CO2 WARM LIQUID DEFROST WITH HEATING SECTION CONTROL

Description

TECHNICAL FIELD

This disclosure relates generally to refrigeration systems. More particularly, in certain embodiments, this disclosure relates to carbon dioxide (CO2) warm liquid defrost with heating section control.

BACKGROUND

Refrigeration systems are used to regulate environmental conditions within an enclosed space. Refrigeration systems are used for a variety of applications, such as in supermarkets and warehouses, to cool stored items. For example, refrigeration systems may provide cooling operations for refrigerators and freezers.

SUMMARY OF THE DISCLOSURE

During the operation of refrigeration systems, ice may build up on evaporators. These evaporators then need to be defrosted to remove the ice buildup and prevent a loss of performance. Current defrost processes are limited in terms of their efficiency and effectiveness. For example, they may take a relatively long time and consume a relatively large amount of energy. Users of refrigeration systems often want the defrost process to take less than thirty minutes. However, this is not always possible without adding additional components directly to the evaporators. Adding additional components is not a desirable solution as it uses more energy, may potentially reduce the life of the evaporator and/or other components, may increase costs, and may cause an unacceptable change in the temperature of the environment being cooled by the evaporators.

This disclosure provides technical solutions to the problems of previous technology, including those described above. In one or more embodiments, a refrigeration system is provided that includes a heater enclosed in a heat box for heating refrigerant that is used for defrosting an evaporator. The refrigeration system may include additional components, for example, a flash tank. The refrigeration system facilitates improved evaporator defrost using refrigerant from the flash tank, which is maintained at a higher temperature using a heat box containing a heater. The amount of heat added to the refrigerant from the flash tank may be controlled in such a way as to adjust the defrost time based on current conditions, system design, an operator’s needs, regulatory requirements, and other criteria. The refrigeration system may also include a controller, a first evaporator, a second evaporator, one or more compressors, a flash tank, a heat box, and at least four valves.

In one or more embodiments, when the controller determines that the first evaporator should be operated in a defrost mode, it operates valves to allow defrost refrigerant to pass from the flash tank through the heat box to the first evaporator. The defrost time may then be controlled by changing the amount of heat provided by the heat box to the liquid defrost refrigerant being passed to the first evaporator. The defrost refrigerant is caused to flow to the first evaporator, causing it to defrost, and the refrigerant is then passed to the second evaporator and the compressors. When the second evaporator needs to defrost, the valves are reversed, causing the defrost refrigerant to flow to the second evaporator and then to the first evaporator and the compressors.

In an embodiment, a refrigeration system includes a heat box configured to pass liquid refrigerant to a first evaporator. The heat box includes a heater and a coil that the liquid refrigerant passes through before being passed to the first evaporator. The first evaporator is configured to receive the liquid refrigerant from the heat box and, when in defrost mode, use the heat from the liquid refrigerant that the heat box has warmed to defrost the first evaporator. When operated in a refrigeration mode, the first evaporator transfers heat from a space to the liquid refrigerant. The first evaporator is positioned downstream from the heat box and at a separate location from the heat box.

In one or more embodiments, the refrigeration system also includes a controller communicatively coupled to the heat box and the first evaporator. The controller is configured to determine if a first condition is met. The first condition is associated with a first measurable aspect of the first evaporator, and the first condition is met when the first measurable aspect indicates that the first evaporator needs defrosting. When the first condition is met, the controller causes the first evaporator to operate in the defrost mode by providing electrical power to the heater in order to produce a predetermined amount of additional heat in a liquid refrigerant to produce a heated liquid refrigerant, that is used to defrost the first evaporator.

The refrigeration system includes at least one additional evaporator in one or more embodiments. The evaporator includes a first valve, a second valve, a third valve, and a fourth valve. The first valve is positioned between the heat box and the first evaporator and configured to pass, when open, defrost refrigerant to the first low-temperature evaporator. The second valve is positioned between the first low-temperature evaporator and one or more compressors and configured to pass, when open, output refrigerant from the first low-temperature evaporator to the one or more compressors. The third valve is positioned between the heat box and the second low-temperature evaporator and configured to pass, when open, defrost refrigerant to the second low-temperature evaporator. The fourth valve is positioned between the second low-temperature evaporator and the one or more compressors configured to pass when open, output refrigerant from the second low-temperature evaporator to the one or more compressors. The controller is communicatively coupled to the first, second, third, and fourth valves. When the controller determines that the first condition is met, the controller opens the first valve to allow defrost refrigerant to pass to the first evaporator, closes the second valve to prohibit output refrigerant from the first evaporator from passing to the one or more compressors, closes the third valve to prohibit defrost refrigerant passing to the second low-temperature evaporator, and opens the fourth valve to allow output refrigerant from the second low-temperature evaporator to flow to the one or more compressors. This causes defrost refrigerant from the first low-temperature evaporator to flow to the second evaporator.

The controller is further configured to determine if a second condition is met. The second condition is associated with a second measurable aspect of the second evaporator, and the second condition is met when the second measurable aspect indicates that the second evaporator needs defrosting. When the second condition is met, the controller causes the second evaporator to operate in a defrost mode. The controller causes the first valve to prohibit defrost refrigerant from passing to the first low-temperature evaporator, opens the second valve to allow output refrigerant from the first evaporator to pass to the one or more compressors, opens the third valve to allow defrost refrigerant to pass to the second evaporator, and closes the fourth valve to prohibit output refrigerant from the second evaporator from flowing to the one or more compressors. This causes defrost refrigerant from the second low-temperature evaporator to flow to the first evaporator.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, reference is now made to the following description, taken in conjunction with the accompanying drawings in which:

FIG. 1 is a diagram of an example refrigeration system of this disclosure configured to operate the first evaporator in a defrost mode;

FIG. 2 is a diagram of the example refrigeration system of FIG. 1 configured to operate the second evaporator in a defrost mode;

FIG. 3 is a diagram of an example of the heat box used in the refrigeration system of FIGS. 1 and 2; and

FIG. 4 is a flowchart of an example method of operating the refrigeration system of FIGS. 1 and 2 to provide improved evaporator defrost.

