Patent Application
20080156014
The application generally relates to multichannel heat exchanger applications in HVAC&R systems. The application relates more specifically to improved refrigerant distribution in a condenser that uses multichannel heat exchangers.
In a typical multichannel heat exchanger or coil slab, a series of tube sections are connected (physically and thermally) by fins that are configured to permit airflow through the heat exchanger in order to provide for heat transfer between the airflow and a circulating fluid, e.g., water or refrigerant. The tube sections of the heat exchanger are oriented to extend either horizontally or vertically and each tube section has several tubes or channels that are used to circulate the fluid. The outside of the tube section is a continuous surface typically having a rectangular shape.
Multichannel heat exchangers can offer significant cost and performance advantages when used in an air-cooled condenser of a HVAC&R system compared to conventional round-tube condenser coils. One performance advantage offered by a multichannel heat exchanger is a reduced air pressure drop through the condenser compared to a conventional round-tube coil. The multichannel heat exchanger can be designed so that a single heat exchanger or row performs the de-superheating and sub-cooling process in the condenser based on the number of passes in the heat exchanger. In a two-pass design, the two phase refrigerant exiting the first pass is mixed in an intermediate header before entering the second pass where condensation is completed and sub-cooling is done. Further, a multichannel heat exchanger may be constructed of aluminum, which can reduce material cost and enhance performance in a refrigeration system. The reduced air pressure drop in a multichannel heat exchanger forces and uneven air distribution between the coils. This uneven air distribution in multichannel coils results in large variations in refrigerant liquid temperature. Therefore, what is needed is a system and method for more evenly distributing the refrigerant flow in multichannel coils, thereby improving the distribution of refrigerant liquid temperature as well.
Intended advantages of a system and/or method satisfy one or more of these needs or provide other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments that fall within the scope of the claims, regardless of whether they accomplish one or more of the aforementioned needs.
One embodiment is directed to an HVAC&R system having a compressor, a condenser, an evaporator, and an expansion valve connected in a closed refrigerant loop. The condenser has at least two fluid flow paths that are cooled by an air flow drawn through the condenser by at least one condenser fan. The at least two fluid flow paths each have an inlet and an outlet and a fluid flow between the inlet and the outlet. The at least two fluid flow paths have a variable air flow for cooling the fluid in the at least two fluid flow paths. At least one flow regulator is disposed in at least one outlet to regulate at least one fluid flow in response to the variable air flow in the condenser. The flow regulator regulates the fluid flow in the at least two flow paths to provide a fluid having a substantially equal temperature in the at least two flow paths.
Another embodiment is directed to a condenser has at least two fluid flow paths that are cooled by an air flow drawn or directed through the condenser by at least one condenser fan. The at least two fluid flow paths each have an inlet and an outlet and a fluid flow between the inlet and the outlet. The at least two fluid flow paths have a variable air flow for cooling the fluid flow in the at least two fluid flow paths. At least one flow regulator is disposed in at least one outlet to regulate at least one fluid flow in response to the variable air flow in the condenser. The flow regulator regulates the fluid flow in the at least two flow paths to provide a fluid having a substantially equal temperature in the at least two flow paths.
Yet another embodiment is directed to a condenser, which has a multichannel heat exchanger. The multichannel heat exchanger has at least two fluid flow paths that are cooled by an air flow drawn or otherwise directed through the condenser by at least one condenser fan. The at least two fluid flow paths each have an inlet and an outlet and a fluid flow between the inlet and the outlet. The at least two fluid flow paths have a variable air flow for cooling the fluid in the at least two fluid flow paths. At least one flow regulator is disposed in at least one outlet to regulate at least one fluid flow in response to the variable air flow in the condenser. The flow regulator regulates the fluid flow in the at least two flow paths to provide a fluid having a substantially equal temperature in the at least two flow paths.
One advantage is improved liquid subcooling temperatures of the refrigerant to assure reliable performance of the expansion valve.
Another advantage is improved protection against equipment performance degradation.
