US20100101246A1

US20100101246A1 - System and Method For Controlling Working Fluid Charge In A Vapor Compression Air Conditioning System

Info

Publication number: US20100101246A1
Application number: US12/650,249
Authority: US
Inventors: Jonathan David Douglas; James Thomas SCHAEFER, JR.; Gregory F. Walters
Original assignee: Trane International Inc
Current assignee: Trane International Inc
Priority date: 2006-07-14
Filing date: 2009-12-30
Publication date: 2010-04-29
Also published as: US20080011003A1; US7866172B2

Abstract

Vapor compression air conditioning systems are provided with a flow restrictor for transferring working fluid to and from at least one of the compressor low pressure inlet conduit and compressor high pressure outlet conduit to provide for accurate charge adjustment to achieve predetermined fluid sub-cooling. Pressure and temperature measurements are taken at a condenser fluid outlet conduit and provided to a microcontroller for determining fluid sub-cooling and comparing sub-cooling with a predetermined target sub-cooling. A charge addition or recovery apparatus may include a solenoid valve controlled by the microcontroller to more accurately control the addition or recovery of refrigerant fluid charge.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional application of the prior filed and co-pending U.S. patent application Ser. No. 11/486,874 filed Jul. 14, 2006 and entitled “System And Method For Controlling Working Fluid Charge In A Vapor Compression Air Conditioning System” which is incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

Vapor compression refrigeration, air conditioning and heating (heat pump) systems have long been plagued with less than optimum operating efficiencies due to an inadequate or excessive working fluid charge within the system. Vapor compression air conditioning and heat pumps systems, for example, typically are designed to operate with a working fluid charge which provides a small amount of sub-cooling of the working fluid in its condensed state. However, initial installation, servicing and repair operations are difficult to carry out with respect to providing a proper fluid charge within the system. For example, when removing fluid or adding fluid to the system, there is often inadequate control of flow of the fluid (refrigerant) resulting in an excessive charge of fluid to a system or a system which is undercharged. Historically, it has been necessary to add or subtract fluid and operate the system to “wait and see” if the system comes into a balanced condition or achieves the desired amount of sub-cooling of the fluid in its condensed state. However, the present invention overcomes the inaccuracies and excessive delays in providing properly charged vapor compression air conditioning systems, in particular.

SUMMARY OF THE INVENTION

The present invention provides a vapor compression air conditioning (heating, cooling or both heating and cooling) or refrigeration system adapted for optimum operating efficiency with respect to the proper quantity or charge of working fluid disposed in the system. The present invention also provides a method, particularly, for adding working fluid to a vapor compression-type air conditioning or refrigeration system. However, a method of extracting fluid is also contemplated.
In accordance with one aspect of the present invention, a vapor compression air conditioning or refrigeration system is adapted for connection to a fluid adding or fluid extracting unit which may include at least one reservoir of working fluid and one or more conduits for connection to fluid conduits associated with the working fluid compressor of the air conditioning system. A fluid flow restrictor device may be provided in one or more conduits adapted to be connected to the so-called low pressure side of a compressor as well as the high pressure side for adding fluid to or removing fluid from the system circuit, respectively. The flow restrictor device may be adapted for throttling fluid flow in one direction while providing for substantially unrestricted flow of fluid in an opposite direction. The flow restrictor devices may be connected to a portable fluid adding and fluid extracting unit or the devices may be permanently connected to the working fluid conduits associated with or connected to the compressor of a vapor compression air conditioning or refrigeration system.
In accordance with another aspect of the present invention, a vapor compression-type air conditioning system or refrigeration system is adapted to include a control circuit or controller and associated instrumentation which monitors the operating condition of the system during a working fluid charge adding or extracting process to calculate actual sub-cooling of the working fluid as it leaves a condenser unit of the system. The controller is operable to provide a suitable output signal indicating the need to remove additional fluid, add additional fluid or indicate no action needed. Still further, the controller may be adapted to automatically shutoff the flow of working fluid to the system when an optimum operating or selected operating condition is reached.
In accordance with yet a further aspect of the present invention, an improved method is provided for adding working fluid to or subtracting working fluid from a vapor compression air conditioning or refrigeration system which achieves an optimum fluid charge, or at least a fluid charge providing a selected amount of sub-cooling of the working fluid flowing in the system.
Those skilled in the art will further appreciate the above-mentioned advantages and superior features of the invention as well as other important aspects thereof upon reading the detailed description which follows in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a vapor compression air conditioning system including a working fluid charge adding and evacuating unit and a controller in accordance with the invention;

