EP4597005A1

EP4597005A1 - Heat source unit and air conditioning device

Info

Publication number: EP4597005A1
Application number: EP23872363.9A
Authority: EP
Inventors: Hiroki Andou; Shota AZUMA; Hiromune Matsuoka; Seisuke ITOU
Original assignee: Daikin Industries Ltd
Current assignee: Daikin Industries Ltd
Priority date: 2022-09-30
Filing date: 2023-09-26
Publication date: 2025-08-06
Also published as: EP4597005A4; US20250224122A1; JP2025010623A; CN119895213A; WO2024071140A1

Abstract

There is proposed a heat source unit of an air conditioner that suppresses occurrence of pressure abnormality in a refrigerant flow path due to filled carbon dioxide refrigerant becoming supercritical. The heat source unit is connected to a utilization unit and constitutes the air conditioner. The heat source unit includes a compressor, a heat source heat exchanger, a first shutoff valve, a second shutoff valve, a refrigerant flow path, and a refrigerant. The refrigerant flow path is a flow path in which the compressor, the heat source heat exchanger, the first shutoff valve, and the second shutoff valve are connected by a refrigerant pipe. The refrigerant flow path is filled with the refrigerant. The refrigerant includes carbon dioxide. A filling amount V1 (kg) of the refrigerant filled in the refrigerant flow path, a volume V2 (L) of the refrigerant flow path, and a design pressure P (MPa) of the refrigerant flow path satisfy the following relationship. V1 × a ≤ V2 ≤ V1 × b, a = 0.078 × P² - 2.111 × P + 15.771, and b = 0.055 × P² - 1.768 × P + 16.144

Description

TECHNICAL FIELD

The present disclosure relates to a heat source unit and an air conditioner.

BACKGROUND ART

An air conditioner using carbon dioxide as a refrigerant is known. Patent Literature 1 ( JP 2008-045769 A ) discloses a method for filling a carbon dioxide refrigerant for the purpose of improving the efficiency of installation work of an air conditioner.
In order to further improve the efficiency of installation work of the air conditioner, a technique is known in which a heat source unit (outdoor unit) is filled with a refrigerant in advance in a manufacturing factory, and a refrigerant circuit is filled with the refrigerant by connecting the heat source unit and a utilization unit (indoor unit) at an installation site.

SUMMARY OF THE INVENTION

When carbon dioxide is used as the refrigerant to be filled in the outdoor unit in advance, the refrigerant in a refrigerant flow path may become supercritical due to an increase in outside air temperature. Since the pressure of the supercritical refrigerant rapidly increases, there is a possibility that pressure abnormality occurs in the refrigerant flow path.
The present disclosure proposes a heat source unit of an air conditioner that suppresses occurrence of pressure abnormality in a refrigerant flow path due to filled carbon dioxide refrigerant becoming supercritical.

A heat source unit according to a first aspect is connected to a utilization unit and constitutes an air conditioner. The heat source unit includes a compressor, a heat source heat exchanger, a first shutoff valve, a second shutoff valve, a refrigerant flow path, and a refrigerant. The refrigerant flow path is a flow path in which the compressor, the heat source heat exchanger, the first shutoff valve, and the second shutoff valve are connected by a refrigerant pipe. The refrigerant flow path is filled with the refrigerant. The refrigerant includes carbon dioxide.
A filling amount V1 (kg) of the refrigerant filled in the refrigerant flow path, a volume V2 (L) of the refrigerant flow path, and a design pressure P (MPa) of the refrigerant flow path satisfy the following relationship. $V 1 \times a \leq V 2 \leq V 1 \times b$ $a = 0.078 \times P^{2} - 2.111 \times P + 15.771$ $b = 0.055 \times P^{2} - 1.768 \times P + 16.144$
The heat source unit suppresses occurrence of pressure abnormality in the refrigerant flow path due to the filled carbon dioxide refrigerant becoming supercritical.
A heat source unit according to a second aspect is the heat source unit according to the first aspect, in which a design pressure P is 10 MPa or more and 14 MPa or less.
A heat source unit according to a third aspect is the heat source unit according to the first or second aspect, and further includes a refrigerant storage container that stores the refrigerant.
A volume V3 (L) of the refrigerant storage container satisfies the following relationship. $0.4 \times V 2 \leq V 3 < 0.9 \times V 2$
Since the heat source unit can store the refrigerant not only in the refrigerant flow path but also in the refrigerant storage container in the refrigerant flow path, the volume V2 can be sufficiently secured to effectively suppress the occurrence of pressure abnormality in the refrigerant flow path.
A heat source unit according to a fourth aspect is the heat source unit according to any of the first to third aspects, and further includes a flow path switching mechanism and a refrigerant storage container. The flow path switching mechanism switches a direction in which the refrigerant flows in the refrigerant flow path. The refrigerant storage container is a container that stores the refrigerant.
The refrigerant storage container can store not only the filled refrigerant but also a surplus refrigerant generated due to a change in an operation load generated between a cooling operation and a heating operation.
An air conditioner according to a fifth aspect includes the heat source unit according to any of the first to fourth aspects and the utilization unit. The utilization unit is connected to the heat source unit via a connecting pipe. The connecting pipe has a length that is changed in accordance with installation positions of the heat source unit and the utilization unit, and has a first length that does not require additional filling of the refrigerant into the refrigerant circuit formed by connecting the heat source unit and the utilization unit via the connecting pipe. The heat source unit is filled with an amount of refrigerant corresponding to the required refrigerant amount in the refrigerant circuit when the connecting pipe has the first length.
An air conditioner according to a sixth aspect includes the heat source unit according to any of the first to fourth aspects and the utilization unit. The utilization unit is connected to the heat source unit via a connecting pipe. The length of the connecting pipe is changed in accordance with the installation positions of the heat source unit and the utilization unit. The filling amount of refrigerant filled in the refrigerant flow path of the heat source unit is more than the required refrigerant amount in the refrigerant circuit formed by connecting the heat source unit and the utilization unit via the connecting pipe when the connecting pipe is shorter than the predetermined first length.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of an air conditioner 1 including a heat source unit 2 according to a first embodiment.
FIG. 2 is a Mollier diagram of R32.
FIG. 3 is a Mollier diagram of carbon dioxide.
FIG. 4 is a schematic configuration diagram of an air conditioner 1a including a heat source unit 2a according to a second embodiment.