DETAILED DESCRIPTION

Embodiments of the present disclosure and its advantages are best understood by referring to FIGS. 1-4 of the drawings, like numerals being used for like and corresponding parts of the various drawings.

As described above, conventional refrigeration system defrost operations suffer from certain inefficiencies and drawbacks. This disclosure's refrigeration system improves defrost performance and energy efficiency. In one or more embodiments, the refrigeration system of this disclosure uses warm refrigerant received from compressors and other components such as, but not limited to, a flash tank to defrost one or more evaporators. This warm refrigerant, however, does not always have sufficient heat to efficiently or timely defrost one or more evaporators, which are typically used in a refrigeration mode to cool a space or environment by extracting heat from the surrounding space. The disclosure utilizes a heat box that includes a heater to heat the warm refrigerant in a controlled manner to provide additional heat to the warm refrigerant. By controlling the amount of heat provided by the heat box, one or more evaporators may be defrosted more efficiently and timely within a user or organization’s desired time period, such as but not limited to thirty minutes, without the need for additional electrical heat being applied directly to the coils or other components of the one or more evaporators.

In one or more embodiments, the refrigeration system of this disclosure may be a CO₂ refrigeration system. CO₂ refrigeration systems may differ from conventional refrigeration systems in that these systems circulate refrigerant that may become a supercritical fluid (i.e., where distinct liquid and gas phases are not present) above the critical point. For example, the critical point for carbon dioxide (CO₂) is 31°C and 73.8 MPa, and above this point, CO₂ becomes a homogenous mixture of vapor and liquid called a supercritical fluid. This unique characteristic of transcritical refrigerants is associated with certain operational differences between transcritical and conventional refrigeration systems. For example, transcritical refrigerants are typically associated with discharge temperatures that are higher than their critical temperatures and discharge pressures that are higher than their critical pressures. When a transcritical refrigerant is at or above its critical temperature and/or pressure, the refrigerant may become a “supercritical fluid” — a homogenous mixture of gas and liquid. Supercritical fluid does not undergo a phase change process (vapor to liquid) in a gas cooler as occurs in a condenser of a conventional refrigeration system circulating traditional refrigerant. Rather, supercritical fluid cools down to a lower temperature in the gas cooler. Stated differently, the gas cooler in a CO₂ transcritical refrigeration system may receive and cool supercritical fluid, and the transcritical refrigerant undergoes a partial state change from gas to liquid as it is discharged from an expansion valve.

While in one or more embodiments, the refrigeration system of this disclosure is described as a CO₂ refrigerant system, the disclosure is not limited to a CO₂ refrigeration system. The refrigeration system may use other fluids with similar properties to CO₂. Alternatively, the refrigeration system of this disclosure may use any refrigerant or system that, combined with compressors and a plurality of valves, allows for defrosting one or more evaporators. In one or more embodiments, the refrigeration system does not need or use electrical heat directly applied to the evaporators.

Refrigeration System

FIGS. 1 and 2 illustrate examples of refrigeration systems 100 and 200 configured for improved defrost operation. The refrigeration systems 100 and 200 include a first low temperature (LT) evaporator 106 and a second low temperature (LT) evaporator 108, along with one or more compressors, e.g., 102 and 104, a flash tank 114, and a heat box 116. The refrigeration system 100, shown in FIG. 1, is configured to operate a first LT evaporator 106 in a defrost mode, while a second LT evaporator 108 is operated in a refrigeration mode. Similarly, the refrigeration system 200, shown in FIG. 2, is configured to operate the first LT evaporator 106 in a refrigeration mode while the second LT evaporator 108 is operated in a defrost mode. At least the first through fourth valves 130, 132, 134, and 136 are controlled by a controller 150. The systems 100 and 200 of FIGS. 1 and 2 may include more or fewer components than shown in FIGS. 1 and 2, and the disclosure is not limited to the number and specific components shown in FIGS. 1 and 2. For example, in a non-limiting example, the system may only include one or more compressors 104, the heat box 116, a first evaporator 106, conduit 178-182, and a controller 150 without departing from the disclosure.

Refrigeration system 100 may include a plurality of compressors, e.g., 102 and 104. The one or more compressors, e.g., 102 and 104, may include one or more low-temperature (LT) compressors 104 and one or more optional medium-temperature (MT) compressors 102. In one or more embodiments, the MT compressor(s) 102 and LT compressor(s) 104 may be different types of compressors or maybe the same type of compressor. The optional MT compressor(s) 102 are configured to compress refrigerant discharged from the LT compressor(s) 104 as well as vapor discharged from the flash tank 114 and optional MT evaporator(s) 110. LT compressors 104 are configured to compress refrigerant discharged from one or more evaporators, e.g., 106.

Refrigeration system 100 may include any suitable number of MT compressors 102 and LT compressors 104. The MT compressor(s) 102 and LT compressor(s) 104 may vary by design and/or by capacity. For example, some compressor designs may be more energy efficient than others, and some MT compressors 102 and LT compressors 104 may have modular capacity (e.g., a capability to vary capacity). The controller 150 communicates with the MT compressors 102 and LT compressors 104 and controls their operation.

