Flash tank pressure control for transcritical system with ejector(s)

Patent metadata

Field	Value
Publication number	US-10208985-B2
Application number	US-201615395645-A
Country	US
Kind code	B2
Filing date	Dec 30, 2016
Priority date	Dec 30, 2016
Publication date	Feb 19, 2019
Grant date	Feb 19, 2019

Abstract

In certain embodiments, a transcritical refrigeration system provides refrigeration by circulating carbon dioxide (CO2) refrigerant through the system. A flash tank of the transcritical refrigeration system is operable to supply the CO2 refrigerant, in liquid form, to a low temperature refrigeration case and a medium temperature refrigeration case. A low temperature compressor is operable to compress the CO2 refrigerant discharged from the low temperature refrigeration case. A medium temperature compressor, a parallel compressor, and an ejector are each operable to compress the CO2 refrigerant discharged from the medium temperature refrigeration case, the CO2 refrigerant discharged from the low temperature compressor, and/or CO2 flash gas discharged from the flash tank. A gas cooler is operable to cool the CO2 refrigerant discharged from the medium temperature compressor and the parallel compressor. A controller is operable to dynamically adjust a pressure set point for the flash tank.

First claim

The invention claimed is:

1. A transcritical refrigeration system operable to circulate carbon dioxide (CO 2 ) refrigerant through the transcritical refrigeration system in order to provide refrigeration, the transcritical refrigeration system comprising:
a flash tank operable to supply the CO 2 refrigerant, in liquid form, to a low temperature refrigeration case and a medium temperature refrigeration case;
a low temperature compressor operable to compress the CO 2 refrigerant discharged from the low temperature refrigeration case;
a medium temperature compressor operable to compress at least one of the CO 2 refrigerant discharged from the medium temperature refrigeration case and the CO 2 refrigerant discharged from the low temperature compressor;
a parallel compressor operable to compress CO 2 flash gas discharged from the flash tank;
an ejector operable to compress at least one of the CO 2 refrigerant discharged from the medium temperature refrigeration case and the CO 2 refrigerant discharged from the low temperature compressor;
a gas cooler operable to cool the CO 2 refrigerant discharged from the medium temperature compressor and the parallel compressor; and
a controller operable to dynamically adjust a pressure set point for the flash tank, wherein the controller dynamically adjusts the pressure set point for the flash tank based on a temperature at an outlet of the gas cooler;
wherein in response to determining that the temperature at the outlet of the gas cooler has increased such that it exceeds a temperature threshold, the controller adjusts the pressure set point for the flash tank in order to increase Δp, wherein Δp is the difference between the pressure of the flash tank and suction pressure of the medium temperature compressor.

2. The transcritical refrigeration system of claim 1 , wherein in response to determining that the temperature at the outlet of the gas cooler is less than or equal to 30° C., the controller adjusts the pressure set point for the flash tank such that Δp is less than or equal to 8 bar, wherein Δp is the difference between the pressure of the flash tank and suction pressure of the medium temperature compressor.

3. The transcritical refrigeration system of claim 1 , wherein in response to determining that the temperature at the outlet of the gas cooler is greater than or equal to 32° C., the controller adjusts the pressure set point for the flash tank such that Δp is greater than or equal to 8 bar, wherein Δp is the difference between the pressure of the flash tank and suction pressure of the medium temperature compressor.

4. The transcritical refrigeration system of claim 1 , the controller further operable to:
determine one or more compression set points operable to cause a measured pressure of the flash tank to move toward the pressure set point for the flash tank; and
instruct each of the medium temperature compressor, the parallel compressor, and/or the ejector to operate according to its respective compression set point.