DESCRIPTION OF EMBODIMENTS

(1) Overall configuration

FIG. 1 is a schematic configuration diagram of an air conditioner 1 including a heat source unit 2 according to a first embodiment. The air conditioner 1 performs a vapor compression refrigeration cycle operation and executes an air conditioning operation (a cooling operation and a heating operation) in an air conditioning target space (not illustrated) such as an indoor space. The air conditioner 1 includes one heat source unit 2, one utilization unit 3, and a first connecting pipe 6 and a second connecting pipe 7 that connect the heat source unit 2 and the utilization unit 3. The heat source unit 2, the utilization unit 3, and the connecting pipes 6 and 7 connected to each other constitute a refrigerant circuit 10. A refrigerant filled in the refrigerant circuit 10 includes carbon dioxide. Hereinafter, the first connecting pipe 6 and the second connecting pipe 7 are also collectively referred to as connecting pipes 6 and 7.
Although details will be described later, the refrigerant to be filled in the refrigerant circuit 10 is filled in the heat source unit 2 in a manufacturing factory or the like. The heat source unit 2 and the utilization unit 3 are connected to each other via the connecting pipes 6 and 7 at an installation site of the air conditioner 1 or the like, and thus, the refrigerant circuit 10 is filled with the refrigerant filled in the heat source unit 2.

(2) Detailed configuration

(2-1) Utilization unit

The utilization unit 3 is installed in the air conditioning target space. The utilization unit 3 includes a utilization refrigerant flow path 30 constituting a part of the refrigerant circuit 10. The utilization refrigerant flow path 30 includes a utilization heat exchanger 31.

(2-1-1) Utilization heat exchanger

The utilization heat exchanger 31 exchanges heat between the refrigerant flowing inside and air in the air conditioning target space. The utilization heat exchanger 31 has one end connected to the first connecting pipe 6 via a refrigerant pipe 30a. The other end of the utilization heat exchanger 31 is connected to the second connecting pipe 7 via the refrigerant pipe 30a.

(2-2) Heat source unit

The heat source unit 2 is installed outside the air conditioning target space (outdoor space or the like). The heat source unit 2 includes a heat source refrigerant flow path 20 constituting a part of the refrigerant circuit 10. The heat source refrigerant flow path 20 includes a compressor 21, a flow path switching mechanism 22, a heat source heat exchanger 23, a heat source expansion mechanism 24, a first shutoff valve 25, a second shutoff valve 26, and an accumulator 27. The compressor 21, the flow path switching mechanism 22, the heat source heat exchanger 23, the heat source expansion mechanism 24, the first shutoff valve 25, the second shutoff valve 26, and the accumulator 27 are connected to each other via a refrigerant pipe 20a. The heat source refrigerant flow path 20 is an example of a refrigerant flow path.

(2-2-1) Compressor

The compressor 21 sucks a low-pressure refrigerant in a refrigeration cycle from a suction pipe 21a, compresses the refrigerant by a compression mechanism (not illustrated), and discharges the compressed refrigerant as a high-pressure refrigerant to a discharge pipe 21b. In the present embodiment, the heat source unit 2 includes only one compressor 21, but in some embodiments, the number of compressors 21 is not limited to one and may be plural. The activation, stop, and capacity control of the compressor 21 can be performed by a control unit (not illustrated).

(2-2-2) Flow path switching mechanism

The flow path switching mechanism 22 switches a flow direction of the refrigerant and changes a state of the refrigerant circuit 10 between a first state and a second state. When the refrigerant circuit 10 is in the first state, the heat source heat exchanger 23 functions as a radiator for the refrigerant, and the utilization heat exchanger 31 functions as an evaporator for the refrigerant. When the refrigerant circuit 10 is in the second state, the heat source heat exchanger 23 functions as an evaporator for the refrigerant, and the utilization heat exchanger 31 functions as a radiator for the refrigerant. The state of the flow path switching mechanism 22 can be changed by a control unit (not illustrated).
In the present embodiment, the flow path switching mechanism 22 is a four-way switching valve having four ports P1, P2, P3, and P4. The port P1 is connected to one end of the heat source heat exchanger 23. The port P2 is connected to the discharge pipe 21b of the compressor 21. The port P3 is connected to the accumulator 27. The port P4 is connected to the second shutoff valve 26. In the first state, the port P1 communicates with the port P2, and the port P3 communicates with the port P4. In the second state, the port P1 communicates with the port P3, and the port P2 communicates with the port P4.
The flow path switching mechanism 22 is not required to be a four-way switching valve. For example, the flow path switching mechanism 22 may be configured by combining a plurality of electromagnetic valves and refrigerant tubes so that the flow direction of the refrigerant can be switched as described above.