FIG. 2 is a longitudinal central section view of one preferred embodiment of a flow restrictor device in accordance with the invention and for use with the system of the invention;

FIG. 3 is a detail section view taken generally along the line 3-3 of FIG. 2;

FIG. 4 is a flow diagram illustrating at least the major steps in a process for adding or subtracting working fluid with respect to a vapor compression air conditioning or refrigeration system in accordance with the invention; and

FIG. 5 is a schematic diagram of an alternate embodiment of a system in accordance with the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the description which follows like elements are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures are not necessarily to scale and certain features may be shown in generalized or schematic form in the interest of clarity and conciseness.
Referring to FIG. 1, there is illustrated a schematic diagram of a vapor compression-type air conditioning system which may also be configured as a refrigeration system, and generally designated by the numeral 10. The system 10 includes respective heat exchangers 12 and 14 operably interconnected by a compressor 16. For the sake of discussion, the system 10 may be considered to be an air conditioning (cooling) system although it will be understood by those skilled in the art that the invention may be used in connection with a so called heat pump system, both reversible and nonreversible and the invention may also be used in connection with a refrigeration system used for purposes other than conditioning ambient air for human comfort or the like.
The compressor 16 is connected to heat exchanger 14 acting as a condenser by way of a high pressure discharge conduit 18 and condenser 14 is connected to heat exchanger 12, acting as an evaporator unit, by way of a further high pressure conduit 20 and an expansion device 22. Typically, the heat exchanger 12, expansion device 22 and a portion of a conduit 24 interconnecting the compressor 16 with the heat exchanger 12 are located within the interior of a structure being cooled. A system controller 26 is operably connected to certain components including an indoor fan or blower, not shown, and a second portion 28 of the controller is provided for controlling on and off operation of compressor 16 and for controlling flow of air over heat exchanger 14 by way of a motor driven fan 30. A heat exchange medium other than forced air may be used to control heat exchange by one or both of the heat exchangers 12 and 14. When used as an air conditioning or heat pump system, the system 10 also includes a thermostat 32 connected to controller units 26 and 28. Controller unit 26 is also connected to a source of electrical power via conductor means 36 and for communicating such power to controller unit 28.
Conduit 24 is considered a so-called low pressure conduit leading to compressor 16 for delivering working fluid thereto for compression to a higher pressure. Conduit 24 includes a suitable releasable connector 25 a associated therewith disposed in proximity to the compressor 16 and including a one way poppet valve 25 c, or so-called Schrader valve known in the art, for conducting refrigerant fluid to or from the system 10, which fluid may be one of several types known to those skilled in the art and used as the working fluid in vapor compression systems. A second releasable connector 27 a is connected to high pressure conduit or so called liquid line 20, but may be connected to conduit 18, alternatively. Connector 27 a includes a Schrader valve 27 c. Conduit 18 is connected to the so-called high pressure side of compressor 16 for conducting heated vapor to heat exchanger 14 for at least partial condensation therein and then discharge to conduit 20.
Accordingly, working fluid flowing out of the heat exchanger 14 through conduit 20 to expansion device 22 is typically in liquid form and the pressure and temperature of such fluid may be sensed by respective temperature and pressure sensors 40 and 42, as shown in FIG. 1. Sensors 40 and 42 may include direct readout displays or gauges 40 a and 42 a and are operatively connected to a further controller unit or circuit 44 which may be operably connected to the controller unit 28 to receive power therefrom and deliver certain control signals thereto. Controller 44 may be a suitable programmable microcontroller or an application specific integrated circuit previously programmed for operation in accordance with the invention. Controller 44 includes a part 45 including visual indicators 46 and 48 for indicating the status of a refrigerant or working fluid charge in the system 10. A visual display 48 a may also be provided for displaying information to a user. The controller part 45 is also adapted to provide an electric output signal to conductor means 50 which may be releasably connected to the controller part 45 at a plug or connector 52.