The one or more LT compressors 104 receive refrigerant from the evaporators 106 and 108 after the refrigerant has been used to provide refrigeration through at least one evaporator, e.g., 108, and/or for defrosting at least one evaporator, e.g., 106. The LT compressor(s) 104 compresses the refrigerant and then provides the refrigerant through conduit 178 to the MT compressor(s) 102 for further compression. In one or more embodiments, the MT compressor(s) 102 provides supplemental compression to the refrigerant discharged from the LT compressor(s) 104. The MT compressor(s) 102 may also receive the vapor from the flash tank 114 through conduit 174. The received refrigerant, which is warmer than that received by the LT compressor(s) 104, is then compressed by the MT compressor(s) 102 and provided to an optional gas cooler 112 through conduit 170.

The optional gas cooler 112 is configured to receive compressed refrigerant from the MT compressor(s) 102 and/or LT compressor(s) 104 through conduit 170. The gas cooler 112 is generally operable to apply cooling to the received compressed refrigerant. In some embodiments, gas cooler 112 is a heat exchanger comprising cooler tubes configured to circulate the received refrigerant and coils through which ambient air is forced. Inside gas cooler 112, the coils may absorb heat from the refrigerant, thereby cooling the refrigerant. The cooled compressed refrigerant is passed through conduit 172 to a flash tank 114.

Flash tank 114 is configured to receive mixed-state refrigerant and separate the received refrigerant into flash gas or vapor and warm liquid refrigerant. Flash tank 114 may include one or more tanks operable to hold refrigerant at least temporarily. Typically, the flash gas collects near the top of flash tank 114, and the liquid refrigerant is collected at the bottom of flash tank 114. A valve 118 may be disposed at or near an inlet of the flash tank 114 to reduce the pressure of refrigerant received by the flash tank 114.

In one or more embodiments, the flash gas or vapor from the flash tank 114 is sent through an outlet through conduit 174 to the MT compressor(s) 102. In one or more embodiments, conduit 174 may include an optional valve 120 to reduce the pressure of the vapor directed from the flash tank 114 to the MT compressor(s) 102. Similarly, the warm liquid condensed from the flash tank 114 is directed to the heat box 116 and an optional MT evaporator 110. The warm liquid directed toward the MT evaporator 110 may pass through valve 122, which may be actuated to reduce the pressure of the refrigerant received by the MT evaporator 110.

The optional MT evaporator 110 receives liquid refrigerant, which has not passed through the heat box 116 from the flash tank 114, and uses the liquid refrigerant to provide cooling. For example, the MT evaporator 110 may be part of a refrigerated case and/or cooler for storing items that must be kept at particular temperatures. The refrigeration system 100 may include any appropriate number of MT evaporators 110 with the same or a similar configuration to that shown for the example MT evaporator 110 shown in FIGS. 1 and 2. The MT evaporator 110 may include an expansion valve 122 configured to receive the liquid refrigerant from flash tank 114 and reduce the pressure of the received refrigerant. In some embodiments, this reduction in pressure causes some of the refrigerant to vaporize. Expansion valve 122 may be configured to achieve a refrigerant temperature into the evaporator 110 at a predefined temperature for a given application (e.g., about -6 °C). Refrigerant from the MT evaporator 110 operating in refrigeration mode is provided to the one or more MT compressors 102 through conduit 176.

The various conduits 170-192 may form a refrigerant conduit subsystem that facilitates the movement of refrigerant (e.g., CO₂) through a refrigeration cycle and defrost cycles, such that the refrigerant flows in the refrigeration mode, as illustrated by the arrows in FIGS. 1 and 2. The subsystem includes conduit, tubing, piping, and the like that facilitate refrigerant movement between components of the refrigeration system 100. The conduit 170-192 may be a copper conduit or other types of appropriate conduit, tubing, or piping. Different sections of the conduit, e.g., 170, may be made of different materials or take different forms.

When in refrigeration mode, the warm liquid refrigerant from the flash tank 114 flows to and cools the evaporators 110, 106, and 108. Similarly, the warm liquid refrigerant may be used to defrost at least one evaporator, e.g., 106. Pressure valves 122, 124, and 126 may be operated to moderate the pressure of the warm liquid refrigerant to ensure proper operation of the evaporators 106-110.

A heat box 116 is provided between the flash tank 114 and at least the low temperature (LT) evaporators 106 and 108 in one or more embodiments. The heat box 116 is at a separate location from the first evaporator 106 and/or second evaporator 108 and does not provide heat directly to the evaporators, e.g., 106. Conduit 180 connects the flash tank 114 to the LT evaporators 106 and 108, as well as the heat box 116. In one or more embodiments, the heat box 116 may be placed before the optional MT evaporator 110 or may be located after the optional MT evaporator 110, as shown in FIGS. 1 and 2. When placed after, as shown in FIGS. 1 and 2, the heat box 116 only provides heat to the warm liquid that forms the defrost refrigerant that is passed through conduit 186 to the LT evaporators 106 and 108 during a defrost cycle.

Heat box 116 is located downstream of the flash tank 114 and configured to receive the warm liquid refrigerant from the flash tank 114 and/or MT compressor(s) 102 and optional gas cooler 112. The heat box 116 may include one or more tubes and/or coils that carry the received warm liquid refrigerant and one or more electrical heaters that may provide additional heat to the warm liquid refrigerant to produce defrost refrigerant when an evaporator, e.g., 106 is undergoing a defrosting operation. The heated defrost refrigerant is then output through conduit 180 to at least the selected evaporator, e.g., 106 undergoing defrosting. FIG. 1 shows the example when the first LT evaporator 106 is operating in the defrost mode, while FIG. 2 shows the flow when the second LT evaporator 108 is operated in the defrost mode. In the examples shown in FIGS. 1 and 2, the opposite LT evaporator, e.g., 106 or 108, is then operated in refrigeration mode.