(2-2-3) Heat source heat exchanger

The heat source heat exchanger 23 causes heat exchange between a refrigerant flowing inside and air at an installation site of the heat source unit 2 (heat source air). One end of the heat source heat exchanger 23 is connected to the port P1 of the flow path switching mechanism 22. The other end of the heat source heat exchanger 23 is connected to the heat source expansion mechanism 24.

(2-2-4) Heat source expansion mechanism

The heat source expansion mechanism 24 adjusts a flow rate of the refrigerant flowing through the heat source refrigerant flow path 20 and decompresses the refrigerant by controlling an opening degree. The heat source expansion mechanism 24 has one end connected to the heat source heat exchanger 23. The other end of the heat source expansion mechanism 24 is connected to the first shutoff valve 25. The opening degree of the heat source expansion mechanism 24 can be controlled by the control unit (not illustrated).

(2-2-5) First shutoff valve and second shutoff valve

The first shutoff valve 25 is a valve provided at a connecting portion between the heat source refrigerant flow path 20 and the first connecting pipe 6. When the first shutoff valve 25 is closed, a flow of the refrigerant between the heat source refrigerant flow path 20 and the first connecting pipe 6 is restricted. The first shutoff valve 25 is, for example, a manually operated valve. In the present embodiment, the first shutoff valve 25 is a three-way valve including a service port communicable with the outside of the refrigerant circuit 10.
The second shutoff valve 26 is a valve provided at a connecting portion between the heat source refrigerant flow path 20 and the second connecting pipe 7. When the second shutoff valve 26 is closed, a flow of the refrigerant between the heat source refrigerant flow path 20 and the second connecting pipe 7 is restricted. The second shutoff valve 26 is, for example, a manually operated valve. In the present embodiment, the second shutoff valve 26 is a three-way valve including a service port communicable with the outside of the refrigerant circuit 10.
The first shutoff valve 25 and the second shutoff valve 26 are closed at a time of shipment at a manufacturing factory, and are opened at an end of an installation work of the air conditioner 1. After the end of the installation work, the first shutoff valve 25 and the second shutoff valve 26 are normally kept open.

(2-2-6) Accumulator

The accumulator 27 is a container that stores a surplus refrigerant generated in the refrigerant circuit 10 in accordance with a change in an operation load of the utilization unit 3. The accumulator 27 is provided between the port P3 of the flow path switching mechanism 22 and the suction pipe 21a of the compressor 21. The accumulator 27 is an example of a refrigerant storage container.

(2-2-7) Relationship between filling amount of refrigerant and volume of heat source refrigerant flow path

In the heat source unit 2 as a single unit not connected to any of the utilization unit 3 and the connecting pipes 6 and 7, the refrigerant is filled in the heat source refrigerant flow path 20. The amount of the refrigerant filled in the heat source refrigerant flow path 20 is an amount of the refrigerant filled in the refrigerant circuit 10 for the air conditioner 1 to execute the refrigeration cycle operation with required performance. Specifically, a filling amount V1 (kg) of the refrigerant filled in the heat source refrigerant flow path 20 satisfies the following relationship of (Formula 1) between a volume V2 (L) of the heat source refrigerant flow path 20 and a design pressure P (MPa) of the heat source refrigerant flow path 20. $\begin{array}{l} V 1 \times a \leq V 2 \leq V 1 \times b \\ a = 0.078 \times P^{2} - 2.111 \times P + 15.771 \\ b = 0.055 \times P^{2} - 1.768 \times P + 16.144 \end{array}$
V2, which is the volume of the heat source refrigerant flow path 20, is a volume of a space in which the compressor 21, the flow path switching mechanism 22, the heat source heat exchanger 23, the heat source expansion mechanism 24, the first shutoff valve 25, the second shutoff valve 26, and the accumulator 27 are connected to each other by using the refrigerant pipe 20a and are closed from the outside by the first shutoff valve 25 and the second shutoff valve 26.
In the present embodiment, the design pressure P (MPa) of the heat source refrigerant flow path 20 is 10 MPa or more and 14 MPa or less.
A volume V3 (L) of the accumulator 27 may satisfy the following relationship of (Formula 2) with the volume V2 (L) of the heat source refrigerant flow path 20. $0.4 \times V 2 \leq V 3 < 0.9 \times V 2$
The heat source refrigerant flow path 20 is typically filled with the refrigerant at a manufacturing factory of the heat source unit 2. When the first shutoff valve 25 and the second shutoff valve are closed after the refrigerant is filled, the refrigerant is prevented from leaking from the heat source refrigerant flow path 20 after the heat source unit 2 is shipped from the manufacturing factory until the air conditioner 1 is installed.

(2-3) Connecting pipes

The connecting pipes 6 and 7 are connection pipes connecting the heat source refrigerant flow path 20 and the utilization refrigerant flow path 30 (in other words, the heat source unit 2 and the utilization unit 3). The heat source refrigerant flow path 20, the utilization refrigerant flow path 30, the first connecting pipe 6, and the second connecting pipe 7 are connected to constitute the refrigerant circuit 10.
The length of each of the connecting pipes 6 and 7 is arbitrarily changed in accordance with a distance between the heat source unit 2 and the utilization unit 3 or the like with an upper limit of about 100 m.

(3) Operation of air conditioner

Next, a description will be given of operations of components of the air conditioner 1 in an air conditioning operation.

