Apparatus for monitoring solenoid expansion valve flow rates

• US 5,035,119 A
• Filed: 06/30/1986
• Issued: 07/30/1991
• Est. Priority Date: 08/08/1984
• Status: Expired due to Term

• Current Assignee: Richard H. Alsenz
• Original Assignee: Richard H. Alsenz
• Inventors: Alsenz, Richard H.
• Primary Examiner(s): Tanner, Harry B.
• Application Number:
  US06/880,677
• Time in Patent Office: 1,856 Days
• Field of Search: 62/200, 62/199, 62/226, 62/227, 62/228.5, 62/228.4, 62/204, 62/210, 62/211, 62/212, 62/222, 62/223, 62/224, 62/225, 62/175, 62/129, 236/1 B, 236/1 EA, 364/557, 364/556, 364/551
• US Class Current: 62/225
• CPC Class Codes: F25B 2400/075 with parallel compressors
• CPC Class Codes: F25B 2500/15 Hunting, i.e. oscillation of controlled refrigeration variables reaching undesirable values
• CPC Class Codes: F25B 2600/21 Refrigerant outlet evaporator temperature
• CPC Class Codes: F25B 2600/2513 Expansion valves
• CPC Class Codes: F25B 2700/21173 at the outlet
• CPC Class Codes: F25B 2700/21174 of the refrigerant at the inlet of the evaporator
• CPC Class Codes: F25B 2700/21175 of the refrigerant at the outlet of the evaporator
• CPC Class Codes: F25B 41/347 with the valve member being opened and closed cyclically, e.g. with pulse width modulation
• CPC Class Codes: F25B 49/02 for compression type machines, plants or systems
• CPC Class Codes: G05D 23/1913 delivering a series of pulses
• CPC Class Codes: G05D 23/20 with sensing elements having variation of electric or magnetic properties with change of temperature G05D23/13 takes precedence
• CPC Class Codes: Y02B 30/70 Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating

Abstract

A microprocessor controlled system for use in a refrigeration system which includes a plurality of pulse controlled solenoid flow control valves suitable for use as expansion valves is disclosed. A pulse width modulated control signal is generated for cyclically opening and closing the flow through the solenoid expansion valve. The duty cycle of the pulsed control signal determines the average flow rate through the valve. The microprocessor responds to the flow rate through each of the solenoid valves to determine, on a system-wide basis, if each fixture in the system, as indicated by the flow rate through the expansion valve associated therewith, is operating properly.

Claims

1. A refrigeration system having in a closed loop connection:

(a) a compressor means having an inlet and an outlet end;

(b) a condenser means connected to the outlet end of said compressor and responsive to a high pressure gaseous phase recirculating refrigerant for condensing the refrigerant from its gaseous to its liquid phase;

(c) a plurality of evaporator means, each having an inlet and an outlet end and connected to said condenser means and to inlet end of said compressor;

(d) each said evaporator means having an associated solenoid expansion valve having an inlet and an outlet end connected between the outlet end of said condenser and the inlet end of said associated evaporator, said condenser delivering high pressure liquid refrigerant to the inlet end of said expansion valves, said refrigerant expanding as it flows through said expansion valves;

(e) each said solenoid expansion valve including an associated on-off modulator responsive to the superheat of said refrigerant in said associated evaporator for generating a variable duty cycle on-off modulated solenoid control signal said solenoid control signal, alternately energizing and deenergizing said associated solenoid each cycle of said solenoid control signal to slowly cycle said valve from a first flow rate position to a second flow rate position without imparting any substantial pressure shock waves to the refrigerant thereby to obtain an average flow rate of refrigerant through the valve which results in a desired superheat for the refrigerant, said valve further including an indicating means for generating a flow rate signal, said flow rate signal being a function of the duty cycle of the on-off modulated solenoid signal and indicative of the average opening size of the valve for passage of liquid refrigerant therethrough; and

(f) a central controller means responsive to each said flow rate signal for monitoring on a system wide basis operating conditions of each said evaporator means.

2. The system of claim 1 wherein said indicating means further includes means for indicating to said central controller means the operating temperature of the area cooled by its said associated evaporator coil, the operating superheat temperatures of said associated evaporator coil and the operating temperatures at the inlet and outlet ends of said associated expansion valve.

