EP3599433B1

EP3599433B1 - Heat source unit for refrigeration apparatus

Info

Publication number: EP3599433B1
Application number: EP19186987.4A
Authority: EP
Inventors: Shun Yoshioka; Yoshiyuki Matsumoto; Tomoki HIROKAWA; Tomohiko Sakamaki
Original assignee: Daikin Industries Ltd
Current assignee: Daikin Industries Ltd
Priority date: 2018-07-25
Filing date: 2019-07-18
Publication date: 2022-08-31
Anticipated expiration: 2039-07-18
Also published as: JP2020016391A; ES2928916T3; JP2024057108A; EP3599433A1

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a heat source unit for a refrigeration apparatus that uses CO₂ refrigerant and that exchanges heat between the CO₂ refrigerant and another fluid.

2. Description of the Related Art

In some refrigeration apparatuses that uses CO₂ refrigerant, a compressor that performs two-stage compression and an intermediate heat exchanger are used. Japanese Unexamined Patent Application Publication No. 2009-150641 describes a refrigeration apparatus in which an intermediate heat exchanger is disposed on or above a heat-source-side heat exchanger.
Other example of the prior art can be found in documents US 2010/0300141 A1 , US 2015/052927 A1 , and US 2010/032133 A1 .

SUMMARY OF THE INVENTION

It is desirable that the intermediate heat exchanger operate more efficiently in the refrigeration apparatus that uses CO₂ refrigerant.
It is also desirable that, in a case where the heat-source-side heat exchanger includes a main heat exchanger and a sub-heat exchanger, the efficiency of the sub-heat exchanger be improved.
A heat source unit according to the present invention is defined by claims 1, 2 and 3, respectively.
A heat source unit according to a first aspect of the present invention is a heat source unit for a refrigeration apparatus that uses CO₂ refrigerant and that exchanges heat between the CO₂ refrigerant and another fluid, the heat source unit. The heat source unit includes a compressor, a main heat exchanger, and a sub-heat exchanger. The compressor performs multi-stage compression of two or more stages. The main heat exchanger exchanges heat between the refrigerant and the fluid. The sub-heat exchanger is disposed independently from the main heat exchanger and exchanges heat between the refrigerant and the fluid. The sub-heat exchanger is disposed on an upstream side or a downstream side of the main heat exchanger in a flow of the fluid. Here, the term "independently" means that a fin of the main heat exchanger and a fin of the sub-heat exchanger are not connected to each other, and the main heat exchanger and the sub-heat exchanger have separate refrigerant inlets and outlets.
The heat source unit according to the first aspect, which is a heat source unit that uses CO₂ refrigerant whose temperature changes considerably in a heat exchanger, reliably maintains a sufficient temperature difference between the fluid and the refrigerant and increases heat exchange efficiency.
In the heat source unit according to the first aspect, the sub-heat exchanger is an intermediate heat exchanger. The intermediate heat exchanger exchanges heat between the refrigerant and the fluid after the compressor has performed first-stage compression and before the compressor performs final-stage compression. The intermediate heat exchanger is disposed on the upstream side of the main heat exchanger in the flow of the fluid.
Because the intermediate heat exchanger is disposed independently from and on the upstream side of the main heat exchanger, the heat source unit according to the first aspect can perform sufficient heat exchange between the fluid and the refrigerant and improves heat exchange efficiency.
In the heat source unit according to the first aspect, the heat source unit further includes a fan and a housing. In the first aspect, the fluid is air. The fan is for moving the air to the main heat exchanger. The housing contains the compressor, the main heat exchanger, the fan, and the intermediate heat exchanger. The fan sucks the air from a side of the housing and blows out the air upward from a top of the housing.
The heat source unit according to the first aspect efficiently increases the heat exchange between air and the refrigerant.
In the heat source unit according to the first aspect, the intermediate heat exchanger is disposed at a height above half _the height of the main heat exchanger.
Because the intermediate heat exchanger is disposed at a position where airflow speed is high, the heat source unit according to the first aspect increases the heat exchange amount of the intermediate heat exchanger and improves efficiency.
A heat source unit according to a second aspect of the present invention is a heat source unit for a refrigeration apparatus that uses CO2 refrigerant and that exchanges heat between the CO2 refrigerant and another fluid, the heat source unit. The heat source unit includes a compressor, a main heat exchanger, and a sub-heat exchanger. The compressor performs multi-stage compression of two or more stages. The main heat exchanger exchanges heat between the refrigerant and the fluid. The sub-heat exchanger is disposed independently from the main heat exchanger and exchanges heat between the refrigerant and the fluid. The sub-heat exchanger is disposed on an upstream side or a downstream side of the main heat exchanger in a flow of the fluid. In addition, the heat source unit according to the second aspect further includes an expansion mechanism. The expansion mechanism expands the refrigerant. The sub-heat exchanger is connected between the main heat exchanger and the expansion mechanism in a refrigerant circuit. The sub-heat exchanger is disposed on the upstream side of the main heat exchanger in the flow of the fluid.
Because the sub-heat exchanger is disposed on the upstream side of the main heat exchanger, the heat source unit according to the second aspect can reliably maintain a sufficient temperature difference between low-temperature refrigerant that flows in the sub-heat exchanger and the fluid and can increase heat exchange efficiency when operating the main heat exchanger as a radiator. The heat exchange amount of the intermediate heat exchanger increases and efficiency improves.
The heat source unit according to the second aspect includes a fan and a housing. In the second aspect, the fluid is air. The fan is for moving the air to the main heat exchanger. The housing contains the compressor, the main heat exchanger, the fan, and the sub-heat exchanger. The fan sucks the air from a side of the housing and blows out the air upward from a top of the housing.
The heat source unit according to the second aspect increases efficiently of heat exchange between air and the refrigerant.
In the heat source unit according to the second aspect, the sub-heat exchanger is disposed at a height above half the height of the main heat exchanger.
Because the sub-heat exchanger is disposed at a position where airflow speed is high, the heat source unit according to the second aspect increases the heat exchange amount of the sub-heat exchanger and improves efficiency.
A heat source unit according to a third aspect of the present invention is a heat source unit for a refrigeration apparatus that uses CO2 refrigerant and that exchanges heat between the CO2 refrigerant and another fluid, the heat source unit. The heat source unit includes a compressor, a main heat exchanger, and a sub-heat exchanger. The compressor performs multi-stage compression of two or more stages. The main heat exchanger exchanges heat between the refrigerant and the fluid. The sub-heat exchanger is disposed independently from the main heat exchanger and exchanges heat between the refrigerant and the fluid. The sub-heat exchanger is disposed on an upstream side or a downstream side of the main heat exchanger in a flow of the fluid. In addition, the heat source unit according to the third aspect further includes an expansion mechanism. The expansion mechanism expands the refrigerant. The sub-heat exchanger is connected, in a refrigerant circuit, to either of the refrigerant inlet or the outlet of the main heat exchanger that is farther from the expansion mechanism. The sub-heat exchanger is disposed on the downstream side of the main heat exchanger in the flow of the fluid.
Although the sub-heat exchanger is disposed on the downstream side of the main heat exchanger, because the temperature of the refrigerant that flows in the sub-heat exchanger is high, the heat source unit according to the third aspect can reliably maintain a sufficient temperature difference between the refrigerant and the fluid when operating the main heat exchanger as a radiator. In the entirety, heat exchange efficiency can be increased.
The heat source unit according to the third aspect further includes a fan and a housing. In the third aspect, the fluid is air. The fan is for moving the air to the main heat exchanger. The housing contains the compressor, the main heat exchanger, the fan, and the sub-heat exchanger. The fan sucks the air from a side of the housing and blows out the air upward from a top of the housing.
The heat source unit according to the third aspect increases efficiently of heat exchange between air and the refrigerant.
In the heat source unit according to the third aspect, the sub-heat exchanger is disposed at a height above half a height of the main heat exchanger.
Because the sub-heat exchanger is disposed at a position where airflow speed is high, the heat source unit according to the third aspect increases the heat exchange amount of the sub-heat exchanger and improves efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a refrigerant circuit diagram of a refrigeration apparatus according to a first embodiment of the present invention;
Fig. 2 is a schematic perspective view of a heat source unit according to the first embodiment;
Fig. 3 is a partial schematic perspective view of a heat-source-side heat exchanger according to the first embodiment;
Fig. 4A is a side view of a region near a reversely bent portion of the heat exchanger according to the first embodiment;
Fig. 4B is a side view of a region near a reversely bent portion of a heat exchanger according to modification 1A;
Fig. 5A is a vertical sectional view of a joint according to the first embodiment;
Fig. 5B is a horizontal sectional view of the joint according to the first embodiment;
Fig. 6A is a sectional view of heat transfer tubes of a heat exchanger according to modification 1E, taken along a section S;
Fig. 6B is a sectional view of heat transfer tubes of a heat exchanger according to modification 1D, taken along a section S;
Fig. 7A is a side view of a first end portion of the heat exchanger according to modification 1D;
Fig. 7B is a side view of a second end portion of the heat exchanger according to modification 1D;
Fig. 8A is a top view of the heat exchanger and an intermediate heat exchanger according to the first embodiment;
Fig. 8B is a sectional view of the heat exchanger and the intermediate heat exchanger according to the first embodiment, taken along a section S;
Fig. 9A is a top view of a heat exchanger and a sub-heat exchanger according to a second embodiment;
Fig. 9B is a sectional view of the heat exchanger and the sub-heat exchanger according to the second embodiment, taken along a section S;
Fig. 10A is a top view of a heat exchanger and a sub-heat exchanger according to a third embodiment; and
Fig. 10B is a sectional view of the heat exchanger and the sub-heat exchanger according to the third embodiment, taken along a section S.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

