BACKGROUND
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Exemplary embodiments of the present invention relate to the art of condensers, and more particularly, to a vapor compression system having various means for removing heat from a refrigerant therein.
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Conventional vapor compression systems have a condenser that is sized based on a maximum load at a maximum ambient temperature. However, the maximum load and the maximum ambient temperature are not always present. Sizing the heat exchanger system for the maximum heat load at continuous duty cycle in the maximum expected ambient air condition results in an oversized, overweight, and overpowered condensing unit for those portions of the duty cycle that are not near the limits of the system. Further, because of the increased cost of electricity during peak hours, such as when the ambient temperature is greatest, it is desirable to shift operational reliance of a vapor compression cycle on electricity to off-peak times, such as during the early morning, middle of the day, and nighttime hours.
BRIEF DESCRIPTION
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According to an aspect of the invention, a vapor compression system includes a compressor, a condenser, an expansion device, and an evaporator fluidly connected to form a closed fluid loop having a working fluid circulating therethrough. A thermal storage device includes a storage material and the thermal storage device is thermally coupled to the closed fluid loop downstream from the expansion device relative to a flow of the working fluid. The vapor compression system is controllable such that the thermal storage device is operable to both store heat and release heat as the working fluid circulates through the closed fluid loop in a given direction.
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In any of the aspects or embodiments described above or herein, the vapor compression system may include a reverse flow valve such that the working fluid is movable through the closed fluid loop in a first direction associated with a cooling mode and an opposite, second direction associated with a heating mode.
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In any of the aspects or embodiments described above or herein, the thermal storage device may be operable to both store heat and release heat when the vapor compression system is in the cooling mode.
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In any of the aspects or embodiments described above or herein, a controller may be operably coupled to the compressor and/or the expansion device and the controller is operable to control a superheat of the working fluid at the inlet of the compressor.
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In any of the aspects or embodiments described above or herein, the controller may be operable to adjust a position of the expansion device to control the superheat of the working fluid at the inlet of the compressor.
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In any of the aspects or embodiments described above or herein, the storage material may be or comprise a phase change material.
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According to another aspect of the invention, a vapor compression system includes a compressor, a condenser, an expansion device, and an evaporator fluidly connected to form a closed fluid loop having a working fluid circulating therethrough. A thermal storage device includes a storage material and the thermal storage device is thermally coupled to the closed fluid loop downstream from the compressor and upstream from the expansion device relative to a flow of the working fluid. The vapor compression system is controllable such that the thermal storage device is operable to both store heat and release heat as the working fluid circulates through the closed fluid loop in a given direction.
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In any of the aspects or embodiments described above or herein, the vapor compression system may include a reverse flow valve such that the working fluid is movable through the closed fluid loop in a first direction associated with a cooling mode and an opposite, second direction associated with a heating mode.
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In any of the aspects or embodiments described above or herein, the thermal storage device may be operable to both store heat and release heat when the vapor compression system is in the cooling mode.
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In any of the aspects or embodiments described above or herein, a controller may be operably coupled to the compressor and/or the expansion device and the controller is operable to control a superheat of the working fluid at the inlet of the compressor.
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In any of the aspects or embodiments described above or herein, the controller may be operable to adjust a position of the expansion device to control the superheat of the working fluid at the inlet of the compressor.
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According to another aspect of the invention, a method of operating a vapor compression system includes circulating a working fluid through a closed fluid loop including a compressor, a condenser, an expansion device, and an evaporator, and discharging a thermal storage device thermally coupled to the closed fluid loop by controlling a superheat of the working fluid at the compressor.
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In any of the aspects or embodiments described above or herein, controlling the superheat of the working fluid may include controlling a position of the expansion device.
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In any of the aspects or embodiments described above or herein, discharging the thermal storage device may comprise decreasing the superheat of the working fluid.
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In any of the aspects or embodiments described above or herein, decreasing the superheat of the working fluid may be performed by increasing a flow of the working fluid at the expansion device.
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In any of the aspects or embodiments described above or herein, charging the thermal storage device thermally coupled to the closed fluid loop may comprise controlling the superheat of the working fluid at the compressor.
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In any of the aspects or embodiments described above or herein, the working fluid may circulate through the closed fluid loop in a same direction during both charging the thermal storage device and discharging the thermal storage device.
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In any of the aspects or embodiments described above or herein, charging the thermal storage device may include transferring thermal energy to a storage material of the thermal storage device from the working fluid.