(3-1) Cooling operation

During the cooling operation, the flow path switching mechanism 22 is controlled to the first state. The opening degree of the heat source expansion mechanism 24 is controlled in accordance with a load of the utilization heat exchanger 31.
In this state, when the compressor 21 is activated, the low-pressure refrigerant in the refrigeration cycle is sucked from the suction pipe 21a of the compressor 21, compressed, and discharged from the discharge pipe 21b as a high-pressure refrigerant. The high-pressure refrigerant discharged from the compressor 21 is sent to the heat source heat exchanger 23 via the flow path switching mechanism 22, exchanges heat with the heat source air, and is cooled. In other words, the heat source heat exchanger 23 functions as a radiator. The high-pressure refrigerant cooled in the heat source heat exchanger 23 is decompressed when passing through the heat source expansion mechanism 24 to become a low-pressure refrigerant in a gas-liquid two-phase state. The low-pressure refrigerant in the gas-liquid two-phase state is sent to the utilization unit 3 via the first shutoff valve 25 and the first connecting pipe 6. The refrigerant sent to the utilization unit 3 exchanges heat with air in the air conditioning target space to be heated in the utilization heat exchanger 31, and evaporates to become a low-pressure refrigerant. In other words, the utilization heat exchanger 31 functions as an evaporator. The low-pressure refrigerant heated in the utilization heat exchanger 31 is sent to the heat source unit 2 via the second connecting pipe 7, and flow into the accumulator 27 via the second shutoff valve 26 and the flow path switching mechanism 22. The low-pressure refrigerant having flowed into the accumulator 27 is sucked into the compressor 21 again.

(3-2) Heating operation

During the heating operation, the flow path switching mechanism 22 is controlled to the second state. The heat source expansion mechanism 24 is controlled to have an opening degree at which the refrigerant can be decompressed to such a pressure as to be evaporated in the heat source heat exchanger 23.
In this state, when the compressor 21 is activated, the low-pressure refrigerant in the refrigeration cycle is sucked from the suction pipe 21a of the compressor 21, compressed, and discharged from the discharge pipe 21b as a high-pressure refrigerant. The high-pressure refrigerant discharged from the compressor 21 is sent to the utilization unit 3 via the flow path switching mechanism 22, the second shutoff valve 26, and the second connecting pipe 7. The high-pressure refrigerant sent to the utilization unit 3 exchanges heat with air in the air conditioning target space in the utilization heat exchanger 31 to be cooled. In other words, the utilization heat exchanger 31 functions as a radiator. The high-pressure refrigerant cooled in the utilization heat exchanger 31 is sent to the heat source unit 2 via the first connecting pipe 6. The refrigerant sent to the heat source unit 2 passes through the first shutoff valve 25, is thereafter decompressed when passing through the heat source expansion mechanism 24 to become a low-pressure refrigerant in a gas-liquid two-phase state, and flows into the heat source heat exchanger 23. The low-pressure refrigerant in the gas-liquid two-phase state that has flowed into the heat source heat exchanger 23 exchanges heat with the heat source air and is heated to evaporate and become a low-pressure refrigerant. In other words, the heat source heat exchanger 23 functions as an evaporator. The low-pressure refrigerant heated by the heat source heat exchanger 23 flows into the accumulator 27 via the flow path switching mechanism 22. The low-pressure refrigerant having flowed into the accumulator 27 is sucked into the compressor 21 again.

(4) Refrigerant filling method

Next, a method of filling the refrigerant circuit 10 with the refrigerant in the installation work of the air conditioner 1 will be described.
The installation work of the air conditioner 1 includes a step of installing the heat source unit 2 and the utilization unit 3 at the installation site, and a step of connecting the heat source refrigerant flow path 20 and the utilization refrigerant flow path 30 via the connecting pipes 6 and 7.
In the air conditioner 1, since the heat source refrigerant flow path 20 of the heat source unit 2 is filled with the refrigerant, the heat source refrigerant flow path 20 and the utilization refrigerant flow path 30 are connected via the connecting pipes 6 and 7, and thus, the refrigerant filled in the heat source unit 2 is sent to the utilization unit 3 via the connecting pipes 6 and 7 to be filled in the refrigerant circuit 10. As described above, in the installation work of the air conditioner 1, the heat source refrigerant flow path 20 and the utilization refrigerant flow path 30 are connected via the connecting pipes 6 and 7, and thus, the refrigerant circuit 10 is filled with the refrigerant. Therefore, the work of filling the refrigerant circuit 10 with the refrigerant from the outside is unnecessary. Therefore, the air conditioner 1 including the heat source unit 2 allows the installation work to be performed efficiently.

(5) Characteristics

(5-1)

