Patent Application
20080302117
The present disclosure relates generally to the field of heating and cooling systems. In particular, the disclosure more specifically relates to a variable capacity evaporator employed in an air conditioning system.
Many air conditioning systems include a metering device (e.g., an expansion valve) which regulates the flow of liquid refrigerant into an evaporator. These devices may include simple capillary tubes, thermostatic expansion valves, constant pressure valves, electronic needle valves, and other components. The metering devices tend to be carefully matched to the evaporator and other system components so enough refrigerant is fed to fill the evaporator but not so much that liquid refrigerant is allowed to flow out the exit tube. The amount of refrigerant required may depend on the operating temperature and cooling capacity of the system. Metering in too little refrigerant may reduce the efficiency of the system by failing to take full advantage of the heat exchange surface offered by the evaporator. Conversely, metering in too much refrigerant may allow liquid to pass through the evaporator and into the compressor, risking damage
To prevent such problems, conventional systems may employ a metering device and evaporator that work together to ensure about 100% evaporation of the liquid refrigerant within the evaporator. Such a design typically includes the ability to maintain a stable preset “superheat”—the temperature difference between the refrigerant boiling temperature and the temperature of the gas as it exits the evaporator.
Standard industry practice, both in the design of the metering devices and air conditioning system itself, generally increases the energy efficiency of the system by ensuring a sufficiently regulated supply of refrigerant into the evaporator to maintain a relatively stable superheat of the refrigerant under most conditions.
According to a disclosed embodiment an air conditioning system is provided. The system includes an evaporator containing refrigerant and a metering device for regulating the flow of refrigerant into the evaporator. The metering device is configured to regulate the flow the evaporator based at least in part on the pressure sensed in a flow path to the evaporator. The system also includes a compressor for compressing refrigerant and providing liquid refrigerant to the metering device. The system is configured so that refrigerant flowing from the metering device into the evaporator passes through a flow regulating device located in the flow path.
According to another disclosed embodiment an air conditioning system including a variable speed compressor configured to operator at faster and slower speeds is provided. The system also includes an evaporator and a thermal expansion valve for regulating the flow of a refrigerant from the compressor to the evaporator. The thermal expansion valve is configured to control the flow of the refrigerant into the evaporator based on a temperature sensed at the outlet of the evaporator and a pressure sensed at the inlet to the evaporator. The system includes a flow restriction device in a flow path from the thermal expansion valve to the evaporator thereby increasing the efficiency of the system when the compressor is operating at slower speeds.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.
These and other features, aspects, and advantages will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below.
The energy efficiency of small and mid-size air conditioning systems can be improved through the use of variable-speed compressors. The use of variable speed compressors offers the ability to more closely match the capacity of the system with the varying load resulting in lower energy consumption. In such systems, the compressor changes speed so that the evaporator temperature remains stable as the heat load changes. As with non-variable speed systems, the role of the metering device remains the same—to maintain a relatively stable superheat setting.
Air conditioning systems employing variable speed compressors are intended to produce a required cooling capacity with a minimum use of input power. To accomplish this, as the load changes, the system capacity changes as well. In this way, the heat load and system capacity remain in relative balance. This approach to maximizing energy efficiency may be appropriate when unlimited electrical power is available and the primary goal of the air conditioning system is to provide sufficient cooling power to match the heat load. While it may be desirable to reduce the power needed to provide this cooling, the energy consumption is generally secondary to the primary goal of providing full cooling power.
When an air conditioning system is powered by a limited energy source (e.g., a battery-power system), the availability of power may take priority over the desire to provide full cooling capacity. In such a system it may be more desirable to provide a modest amount of cooling over a longer period of time than to provide full cooling capacity for a shorter period. The priority may become the rate of energy consumption while the maximization of effective cooling is a secondary consideration.
In a variable-speed high efficiency air conditioning system the compressor speed is varied to match a changing heat load. This typically results in a more stable and optimally determined evaporator temperature. The speed may vary from slower to faster speeds. The speed may be continuously variable or variable between certain predetermined speeds.
However, in a limited energy capacity system, the compressor speed is varied according to the availability of electrical power regardless of the heat load. The result is that the evaporator temperature may rise to an unacceptably high level. This high evaporator temperature may result in poor cooling performance due to excessively high discharge air temperature.
To maintain acceptable cooling performance when the compressor speed is reduced (i.e., minimizing power draw) and while the heat load remains relatively high, the size of the evaporator may be reduced. This may be done by increasing the amount of superheat maintained by the metering device in proportion to the difference between heat load and compressor capacity.
Therefore, there is a need to provide an evaporation system with improved cooling efficiency that uses commonly available and generally low-cost metering devices. There is also a need for an improved system and method for regulating the flow of refrigerant into the evaporator coil of a variable-capacity evaporator system operating from a power supply of limited capacity.
Referring to
The compressor 12 is typically a variable speed compressor, but according to other exemplary embodiments may be a fixed speed compressor. According to various exemplary embodiments, the compressor 12 (i.e., variable speed or fixed speed) may be any be of any past, present, or future design capable of providing refrigerant in the evaporator system 10.