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In any of the aspects or embodiments described above or herein, charging the thermal storage device may include decreasing the superheat of the working fluid.
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In any of the aspects or embodiments described above or herein, decreasing the superheat of the working fluid may be performed by adjusting the position of the expansion device to decrease the flow of the working fluid at the expansion device.
BRIEF DESCRIPTION OF THE DRAWINGS
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The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:
- FIG. 1 is a schematic diagram of a vapor compression system in a cooling mode;
- FIG. 2 is a schematic diagram of the vapor compression system of FIG. 1 in a heating mode;
- FIG. 3 is a schematic diagram of another vapor compression system in a cooling mode; and
- FIG. 4 is a schematic diagram of another vapor compression system in a cooling mode.
DETAILED DESCRIPTION
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A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.
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With reference now to FIG. 1, an example of a vapor compression system 20 having a closed fluid loop within which a working fluid R, circulates such as refrigerant for example, is provided. As shown, the vapor compression system 20 includes one or more compressors 22, a first heat exchanger 24, an expansion device 26, and a second heat exchanger 28. In operation, the compressor 22 receives a working fluid vapor from the second heat exchanger 28 and compresses it to a high temperature and pressure. The relatively hot working fluid vapor R is then delivered to the first heat exchanger 24 where it is cooled and condensed to a liquid state via a heat exchange relationship with a cooling medium C1, such as air or water for example. Accordingly, the first heat exchanger 24 is a heat rejection heat exchanger or a condenser.
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The cooled liquid working fluid R flows from the first heat exchanger 24 to the expansion device 26, such as an expansion valve for example, in which the working fluid R is expanded to a lower pressure where the temperature is reduced and the working fluid R may exist in a two-phase liquid/vapor state. From the expansion device 26, the working fluid R is provided to the second heat exchanger 28. Because heat is transferred from a secondary medium C2, such as air for example, to the refrigerant R within the second heat exchanger 28, causing any refrigerant R in the liquid phase to vaporize, the second heat exchanger 28 functions as a heat absorption heat exchanger or an evaporator. From the second heat exchanger 28, the low-pressure vapor working fluid R returns to the compressor 22 so that the cycle may be repeated. In an embodiment, as shown, the system 20 may additionally include an accumulator or separator 32 positioned directly upstream from the inlet of the compressor 22. In such embodiments, any liquid working fluid may be collected within the separator 32 such that only vaporized working fluid R is provided to the compressor 22.
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In an embodiment, the vapor compression system 20 may be a heat pump. In such an embodiment, the vapor compression system 20 includes a reverse flow valve 30 operable to control a direction of flow of the working fluid R within the system 20. For example, when the reverse flow valve 30 is in a first position, as shown in FIG. 1, the vapor compression system 20 may be considered to be in a "cooling" mode, and the working fluid R may flow in a manner as described above. When the reverse flow valve 30 is in a second position, as shown in FIG. 2, the vapor compression system 20 may be considered to be in a "heating" mode. In the heating mode, the working fluid R may flow in a reverse direction, such as from the compressor 22 to the second heat exchanger 28, to the expansion device 26, and to the first heat exchanger 24 before returning to the compressor 22 to repeat the cycle. Although only a single expansion device 26 is illustrated and described herein, it should be understood that embodiments where the vapor compression system 20 includes a first expansion device and a second expansion device are also within the scope of the invention as defined by the claims. In such embodiments, the first expansion device may be associated with a cooling mode and flow of the working fluid in a first direction and the second expansion device may be associated with operation in a heating mode and flow of the working fluid in a second direction.
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In each of the illustrated, non-limiting embodiments, the vapor compression system 20 is thermally coupled to a thermal storage device 40 containing a storage material. In the illustrated, non-limiting embodiment, the vapor compression system 20 is indirectly thermally coupled to the thermal storage device 40 via a heat exchanger 42. The thermal storage device 40 and the heat exchanger 42 are fluidly coupled to form a closed loop through which a heat transmission fluid circulates. The closed loop may include a pump 44 operable to drive movement of the heat transmission fluid between the heat exchanger 42 and the thermal storage device 40. When the vapor compression cycle is indirectly thermally coupled to the thermal storage device 40, the refrigerant R of the vapor compression system 20 is arranged in a heat transfer relationship with the heat transmission fluid at the heat exchanger 42. However, in other embodiments, the working fluid R may be directly thermally coupled to the thermal storage device 40. For example, all or at least a portion of the working fluid R within the vapor compression system 20 may be configured to flow through one or more passages formed in the thermal storage device 40.