Yet another advantage is increased chiller cooling capacity.
Still another advantage is a reduced cost system and increased system efficiency, when compared to conventional systems.
Alternative exemplary embodiments relate to other features and combinations of features as may be generally recited in the claims.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
Turning now to the drawings, and referring first to
In operation, when the system shown in
In operation, the outdoor unit draws in environmental air through sides as indicated by the arrows directed to the sides of unit OU, forces the air through the outer unit coil by a means of a fan (not shown) and expels the air as indicated by the arrows above the outdoor unit. When operating as an air conditioner, the air is heated by the condenser coil within the outdoor unit and exits the top of the unit at a temperature higher than it entered the sides. On the contrary, air is circulated over the indoor coil IC, and is then circulated through the residence by means of duct work D, as indicated by the arrows in
When the unit in
In operation, the chiller, which includes heat exchangers for both evaporating and condensing a refrigerant as described above, cools water that is circulated to the air handlers. Air blown over additional coils that receive the water in the air handlers causes the water to increase in temperature and the circulated air to decrease in temperature. The cooled air is then routed to various locations in the building via additional duct work. Ultimately, distribution of the air is routed to diffusers that deliver the cooled air to offices, apartments, hallways, and any other interior spaces within the building. In many applications, thermostats or other command devices (not shown in
The system 10 cools an environment by cycling refrigerant within the closed refrigeration loop 12 through condenser 16, compressor 18, expansion device 20, and evaporator 22. The refrigerant enters the condenser 16 as a high pressure and temperature vapor and flows through the multichannel tubes of the condenser 16. A fan 24, which is driven by a motor 26, draws air across the multichannel tubes. The fan 24 may push or pull air across the tubes. Heat transfers from the refrigerant vapor to the air producing heated air 28 while causing the refrigerant vapor to condense into a liquid. The liquid refrigerant then flows into an expansion device 20 where the refrigerant expands to become a low pressure and temperature liquid. Typically, the expansion device 20 will be a thermal expansion valve (TXV); however, in other embodiments, the expansion device may be an orifice or a capillary tube. As those skilled in the art will appreciate, after the refrigerant exits the expansion device, some vapor refrigerant may be present in addition to the liquid refrigerant.
From the expansion device 20, the refrigerant enters the evaporator 22 and flows through the evaporator multichannel tubes. A fan 30, which is driven by a motor 32, draws air across the multichannel tubes. Heat transfers from the air to the refrigerant liquid producing cooled air 34 and causing the refrigerant liquid to boil into a vapor. As will be appreciated by those skilled in the art, the fan may be replaced by a pump, which draws fluid across the multichannel tubes.
The refrigerant then flows to compressor 18 as a low pressure and temperature vapor. The compressor 18 reduces the volume available for the refrigerant vapor, consequently, increasing the pressure and temperature of the vapor refrigerant. The compressor may be any suitable compressor such as a screw compressor, reciprocating compressor, rotary compressor, swing link compressor, scroll compressor, centrifugal compressor or turbine compressor. The compressor 18 is driven by a motor 36, which receives power from a variable speed drive (VSD) or a direct AC or DC power source. In one embodiment, the motor 36 receives fixed line voltage and frequency from an AC power source although in some applications the motor may be driven by a variable voltage or frequency drive. The motor may be a switched reluctance (SR) motor, an induction motor, an electronically commutated permanent magnet motor (ECM), or any other suitable motor type. The refrigerant exits the compressor 18 as a high temperature and pressure vapor that is ready to enter the condenser and begin the refrigeration cycle again.