Referring further to FIG. 1, a working fluid adding and evacuation or subtracting apparatus is illustrated and generally designated by the numeral 54. The apparatus 54 includes a pressure vessel and reservoir 56 for new working fluid, such as one of the common refrigerant fluids previously mentioned. A conduit 58 is connected to reservoir 56 and to a motor operated or solenoid type valve 60 connected to conductor means 50 and to the controller part 45 via the connector 52. Conduits 62, 64 and 66 are operable to be in communication with the reservoir 56 by way of the valve 60. Suitable manual or remotely controllable valves 63, 65 and 67 may be arranged as illustrated for controlling the flow of working fluid between the new fluid reservoir 56, a fluid recovery reservoir 70 and connector parts 25 b and 27 b which are operable to connect the apparatus 54 to the conduit 24 and the conduit 20, respectively. Connector parts 25 a and 27 a are associated with Schrader valves 25 c and 27 c operably connected to the respective conduits 24 and 20, as illustrated and previously described. When connectors 25 a and 25 b are engaged, valve 25 c is open and when connectors 27 a and 27 b are engaged, valve 27 c is open.
Referring to FIGS. 2 and 3, a flow restrictor 72 is shown in one preferred and exemplary embodiment and is characterized by a housing 74 having suitable ports 76 and 78 opening to opposed housing end faces 77 and 79, respectively. An enlarged, internal, longitudinal passage 80 is provided in housing 74 in communication with ports 76 and 78. Suitable guide bosses 82 are opposed to each other, as illustrated in FIGS. 2 and 3, for journaling a flow restrictor element in the form of a somewhat bullet-shaped movable plug or closure member 84 slidably disposed in passage 80 and operable to engage a seat 86 formed in housing 74 adjacent port 78. Plug or closure member 84 is also operable to engage internal stops 88 opposed to each other and aligned with the guide bosses 82 when the closure member moves in a direction toward the port 76. Housing 74 would normally be fabricated in two or more parts to enable insertion and removal of plug 84. A conical or tapered wall 90 remains spaced from the closure plug 84 when the plug engages the stops 88 to provide a substantially unrestricted flow path from port 78 to port 76. However, when the closure member 84 engages seat 86, flow from port 76 to port 78 is restricted and must flow through a reduced diameter passage 85 formed in the closure member 84, as shown. Alternatively, fixed orifice type flow restrictors or capillary (small diameter) tubes could be used in place of devices 72 for restricting fluid flow.
As previously mentioned, flow restrictor devices 72 may be interposed in conduits 62 and 66, as illustrated or mounted on and connected to conduits 24 and 20. One preferred arrangement for the devices 72 is to be interposed in the conduits 62 and 66, as indicated in FIG. 1, wherein when the conduit 62 is connected to the conduit 24 via connector parts 25 a and 25 b and Schrader valve 25 c, flow of working fluid into conduit 24 is restricted since the closure member 84 will move to the position shown in FIG. 2 forcing working fluid to flow through the restricted passage 85 from port 76 through port 78 into conduit 24. Typically, when adding fluid to system 10 via conduit 62, valves 65 and 67 are closed and valves 60 and 63 are opened, see FIG. 1. However, if device 72 connected to conduit 62 is arranged as shown in FIG. 1, or mounted permanently on system 10 and oriented in the same direction, and it is desired to evacuate fluid from the system by way of conduit 24, for example, substantially unrestricted flow of fluid will occur since the closure member 84 will move to the left, viewing FIG. 2, allowing such unrestricted flow of fluid between ports 78 and port 76.
If it is desired to evacuate working fluid from the system 10 in the event of a fluid overcharge, conduit 66 may be connected to conduit 20 via connector parts 27 a and 27 b and the arrangement of the flow restrictor device 72 interposed in conduit 66 is such as to provide restricted flow of fluid from conduit 20 to conduit 66 so that control of evacuation of working fluid from the system 10 may be more closely maintained than if there was substantially no restriction to flow of fluid from conduit 20 to conduit 66. When evacuating fluid, valve 67 is opened, valve 65 or valves 60 and 63 are closed, and fluid flows from conduit 66 through valve 67 and conduit 69 to recovery reservoir 70. Accordingly, the flow restrictor devices 72 may be arranged as illustrated in FIG. 1 or may be mounted directly on the conduits 20 and 24 in the orientation shown and described for a permanent installation in the system 10. Moreover, the arrangements of the flow restrictor devices 72 may be reversed if desired to provide flow restriction in one direction of flow and substantially unrestricted flow in the opposite direction.
Accordingly, the devices 72, whether mounted permanently on system 10 in communication with the conduits 24 and 20, or mounted on a fluid charge adding and evacuation apparatus, such as the apparatus 54, assist in providing an improved method for adjusting the charge of working fluid in a vapor compression system, such as the system 10 or an equivalent. Thanks to the provision of the programmable controller unit 44, including part 45, a process may be carried out for adding a charge of working fluid to the system 10 or evacuating a portion of the charge of working fluid from the system 10 to provide the desired degree of sub-cooling of the fluid as it exits a heat exchanger, such as the condenser 14. By monitoring the temperature and pressure of the fluid flowing through the conduit 20, for example, restricted flow of fluid into or out of the system allows for adjusting a steady state operating condition and the desired degree of sub-cooling of the fluid.
