REFRIGERATION SYSTEM WITH THERMAL CONDUCTIVE DEFROST

Abstract

A refrigeration system including a compressor, a condenser, and an evaporator in heat exchange relationship with a fluid deliverable to a space. The evaporator is connected to the condenser via an inlet line and to the compressor via a suction line. A refrigeration circuit is defined by the compressor, condenser, inlet line, evaporator, and suction line. A refrigeration mode of the refrigeration circuit transfers heat from the fluid to a refrigerant in the evaporator and accumulates frost on the evaporator. The evaporator, a bypass line connected to the suction line and to the inlet line, a portion of the suction line, and a portion of the inlet line define a defrost circuit that circulates refrigerant in a defrost mode to transfer heat from the refrigerant to the frost on the evaporator. The refrigerant flows by gravity from the evaporator to one of the portion of the suction line and the portion of the inlet line in the defrost mode.

Description

BACKGROUND

The present invention relates to a defrost system for an evaporator of a refrigeration system. More particularly, the invention relates to a refrigeration system that includes a refrigeration mode that generates frost on an evaporator and a defrost mode that removes frost from the evaporator.

Refrigeration systems are well known and widely used in supermarkets and warehouses to refrigerate food product displayed in a product display area of a refrigerated merchandiser or display case. Conventional refrigeration systems include an evaporator, a compressor, and a condenser. The evaporator allows heat transfer between a refrigerant and a fluid passing over coils of the evaporator. The evaporator transfers heat from the fluid to the refrigerant so that the fluid cools the product display area. The refrigerant absorbs heat from the fluid in a refrigeration mode. In the refrigeration mode the compressor mechanically compresses the evaporated refrigerant from the evaporator and feeds the superheated refrigerant to the condenser, which cools the refrigerant. From the condenser, the cooled refrigerant is fed through one or more expansion valves to reduce the temperature and pressure of the refrigerant, and then the refrigerant is directed through the evaporator.

Since most evaporators operate at evaporating refrigerant temperatures that are lower than the freezing point of water (i.e., 32 degrees Fahrenheit), water vapor from the fluid freezes on the evaporator coils and creates frost. The frost decreases the efficiency of the heat transfer between the evaporator and the fluid, which causes the temperature of the refrigerated space to increase above a desired level. Maintaining the correct temperature of the refrigerated space is important to maintain the quality of the stored food products. To do this, the evaporators must be defrosted regularly in order to reestablish efficiency.

During defrost, the refrigeration system no longer refrigerates the food products. Some existing refrigeration systems defrost the evaporator using a heating element in communication with the fluid to heat the fluid. The heated fluid then warms the outside of the evaporator above the freezing point to melt the frost. The heated fluid further deposits the accumulated moisture as frost on cold surfaces of the refrigerated merchandiser, causing buildup of frost on the merchandiser. This method also results in wasted heat because some of the heated fluid escapes into the product display area, potentially spoiling the food product.

Other conventional refrigeration systems include valves that allow superheated vapor to flow from a discharge line of the compressor into the evaporator to defrost the coils. However, the process increases energy costs necessitated by operation of the compressors that compress the superheated vapor.

Still other conventional refrigeration systems include a reservoir from which evaporated refrigerant is drawn. These systems are sometimes called “hot” refrigerant gas defrost systems. Typically, hot refrigerant from a common discharge manifold or from an upper part of a refrigerant receiver is fed backward through the refrigeration system in a reverse flow to the evaporator to defrost the evaporator. The hot refrigerant gas is liquefied during its passage through the evaporator and the latent heat is used to melt the frost on the evaporator coils. The duration of the defrost period is directly proportional to the refrigerant mass flow. The higher the mass flow, the shorter the defrost period will be. However, the refrigerant mass flow depends on the condensing pressure of the refrigeration system. During the colder periods of the year the refrigerant mass flow is reduced, which thereby reduces the refrigerant mass flow and creates an economically unacceptable system. Further, the liquid refrigerant obtained during defrost of the evaporator is returned to the liquid line of the refrigeration system. This has a disruptive effect on the quality of the liquid refrigerant fed to the evaporators in normal operation (e.g., “flash gas”, higher liquid refrigerant temperature, etc.). These reverse flow systems are often complex, difficult to maintain, and substantially add to the cost of the refrigeration system.

