HVAC system with back-pressure limiting expansion device and method of operating such an HVAC system

Abstract

A fluid conditioning system (120) includes a compressor (122), a first heat exchanger (124), a second heat exchanger (128), and a first expansion device (126a), and a second expansion device (126b) fluidly connected to form a closed loop through which a working fluid (F) circulates. The first expansion device (126a) is associated with operation of the fluid conditioning system (120) in a first mode and the second expansion device (126b) is associated with operation of the fluid conditioning system (120) in a second mode. The second expansion device (126b) is a thermostatic expansion device. An accumulator (130) is fluidly connected to the closed loop upstream from the compressor (122) relative to a flow of the working fluid (F). A back pressure regulator (132) is fluidly coupled to the first heat exchanger (124), the second heat exchanger (128), and the second expansion device (126b).

Description

BACKGROUND

[0001] Embodiments of the present disclosure pertain to the art of fluid conditioning systems, for instance heating, ventilation, and air-conditioning (HVAC) systems.

[0002] Heat pumps are used in a variety of settings, for example, in heating, ventilation, and air fluid conditioning (HVAC) systems that provide a desired air temperature in a facility. Such heat pumps commonly include a compressor, evaporator, expansion device, and condenser. The heat pumps input work to the refrigerant, e.g., by driving the compressor, thereby enabling the refrigerant to move heat from a colder heat reservoir to a warmer heat sink.BRIEF DESCRIPTION

[0003] According to a first aspect of the invention there is provided a fluid conditioning system including a compressor, a first heat exchanger, a second heat exchanger, a first expansion device, and a second expansion device fluidly connected to form a closed loop through which a working fluid circulates. The first expansion device is associated with operation of the fluid conditioning system in a first mode and the second expansion device is associated with operation of the fluid conditioning system in a second mode. The second expansion device is a thermostatic expansion device. An accumulator is fluidly connected to the closed loop upstream from the compressor relative to a flow of the working fluid. A back pressure regulator is fluidly coupled to the first heat exchanger, the second heat exchanger, and the second expansion device.

[0004] According to a second aspect of the invention there is provided a fluid conditioning system comprising: a compressor, a first heat exchanger, a second heat exchanger, and a first expansion device, and a second expansion device fluidly connected to form a closed loop through which a working fluid circulates, wherein the first expansion device is associated with operation of the fluid conditioning system in a first mode, and the second expansion device is associated with operation of the fluid conditioning system in a second mode, the second expansion device being a thermostatic expansion device; an accumulator fluidly connected to the closed loop upstream from the compressor relative to a flow of the working fluid; and a back pressure regulator fluidly coupled to the first heat exchanger and the second heat exchanger, second expansion device.

[0005] Optionally, an internal working fluid volume of the first heat exchanger is greater than the internal working fluid volume of the second heat exchanger such that the fluid conditioning system has a charge imbalance.

[0006] The second heat exchanger may be a microchannel heat exchanger.

[0007] Optionally, the fluid conditioning system comprises a reversing valve which allows the working fluid to move through the closed loop in a first direction associated with the first mode of operation and in an opposite, second direction associated with the second mode of operation.

[0008] The first mode may be a cooling mode and the second mode may be a heating mode.

[0009] Optionally, the fluid conditioning system is a heat pump having an indoor unit and an outdoor unit and the back pressure regulator is located at the outdoor unit.

[0010] The back pressure regulator may be configured such that working fluid bypasses the back pressure regulator during the cooling mode.

[0011] Optionally, a first portion of the working fluid is provided to the thermostatic expansion device and a second portion of the working fluid is provided to the back pressure regulator. The first portion of the working fluid and the second portion of the working fluid may be mixed within the closed loop.

[0012] Optionally, a first branch extends downstream from the thermostatic expansion device and a second branch extends downstream from the back pressure regulator. The first branch and the second branch may be joined at a mixing location arranged upstream from the first heat exchanger relative to a second direction of flow of the working fluid. The first portion of the working fluid and the second portion of the working fluid may be mixed at the mixing location.