The heat source unit 2 is connected to the utilization unit 3 and constitutes the air conditioner 1. The heat source unit 2 includes the compressor 21, the heat source heat exchanger 23, the first shutoff valve 25, the second shutoff valve 26, the heat source refrigerant flow path 20, and the refrigerant. The heat source refrigerant flow path 20 is a flow path in which the compressor 21, the heat source heat exchanger 23, the first shutoff valve 25, and the second shutoff valve 26 are connected by the refrigerant pipe 20a. The heat source refrigerant flow path 20 is filled with the refrigerant. The refrigerant includes carbon dioxide.
The filling amount V1 (kg) of the refrigerant filled in the heat source refrigerant flow path 20, the volume V2 (L) of the heat source refrigerant flow path 20, and the design pressure P (MPa) of the heat source refrigerant flow path 20 satisfy the following relationship of (Formula 1).
$\begin{array}{l} V 1 \times a \leq V 2 \leq V 1 \times b . . . (1) \\ a = 0.078 \times P^{2} - 2.111 \times P + 15.771 . . . (2) \\ b = 0.055 \times P^{2} - 1.768 \times P + 16.144 . . . (3) \end{array}$
The carbon dioxide refrigerant is known to have a more rapid increase in pressure when becoming supercritical compare to other refrigerants. FIG. 2 is a Mollier diagram of R32. FIG. 3 is a Mollier diagram of carbon dioxide.
As illustrated in FIG. 2, R32 in a gas-liquid two-phase state can maintain the gas-liquid two-phase state even at 70°C, which is an upper limit of a refrigerant temperature increased by the outside air temperature, direct sunlight, and the like normally assumed for the heat source unit during non-operation, and the pressure at that time is about 5.0 MPa.
On the other hand, as illustrated in FIG. 3, carbon dioxide in a gas-liquid two-phase state becomes supercritical when exceeding a critical point CP(critical temperature: about 31.1°C, critical pressure: about 7.38 MPa). For example, when a density of carbon dioxide that has become supercritical is 500 kg/m³, the pressure of about 9 MPa (Pr1) at 40°C rapidly increases to about 14.9 MPa (Pr2) at 70°C, which is the upper limit of the refrigerant temperature increased by the normally assumed outside air temperature or direct sunlight. Therefore, in the heat source refrigerant flow path 20 filled with the carbon dioxide refrigerant, pressure abnormality may occur in which the pressure of the refrigerant that has become supercritical due to an increase in the outside air temperature or the like exceeds the design pressure P of the heat source refrigerant flow path 20, and the pressure abnormality may cause damage to each component constituting the heat source refrigerant flow path 20.
In the heat source unit 2, the relationship between the filling amount V1 of the refrigerant and the volume V2 of the heat source refrigerant flow path 20 is set on the basis of (Formula 1) obtained from the characteristics between the temperature and the pressure of the carbon dioxide refrigerant and an assumed temperature range of the refrigerant. Here, the assumed temperature range of the refrigerant is 50°C or more and 70°C or less. The temperature 50°C is a temperature assumed in a place such as a warehouse or the like where the heat source unit 2 is stored (for example, the temperature in the warehouse) in summer or the like. The temperature 70°C is an upper limit of a refrigerant temperature raised by the outside air temperature or direct sunlight in a place such as the warehouse or the like where the heat source unit 2 is stored.
(2) of Formula 1 determines a specific volume at which each component constituting the heat source refrigerant flow path 20 having the design pressure P is prevented from being damaged due to a pressure rise when the temperature of the refrigerant is 50°C.
(3) of Formula 1 determines a specific volume at which an increase in size of the heat source refrigerant flow path 20 having the design pressure P is suppressed when the temperature of the refrigerant is 70°C, the heat source refrigerant flow path 20 having a volume larger than necessary.
When the design pressure P of the heat source refrigerant flow path 20 is arbitrarily selected at an arbitrary refrigerant amount V1, the volume V2 of the heat source refrigerant flow path 20 is set to satisfy equal to or more than the volume V1 × a calculated on the left side (1) of Formula 1 and equal to or less than the volume V1 × b calculated on the right side (1) of Formula 1. Thus, occurrence of pressure abnormality in the refrigerant flow path due to the carbon dioxide refrigerant filled in the heat source refrigerant flow path 20 becoming supercritical is suppressed while an increase in size of the heat source refrigerant flow path 20 is suppressed.
Therefore, the heat source unit 2 suppresses occurrence of pressure abnormality in the refrigerant flow path due to the carbon dioxide refrigerant filled in the heat source refrigerant flow path 20 becoming supercritical while suppressing an increase in size of the heat source refrigerant flow path 20.

(5-2)

The design pressure P is 10 MPa or more and 14 MPa or less.
A point calculated by (2) of Formula 1 when the pressure of the refrigerant becomes 14 MPa is a first point Pa in FIG. 3, and a point calculated by (3) of Formula 1 is a second point Pb in FIG. 3. Furthermore, a point calculated by (2) of Formula 1 when the pressure of the refrigerant becomes 10 MPa is a third point Pc in FIG. 3, and a point calculated by (3) of Formula 1 is a fourth point Pd in FIG. 3. Then, when the volume V2 of the heat source refrigerant flow path 20 satisfies (1) of Formula 1, the refrigerant filled in the heat source refrigerant flow path 20 falls within a range indicated by diagonal hatching in FIG. 3.

(5-3)

The volume V3 (L) of the accumulator 27 preferably satisfies the following relationship of (Formula 2) with the volume V2 (L) of the heat source refrigerant flow path 20. $0.4 \times V 2 \leq V 3 < 0.9 \times V 2$
Since the heat source unit 2 can store the refrigerant not only in the heat source refrigerant flow path 20 but also in the accumulator 27 in the heat source refrigerant flow path 20, the volume V2 can be sufficiently secured to effectively suppress the occurrence of pressure abnormality in the refrigerant flow path.

(5-4)

The heat source unit 2 further includes the flow path switching mechanism 22 that switches the direction in which the refrigerant flows in the heat source refrigerant flow path 20, and the accumulator 27 that stores the refrigerant.
The accumulator 27 can store not only the filled refrigerant but also a surplus refrigerant generated due to a change in an operation load generated between the cooling operation and the heating operation.

(6) Modifications

(6-1) Modification A1

The air conditioner 1 may be a multi-type air conditioner including one heat source unit 2 and a plurality of utilization units 3.

(6-2) Modification A2

The air conditioner 1 is not required to include the flow path switching mechanism 22 and, may be configured to perform only one of the cooling operation or the heating operation as the air conditioning operation.

