WO2013151644A1

WO2013151644A1 - Vapor compression system with pressure-actuated control valve

Info

Publication number: WO2013151644A1
Application number: PCT/US2013/028842
Authority: WO
Inventors: Michael A. Stark
Original assignee: Carrier Corporation
Priority date: 2012-04-03
Filing date: 2013-03-04
Publication date: 2013-10-10

Abstract

A vapor compression system (20) has a high side (522) and a low side (520). A first flowpath (512) from the high side to the low side extends through a pressure-actuated valve (70). A second flowpath (514) from the high side to the low side passes through a control valve (122) and a restriction (124). An actuator (94) of the pressure-actuated valve is exposed to a pressure at a location (130) in the second flowpath between the control valve and the restriction.

Description

VAPOR COMPRESSION SYSTEM WITH PRESSURE- ACTUATED CONTROL VALVE

CROSS-REFERENCE TO RELATED APPLICATION

[0001] Benefit is claimed of US Patent Application Ser. No. 61/619,644, filed April 3, 2012, and entitled "Vapor Compression System with Pressure- Actuated Control Valve", the disclosure of which is incorporated by reference herein in its entirety as if set forth at length.

BACKGROUND

[0002] The disclosure relates to vapor compression systems. More particularly, the disclosure relates to controllable expansion devices for vapor compression systems and chiller systems, particularly.

[0003] An exemplary controllable expansion device in a chiller comprises an

electromechanically-actuated or pneumatically-actuated valve. An exemplary

electromechanically-actuated valve includes an actuator at least partially outside the refrigerant environment and penetrating into the refrigerant environment. This presents issues of sealing. Alternatively, there may be hermetic devices wherein the actuator is entirely within the refrigerant. Such hermetic devices eliminate the sealing of a moving mechanical member but entail additional mechanical and operational issues. SUMMARY

[0004] One aspect of the disclosure involves a vapor compression system having a high side and a low side. A first flowpath from the high side to the low side extends through a

pressure-actuated valve. A second flowpath from the high side to the low side passes through a control valve and an restriction. An actuator of the pressure-actuated valve is exposed to a pressure at a location in the second flowpath between the control valve and the restriction.

[0005] In various implementations, a compressor may be coupled to the high side and the low side to compress a refrigerant from the low side and deliver compressed refrigerant to the high side. The system may be a chiller system. The restriction may be a fixed orifice device. The actuator may comprise an actuator piston having a first face exposed to the pressure in the location in the second flowpath. The piston may have a second face, opposite the first face, essentially exposed to a discharge chamber of the pressure-actuated valve. The pressure-actuated valve may include a valve element having a first surface exposed to an inlet chamber of the pressure-actuated valve and a second surface exposed to the discharge chamber. The pressure-actuated valve may further include a bias spring, biasing the valve element from a relatively closed condition toward a relatively open condition.

[0006] Other aspects of the disclosure involve methods for operating or controlling such systems. In an exemplary method, the control valve is opened from a relatively closed condition to a relatively open condition. The opening of the control valve increases pressure at the location and causes at least partial closing of the pressure-actuated valve.

[0007] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a partially schematic view of a chiller system.

[0009] FIG. 2 is a view of a control valve subsystem of the system of FIG. 1 in a fully closed condition.

[0010] FIG. 3 is a view of a control valve subsystem of the system of FIG. 1 in a fully open condition.

[0011] FIG. 4 is a control flowchart.

[0012] Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0013] FIG. 1 shows a vapor and compression system 20 having a compressor 22 with an inlet/suction port 24 on a low pressure side (low side) 520 of the system and an outlet/discharge port 26 on a high pressure side (high side) 522. A discharge line 28 extends along a refrigerant flowpath 510 from the discharge port 26 to an inlet 30 of a first heat exchanger 32. The exemplary system 20 is a chiller system wherein the first heat exchanger 32 is, in a normal chiller mode of operation (e.g., distinguished from a heat pump mode with reversed refrigerant flow), a heat rejection heat exchanger. The exemplary exchanger 32 comprises a vessel 34 with a primary refrigerant outlet 36, a secondary refrigerant outlet 38, a heat transfer fluid inlet 40 and a heat transfer fluid outlet 42. Inside the vessel 34, heat transfer fluid passing through a coil, tubes, or other conduits is in heat transfer relation with refrigerant passing from the inlet 30. In the exemplary system the heat transfer fluid is passing along a water loop 44. A primary refrigerant line 50 along a primary branch 512 of the refrigerant flowpath passes from the primary outlet 36 to the refrigerant inlet 52 of a second heat exchanger 54. The branch 512 forms a primary flowpath (segment) from the high side to the low side. The exemplary second heat exchanger 54 includes a vessel 56 and a refrigerant outlet 58. It further includes a heat transfer fluid inlet 60 and a heat transfer fluid outlet 62. In the exemplary chiller system, the heat exchanger 54 is, in the normal chiller mode of operation, a heat rejection heat exchanger or evaporator. The exemplary heat transfer fluid is water which passes along a water loop 66. Within the vessel 54 the water loop passes through a coil or tubes and is in heat transfer relation with refrigerant passing from the inlet 52 to the outlet 58. In the normal chiller operational mode, the vessel 34 is thus a "high side" vessel at a high side pressure; whereas, the vessel 56 is a "low side" vessel at a low side pressure.

