Fin type heat exchanger, heat exchange assembly and air-cooled heat pump unit

Abstract

The embodiment of the utility model discloses a fin type heat exchanger, a heat exchange assembly and an air-cooled heat pump unit, and belongs to the field of heat exchange, a heat exchange space with six side faces is used for heat exchange, and the problem that the heat exchange efficiency is low is solved. The heat exchanger comprises at least two heat exchange units in the same shape, each heat exchange unit comprises at least two heat exchange parts, and all the heat exchange units are symmetrically arranged so as to define a hexagonal prism-shaped heat exchange space based on all the heat exchange parts.

Description

Technical Field

[0001] This application relates to the field of heat exchange, and more particularly to a finned heat exchanger, heat exchange components, and an air-cooled heat pump unit. Background Technology

[0002] Air-cooled heat pump units offer advantages such as high equipment utilization and energy efficiency, and are widely used in commercial and residential buildings. These units provide cooling and heating for both buildings and residences. Current air-cooled heat pump units typically employ finned heat exchangers with heat exchange on four sides. However, this design results in a relatively small heat exchange area per unit volume within the ventilated area, leading to lower heat exchange efficiency. Therefore, under certain heat exchange area requirements, this results in a relatively large unit size, leading to higher manufacturing and transportation costs, and ultimately failing to meet user needs. Utility Model Content

[0003] This application provides a finned heat exchanger, a heat exchange component, and an air-cooled heat pump unit for heat exchange.

[0004] The first aspect of this application provides a finned heat exchanger, including at least two heat exchange units of the same shape, each heat exchange unit including at least two heat exchange sections, and all the heat exchange units are symmetrically arranged to form a hexagonal prism-shaped heat exchange space based on all the heat exchange sections.

[0005] Optionally, if the number of heat exchange units is two, each heat exchange unit includes a first heat exchange section, a second heat exchange section, and a third heat exchange section. The first heat exchange section and the second heat exchange section are arranged at an obtuse angle, and the second heat exchange section and the third heat exchange section are arranged at an obtuse angle. The first heat exchange section, the second heat exchange section, and the third heat exchange section are connected to form a U-shaped three-dimensional structure.

[0006] Optionally, if the number of heat exchange units is four, each heat exchange unit includes a first heat exchange section and a second heat exchange section, the first heat exchange section and the second heat exchange section being arranged at an obtuse angle; the first heat exchange section and the second heat exchange section are connected to form an L-shaped three-dimensional structure.

[0007] The second aspect of this application provides a heat exchange assembly, including the finned heat exchanger as described above, and further including: a top frame, side plates, a water receiving tray, a chassis, and multiple columns;

[0008] The top frame, the water receiving tray, and the side plates are hexagonal in shape to fit the finned heat exchanger. The top frame is located on the top surface of the finned heat exchanger, the water receiving tray is located on the bottom surface of the finned heat exchanger, and the side plates are vertically located between the side of the top frame and the side of the water receiving tray. The side plates are used to fix the junctions between different heat exchange units of the finned heat exchanger, forming a heat exchange space.

[0009] The water receiving tray, the multiple uprights, and the chassis constitute the component installation space;

[0010] The top frame, the water receiving tray, and the base are detachably fixed to the multiple columns from top to bottom.

[0011] Optionally, the component mounting space and the heat exchange space are arranged in an upper and lower structure.

[0012] Optionally, the chassis is rectangular in shape, and the area of ​​the chassis is smaller than the area of ​​the top frame.

[0013] Optionally, the chassis is square in shape, and the area of ​​the chassis is smaller than the area of ​​the top frame.

[0014] Optionally, the heat exchange assembly further includes: a fan assembly;

[0015] The top frame is provided with through holes adapted to the fan assembly, the fan assembly is fixed in the through holes, and the fan assembly is used to promote the flow of air in the heat exchange space.

[0016] Optionally, the number of the wind turbine components may be one or more.

