US20220074632A1

US20220074632A1 - Outdoor unit of air conditioner

Info

Publication number: US20220074632A1
Application number: US17/464,924
Authority: US
Inventors: Mahiro Hachiya; Minoru Yoshikawa
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 2020-09-10
Filing date: 2021-09-02
Publication date: 2022-03-10
Also published as: JP2022046305A

Abstract

An outdoor unit includes a fan, a heat exchanger, a vapor pipe, a liquid pipe, and a refrigerant flowing through these pipes, in which the heat exchanger is a parallel flow heat exchanger divided into a plurality and connected in parallel between the vapor pipe and the liquid pipe. The heat exchanger is connected from the vapor pipe via a vapor branch pipe, and the heat exchanger is connected from the vapor pipe via the vapor branch pipe. In addition, the liquid pipe is connected from the heat exchanger via the liquid branch pipe, and the liquid pipe is connected from the heat exchanger via the liquid branch pipe.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a cooling device for an electronic device. In particular, it relates to an outdoor unit of an air conditioner for a data center using a refrigeration cycle.

Description of Related Art

An air conditioner that uses a refrigeration cycle, which is generally called a packaged air conditioner, is used for cooling a server room of a data center.
A large heat exchanger is used for the outdoor unit of an air conditioner, with one or two heat exchangers being installed obliquely inside the housing in order to secure a heat dissipation area. Generally, as a large heat exchanger, a serpentine heat exchanger (a heat exchanger in which flow paths of the refrigerant are connected in series) is used. The fan is installed horizontally at the upper part of the housing. The structure is such that air is taken in from the lower part of the housing and exhausted from the upper part of the housing.
However, the aforementioned structure has the following issues.
The refrigerants used in conventional air conditioners are high-pressure hydrofluorocarbons (HFCs), in which the difference between the evaporation pressure and condensation pressure is on the order of 1,000 kPa. However, with the tightening of regulations on freon gas due to global warming, there is expected to be a switch to low-pressure hydrofluoroolefins (HFOs) which have a difference between the evaporation pressure and condensation pressure on the order of 100 kPa and a maximum vapor pressure of 1,000 kPa or less.
However, in the case of a low-pressure refrigerant (for example, a fluorine compound gas having a vapor pressure of 1 MPa or less when stored and transported in a normal environment), since the amount of heat that can be moved per unit flow rate is small, despite the fact that a greater flow is required in order to obtain the required cooling capacity, a reduction of power consumption accompanying the increase in the flow rate was not given special consideration in Japanese Unexamined Patent Application Publication No. S61-128074 and Japanese Unexamined Patent Application Publication No. 2014-163530.
An object of the present invention is, for example, even when using a low-pressure refrigerant in an outdoor unit of an air conditioner used for a data center, to make the increase in compressor power arising from the increase in pressure loss in the refrigerant flow path in a heat exchanger equal to or less than that when using a high-pressure refrigerant, while maintaining the heat exchange performance of the outdoor unit.

SUMMARY OF THE INVENTION

In order to solve the above problems, the outdoor unit of the air conditioner according to the present invention is provided with a fan, a heat exchanger, a vapor pipe, a liquid pipe, and a refrigerant flowing through these pipes, in which the refrigerant is a low-pressure refrigerant, and the heat exchanger is a parallel flow heat exchanger divided into a plurality and connected in parallel between the vapor pipe and the liquid pipe.
According to the present invention, for example, in an outdoor unit of an air conditioner used for applications such as data centers, it is possible to make an increase in compressor power due to the increase in pressure loss in the refrigerant flow path in the heat exchanger equal to or less than when a high-pressure refrigerant is used while maintaining the heat exchanger performance of the outdoor unit even when a low-pressure refrigerant is used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an outdoor unit of an air conditioner according to a minimum configuration example of the present invention.

FIG. 2 is a front view showing a cross section of the outdoor unit in an air-conditioned period according to the first embodiment of the present invention.

FIG. 3 is a schematic view showing a part of a pipe connection structure in the vicinity of the heat exchanger according to the first embodiment of the present invention.

FIG. 4 is a graph showing (1) pressure loss in the refrigerant flow path in the heat exchanger, (2) a decrease in condensation temperature, and (3) an increase in compressor power during heat dissipation.