SUMMARY

In one embodiment, the invention provides a refrigeration system that includes a compressor, a condenser fluidly connected to the compressor, and an evaporator. The evaporator is fluidly connected to the condenser via an inlet line and fluidly connected to the compressor via a suction line. The evaporator is further in heat exchange relationship with a fluid that is deliverable to a space. The compressor, condenser, inlet line, evaporator, and suction line define a refrigeration circuit, and the refrigeration system includes a refrigeration mode that is operable to circulate refrigerant through the refrigeration circuit to transfer heat from the fluid to the refrigerant in the evaporator to cool the space and to accumulate frost on the evaporator.

The refrigeration system further includes a bypass line having a first end fluidly connected to the suction line between the evaporator and the compressor, and a second end fluidly connected to the inlet line between the condenser and the evaporator. A defrost circuit of the refrigeration system is defined by the evaporator, a portion of the suction line between the evaporator and the first end, the bypass line, and a portion of the inlet line between the second end and the evaporator. The refrigeration system further includes a defrost mode that is operable to circulate refrigerant through the defrost circuit to transfer heat from the refrigerant to the frost on the evaporator. The evaporator is configured to allow the refrigerant to flow by gravity from the evaporator to one of the portion of the suction line and the portion of the inlet line in the defrost mode.

In another embodiment, the refrigeration system further includes a bypass line having a first end fluidly connected to the suction line between the evaporator and the compressor, and a second end fluidly connected to the inlet line between the condenser and the evaporator. A defrost circuit of the refrigeration system is defined by the evaporator, a portion of the suction line between the evaporator and the first end, the bypass line, and a portion of the inlet line between the second end and the evaporator. A heat source is in heat transfer relationship with the defrost circuit such that the heat source is operable to transfer heat to the refrigerant in the defrost circuit. The refrigeration circuit further includes a defrost mode that is operable to circulate refrigerant through the defrost circuit to transfer heat from the refrigerant to the frost on the evaporator.

In yet another embodiment the invention provides a method of operating a refrigeration system. The method includes providing a defrost circuit including the evaporator, a portion of the suction line between the evaporator and the first end, the bypass line, and a portion of the inlet line between the second end and the evaporator, providing a heat source in heat transfer relationship with the defrost circuit, and operating the refrigeration system in a defrost mode. The method further includes circulating refrigerant through the defrost circuit in the defrost mode, transferring heat in the defrost mode from the heat source to the refrigerant in the defrost circuit, and transferring heat in the defrost mode from the refrigerant to the frost on the evaporator.

Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a refrigeration system including a refrigeration circuit and a defrost circuit; and

FIG. 2 is an enlarged perspective view of the defrost circuit of FIG. 1.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.

FIG. 1 shows a refrigeration system 10 that may be used in commercial, industrial, residential or any other applications providing a container or case (not shown) having an open or closed configuration for refrigeration of food product and other materials disposed in a space of the container or case. The refrigeration system 10 is adapted to be used in any of a variety of configurations (e.g., refrigerated display case, refrigerated merchandiser freezer, cooler, temperature-controlled storage, etc.) and includes a refrigerant in heat transfer relationship with a fluid to cool the space.

The refrigeration system 10 includes a refrigeration circuit 15 and a defrost circuit 20. The refrigeration circuit 15 is defined by a compressor 25, a condenser 30, an evaporator 35, a suction line 40, and an inlet line 45. The compressor includes a high pressure side in fluid communication with the condenser 30 and a low pressure or suction side in fluid communication with the evaporator 35. The condenser 30 is coupled to the compressor 25 and the evaporator 35, and includes a series of looped conduits 50 to facilitate heat transfer between the refrigerant and the environment. The refrigerant is cooled by the condenser 30 while maintaining the refrigerant at a relatively high pressure. In some constructions, the condenser 30 is located on a rooftop to discharge the energy to the surrounding atmosphere.

The evaporator 35 is fluidly coupled with the compressor 25 via the suction line 40 and is fluidly coupled with the condenser 30 via the inlet line 45, and includes coils 55 in heat exchange relationship with the fluid. The suction line 40 couples an outlet of the evaporator 35 with the low pressure side of the compressor 25 to deliver evaporated refrigerant from the evaporator 35 to the compressor 25. The inlet line 45 couples with an exit side of the condenser 30 and an inlet of the evaporator 35 to convey condensed refrigerant from the condenser 30 to the evaporator 35. The inlet line 45 is coupled with the evaporator 35 at a position vertically above the attachment of the suction line 40 to the evaporator 35 such that refrigerant flow through the evaporator 35 is generally in a downward direction.