[0017] The third aspect of this application provides an air-cooled heat pump unit, including a plurality of heat exchange components as described above, and further including: a base;

[0018] Multiple heat exchange components are arranged parallel to each other and close to each other on the base in the width direction of the heat exchange components. The heat exchange spaces of the multiple heat exchange components form a triangular space to improve heat exchange efficiency. The component installation spaces of the multiple heat exchange components form a cuboid maintenance space, which is used for system maintenance.

[0019] As can be seen from the above technical solutions, the embodiments of this application have the following advantages:

[0020] The finned heat exchanger of this application includes at least two heat exchange units, which form a hexagonal prism-shaped heat exchange space, i.e., six sides are used for heat exchange. Compared with the existing solution, the heat exchange area is larger and the heat exchange efficiency is higher, which meets the user's needs.

[0021] The heat exchange component of this application is divided into two parts: a heat exchange space and a component installation space. The hexagonal prism-shaped heat exchange space can perform heat exchange treatment on the hot air entering the heat exchange space, while the component installation space can place heat exchange-related devices. When these related devices need to be repaired, maintenance personnel can easily repair the related devices in the component installation space, which brings great convenience to maintenance personnel.

[0022] The air-cooled heat pump unit of this application includes multiple heat exchange components. The heat exchange spaces of these components form a triangular space that gradually expands from the inside out, which facilitates gas reception and heat exchange, thereby improving heat exchange efficiency. The component installation spaces of the multiple heat exchange components form a cuboid maintenance space, providing maintenance personnel with sufficient space to repair related components and facilitating system maintenance. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a finned heat exchanger disclosed in this application;

[0024] Figure 2 This is a schematic diagram of a finned heat exchanger with two heat exchange units disclosed in this application;

[0025] Figure 3 This is a schematic diagram of a finned heat exchanger with four heat exchange units disclosed in this application;

[0026] Figure 4 This is a schematic diagram of an embodiment of a heat exchange component disclosed in this application;

[0027] Figure 5 This is a top view of a heat exchange component disclosed in this application;

[0028] Figure 6 This is a schematic diagram of another embodiment of a heat exchange component disclosed in this application;

[0029] Figure 7 This is an overall schematic diagram of an air-cooled heat pump unit disclosed in this application;

[0030] Figure 8 This is a top view of an air-cooled heat pump unit disclosed in this application;

[0031] Figure 9 This is a front view of an air-cooled heat pump unit disclosed in this application. Detailed Implementation

[0032] The present application is further described in detail below with reference to the accompanying drawings.

[0033] This application provides a finned heat exchanger, a heat exchange component, and an air-cooled heat pump unit for heat exchange.

[0034] Existing air-cooled heat pump unit designs typically employ four heat exchange surfaces with heights close to the unit's overall height. However, only four sides are used for heat exchange. Furthermore, system components housed in the lower part of the unit obstruct the heat exchange channels beneath these surfaces, resulting in a small heat exchange area, higher cost, and lower efficiency. Additionally, when the unit is integrated, maintenance requires opening the side panels, which are often cramped, hindering component placement and maintenance, and also consuming considerable space. To address these issues, this application provides a finned heat exchanger, heat exchange components, and an air-cooled heat pump unit that utilizes six sides for heat exchange, improving efficiency. The unit features a vertical structure, with the upper section providing the heat exchange space and the lower section serving as the component system installation space, ensuring high heat exchange efficiency while facilitating component placement and maintenance. This application significantly improves heat exchange efficiency and simplifies system maintenance, providing users with considerable convenience.

[0035] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0036] The terms "first," "second," "third," "fourth," etc., used in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0037] The following describes a finned heat exchanger according to this application. Please refer to... Figure 1 One embodiment of a finned heat exchanger according to this application includes at least two heat exchange units 51 of the same shape. Each heat exchange unit 51 includes at least two heat exchange sections. All heat exchange units 51 are symmetrically arranged to form a hexagonal prism-shaped heat exchange space 7 based on all heat exchange sections. Specifically, the number of heat exchange units 51 can be greater than or equal to two, and the shape of the heat exchange units 51 is not limited; all heat exchange units 51 can have the same shape, which can be set according to actual needs and is not limited here. The number of heat exchange sections in each heat exchange unit 51 is also at least two, and can be two, three, etc., and is not limited here. Connecting the heat exchange sections of each heat exchange unit 51 can form a hexagonal prism-shaped heat exchange space 7.

