arrangement. The coil temperature sensor can include any type of sensor capable of measuring the temperature of the outdoor coil  114 . For example, the coil temperature sensor can be or include a thermocouple, a resistor temperature detector (RTD), a thermistor, an infrared sensor, a semiconductor, or any other suitable type of sensor for the application. 
     Alternatively or in addition, the one or more sensors can include an ambient temperature sensor (e.g., a thermocouple, an RTD, a thermistor, an infrared sensor, a semiconductor), which can be configured to detect a temperature of the ambient air to indicate environmental conditions near the outdoor coil  114 . Alternatively or in addition, the one or more sensors can include a humidity sensor (e.g., capacitive, resistive, thermal), which can be configured to detect a humidity of the ambient air (e.g., relative humidity). 
     Optionally, the blower  113  and/or the fan  115  can be configured to utilize a VFD. As will be appreciated, this can enable the system  100  to modulate the speed of the blower  113  and/or the fan  115  to provide an increased or decreased amount of air flow, which can be modulated based on the amount of heating or cooling required, as a non-limiting example. It should also be understood that, while the terms “blower” and “fan” are used herein, either term refers generally to any air moving device configured to move air across an iMCHX. 
     Referring to  FIG. 4 , the controller  400  of the air system  100  can be configured to control operation of various components of the air system  100 , such as the various compressors  116  and/or valves (e.g., reversing valves  117  as described more fully herein). The controller  400 , as illustrated in  FIG. 4 , can have memory  402 , one or more processors  404 , a communication interface  406 , and/or a user interface  408 . The memory  402  can have instructions stored thereon that, when executed by the processor(s)  404 , cause the air system  100  to perform actions, methods, or processes, such as those described herein. More specifically, the controller  400  can be configured to receive data (e.g., via the communication interface  406 ) from one or more sensors (e.g., temperature sensor(s) configured to measure refrigerant temperature at or near one or both heat exchangers  102 ,  104 , ambient temperature sensor(s) located at or near one or both heat exchangers  102 ,  104 , humidity sensor(s) located at or near one or both heat exchangers  102 ,  104 ), make certain determinations as discussed more fully herein, and output instructions (e.g., via the communication interface  406 ) for operation of one or more components of the air system  100  (e.g., compressor(s)  116 , fan  113 , fan  115 , and/or reversing valve(s)  117 ). 
     One of skill in the art will understand that the controller  400  can be installed in any location, provided the controller  400  is in communication with at least some of the components of the air system  100 . Furthermore, the controller  400  can be configured to send and receive wireless or wired signals and the signals can be analog or digital signals. The wireless signals can include Bluetooth™, BLE, WiFi™, ZigBee™, infrared, microwave radio, or any other type of wireless communication as may be appropriate for the particular application. The hard-wired signal can include any directly wired connection between the controller and the other components. For example, the controller  400  can have a hard-wired 24 VAC connection to the compressor(s)  116 . Alternatively, the components can be powered directly from a power source and receive control instructions from the controller  400  via a digital connection. The digital connection can include a connection such as an Ethernet or a serial connection and can utilize any appropriate communication protocol for the application such as Modbus, fieldbus, PROFIBUS, SafetyBus p, Ethernet/IP, or any other appropriate communication protocol for the application. Furthermore, the controller  400  can utilize a combination of wireless, hard-wired, and analog or digital communication signals to communicate with and control the various components. One of skill in the art will appreciate that the above configurations are given merely as non-limiting examples and the actual configuration can vary depending on the application. 
     Referring to  FIGS. 5A-5C , operation of the air system  100  during full heating mode, full cooling mode, and defrost mode are illustrated, respectively. “Full heating mode” can refer to an operational mode in which all refrigerant circuits  110  are providing heat to the conditioned space via the indoor coil  112  such that the indoor coil  112  is acting as a condenser. Likewise, “full cooling mode” can refer to an operational mode in which all refrigerant circuits  110  are providing cooling to the conditioned space via the indoor coil  112  such that the indoor coil  112  is acting as an evaporator. To change a given refrigerant circuit  110  between operational modes, the air system  100  (e.g., controller  400 ) can output instructions for the corresponding reversing valve  117  (e.g., a four-way reversing valve) to selectively direct refrigerant through the refrigerant circuit  110  in a particular flow direction. 