An expansion valve 60 is disposed in the inlet line 45 to create a pressure differential and to control the pressure of the refrigerant delivered to the evaporator 35. The expansion valve 60 shown in FIGS. 1 and 2 includes a thermostatic expansion valve, although other configurations of the expansion valve 60 are possible.

FIGS. 1 and 2 show the defrost circuit 20 that is defined by the evaporator 35, a bypass line 65 having a first end 70 and a second end 75, a portion 80 of the suction line 40 between the evaporator 35 and the first end 70, and a portion 85 of the inlet line 45 between the second end 75 and the evaporator 35. The first end 70 is in fluid communication with the suction line 40 between the compressor 25 and the evaporator 35. The second end 75 is in fluid communication with the inlet line 45 between the condenser 30 and the evaporator 35, and is further disposed between the expansion valve 60 and the evaporator 35.

The suction line portion 80 is attached to the evaporator 35 lower than the attachment of the inlet line portion 85 to the evaporator 35. Other embodiments may include the suction line portion 80 attached to the evaporator 35 higher than the attachment of the inlet line portion 85 to the evaporator 35.

The refrigeration system 10 further includes a suction valve 90, a bypass valve 95, a first heater 100, a second heater 105, and a controller 110. Other embodiments of the refrigeration system 10 may include one or more valves (not shown) positioned on the inlet line 45 upstream of the expansion valve 60. The suction valve 90 is disposed in the suction line 40 downstream of the first end 70 and includes an open position and a closed position to regulate refrigerant flow in the refrigeration system 10. In some embodiments, the suction valve 90 is a check valve, although the suction valve may be a solenoid or other valve (e.g., hand valve) having an open position and a closed position.

The bypass valve 95 is disposed in the bypass line 65 adjacent the first end 70 and includes an open position and a closed position to regulate flow of refrigerant in the refrigeration system 10. The bypass valve 95 is similar to the suction valve 90 and may include a check valve, a solenoid valve, or other valve (e.g., hand valve) having open and closed positions.

Other embodiments of the refrigeration system 10 may include a single valve similar to the suction valve 90 and the bypass valve 95 in the refrigeration system 10. In one construction, for example, the valve may be disposed in the suction line 40 to regulate refrigerant flow without a corresponding valve disposed in the bypass line 65. In other constructions, the singular valve may be disposed in the bypass line 65 without a corresponding valve disposed in the suction line 40. In still other constructions, more than one valve can be disposed in at least one of the suction line 40 and the bypass line 45.

The first heater 100 is positioned adjacent the suction line portion 80 such that the first heater 100 is at about the low point in the suction line 40 and upstream of the suction valve 90. The first heater 100 is further in heat transfer relationship with the suction line portion 80.

The second heater 105 is positioned adjacent the bypass line 65 and is in heat transfer relationship with the bypass line 65 to superheat the refrigerant when the refrigeration system 10 is in the defrost mode. Other embodiments of the refrigeration system 10 may include one or more heaters disposed on at least one of the bypass line 65, the suction line portion 80, and the inlet line portion 85.

FIG. 1 illustrates the controller 110 that is in electrical communication with the compressor 25 to selectively operate the compressor 25, and is in electrical communication with the suction valve 90 and the bypass valve 95 to selectively vary the suction valve 90 and the bypass valve 95 between the corresponding open positions and the closed positions. The controller 110 is further in electrical communication with the first and second heaters 100, 105 to selectively activate the first and second heaters 100, 105. In some embodiments, the controller 110 may be electrically coupled with other components of the refrigeration system, such as to the one or more valves positioned on the inlet line 45.

In one embodiment, the controller 110 includes a timing device (not shown). The timing device defines a predetermined time interval or cycle to regulate operation of the refrigeration system 10. In other embodiments, the controller 110 may include one or more sensors (not shown) to regulate operation of the refrigeration system 10.