(6-3) Modification A3

The installation work of the air conditioner 1 may further include a step of additionally filling the refrigerant after the step of connecting the heat source unit 2 and the utilization unit 3 via the connecting pipes 6 and 7. The step of additionally filling the refrigerant is performed when the lengths of the connecting pipes 6 and 7 used for connecting the heat source unit 2 and the utilization unit 3 are more than or equal to a predetermined first length L1.
As described above, the heat source refrigerant flow path 20 of the heat source unit 2 is filled with the refrigerant in an amount (hereinafter, also referred to as required refrigerant amount) that enables the air conditioner 1 to execute the refrigeration cycle operation with the required performance by being filled in the refrigerant circuit 10. However, when the heat source unit 2 and the utilization unit 3 are disposed away from each other, it is necessary to connect the heat source unit 2 and the utilization unit 3 by using the connecting pipes 6 and 7 longer than usually. In such a case, the capacity of the refrigerant circuit 10 becomes larger than initially assumed, and the refrigerant filled in the heat source refrigerant flow path 20 of the heat source unit 2 may be insufficient for the required refrigerant amount. Therefore, in the air conditioner 1 according to Modification A3, a maximum length by which the refrigerant filled in the heat source refrigerant flow path 20 does not become less than the required refrigerant amount is set in advance as the first length L1. In other words, the lengths of the connecting pipes 6 and 7 are changed in accordance with the installation positions of the heat source unit 2 and the utilization unit 3. The connecting pipes 6 and 7 each have, as one of variations in length, the first length L1 that does not require additional filling of the refrigerant into the refrigerant circuit 10 formed by connecting the heat source unit 2 and the utilization unit 3 via the connecting pipes 6 and 7. The heat source unit 2 is filled with an amount of refrigerant corresponding to the required refrigerant amount in the refrigerant circuit 10 when the connecting pipes 6 and 7 have the first length L1.
Thus, a worker or the like who performs the installation work of the air conditioner 1 determines whether the lengths of the connecting pipes 6 and 7 required for the installation work of the air conditioner 1 are more than or equal to the first length L1.
When the lengths of the connecting pipes 6 and 7 are less than the first length L1, the refrigerant filled in the heat source refrigerant flow path 20 is more than the required refrigerant amount, and thus, the step of additionally filling the refrigerant is unnecessary. Therefore, the step of additionally filling the refrigerant is not performed, and after the step of connecting the heat source unit 2 and the utilization unit 3 via the connecting pipes 6 and 7 is performed, the installation work ends. In other words, the filling amount of refrigerant filled in the heat source refrigerant flow path 20 of the heat source unit 2 is more than the required refrigerant amount in the refrigerant circuit 10 formed by connecting the heat source unit 2 and the utilization unit 3 via the connecting pipes 6 and 7 when the connecting pipes 6 and 7 are shorter than the first length L1.
On the other hand, when the lengths of the connecting pipes 6 and 7 are more than or equal to the first length L1, the refrigerant filled in the heat source refrigerant flow path 20 is insufficient for the required refrigerant amount, and thus, the step of additionally filling the refrigerant is necessary. Therefore, the step of additionally filling the refrigerant is performed, and the refrigerant circuit 10 is additionally filled with an amount of refrigerant corresponding to the lengths of the connecting pipes 6 and 7. The refrigerant is additionally filled, for example, from the service port of the first shutoff valve 25 or the second shutoff valve 26.
When the air conditioner 1 is a pair type air conditioner including one heat source unit 2 and one utilization unit 3, the first length L1 is, for example, about 15 m. When the air conditioner 1 is a multi type air conditioner including one heat source unit 2 and a plurality of utilization units 3, the first length L1 is, for example, from about 30 m to about 70 m.

(6-4) Modification A4

The heat source refrigerant flow path 20 of the heat source unit 2 may further include a receiver that stores the surplus refrigerant. In this case, V3 includes a volume of the receiver in addition to the volume of the accumulator 27.

(1) Overall configuration

A heat source unit 2a according to a second embodiment will be described focusing on differences from the heat source unit 2. Similarly to the heat source unit 2, the heat source unit 2a is connected to one or more utilization units 3 by using the first connecting pipe 6 and the second connecting pipe 7 to constitute an air conditioner 1a. Hereinafter, characteristics that are the same as or correspond to the characteristics of the first embodiment are denoted by the same reference signs, and description thereof is omitted. FIG. 4 is a schematic configuration diagram of the air conditioner 1a including the heat source unit 2a according to the second embodiment.
A main difference between the heat source unit 2a and the heat source unit 2 is that the heat source unit 2a further includes a refrigerant amount adjuster 28. The refrigerant amount adjuster 28 stores the refrigerant to be filled in the installation work of the air conditioner 1a, and stores the surplus refrigerant generated in the refrigerant circuit 10 in accordance with the change in the operation load of the utilization unit 3 or the like. The refrigerant amount adjuster 28 is included in the heat source refrigerant flow path 20 of the heat source unit 2a. As a result, in the heat source unit 2a, the heat source refrigerant flow path 20 is filled with a larger amount of refrigerant than in the heat source unit 2. The refrigerant amount adjuster 28 includes a refrigerant storage container 28a, a pressure adjustment valve 28b, a check valve 28c, an electromagnetic valve 28d, and an expansion mechanism 28e.

