EP2916086A1

EP2916086A1 - Heat exchanger and air conditioner employing the same

Info

Publication number: EP2916086A1
Application number: EP15157890.3A
Authority: EP
Inventors: Hiroshi Kanbara; Michiaki Nakanishi
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Thermal Systems Ltd
Priority date: 2014-03-07
Filing date: 2015-03-05
Publication date: 2015-09-09
Also published as: JP2015169387A; JP6494916B2

Abstract

Provided is a heat exchanger with which it is possible to ensure a high enough heat exchange performance by optimizing the heat transfer coefficient and pressure loss of refrigerant by optimizing the configuration of branched circuits, and as well as an air conditioner employing such a heat exchanger.

In a fin-tube-type heat exchanger (9) in which HFO refrigerant is employed and the refrigerant is circulated through numerous refrigerant tubes (11) by being branched to and collected from multiple circuits, a maximum number of branched circuits among the numerous refrigerant tubes (11) is six circuits, and, of the total number of the numerous refrigerant tubes (11), the proportion accounted for by a one-circuit portion (13A) and two- and four-circuit portions (13B and 13C) is set within a range from 7 to 30 % in accordance with the capacity of the heat exchanger (9).

Description

{Technical Field}

The present invention relates to a heat exchanger that is suitable when R1234yf refrigerant (hydrofluoroolefin; hereinafter, also referred to simply as HFO refrigerant) having a low Global Warming Potential (GWP) is employed as a refrigerant, and to an air conditioner employing such a heat exchanger.

{Background Art}

R1234yf refrigerant (HFO refrigerant) is known to be a low-GWP refrigerant whose Global Warming Potential (GWP) is lower than widely employed HFC refrigerants such as R410A refrigerant, R134a refrigerant, and so forth in the related art. However, with this HFO refrigerant, because the overall refrigerant temperature is decreased by about 10 to 20 degrees as compared with R410A refrigerant or the like due to the physical properties of the refrigerant, the heating performance may possibly be deteriorated due to a decrease in the amount of radiated heat.
Therefore, Patent Literature 1 provides an invention designed to achieve a capacity equivalent to a unit employing R410A refrigerant even in the case in which HFO refrigerant is employed. With this invention, in refrigerant pipes through which gaseous refrigerant passes during heating and that constitute an outdoor heat exchanger, as well as in connecting pipes between the exit of the outdoor exchanger and the intake port of a compressor, the fluid passage area is set so as to make refrigerant flow rates therein equal to or less than a predetermined value, or, alternatively, assuming that the inner diameter of refrigerant pipes constituting the outdoor heat exchanger is D mm, and that the number of paths thereof is P, the pipes are configured so as to satisfy the condition (3.1415 × D² × P)/4 ≥ 169.3 mm², so that the pressure loss at a point through which the gaseous refrigerant passes during heating will be an appropriate level of pressure loss equivalent to the case in which R410A refrigerant is employed.
In addition, Patent Literature 2 discloses an invention that relates to a distributor that distributes refrigerant to a plurality of heat-conducting tubes of a heat exchanger and a to refrigerator provided with that distributor, and that relates, in particular, to a distributor structure in which the number of refrigerant paths is changed in accordance with the operating conditions. In addition, Patent Literature 3 discloses an invention in which, with a heat exchanger having at least two paths including N tubes divided into two sets of tubes, the amount of heat exchange is optimized by setting the ratio N1/N to 15 to 50 % when a first set of tubes includes N1 tubes between a pair of collectors and a second set of tubes includes N2 tubes between a pair of collectors.