The LT evaporators 106 and 108 are generally similar to the MT evaporator 110 but are configured to operate at lower temperatures than the MT evaporator 110, such as, for example, near about -30 °C or the like. Both the MT evaporator 110 and the LT evaporators 106 and 108 may be operated at any temperature, and the disclosure is not limited to operating at different temperatures or any particular temperature. The operation temperature is determined by the application as well as, or instead, the preferences of the operator of the refrigeration system 100.

When operated in refrigeration mode, the LT evaporators 106 and 108 both receive cooled liquid refrigerant from the flash tank 114 without additional heat being added by the heat box 116. This cooled liquid refrigerant is used to provide cooling to an environment around each of the LT evaporators 106 and 108. For example, in a non-limiting example, the first LT evaporator 106 may be part of a deep freezer for relatively long-term storage of perishable items that must be kept at particular temperatures.

While the refrigeration system 100 is shown with only two LT evaporators, 106 and 108, the system 100 may include any appropriate number of LT evaporators, e.g., 106, with additional corresponding valves, e.g., 126, 136, and 144. For example, a third LT evaporator (not shown) may be provided in a non-limiting example. When the first LT evaporator, 106, is in a defrost mode, the second and third LT evaporators, e.g., 108, are caused to operate in a refrigeration mode. In another example, the first LT evaporator 106 and the second LT evaporator 108 may be operated in a defrost mode, while the third LT evaporator (not shown) is operated in a refrigeration mode. The first LT evaporator 106, second LT evaporator 108, and third LT evaporator (not shown) may be operated in refrigeration modes or defrost modes as appropriate, and any combination of LT evaporators in defrost modes and refrigeration modes may be used without departing from the disclosure.

The first LT evaporator 106 includes valves 130, 124, 132, 138, and 140 to facilitate the operation of the first LT evaporator 106 in either a defrost mode (see FIG. 1) or a refrigeration mode (see FIG. 2). Similarly, the second LT evaporator 108 includes valves 134, 126, 136, 142, and 144 to facilitate the operation of the second LT evaporator 108 in either a refrigeration mode (see FIG. 1) or a defrost mode (see FIG. 2).

As shown in FIG. 1, when the first LT evaporator 106 is operated in the defrost mode, first valve 130 is opened, and third valve 134 is closed. The closed third valve 134 prohibits defrost refrigerant from reaching the second LT evaporator 108. Alternatively, if both evaporators 106 and 108 are undergoing defrosting, the third valve 134 would also be opened, and the output from both evaporators 106 and 108 may be directed to additional evaporators (not shown) or to the LT compressor(s) 104. Warm liquid refrigerant is received from the heat box 116 and used to defrost the first LT evaporator 106. Once the refrigerant is used by the first LT evaporator 106, the output refrigerant is then passed through the opened second bypass valve 140 into conduits 184 and 192 and then passes through expansion valve 126 to the second LT evaporator 108, where it is used to provide refrigeration to the environment surrounding the second evaporator 108. When the first LT evaporator 106 performs defrosting and the second LT evaporator 108 provides refrigeration, the output refrigerant from the first LT evaporator 106 is used by the second LT evaporator 108 to transfer heat from the surrounding environment to the refrigerant. The resulting refrigerant is then passed through the open fourth valve 136 through conduit 186 to the one or more LT compressor(s) 104.

As shown in FIG. 2, when the second LT evaporator 108 is operated in the defrost mode, the first valve 130 is closed, the second valve 132 is opened, the third valve 134 is opened, and the fourth valve 136 is closed. Closing the first valve 130 prohibits defrosting refrigerant from the heat box 116 from reaching the first LT evaporator 106. Warm liquid defrost refrigerant is received from the heat box 116 and used to defrost the second LT evaporator 108. Once the refrigerant is used by the second LT evaporator 108, it then passes through an opened fourth bypass valve 144 into conduits 188, 192, and 190. Then, it passes through the first open bypass valve 138, through the expansion valve 124, and to the first LT evaporator 106, which provides refrigeration to the space or environment surrounding the first evaporator 106. When providing refrigeration, the output refrigerant from the second LT evaporator 108 is used by the first LT evaporator 106 to extract heat from the space or environment surrounding the first LT evaporator 106 to the refrigerant. The resulting refrigerant is then passed through conduit 182, the open second valve 132, and through conduit 186 to the one or more LT compressor(s) 104.

Expansion valves 124 and 126 may be expansion valves that are the same as or are similar to the expansion valve 122 described above. Expansion valves 124 and 126 may be configured to receive liquid refrigerant from the flash tank 114 or an LT evaporator, e.g., 106 undergoing defrosting, and reduce the pressure of the received refrigerant. In some embodiments, this reduction in pressure causes some of the refrigerant to vaporize. Valves 124 and 126, as well as 122, may be any appropriate motorized or electronically controllable valves, such as motorized ball valves, solenoid valves, and/or the like. The controller 150 is in communication with valves 122-126 and controls their operation.