     In defrost mode, at least one of the refrigerant circuits  110  is operating in a heating mode such that heat is discharged from the corresponding refrigerant at the indoor coil  112  (illustrated in  FIG. 5C  as refrigerant circuits  110   b ,  110   c ), while at least one other refrigerant circuit  110  is operating in a cooling mode such that heat is discharged from the corresponding refrigerant at the outdoor coil  114  (illustrated in  FIG. 5C  as refrigerant circuit  110   a ). As such, the heat discharged at the outdoor coil  114  can help melt or prevent frost or ice accumulation on the outdoor coil  114 . Once the temperature of the outdoor coil  114  has been sufficiently increased (or other metrics become satisfied), operation in the defrost mode can cease. As such, the flow of refrigerant in the refrigerant circuit  110  that was discharging heat at the outdoor coil  114  can be reversed (such that heat is no longer being discharged at the outdoor coil  114  but is instead being discharged at the indoor coil  114 ) or ceased (i.e., the corresponding compressor  116  can be turned off). During defrost mode, the controller  400  can be configured to operate any number of refrigerant circuits  110  to discharge heat at the outdoor coil  114 . For example, as illustrated, the defrost mode can include one refrigerant circuit  110  discharging heat at the outdoor coil  114 . Alternatively, the defrost mode can include all refrigerant circuits  110  except one discharging heat at the outdoor coil  114 . The particularly refrigerant circuit(s)  110  and/or the number of refrigerant circuits(s) operated to discharge heat at the outdoor coil  114  can be based at least in part on the temperature of the outdoor coil, the ambient environmental conditions (e.g., temperature, humidity), the current indoor temperature, and/or the indoor heating load. 
     Regardless, when the temperature of the outdoor coil  114  falls below a certain temperature threshold, (e.g., 50° F.), the air system  100  can be unable to efficiently provide heat to the indoor space. Indeed, condensation accumulated on the outdoor coil  114  can freeze, causing a buildup of frost and ice. In these conditions, frost can accumulate to the point where the air system  100  operates with a degraded performance or components become damaged. Accordingly, the air system  100  (e.g., controller  400 ) can be configured to transition to defrost mode upon detection that the measured temperature (e.g., coil temperature, ambient temperature) is less than a corresponding temperature threshold value and/or the measured humidity is greater than a humidity threshold value. 
       FIGS. 6A-6C  illustrate schematic diagrams of a single refrigerant circuit  110  for a given interlaced microchannel heat exchanger (e.g., indoor coil  112  or outdoor coil  114 ). As shown in  FIG. 6A , refrigerant can flow into the heat exchanger  112 ,  114  via an inlet  602  and into an inlet header  604 . The inlet header  604  can be in fluid communication with several heat exchanger tubes  606 , and the inlet header  604  can therefor distribute the refrigerant among the heat exchanger tubes  606 . As described more fully herein, each heat exchanger tube  606  includes multiple microchannels, each microchannel having its own flow path through the heat exchanger tube  606 . The tubes can be stacked and/or can have a generally flat profile or shape. The refrigerant can flow out of the various heat exchanger tubes  606  into the outlet header  608  and can ultimately exit the heat exchanger  112 ,  114  via the outlet  610 . 
     As will be appreciated, various heat exchanger designs can have varying airflow concentrations as air flows across the heat exchanger tubes  606  of the heat exchanger  112 ,  114 . As such, it can be desirable to direct refrigerant to those areas with a high airflow concentration and restrict refrigerant from flowing to areas with low airflow concentration. In this way, the heat transfer efficiency of the heat exchanger  112 ,  114  can be increased. Referring to  FIGS. 6B and 6C , a distributor tube  612  can be included. The distributor tube  612  can be configured to selectively permit refrigerant to pass to a given heat exchanger tube  606  and/or to a given microchannel of a given heat exchanger tube  606 . The distributor tube  612  can be a tube having an external diameter that is approximately equal to an internal diameter of the inlet header  604 . The distributor tube  612  can have a plurality of apertures extending through the sidewall of the distributor tube  612 , and each aperture can be configured to align with some or all of a given heat exchanger tube  606 . As such, the apertures can permit refrigerant to enter the corresponding heat exchanger tube(s)  606 . 
     The heat exchanger  112 ,  114  can include the same distributor tube  612  for each refrigerant circuit  110 . Alternatively, the heat exchanger  112 ,  114  can include one or more different distributor tubes  612  for different refrigerant circuits  110 . For example, as shown in  FIG. 6B , a first distributor tube  612  can be configured to permit refrigerant to flow through all heat exchanger tubes  606  of a first refrigerant flow path (e.g., refrigerant flow path  110   a ), while, as shown in  FIG. 6C , a second distributor tube  612  can be configured to permit refrigerant to flow through only some heat exchanger tubes  606  of a second refrigerant flow path (e.g., refrigerant flow path  110   b ). That is to say, the distributor tube  612  can be configured to block passage through some or all of a given heat exchanger tube  606 . Alternatively or in addition, the distributor tube can be configured to increase an amount or flow rate of the refrigerant flowing through one or some of microchannels (e.g., microchannels  702  as discussed more fully herein) and/or can increase an amount or flow rate of the refrigerant flowing through one or some of the heat exchanger tubes  606  (e.g., as an effect of blocking, preventing, and/or limiting flow in one or more other heat exchanger tubes  606  and/or one or more other microchannels (e.g., microchannels  702 ). 