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The thermal storage device 40 may be filled with a phase change material P transformable between a first phase and a second phase. The phase change material P may be transformable between a solid and a liquid. In an embodiment, the phase change material P is a low temperature melting material, such as having a transition temperature between a solid to a liquid less than about 11°C. For example, the phase change material P may be a low temperature melting inorganic salt hydrate, which transitions between a solution of the salt hydrate in the liquid at high temperature to a crystalline salt hydrate in the liquid at low temperatures. However, other suitable phase change materials P, such as organic paraffin waxes, organic esters (e.g., dimethyl adipate), or ice for example, are also within the scope of the invention.
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The thermal storage device 40 may be used to remove heat from or release heat to the working fluid R within the vapor compression system 20. In an embodiment, the same stream of working fluid R may be used to both charge (provide thermal energy to) and discharge (remove thermal energy from) the thermal storage device 40. This charging and discharging may be performed by controlling the superheat of the working fluid R prior to entering the compressor 22. In the illustrated, non-limiting embodiment, the location where the superheat of the working fluid R is controlled is arranged directly upstream from the compressor 22 and is represented by numeral 60. In an embodiment, the compressor 22 is a variable speed compressor.
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In the illustrated, non-limiting embodiment of FIG. 1, the thermal interface or connection between the vapor compression system 20 and the thermal storage device 40 is located between the expansion device 26 and the second heat exchanger 28 relative to a flow of the working fluid R. In the non-limiting embodiment of FIG. 2, the thermal coupling between the closed fluid loop of the working fluid R and the thermal storage device 40 is located upstream from the expansion device 26 and downstream from a corresponding heat exchanger operable as a condenser. In embodiments including a first and second expansion device, the thermal storage device 40 may be thermally coupled to the closed fluid loop at a location between the first and second expansion devices.
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However, embodiments where a thermal storage device 40 is arranged at another location about the vapor compression system 20 are also contemplated herein. For example, in the non-limiting embodiment of a vapor compression system 20 illustrated in FIG. 3, the thermal interface or connection between the vapor compression system 20 and a thermal storage device 40 is located between an outlet of the compressor 22 and upstream from a corresponding heat exchanger operable as a condenser relative to a direction of flow of the working fluid R in a cooling mode. In another embodiment, illustrated in FIG. 4, the thermal storage device is thermally coupled to the vapor compression system 20 at a location between the first heat exchanger 24 and the expansion device 26 relative to a direction of flow of the working fluid R in a cooling mode.
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As described with respect to the embodiment illustrated in FIGS. 1 and 2, the thermal storage device 40 may be directly thermally coupled to the vapor compression system 20, or alternatively, may be indirectly thermally coupled thereto. As shown, the thermal storage device 40 is fluidly connected to a heat exchanger 42 and a pump 44, and flow of the working fluid R is configured to pass through the heat exchanger 42. The thermal storage device 40 may be filled with a phase change material P transformable between a first phase and a second phase, such as between a solid and a liquid. In embodiments where the thermal storage device 40 is located downstream from the compressor 22 and upstream from the expansion device 26 relative to a flow of the working fluid R in a cooling mode (FIGS. 3 and 4), the phase change material P is a high-temperature melting material, such as having a transition temperature between a solid and a liquid between about 75°C and 100°C when the thermal storage device 40 is upstream from the condenser 24 or between about 30°C and 50°C when the thermal storage device 40 is downstream from the condenser 24.
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The superheat of the working fluid R of the vapor compression system 20, identified at numeral 60 in the FIGS., may be controlled to selectively store heat within (i.e., charge) or expel heat from (i.e., discharge) the thermal storage device 40. The expansion device 26 of the vapor compression system 20 may be adjusted on demand, such as by a controller 50 for example, to achieve a desired superheat of the working fluid R at the compressor 22. For example, the expansion device 26, can be adjusted to reduce the flow of the working fluid R therethrough, thereby increasing the superheat. Increasing the superheat temperature of the working fluid R at location 60 reduces the temperature of the working fluid R directly downstream from the expansion device 26. Alternatively, or in addition, the expansion device 26 can be adjusted to increase the flow of working fluid R therethrough, thereby reducing the superheat within the system 20. As a result, the temperature of the working fluid R directly downstream from the expansion device 26, directly upstream from the expansion device 26, or directly upstream from the first heat exchanger 24 when in a cooling mode may be controlled based on a desired superheat of the vapor compression system 20. Reducing the superheat temperature of the working fluid R increases the temperature of the working fluid R directly downstream from the expansion device 26.