5. A controller for a refrigeration system, the controller comprising one or more processors and logic encoded in non-transitory computer readable memory, the logic, when executed by one or more processors, operable to:
dynamically adjust a pressure set point for a flash tank based on a temperature value, the temperature value determined from at least one of an ambient air temperature and a gas cooler outlet temperature;
determine that the temperature value has increased such that it exceeds a temperature threshold; and
adjust the pressure set point for the flash tank in order to increase Δp, wherein Δp is the difference between the pressure of the flash tank and suction pressure of a compressor of the refrigeration system.

6. The controller of claim 5 , wherein the logic is operable to
determine one or more compression set points operable to cause a measured pressure of the flash tank to move toward the pressure set point for the flash tank; and
instruct the compressor to operate according to the compression set point.

7. The controller of claim 5 , wherein the refrigeration system that the controller is operable to control comprises a transcritical refrigeration system that circulates carbon dioxide (CO 2 ) refrigerant.

8. The controller of claim 7 , wherein the refrigeration system that the controller is operable to control comprises:
the flash tank operable to supply the CO 2 refrigerant, in liquid form, to a low temperature refrigeration case and a medium temperature refrigeration case;
a low temperature compressor operable to compress the CO 2 refrigerant discharged from the low temperature refrigeration case;
a medium temperature compressor, a parallel compressor, and an ejector each operable to compress the CO 2 refrigerant discharged from the medium temperature refrigeration case, the CO 2 refrigerant discharged from the low temperature compressor, and/or CO 2 flash gas discharged from the flash tank; and
a gas cooler operable to cool the CO 2 refrigerant discharged from the medium temperature compressor and the parallel compressor;
wherein the controller determines the temperature value based on information from a sensor that measures temperature at the outlet of the gas cooler.

9. The controller of claim 8 , wherein:
in response to determining that the temperature at the outlet of the gas cooler is less than or equal to 28° C., the controller adjusts the pressure set point for the flash tank such that Δp is less than 8 bar, wherein Δp is the difference between the pressure of the flash tank and suction pressure of the medium temperature compressor; and
in response to determining that the temperature at the outlet of the gas cooler is greater than or equal to 34° C., the controller adjusts the pressure set point for the flash tank such that the Δp is greater than 8 bar.

10. A method of operating a refrigeration system, the method comprising:
determining a temperature associated with an outlet of a gas cooler that is operable to cool refrigerant received from one or more compressors and discharge the refrigerant to a flash tank via one or more ejectors;
performing a comparison that compares the temperature associated with the outlet of the gas cooler to a temperature threshold;
adjusting a pressure set point for the flash tank based on the comparison; and
instructing one or more components of the refrigeration system to operate according to a configuration that causes a measured pressure of the flash tank to move toward the pressure set point for the flash tank.

11. The method of claim 10 , wherein in response to determining that the temperature associated with the outlet of the gas cooler has increased such that it exceeds the temperature threshold, adjusting the pressure set point for the flash tank in order to increase Δp, wherein Δp is the difference between the pressure of the flash tank and suction pressure of one of the compressors.

12. The method of claim 10 , wherein the method operates a transcritical refrigeration system that circulates CO 2 refrigerant and, in response to determining that the temperature associated with the outlet of the gas cooler is less than or equal to 30° C., adjusting the pressure set point for the flash tank such that Δp is less than or equal to 8 bar, wherein Δp is the difference between the pressure of the flash tank and suction pressure of one of the compressors.

13. The method of claim 10 , wherein the method operates a transcritical refrigeration system that circulates CO 2 refrigerant and, in response to determining that the temperature associated with the outlet of the gas cooler is greater than or equal to

Assignees

• Heatcraft Refrigeration Products Llc

Inventors

• Najafifard Fardis

Classifications

• F25B5/02

  arranged in parallel · CPC title

• F25B9/008 Primary

  the refrigerant being carbon dioxide · CPC title

• F25B2309/061

  with cycle highest pressure above the supercritical pressure · CPC title

• F25B2700/2102

  at the outlet of the gas cooler · CPC title

• F25B2400/075

  with parallel compressors · CPC title