[0038] The working principle is as follows: external gas passes through the heat exchange section of heat exchange unit 51 to the heat exchange space 7 inside finned heat exchanger 5 for heat exchange. External gas can enter the heat exchange space 7 from six sides and is discharged after heat exchange is completed.

[0039] In this embodiment, the finned heat exchanger 5 includes at least two heat exchange units 51, which form a hexagonal prism-shaped heat exchange space 7, i.e., six sides are used for heat exchange. Compared with the existing solution, the heat exchange area is larger and the heat exchange efficiency is higher, which meets the user's needs.

[0040] The number of heat exchange units 51 can be set according to actual needs. For ease of understanding, the following explanation assumes that the number of heat exchange units 51 is two or four. If the number of heat exchange units 51 is two, please refer to [link to relevant documentation]. Figure 2 In another embodiment of the finned heat exchanger of this application, each heat exchange unit 51 includes three heat exchange sections, and two heat exchange units 51 are symmetrically arranged to form a hexagonal prism-shaped heat exchange space 7 based on a total of six heat exchange sections. Each heat exchange unit 51 includes a first heat exchange section 511, a second heat exchange section 512, and a third heat exchange section 513. The first heat exchange section 511 and the second heat exchange section 512 are arranged at obtuse angles, and the second heat exchange section 512 and the third heat exchange section 513 are also arranged at obtuse angles. The first heat exchange section 511, the second heat exchange section 512, and the third heat exchange section 513 are connected to form a U-shaped three-dimensional structure. Specifically, the aforementioned obtuse angles can be set according to actual needs, as long as they can form a hexagonal prism. In one embodiment, all obtuse angles can be set to 120 degrees, making the heat exchange space 7 a regular hexagonal prism.

[0041] The working principle is similar to that of the above embodiments, and will not be described again here.

[0042] In this embodiment, the finned heat exchanger 5 includes two heat exchange units 51, which are symmetrically arranged to form a hexagonal prism-shaped heat exchange space 7, that is, six sides are used for heat exchange. Compared with the existing solution, the heat exchange area is larger and the heat exchange efficiency is higher, which meets the user's needs.

[0043] If the number of heat exchange units 51 is four, please refer to Figure 3In another embodiment of the finned heat exchanger of this application, each heat exchange unit 51 includes two heat exchange sections, and four heat exchange units 51 are symmetrically arranged in pairs to form a hexagonal prism-shaped heat exchange space 7 based on a total of eight heat exchange sections. Each heat exchange unit 51 includes a first heat exchange section 511 and a second heat exchange section 512, which are arranged at obtuse angles. The first heat exchange section 511 and the second heat exchange section 512 are connected to form an L-shaped three-dimensional structure. Specifically, the obtuse angles can be set according to actual needs, as long as they can form a hexagonal prism. In one embodiment, all obtuse angles can be set to 120 degrees, making the heat exchange space 7 a regular hexagonal prism.

[0044] The working principle is similar to that of the above embodiments, and will not be described again here.

[0045] In this embodiment, the finned heat exchanger 5 includes four heat exchange units 51. The four heat exchange units 51 are arranged symmetrically in pairs to form a hexagonal prism-shaped heat exchange space 7, that is, there are six sides for heat exchange. Compared with the existing solution, the heat exchange area is larger and the heat exchange efficiency is higher, which meets the user's needs.

