Constant temperature maintaining refrigeration system using proportional flow throttling valve and controlled bypass loop

• US 4,742,689 A
• Filed: 03/18/1986
• Issued: 05/10/1988
• Est. Priority Date: 03/18/1986
• Status: Expired due to Term

• Current Assignee: Mydax Incorporated
• Original Assignee: Mydax Incorporated
• Inventors: Lowes, Albert R.
• Primary Examiner(s): Tanner, Harry B.
• Application Number:
  US06/840,847
• Time in Patent Office: 784 Days
• Field of Search: 62/197, 62/113, 62/513, 62/222, 62/223, 62/224, 62/225, 62/196.4, 62/205, 62/206
• US Class Current: 62/197
• CPC Class Codes: F25B 40/00 Subcoolers, desuperheaters or superheaters
• CPC Class Codes: F25B 41/20 Disposition of valves, e.g. of on-off valves or flow control valves expansion valves F25B41/31

Abstract

A vapor-compression refrigeration system has a continuously operating compressor, with loading on the compressor varied in accordance with conditions and cooling needs. The system avoids any on/off cycling of the compressor or valves in the system, but instead keeps cooling and bypass valves open to varying and proportional degrees depending upon requirements. The system includes several bypass loops, for bypassing coolant fluid to a proportional degree when a desired temperature is approached in a body to be cooled; and when temperature of return gas to the compressor approaches a limit temperature beyond which the compressor should not operate. In the latter case, cool liquid is injected, while expanding and vaporizing, into the hot gas for cooling, to protect the compressor. The system operates in a very hot environment to effect the maximum cooling possible without exceeding the limits of the compressor, by reducing the refrigerant flow to the evaporator to continue operating at reduced load, reducing more and more of the cooling flow as the desired set point temperature is approached and controlling bypass flow to maintain evaporator pressure or temperature. Proportional flow valves used in the system enjoy long life due to the absence of stressful on/off cycling.

Claims

1. A vapor-compression refrigeration system utilizing a liquid-gas refrigerant in a closed flow loop for maintaining a substantially constant set point temperature in a body of fluid to be cooled and having a continuously-operating compressor, a condenser downstream of the compressor in a main loop for cooling compressed gas refrigerant, and an evaporator in a first branch of the main loop, for transferring heat from the fluid to be cooled to the refrigerant, the system including a first, smoothly variable, analog refrigerant flow controllable throttling valve in the first branch immediately upstream from the evaporator, a second branch of the main loop bypassing said first throttling valve in said first branch and including a second, smoothly variable, analog refrigerant flow controllable throttling valve, and electrical control means, including first temperature sensor means for sensing temperature of the refrigerant immediately downstream of said first throttling valve, second temperature sensor means for sensing temperature of the body of fluid to be cooled and input means for receiving said set point temperatures for the fluid, said electrical control means for scanning the first and second temperature sensor means and the input means for generating a control value for each said throttling valve for modulating the flow rate of refrigerant through each said throttling valve in response to difference between set point temperature and sensed fluid temperature in a manner which enables said compressor to remain in continuous operation.

2. The system set forth in claim 1 comprising a second fluid flow loop leading from the compressor'"'"'s outlet directly through the evaporator and back to the compressor'"'"'s inlet and comprising a second fluid line leading from the main loop just downstream of the compressor, through a hot gas flow valve and back into the first line at a first point downstream of the throttling valve and upstream of the evaporator.

3. The system set forth in claim 2 wherein the hot gas flow valve comprises an automatic expansion valve (AEV).

4. The system of claim 1 wherein said system includes heat exchange means between the second branch downstream of said second throttling valve and the main loop just downstream of the compressor so that heat in the compressed refrigerant is transferred to the refrigerant flowing in the second branch.

5. The system of claim 4 wherein said second branch terminates downstream of said first throttling valve and upstream of said evaporator so that a precisely controllable amount of heat present in said refrigerant passing through said second branch may be transferred to the fluid body at the evaporator.

6. The system of claim 4 wherein said second branch terminates downstream of said evaporator so that refrigerant passing through said second branch is controllably transferable to the inlet of the compressor to limit the difference in pressure thereacross as derived from sensed temperatures of said refrigerant entering and leaving said compressor.

7. The system of claim 1, further comprising third temperature sensor means for determining the temperature of the refrigerant at a point just upstream of the inlet to the compressor, reflecting pressure at the inlet to the compressor and wherein said control means additionally scans said third temperature sensor means in order to determine temperature and derives therefrom the pressure of said refrigerant entering said compressor.

8. The system of claim 1 wherein the control means includes means for maintaining a substantially constant degree of superheat.

9. The system of claim 1 wherein said second branch terminates downstream of said evaporator so that refrigerant passing through said second branch may be transferred to the inlet of the compressor and further comprising third temperature sensor means for determining the temperature of the refrigerant at a point just upstream of the inlet to the compressor, and wherein said control means additionally scans said third temperature sensor means in order to determine temperature of said refrigerant entering said compressor, thereby to control operation of said second throttling valve to limit the temperature of refrigerant entering the compressor.