In accordance with a preferred process of the present invention, the controller unit 44, 45 is operable to monitor the addition or subtraction of working fluid with respect to the system 10 by causing the controller to enter the so-called charging mode at step 100, see FIG. 4. At step 102 the controller 44, 45 and system 10 are caused to become ready to check the charge condition by querying whether or not the system has been running more than a preset period of time, such as “y” minutes indicated at step 104. If the system 10 has been running less than a preset period of time and the variance of sub-cooling of the fluid, as measured by the sensors 40 and 42, is less than a “z” predetermined amount for “x” predetermined period of time, as measured at step 106, or if the run time at step 104 is greater than the preset period of time, the process proceeds to step 108. If steps 104 and 106 are both “false”, the process repeats itself as indicated by step 110 and a signal may be provided to the user indicating time to complete the process.
At step 108, controller unit 44, 45 reads the fluid pressure and temperature and calculates the actual fluid sub-cooling or a pressure representation thereof. The process proceeds to step 112 to determine if the actual sub-cooling of the working fluid is greater than or less than a so-called target sub-cooling condition and a charge error is calculated at step 114. If the charge error indicates excessive sub-cooling at step 116, a suitable indicator is illuminated, such as one of the indicators 46 or 48, or a message is provided at visual display 48 a, indicating the need to reduce the charge of working fluid in the system 10, as indicated at step 118. Such may be carried out by pumping fluid or allowing the bleeding of fluid through device 72 connected to conduit 66 for recovery into the reservoir 70. Thanks to the restriction of fluid flow through the device 72 connected to conduit 66 the rate of change of sub-cooling can be closely monitored. In fact, as the process continues to monitor removal of fluid until the total charge is correct at step 120 and the process repeats itself, the controller 44 may generate a suitable control signal or a visual or audible signal.
However, if it is determined at step 116 that recovery or evacuation of working fluid from system 10 is not required but addition of fluid is required, such as indicated at step 122, controller unit 44 may energize valve 60, FIG. 1, for example, causing same to open and to allow fluid to flow from pressure vessel or reservoir 56 through conduit 62 and device 72 at a restricted flow rate to add working fluid to system 10 via valve 25 c and conduit 24 until the total fluid charge is correct, as measured by the amount of sub-cooling at sensors 40 and 42 and monitored by controller 44, 45. Steps 124 and 126 reflect this process.
If no addition of working fluid is required at step 122, a suitable indicator is illuminated, such as indicator 46, or a message is displayed at display 48 a at step 128 advising the operator or user to cease adding fluid to or removing fluid from the system 10, as indicated at step 130. The process is then completed as indicated at step 132. Operation of the valves 63, 65 and 67 to allow flow of fluid between reservoirs 56 and 70 and the system 10, as required by the process described above, is believed to be within the purview of one skilled in the art.
Referring briefly to FIG. 5, a system 10 a, illustrated schematically, is substantially like that shown and described with regard to FIG. 1 with the exception that the devices 72 are essentially permanently mounted to the system in communication with the conduits 24 and 20 in the manner illustrated whereby restricted flow of fluid into the system 10 a is provided by the device 72 connected to conduit 24 but substantially unrestricted flow out of the system may be provided when the connector 25 a is connected to a modified charge addition or evacuation apparatus 54 a, for example. In like manner restricted flow of fluid out of the system 10 a may be provided by the so-called permanent connection between a device 72 and conduit 20 for purposes of fluid evacuating at a controlled or restricted rate from the system if an overcharge, and consequent excessive sub-cooling, is occurring.
In the arrangement of FIG. 5, a charge addition and subtraction apparatus 54 a may be connected to either connector 25 a or 27 a and the aforementioned check valves or so-called Schrader valves 25 c and 27 c may be interposed the respective connectors 25 a and 27 a and the devices 72, as shown in FIG. 5. The valves 25 c and 27 c are, of course, held open by the connectors 25 a, 25 b and 27 a, 27 b when such are engaged in a known manner. In all other respects the system 10 a and the charge addition or evacuation apparatus 54 a are substantially like the system 10 and apparatus 54.
Accordingly, in accordance with the systems and process described above, vapor compression air conditioning and refrigeration systems may be properly charged with working fluid to prevent flooding of the compressor, provide a faster method of charging and greater accuracy of obtaining the proper charge of working fluid in a system of the types described. Although preferred embodiments of a system and method have been disclosed in detail herein, those skilled in the art will appreciate that various substitutions and modifications may be made without departing from the scope and spirit of the appended claims.