(1) Structure of Refrigerant Circuit of Refrigeration Apparatus 1

Fig. 1 illustrates the structure of a refrigerant circuit of a refrigeration apparatus 1 according to a first embodiment. The refrigeration apparatus 1 according to the present embodiment is an apparatus that uses carbon dioxide, which is a refrigerant that operates in a supercritical region, and that performs two-stage-compression refrigeration cycle. The refrigeration apparatus 1 according to the present embodiment can be used as an air conditioner that performs cooling and heating, a water cooler/heater, or the like.
A refrigerant circuit of the refrigeration apparatus 1 according to the present embodiment mainly includes a compressor 2, a four-way switching valve 3, a heat-source-side heat exchanger 4, an expansion mechanism 5, a use-side heat exchanger 6, and an intermediate heat exchanger 7.
The compressor 2 is a two-stage compressor that compresses refrigerant in two stages by using two compression elements 2c and 2d. The compressor 2 sucks refrigerant from a suction pipe 2a, compresses the sucked refrigerant by using the first-stage compression element 2c, and then discharges the refrigerant to an intermediate refrigerant pipe 8. The refrigerant discharged to the intermediate refrigerant pipe 8 is further sucked into the second-stage compression element 2d and compressed, and discharged to a discharge pipe 2b. The discharge pipe 2b is a refrigerant pipe through which the refrigerant discharged from the compressor 2 flows to the four-way switching valve 3. An oil separator 41 and a check valve 42 are disposed in the discharge pipe 2b. The oil separator 41 separates refrigeration oil, which is mixed in the refrigerant discharged from the compressor 2, from the refrigerant. The separated oil is decompressed in a capillary tube 41c, passes through an oil return pipe 41b, and is returned to the suction pipe 2a of the compressor 2.
The refrigeration oil in the present embodiment is not limited, as long as the refrigeration oil can be used for CO₂ refrigerant. Examples of the refrigeration oil include polyalkylene glycols (PAG) and polyol esters (POE).
The four-way switching valve 3 can switch the direction of flow of refrigerant, between a forward direction and a backward direction, in a path connecting the heat-source-side heat exchanger 4, the expansion mechanism 5, and the use-side heat exchanger 6. During a cooling operation, the four-way switching valve 3 allows refrigerant flowed out from the compressor 2 to flow from the heat-source-side heat exchanger 4 to the use-side heat exchanger 6. At this time, the heat-source-side heat exchanger 4 is a radiator, and the use-side heat exchanger 6 is an evaporator. During a heating operation, conversely, the four-way switching valve 3 allows refrigerant flowed out from the compressor 2 to flow from the use-side heat exchanger 6 to the heat-source-side heat exchanger 4. At this time, the use-side heat exchanger 6 is a radiator, and the heat-source-side heat exchanger 4 is an evaporator.
The intermediate heat exchanger 7 and a check valve 15 are disposed in the intermediate refrigerant pipe 8. That is, the refrigerant compressed by the first-stage compression element 2c exchanges heat with air in the intermediate heat exchanger 7, and flows into the second-stage compression element 2d again.
An intermediate-heat-exchanger bypass pipe 9 is disposed in the intermediate refrigerant pipe 8 so as to bypass the intermediate heat exchanger 7. That is, the refrigerant flowed through the first-stage compression element 2c and the intermediate-heat-exchanger bypass pipe 9 bypasses the intermediate heat exchanger 7 and flows into the second-stage compression element 2d. On-off valves 11 and 12 switch the path of flow of the refrigerant between a path through the intermediate heat exchanger 7 and a path through the intermediate-heat-exchanger bypass pipe 9. Basically, the on-off valves 11 and 12 are controlled so that the refrigerant flows through the intermediate heat exchanger 7 when the use-side heat exchanger 6 is used as an evaporator and so that the refrigerant flows through the intermediate-heat-exchanger bypass pipe 9 when the use-side heat exchanger 6 is used as a radiator. That is, basically, the intermediate heat exchanger 7 is used during a cooling operation.
Although a two-stage compressor is used in the refrigeration apparatus 1 according to the present embodiment, two compressors may be used in a similar way. A compressor or a compression mechanism that performs compression of three or more stages may be used.
The expansion mechanism 5 is an expansion valve, a capillary tube, or an expansion machine.