       FIG. 7A  illustrates an end view of a heat exchanger tube  606  having multiple microchannels  702 . As shown in  FIG. 7B , the distributor tube  612  can have a plurality of apertures  712 , with each aperture aligned with a corresponding microchannel  702 . In this way, the distributor tube  612  can be configured to permit refrigerant to flow through all of the microchannels  702  of that particular heat exchanger tube  606 . Alternatively, the same effect can be achieved by the distributor tube  612  including a single aperture permitting refrigerant to flow to all microchannels  702  of the heat exchanger tube  606 . 
     As explained, it can be advantageous to restrict refrigerant from flowing through certain heat exchanger tubes  606 . Likewise, it can be advantageous to restrict refrigerant from flowing through certain microchannels  702  of a given heat exchanger tube  606 , such that the heat exchanger tube  606  is passing less than a maximum throughput of refrigerant.  FIG. 7C  illustrates a first example configuration of apertures resulting in a corresponding configuration of open and blocked microchannels  702 , and  FIG. 7D  illustrates a first example configuration of apertures resulting in a corresponding configuration of open and blocked microchannels  702 . The disclosed technology is not so limited, however, and includes any combination of apertures or lack thereof to provide any configuration of open and blocked microchannels  702 . 
     One, some, or all of the apertures  712  can have a size (e.g., diameter) that is approximately the same size as, or larger than, one or more corresponding microchannels  702  such that the corresponding microchannel(s)  702  is entirely open to receive a maximum capacity and/or throughput of refrigerant. Alternatively or in addition, the distributor tube  612  can include differently sized apertures. For example, the distributor tube  612  can include one or more apertures of a first size (e.g., first diameter) and one or more apertures of a second size (e.g., second diameter). As illustrated in  FIG. 7E , the distributer tube  612  can be configured to permit full flow through some microchannels  702 , permit partial flow through another microchannel  702  (due to the smaller sized aperture  712 ), and prevent flow through another microchannel  702  (due to the lack of a corresponding aperture  712 ). As illustrated in  FIG. 7F , the distributor tube  612  can include multiple different sizes (e.g., diameters) of apertures  712 . Although the apertures  712  and microchannels  702  are shown herein as being circular in shape, the disclosed technology includes apertures  712  and/or microchannels  702  of different shapes, such as an oval, ellipse, triangle, square, or any other polygonal shape. 
     As discussed, various heat exchanger designs can have varying airflow concentrations as air flows across the heat exchanger tubes  606  of the heat exchanger  112 ,  114  based on various characteristics and design elements of the heat exchanger  112 ,  114 . Many heat exchangers  112 ,  114  include fins  802  to help facilitate heat transfer and increase the heat transferability and/or efficiency of the system. In certain designs, there are portions of the heat exchanger tubes  606  that do not include fins  802  and thus include a gap  804  between adjacent heat exchanger tubes  606 , as shown in  FIG. 8A . Alternatively or in addition, the separation between adjacent heat exchanger tubes  606  can vary (e.g., due to bends in the tubes at or near the ends of the heat exchanger  112 ,  114 . Regardless of the cause, certain heat exchanger designs can include undesirable gaps  804  and/or gaps of an undesirable size such that an amount of air travels through the heat exchanger  112 ,  114  at a location with low heat transferability and/or efficiency. To help correct this issue, the disclosed technology can include one of more baffles  806 . The baffle(s)  806  can be attached to the heat exchanger  112 ,  114  at a location corresponding to one or more gaps  804  and/or gaps of an undesirable size. For example, as illustrated in  FIG. 8B , the baffle(s)  806  can be located at one or both ends of the heat exchanger tubes  606 , thereby preventing or inhibiting air flow through the underlying gaps  804 . 
     As described, the disclosed technology provides, among other things, an inexpensive design for providing enhanced partial-load efficiency in an air system, such as an air conditioning system and/or a heat pump system. 
     Further, certain methods and processes are described herein. It is contemplated that the disclosed methods and processes can include, but do not necessarily include, all steps discussed herein. That is, methods and processes in accordance with the disclosed technology can include some of the disclosed while omitting others. Moreover, methods and processes in accordance with the disclosed technology can include other steps not expressly described herein. 
     While certain examples of this disclosure have been described in connection with what is presently considered to be the most practical and various examples, it is to be understood that this disclosure is not to be limited to the disclosed examples, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 
     This written description uses examples to disclose certain examples of the technology and also to enable any person skilled in the art to practice certain examples of this technology, including making and using any apparatuses or systems and performing any incorporated methods. The patentable scope of certain examples of the technology is defined in the claims and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.