FIG. 5 is a graph showing a p-h diagram of a refrigeration cycle when a low-pressure refrigerant is used.

EXAMPLE EMBODIMENTS

The outdoor unit according to the minimum configuration example of the first aspect of the present invention will be described with reference to FIG. 1. This outdoor unit is provided with a fan 1, heat exchangers 2 a and 2 b, a vapor pipe 4, a liquid pipe 5, and a refrigerant flowing through these pipes. The refrigerant is a low-pressure refrigerant, while the heat exchangers 2 a and 2 b are parallel flow heat exchangers connected in parallel between the vapor pipe 4 and the liquid pipe 5. In the illustrated example, the heat exchanger 2 a is connected to the vapor pipe 4 via a vapor branch pipe 4 a, and the heat exchanger 2 b is connected to the vapor pipe 4 via a vapor branch pipe 4 b. Further, the liquid pipe 5 is connected to the heat exchanger 2 a via a liquid branch pipe 5 a, and the liquid pipe 5 is connected to the heat exchanger 2 b via the liquid branch pipe 5 b.
According to the above configuration, since the plurality of heat exchangers 2 a and 2 b are connected in parallel between the vapor pipe 4 and the liquid pipe 5, it is possible to reduce the pressure loss in the flow path of the refrigerant supplied to the heat exchangers 2 a and 2 b and cut the power required for the flow of the required refrigerant flow rate.