The refrigeration system 10 operates in a refrigeration mode and in a defrost mode. The refrigeration mode circulates the refrigerant through the refrigeration circuit 15 and transfers heat from the fluid to the refrigerant. During operation in the refrigeration mode, the compressor 25 is engaged by the controller 110 and compresses low-pressure refrigerant drawn through the suction line 40. In some embodiments, an operation time in the refrigeration mode is stored by the controller 110 and compared to the predetermined time interval. When the operation time exceeds the predetermined time interval, the controller 110 switches the refrigeration system 10 from the refrigeration mode to the defrost mode.

The suction valve 90 is open and the bypass valve 95 is closed in the refrigeration mode to circulate the refrigerant through the refrigeration circuit 15. The refrigerant is compressed by the compressor 25 and flows through the condenser 30 where the refrigerant is condensed by the looped conduit 50. The condenser 30 releases energy from the refrigerant and condenses the superheated refrigerant discharged from the compressor 25. The cooled refrigerant then passes through the inlet line 45 and the expansion valve 60. The expansion valve 60 lowers the pressure of the refrigerant prior to the refrigerant reaching the evaporator 35. The expansion valve 60 varies the refrigerant from a high pressure refrigerant liquid to a low pressure refrigerant two-phase liquid vapor prior to entry into the evaporator 35.

The evaporator 35 transfers heat from the fluid passing over the coils 55 to the refrigerant in the coils 55. The heat transfer from the fluid to the refrigerant in the coils 55 cools the fluid and causes water vapor to condense on the coils 55. Over time, the water vapor accumulates as frost (not shown) on the evaporator 35. The suction line 40 receives evaporated refrigerant from the evaporator 35 and delivers the refrigerant to the compressor 25. The evaporated refrigerant flows from the evaporator 35 by pressure from high pressure refrigerant entering the evaporator 35 from the inlet line 45. In embodiments that include the inlet line 45 attached to the evaporator 35 higher than the attachment of the suction line 40, refrigerant in the refrigeration mode flows generally downward through the evaporator 35 and is assisted by gravity. In embodiments that include the inlet line 45 attached to the evaporator 35 lower than the attachment of the suction line 40, refrigerant in the refrigeration mode flows generally upward through the evaporator 35.

Buildup of frost during operation of the refrigeration system 10 in the refrigeration mode must be removed to allow efficient operation of the evaporator 35. The controller 110 switches the refrigeration system 10 from the refrigeration mode to the defrost mode in response frost buildup on the coils 55. In some embodiments, the timing device generates a signal that is received by the controller 110 to vary the refrigeration system 10 between the refrigeration mode and the defrost mode. In other embodiments, the sensors generate a signal indicative of the amount of frost buildup. The controller 110 compares the signal with a predetermined level of frost buildup and selectively varies the refrigeration system 10 between the refrigeration mode and the defrost mode in response to the signal. In still other embodiments, the sensor may detect a predetermined temperature and/or pressure of the fluid that corresponds to frost buildup on the evaporator 35. The sensor then generates a signal indicative of the temperature and/or pressure that is received by the controller 110. The controller 110 varies the refrigeration system 10 between the refrigeration mode and the defrost mode in response to the signal.

The controller 110 disengages the compressor 25 when the defrost mode is activated. The defrost mode circulates the refrigerant through the defrost circuit 20 to transfer heat from the refrigerant to the frost accumulated on the evaporator 35. The defrost mode directly transfers heat between the refrigerant and the frost without substantially heating air adjacent the evaporator 35. The heat transfer from the refrigerant to the frost on the coils 55 melts the frost and at least partially liquefies the refrigerant. The controller 110 further restricts flow of refrigerant through the refrigeration circuit 15 by adjusting the suction valve 90 from the open position to the closed position, and adjusting the bypass valve 95 from the closed position to the open position. Closing the suction valve 90 and opening the bypass valve 95 ensures that the refrigerant will flow through the defrost circuit 20 and will not flow through the refrigeration circuit 15.

The defrost circuit 20 bypasses a substantial portion of the refrigeration circuit 15 using the bypass line 65. The suction valve 90 closes to allow refrigerant to flow through the bypass line 65 and into the evaporator 35 without passing through the compressor 25, the condenser 30, and the expansion valve 60. In embodiments that include valves positioned on the inlet line 45, the valves may be opened or closed to regulate flow of refrigerant into the defrost circuit 20. The refrigerant in the defrost circuit 20 circulates through the suction line portion 80, the bypass line 65, the inlet line portion 85, and the evaporator 35 to melt the frost that accumulated on the coils 55 during the refrigeration mode. The refrigerant flows by gravity from the evaporator 35 toward a low point of the defrost circuit 20, circulating the refrigerant through the remaining portions of the defrost circuit 20.