The operation of the refrigeration cycle is governed by control devices 14 which include control circuitry 38, a thermostat 40, and a temperature sensor 42. The control circuitry 38 is coupled to motors 26, 32, 36 which drive the condenser fan 24, the evaporator fan 30, and the compressor 18, respectively. The control circuitry uses information received from the thermostat 40 and the sensor 42 to determine when to operate the motors 26, 32, 36 that drive the air conditioning system. For example, in a residential air conditioning system, the thermostat 40 may be a programmable 24 volt thermostat that provides a temperature set point to the control circuitry 38. The sensor 42 determines the ambient air temperature and provides the temperature to the control circuitry 38. The control circuitry 38 then compares the temperature received from the sensor to the temperature set point received from the thermostat. If the temperature is higher than the set point, the control circuitry may turn on the motors 26, 32, 36 to run the air conditioning system 10. Additionally, the control circuitry may execute hardware or software control algorithms to regulate the air conditioning system. In some embodiments, the control circuitry 38 may include an analog to digital (A/D) converter, a microprocessor, a non-volatile memory, and an interface board. Other devices may, of course, be included in the system, such as additional pressure and/or temperature transducers or switches that sense temperatures and pressures of the refrigerant, the heat exchangers, the inlet and outlet air, and so forth.
The heat pump system 44 includes an outside coil 50 and an inside coil 52 that both operate as heat exchangers. As noted above, the coils may function as either an evaporator or a condenser depending on the heat pump operation mode. For example, when the heat pump system 44 is operating in cooling (or “AC”) mode, the outside coil 50 functions as a condenser, releasing heat to the outside air, while the inside coil 52 functions as an evaporator, absorbing heat from the inside air. On the contrary, when the heat pump system 44 is operating in heating mode, the outside coil 50 functions as an evaporator, absorbing heat from the outside air, while the inside coil 52 functions as a condenser, releasing heat to the inside air. A reversing valve 54 is positioned on the reversible loop 46 between the coils to control the direction of refrigerant flow and thereby to switch the heat pump between heating mode and cooling mode.
The heat pump system 44 also includes two metering devices 56, 58 for decreasing the pressure and temperature of the refrigerant before it enters the evaporator. As will be appreciated by those skilled in the art, the metering device also acts to regulate refrigerant flow into the evaporator so that the amount of refrigerant entering the evaporator equals the amount of refrigerant exiting the evaporator. The metering device used depends on the heat pump operation mode. For example, when the heat pump system is operating in cooling mode, refrigerant bypasses metering device 56 and flows through metering device 58 before entering the inside coil 52, which acts as an evaporator. Similarly, when the heat pump system is operating in heating mode, refrigerant bypasses metering device 58 and flows through metering device 56 before entering the outside coil 50, which acts as an evaporator. In other embodiments, a single metering device may be used for both heating mode and cooling mode. The metering devices 56, 58 typically are thermal expansion valves (TXV), but also may be orifices or capillary tubes.
The refrigerant enters the evaporator, which is the outside coil 50 in heating mode and the inside coil 52 in cooling mode, as a low temperature and pressure liquid. As will be appreciated by those skilled in the art, some vapor refrigerant may also be present as a result of the expansion process that occurs in the metering device 56, 58. The refrigerant flows through multichannel tubes in the evaporator and absorbs heat from the air changing the refrigerant into a vapor. In cooling mode, the indoor air passing over the multichannel tubes also may be dehumidified. The moisture from the air may condense on the outer surface of the multichannel tubes and consequently be removed from the air.
After exiting the evaporator, the refrigerant passes through the reversing valve 54 and into the compressor 60. The compressor 60 decreases the volume of the refrigerant vapor, consequently, increasing the temperature and pressure of the vapor. Here again, the compressor may be any suitable compressor such as a screw compressor, reciprocating compressor, rotary compressor, swing link compressor, scroll compressor, centrifugal compressor or turbine compressor.
From the compressor, the increased temperature and pressure vapor refrigerant flows into a condenser, the location of which is determined by the heat pump mode. In cooling mode, the refrigerant flows into outside coil 50 (acting as a condenser). A fan 62, which is powered by a motor 64, draws air over the multichannel tubes containing refrigerant vapor. As will be appreciated by those skilled in the art, the fan may be replaced by a pump, which draws fluid across the multichannel tubes. The heat from the refrigerant is transferred to the outside air causing the refrigerant to condense into a liquid. In heating mode, the refrigerant flows into inside coil 52 (acting a condenser). A fan 66, which is powered by a motor 68, draws air over the multichannel tubes containing refrigerant vapor. The heat from the refrigerant is transferred to the inside air causing the refrigerant to condense into a liquid.