[0013] According to a third aspect of the invention there is provided a method of operating a fluid conditioning system including providing a closed loop circuit including a compressor, a first heat exchanger, a first expansion device, a second expansion device, and a second heat exchanger. The second expansion device is a thermostatic expansion device. The method includes operating the fluid conditioning system in a first mode and during the first mode, circulating a working fluid through the compressor, the first heat exchanger, the first expansion device, and the second heat exchanger of the closed loop circuit in a first direction. The method includes operating the fluid conditioning system in a second mode and during the second mode, circulating the working fluid through the compressor, the second heat exchanger, the second expansion device, and the first heat exchanger of the closed loop circuit in a second direction. The closed loop includes a back pressure regulator arranged in parallel with the second expansion device and circulating the working fluid through the closed loop circuit during the second mode includes dividing the working fluid into a first portion provided to the second expansion device and a second portion provided to the back pressure regulator.

[0014] The method may comprise adjusting a position of a reversing valve of the closed loop to transform the fluid conditioning system from operating in the first mode to operating in the second mode.

[0015] During operation in the first mode, the working fluid may bypass the second expansion device and the back pressure regulator.

[0016] The method may comprise collecting liquid working fluid within an accumulator during operation in the second mode.

[0017] The method may comprise adjusting a position of the back pressure regulator to maintain a pressure upstream from the back pressure regulator at a desired threshold.

[0018] Adjusting the position of the back pressure regulator may include increasing the second portion provided to the back pressure regulator in response to an increase in the pressure at an inlet of the thermostatic expansion device.

[0019] Adjusting the position of the back pressure regulator may reduce superheat of the working fluid upstream from the compressor.

[0020] Optionally, an internal working fluid volume of the first heat exchanger is greater than the internal working fluid volume of the second heat exchanger such that the fluid conditioning system has a charge imbalance.

[0021] The second heat exchanger may be a microchannel heat exchanger.

[0022] Optionally, the fluid conditioning system is a heat pump having an indoor unit and an outdoor unit and the back pressure regulator is located at the outdoor unit.BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Certain exemplary embodiments will now be described in greater detail by way of example only and with reference to the accompanying drawings, in which like elements are numbered alike and: FIG. 1A is a schematic diagram of a prior art vapor compression cycle; FIG. 1B is a schematic diagram of a prior art vapor compression cycle of a heat pump; FIG. 2A is a schematic diagram of a vapor compression cycle having a back pressure regulator in a cooling mode; and FIG. 2B is a schematic diagram of a vapor compression cycle having a back pressure regulator in a heating mode. DETAILED DESCRIPTION

[0024] A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.

[0025] With reference now to FIG. 1A, a schematic diagram of an example of a basic vapor compression cycle of a fluid conditioning system 20, such as an air conditioning system for example, is illustrated. The vapor compression cycle of the fluid conditioning system 20 includes one or more compressors 22, a first heat exchanger 24, an expansion device 26, and a second heat exchanger 28 arranged in a closed loop. A working fluid, such as a refrigerant for example, is configured to circulate through the vapor compression cycle, such as in a counterclockwise direction for example.

[0026] In operation, the compressor 22 receives a working fluid vapor from the second heat exchanger 28 and compresses it to a high temperature and pressure. The relatively hot working fluid vapor is then delivered to the first heat exchanger 24 where it is cooled and condensed to a liquid state via heat exchange relationship with a cooling medium C, such as air or water. Accordingly, when the first heat exchanger 24 receives the refrigerant output from the compressor 22, the first heat exchanger functions as a condenser. The cooled liquid refrigerant flows from the first heat exchanger 24 to the expansion device 26, such as an expansion valve for example, in which the working fluid is expanded to a lower pressure where the temperature is reduced and the working fluid may exist in a two-phase liquid / vapor state. From the expansion device 26, the working fluid is provided to the second heat exchanger 28. Because heat is transferred from a secondary medium, such as air for example, to the working fluid within the second heat exchanger 28, causing any refrigerant in the liquid phase to vaporize, the second heat exchanger 28 functions as an evaporator. From the second heat exchanger 28, the low-pressure vapor working fluid returns to the compressor 22 so that the cycle may be repeated. As will be described in more detail below, the fluid conditioning system 20 may additionally include an accumulator 30 operable to collect liquid working fluid.