[0046] A heat exchange component according to this application is described below. Please refer to... Figure 4 One embodiment of a heat exchange component of this application includes: a top frame 1, a side plate 52, a water receiving tray 2, a chassis 3, multiple columns 4, and the aforementioned finned heat exchanger 5;

[0047] The top frame 1, the water receiving tray 2, and the side plate 52 are hexagonal in shape to fit the finned heat exchanger 5. The top frame 1 is disposed on the top surface of the finned heat exchanger 5, the water receiving tray 2 is disposed on the bottom surface of the finned heat exchanger 5, and the side plate 52 is vertically disposed between the side of the top frame 1 and the side of the water receiving tray 2. The side plate 52 is used to fix the junction between different heat exchange units of the finned heat exchanger 5, forming a heat exchange space 7.

[0048] The water receiving tray 2, the multiple uprights 4, and the chassis 3 constitute the component installation space 8;

[0049] The top frame 1, the water receiving tray 2, and the base 3 are detachably fixed to the multiple columns 4 from top to bottom.

[0050] In this embodiment, the heat exchange assembly is divided into two parts: a heat exchange space 7 and a component mounting space 8. The hexagonal prism-shaped heat exchange space 7 can exchange heat with the hot air entering it, while the component mounting space 8 can house related components and provide sufficient space for maintenance personnel to perform repairs. This allows maintenance personnel to perform repairs in a sufficiently spacious environment, greatly facilitating their work.

[0051] Please see Figures 1 to 6 Another embodiment of a heat exchange component of this application includes: a top frame 1, a water receiving tray 2, a chassis 3, multiple columns 4, a side plate 52, a finned heat exchanger 5, and a fan assembly 6;

[0052] The top frame 1, the water receiving tray 2, and the side plate 52 are hexagonal in shape to fit the finned heat exchanger 5. The top frame 1 is disposed on the top surface of the finned heat exchanger 5, the water receiving tray 2 is disposed on the bottom surface of the finned heat exchanger 5, and the side plate 52 is vertically disposed between the side of the top frame 1 and the side of the water receiving tray 2. The side plate 52 is used to fix the junction between different heat exchange units of the finned heat exchanger 5, forming a heat exchange space 7.

[0053] The water receiving tray 2, the multiple uprights 4, and the chassis 3 constitute the component installation space 8;

[0054] The top frame 1, the water receiving tray 2, and the base 3 are detachably fixed to the multiple columns 4 from top to bottom.

[0055] The relative positions of the component mounting space 8 and the heat exchange space 7 can be set according to actual needs, and are not limited here. In this embodiment, the component mounting space 8 and the heat exchange space 7 are an upper and lower structure. For ease of description, in one embodiment, the heat exchange space 7 is located above the component mounting space 8.

[0056] Specifically, in this embodiment, the heat exchange space 7 is in the shape of a right hexagonal prism. The top frame 1 is the top of the heat exchange component body, the base 9 is the bottom of the heat exchange component body, and the water receiving tray 2 is set in the middle, dividing the heat exchange component body into the heat exchange space 7 and the component installation space 8. The planes on which the top frame 1, the water receiving tray 2, and the base 3 are located are parallel to each other.

[0057] The fan assembly 6 of the heat exchange component is disposed on the top of the main body of the heat exchange component. Specifically, the top frame 1 is provided with a through hole adapted to the fan assembly 6, and the fan assembly 6 is fixed in the through hole. The fan assembly 6 is used to promote the airflow in the heat exchange space 7. The number of fan assemblies 6 can be one or more, which can be set according to actual needs. For ease of description, this embodiment uses two fan assemblies 6 for illustration.

[0058] It is understandable that there are multiple implementations of the finned heat exchanger 5. The finned heat exchanger 5 can be fixed to the top frame 1 and the water tray 2, or fixed to the columns 4. The specific implementation is not limited here. One implementation is that the side plate 52 is fixedly connected between the side of the top frame 1 and the side of the water tray 2, and at least one heat exchange unit 51 is connected to the at least one side plate 52. Simply put, a side plate 52 is provided on the side, and multiple heat exchange units 51 are fixed to the side plate 52. Another implementation is that at least one heat exchange unit 51 is fixedly connected to the multiple columns 4. Simply put, the heat exchange unit 51 is directly fixed to the columns 4. For ease of description, this embodiment will describe the first implementation, that is, fixing the heat exchange unit 51 by the side plate 52.