Similarly, first valve 130, second valve 132, third valve 134, and fourth valve 136 may be any appropriate motorized or electronically controllable valves, such as motorized ball valves, solenoid valves, and/or the like. The controller 150 is in communication with valves 130-136 and controls their operation as is described above and will be described in more detail below with regards to FIG. 4. The controller 150 also controls first bypass valve 138, second bypass valve 140, third bypass valve 142, and fourth bypass valve 144 to direct the refrigerant from the LT evaporator, e.g., 106 undergoing defrosting, to the LT evaporator, e.g., 108 that is in a refrigeration mode. The bypass valves 138-144 may be any appropriate motorized or electronically controllable valves, such as motorized ball valves, solenoid valves, and/or the like. By directing the warm liquid refrigerant from the heat box 116 first to a defrosting LT evaporator, e.g., 106, and then to an LT evaporator e.g., 108 that is being operated in a refrigeration mode, the resulting refrigerant may be efficiently used to both defrost the defrosting LT evaporator, e.g., 106 and the be used for refrigeration in the refrigeration LT evaporator, e.g., 108 increasing the efficiency and better utilizing the heat generated by the various components of the refrigeration system 100 and 200 of FIGS. 1 and 2.

Sensors 128A-128D and 129 may be provided to determine when the evaporators 106-110 need to be defrosted and other information related to their operation. The sensors 128A-128D may take the form of temperature and/or pressure sensors. They may be disposed on, in, or near the corresponding evaporators 106-110 (sensors 128B-128D) or refrigerant conduit 180 connected to the heat box 116 to the first LT evaporator 106 and second LT evaporator 108 (sensor 128A). A sensor 129 may also be provided in the conduit 186 before or at the one or more LT compressor(s) 104. In one or more embodiments, sensor 129 is a pressure sensor that detects the suction pressure of conduit 186.

Measurements and/or information from sensors 128A-128D and 129 may assist in determining when a first condition or a second condition is met, indicating that operation of the evaporator, e.g., 106 associated with the measurement, should be operated in a defrost mode. Additionally, measurements and/or information from the sensors 128A-128D and 129 may indicate that the defrost mode should be ended. For example, a first condition is met, indicating a defrost mode operation may be needed for the first LT evaporator 106 when a first measurement of an aspect of the first LT evaporator 106, such as the temperature and/or pressure measured by sensor 128B, indicates the potential freezing of the first LT evaporator 106. In another example, a second condition is met, indicating a defrost mode operation may be needed for the second LT evaporator 108 when a second measurement of an aspect of the second LT evaporator 108, such as the temperature and/or pressure measured by the sensor 128C, indicates the potential freezing of the second LT evaporator 108. In yet another example, defrost mode operation may be indicated when sensor 129 determines that the suction pressure in conduit 186 is greater than the threshold, indicating that at least one evaporator, e.g., 106, needs to be defrosted.

In one or more embodiments, sensors 128A and/or 129 may determine when the heat of the warm liquid refrigerant from the heat box 116 is sufficient to defrost an LT evaporator, e.g., 106, and/or when adjustments should be made to the amount of heat added to the refrigerant by the heat box 116. While sensors 128A-128D and 129 are provided in one or more embodiments to determine when one or more evaporators 106-110 need to be defrosted, these sensors may not be necessary, and defrost mode operations may be determined entirely by schedules and settings stored in the memory 154, without departing from the disclosure.

The components of the refrigeration system, 100 and 200, may be controlled by the controller 150. The controller 150 may provide instructions 158 for adjusting valves 118-144 to open or close to achieve the configurations described above for refrigeration and defrost mode operation. Instruction 158, implemented by a processor 152 of the controller 150, may determine that the operation of the first LT evaporator 106 or second LT evaporator 108 should be in a defrost mode based on measurements from sensors 128A-128C and/or 129, or the instructions 158 may use information stored in memory 154 such as defrost time 162 and threshold 164 related to a schedule and/or information from the sensors 128A-128D and 129. For example, instruction 158, stored by controller 150, may indicate that defrost mode operation is needed on a specific schedule or based on a certain measured amount of time, such as the amount of time since the first LT evaporator 106 was previously operated in a defrost mode.

The instructions may determine when a first condition is met and/or a second condition is met. The first and second conditions may be associated with measurable aspects of the evaporators, e.g., 106. The measurable aspects may be a measurement of pressure, temperature, or other aspects of an evaporator, e.g., 106, and/or the system, e.g., 100. When the measurable aspects of the evaporator are greater (e.g., when measuring pressure) or less (e.g., when measuring temperature) than a predetermined threshold, 164 stored in the memory 154, the associated first or second condition may be met. In one or more embodiments, the first and second conditions may be met when the amount of time since a selected LT evaporator, e.g., 106, was previously operated in a defrost mode. The first and second conditions and the related aspects may take any form, and the disclosure is not limited to those described herein. The first and second conditions may be related to more than one measurement and/or aspect. Similarly, the thresholds may be any quantity and may be set by a user, operator, manufacturer, or other entity based on the desired operation parameters of the system, e.g., 100. For example, in a non-limiting example, where the threshold is an amount of time, it may be determined by the manufacturer operating the system 100 prior to deployment using sensors 128A-128D and 129 to determine how often an evaporator, e.g., 106 needs to be operated in a defrost mode to maintain high-efficiency operation and minimal ice build-up.

The controller 150 adjusts the operation of components of the refrigeration systems 100 and 200 to operate the LT evaporators 106 and 108 in a refrigeration mode or a defrost mode, as described herein. The controller 150 includes a processor 152, memory 154, and input/output (I/O) interface 156. The processor 152 includes one or more processors operably coupled to the memory 154. The processor 152 is any electronic circuitry including, but not limited to, state machines, one or more central processing unit (CPU) chips, logic units, cores (e.g., a multi-core processor), field-programmable gate array (FPGAs), application-specific integrated circuits (ASICs), or digital signal processors (DSPs) that communicatively couples to memory 154 and controls the operation of the refrigeration system 100.