[0027] In embodiments where the fluid conditioning system 20 is a heat pump, such as shown in FIG. 1B, the fluid conditioning system 20 includes a reversing valve V operable to control a direction of flow of working fluid within the vapor compressor cycle. When the valve V is transformed from a first position to a second position, the working fluid may flow clockwise from the compressor 22 to the second heat exchanger 28, the expansion device 26, and the first heat exchanger 24 sequentially. In such instances, the working fluid within the second heat exchanger 28 is cooled and condensed to a liquid state and the refrigerant within the first heat exchanger is heated to form a low-pressure vapor. Accordingly, when operating in this reverse flow direction, the second heat exchanger 28 functions as the condenser and the first heat exchanger 24 functions as the evaporator of the vapor compression cycle.

[0028] When the fluid conditioning system 20 is configured as a heat pump, the fluid conditioning system 20 may include a first expansion device 26a and a second expansion device 26b. A corresponding check valve 27a, 27b may be arranged in parallel with each respective expansion device 26a, 26b. Although the expansion devices 26a, 26b and corresponding check valves 27a, 27b are schematically illustrated as separate components, it should be appreciated that in some embodiments an expansion device and a check valve operable to control a flow that bypasses the expansion device may be integrated into a single unit. In the illustrated, non-limiting embodiment, the expansion device 26a, 26b configured to receive a flow of working fluid during a mode of operation of the fluid conditioning system 20 is located directly upstream from the heat exchanger 24, 28 operable as the evaporator during that mode of operation.

[0029] The first expansion device 26a may be associated with operation of the fluid conditioning system 20 in a first cooling mode and flow of the working fluid F in a first direction. For example, the flow of condensed working fluid F output from the first heat exchanger 24 is configured to pass through the second check valve 27b arranged in parallel with the second expansion device 26b before being provided to the downstream first expansion device 26a. Similarly, the second expansion device 26b may be associated with operation of the fluid conditioning system 20 in a heating mode and the flow of the working fluid F in a second direction. For example, in the heating mode, the flow of condensed working fluid F output from the second heat exchanger 28 is provided to the check valve 27a arranged in parallel with the first expansion device 26a before being delivered to the second expansion device 26b.

[0030] In embodiments of the fluid conditioning system 20 having a charge imbalance, such as where an internal working fluid volume of the second heat exchanger 28 is significantly smaller than the internal working fluid volume of the first heat exchanger 24, the fluid conditioning system 20 may include an accumulator 30 operable to store excess charge during operation of the system in a heating mode. In operation, the accumulator 30 is configured to trap working fluid in a liquid phase while allowing vapor working fluid to pass therethrough. Accordingly, embodiments of the fluid conditioning system 20 including an accumulator 30, the working fluid at the outlet of the evaporator is generally a two-phase vapor and liquid mixture.

[0031] Several different types of expansion devices may be used in a fluid conditioning system, such as a thermostatic expansion valve and a fixed orifice expansion valve. A thermostatic expansion valve is more efficient than a fixed orifice expansion valve. However, a thermostatic expansion valve includes a measuring bulb, generally positioned downstream from an outlet of the second heat exchanger 28, such as between the second heat exchanger 28 and the compressor 22 for example, and a fluid conditioning system including a thermostatic expansion valve requires the working fluid circulating therein to be superheated at the location of the measuring bulb. A superheated working fluid is not suitable for use in a fluid conditioning system having a charge imbalance and an accumulator because a superheated working fluid is a vapor and contains no liquid to be collected by the accumulator. Accordingly, a thermostatic expansion valve is not suitable for use in the fluid conditioning systems 20 shown in FIGS. 1A and 1B.