[0059] It is understood that the number of heat exchange units 51 can be set according to actual needs, and is not limited here, as can be seen in the relevant description of the above embodiments. In this embodiment, four heat exchange units 51 are used as an example. Simply put, the heat exchange unit 51 is an L-shaped three-dimensional structure, in which two side plates 52 are symmetrically distributed along the length direction of the heat exchange space 7, and the other two side plates 52 are symmetrically distributed along the width direction of the heat exchange space 7. One side of each heat exchange unit 51 is fixedly connected to one side plate 52 in the length direction, and the other side is fixedly connected to one of the side plates 52 in the width direction, so as to enclose and form the heat exchange space 7. Simply put, in the figure, two of the four side plates 52 are symmetrically distributed left and right, and two are symmetrically distributed top and bottom. The four heat exchange units 51 are distributed at the four corners, and the eight of them can be assembled to form the heat exchange space 7.

[0060] To save floor space, the chassis 3 does not need to have the same bottom shape as the heat exchange space 7. It can be set to any space-saving shape according to actual needs, and no specific limitation is made here. Specifically, in one embodiment, the chassis 3 can be set to a rectangular shape, and the area of ​​the chassis 3 is smaller than the area of ​​the top frame 1. In another embodiment, the chassis 3 can be set to a square shape, and the area of ​​the chassis 3 is smaller than the area of ​​the top frame 1. For ease of description, this embodiment will be described using the first embodiment, i.e., a rectangle.

[0061] The working principle of the heat exchange component in this embodiment is described below with an example. Please refer to [link / reference]. Figures 1 to 6 The top frame 1 and water tray 2 of the heat exchange assembly are hexagonal, and the heat exchange space 7 is a right hexagonal prism. The four heat exchange units 51 of the heat exchange assembly can absorb heat from the external space into the heat exchange space 7 from six sides, and the heat is treated by the fan assembly 6 in operation. The water tray 2 enables the heat exchange space 7 to form a relatively sealed space to improve heat exchange efficiency. The lower component installation space 8 can place heat exchange-related devices and provide sufficient space for maintenance.

[0062] In this embodiment, the heat exchange assembly is divided into two parts: an upper heat exchange space 7 and a lower component mounting space 8. The heat exchange space 7, which is shaped like a right hexagonal prism, can exchange heat with the hot air entering it. The component mounting space 8 can house related devices and also provide sufficient space for maintenance personnel to perform repairs. This allows maintenance personnel to perform repairs in a sufficiently spacious environment, greatly facilitating their work.

[0063] The above describes a heat exchange component according to an embodiment of this application. The following describes a heat exchange unit according to an embodiment of this application. Please refer to... Figures 7 to 9 One embodiment of a heat exchange unit in this application includes: a plurality of heat exchange components of the aforementioned embodiments, and further includes: a base 9;

[0064] Multiple heat exchange components are arranged parallel to each other and close to each other on the base 9 in the width direction of the heat exchange components. A triangular space 10 is formed between the heat exchange spaces 7 of the multiple heat exchange components to improve heat exchange efficiency. A cuboid maintenance space 11 is formed between the component installation spaces 8 of the multiple heat exchange components. The maintenance space 11 is used for system maintenance.

[0065] Specifically, when the top frame 1 of the heat exchange assembly is hexagonal (and the heat exchange space 7 is a right hexagonal prism), a triangular space 10 is formed between the heat exchange spaces 7, gradually increasing in size from the inside out to improve heat exchange efficiency. The cuboid maintenance space 11 formed between the component mounting spaces 8 also facilitates maintenance personnel. For details on the specific structure of the heat exchange assembly, please refer to the aforementioned embodiments and... Figures 1 to 6 This will not be elaborated upon here.

[0066] The working principle of the heat exchange unit in this embodiment is as follows: When the external ambient air is hot, the heat exchange unit is activated. Hot air passes through the heat exchange unit 51 of each heat exchange component to the heat exchange space 7. All the fan components 6 perform heat exchange treatment and exhaust the hot air. The lower component installation space 8 can place related devices. The component installation space 8 and the maintenance space 11 facilitate maintenance work by maintenance personnel.