The processor 152 may be a programmable logic device, a microcontroller, a microprocessor, or any suitable combination of the preceding. The processor 152 is communicatively coupled to and in signal communication with the memory 154. The one or more processors 152 are configured to process data and may be implemented in hardware or software. For example, the processor 152 may be 8-bit, 16-bit, 32-bit, 64-bit, or of any other suitable architecture. The processor 152 may include an arithmetic logic unit (ALU) for performing arithmetic and logic operations; processor registers that supply operands to the ALU and store the results of ALU operations, and a control unit that fetches instructions from memory 154 and executes them by directing the coordinated operations of the ALU, registers, and other components. The processor 152 may include other hardware and software that operates to process information, control the refrigeration system 100, and perform any of the functions described herein (e.g., with respect to FIGS. 1-4). The processor 152 is not limited to a single processing device and may encompass multiple processing devices. Similarly, the controller 150 is not limited to a single controller but may encompass multiple controllers.

The memory 154 includes one or more disks, tape drives, or solid-state drives. It may be used as an over-flow data storage device to store programs when such programs are selected for execution and to store instructions 158 and data read during program execution. The memory 154 may be volatile or non-volatile and may include ROM, RAM, ternary content-addressable memory (TCAM), dynamic random-access memory (DRAM), and static random-access memory (SRAM). The memory 154 is operable (or configured) to store information used by the controller 150 and/or any other logic and/or instructions for performing the function described in this disclosure.

The I/O interface 156 is configured to communicate data and signals with other devices. For example, the I/O interface 156 may be configured to communicate electrical signals with components of the refrigeration system 100, including, but not limited to, the heat box 116, valves 130-136, and bypass valves 138-144. The I/O interface 156 may be configured to communicate with other devices and systems and is not limited to those just described or those present in FIGS. 1-3. The I/O interface 156 may provide and/or receive, for example, compressor speed signals, compressor on/off signals, valve open/close signals, temperature signals, pressure signals, temperature setpoints, environmental conditions, and an operating mode status for the refrigeration system 100 and 200 and send electrical signals to the components of the refrigeration system 100 and 200. The I/O interface 156 may include ports or terminals for establishing signal communications between the controller 150 and other devices. The I/O interface 156 may be configured to enable wired and/or wireless communications.

Although this disclosure describes and depicts refrigeration systems 100 and 200, including specific components, it recognizes that refrigeration systems 100 and 200 may include any suitable components. For example, refrigeration systems 100 and 200 may include one or more additional sensors configured to detect temperature and/or pressure information.

In an example operation of the refrigeration system 100, LT evaporators 106 and 108 initially operate in the refrigeration mode. As illustrated in FIG. 1, the first LT evaporator 106 is placed in a defrost mode by controller 150 when a first condition is met. In this mode, the first valve 130 is opened, the second valve 132 is closed, the third valve 134 is closed, and the fourth valve 136 is opened. Additionally, the first bypass valve 138 is closed, the second bypass valve 140 is opened, the third bypass valve 142 is opened, and the fourth bypass valve 144 is closed. The heat box 116 is provided with electrical power that is determined to produce a predetermined amount of additional heat in the liquid refrigerant. This heated liquid refrigerant then passes through the opened first valve 130 to the first LT evaporator 106, which is then heated to perform defrosting by the warm liquid refrigerant; the refrigerant then passes through the open second bypass valve 140 and the third opened bypass valve 142 to the second LT evaporator 106 which uses the refrigerant for refrigeration. The refrigerant then flows through the open fourth valve 136 to the LT compressor 104 through conduit 186.

At another point, as shown in FIG. 2, during the operation of the refrigeration system 200, the controller 150 determines that the second LT evaporator 108 should operate in a defrost mode when a second condition is met. The first LT evaporator 106 is placed in refrigeration mode, and the second LT evaporator 108 is placed in defrost mode by the controller 150. In this mode, the first valve 130 is closed, the second valve 132 is opened, the third valve 134 is opened, and the fourth valve 136 is closed. Additionally, the first bypass valve 138 is opened, the second bypass valve 140 is closed, the third bypass valve 142 is closed, and the fourth bypass valve 144 is opened. As before, the electrical power is provided to the heat box 116 to produce a predetermined amount of additional heat in the liquid refrigerant received from the flash tank 114. This heated liquid refrigerant passes through the opened third valve 134 to the second LT evaporator 106, which is then heated to perform defrosting by the warm liquid refrigerant; the refrigerant then passes through the open fourth bypass valve 144 and the open first bypass valve 138 to the first LT evaporator 106 which uses the refrigerant for refrigeration. The refrigerant then flows through the open second valve 132 to the LT compressor 104.

Example of a Heat Box

FIG. 3 illustrates a non-limiting example of a heat box 116 configured for improved defrost operation. The heat box 116 and heater 330 may take any form and are not limited to that shown in FIG. 3. In one or more embodiments, refrigerant from the flash tank 114 enters the housing 310 of the heat box 116 in a conduit such as but not limited to, a coil 320, is heated by a heater 330, and then exits the housing to flow through conduit 180 to at least one LT evaporator, e.g., 106. The heater 330 is controlled by the controller 150 to provide different amounts of heat to the refrigerant that flows through coil 320.

In one or more embodiments, the housing 310 of the heat box 116 may take the form of a metal or wood rectangular container that includes one or more walls. The housing 310 may enclose the heater 330 and at least a portion of the coil 320 inside the walls of the housing 310. In one or more other embodiments, the housing 310 may be cylindrical or any other shape and be made of any material. The housing 310 may, in one or more embodiments, include insulation. This keeps the heat from the heater from exiting the heat box 116. The insulation may take any suitable form and is intended to reflect the heat from the heater 330 back onto the coils 320, increasing efficiency.