After exiting the condenser, the refrigerant flows through the metering device (56 in heating mode and 58 in cooling mode) and returns to the evaporator (outside coil 50 in heating mode and inside coil 52 in cooling mode) where the process begins again.
In both heating and cooling modes, a motor 70 drives the compressor 60 and circulates refrigerant through the reversible refrigeration/heating loop 46. The motor may receive power either directly from an AC or DC power source or from a variable speed drive (VSD). As in the previous example, the motor may be a switched reluctance (SR) motor, an induction motor, an electronically commutated permanent magnet motor (ECM), or any other suitable motor type.
The operation of the motor 70 is controlled by control circuitry 72. The control circuitry 72 receives information from a thermostat 74 and sensors 76, 78, 80 and uses the information to control the operation of the heat pump system 44 in both cooling mode and heating mode. For example, in cooling mode, the thermostat provides a temperature set point to the control circuitry 72. The sensor 80 measures the ambient indoor air temperature and provides it to the control circuitry 72. The control circuitry 72 then compares the air temperature to the temperature set point and engages the compressor motor 70 and fan motors 64 and 68 to run the cooling system if the air temperature is above the temperature set point. Likewise, in heating mode, the control circuitry 72 compares the air temperature from the sensor 80 to the temperature set point from the thermostat 74 and engages the motors 64, 68, 70 to run the heating system if the air temperature is below the temperature set point.
The control circuitry 72 also uses information received from the thermostat 40 to switch the heat pump system 44 between heating mode and cooling mode. For example, if the thermostat is set to cooling mode, the control circuitry 72 will send a signal to a solenoid 82 to place the reversing valve 54 in the air conditioning position 84. Consequently, the refrigerant will flow through the reversible loop 46 as follows: the refrigerant exits compressor 60, is condensed in outside coil 50, is expanded by metering device 58, and is evaporated by inside coil 52. On the contrary, if the thermostat is set to heating mode, the control circuitry 72 will send a signal to solenoid 82 to place the reversing valve 54 in the heat pump position 86. Consequently, the refrigerant will flow through the reversible loop 46 as follows: the refrigerant exits compressor 60, is condensed in inside coil 52, is expanded by metering device 56, and is evaporated by outside coil 50.
The control circuitry 72 may execute hardware or software control algorithms to regulate the heat pump system 44. In some embodiments, the control circuitry may include an analog to digital (A/D) converter, a microprocessor, a non-volatile memory, and an interface board.
The control circuitry also may initiate a defrost cycle when the system 44 is operating in heating mode. When the outdoor temperature approaches freezing, moisture in the outside air that is directed over outside coil 50 may condense and freeze on the coil. The sensor 76 measures the outside air temperature, and the sensor 78 measures the temperature of the outside coil 50. These sensors provide the temperature information to the control circuitry which determines when to initiate a defrost cycle. For example, if either of the sensors 76, 78 provides a temperature below freezing to the control circuitry, the system 44 may be placed in defrost mode. In defrost mode, the solenoid 82 is actuated to place the reversing valve 54 to air conditioning position 84, and the motor 64 is shut off to discontinue air flow over the multichannels. The system 44 then operates in cooling mode until the increased temperature and pressure refrigerant flowing through the outside coil defrosts the coil 50. Once the sensor 78 detects that the coil 50 is defrosted, the control circuitry 72 returns the reversing valve 54 to heat pump position 86. As will be appreciated by those skilled in the art, the defrost cycle can be set to occur at many different time and temperature combinations.