3. The system of claim 1 wherein said central controller means comprises a microprocessor means.

4. The system of claim 3 wherein said microprocessor means includes means for determining the average flow rate of all of said expansion valves in said system, comparing each said flow rate signal to said average, and indicating a deviation therefrom.

5. The system of claim 1 wherein said first flow rate position results in a fully open maximum flow rate therethrough, and said second flow rate position results in a fully closed zero flow rate therethrough, said average flow rate being determined by the duty cycle of said solenoid control signal.

6. The system of claim 1 wherein said valve further includes a closure rate control means controlling the rate of change in flow rate positions of said valve between said first and said second flow rate positions, and vice versa, thereby to minimize any pressure shock waves in said refrigerant on opening or closing of said valve.

7. The system of claim 5 wherein said valve further includes a closure rate control means for controlling the rate of change in flow rate positions of said valve between said fully open and said fully closed positions, and vice versa, thereby to minimize any pressure shock waves in said liquid refrigerant on opening or closing of said valve.

8. The system of claims 6 or 7 wherein said closure rate control means is an electronic circuit which controls the slope of the pulse edges in the on-off solenoid control signal.

9. The system of claim 3 wherein each said on-off modulator further includes a low ambient start-up means responsive to the presence of liquid refrigerant at the inlet end of said associated expansion valve for overriding normal operations of said valve and maintaining said expansion valve open for refrigerant flow therethrough when liquid refrigerant is not present, said low ambient start-up means returning control for normal operations of said valve when liquid refrigerant is present.

10. The system of claim 9 wherein said low ambient start-up means comprises:

(a) a first temperature sensor coupled proximal to the inlet end of said associated expansion valve, said first sensor generating a voltage representative of the temperature of the liquid refrigerant from said condenser;

(b) a second temperature sensor coupled proximal to the outlet end of said associated expansion valve, said second means generating a voltage representative of the temperature of the expanding liquid refrigerant into the inlet end of said associated evaporator;

(c) a comparator circuit responsive to the voltages from said first and second temperature sensors for generating a low ambient start signal when the temperature differential between said first and second sensors is less than a temperature threshold; and

(d) a clamping means responsive to the low ambient start signal for overriding normal control for said associated expansion valve and maintaining said expansion valve open for refrigerant flow therethrough until the temperature differential between said first and second sensors is greater than the temperature threshold indicating expansion of liquid refrigerant through said valve.

11. The system of claim 3 wherein each said on-off modulator further includes a flood detector means responsive to the outlet-to-inlet temperature differential across said associated evaporator coil for throttling down the flow rate through said associated expansion valve when the temperature differential is less than a temperature threshold, said flood detector means generating a throttling control signal representative of a lower heat load condition on said associated evaporator coil to said associated valve as long as the temperature differential is less than said temperature threshold, said associated valve resuming normal operation from the throttled-down condition when said temperature differential is greater than said temperature threshold.

12. The system of claim 11 wherein said flood detector means comprises:

(a) a first temperature sensor responsive to the temperature of the refrigerant at the inlet end of said associated evaporator;

(b) a second temperature sensor responsive to the temperature of the refrigerant at the outlet end of said associated evaporator; and

(c) a first comparator means responsive to said first and second temperature sensors for generating a flood condition signal when the temperature differential between said first and second sensors is less than said temperature threshold, said flood condition control signal representing a reduced heat load demand condition on said associated evaporator and which is applied to said associated valve to effect throttling down of the flow of liquid refrigerant therethrough, said first comparator means returning normal control to said expansion valve when said temperature differential between said first and second sensors is greater than said temperature threshold.

13. The system of claim 12 wherein each said on-off modulator further includes a second comparator means responsive to the absolute temperature of said liquid refrigerant at said inlet end of said associated evaporator and to a maximum operating refrigerant temperature signal for outputting a maximum operating temperature control signal to throttle down the flow of refrigerant through said associated expansion valve when the temperature of said liquid refrigerant at the inlet end of said associated evaporator coil is greater than the maximum operating refrigerant temperature, said second comparator means returning normal control to said associated expansion valve when said evaporator inlet temperature is less than the maximum refrigerant temperature.

14. The system of claim 1 wherein each said on-off modulator further includes a low refrigerant detection means responsive to the percent on time of said associated valve for generating a low refrigerant alarm signal when the percent on time of the associated valve exceeds a threshold value for a period of time.