[0032] In the non-limiting embodiment of a fluid conditioning system 120 shown in FIGS. 2A and 2B, the fluid conditioning system 120 similarly includes a compressor 122, a first heat exchanger 124, a first expansion device 126a, a second expansion device 126b, a first expansion device bypass 127a, a second expansion device bypass 127b, a second heat exchanger 128, and an accumulator 130 as previously described. The internal working fluid volume of the first heat exchanger 124 may be different, for example greater than the internal working fluid volume of the second heat exchanger 128, resulting in a charge imbalance within the fluid loop of the fluid conditioning system 120. In an embodiment, the second heat exchanger 128 is a microchannel heat exchanger. However, it should be understood that a second heat exchanger 128 having a small internal working fluid volume and formed via any suitable construction is within the scope of the invention as set out in the appended claims.

[0033] The fluid conditioning system 120 additionally includes a reversing valve V (see FIG. 2B) operable to control the flow of working fluid F between a first direction associated with operation in a first, cooling mode (FIG. 2A), and a second direction associated with operation in a second, heating mode (FIG. 2B). In embodiments where the fluid conditioning system 120 is a heat pump, as is known, the components of the heat pump may be separated into an indoor unit and an outdoor unit.

[0034] Similar to the embodiment of FIGS. 1A and 1B, when the fluid conditioning system 120 is operated in the cooling mode, the compressor 122 compresses a working fluid to a high temperature and pressure. The relatively hot working fluid vapor output from the compressor 122 is provided to the first heat exchanger 124 where it is cooled and condensed to a liquid state via heat exchange relationship with the cooling medium C. The cooled liquid working fluid flows from the first heat exchanger 124 to an expansion device, such as the first expansion valve 126a for example. Within the expansion valve 126a, the working fluid is expanded to a lower pressure where the temperature is reduced and the working fluid may exist in a two-phase liquid / vapor state. From the first expansion device 126a, the working fluid is provided to a downstream check valve 127b arranged within a bypass conduit 129b located in parallel with the second expansion device 126b. From the check valve 127b, the working fluid is provided to the second heat exchanger 128. Heat is transferred from a secondary medium H to the working fluid within the second heat exchanger 128, causing at least a portion of the working fluid to vaporize. From the second heat exchanger 128, the low-pressure vapor working fluid returns to the compressor 122.

[0035] In an embodiment, the expansion device 126b associated with operation of the fluid conditioning system 120 in a heating mode is a thermostatic expansion device, such as a thermostatic expansion valve. In such embodiments, the fluid conditioning system 120 may further include a back pressure regulator 132. In an embodiment, the back pressure regulator 132 is arranged in parallel with the thermostatic expansion valve 126b relative to a flow of working fluid F through the fluid conditioning system 120 in a heating mode of operation. Although the back pressure regulator 132 is illustrated and described herein as being separate from the thermostatic expansion valve 126b, embodiments where the thermostatic expansion valve 126b and the back pressure regulator 132 are integrated into a single unit are also within the scope of the invention as set out in the appended claims. In embodiments where the fluid conditioning system 120 is a heat pump, the back pressure regulator 132 may be arranged within the outdoor unit of the heat pump.

[0036] The back pressure regulator 132 and the thermostatic expansion valve 126b are arranged downstream from an outlet 140 of the second heat exchanger 128 when the fluid conditioning system 120 is operating in a second, heating mode. As shown, a conduit 142 extending from the outlet 140 splits into a first branch 144 fluidly connected to an inlet of the thermostatic expansion valve 126b and a second branch 146 fluidly connected to an inlet of the back pressure regulator 132. Accordingly, the working fluid F output from the outlet 140 of the second heat exchanger 128 is divided into a first portion F1 provided to the thermostatic expansion valve 126 and a second portion F2 provided to the back pressure regulator 132.