First Embodiment

The first embodiment according to the present invention will be described. FIG. 2 shows a conceptual diagram of a cross section of the outdoor unit according to the present embodiment as viewed from the front, and FIG. 3 shows a schematic diagram of a part of the piping structure in the vicinity of the heat exchangers.
The structure of the outdoor unit 10 according to the present embodiment is provided with a housing 100, a plurality of small heat exchangers 200, a vapor pipe 300 as a header for supplying a refrigerant to each small heat exchanger 200, a liquid pipe 400 as a header for collecting the refrigerant from each small heat exchanger 200, an adjusting mechanism 500, and a fan 600.
The housing 100 includes an intake port 110 at the lower part and an exhaust port 120 at the upper part. The small heat exchangers 200 are installed in two rows in a V shape when viewed from the front. That is, the small heat exchangers 200 are arranged so as to be inclined with respect to the flow direction of the intake air indicated by the arrows A in the figure and the exhaust air indicated by the arrows B in the figure.
In this embodiment, a parallel flow type small heat exchanger 200 is divided in two in the vertical direction of the housing 100 and the wind flow direction, with the refrigerant being supplied in parallel to each. This is done so that the total cross-sectional area of the refrigerant flow path inside each small heat exchanger 200 becomes about 10 times that of the conventional cross-sectional area while the flow path length becomes about 1/20^thof the conventional length in order to reduce the pressure loss of the refrigerant flow path in the heat exchanger to 1/10th or less as compared with a large serpentine heat exchanger using a conventional high-pressure refrigerant.
More specifically, the small heat exchanger 200 adopts a configuration in which an upstream heat exchanger 210 and a downstream heat exchanger 220 both having the same planar shape are stacked along the flow direction of the fan 600.
The small heat exchangers 200 are also arranged side by side in the respective surface directions of the surfaces forming the V-shape. At a position facing each small heat exchanger 200 is installed the small fan 600, which has as a drive source for example the DC power source used in a data center or the like.
Further, in the embodiment, the cooling air is supplied to each small heat exchanger 200 by a plurality of the fans 600. Further, the fans 600 are arranged in a matrix not only in the direction of the paper surface of FIG. 2 but also in the direction orthogonal to the paper surface of FIG. 2, being arranged so as to cover the entire surface of the heat exchanger 200.
Further, a plurality of vapor branch pipes 310 a and 310 b and liquid branch pipes 410 a and 410 b branch off in parallel, respectively, from the vapor pipe 300 and the liquid pipe 400. The divided heat exchangers 210 and 220 on the upwind side and downwind side are connected between the pair of vapor branch pipe 310 a and liquid branch pipe 410 a and the pair of vapor branch pipe 310 b and liquid branch pipe 410 b, whereby parallel refrigerant flow paths are formed. In each of the vapor branch pipes 310 a, 310 b, the adjusting mechanism 500, which adjusts the amount of refrigerant to be distributed to each small heat exchanger 200, such as a valve or an orifice, is installed. The fan 600 is installed near the ventilation surface of the small heat exchanger 200 so as to be parallel to the ventilation surface of the small heat exchanger 200.
The number, size, shape, and the like of the small heat exchanger 200, the adjusting mechanism 500, and the fan 600 of the outdoor unit 10 are not limited. The small heat exchanger 200 and the fan 600 are installed in a V shape when viewed from the front of the housing 100, but may also be installed in a W shape or the like. The small heat exchanger 200 is divided into two in the vertical direction and two in the wind direction of the housing 100, but the division direction may be only one direction, and the number of divisions in each direction may be three or more. The adjusting mechanism 500 is installed in all the vapor branch pipes 310 a and 310 b, but may be installed in only some of the vapor branch pipes 310 a and 310 b (for example, the adjusting mechanism 500 may be configured so as to reduce the flow rate by being installed only in those vapor branch pipes in which the flow rate is predicted to be smaller than that of other refrigerant flow paths during heat exchange). Further, the adjusting mechanism 500 may be installed in the liquid branch pipes 410 a and 410 b. Although the fan 600 is installed on the exhaust side of the small heat exchanger 200, installation is also possible on the intake side.
For example, low-pressure HFOs are adopted as the low-pressure refrigerant used in this air conditioner. This low-pressure refrigerant includes components of the refrigerant flow path of the entire air conditioner, such as a compressor, an expander, a refrigerant tank, and a pipeline connecting them. It also includes electronic components that control the air conditioner motor, valves, and the like, such as power cables and electronic boards.
A pump for circulating the refrigerant liquid, a compressor for raising the temperature of the refrigerant vapor, or the like may be provided.
The operation of the outdoor unit of the first embodiment will be described.
When the outdoor unit 10 is operated, the fan 600 starts rotating. As a result, the outside air is sucked into the inside of the housing 100 in the direction of arrows A through the intake port 110 provided at the lower part of the housing 100. Next, the outside air passes through the small heat exchanger 200. Finally, the outside air is discharged to the outside of the housing 100 in the direction of the arrows B through the exhaust port 120 provided at the upper part of the housing 100.
The refrigerant liquid heated by the indoor unit evaporates and undergoes a phase change to refrigerant vapor. The refrigerant vapor then moves from the indoor unit to the outdoor unit 10 through the vapor pipe 300, and passes through the vapor branch pipes 310 a and 310 b to be distributed to the plurality of small heat exchangers 200 (the upstream side and downstream side heat exchangers 210 and 220). By being distributed to the plurality of small heat exchangers 200 connected in parallel, the flow velocity of the refrigerant vapor flowing through the heat exchangers 210 and 220 and the vapor branch pipes 310 a and 310 b become slow.
When distributing the refrigerant to the upwind and downwind heat exchangers 210 and 220, the outside air whose temperature has risen during heat exchange by the upwind side small heat exchanger 210 is supplied to the downwind side small heat exchanger 220. In consideration of the above, the amount of refrigerant distributed to the heat exchanger 220 on the down-wind side is reduced by the adjusting mechanism 500 by an amount corresponding to the reduction in heat dissipation. The refrigerant vapor dissipates heat to the outside air via the small heat exchanger 200, condenses and changes phase to the refrigerant liquid.
The refrigerant liquid condensed by each small heat exchanger 200 collects through the liquid branch pipes 410 a and 410 b, and moves from the outdoor unit 10 to the indoor unit through the liquid pipe 400. In this way, the room is cooled by transferring heat to the outside air by utilizing the circulation of the refrigerant and the phase changing thereof. The flow rate of the refrigerant may be adjusted in response to variations in the heat dissipation amount of the plurality of heat exchangers 200 caused not only by the difference in the respective heat dissipation amounts of the heat exchangers 210 and 220 on the upstream side and downstream side, but also by the air volume and temperature distribution in the plane direction (direction of the plane orthogonal to the air flow).
According to the operation of the first embodiment, the increase in compressor power caused by the pressure loss of the refrigerant flow path in the heat exchanger can be equal to or less than that when the high pressure refrigerant is used.
In this embodiment, the small heat exchangers 200, consisting of a parallel flow type heat exchanger divided into two in the vertical direction and into two in the wind direction of the housing 100, are connected in parallel so as to distribute and collect the refrigerant to/from the heat exchangers 210 and 220 by the vapor branch pipes 310 a and 310 b and the liquid branch pipes 410 a and 410 b.
As a result, even when using a low-pressure refrigerant, an increase in compressor power was eliminated by reducing the pressure loss of the refrigerant flow path in the heat exchanger to 1 kPa, which is 1/10 of the conventional loss, with the same heat dissipation capacity as a conventional serpentine heat exchanger, and suppressing the drop in condensation temperature to 0.1° C. Refer in FIG. 4 to the bar graph with the dotted hatching. FIG. 4 is an example of a graph that compares, when dissipating heat equivalent to 40 kW, (1) pressure loss of the refrigerant flow path in the heat exchanger, (2) the amount of decrease in condensation temperature, and (3) the amount of increase in compressor power. FIG. 5 is a schematic diagram of a p-h diagram of a refrigeration cycle when a low-pressure refrigerant is used.
In the case of a combination of a conventional large serpentine heat exchanger and a high-pressure refrigerant (bar graph with diagonal line hatching in FIG. 4), the pressure loss of the refrigerant flow path in the heat exchanger is 9 kPa, and the condensation temperature drops only 0.1° C. Therefore, the compressor power hardly increases.
However, when the refrigerant is changed to a low-pressure refrigerant (bar graph with horizontal line hatching in FIG. 4), the low-pressure refrigerant has a smaller latent heat of vaporization and vapor density than the high-pressure refrigerant, so even if the amount of heat dissipation is the same, the flow rate of the refrigerant vapor is about 10 times higher. Due to this, the pressure loss of the refrigerant flow path in the heat exchanger increases to 115 kPa, and the condensation temperature decreases by 11.6° C. For this reason, it is necessary to additionally raise the temperature by the amount of decrease in the condensation temperature, and so the compressor power increases by 2.1 kW (FIG. 5).
While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims.
According to the present invention, it is possible to reduce the compressor power caused by an increase in the pressure loss of the refrigerant flow path in the heat exchanger, so that it is possible to provide an outdoor unit using a low pressure refrigerant.
Priority is claimed on Japanese Patent Application No. 2020-152273, filed Sep. 10, 2020, the content of which is incorporated herein by reference.