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With continued refence to FIGS. 1 and 2, to "charge" the thermal storage device 40, the vapor compression system 20 may be operated with a first, relatively low superheat. This first superheat may be selected such that the temperature of the working fluid R directly downstream from the expansion device 26 configured to expand the working fluid R has a temperature exceeding the temperature of the storage material. In embodiments where the storage material is a phase change material, the temperature of the working fluid R exceeds the phase change temperature of the phase change material during charging (melting) of the thermal storage device 40. The vapor compression system 20 may maintain such operating parameters until a fraction or the entirety of the phase change material within the thermal storage device 40 has transformed from a first state to a second state in response to absorbing thermal energy from the working fluid R. The controller 50 may include or may be operably coupled to a sensor operable to detect when the phase change material has reached its maximum thermal storage capacity. In other embodiments, the controller 50 may simply maintain the operating conditions for a fixed period of time associated with charging the thermal storage device 40.
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To discharge heat from the thermal storage device 40, the vapor compression system 20 may be operated with a second, relatively increased superheat. As noted previously, this increased superheat may be achieved by reducing the flow of the working fluid R at a respective expansion device 26. The second superheat temperature is elevated relative to the first superheat temperature. This second superheat temperature may be selected such that the temperature of the working fluid R directly downstream from the expansion device 26 has a temperature less than the phase change temperature of the phase change material during discharging of the thermal storage device 40. Accordingly, as the working fluid R output from the expansion device 26 is arranged in thermal communication with the phase change material, heat is transferred from the phase change material to the working fluid R.
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The vapor compression system 20 may maintain such operating parameters until a fraction or the entirety of the phase change material within the thermal storage device 40 has transformed from the second state to the first state in response to releasing thermal energy to the working fluid R. As previously noted, the controller 50 may sense when the phase change material has reached a minimum thermal storage capacity and may adjust operation of the vapor compression system in response to such a determination. Alternatively, the controller 50 may maintain the operating conditions for a fixed period of time associated with fully discharging the thermal storage device 40.
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Similarly, with reference to FIG. 4, operation of the vapor compression system 20 with a first, relatively low superheat results in a temperature upstream from the expansion device 26 that exceeds the temperature of the storage material. Accordingly, the thermal storage device 40 located between the first heat exchanger 24 and the expansion device 26 may be charged when operated with a first superheat. As the superheat of the vapor compression system is increased, the temperature of the working fluid R downstream from the first heat exchanger 24 will decrease, such as to a temperature less than the phase change temperature of the phase change material of the thermal storage device 40. Accordingly, as the working fluid R output from the first heat exchanger 24 is arranged in thermal communication with the phase change material, heat is transferred from the phase change material to the working fluid R.
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With reference to FIG. 3, when operating in a cooling mode, operation of the vapor compression system 20 with a first, relatively low superheat results in a temperature downstream from the compressor 22 and upstream from the first heat exchanger 24 that is lower than the phase change temperature of the phase change material of the thermal storage device 40. Accordingly, as the working fluid R output from the compressor 22 is arranged in thermal communication with the phase change material, heat is transferred from the phase change material to the working fluid R. As the superheat of the vapor compression system is increased, the temperature of the working fluid R downstream from the first heat exchanger 24 will increase, such as to a temperature greater than the phase change temperature of the phase change material of the thermal storage device 40. Accordingly, in embodiments where the thermal storage device 40 is thermally coupled to the vapor compression circuit at a location between the compressor 22 and the first heat exchanger 24 in a cooling mode, increasing the superheat may be used to charge the thermal storage device 40.
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In an embodiment, the controller 50 may control the superheat of the vapor compression system 20, to reduce the energy required by the compressor 22. Specifically, the controller 50 can control the discharging of the thermal storage device 40 to reduce the energy required by the compressor 22.
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A vapor compression system 20 as described herein incorporates a thermal storage device in a simplified manner. Unlike existing systems which rely on complex valving and piping arrangements to direct evaporating refrigerant to solidify a phase change material and condensing refrigerant to melt a phase change material, the same flow of refrigerant is operable to both melt and solidify a phase change material without complex piping and valving.
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The term "about" is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application.
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The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof.
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While the present invention has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the present invention will include all embodiments falling within the scope of the claims.