[0037] A first branch 148 of another conduit 152 similarly extends from the thermostatic expansion valve 126 towards the bypass conduit 129a and check valve 127a arranged in parallel with the first expansion device 126a, and a second branch 150 of the another conduit 152 extends from the back-pressure regulator 132 toward the bypass conduit 129a. The first branch 148 and the second branch 150 join together at a mixing location M1 upstream from the bypass conduit 129a. In such embodiments, the flow of working fluid F1 provided to the thermostatic expansion valve 126 is mixed with the flow of working fluid F2 provided to the back pressure regulator 132 at the mixing location M1, and the resulting flow F is configured to bypass the first expansion device 126a via the check valve 127a before flowing to an inlet 154 of the first heat exchanger 124. In an embodiment, fluid is only able to flow through the back pressure regulator 132 in a single direction, and the direction of flow of the working fluid F when the fluid conditioning system 120 is operated in the cooling mode is opposite the allowable flow through the back-pressure regulator 132.

[0038] Upon the initial start-up of the fluid conditioning system 120 in the heating mode, the back-pressure regulator 132 is fully closed such that no flow of working fluid F2 passes therethrough. Accordingly, all of the working fluid F forms the first portion F1 of the working fluid provided to the thermostatic expansion valve 126. In embodiments of the fluid conditioning system 120 where the fluid conditioning system 120 is charge imbalanced, such as where the second heat exchanger 128 has a smaller internal working fluid volume than the first heat exchanger 124, the pressure at the inlet of the thermostatic expansion valve 126b will gradually increase. This increase in the pressure will also act on the inlet of the back pressure regulator 132, causing the back pressure regulator 132 to open to maintain the pressure upstream from the back pressure regulator 132 at a desired threshold. Once the back pressure regulator 132 is open, the flow of working fluid F is divided between the thermostatic expansion valve 126b and the back pressure regulator 132. Accordingly, the open back pressure regulator 132 provides an alternate expansion path for the second portion F2 of the working fluid.

[0039] When working fluid F is able to pass through both the thermostatic expansion valve 126b and the back pressure regulator 132, the flow provided to the inlet 154 of the first heat exchanger is increased. As a result, the working fluid F at the outlet of the first heat exchanger 124 becomes a two-phase mixture and the liquid portion of the working fluid F will start to accumulate within the accumulator 130. Therefore, allowing the working fluid F to pass through the back pressure regulator 132 reduces and / or eliminates the superheat of the working fluid F at the inlet of the compressor 122. As the superheat is reduced, the thermostatic expansion valve 126b will gradually close until all of the working fluid F forms the second portion F2 of the working fluid provided to the back pressure regulator 132. The fluid conditioning system 120 would eventually stabilize at a constant predetermined expansion valve inlet pressure, and in some embodiments, the constant predetermined expansion valve inlet pressure is equal to the compressor discharge pressure.

[0040] A fluid conditioning system 120 including a thermostatic expansion device 126b and a back pressure regulator 132 arranged in parallel for use during a heating mode of operation allows for more efficient operation of a system having a charge imbalance. The efficiency improvement will be especially evident on multi stage or variable speed heat pumps since a fixed orifice is less well suited in these applications. Further, the thermostatic expansion device 126b and back pressure regulator 132 in combination does not require expensive electronic controls for operation thereof.

[0041] The term "about" is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application.

[0042] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and / or groups thereof.

[0043] While the present invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present invention, as set out in the appended claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the scope of the invention. Therefore, it is intended that the present invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present invention, but that the present invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A fluid conditioning system (120) comprising: a compressor (122), a first heat exchanger (124), a second heat exchanger (128), a first expansion device (126a), and a second expansion device (126b) fluidly connected to form a closed loop through which a working fluid (F) circulates, wherein the first expansion device is associated with operation of the fluid conditioning system in a first mode, and the second expansion device is associated with operation of the fluid conditioning system in a second mode, the second expansion device being a thermostatic expansion device; an accumulator (130) fluidly connected to the closed loop upstream from the compressor relative to a flow of the working fluid; and a back pressure regulator (132) fluidly coupled to the first heat exchanger, the second heat exchanger, and the second expansion device.