In one or more embodiments, the housing 310 may be kept in a partial vacuum or include one or more fluids that insulate or improve the performance of the heater 330 and/or the transfer of heat from the heater 330 to the coils 320. In yet another one or more embodiments, no insulation may be provided, and/or housing 310 may be eliminated, with the heat box 116 only comprising the coils 320 or conduit 180 and a heater 330.

In one or more embodiments, the heater 330 may take any form. The heater 330 may be in the form of heat tape that is directly attached to the coils 320 or conduit 180 or take any other well-known form that produces heat from electricity using resistance and/or radiant heating to provide heating to the refrigerant inside the coils 320. The heater 330 may be in the form of a plate, one or more conductors, a square, as shown in FIG. 3, or any other useful form. The disclosure is not limited to the heater 330 having a particular shape or being of a particular type.

The heater 330 in one or more embodiments is an adjustable capacity heater 330 controlled by the controller 150 to control the amount of heat produced. The controller 150 may change the amount of power or watts, voltage, or resistance delivered to the heater 330, which changes the amount of heat produced by the heater 330. The controller 150 may change the amount of power to increase or decrease the amount of heat produced by the heater 330 depending on the heater temperatures 160 stored in memory 154 and/or feedback from the one or more sensors 128A-128D and 129. In one or more embodiments, the controller 150 determines the temperature of the heated refrigerant exiting the heat box 116 with sensor 128A and adjusts power delivered to the heater 330 based on the feedback from the sensor in order to obtain an ideal amount of heat to defrost a selected LT evaporator, e.g., 106 in a predetermined amount of time.

In one or more embodiments, the coil 320 may include one or more curves or bends, as shown in FIG. 3. The coil 320 may have a curved, serpentine shape, a zig-zag shape, or any other shape that allows the coils 320 to fit in the housing 310 and have sufficient surface area for absorbing heat produced by the heater 330. Further, having coils 320 in a curved or serpentine shape may create turbulence in the refrigerant, making heating more efficient. This may be enhanced by adding rifling or cross-hatching inside the coils 320. However, the coils do not have to be curved or bent, and the disclosure is not limited to a specific shape or configuration of the coils 320. For example, in one or more embodiments, conduit 180 may be passed through the housing 310 of the heat box 116 without altering the shape or material of the conduit 180.

In one or more embodiments, the coils may be copper tubing. Other heat-conducting materials, such as aluminum or steel, may also make up the coils. In one or more embodiments, the heater 330 may be directly attached to the coils 320, such as in the case of heat tape. In other embodiments, aluminum extrusion may surround the coils 320 and provide efficient transfer from other types of heaters 330 and/or heat tape. The coils 320 of FIG. 3, along with the other components of the heat box 116, may take any form and include any materials without departing from the disclosure. The specific parts and configuration of the heat box 116 in FIG. 3 is merely a non-limiting example.

Example method of operation

FIG. 4 illustrates an example method 400 of operating the refrigeration systems 100 and 200 described above with respect to FIGS. 1 and 2. The method 400 may be implemented using the processor 152, memory 154, and I/O interface 156 of the controller 150 of FIGS. 1 and 2. The method 400 may begin at operation 405.

In operation 405, the controller 150 determines if one or more LT evaporators 106 and 108 need to be operated in a defrost mode. This may be determined using the sensors 128B and 128C associated with one or more LT evaporators 106 and 108. Alternatively, sensors at the LT compressor(s) 104 or at other positions may determine the temperature or pressure associated with the discharge from one or more LT evaporators 106 and 108, indicating that at least one of the LT evaporators, e.g., 106 may need to be defrosted. In one or more embodiments, the controller 150 may determine that at least one of the LT evaporators, e.g., 106, needs to be defrosted when a pressure sensor 129 measures a suction pressure that indicates that a selected LT evaporator, e.g., 106, needs to be defrosted. In yet another alternative, the determination to operate a selected at least one of the LT evaporators, e.g., 106 in a defrost mode, may be determined based on a predetermined schedule or another schedule, such as once every six hours, twelve hours, every day, every week, or any other schedule that a user, operator, installer, or manufacture deems appropriate to maintain the efficiency and/or life of the selected evaporator, e.g., 106.

Once the controller 150 determines that a selected evaporator, e.g., 106, needs to be operated in a defrost mode, the controller 150 causes the first valve 130, second valve 132, third valve 134, and fourth valve 136 to pass defrost refrigerant to the appropriate selected evaporator, e.g., 106, while passing refrigerant to at least one other evaporator, e.g., 108 for operating the other evaporator, e.g., 108 in a refrigeration mode in operation. For example, in one or more embodiments, when the first evaporator 106 is determined to need to be operated in a defrost mode, while the second evaporator 108 is operated in a refrigeration mode, first valve 130 is opened, the second valve 132 is closed, the third valve 134 is closed and the fourth valve 136 is opened as shown in FIG. 1. This allows the defrost refrigerant to defrost the evaporator 106 while using refrigerant to be used to continue providing refrigeration at the second evaporator 108. The refrigerant is then returned to the LT compressor(s) 104. In yet another example, one or more embodiments, when the second evaporator 108 is determined to need to be operated in a defrost mode, while the first evaporator 106 is operated in a refrigeration mode, first valve 130 is closed, the second valve 132 is opened, the third valve 134 is opened, and the fourth valve 136 is closed as shown in FIG. 2. The number of evaporators 106 and 108 is not limited to two and more than one evaporator; e.g., 106 and 108 may be operated simultaneously in defrost mode without departing from the disclosure.