(2) Structure of Heat Source Unit 10 of Refrigeration Apparatus 1

(2-1) Overall Structure of Heat Source Unit 10

Fig. 1 illustrates, in a dotted line, constituent elements of the heat source unit 10 of the refrigeration apparatus 1 according to the present embodiment. Fig. 2 is an external perspective view illustrating the constituent elements.
The heat source unit 10 has a housing 20 that contains a fan 40, the compressor 2, the heat-source-side heat exchanger 4, the intermediate heat exchanger 7, the expansion mechanism 5, the four-way switching valve 3, and the oil separator 41.

(2-2) Heat-Source-Side Heat Exchanger 4

Fig. 2 is an external perspective view of the heat source unit 10. Fig. 3 is a partial perspective view of the heat-source-side heat exchanger 4.
As illustrated in Fig. 2, the heat-source-side heat exchanger 4 according to the present embodiment is disposed on three sides of the inside of the housing 20 of the heat source unit 10. When the fan 40 rotates, air around the housing 20 is sucked from the three sides and passes through the heat-source-side heat exchanger 4. The air sucked into the housing 20 passes through the fan 40 and is blown upward from the top of the housing 20 to the outside. Accordingly, the heat source unit 10 according to the present embodiment is a top-blow-type unit. The air is heated or cooled by exchanging heat with refrigerant while passing through the heat exchanger 4.
Fig. 3 is a schematic perspective view illustrating one side of the heat-source-side heat exchanger 4 according to the present embodiment. The heat exchanger 4 includes heat transfer tubes 30, in which refrigerant flows, and metal fins 50, which promote heat exchange between the refrigerant and air. Each of the heat transfer tubes 30 according to the present embodiment is a multi-hole flat pipe. In the multi-hole flat pipe, a plurality of holes, through which refrigerant flows, are arranged in the width direction.
As illustrated in Fig. 2, in the heat exchanger 4 according to the present embodiment, refrigerant is supplied from the outside of the heat exchanger 4 into the heat transfer tubes 30 at a first end portion 4a. The refrigerant flows from the first end portion 4a along three sides of the heat transfer tubes 30, each of which is bent by 90° at two positions, and reaches a second end portion 4b. At the second end portion 4b, the direction of flow of refrigerant is reversed by 180°. Then, the refrigerant flows along the three sides again and returns to the first end portion 4a. At the first end portion 4a, the refrigerant flows out from the heat transfer tubes 30 to the outside of the heat exchanger 4. Here, heat transfer tubes that form refrigerant channels extending from the first end portion 4a to the second end portion 4b will be referred to as first heat transfer tubes 30a, and heat transfer tubes through which refrigerant flows in the opposite direction will be referred to as second heat transfer tubes 30b.
As illustrated in Fig. 3, in the present embodiment, the heat transfer tubes 30 are arranged in two rows with respect to the flow of air. In each of the rows, the first heat transfer tubes 30a and the second heat transfer tubes 30b are arranged alternately in the vertical direction.
In the present description, the direction of flow of refrigerant in the heat exchanger 4 is basically the direction in which the refrigerant flows when the heat exchanger is used as a radiator. When the heat exchanger 4 is used as an evaporator, the direction of flow of refrigerant is reversed.