[0014] A pressure-actuated valve 70 is positioned along the primary flowpath branch 512 between the heat exchangers 32 and 54. In the exemplary implementation, the valve 70 is along the refrigerant line 50. The valve 70 has a housing or body 72. The valve 70 and its housing 72 define a primary inlet port 74 and a primary outlet port 76 along the refrigerant line 50. The inlet

74 is an inlet to an inlet chamber 80 and the outlet 76 is an outlet from an outlet chamber 82. A port 84 separates the inlet chamber 80 from the outlet chamber 82. The 84 is circumscribed by a valve seat 86. A valve moving element 88 has a head 90 for selectively blocking and unblocking the port. The valve element 88 also includes an actuator piston 94. The actuator piston 94 is mounted for reciprocal movement in an actuator compartment 96 of the valve 70. The piston 94 includes a first surface 98 exposed to the headspace 100 of compartment 96 and a second opposite surface 102 exposed, via a port 104, to the discharge chamber 88. They valve 70 has an additional port 110 exposed to the headspace 100. In the exemplary valve, motion of the piston expanding the chamber 100 drives the head 90 toward the closed/blocking condition/position.

[0015] A secondary flowpath branch 514 from the heat exchanger 32 to the heat exchanger 54 at least partially bypasses the primary flowpath branch 512 to form a secondary flowpath from the high side to the low side. More particular, the secondary flowpath bypasses the valve inlet 74. The exemplary secondary flowpath passes along a conduit 120 from the secondary outlet 38. The exemplary secondary flowpath and conduit 120 merge with the primary flowpath and conduit 50 downstream of the valve outlet 76.

[0016] A control valve (pilot valve) 122 is positioned along the secondary flowpath and conduit 120. An exemplary control valve 122 may be a multi-step control valve or electronic expansion valve (EEV). An exemplary multi-step control valve is an electrically actuated valve with stepper motor. An exemplary EEV may be a relatively inexpensive off-the-shelf EEV used to expand/control refrigerant flows much smaller than the typical flow through the primary flowpath, less than 1% of the primary flow (e.g., less than 20% or less than 5%, or an exemplary less than 1.0%).

[0017] Downstream of the valve 122 is a restriction 124. An exemplary restriction is a fixed orifice. An exemplary fixed orifice provides a restriction to less than 20% of the area of the secondary flow path (e.g., 2-15% or an exemplary about 10%). The port 110 is exposed to a pressure in the secondary flowpath and conduit 120 at a location 130 (e.g., via a branch conduit 132). The exemplary control valve may be controlled by a controller 140.

[0018] In the exemplary implementation, the port 36 is positioned relatively low on the high side vessel so as to intake liquid refrigerant from the high side vessel. By contrast, the port 38 is relatively higher so as to (in normal operation) intake gas/vapor refrigerant. Alternative implementations might, however, feed the valve 122 with liquid (e.g., via bypassing the inlet of the line 120 off the line 50). In such a situation, the port 38 may be replaced by a port 38' along the line 50 or directly on the vessel at similar height to the port 36. Such alternatives may reduce parasitic losses.

[0019] FIG. 2 shows the valve 70 in a fully closed condition. FIG. 3 shows the valve 70 in a fully open condition. The valve head 90 has a first surface 150 generally exposed to the inlet chamber 80 and a second surface 152 generally exposed to the discharge chamber 82. The valve 74 further includes a spring 160 biasing the valve element from the fully closed/blocking condition toward the fully open/unblocking condition.

[0020] In operation, a pressure increase at the location 130 will cause a pressure increase in the headspace 100 driving the actuator piston distally and thereby driving the valve element in a closing direction toward the fully closed condition against bias of the spring 160. Similarly, a pressure decrease at the location 130 will cause a pressure decrease in the headspace 100 allowing the spring bias to drive/shift the valve element in an opening direction toward the fully open condition. An increase in pressure at the location 130 may be achieved by opening the valve 122. Similarly, a decrease in pressure at location 130 may be achieved by closing the valve 122. Such increases and decreases and the associated opening and closing may be incremental. The presence of the restriction 124 allows the location 130 to be at a pressure above a pressure at the valve outlet 76 and heat exchanger inlet 52 (the low side pressure).

[0021] Use of the valve 122 to pilot the valve 70 may provide one or more of several advantages relative to a baseline system. An exemplary baseline system involves a valve of similar capacity to the valve 70 but controlled via electromechanical actuator (e.g., an electric motor) or pneumatic actuator. Such a baseline may be large and expensive and

power-consuming. It also may involve a penetration of the actuator linkage between external atmosphere and the refrigerant flowpath. Such penetration requires the expense of seals which also require maintenance issues. Depending upon the particular type of control valve 122 chosen, the sealing of a mechanical linkage may be eliminated. For example, some actuators may be small enough to readily be hermetically contained within the associated refrigerant flowpath. Otherwise, the amount of sealing required may still be reduced in accordance with the small size of valve 122 relative to the baseline expansion valve. Manufacturing costs may be reduced by the smaller actuator and actuation power costs may similarly be reduced.