This may include operating the first bypass valve 138, the second bypass valve 140, the third bypass valve 142, and the fourth bypass valve 144 to allow refrigerant to flow from the first evaporator 106 to the second evaporator 108 or when the selected evaporator, e.g., 108 is the second evaporator 108, operating the first bypass valve 138, second bypass valve 140, third bypass valve 142, and fourth bypass valve 144, to allow refrigerant to flow from the second evaporator 108 to the first evaporator 106 

Once controller 150 operates the valves, e.g., 130, to provide defrost refrigerant to one or more evaporators, the heater 330 in the heat box 116 is activated in operation 415. The controller 150 causes electrical power to be provided to the heater 330. The amount of power is determined by the controller 150 based on the heater temperatures 160 stored in memory 154. The heater temperatures 160 in one or more embodiments comprise a table that equates a specific voltage or current to a desired increase in temperature of the liquid refrigerant. By activating the heater 330 in operation 415 and operating the first, second, third, and fourth valves in operation 410, the selected evaporator, e.g., 106, begins to defrost.

Based on the amount of heat being provided by the activated heater 330 in operation 415, controller 150 then determines the remaining time for defrost in operation 420. The calculated remaining time may be determined from a table stored in the memory 154 as defrost time 162. Once the remaining time is determined, the controller 150 determines in operation 425 if the defrost time is less than a predetermined time. If the defrost time is less than a predetermined time, the temperature of the heater 330 is increased in operation 430. If, however, the controller 150 determines in operation 425 that the defrost time is not less than the predetermined time and the controller 150 determines in operation 435 that the defrost time is greater than the predetermined time, the controller 150 decreases the temperature of the heater 330 in operation 445. If the controller 150 determines in operation 435 that the defrost time is not greater than the predetermine time, which may occur when the defrost time is equal to the predetermined time, the controller 150 maintains the temperature of the heater 330 in operation 440.

In one or more embodiments, the threshold predetermined time is the amount of time that a user or operator of the refrigeration system, e.g., 100, desires for a select evaporator, e.g., 106, to defrost. For example, an operator may desire for the first LT evaporator 106 to take thirty minutes to defrost, as this allows for defrosting without the environment in which the first LT evaporator 106 is cooling from getting too warm or exceeding refrigeration requirements. Alternatively, the threshold predetermined time may be determined by the manufacture of the refrigeration system, e.g., 100, or the manufacture of the evaporator, e.g., 106, based on performance structural and/or performance requirements for the evaporator, e.g., 106 and/or other parts of the refrigeration system, e.g., 100.

The combination of operations 425-445 will cover multiple defrost cycles and determine the ideal heater temperature 160 that obtains a defrost time 162 in the predetermined time period within at least an acceptable margin of error. For example, if the operator of the refrigeration system, e.g., 100, desires the defrost cycle to take place in thirty minutes, the acceptable margin of error may be selected by the operator or manufacturer to be within five minutes. These determinations in operations 425-445 may be made during testing at the manufacturer or obtained during real-world use of the systems 100 and 200.

Other margins of errors and predetermined times may be used without departing from the disclosure. The margin of error and predetermined times may also change based on the use of the refrigeration system, e.g., 100, and the environment of the refrigeration system, e.g., 100. For example, a refrigeration system, e.g., 100, used to cool pharmaceuticals may have a smaller margin of error than that used to cool certain food items. In another example, the predetermined time may be adjusted based on humidity, time of day, and other factors that may affect the ability of the system to defrost in the predetermined amount of time or make longer or shorter predetermined amounts of time desirable from efficiency or cost considerations.

Once the heater temperature is either increased, maintained, or decreased in one of the operations 430, 440, or 445, controller 150 then determines if the selected evaporator, e.g., 106, still needs defrosting in operation 450. In one or more embodiments, the controller 150 determines how long to operate the selected evaporator, e.g., 106 in a defrost mode based on defrost time 162 stored in the memory 154. This may be based on times determined by the manufacturer, experimental defrost cycles, or based on previous defrost cycles. Alternatively, or in addition, the controller 150 may use sensors 128B and 128C associated with the selected evaporator, e.g., 106, suction sensor 129 associated with conduit connecting the LT evaporators 106 and 108 to the LT compressor(s) 104 or other sensors to determine if the defrosting is complete and/or if changes to the defrost cycle are needed.

If the controller 150 determines that defrosting is not complete in operation 455, then the method 400 returns to operation 420, and operations 420-455 are repeated until defrosting is complete. When the controller 150 determines that defrosting is complete in operation 455, the controller places the selected evaporator in a refrigeration mode in operation 460, and the method 400 ends. In one or more embodiments, when the selected evaporator, e.g., 106, is returned to refrigeration mode, the controller 150 may determine the total time for defrosting and then record any changes to defrost time 162, heater temperatures 160 and thresholds 164 in the memory 154.

Method 400 may include more, fewer, or other operations. For example, operations may be performed in parallel or in any suitable order. In one or more embodiments, the controller 150 may then repeat method 400 for one or more of the other evaporators, e.g., 108, or wait until a sensor, e.g., 128B associated with the evaporators, e.g., 106 and 108, indicates that defrosting is needed, or a predetermined time has passed since the last defrost cycle. Modifications, additions, or omissions may be made to method 400, depicted in FIG. 4. While at times discussed as controller 150, refrigeration system 100, or components thereof performing the operations, any suitable refrigeration system or components of the refrigeration system may perform one or more operations of method 400.

While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated into another system, or certain features may be omitted or not implemented.

In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component, whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.

To aid the Patent Office and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants note that they do not intend any of the appended claims to invoke 35 U.S.C. § 112(f) as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.