BACKGROUND

The present disclosure relates generally to refrigeration systems and more particularly to systems and methods for controlling refrigerant flow, oil flow, and defrosting operations in refrigeration systems.

It is desirable in refrigeration systems to ensure that any refrigerant entering a compressor of the refrigeration system is in a gas or vapor state because feeding liquid refrigerant into the compressor can damage the compressor. Conventional refrigeration systems use temperature sensors and pressure sensors at the outlet of the evaporator to calculate the degree of superheat of the refrigerant to ensure that the refrigerant has fully evaporated and no liquid remains. An expansion device of the refrigeration system can then be operated to reach a target level of superheat. However, high amounts of superheat indicate that the refrigerant is being heated more than necessary to avoid damage to the compressor, which can lower the efficiency of the refrigeration system.

Some refrigeration systems include vapor quality sensors or void fraction sensors to determine the thermodynamic vapor quality of the refrigerant and operate the expansion valve based on the vapor quality. However, vapor quality sensors are typically incapable of measuring degrees of superheat and will provide misleading measurements when the refrigerant has any amount of superheat. Additionally, it can be difficult to use the feedback from vapor quality sensors to operate the expansion valve when the refrigeration system includes a long run of pipes through the evaporator because the feedback from the vapor quality sensor may not reflect instantaneous conditions at the location of the expansion device. It would be desirable to provide a refrigeration system capable of controlling the expansion device to prevent compressor damage while ensuring efficient operation of the refrigeration system and overcoming the challenges associated with vapor quality sensors.

SUMMARY

One implementation of the present disclosure is a refrigeration system including an evaporator configured to receive a flow of refrigerant and transfer heat into the refrigerant within the evaporator to provide cooling for a temperature-controlled space, an expansion valve operable to modulate the flow of refrigerant into the evaporator, a liquid level sensor configured to measure a level of liquid accumulated within a component of the refrigeration system, and a controller configured to operate the expansion valve to increase the flow of refrigerant into the evaporator or decrease the flow of refrigerant into the evaporator based on the level of liquid measured by the liquid level sensor.

In some embodiments, the refrigeration system includes an oil level sensor configured to measure a level of oil accumulated within the component of the refrigeration system. The level of liquid may be a total level of oil and liquid refrigerant accumulated within the component of the refrigeration system. The controller may be configured to determine a level of liquid refrigerant accumulated within the component of the refrigeration system by subtracting the level of oil from the total level of oil and liquid refrigerant and operate the expansion valve to increase the flow of refrigerant into the evaporator or decrease the flow of refrigerant into the evaporator based on the level of liquid refrigerant.

In some embodiments, the refrigeration system includes a liquid collection header coupled to the evaporator. The liquid collection header may be the component of the refrigeration system within which the liquid is accumulated and the level of liquid is measured.

In some embodiments, the refrigeration system includes a liquid/vapor separator fluidly coupled to a refrigerant outlet of the evaporator and configured to receive a flow of the refrigerant exiting the evaporator. The liquid/vapor separator may be the component of the refrigeration system within which the liquid is accumulated and the level of liquid is measured.

In some embodiments, the controller is configured to compare the level of liquid accumulated within the component of the refrigeration system to a threshold value, modulate the expansion valve toward a fully open position to increase the flow of refrigerant into the evaporator in response to the level of liquid accumulated within the component of the refrigeration system being less than the threshold value, and modulate the expansion valve toward a fully closed position to decrease the flow of refrigerant into the evaporator in response to the level of liquid accumulated within the component of the refrigeration system being greater than the threshold value.

In some embodiments, the refrigeration system includes one or more sensors configured to measure at least one of a temperature or a pressure of the refrigerant at a location within the refrigeration system. The controller may be configured to determine an amount of superheat of the refrigerant at the location within the refrigeration system using one or more measurements from the one or more sensors and operate the expansion valve to increase the flow of refrigerant into the evaporator or decrease the flow of refrigerant into the evaporator based on both the level of liquid measured by the liquid level sensor and the amount of superheat of the refrigerant at the location within the refrigeration system.

In some embodiments, the controller is configured to compare the amount of superheat to a threshold value, modulate the expansion valve toward a fully open position to increase the flow of refrigerant into the evaporator in response to the amount of superheat being greater than the threshold value, and modulate the expansion valve toward a fully closed position to decrease the flow of refrigerant into the evaporator in response to the amount of superheat being less than the threshold value.

Another implementation of the present disclosure is a refrigeration system including a compressor configured to circulate a refrigerant within the refrigeration system, an evaporator configured to transfer heat into the refrigerant within the evaporator to provide cooling for a temperature-controlled space, and a liquid/vapor separator configured to separate the refrigerant into vapor refrigerant and liquid refrigerant. The liquid/vapor separator includes an inlet fluidly coupled to an outlet of the evaporator and configured to receive the refrigerant from the evaporator, a vapor refrigerant outlet fluidly coupled to the compressor and configured to discharge the vapor refrigerant to the compressor, and a liquid refrigerant outlet fluidly coupled to the evaporator and configured to return the liquid refrigerant to the evaporator.