(2-3) Structure of Reversely Bent Portion 33

The structure of the heat-source-side heat exchanger 4 according to the present embodiment near the second end portion 4b will be described with reference to the drawings. Reversely bent portions 33 are disposed at the second end portion 4b. Fig. 4A is a vertical sectional view of one of the reversely bent portions 33 for reversing the flow of refrigerant. Here, a portion of the first heat transfer tube 30a near the second end portion 4b will be referred to as a first linear portion 31, and a portion of the second heat transfer tube 30b near the second end portion 4b will be referred to as a second linear portion 32.
The reversely bent portion 33 reverses the direction of flow of refrigerant that has flowed through the first linear portion 31 of the heat transfer tube 30 (a multi-hole flat pipe 300) and allows the refrigerant to flow to the second linear portion 32 below the first linear portion 31.
The reversely bent portion 33 is formed from two joints 34a and 34b and a U-shaped pipe 350. The joints 34a and 34b connect the heat transfer tubes 30 and the U-shaped pipe 350.
In the present embodiment, the heat transfer tube 30 may be a multi-hole flat pipe or a cylindrical pipe, and is not limited. In the present embodiment, the multi-hole flat pipe 300 is used. A multi-hole flat pipe has high performance in transferring heat of refrigerant. In the multi-hole flat pipe 300 according to the present embodiment, a plurality of holes are arranged in a row. The direction in which the holes of the multi-hole flat pipe are arranged will be referred to as the width direction, and the direction that is perpendicular to the width direction and the direction of flow of refrigerant will be referred to as the thickness direction. W > T holds, where T is the thickness (length in the thickness direction) and W is the width (length in the width direction) of the multi-hole flat pipe.
In the present embodiment, refrigerants that have flowed through channels, which are the plurality of holes of the multi-hole flat pipe 300, are collected to one channel in the reversely bent portion 33. Then, in the reversely bent portion 33, that is, in the joints 34a and 34b and the U-shaped pipe, the refrigerants can be made uniform.
In the present embodiment, the thickness T of the heat transfer tube 30 in the vertical direction is 3 mm or smaller. The distance DP between the center of the first linear portion 31 and the center of the second linear portion 32 in the vertical direction is 0 mm to 21 mm.
In the present embodiment, in the heat exchanger 4 that uses CO₂ refrigerant, the first linear portion 31 and the second linear portion 32, between which the reversely bent portion 33 of the heat transfer tube 30 is located, are disposed close to each other. Therefore, nonuniformity in the temperature of passing air can be suppressed. Thus, heat exchange efficiency is also improved.
In the heat exchanger 4 according to the present embodiment, the distance DP between the center of the first linear portion 31 and the center of the second linear portion 32 in the vertical direction is smaller than or equal to five times the thickness of the heat transfer tubes 30 in the vertical direction.
In the present embodiment, in the heat exchanger 4 that uses CO₂ refrigerant, the first linear portion 31 and the second linear portion 32, between which the reversely bent portion 33 of the heat transfer tube 30 is located, are disposed close to each other. Therefore, nonuniformity in the temperature of passing air can be suppressed.
The heat exchanger 4 according to the present embodiment further includes the plurality of fins 50. The fins 50 are fixed to the heat transfer tubes 30 and promote heat exchange between the heat transfer tubes 30 and air. The fin pitch of the plurality of fins 50 is 1.3 mm or larger, and preferably 1.4 mm or larger.
In the heat exchanger 4 according to the present embodiment, the thickness T of the heat transfer tube 30 in the vertical direction is 3 mm or smaller. By making the fin pitch 1.3 mm or larger, heat exchange efficiency can be improved.
When the heat exchanger 4 according to the present embodiment is used as a radiator, the temperature difference between the refrigerant inlet temperature and the refrigerant outlet temperature of the heat exchanger 4 is 40°C or larger.
In the present embodiment, CO₂ refrigerant is used as the refrigerant. CO₂ refrigerant is a refrigerant used in a supercritical region, and decrease of the temperature of the refrigerant in the radiator is large. The temperature decreases by 40°C or more. Because the temperature difference of the refrigerant is large, the effect of disposing the first linear portion 31 and the second linear portion 32 close to each other is also large.
In the heat exchanger 4 according to the present embodiment, the second linear portion 32 is located above or below the first linear portion 31.
Because the first linear portion 31 is disposed above or below the second linear portion 32 and the distance between these is small, the heat exchanger 4 according to the present embodiment can further suppress nonuniformity in temperature of passing air. Because spaces above and below the heat transfer tube 30 are connected by the fins 50, the surrounding temperatures of regions around the heat transfer tube 30 become close to each other via the fins 50.
Heretofore, a case where the direction of refrigerant that has flowed through the first linear portion 31 is reversed downward to the second linear portion 32 has been described. The same applies to a case where the direction of refrigerant is reversed upward.

(2-4) Detailed Description of Joint 34

Fig. 5A is a vertical sectional view of a joint 34, and Fig. 5B is a horizontal sectional view of the joint 34. As illustrated in Figs. 5A and 5B, the joint 34 according to the present embodiment connects the multi-hole flat pipe 300 and a cylindrical pipe 35. In the present embodiment, the cylindrical pipe 35 is the U-shaped pipe 350. Refrigerant that flows through these pipes is CO₂ refrigerant.
The joint 34 includes a first connection portion 301, a body 302, and a second connection portion 303. The first connection portion 301 covers the outside of an end portion of the multi-hole flat pipe 300. The body 302 is continuous from the first connection portion 301. The second connection portion 303 is continuous from the body 302. The second connection portion 303 covers the outside of an end portion of the cylindrical pipe 35.
As illustrated in Fig. 5A, when seen in the vertical direction, the inside dimension L₃₀₁ of the first connection portion 301 in the vertical direction is slightly larger than the thickness T of the multi-hole flat pipe 300. The inside dimension L₃₀₂ of the body 302 in the vertical direction is larger than the inside dimension L₃₀₁ of the first connection portion 301 in the vertical direction. The inside dimension L₃₀₂ of the body 302 in the vertical direction increases with increasing distance from the first connection portion 301, and becomes constant at some portion.
In the joint 34 according to the present embodiment, the inside dimension L₃₀₂ of the body 302 in the vertical direction is larger than the inside dimension L₃₀₁ of the first connection portion 301 in the vertical direction. Therefore, oil is unlikely to stagnate in a region near a connection portion of the inner peripheral surface of the joint 34.
Moreover, the joint 34 according to the present embodiment includes a region where the inside dimension thereof in the vertical direction gradually increases with increasing distance from the first connection portion 301. With such a structure, oil is more unlikely to stagnate in a region near a connection portion of the inner peripheral surface of the joint 34.
As illustrated in Fig. 5B, when seen in the horizontal direction, the inside dimension W₃₀₁ of the first connection portion 301 in the horizontal direction is slightly larger than the width W of the multi-hole flat pipe 300. The inside dimension W₃₀₂ of the body 302 in the horizontal direction is larger than the inside dimension W₃₀₁ of the first connection portion 301 in the horizontal direction. The inside dimension W₃₀₂ of the body 302 in the horizontal direction decreases with increasing distance from the first connection portion 301, and becomes constant at some portion. The length of the portion where the inside dimension W₃₀₂ in the horizontal direction is constant is the same as the length of the portion where the inside dimension L₃₀₂ in the vertical direction is constant.
Because the inside dimension L₃₀₂ of the body 302 of the joint 34 in the vertical direction is larger than the inside dimension L₃₀₁ of the first connection portion 301 in the vertical direction, oil is unlikely to stagnate in a region near the multi-hole flat pipe 300 on the inner peripheral surface of the first connection portion 301.
As illustrated in Fig. 5A, in the present embodiment, the inside diameter of the cylindrical pipe 35, which is connected to one of the joints 34, is larger than the dimension of a hole of the multi-hole flat pipe 300, which is connected to the other joint 34, in the thickness direction.
Moreover, the wall thickness of the pipe of the joint 34 is larger than the wall thickness of the cylindrical pipe 35. The wall thickness of the pipe of the joint 34 is made larger, because the joint 34 has a flat portion and needs to have higher strength than the cylindrical pipe 35.
Preferably, the joint 34 according to the present embodiment further includes a reinforcement member 304 that is disposed in a refrigerant channel so as to extend in the vertical direction. The reinforcement member 304 is disposed near the first connection portion 301. The reinforcement member 304, which connects upper and lower parts of the pipe of the joint 34, serves as a reinforcement in a case where a tensile stress is applied and in a case where a compressive stress is applied in the vertical direction in Fig. 5A. Preferably, the reinforcement member 304 is used, because CO₂ refrigerant has high pressure and the first connection portion 301 has a flat shape.