{Citation List}

{Patent Literature}

{PTL 1} Japanese Unexamined Patent Application, Publication No. 2011-2217
{PTL 2} Japanese Unexamined Patent Application, Publication No. 2010-261683
{PTL 3} Japanese Translation of PCT International Application, Publication No. 2013-501909

{Summary of Invention}

{Technical Problem}

However, in an indoor heat exchanger (fin-tube-type heat exchanger) in which refrigerant flows through numerous refrigerant tubes by being branched to and collected from multiple circuits, the inventions disclosed in Patent Literatures 1 to 3 are not designed for ensuring a high enough heat exchange performance, and therefore heating performance, by adjusting the heat transfer coefficient and pressure loss of the refrigerant by appropriately configuring the branching and collecting structure when employing a multi-circuit form, in order to compensate for the deterioration of the heating performance in the case in which HFO refrigerant is employed.
Specifically, in order to ensure a high enough heating performance by suppressing a decrease in the amount of radiated heat, it is effective to increase the refrigerant flow rate and to thereby improve the heat transfer coefficient; however, increasing the refrigerant flow rate causes pressure loss, and therefore, it is important to appropriately configure refrigerant flow channels in the heat exchanger. On the other hand, however, from the design viewpoint of reducing the size of an indoor unit of an air conditioner, it is not desirable to unnecessarily increase the number of branched circuits because doing so will increase the size of the indoor heat exchanger.
The present invention has been conceived in light of the above-described circumstances, and an object thereof is to provide a heat exchanger with which it is possible to ensure a high enough heat exchange performance by optimizing a heat transfer coefficient and pressure loss of a refrigerant by optimizing the configuration of branched circuits, and to provide an air conditioner employing such a heat exchanger.