The thermal expansion valve 14 (e.g., an internally equalized thermostatic expansion valve) is connected to supply fluid refrigerant to the inlet 16 of the evaporator 20. The expansion valve 14 may include a needle valve 24, a diaphragm 26, a pressure sensing bulb 28, and an internal port 30. The flow of refrigerant is regulated by the needle valve 24, which may move toward the fully open or fully closed positions depending on the differential pressure applied across the diaphragm 26. Pressure on one side of the diaphragm may be determined by the temperature of the fluid-filled sensing bulb 28, which is coupled to the outlet 22 of the evaporator 20. Pressure on the other side of the diaphragm may be based on the pressure at the internal port 30 located near the connection point to the evaporator inlet 16. According to various exemplary embodiments, the needle valve 24 may be of any past, present, or future valve design. According to other exemplary embodiments, a ball valve, a globe valve, a diaphragm valve, a butterfly valve, or any other valve capable of controlling fluid flow in the evaporator system 10 may be substituted for the needle valve.
The evaporator 20 is configured to provide a heat exchange area with the environment around it. Refrigerant (e.g., liquid refrigerant) is fed into the evaporator 20 and flows near a heat source, for example the environment around the evaporator 20. In one embodiment, air is blown across the evaporator coil by a blower or fan. A liquid refrigerant 32 absorbs heat from the environment, thus cooling the environment and converting the refrigerant into a gas 34. The gas exits the evaporator via the outlet 22 and returns to the compressor. According to various exemplary embodiments, the evaporator 20 may include more or fewer than the illustrated number of coils. According to another exemplary embodiment, a plate-type evaporator may be used.
Referring to
Referring to
The flow restricting device 18 is located in the flow path from the thermal expansion valve 14 and the inlet 16 to the evaporator. The flow restricting device 18 is intended to change the relationship of the pressure applied to one side of the diaphragm via the internal port 30 and the pressure applied to the other side by the temperature sensing bulb 28. The restricting device 18 may increase the pressure of the internal port 30 relative to that of the sensing bulb 28, effectively increasing the flow of refrigerant into the evaporator 20 (thus reducing superheat) as the speed of the compressor increases. When the compressor slows down, the pressure drop created by the restricting device 18 is reduced and the pressure at the internal port 30 may more closely match the pressure of the evaporator 20.
The flow restricting device 18 may include an orifice in the flow path. The device 18 may also provide variable throttling to the refrigerant flow. For example, a throttle valve may be provided. The throttle valve may be controllable (e.g., a solenoid valve) so that flow restriction is increased at slower compressor speeds. is located in the flow path from the thermal expansion valve 14 and the the inlet 16 to the evaporator.
Although evaporator system 10 is illustrated as including multiple features utilized in conjunction with one another, evaporator system 10 may alternatively utilize more or less than all of the noted mechanisms or features. For example, in other exemplary embodiments, the flow restricting device 18 may be a single unitary portion of expansion valve 14. For example, an orifice located in the refrigerant outlet of the expansion valve 14.
Although specific shapes of each element have been set forth in the drawings, each element may be of any other shape that facilitates the function to be performed by that element. For example, sensing bulb 28 is shown to be of a generally rectangular shaped cross-section, however, in other embodiments the structure may define that of a more curvilinear form.
For purposes of this disclosure, the term “coupled” means the joining of two components (electrical or mechanical) directly or indirectly to one another. Such joining may be stationary in nature or movable in nature. Such joining may be achieved with the two components (electrical or mechanical) and any additional intermediate members being integrally defined as a single unitary body with one another or with the two components or the two components and any additional member being attached to one another. Such joining may be permanent in nature or alternatively may be removable or releasable in nature
The present disclosure has been described with reference to example embodiments, however workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the claimed subject matter. For example, although different example embodiments may have been described as including one or more features providing one or more benefits, it is contemplated that the described features may be interchanged with one another or alternatively be combined with one another in the described example embodiments or in other alternative embodiments. Because the technology of the present disclosure is relatively complex, not all changes in the technology are foreseeable. The present disclosure described with reference to the example embodiments and set forth in the following claims is manifestly intended to be as broad as possible. For example, unless specifically otherwise noted, the claims reciting a single particular element also encompass a plurality of such particular elements.
It is also important to note that the construction and arrangement of the elements of the system as shown in the preferred and other exemplary embodiments is illustrative only. Although only a certain number of embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited. For example, elements shown as integrally formed may be constructed of multiple parts or elements shown as multiple parts may be integrally formed, the operation of the assemblies may be reversed or otherwise varied, the length or width of the structures and/or members or connectors or other elements of the system may be varied, the nature or number of adjustment or attachment positions provided between the elements may be varied. It should be noted that the elements and/or assemblies of the system may be constructed from any of a wide variety of materials that provide sufficient strength or durability. Accordingly, all such modifications are intended to be included within the scope of the present disclosure. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the preferred and other exemplary embodiments without departing from the spirit of the present subject matter.