(2-4-1) Method of Manufacturing Joint 34

Two methods of manufacturing the joint 34 according to the present embodiment will be described.
A first method of manufacturing the joint 34 is a method in which a cylindrical pipe is used.
The cylindrical pipe is an ordinary cylindrical pipe having a uniform inside diameter. The wall thickness of a cylindrical pipe used as a material is larger than the wall thickness of the cylindrical pipe 35 to be connected. In order to form the first connection portion 301, one end of the cylindrical pipe is flattened. Then, the cylindrical pipe is processed so that the inside dimension L₃₀₁ of an end portion in the vertical direction becomes slightly larger than the thickness T of the multi-hole flat pipe 300 and so that the inside dimension W₃₀₁ of the end portion in the horizontal direction becomes slightly larger than the width W of the multi-hole flat pipe 300 in the horizontal direction.
As described above, the joint 34 according to the present embodiment is formed by processing one end of the cylindrical pipe by using the manufacturing method. The wall thickness of the cylindrical pipe used as a material is larger than the wall thickness of the cylindrical pipe 35 to be connected. The original portion of the cylindrical pipe used as a material becomes the portion of the body 302 where the inside dimensions L₃₀₂ and W₃₀₂ are uniform.
Because the joint 34 according to the present embodiment can be manufactured by performing simple processing on a cylindrical pipe, the manufacturing cost of the joint 34 can be suppressed.
Although the manufacturing method is comparative easy, it is difficult to insert the reinforcement member 304. Accordingly, this manufacturing method is used in a case where the reinforcement member 304 is not used.
A second method of manufacturing the joint 34 is a method in which bonding is used.
Regarding the joint 34 illustrated in Fig. 5A, an upper portion above the center and a lower portion below the center are prepared separately. These portions need not be each a half of the joint 34, and one of the portions may be larger.
The reinforcement member 304 is bonded to the upper portion or the lower portion beforehand by brazing or the like. The upper portion and the lower portion are bonded to each other by brazing or the like to form the joint 34.
The joint 34 according to the present embodiment may be manufactured by bonding two or more members as described above. By using the bonding method, a joint having a complex structure, such as a joint including the reinforcement member 304, can be easily manufactured.

(2-5) Intermediate Heat Exchanger 7

Referring Fig. 8A, which is a top view, and Fig. 8B, which is a sectional view, the disposition of the intermediate heat exchanger 7 according to the present embodiment will be described.
As illustrated in Fig. 8A, the intermediate heat exchanger 7 according to the present embodiment is disposed, independently from the heat exchanger 4, inside of the housing 20 and outside of the heat exchanger 4. Here, the term "independently" means that the fins 50 of the heat exchanger 4 and fins (not shown) of the intermediate heat exchanger 7 are not connected, and that the heat exchanger 4 and the intermediate heat exchanger 7 have separate refrigerant inlets and outlets.
As illustrated in Fig. 8B, the intermediate heat exchanger is disposed at a height above half the height of the heat exchanger 4.
In the heat source unit 10 according to the present embodiment, the fan 40 is disposed above the heat exchanger 4 and the intermediate heat exchanger 7, and the airflow speed increases upward along a side of the heat exchanger 4.
The intermediate heat exchanger 7, which is disposed on the upstream side of the heat exchanger 4, can reliably maintain a sufficient temperature difference between air and refrigerant, and can increase the heat exchange amount.
Moreover, because the intermediate heat exchanger 7 is disposed at an upper part, the intermediate heat exchanger 7 can receive a comparatively large amount of airflow and can increase the heat exchange amount.

(3) Features

(3-1)
The heat source unit 10 according to the present embodiment is the heat source unit 10 of the refrigeration apparatus 1 that uses CO₂ refrigerant and that exchanges heat between the CO₂ refrigerant and another fluid. The heat source unit 10 includes the compressor 2, the heat-source-side heat exchanger 4, and the intermediate heat exchanger 7. The compressor 2 performs multi-stage compression of two or more stages. The heat-source-side heat exchanger 4 exchanges heat between the refrigerant and the fluid. The intermediate heat exchanger 7 exchanges heat between the refrigerant and the fluid after the compressor 2 has performed first-stage compression and before the compressor 2 performs final-stage compression. The intermediate heat exchanger 7 is disposed, independently from the heat-source-side heat exchanger 4, on the upstream side of the heat-source-side heat exchanger 4 in the flow of the fluid. Here, the term "independently" means that the fins 50 of the heat exchanger 4 and fins (not shown) of the intermediate heat exchanger 7 are not connected, and that the heat exchanger 4 and the intermediate heat exchanger 7 have separate refrigerant inlets and outlets.
Because the intermediate heat exchanger 7 according to the present embodiment is disposed on the upstream side of the heat-source-side heat exchanger 4, the intermediate heat exchanger 7 can easily and reliably maintain a sufficient temperature difference between Co₂ refrigerant and air even when the temperature of the refrigerant is comparatively low and can perform efficient heat exchange.
(3-2)
In the present embodiment, the heat source unit 10 further includes the fan 40 and the housing 20. The fan 40 is a device for moving air to the heat-source-side heat exchanger 4. The housing 20 contains the compressor 2, the heat-source-side heat exchanger 4, the fan 40, and the intermediate heat exchanger 7. The fan 40 sucks air from a side of the housing and blows out the air upward from the top of the housing.
In the heat source unit 10 according to the present embodiment, further, the intermediate heat exchanger 7 is disposed at a height that is above half the height of the heat-source-side heat exchanger 4.
Because the intermediate heat exchanger 7 is disposed at a position where airflow speed is high, the heat source unit 10 according to the present embodiment increases the heat exchange amount of the intermediate heat exchanger 7 and improves efficiency.