(2) Detailed configuration

(2-1) Refrigerant storage container

The refrigerant storage container 28a is a container (tank) that stores at least a part of the refrigerant to be filled in the heat source refrigerant flow path 20 and stores the surplus refrigerant generated in the refrigerant circuit 10. The refrigerant storage container 28a has a first port 28aa and a second port 28ab. The refrigerant storage container 28a is an example of a refrigerant storage container.
The first port 28aa is a port provided for adjusting the pressure inside the refrigerant storage container 28a. The first port 28aa is connected to, via a pressure adjusting pipe 20b, the refrigerant pipe 20a connected to the port P3 of the flow path switching mechanism 22 and the accumulator 27 and the discharge pipe 21b of the compressor 21.
The second port 28ab is a port through which the refrigerant flows. The second port 28ab is connected to the suction pipe 21a of the compressor 21 via the refrigerant pipe 20a.

(2-2) Pressure adjustment valve

The pressure adjustment valve 28b is a valve that prevents the pressure of the refrigerant in the refrigerant storage container 28a from becoming excessively high. The pressure adjustment valve 28b is provided in the pressure adjusting pipe 20b connected to the refrigerant pipe 20a connected to the port P3 of the flow path switching mechanism 22 and the accumulator 27. The pressure adjustment valve 28b opens when the pressure of the refrigerant in the refrigerant storage container 28a reaches or exceeds a predetermined value, and releases the high-pressure refrigerant to the accumulator 27.

(2-3) Check valve and electromagnetic valve

The check valve 28c and the electromagnetic valve 28d are valves used to increase the pressure of the refrigerant in the refrigerant storage container 28a. The check valve 28c and the electromagnetic valve 28d are provided in the pressure adjusting pipe 20b connected to the discharge pipe 21b of the compressor 21. When the electromagnetic valve 28d is opened during the operation of the compressor 21, a high-pressure refrigerant discharged from the compressor 21 is sent to the refrigerant storage container 28a. The electromagnetic valve 28d is opened typically when the refrigerant circuit 10 is filled with the refrigerant in the refrigerant storage container 28a. The check valve 28c prevents the refrigerant from flowing from the refrigerant storage container 28a to the discharge pipe 21b of the compressor 21. The electromagnetic valve 28d can be opened and closed by a control unit (not illustrated). The check valve 28c and the electromagnetic valve 28d may be a flow rate adjustment mechanism including an electric valve.

(2-4) Expansion mechanism

The expansion mechanism 28e adjusts a flow rate of the refrigerant flowing through the refrigerant pipe 20a connecting the suction pipe 21a of the compressor 21 and the refrigerant storage container 28a and decompresses the refrigerant. An opening degree of the expansion mechanism 28e can be controlled by a control unit (not illustrated).

(2-5) Relationship between filling amount of refrigerant and volume of heat source refrigerant flow path

Similarly to the heat source unit 2, in the heat source unit 2a, the refrigerant is filled in the heat source refrigerant flow path 20 as a single unit not connected to any of the utilization unit 3 and the connecting pipes 6 and 7. The amount of the refrigerant filled in the heat source refrigerant flow path 20 is an amount of the refrigerant filled in the refrigerant circuit 10 for the air conditioner 1a to execute the refrigeration cycle operation with required performance. At this time, the filling amount V1 (kg) of the refrigerant filled in the heat source refrigerant flow path 20 satisfies the above relationship of (Formula 1) between the volume V2 (L) of the heat source refrigerant flow path 20 and the design pressure P (MPa) of the heat source refrigerant flow path 20.
In the heat source unit 2a, V3 includes a volume of the refrigerant storage container 28a in addition to the volume of the accumulator 27. V3 (L) satisfies the above relationship of (Formula 2) with the volume V2 (L) of the heat source refrigerant flow path 20.

(3) Operation of air conditioner

In both the cooling operation and the heating operation, the opening degrees of the expansion mechanism 28e and the electromagnetic valve 28d are controlled to be fully open or nearly fully open at the time of supplying the refrigerant. When the refrigerant supply is finished, the expansion mechanism 28e and the electromagnetic valve 28d are controlled in opening degree to be fully closed or nearly fully closed. As a result, a necessary refrigerant is supplied into the refrigerant circuit 10 of the air conditioner 1a. Of the refrigerant filled in the refrigerant storage container 28a in advance, a surplus refrigerant is reserved in the refrigerant storage container 28a without being supplied into the refrigerant circuit 10.
The operation of the other components of the air conditioner 1a in the air conditioning operation is similar to that of the air conditioner 1, and will not be described.

(4) Refrigerant filling method

The installation work of the air conditioner 1a further includes a step of sending the refrigerant stored in the refrigerant storage container 28a to the refrigerant circuit 10, in addition to the step of installing the heat source unit 2 and the utilization unit 3 at the installation sites, and the step of connecting the heat source unit 2 and the utilization unit 3 via the connecting pipes 6 and 7.
In the step of sending the refrigerant stored in the refrigerant storage container 28a to the refrigerant circuit 10, the opening degrees of the heat source expansion mechanism 24, the electromagnetic valve 28d, and the expansion mechanism 28e are controlled to be fully open or nearly fully open. When the compressor 21 is activated in this state, the high-pressure refrigerant discharged from the compressor 21 passes through the first port 28aa and pushes out the refrigerant stored in the refrigerant storage container 28a from the second port 28ab. As a result, the refrigerant having passed through the expansion mechanism 28e is sucked from the suction pipe 21a of the compressor 21 to be filled in the refrigerant circuit 10. When the compressor 21 is stopped, this step ends.
In the air conditioner 1a, since the heat source unit 2a further includes the refrigerant amount adjuster 28, the heat source refrigerant flow path 20 is filled with more refrigerant than in the heat source unit 2. Therefore, in the air conditioner 1a including the heat source unit 2a, even when the plurality of utilization units 3 is provided, the heat source unit 2a can sufficiently store the required refrigerant amount in the heat source refrigerant flow path 20.