In some embodiments, the construction of the first tubes 94 may differ from the construction of the second tubes 96. Tubes may also differ within each section. For example, the tubes may all have identical cross sections, or the tubes in the first section may be rectangular while the tubes in the second section are oval. The internal construction of the tubes, as described below with regard to
Returning to
Fins 104 are located between the multichannel tubes 92 to promote the transfer of heat between the tubes 92 and the environment. In one embodiment, the fins are constructed of aluminum, brazed or otherwise joined to the tubes, and disposed generally perpendicular to the flow of refrigerant. However, in other embodiments the fins may be made of other materials that facilitate heat transfer and may extend parallel or at varying angles with respect to the flow of the refrigerant. Additionally, the fins may be louvered fins, corrugated fins, or any other suitable type of fin.
As noted above, in a typical evaporator heat exchanger application, the majority of the heat transfer occurs due to a phase change of the refrigerant. Refrigerant exits the expansion device as a low pressure and temperature liquid and enters the evaporator. As the liquid travels through the first multichannel tubes 94, the liquid absorbs heat from the outside environment causing the liquid to warm from its subcooled temperature (i.e., a number of degrees below the boiling point). Then, as the liquid refrigerant travels through the second multichannel tubes 96, the liquid absorbs more heat from the outside environment causing it to boil into a vapor. Although evaporator applications typically use liquid refrigerant to absorb heat, some vapor may be present along with the liquid due to the expansion process. The amount of vapor may vary based on the type of refrigerant used. In some embodiments, the refrigerant may contain approximately 15% vapor by weight and 90% vapor by volume. This vapor has a lower density than the liquid, causing the vapor to separate from the liquid within the manifold 88. Consequently, certain flow channels of tubes 92 may contain only vapor.
After flowing through the channel section 110, the refrigerant reaches the open section 112. In the open section, the interior walls that form the flow channels have been removed or interrupted. Consequently, the open section includes an open channel 114 spanning the width W of the tube 92 where mixing of the two phases of refrigerant can occur. Mixed flow 118 occurs within this section causing the fluid flow 108 from the flow channels 106 to cross paths and mix. Thus, flow channels containing all (or primarily) vapor phase may mix with flow channels containing all (or primarily) liquid phase, providing a more homogenous distribution of refrigerant. Additionally, flow channels containing different percentages of vapor and liquid may also mix.
From the open section 112, the refrigerant enters flow channels 120 contained within channel section 122. The fluid flow 124 through these channels may contain a more even distribution of vapor and liquid phases due to the mixed flow 118 that occurred within the open channel 114. The tube 92 may contain any number of open sections 112 where mixing may occur. Thus, rather than allowing vapor alone to be channeled through certain flow paths, the internal wall interruptions permit mixing of the phases, allowing increased phase change to occur in all of the flow paths (through which an increasingly mixed phase flow will be channeled). The internal wall interruptions also allow the tubes to be segregated into sections for repair purposes. For example, if a flow channel contained within channel section 110 becomes blocked, plugged, or requires repair, that section of the flow channel may be removed from service or bypassed while the corresponding flow channel within channel section 122 continues to receive refrigerant flow.
In the arrangement shown in
To regulate the flow of refrigerant in the coils a valve or orifice 220 may be disposed in the outlet 100 of at least one of the coils. The valve or orifice 220 provides the necessary refrigerant flow for each individual coil, depending on the amount of air flow the coil receives. The refrigerant is regulated to allow the air flow to cool the refrigerant in the flow channel and provide a more efficient chiller.
In one embodiment, one or more valves or orifices 220 may be incorporated in coils 200, 202, 204, 206, 208, and 210 as a unitary part of the coil. Table 2, below, provides sample refrigerant temperatures at the exit of each coil in which coils 202 and 208 include a valve or orifice 220 in the discharge connection. The temperatures of the coils are now closer in range, resulting in a more efficient chiller system.