(4) Modifications

(4-1) Modification 1A

In the first embodiment, a case where the reversely bent portion 33 is formed from the joint 34 and the U-shaped pipe 350 has been described. In modification 1A, as illustrated in Fig. 4B, the first linear portion 31, the reversely bent portion 33, and the second linear portion 32 are formed by bending one heat transfer tube. In modification 1A, the heat transfer tube 30 may be a cylindrical pipe or a multi-hole flat pipe. In modification 1A, a multi-hole flat pipe is selected. The multi-hole flat pipe is bent by 180° in the thickness direction while keeping the original shape in the width direction. The thickness T of the heat transfer tube in the vertical direction is 3 mm or smaller. In the present embodiment, the distance DP between the center of the first linear portion 31 and the center of the second linear portion 32 in the vertical direction is 21 mm or smaller.
The number of components of a heat exchanger 4 according to modification 1A is small, because the reversely bent portion 33 is formed by bending the heat transfer tube 30, which is one pipe. Moreover, because the reversely bent portion 33 does not have a connection portion, refrigerant leakage at a connection portion is not likely to occur.

(4-2) Modification 1B

In the first embodiment, a case where the reversely bent portion 33 is formed from the joint 34 and the U-shaped pipe 350 has been described. In modification 1B, a manifold is used as the reversely bent portion 33. In the manifold, refrigerants that have passed through the plurality of heat transfer tubes 30a are temporarily mixed, the direction of flow of the mixed refrigerant is reversed, and the refrigerant is supplied to the other heat transfer tubes 30b. In other respects, modification 1B is the same as the first embodiment.
In the reversely bent portion 33 according to the modification 1B, in which a manifold is used, refrigerants that have flowed through the plurality of heat transfer tubes 30a are joined in the manifold. Thus, the refrigerant temperature can be made uniform.

(4-3) Modification 1C

In the first embodiment, the joint 34 is separate from the multi-hole flat pipe 300 and the cylindrical pipe 35. In modification 1C, the joint 34 is integrated with the cylindrical pipe 35. In other respects, modification 1C is similar to the first embodiment.
In the joint 34 according to modification 1C, as with the joint 34 according to the first embodiment, the inside dimension L₃₀₂ of the body 302 in the vertical direction is larger than the inside dimension L₃₀₁ of the first connection portion in the vertical direction. Therefore, oil is unlikely to stagnate in a region near a connection portion of the inner peripheral surface of the joint 34.
As an application of the joint 34 according to modification 1A, the reversely bent portion 33 illustrated in Fig. 4A may be formed by integrating the joint 34a, the U-shaped pipe 350, and the joint 34b.

(4-4) Modification 1D

(4-4-1) Structure of Heat Exchanger 4 according to Modification 1D

In the heat exchanger 4 according to each of the first embodiment and modification 1A, the heat transfer tube 30 is reversely bent vertically. That is, the first linear portion 31 and the second linear portion 32 belong to the same row. In a heat exchanger 4 according to modification 1D, the heat transfer tube 30 is reversely bent across rows. In other respects, the structure of a refrigeration apparatus 1 according to modification 1D is the same as that of each of the first embodiment and modification 1A.
The structure of the heat exchanger 4 according to modification 1D will be described with reference to the drawings. Figs. 7A and 7B are side views of the first end portion 4a and the second end portion 4b as seen in the direction in which refrigerant flows. Fig. 6B is a sectional view of a middle portion between the first end portion 4a and the second end portion 4b, taken along a section S perpendicular to the direction in which refrigerant flows. As in the first embodiment, the first heat transfer tubes 30a are heat transfer tubes through which refrigerant flows from the first end portion 4a to the second end portion 4b, and the second heat transfer tubes 30b are heat transfer tubes through which refrigerant flows in the opposite direction. Also in modification 1D, flow or refrigerant when the heat exchanger 4 is used as a radiator will be described. When the heat exchanger 4 is used as an evaporator, the direction of flow of refrigerant is reversed. In modification 1D, a multi-hole flat pipe is used as a heat transfer tube. The thickness T of the heat transfer tube 30 in the vertical direction is 3 mm or smaller.
In the heat exchanger 4 according to modification 1D, refrigerant flows into a first refrigerant port 401 illustrated in Fig. 7A. The refrigerant flows through the first heat transfer tube 30a from the first refrigerant port 401, passes along three sides of the heat exchanger 4, exchanges heat with air, and reaches the second end portion 4b.
The refrigerant that has reached the second end portion 4b is reversed by the reversely bent portion 33 to another row (here, an adjacent row on the upstream side in the airflow direction). The distance DP between the center of the first heat transfer tube 30a (the first linear portion 31) and the center of the second heat transfer tube 30b (the second linear portion 32) in the vertical direction is 21 mm or smaller. The structure of the reversely bent portion 33 according to modification 1D is similar to that of modification 1A. That is, the first heat transfer tube 30a and the second heat transfer tube 30b are connected via two joints 34 and the U-shaped pipe 350 that connects the two joints 34.
The heat transfer tubes 30a and 30b according to modification 1D are arranged vertically at a pitch P. The distance DP between the center of the first heat transfer tube 30a (the first linear portion 31) and the center of the second heat transfer tube 30b (the second linear portion 32) in the vertical direction is larger than 0 and smaller than P. That is, 0 < DP < P.
The refrigerant that has been reversed in the second end portion 4b flows through the second heat transfer tubes 30b, exchanges heat with air while passing along three sides, and reaches the first end portion 4a. The refrigerant that has reached the first end portion flows out from a second refrigerant port 402 to a refrigerant circuit outside of the heat exchanger 4.
In modification 1D, a case where the first heat transfer tube 30a is disposed downstream in the airflow direction and the second heat transfer tube 30b is disposed upstream in the airflow direction has been described. The disposition may be opposite to this.
In modification 1D, a case where the heat transfer tube 30 extends only one cycle between the first end portion 4a and the second end portion 4b has been described. The present disclosure is effective also in a case where the heat transfer tube 30 extends two or more cycles between the first and second end portions 4a and 4b.