10. In a vapor-compression refrigeration system utilizing a liquid-gas coolant and having a continuouslyoperating compressor, a condenser, a throttling valve and an evaporator, a control system for maintaining a substantially constant selected temperature in a body of fluid to be cooled and for protecting the compressor of the system against overheating, comprising:

a first coolant fluid flow loop leading from an output of the compressor and ultimately back to an inlet of the compressor and comprising a first fluid line leading from the compressor'"'"'s outlet through the condenser, through the throttling valve, through the evaporator and back to the inlet of the compressor,

a second fluid flow loop leading from the compressor'"'"'s outlet directly through the evaporator and back to the compressor'"'"'s inlet and comprising a second fluid line leading from the first line, just downstream of the compressor, through a hot gas flow valve and back into the first line at a first point downstream of the throttling valve and upstream of the evaporator,

a third fluid flow loop leading from the compressor'"'"'s outlet through the condenser and then directly back to the compressor'"'"'s inlet and including a third fluid line leading from the first line, at a point downstream of the condenser and upstream of the throttling valve, through a compressor-protecting valve and back into the first line at a second point downstream of the evaporator and upstream of the compressor,

all of said valves comprising proportional-flow valves controllable to open to an extent demanded, and

control means including temperature sensors and controllers regulating said throttling valve, said hot gas flow valve and said compressor-protecting valve for causing coolant fluid to flow substantially exclusively through said first loop under normal conditions wherein cooling is required in said body of fluid, for regulating inlet pressure to the compressor within preselected limits, for causing at least some of the coolant gas from the compressor to flow through said second loop when warming is required in said body of fluid, and to cause at least some of the coolant fluid in said first line to bypass through said third loop when the temperature of fluid entering the compressor becomes so high as to endanger the compressor,

whereby the system operates to maintain said body of fluid substantially at the selected temperature in both hot and cold ambient temperatures through said first and second loops, unless the ambient temperature becomes too high for the compressor'"'"'s range of operation, in which condition fluid is bypassed through said third loop to protect the compressor and cooling of said body of fluid is limited.

11. A proportional-flow refrigeration system utilizing liquid-gas coolant fluid and having a continuously-operating compressor, a condenser, a smoothly variable, proportional-flow throttling valve and an evaporator, for maintaining a body of load fluid at a substantially constant selected temperature, comprising,

a first coolant fluid flow loop leading from an output of the compressor and ultimately back to an inlet of the compressor and comprising a first fluid line leading from the compressor'"'"'s outlet through the condenser, through the throttling valve, through the evaporator and back to the inlet of the compressor,

at least one flow controllable bypass flow loop for bypassing coolant from said frist fluid line from a point downstream of the condenser and upstream of the throttling valve, back to said first fluid line just upstream of the compressor'"'"'s inlet, bypassing the throttling valve and the evaporator,

sensor means including first temperature sensor means for determining temperature in the body of fluid to be cooled, and second temperature sensor means for determining temperature of the coolant fluid in the first line just upstream of the the compressor'"'"'s inlet,

control means in association with the sensor means, for normally opening the throttling valve when cooling is needed in said body of fluid and to an extent reflecting the difference between the actual temperature and the desired temperature of the body of fluid, for limiting the extent of opening at the throttle valve in accordance with a preselected limit for inlet pressure to the compressor in accordance with sensed temperature differential of the refrigerant entering and leaving the compressor, for controlling bypass of coolant fluid through said bypass flow loop when the temperature in the body of fluid approaches the desired temperature, proportionally in accordance with proximity to the desired temperature, and for controlling bypass of coolant fluid through said bypass flow loop when the second temperature sensor means determines that the temperature of coolant fluid entering the compressor approaches a preselected limit temperature, proportionally in accordance with proximity to said preselected limit temperature,

whereby flow of gas is constant through the continuously-operating compressor, the compressor is protected against overheating, compressor inlet pressure is maintained within design limits, and transition between modes is smooth, protecting the system against shock.

12. A vapor-compression thermal load temperature control system utilizing a liquid-gas refrigerant in a closed flow loop for maintaining a substantially constant set point temperature in a thermal load to be cooled and having a continuously-operating compressor in the closed flow loop wherein the compressor transfers internally generated heat to refrigerant passing therethrough to operate below a maximum operating temperature, a condenser connected to a discharge segment downstream of the compressor in the closed flow loop for cooling compressed gas refrigerant discharged from the compressor, and an evaporator in a first branch of the closed flow loop for transferring heat from the thermal load to the refrigerant and returning warmed refrigerant to a suction inlet segment of the closed flow loop leading to a suction inlet of the continuously-operating compressor,

the system including a first smoothly variable analog refrigerant flow controllable throttling valve in the first branch immediately upstream from the evaporator and first temperature sensor means immediately downstream from the first throttling valve for sensing temperature of the refrigerant at the evaporator,

the system including a second branch of the closed flow loop extending from a midsegment of the closed flow loop downstream of the condenser and leading to the first branch immediately upstream of the evaporator, the second branch having a second smoothly variable analog refrigerant flow controllable throttling valve, a second temperature sensor means immediately downstream of the second throttling valve for sensing temperature of refrigerant leaving said second valve and a heat exchanger downstream of the second sensor means for transferring heat from compressed refrigerant flowing in the discharge segment to a controllable amount of vaporized refrigerant flowing in the second branch so that heat from the compressor may be transferred via the second branch to the thermal load via the evaporator,

the system including a third branch of the closed flow loop extending from the midsegment and leading to the suction inlet segment, the third branch having a third smoothly variable analog refrigerant flow controllable throttling valve for providing a controllable amount of cooling to the suction inlet segment so that the compressor may be operated continuously below its upper thermal limit, and further including third temperature sensor means in the suction inlet segment for sensing temperature of refrigerant gas entering the compressor, and fourth temperature sensor means for sensing temperature of the thermal load,

the system further including electrical control means for receiving a set point for the fluid as an electrical value from an external source including and converting sensed temperature into an electrical value, for receiving a set point for the fluid as an electrical value from an external source, for scanning said first, second and third temperature sensor means and for generating controls for modulating the flow rate of refrigerant through the first, second and third throttling valves by generating electrical control signals applied thereto so that said system may operate over a wide thermal range and approach thermal equalibrium between sensed thermal load temperature and set point temperature while enabling said compressor to operate continuously at an operating temperature below its maximum operating temperature.