2. The fluid conditioning system (120) of claim 1, wherein an internal working fluid volume of the first heat exchanger (124) is greater than the internal working fluid volume of the second heat exchanger (128) such that the fluid conditioning system has a charge imbalance.

3. The fluid conditioning system (120) of claim 1 or 2, wherein the second heat exchanger (128) is a microchannel heat exchanger.

4. The fluid conditioning system (120) of claim 1, 2 or 3, further comprising a reversing valve (V) such that the working fluid (F) is movable through the closed loop in a first direction associated with the first mode of operation and in an opposite, second direction associated with the second mode of operation.

5. The fluid conditioning system (120) of any preceding claim, wherein the first mode is a cooling mode and the second mode is a heating mode.

6. The fluid conditioning system (120) of any preceding claim, wherein the fluid conditioning system is a heat pump having an indoor unit and an outdoor unit and the back pressure regulator (132) is located at the outdoor unit.

7. The fluid conditioning system (120) of claim 5, wherein the back pressure regulator (132) is configured such that working fluid (F) bypasses the back pressure regulator during the cooling mode.

8. The fluid conditioning system (120) of any preceding claim, wherein a first portion (F1) of the working fluid (F) is provided to the thermostatic expansion device and a second portion (F2) of the working fluid is provided to the back pressure regulator (132), wherein the first portion of the working fluid and the second portion of the working fluid are mixed within the closed loop; optionally wherein a first branch (148) extends downstream from the thermostatic expansion device and a second branch (150) extends downstream from the back pressure regulator, the first branch and the second branch being joined at a mixing location (M1) arranged upstream from the first heat exchanger (124) relative to a second direction of flow of the working fluid, wherein the first portion of the working fluid and the second portion of the working fluid are mixed at the mixing location.

9. A method of operating a fluid conditioning system (120), comprising: providing a closed loop circuit including a compressor (122), a first heat exchanger (124), a first expansion device (126a), a second expansion device (126b), and a second heat exchanger (128), wherein the second expansion device is a thermostatic expansion device; operating the fluid conditioning system in a first mode; during the first mode, circulating a working fluid (F) through the compressor, the first heat exchanger, the first expansion device, and the second heat exchanger of the closed loop circuit in a first direction; operating the fluid conditioning system in a second mode; and during the second mode, circulating the working fluid through the compressor, the second heat exchanger, the second expansion device, and the first heat exchanger of the closed loop circuit in a second direction, the closed loop including a back pressure regulator (132) arranged in parallel with the second expansion device and circulating the working fluid through the closed loop circuit during the second mode includes dividing the working fluid into a first portion (F1) provided to the second expansion device and a second portion (F2) provided to the back pressure regulator.

10. The method of claim 9, further comprising adjusting a position of a reversing valve (V) of the closed loop to transform the fluid conditioning system (120) from operating in the first mode to operating in the second mode.

11. The method of claim 9 or claim 10, wherein during operation in the first mode, the working fluid (F) bypasses the second expansion device (126b) and the back pressure regulator (132).

12. The method of any of claims 9-11, further comprising collecting liquid working fluid (F) within an accumulator (130) during operation in the second mode.

13. The method of any of claims 9-12, further comprising adjusting a position of the back pressure regulator (132) to maintain a pressure upstream from the back pressure regulator at a desired threshold; optionally wherein adjusting the position of the back pressure regulator includes increasing the second portion (F2) provided to the back pressure regulator in response to an increase in the pressure at an inlet of the thermostatic expansion device.

14. The method of claim 13, wherein adjusting the position of the back pressure regulator (132) reduces superheat of the working fluid (F) upstream from the compressor (122).

15. The method of any of claims 9-14, wherein an internal working fluid volume of the first heat exchanger (124) is greater than the internal working fluid volume of the second heat exchanger (128) such that the fluid conditioning system (120) has a charge imbalance; and / or wherein the second heat exchanger is a microchannel heat exchanger; and / or wherein the fluid conditioning system is a heat pump having an indoor unit and an outdoor unit and the back pressure regulator (132) is located at the outdoor unit.

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