The refrigerant exiting the evaporator 35 at the end of the refrigeration mode is initially heated by the heat transfer between the fluid and the refrigerant. This refrigerant may initially have sufficient heat such that the refrigerant circulates through the defrost circuit 20 by pressure differences to melt the frost on the coils 55 without activation of the first and second heaters 100, 105. The initially heated refrigerant is defined by a relatively high pressure that generates flow through the defrost circuit 20. In some embodiments, additional valves may be used to generate flow of refrigerant through the defrost circuit 20.

The heat transfer from the heated refrigerant to the frost on the coils 55 at least partially liquefies or condenses the refrigerant without substantially affecting the temperature of the fluid passing over the coils 55. In embodiments that include the suction line portion 80 positioned lower than the inlet line portion 85, the at least partially condensed refrigerant in the defrost mode flows generally downward through the evaporator 35 to the suction line portion 80 and is further assisted by gravity. In addition, heated refrigerant in the defrost mode from the inlet line portion 85 forces condensed refrigerant into the suction line portion 80 due to a pressure difference between the heated refrigerant entering the evaporator 35 in the defrost mode and the cooled refrigerant leaving the evaporator 35. The condensed refrigerant in the defrost mode flows through the evaporator 35 in a direction (i.e., refrigerant flow from the inlet line 85 to the suction line 80) that is the same as the direction of refrigerant flow during operation of the refrigeration system 10 in the refrigeration mode.

In embodiments that include the inlet line portion 85 positioned lower than the suction line portion 80, the at least partially condensed refrigerant in the defrost mode flows generally downward through the evaporator 35 to the inlet line portion 85 and is further assisted by gravity. In addition, heated refrigerant in the defrost mode from the suction line portion 80 forces condensed refrigerant into the inlet line portion 85 due to a pressure difference between the heated refrigerant entering the evaporator 35 in the defrost mode and the cooled refrigerant leaving the evaporator 35. The condensed refrigerant in the defrost mode flows through the evaporator 35 in a direction (i.e., refrigerant flow from the suction line portion 80 to the inlet line portion 85) opposite the direction of refrigerant flow during operation of the refrigeration system 10 in the refrigeration mode.

The controller 110 selectively engages the first and second heaters 100, 105 in the defrost mode to transfer heat to the condensed refrigerant passing through the suction line portion 80 and the bypass line 65. The heat transfer from the first and second heaters 100, 105 superheats refrigerant in the defrost circuit 20. The first heater 100 at least partially superheats refrigerant in the suction line portion 80 when the refrigeration system 10 is in the defrost mode. The second heater 105 at least partially superheats refrigerant in the bypass line 65 when the refrigeration system 10 is in the defrost mode. The controller 110 manages the temperature of the superheated refrigerant in the defrost circuit 20 through selective activation of the first and second heaters 100, 105. The superheated refrigerant then flows through the remainder of the bypass line 65 and into the evaporator 35. During operation of the refrigeration system 10 in the defrost mode, the refrigerant circulates continuously through the defrost circuit 20 to defrost the coils 55. Other embodiments may operate the refrigeration system 10 in the defrost mode by circulating the refrigerant through the defrost circuit 20 at predetermined intervals to maximize the defrost of the coils 55.

The controller 110 provides a means of cycling one or more of the suction valve 90, the bypass valve 95, the first and second heaters 100, 105, and other components of the refrigeration system 10 (e.g., valves positioned on the inlet line 45). Cycling one or more of these components achieves a desired effect regarding defrost of the coils 55 in the defrost mode. The valves 90, 95 can be varied between the open and closed positions multiple times during a single defrost mode operation. Similarly, the first and second heaters 100, 105 may be engaged and disengaged several times during one defrost mode operation to achieve a temperature of the refrigerant in the defrost circuit that maximizes defrost of the coils 55.