(5) Characteristics

(5-1)

The heat source unit 2a is connected to the utilization unit 3 and constitutes the air conditioner 1a. The heat source unit 2a includes the compressor 21, the heat source heat exchanger 23, the first shutoff valve 25, the second shutoff valve 26, the heat source refrigerant flow path 20, and the refrigerant. The heat source refrigerant flow path 20 of the heat source unit 2a is a flow path in which the compressor 21, the heat source heat exchanger 23, the first shutoff valve 25, the second shutoff valve 26, and the refrigerant amount adjuster 28 are connected by the refrigerant pipe 20a. The heat source refrigerant flow path 20 is filled with the refrigerant. The refrigerant includes carbon dioxide.
The filling amount V1 (kg) of the refrigerant filled in the heat source refrigerant flow path 20, the volume V2 (L) of the heat source refrigerant flow path 20, and the design pressure P (MPa) of the heat source refrigerant flow path 20 satisfy the above relationship of (Formula 1).
Therefore, the heat source unit 2a also suppresses occurrence of pressure abnormality in the refrigerant flow path due to the filled carbon dioxide refrigerant becoming supercritical while suppressing an increase in size of the heat source refrigerant flow path 20.

(5-2)

The volume V3 (L) of the accumulator 27 and the refrigerant storage container 28a preferably satisfies the above relationship of (Formula 3) with the volume V2 (L) of the heat source refrigerant flow path 20.
Since the heat source unit 2a can store the refrigerant not only in the heat source refrigerant flow path 20 but also in the accumulator 27 and the refrigerant storage container 28a in the heat source refrigerant flow path 20, the volume V2 can be sufficiently secured to effectively suppress the occurrence of pressure abnormality in the refrigerant flow path.

(6) Modifications

The air conditioner 1a and the heat source refrigerant flow path 20 may also have the characteristics of Modifications A1 to A5 described above.
The embodiments of the present disclosure have been described above. It will be understood that various changes to modes and details can be made without departing from the gist and scope of the present disclosure recited in the claims.

REFERENCE SIGNS LIST

1, 1a: Air conditioner
2, 2a: Heat source unit
3: Utilization unit
6: First connecting pipe (connecting pipe)
7: Second connecting pipe (connecting pipe)
10: Refrigerant circuit
20: Heat source refrigerant flow path (refrigerant flow path)
20a: Refrigerant pipe
21: Compressor
22: Flow path switching mechanism
23: Heat source heat exchanger
25: First shutoff valve
26: Second shutoff valve
27: Accumulator (refrigerant storage container)
28: Refrigerant amount adjuster
28a: Refrigerant storage container
L1: First length

CITATIONS LIST

PATENT LITERATURE

Patent Literature 1: JP 2008-045769 A

Claims

A heat source unit (2, 2a) that is connected to a utilization unit (3) and constitutes an air conditioner (1, 1a), the heat source unit comprising:
a compressor (21);

a heat source heat exchanger (23);

a first shutoff valve (25);

a second shutoff valve (26);

a refrigerant flow path (20) in which the compressor, the heat source heat exchanger, the first shutoff valve, and the second shutoff valve are connected by a refrigerant pipe; and

a refrigerant filled in the refrigerant flow path, wherein

the refrigerant includes carbon dioxide, and

a filling amount V1 (kg) of the refrigerant filled in the refrigerant flow path, a volume V2 (L) of the refrigerant flow path, and a design pressure P (MPa) of the refrigerant flow path satisfy a relationship in which $V 1 \times a \leq V 2 \leq V 1 \times b,$ $a = 0.078 \times P^{2} - 2.111 \times P + 15.771,$ and $b = 0.055 \times P^{2} - 1.768 \times P + 16.144 .$
The heat source unit according to claim 1, wherein
the design pressure P is 10 MPa or more and 14 MPa or less.
The heat source unit according to claim 1 or 2, further comprising a refrigerant storage container (27, 28a) that stores the refrigerant, wherein
a volume V3 (L) of the refrigerant storage container satisfies a relationship in which $0.4 \times V 2 \leq V 3 < 0.9 \times V 2 .$
The heat source unit according to any one of claims 1 to 3, further comprising:
a flow path switching mechanism (22) that switches a direction in which the refrigerant flows in the refrigerant flow path; and

a refrigerant storage container (27, 28a) that stores the refrigerant.
An air conditioner comprising:
the heat source unit according to any one of claims 1 to 4; and

the utilization unit connected to the heat source unit via a connecting pipe (6, 7), wherein

the connecting pipe has

a length that is changed in accordance with installation positions of the heat source unit and the utilization unit, and

a first length (L1) that does not require additional filling of the refrigerant into a refrigerant circuit (10) formed by connecting the heat source unit and the utilization unit via the connecting pipe, and

the heat source unit is filled with the refrigerant in an amount corresponding to a required refrigerant amount in the refrigerant circuit when the connecting pipe has the first length.
An air conditioner comprising:
the heat source unit according to any one of claims 1 to 4; and

the utilization unit connected to the heat source unit via a connecting pipe (6, 7), wherein

the connecting pipe has a length that is changed in accordance with installation positions of the heat source unit and the utilization unit, and

a filling amount of the refrigerant filled in the refrigerant flow path of the heat source unit is larger than

a required refrigerant amount in a refrigerant circuit (10) formed by connecting the heat source unit and the utilization unit via the connecting pipe when the connecting pipe is shorter than a predetermined first length (L1).