The incorporation of one or more valves or orifices 220 with the discharge connections of the coils can substantially lower refrigerant liquid temperature entering the expansion valve by approximately 1.5 deg. Fahrenheit with no change in condensing temperature. The resulting lower liquid temperature gives an approximate substantially 1% increase in both chiller capacity and efficiency. In addition, the lower liquid temperature substantially eliminates vapor from exiting some of the coils. This is important because refrigerated vapor can create operational problems with expansion valves. Lastly, the incorporation of one or more orifices with the discharge connections of the coils may be incorporated with multichannel and conventional channel applications with uneven air distribution. It should be noted that while reference has been made to air flow cooling the fluid in the flow tubes 106, any type of non volatile fluid may be used, e.g. water. The examples provided above in Table 1 and Table 2 include condensers with six microchannel coils, however, one of ordinary skill in the art would appreciate that any number of coils may be used for the microchannel in the condenser.
It is understood that the present discussion describes the use of the invention in condensers with multiple microchannel coils. The invention may also be used with other types of condenser applications. These condenser applications include, but are not limited to, conventional round-tube coils, water-cooled condensers, individual tubes within condensers or any condenser with tube-side condensation, flow distribution issues, or other problems or issues that create an imbalance in condenser performance.
It is also understood that while the orifice or valve is described as being disposed in the outlet or near the exit of the condenser, the orifice or valve may be placed in liquid headers, at an the outlet individual tubes, in coils with reduced air flow, in coils with higher air temperatures, or in coils with reduced heat transfer. Likewise, the orifice or valve may be applied to water-cooled condensers with tube-side condensation or sections of the condenser with reduced heat transfer or reduced water flow. The invention may also apply to any application with issues or problems with condenser performance.
It should be noted that the present discussion makes use of the term “multichannel” tubes or “multichannel heat exchanger” to refer to arrangements in which heat transfer tubes include a plurality of flow paths between manifolds that distribute flow to and collect flow from the tubes. A number of other terms may be used in the art for similar arrangements. Such alternative terms might include “microchannel” (sometimes intended to imply having fluid passages on the order of a micrometer and less), and “microport”. Other terms sometimes used in the art include “parallel flow” and “brazed aluminum”. However, all such arrangements and structures are intended to be included within the scope of the term “multichannel”. In general, such “multichannel” tubes will include flow paths disposed along the width or in a plane of a generally flat, planar tube, although, again, the invention is not intended to be limited to any particular geometry unless otherwise specified in the appended claims.
It should also be noted that while the present discussion refers to the condenser as being a part of a multichannel heat exchanger or an HVAC&R system, the condenser could be used in any suitable application, such as a chemical process. Further, one of ordinary skill in the art would appreciate that while the term refrigerant is used as the fluid in the coils, any suitable fluid may be used, such as, but not limited to, propane or chlorine. The fluid used on the outside of the tubes may be any suitable liquid or gas such as, but not limited to air, water or brine.
It should also be understood that the application is not limited to the details or methodology set forth in the following description or illustrated in the figures. It should also be understood that the phraseology and terminology employed herein is for the purpose of description only and should not be regarded as limiting.
While the exemplary embodiments illustrated in the figures and described herein are presently preferred, it should be understood that these embodiments are offered by way of example only. Accordingly, the present application is not limited to a particular embodiment, but extends to various modifications that nevertheless fall within the scope of the appended claims. The order or sequence of any processes or method steps may be varied or re-sequenced according to alternative embodiments.
It is important to note that the construction and arrangement of the multichannel coil as shown in the various exemplary embodiments is illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. For example, elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. Accordingly, all such modifications are intended to be included within the scope of the present application. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. In the claims, any means-plus-function clause is intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the present application.
This application claims the benefit of U.S. Provisional Patent Application Nos. 60/882,033 filed on Dec. 27, 2006; 60/914,489 filed on Apr. 27, 2007 and 60/952,280 and filed on Jul. 27, 2007, all of which relate to multichannel technology and are hereby incorporated by reference in their entirety into this application.
| Number | Date | Country | |
|---|---|---|---|
| 60882033 | Dec 2006 | US | |
| 60914489 | Apr 2007 | US | |
| 60952280 | Jul 2007 | US |