(4-4-2) Features of Heat Exchanger according to Modification 1D

(4-4-2-1)
In the heat exchanger 4 according to modification 1D, the first heat transfer tube 30a and the second heat transfer tube 30b that are connected to each other via the reversely bent portion 33 are in rows that are adjacent to and different from each other. Accordingly, when the same row is seen, the first heat transfer tubes 30a and the second heat transfer tubes 30b in which refrigerants having different temperatures flow are not arranged side by side, and nonuniform distribution of temperature in the row is suppressed.
(4-4-2-2)
In the heat exchanger 4 according to modification 1D, the first heat transfer tube 30a and the second heat transfer tube 30b that are connected to each other via the reversely bent portion 33 are in rows that are adjacent to and different from each other. Moreover, the distance DP between the center of the first heat transfer tube 30a (the first linear portion 31) and the center of the second heat transfer tube 30b (the second linear portion 32) in the vertical direction is larger than 0 and smaller than P.
Due to this disposition, the second heat transfer tube 30b does not block airflow to the first heat transfer tube 30a, which is located downstream in the airflow direction, and heat exchange between air and refrigerant is promoted.
(4-4-2-3)
In modification 1D, the first refrigerant port 401 and the second refrigerant port 402 are arranged in different rows. Accordingly, for example, when a refrigerant manifold is additionally disposed at a refrigerant port, a connection pipe can be simply formed easily.

(4-5) Modification 1E

Fig. 6A is a sectional view of a heat exchanger 4 according to modification 1E at a middle portion between the first end portion 4a and the second end portion 4b, taken along a section S perpendicular to the direction in which refrigerant flows. Modification 1E differs from modification 1D in that the distance DP between the center of the first heat transfer tube 30a (the first linear portion 31) and the center of the second heat transfer tube 30b (the second linear portion 32) in the vertical direction at the reversely bent portion 33, for reversing the flow of refrigerant, at the second end portion 4b is 0. In other respects, modification 1E is the same as modification 1D.
The heat exchanger according to modification 1E has features that are similar to those of the heat exchanger 4 according to modification 1D described in (4-4-2-1) and (4-4-2-3).

(4-6) Modification 1F

In the first embodiment, the heat-source-side heat exchanger 4 exchanges heat between CO₂ refrigerant and air. However, a fluid that exchanges heat with the refrigerant is not limited to air. In modification 1F, the fluid is water. The structure of a refrigerant circuit is similar to that illustrated in Fig. 1.
In a heat source unit according to modification 1F, along a pipe in which water flows, the intermediate heat exchanger 7 exchanges heat with water on the upstream side, and the heat-source-side heat exchanger 4 exchanges heat with water on the downstream side.
The heat exchanger according to modification 1F easily and reliably maintains a sufficient temperature difference between water and the refrigerant in the intermediate heat exchanger 7, which has a comparatively low temperature, and can improve heat exchange efficiency, when the heat-source-side heat exchanger 4 functions as a radiator.

Second Embodiment

(5) Sub-Heat Exchanger 46

In the first embodiment, the heat-source-side heat exchanger 4 is one heat exchanger.
In a second embodiment, a heat-source-side heat exchanger 4 is composed of a main heat exchanger 45 and a sub-heat exchanger 46. The main heat exchanger 45 mainly performs heat-source-side heat exchange. The sub-heat exchanger 46 is connected between the main heat exchanger 45 (corresponding to the heat-source-side heat exchanger 4 in Fig. 1) and the expansion mechanism 5 in the refrigerant circuit. In the second embodiment, the intermediate heat exchanger is not necessary. Even in a case where the intermediate heat exchanger 7 is present, the disposition of the intermediate heat exchanger 7 is not limited. In other respects, the second embodiment is similar to the first embodiment.
Referring Fig. 9A, which is a top view, and Fig. 9B, which is a sectional view, the disposition of the main heat exchanger 45 and the sub-heat exchanger 46 according to the present embodiment will be described.
As illustrated in Fig. 9A, the sub-heat exchanger 46 according to the present embodiment is disposed, independently from the main heat exchanger 45, inside of the housing 20 and outside of the main heat exchanger 45. Here, the term "independently" means that the fins 50 of the main heat exchanger 45 and fins (not shown) of the sub-heat exchanger 46 are not connected, and that the main heat exchanger 45 and the sub-heat exchanger 46 have separate refrigerant inlets and outlets. In the refrigerant circuit, further, a refrigerant collecting portion may be disposed between the main heat exchanger 45 and the sub-heat exchanger 46. By disposing the refrigerant collecting portion, refrigerants are temporarily collected, and the refrigerant temperature and the like can be made uniform.
As illustrated in Fig. 9B, the sub-heat exchanger 46 is disposed above half the height of the main heat exchanger 45.
The present structure is particularly effective when the heat-source-side heat exchanger is used as a radiator. That is, in a radiator in a refrigeration cycle using CO₂ refrigerant, the temperature of the refrigerant increases toward a refrigerant inlet and decreases near a refrigerant outlet. That is, in the present embodiment, the temperature of the refrigerant is high in the main heat exchanger 45 and the temperature of the refrigerant is low in the sub-heat exchanger 46. That is, in the sub-heat exchanger 46, the temperature difference between the refrigerant and air is small.
In the heat source unit 10 according to the present embodiment, the fan 40 is disposed above the main heat exchanger 45 and the sub-heat exchanger 46, and the airflow speed increases upward along a side of the heat exchanger 4.
The sub-heat exchanger 46, which is disposed on the upstream side of the main heat exchanger 45, can reliably maintain a sufficient temperature difference between air and the refrigerant, and can increase the heat exchange amount.
Moreover, because the sub-heat exchanger 46 is disposed at an upper part, the sub-heat exchanger 46 can receive a comparatively large amount of airflow and can increase the heat exchange amount.