15. The system of claim 14 wherein said low refrigerant detection means comprises:

(a) a comparator responsive to the input signal to said on-off modulator, such input signal representative of the duty cycle of the solenoid control signal and to a duty cycle threshold signal;

(b) a reset timer coupled to the output from said comparator for generating an output when the duty cycle of the solenoid control signal is above the threshold value for a period of time determined by said timer; and

(c) an alarm circuit responsive to the output from reset timer to indicate a low refrigerant condition in said system.

16. A refrigeration system having in a closed loop connection:

(a) a compressor means having an inlet and an outlet end;

(b) a condenser means connected to the outlet end of said compressor means and a responsive to a high pressure gaseous phase recirculating refrigerant for condensing the refrigerant from its gaseous to its liquid phase;

(c) an evaporator means, each having an inlet and an outlet end and connected to said condenser means and to the inlet end of said compressor means;

(d) said evaporator means having an expansion valve, said expansion valve having an inlet and an outlet end connected between the outlet end of said condenser means and the inlet end of said evaporator, said condenser delivering high pressure liquid refrigerant to the inlet end of said expansion valve, said refrigerant expanding as it flows through said expansion valve;

(e) said expansion valve including an on-off modulator responsive to the superheat of said refrigerant in said evaporator for generating an on-off modulated solenoid control signal alternately energizing and deenergizing said solenoid during each cycle of said solenoid control signal, said energizing and deenergizing of the solenoid slowly opening and closing said valve from an open to a close position without imparting any substantial pressure shock waves to the refrigerant thereby to obtain an average flow rate of refrigerant through the valve which results in a desired superheat for the refrigerant, said valve further including an indicating means for generating a flow rate signal which is a function of the duty cycle of the on-off modulated solenoid signal and indicative of the average opening size of the valve for passage of liquid refrigerant therethrough; and

(f) a controller means responsive to said flow rate signal for monitoring operating conditions of said evaporator means.

17. The system of claim 16 wherein said controller means comprises a microprocessor means.

18. A refrigeration system having in a closed loop connection:

(a) a compressor means having an inlet and an outlet end;

(b) a condenser means connected to the outlet end of said compressor and responsive to a high pressure gaseous phase recirculating refrigerant for condensing the refrigerant from its gaseous to its liquid phase;

(c) an evaporator means having an inlet and an outlet end and connected to said condenser means and to the inlet end of said compressor;

(d) said evaporator means having a solenoid expansion valve, said expansion valve having an inlet and an outlet end connected between the outlet end of said condenser and the inlet end of said evaporator, said condenser delivering high pressure liquid refrigerant to the inlet end of said expansion valve, said refrigerant expanding as it flows through said expansion valve;

(e) said expansion valve including an on-off modulator responsive to the superheat of said refrigerant in said evaporator for generating an on-off modulated solenoid control signal having a variable duty cycle, said solenoid control signal alternately energizing and deenergizing said solenoid during each cycle of said solenoid control signal, said energizing and deenergizing of the solenoid slowly opening and closing said valve from an open to a close position without imparting any substantial pressure shock waves to the refrigerant thereby to obtain an average flow rate of refrigerant through the valve which results in a desired superheat for the refrigerant, said valve further including an indicating means for generating a flow rate signal which is a function of the duty cycle of the on-off modulated solenoid signal and indicative of the average opening size of the valve for passage of liquid refrigerant therethrough.

19. The system of claim 18 wherein said open position results in a fully open maximum flow rate therethrough, and said close position results in a fully closed zero flow rate therethrough, said average flow rate being determined by the duty cycle of said solenoid control signal.

20. The system of claim 18 wherein said valve further includes a closure rate control means controlling the rate of change in flow rate positions of said valve between said open and close positions, and vice versa, thereby to minimize any pressure shock waves in said refrigerant on opening or closing of said valve.

21. The system of claim 19 wherein said valve further includes a closure rate control means for controlling the rate of change in flow rate positions of said valve between said fully open and said fully closed positions, and vice versa, thereby to minimize any pressure shock waves in said liquid refrigerant on opening or closing of said valve.

22. The system of claim 20 wherein said closure rate control means is an electronic circuit which controls the slope of the pulse edges in the on-off solenoid control signal.

23. The system of claim 21 wherein said closure rate control means is an electronic circuit which controls the slope of the pulse edges in the on-off solenoid control signal.