In some embodiments, the first and second heaters 100, 105 superheat refrigerant in the defrost circuit 20 such that very little or no liquid refrigerant remains. Without sufficient liquid refrigerant in the defrost circuit 20, the temperature of the superheated refrigerant substantially increases above a saturation temperature of the refrigerant. As a result, circulation of refrigerant heated well above the saturation temperature stalls and the coils 55 cannot be effectively defrosted. In these embodiments, additional liquid refrigerant may be introduced from the inlet line 45 to maintain the refrigerant in the defrost circuit 20 at about the saturation temperature and to facilitate refrigerant flow through the defrost circuit. Valves positioned on the inlet line 45 can be varied between open and closed positions to allow an appropriate amount of additional liquid refrigerant to enter the defrost circuit 20. Alternatively, the bypass line 65 may be sufficiently large to accommodate additional liquid refrigerant.

Once the coils 55 are sufficiently defrosted during the defrost mode (e.g., after the predetermined interval has elapsed), the controller 110 opens the suction valve 90, closes the bypass valve 95, and disengages the first and second heaters 100, 105. The controller 110 further engages the compressor 25 and the remaining components of the refrigeration circuit 15 to switch from the defrost mode to the refrigeration mode. The refrigeration mode and defrost mode are repeated as necessary to maintain the space at predetermined conditions and to remove buildup of frost on the coils 55.

Thus, the invention provides, among other things, a refrigeration system that includes a refrigeration circuit, an evaporator, and a defrost circuit to defrost the evaporator. Various features and advantages of the invention are set forth in the following claims.

Claims

1. A refrigeration system comprising:

a compressor;

a condenser fluidly connected to the compressor;

an evaporator fluidly connected to the condenser via an inlet line and fluidly connected to the compressor via a suction line, the evaporator in heat exchange relationship with a fluid deliverable to a space, wherein the compressor, condenser, inlet line, evaporator, and suction line define a refrigeration circuit, wherein the system includes a refrigeration mode operable to circulate refrigerant through the refrigeration circuit to transfer heat from the fluid to the refrigerant in the evaporator to cool the space and accumulate frost on the evaporator; and

a bypass line having a first end fluidly connected to the suction line between the evaporator and the compressor and a second end fluidly connected to the inlet line between the condenser and the evaporator, wherein the evaporator, a portion of the suction line between the evaporator and the first end, the bypass line, and a portion of the inlet line between the second end and the evaporator define a defrost circuit, wherein the system includes a defrost mode operable to circulate refrigerant through the defrost circuit to transfer heat from the refrigerant to the frost on the evaporator, and wherein the evaporator is configured to allow the refrigerant to flow by gravity from the evaporator to one of the portion of the suction line and the portion of the inlet line in the defrost mode.

2. The refrigeration system of claim 1, further comprising a valve disposed on the suction line wherein the valve is operable to open in the refrigeration mode and to close in the defrost mode.

3. The refrigeration system of claim 1, further comprising a valve disposed on the bypass line, wherein the valve is operable to close in the refrigeration mode and to open in the defrost mode.

4. The refrigeration system of claim 1, further comprising a first valve in fluid communication with the suction line and a second valve in fluid communication with the bypass line, wherein the first valve is operable to open in the refrigeration mode and to close in the defrost mode, and the second valve is operable to close in the refrigeration mode and to open in the defrost mode.

5. The refrigeration system of claim 1, further comprising a heat source in heat transfer relationship with the defrost circuit, the heat source operable to transfer heat to the refrigerant in the defrost circuit.

6. The refrigeration system of claim 5, wherein the heat source is adjacent at least one of the portion of the suction line and the bypass line to superheat refrigerant in the defrost mode.

7. The refrigeration system of claim 6, wherein the evaporator is configured and oriented to allow the superheated refrigerant to at least partially displace refrigerant in the evaporator.

8. The refrigeration system of claim 5, wherein the heat source includes a first heat source adjacent the portion of the suction line and a second heat source adjacent the bypass line to superheat refrigerant in the defrost mode.

9. A refrigeration system comprising:

a compressor;

a condenser fluidly connected to the compressor;

an evaporator fluidly connected to the condenser via an inlet line and fluidly connected to the compressor via a suction line, the evaporator in heat exchange relationship with a fluid deliverable to a space, wherein the compressor, condenser, inlet line, evaporator, and suction line define a refrigeration circuit, wherein the system includes a refrigeration mode operable to circulate refrigerant through the refrigeration circuit to transfer heat from the fluid to the refrigerant in the evaporator to cool the space and accumulate frost on the evaporator;

a bypass line having a first end fluidly connected to the suction line between the evaporator and the compressor and a second end fluidly connected to the inlet line between the condenser and the evaporator, wherein the evaporator, a portion of the suction line between the evaporator and the first end, the bypass line, and a portion of the inlet line between the second end and the evaporator define a defrost circuit; and

a heat source in heat transfer relationship with the defrost circuit, the heat source operable to transfer heat to the refrigerant in the defrost circuit, wherein the system includes a defrost mode operable to circulate refrigerant through the defrost circuit to transfer heat from the refrigerant to the frost on the evaporator.