[0022] System control may be responsive to a detected/sensed refrigerant level in the system. An exemplary refrigerant level is a level of liquid 300 (shown having a surface 302) interfacing with gas in a headspace 304 of the high side vessel 34. The exemplary level is sensed via a sensor. An exemplary sensor 200 is an optical level sensor (OLS) which is connected to or otherwise in communication with the controller 140. There may be single or multiple such sensors which may output level in various forms (e.g., a continuous output of actual level versus binary outputs indicating one or more thresholds being met or not). [0023] FIG. 4 shows an exemplary control algorithm/process 400 executed by the controller. Such algorithm/process may be superimposed on or otherwise added to the existing control algorithm of a baseline system. The chiller start command is received 402 or otherwise processed. In the exemplary system, the valve 70 will be at a default position of open as a result of spring 160. By definition this will cause a low condition to insure a smooth starting operation until such time as the chiller has stabilized. An exemplary refrigerant level measurement 403 may be from reading the OLS 200. If refrigerant level is determined 404 high, then the valve 122 is opened 406 by an amount based on a proportional integral differential (PID) control solution and the system goes to a delay increment 412 and then repeats the determination 403. The amount of closure is determined by the percentage of high level error counts over a discrete time period as assessed by the PID controller. The opening of the valve 122 has the effect of closing the valve 70. The PID control loop is tuned such to maintain stability of the liquid level 302.

[0024] If level (determined at 404) is not high, then it is determined 408 whether the level is low. If yes, then the valve 122 is closed 410 (to open valve 70) and, after the delay 412, the cycle repeats. The amount of opening is accomplished in reverse of opening such that the percentage of low level error counts as assessed by the PID controller. If the level is not low, then the cycle also repeats after the delay 412.

[0025] Although an embodiment is described above in detail, such description is not intended for limiting the scope of the present disclosure. In the will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, when implemented in the reengineering or remanufacturing of a baseline configuration or system, details of the baseline may influence details of any particular implementation.

Accordingly, other embodiments are within the scope of the following claims.

Claims

CLAIMS What is claimed is:

1. A vapor compression system (20) comprising:

a high side (522);

a low side (520);

a first flowpath (512) from the high side to the low side extending through a

pressure-actuated valve; and

a second flowpath (514) from the high side to the low side passing through a control valve (122) and restriction (124) , an actuator of the pressure-actuated valve being exposed to a pressure at a location (130) in the second flowpath between the control valve and the restriction.

2. The system of claim 1 further comprising:

a compressor (22) coupled to the high side and the low side to compress a refrigerant from the low side and deliver compressed refrigerant to the high side.

3. The system of claim 1 being a chiller system.

4. The system of claim 1 wherein:

the restriction is a fixed orifice device.

5. The system of claim 1 wherein:

the actuator comprises an actuator piston (94) having a first face (98) exposed to said pressure in said location in the second flowpath.

6. The system of claim 5 wherein:

the piston has a second face (102), opposite the first face, essentially exposed to a discharge chamber (82) of the pressure-actuated valve.

7. The system of claim 6 wherein:

the pressure-actuated valve includes a valve element having a first surface (150) exposed to an inlet chamber of the pressure-actuated valve and a second surface (152) exposed to the discharge chamber.

8. The system of claim 7 wherein the pressure-actuated valve further comprises:

a bias spring (160) biasing the valve element from a relatively closed condition toward a relatively open condition.

9. The system of claim 1 wherein:

the first flowpath extends from a first outlet (36) of a vessel on the high side; and the second flowpath extends from a second outlet (38) of the vessel at a level above the first outlet.

10. The system of claim 1 wherein:

the first flowpath extends from a first outlet (36) of a vessel on the high side; and the second flowpath extends from a location (38') along the first flowpath downstream of the first outlet.

11. A method for operating the system of claim 1 , the method comprising:

opening the control valve from a relatively closed condition to a relatively open condition, the opening of the control valve increasing pressure at the location and causing at least partial closing of the pressure-actuated valve.

12. The method of claim 11 comprising:

determining a liquid refrigerant level, said opening being responsive to an excess said determined liquid refrigerant level.

13. The method of claim 12 wherein:

the liquid refrigerant level is repeatedly determined and, responsive to an insufficient said determined liquid refrigerant level, the position control valve is at least incrementally closed.

14. The method of claim 12 wherein:

the liquid refrigerant level is a level in a vessel (34) on the high side.

15. The method of claim 11 wherein: a refrigerant intake of the first flowpath is essentially liquid; and a refrigerant intake of the second flowpath is essentially vapor.