In some embodiments, the compressor is configured to compress the refrigerant to create a high pressure source within the refrigeration system. The refrigeration system may further include a pressurization line fluidly coupling the high pressure source to the liquid/vapor separator and a pressure regulating valve located along the pressurization line and operable to fluidly connect the liquid/vapor separator to the high pressure source and disconnect the liquid/vapor separator from the high pressure source.

In some embodiments, connecting the liquid/vapor separator to the high pressure source causes the liquid refrigerant within the liquid/vapor separator to exit the liquid/vapor separator via the liquid refrigerant outlet and return to the evaporator.

In some embodiments, the refrigeration system includes one or more transfer valves fluidly coupled to the vapor refrigerant outlet of the liquid/vapor separator and adjustable between an open position in which the vapor refrigerant is permitted to exit the liquid/vapor separator via the vapor refrigerant outlet and a closed position in which the vapor refrigerant is prevented from exiting the liquid/vapor separator through the vapor refrigerant outlet.

In some embodiments, the refrigeration system includes a controller configured to perform a liquid refrigerant return process including closing the one or more transfer valves to prevent the vapor refrigerant from exiting the liquid/vapor separator through the vapor refrigerant outlet, connecting the liquid/vapor separator to a high pressure source to pressurize the vapor refrigerant and liquid refrigerant within the liquid/vapor separator, and opening a liquid refrigerant return valve fluidly coupled to the liquid refrigerant outlet of the liquid/vapor separator, causing the liquid refrigerant within the liquid/vapor separator to exit the liquid/vapor separator via the liquid refrigerant outlet and return to the evaporator.

In some embodiments, the refrigerant received from the evaporator includes oil; the liquid/vapor separator is configured to separate the refrigerant into the vapor refrigerant, the liquid refrigerant, and the oil; and the liquid/vapor separator comprises an oil outlet fluidly coupled to the compressor and configured to return the oil to the compressor.

In some embodiments, the refrigeration system includes an oil return valve fluidly coupled to the oil outlet of the liquid/vapor separator and adjustable between an open position in which the oil is permitted to exit the liquid/vapor separator via the oil outlet and a closed position in which the oil is prevented from exiting the liquid/vapor separator through the oil outlet.

In some embodiments, the refrigeration system includes a controller configured to perform an oil return process including closing one or more transfer valves to prevent the vapor refrigerant from exiting the liquid/vapor separator through the vapor refrigerant outlet; connecting the liquid/vapor separator to a high pressure source to pressurize the vapor refrigerant, the liquid refrigerant, and the oil within the liquid/vapor separator; and opening the oil return valve, causing the oil within the liquid/vapor separator to exit the liquid/vapor separator via the oil outlet and return to the compressor.

In some embodiments, the refrigeration system includes a liquid level sensor configured to measure a level of liquid accumulated within the liquid/vapor separator and a controller configured to initiate a liquid refrigerant return process in response to at least one of the level of liquid accumulated within the liquid/vapor separator exceeding a threshold value or a calculated value based on the level of liquid accumulated within the liquid/vapor separator exceeding a threshold value.

In some embodiments, the refrigeration system includes an oil level sensor configured to measure a level of oil accumulated within the liquid/vapor separator. The level of liquid may be a total level of oil and liquid refrigerant accumulated within the liquid/vapor separator. The controller may be configured to determine a level of liquid refrigerant accumulated within the liquid/vapor separator by subtracting the level of oil from the total level of oil and liquid refrigerant and initiate a liquid refrigerant return process in response to the level of liquid refrigerant accumulated within the liquid/vapor separator exceeding the threshold value.

Another implementation of the present disclosure is a method for returning liquid refrigerant from a liquid/vapor separator to an evaporator of a refrigeration system. The method includes closing one or more transfer valves to prevent vapor refrigerant within the liquid/vapor separator from exiting the liquid/vapor separator through a vapor refrigerant outlet of the liquid/vapor separator, connecting the liquid/vapor separator to a high pressure source to pressurize the vapor refrigerant and the liquid refrigerant within the liquid/vapor separator, and opening a liquid refrigerant return valve fluidly coupled to a liquid refrigerant outlet of the liquid/vapor separator, causing the liquid refrigerant within the liquid/vapor separator to exit the liquid/vapor separator via the liquid refrigerant outlet and return to the evaporator.

In some embodiments, the method includes opening an oil return valve fluidly coupled to an oil outlet of the liquid/vapor separator, causing oil within the liquid/vapor separator to exit the liquid/vapor separator via the oil outlet and return to a compressor of the refrigeration system.

In some embodiments, the method includes determining a level of the liquid refrigerant accumulated within the liquid/vapor separator. In some embodiments, closing the one or more transfer valves, connecting the liquid/vapor separator to the high pressure source, and opening the liquid refrigerant return valve in response to a determination that the level of liquid refrigerant accumulated within the liquid/vapor separator violates a threshold condition.