Claims

What is claimed is:

1. An outdoor unit comprising a fan, a heat exchanger, a vapor pipe, a liquid pipe, and a refrigerant flowing through these pipes, wherein the refrigerant is a low-pressure refrigerant, and the heat exchanger is a parallel flow heat exchanger divided into a plurality and connected in parallel between the vapor pipe and the liquid pipe.

2. The outdoor unit according to claim 1, wherein the number of divisions of the heat exchanger and the flow path length of the refrigerant flow path in the heat exchanger are determined so that the pressure loss of the refrigerant flow path in the heat exchanger is 1 kPa or less.

3. The outdoor unit according to claim 1, wherein the heat exchanger is divided in the wind direction.

4. The outdoor unit according to claim 1, further provided with a mechanism for adjusting the flow rate of the refrigerant to be distributed to the plurality of heat exchangers connected in parallel according to the amount of heat dissipated from each of the heat exchangers.

5. The outdoor unit according to claim 3, comprising:

a plurality of heat exchangers that perform heat exchange on supplied refrigerant with air to be cooled and discharge the refrigerant;

a supply header pipe that supplies the refrigerant to each of these heat exchangers;

a discharge header pipe that collects the refrigerant discharged from each of these heat exchangers;

a supply branch pipe that connects the supply header pipe and each of the plurality of heat exchangers;

a discharge branch pipe that connects the discharge header pipe and each of the plurality of heat exchangers; and

with respect to the flow path resistance from the supply header pipe to the exhaust header pipe of a heat exchanger on the upstream side in the flow direction of the air to be cooled, a flow path adjusting unit that performs adjustment so that the flow path resistance from the supply header pipe to the discharge header pipe of a heat exchanger on the downstream side increases.

6. The outdoor unit according to claim 3, comprising:

7. The outdoor unit according to claim 5, wherein a plurality of fans are arranged along a surface intersecting the passing direction of the air to be cooled in the heat exchanger.