Claims

1. A method for adjusting the charge of working fluid in a vapor compression air conditioning system including a compressor, a low pressure conduit, a high pressure conduit, a condenser unit operably connected to said high pressure conduit and to a condenser discharge conduit, a pressure sensor and a temperature sensor operably associated with said condenser discharge conduit for measuring a pressure and a temperature of the working fluid, the temperature and the pressure being related to a working fluid sub-cooling, a working fluid flow restrictor device operably associated with at least one of said conduits for at least one of transferring fluid to and from said system, said method comprising:

measuring the temperature and the pressure of the working fluid within the condenser discharge conduit, the temperature and the pressure corresponding to sub-cooling of the working fluid flowing through said system;

comparing said sub-cooling with a target sub-cooling operating condition of said working fluid to determine if a charge of working fluid should be added to said system or recovered from said system; and

carrying out at least one of adding working fluid to said system and recovering working fluid from said system by restricting the flow of working fluid with said flow restrictor device.

2. The method set forth in claim 1 including the step of:

determining system running time prior to measuring said one or more working fluid parameters.

3. The method set forth in claim 1 including the step of:

determining the variance of sub-cooling of said working fluid over a predetermined interval of time.

4. The method set forth in claim 1 including the step of:

providing a signal to an operator of said system of a need to one of recover working fluid from said system and add working fluid to said system.

5. The method set forth in claim 4 including the step of one of:

recovering working fluid and adding working fluid continuously until a predetermined amount of sub-cooling is measured indicating a desired charge of working fluid.

6. The method set forth in claim 3 including the step of:

providing a fluid charge adding apparatus including a reservoir, a conduit connected to said reservoir and a valve interposed in said conduit; and

providing a signal indicating a condition requiring providing working fluid to said system from said apparatus.

7. The method set forth in claim 6 wherein:

said valve is motor operated and said signal is provided to said valve to provide operation thereof to control flow of working fluid to said system.

8. A method of charging a vapor compression air conditioning system, comprising:

measuring a temperature of a working fluid exiting a condenser of the system;

measuring a pressure of the working fluid exiting the condenser;

determining a working fluid sub-cooling value based on the measured temperature and the measured pressure; and

comparing said determined working fluid sub-cooling with a target sub-cooling to determine if a charge of working fluid should be added to said system or recovered from said system.

9. The method of claim 8, further comprising:

adding working fluid to the system in response to a result of the comparing the determined working fluid sub-cooling with the target sub-cooling.

10. The method of claim 9, wherein the working fluid is added into the system through a flow restriction device.

11. The method of claim 8, further comprising:

evacuating working fluid from the system in response to a result of the comparing the determined working fluid sub-cooling with the target sub-cooling.

12. The method of claim 11, wherein the working fluid is evacuated from the system through a flow restriction device.

13. A method of correcting a working fluid charge of an air conditioning system, comprising:

measuring each of a pressure and a temperature of a working fluid as the working fluid exits a condenser of the system;

calculating one of an actual sub-cooling of the working fluid or a pressure representation thereof;

calculating a charge error by comparing either the actual sub-cooling of the working fluid or the pressure representation thereof to a target sub-cooling; and

adjusting an amount of working fluid within the system in response to the calculated charge error.

14. The method of claim 13, further comprising:

removing a portion of the working fluid from the system if the charge error indicates excessive sub-cooling.

15. The method of claim 13, further comprising:

adding working fluid to the system if the charge error indicates insufficient sub-cooling.

16. The method of claim 13, wherein working fluid is passed through a flow restriction device during the adjusting the amount of working fluid within the system.