[0067] In this embodiment, the heat exchange unit can form a space that gradually increases in size from the inside out, making it easier for hot air to enter the heat exchange space 7 through the heat exchange unit 51 of the heat exchange components to achieve heat exchange and improve heat exchange efficiency. On the other hand, the component installation space 8 and the maintenance space 11 between the component installation spaces 8 also increase the activity space for maintenance personnel, improve the maintenance efficiency of maintenance personnel, and bring convenience to maintenance personnel.

[0068] In the embodiments provided in this application, it should be understood that the disclosed systems or devices can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. The indirect coupling or communication connection of devices or units may be electrical, mechanical, or other forms.

[0069] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0070] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0071] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this invention.

Claims

1. A finned heat exchanger, characterized in that, It includes at least two heat exchange units of the same shape, each heat exchange unit including at least two heat exchange sections, and all the heat exchange units are symmetrically arranged to form a hexagonal prism heat exchange space based on all the heat exchange sections.

2. The finned heat exchanger according to claim 1, characterized in that, If the number of heat exchange units is two, each heat exchange unit includes a first heat exchange section, a second heat exchange section, and a third heat exchange section. The first heat exchange section and the second heat exchange section are arranged at an obtuse angle, and the second heat exchange section and the third heat exchange section are arranged at an obtuse angle. The first heat exchange section, the second heat exchange section, and the third heat exchange section are connected to form a U-shaped three-dimensional structure.

3. The finned heat exchanger according to claim 1, characterized in that, If the number of heat exchange units is four, each heat exchange unit includes a first heat exchange section and a second heat exchange section, wherein the first heat exchange section and the second heat exchange section are arranged at an obtuse angle; the first heat exchange section and the second heat exchange section are connected to form an L-shaped three-dimensional structure.

4. A heat exchange component, characterized in that, The finned heat exchanger as described in any one of claims 1 to 3 further includes: a top frame, side plates, a water receiving tray, a base, and multiple columns; The top frame, the water receiving tray, and the side plates are hexagonal in shape to fit the finned heat exchanger. The top frame is located on the top surface of the finned heat exchanger, the water receiving tray is located on the bottom surface of the finned heat exchanger, and the side plates are vertically located between the side of the top frame and the side of the water receiving tray. The side plates are used to fix the junctions between different heat exchange units of the finned heat exchanger, forming a heat exchange space. The water receiving tray, the multiple uprights, and the chassis constitute the component installation space; The top frame, the water receiving tray, and the base are detachably fixed to the multiple columns from top to bottom.

5. The heat exchange assembly according to claim 4, characterized in that, The component installation space and the heat exchange space are arranged in an upper and lower structure.

6. The heat exchange assembly according to claim 4, characterized in that, The chassis is rectangular in shape, and the area of ​​the chassis is smaller than the area of ​​the top frame.

7. The heat exchange assembly according to claim 4, characterized in that, The chassis is square in shape, and the area of ​​the chassis is smaller than the area of ​​the top frame.

8. The heat exchange assembly according to claim 4, characterized in that, The heat exchange assembly also includes: a fan assembly; The top frame is provided with through holes adapted to the fan assembly, the fan assembly is fixed in the through holes, and the fan assembly is used to promote the flow of air in the heat exchange space.

9. The heat exchange assembly according to claim 8, characterized in that, The number of wind turbine components is one or more.

10. An air-cooled heat pump unit, characterized in that, The device includes multiple heat exchange components as described in any one of claims 4 to 9, and further includes: a base; Multiple heat exchange components are arranged parallel to each other and close to each other on the base in the width direction of the heat exchange components. The heat exchange spaces of the multiple heat exchange components form a triangular space to improve heat exchange efficiency. The component installation spaces of the multiple heat exchange components form a cuboid maintenance space, which is used for system maintenance.

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