Third Embodiment

(6) Sub-Heat Exchanger 47

In the first embodiment, the heat-source-side heat exchanger 4 is one heat exchanger.
In the third embodiment, a heat-source-side heat exchanger 4 is composed of a main heat exchanger 45 and a sub-heat exchanger 47. The main heat exchanger 45 mainly performs heat-source-side heat exchange. The sub-heat exchanger 47 is connected, in the refrigerant circuit, to either of refrigerant inlet or outlet of the main heat exchanger 45 (corresponding to the heat-source-side heat exchanger 4 in Fig. 1) that is farther from the expansion mechanism 5. In the third embodiment, the intermediate heat exchanger is not necessary. Even in a case where the intermediate heat exchanger 7 is present, the disposition of the intermediate heat exchanger 7 is not limited. In other respects, the third embodiment is similar to the first embodiment.
Referring Fig. 10A, which is a top view, and Fig. 10B, which is a sectional view, the disposition of the main heat exchanger 45 and the sub-heat exchanger 47 according to the present embodiment will be described.
As illustrated in Fig. 10A, the sub-heat exchanger 47 according to the present embodiment is disposed, independently from the main heat exchanger 45, inside of the housing 20 and outside of the main heat exchanger 45. Here, the term "independently" means that the fins 50 of the main heat exchanger 45 and fins (not shown) of the sub-heat exchanger 47 are not connected, and that the main heat exchanger 45 and the sub-heat exchanger 47 have separate refrigerant inlets and outlets. In the refrigerant circuit, further, a refrigerant collecting portion may be disposed between the main heat exchanger 45 and the sub-heat exchanger 47. By disposing the refrigerant collecting portion, refrigerants are temporarily collected, and the refrigerant temperature and the like can be made uniform.
As illustrated in Fig. 10B, the sub-heat exchanger 47 is disposed above half the height of the main heat exchanger 45.
The present structure is particularly effective when the heat-source-side heat exchanger is used as a radiator. That is, in a radiator in a refrigeration cycle using CO₂ refrigerant, the temperature of refrigerant increases toward a refrigerant inlet and decreases near a refrigerant outlet. That is, in the present embodiment, the temperature of refrigerant is high in the sub-heat exchanger 47 and the temperature of refrigerant is slightly low in the main heat exchanger 45. That is, in the sub-heat exchanger 47, the temperature difference between the refrigerant and air is large.
In the heat source unit 10 according to the present embodiment, the fan 40 is disposed above the main heat exchanger 45 and the sub-heat exchanger 47, and the airflow speed increases upward along a side of the heat exchanger 4.
Although the sub-heat exchanger 47 is disposed on the downstream side of the main heat exchanger 45, the sub-heat exchanger 47 can maintain a sufficient temperature difference between air and the refrigerant. The main heat exchanger, which is disposed on the upstream side in the airflow direction, can maintain a sufficient temperature difference between air and refrigerant and can increase the heat exchange amount.
Moreover, because the sub-heat exchanger 47 is disposed at an upper part, the sub-heat exchanger 47 can receive a comparatively large amount of airflow and can increase the heat exchange amount.
Heretofore, embodiments of the present invention have been described. It should be understood that the configurations and details of the embodiments can be modified in various ways within the scope of the present invention which is solely defined by the appended claims.

Claims

A heat source unit (10) for a refrigeration apparatus (1) having a refrigerant circuit, the heat source unit is configured to use CO₂ refrigerant and to exchange heat between the CO₂ refrigerant and another fluid, the heat source unit comprising:
a compressor (2) that is configured to perform multi-stage compression of two or more stages;

a main heat exchanger (4, 45) that is configured to exchange heat between the refrigerant and the fluid; and

a sub-heat exchanger (7, 46, 47) that is disposed independently from the main heat exchanger and that is configured to exchange heat between the refrigerant and the fluid,

wherein the sub-heat exchanger is an intermediate heat exchanger (7) that is configured to exchange heat between the refrigerant and the fluid after the compressor has performed first-stage compression and before the compressor performs final-stage compression, and

wherein the intermediate heat exchanger is disposed on the upstream side of the main heat exchanger in the flow of the fluid;

wherein the fluid is air, and,

the heat source unit further comprising:
a fan (40) for moving the air to the main heat exchanger, and

a housing (20) that contains the compressor, the main heat exchanger, the fan, and the intermediate heat exchanger, and

wherein the fan is configured to suck the air from a side of the housing and to blow out the air upward from a top of the housing;

wherein the intermediate heat exchanger is disposed at a height above half the height of the main heat exchanger.
A heat source unit (10) for a refrigeration apparatus (1) having a refrigerant circuit, the heat source unit is configured to use CO₂ refrigerant and to exchange heat between the CO₂ refrigerant and another fluid, the heat source unit comprising:
a compressor (2) that is configured to perform multi-stage compression of two or more stages;

a main heat exchanger (4, 45) that is configured to exchange heat between the refrigerant and the fluid; and

a sub-heat exchanger (7, 46, 47) that is disposed independently from the main heat exchanger and that is configured to exchange heat between the refrigerant and the fluid, the sub-heat exchanger being disposed on an upstream side or a downstream side of the main heat exchanger in a flow of the fluid;

the heat source unit further comprising:
an expansion mechanism (5) that expands the refrigerant,

wherein the sub-heat exchanger (46) is connected between the main heat exchanger (45) and the expansion mechanism, and

wherein the sub-heat exchanger is disposed on the upstream side of the main heat exchanger in the flow of the fluid;

wherein the fluid is air, and,

the heat source unit further comprising:
a fan (40) for moving the air to the main heat exchanger, and

a housing (20) that contains the compressor, the main heat exchanger, the fan, and the sub-heat exchanger, and

wherein the fan is configured to suck the air from a side of the housing and to blow out the air upward from a top of the housing;

wherein the sub-heat exchanger is disposed at a height above half the height of the main heat exchanger.
A heat source unit (10) for a refrigeration apparatus (1) having a refrigerant circuit, the heat source unit is configured to use CO2 refrigerant and that is configured to exchange heat between the CO2 refrigerant and another fluid, the heat source unit comprising:
a compressor (2) that is configured to perform multi-stage compression of two or more stages;

a main heat exchanger (4, 45) that is configured to exchange heat between the refrigerant and the fluid; and

a sub-heat exchanger (7, 46, 47) that is disposed independently from the main heat exchanger and that is configured to exchange heat between the refrigerant and the fluid, the sub-heat exchanger being disposed on an upstream side or a downstream side of the main heat exchanger in a flow of the fluid;

the heat source unit further comprising:
an expansion mechanism (5) that configured to expand the refrigerant,

wherein the sub-heat exchanger (46) is connected to either of the refrigerant inlet or outlet of the main heat exchanger that is farther from the expansion mechanism, and

wherein the sub-heat exchanger is disposed on the downstream side of the main heat exchanger in the flow of the fluid;

wherein the fluid is air, and,

the heat source unit further comprising:
a fan (40) for moving the air to the main heat exchanger, and

a housing (20) that contains the compressor, the main heat exchanger, the fan, and the sub-heat exchanger, and

wherein the fan is configured to suck the air from a side of the housing and to blow out the air upward from a top of the housing;

wherein the sub-heat exchanger is disposed at a height above half the height of the main heat exchanger.