10. The refrigeration system of claim 9, wherein the heat source is adjacent at least one of the portion of the suction line and the bypass line to evaporate refrigerant in one of the portion of the suction line and the bypass line.

11. The refrigeration system of claim 9, wherein the heat source includes a first heat source adjacent the portion of the suction line and a second heat source adjacent the bypass line.

12. The refrigeration system of claim 9, further comprising a valve disposed on the suction line, wherein the valve is operable to open in the refrigeration mode and to close in the defrost mode.

13. The refrigeration system of claim 9, further comprising a valve disposed on the bypass line, wherein the valve is operable to close in the refrigeration mode and to open in the defrost mode.

14. The refrigeration system of claim 9, further comprising a first valve in fluid communication with the suction line and a second valve in fluid communication with the bypass line.

15. The refrigeration system of claim 9, wherein the heat transfer from the refrigerant to the frost is operable to liquefy the refrigerant, and wherein the evaporator is configured and oriented to allow the liquefied refrigerant to flow by gravity from the evaporator to one of the portion of the suction line and the portion of the inlet line in the defrost mode.

16. A method of operating a refrigeration system to cool a space, the refrigeration system including a compressor, a condenser fluidly connected to the compressor, an evaporator fluidly connected to the condenser via an inlet line and fluidly connected to the compressor via a suction line, and a bypass line having a first end fluidly connected to the suction line between the evaporator and the compressor and a second end fluidly connected to the inlet line between the condenser and the evaporator, the evaporator in heat transfer relationship with a fluid that is in fluid communication with the space, the method comprising:

providing a refrigeration circuit including the compressor, condenser, inlet line, evaporator, and suction line;

operating the refrigeration system in a refrigeration mode;

circulating refrigerant through the refrigeration circuit in the refrigeration mode;

transferring heat in the refrigeration mode from the fluid to the refrigerant in the evaporator;

cooling a space in the refrigeration mode;

accumulating frost on the evaporator in the refrigeration mode;

providing a defrost circuit including the evaporator, a portion of the suction line between the evaporator and the first end, the bypass line, and a portion of the inlet line between the second end and the evaporator,

providing a heat source in heat transfer relationship with the defrost circuit;

operating the refrigeration system in a defrost mode;

circulating refrigerant through the defrost circuit in the defrost mode;

transferring heat in the defrost mode from the heat source to the refrigerant in the defrost circuit; and

transferring heat in the defrost mode from the refrigerant to the frost on the evaporator.

17. The method of claim 16, wherein transferring heat in the defrost mode from the refrigerant to the frost further includes melting the frost on the evaporator and condensing the refrigerant.

18. The method of claim 16, further comprising

providing a valve between the evaporator and the compressor;

opening the valve in the refrigeration mode; and

closing the valve in the defrost mode.

19. The method of claim 16, further comprising

providing a valve in the bypass line;

opening the valve in the defrost mode; and

closing the valve in the refrigeration mode.

20. The method of claim 16, further comprising providing a first valve between the suction line and the compressor and providing a second valve in the bypass line.

21. The method of claim 20, wherein operating the refrigeration system in the refrigeration mode further includes opening the first valve and closing the second valve.

22. The method of claim 20, wherein operating the refrigeration system in the defrost mode further includes closing the first valve and opening the second valve.

23. The method of claim 16, wherein providing a heat source in heat transfer relationship with the defrost circuit further includes providing a heat source in heat transfer relationship with the portion of the suction line.

24. The method of claim 16, wherein providing a heat source in heat transfer relationship with the defrost circuit further includes providing a heat source in heat transfer relationship with the bypass line.

25. The method of claim 16, wherein transferring heat in the defrost mode from the heat source to the refrigerant further includes evaporating the refrigerant in the portion of the suction line.

26. The method of claim 16, wherein evaporating the refrigerant in the portion of the suction line further includes displacing the refrigerant in the evaporator to the suction line.