{Solution to Problem}

In order to solve the above-described problems, a heat exchanger of the present invention and an air conditioner employing the same employ the following solutions.
A first aspect of the present invention is a heat exchanger that is a fin-tube-type heat exchanger in which HFO refrigerant is employed, and in which the refrigerant is circulated through numerous refrigerant tubes by being branched to and collected from multiple circuits, wherein a maximum number of the branched circuits among the numerous refrigerant tubes is six circuits, and, of a total number of the numerous refrigerant tubes, a proportion accounted for by a one-circuit portion and two- to four-circuit portions is set within a range from 7 to 30 % in accordance with a capacity of the heat exchanger.
With the heat exchanger according to the above-described first aspect, by limiting the maximum number of the branched circuits among the refrigerant tubes to six, it is possible to suppress pressure loss by ensuring a sufficient number of the branched circuits and to set the pressure loss within an appropriate range while avoiding an increase in the size of branching/collecting units, as well as the size of the heat exchanger, due to an unnecessary increase in the number of circuits. In addition, of the total number of the refrigerant tubes, by setting the proportion accounted for by the one-circuit portion and the two- to four-circuit portions within the range from 7 to 30 % in accordance with the capacity of the heat exchanger, while maintaining the pressure loss within an appropriate range both during cooling and heating, it is possible to prevent, during heating, the deterioration of the heating COP (coefficient of performance) due to the deterioration of the heat transfer coefficient caused by the proportion accounted for by the one-circuit portion and the two- to four-circuit portions falling below 7 % and by a decrease in the flow rate of the refrigerant that is made liquid-rich due to an increase in the number of circuits, and, during cooling, on the other hand, it is possible to prevent the deterioration of the cooling COP due to the deterioration of the heat transfer coefficient caused by the proportion accounted for by the one-circuit portion and the two- to four-circuit portions exceeding 30 %, thus increasing the pressure loss of the refrigerant that has expanded by being vaporized due to a decrease in the number of circuits. Therefore, it is possible to maintain a high COP by setting the heat transfer coefficient and the pressure loss of the refrigerant in the optimal ranges both during cooling and heating, which makes it possible to ensure a high enough heat exchange performance, and therefore heating performance, in a heat exchanger employing HFO refrigerant.
In the above-described heat exchanger, of a total number of the numerous refrigerant tubes, the proportion accounted for by the one-circuit portion and the two- to four-circuit portions may be set within a range from 15 to 30 % in the case of a heat exchanger whose capacity is in a 2-kW to 3.6-kW class, and within a range from 7 to 15 % in the case of a heat exchanger whose capacity is above 3.6-kW class and up to 6-kW class.
With this configuration, by setting the proportion accounted for by the one-circuit portion and the two- to four-circuit portions within the range from 15 to 30 % in the case of the heat exchanger whose capacity is low, namely, in the 2-kW to 3.6-kW class, and that is designed for air conditioners whose driving power is normally 100 V and by setting the proportion accounted for by the one-circuit portion and the two- to four-circuit portions within the range from 7 to 15 % in the case of the heat exchanger whose capacity is high, at above 3.6-kW class and up to 6-kW class, and that is designed for air conditioners whose driving power is 200 V, for each case, it is possible to set the proportion accounted for by the one-circuit portion and the two- to four-circuit portions within the appropriate range in accordance with the capacity, and thus, it is possible to maintain the heat transfer coefficient and the pressure loss within the appropriate ranges. Specifically, with the heat exchanger of above 3.6-kW class and up to 6-kW class, having high capacity, because the pressure loss is increased due to an increase in the refrigerant flow rate caused by an increase in the amount of circulated refrigerant in accordance with the capacity, by decreasing the proportion accounted for by the one-circuit portion and the two- to four-circuit portions by a corresponding amount, it is possible to suppress an increase in the pressure loss by optimizing the multi-circuit form. Therefore, it is possible to ensure a high enough heat exchange performance by maintaining a high COP by appropriately setting the heat transfer coefficient and the pressure loss of the refrigerant in each case in accordance with the capacity of the heat exchanger.
In the above-described heat exchanger, of a total number of the numerous refrigerant tubes, the proportion accounted for by the one-circuit portion may be set within a range from 5 to 15 % in the case of a heat exchanger whose capacity is in a 2-kW to 3.6-kW class, and within a range from 3 to 10 % in the case of a heat exchanger whose capacity is above 3.6-kW class and up to 6-kW class.
With this configuration, by setting the proportion accounted for by the one-circuit portion within the range from 5 to 15 % in the case of the heat exchanger whose capacity is low, namely, in the 2-kW to 3.6-kW class, and that is designed for air conditioners whose driving power is normally 100 V and by setting the proportion accounted for by the one-circuit portion within the range from 3 to 10 % in the case of the heat exchanger whose capacity is high, at above 3.6-kW class and up to 6-kW class, and that is designed for air conditioners whose driving power is 200 V, for each case, it is possible to set the proportion accounted for by the one-circuit portion within the appropriate range in accordance with the capacity. Specifically, at the one-circuit portion, because the pressure loss is increased due to an increase in the refrigerant flow rate, it is possible to suppress an increase in the pressure loss by decreasing the proportion accounted for by the one-circuit portion by a corresponding amount while keeping only the minimum number of one-circuit portion required to ensure a high enough heating performance. Therefore, it is possible to ensure a high enough heat exchange performance by appropriately setting the heat transfer coefficient and the pressure loss of the refrigerant in each case in accordance with the capacity of the heat exchanger.
A second aspect of the present invention is an air conditioner in which a refrigeration cycle is filled with HFO refrigerant, and in which an indoor heat exchanger constituting the refrigeration cycle is any one of the above-described heat exchangers.
With the air conditioner according to the above-described second aspect, even if HFO refrigerant, which is a low-GWP refrigerant, is employed as the refrigerant, by employing the above-described heat exchanger as an indoor heat exchanger, it is possible to enhance the heat exchange performance by maintaining a high COP by setting, both during cooling and heating, the heat transfer coefficient and the pressure loss of the refrigerant within the appropriate ranges. Therefore, by suppressing the deterioration of the heating performance, it is possible to ensure substantially equivalent air conditioning performance to that of air conditioners employing R410A refrigerant.

{Advantageous Effects of Invention}

With a heat exchanger of the present invention, by limiting the maximum number of branched circuits among the refrigerant tubes to six, it is possible to suppress pressure loss by ensuring a sufficient number of branched circuits and to set the pressure loss within an appropriate range while avoiding an increase in the size of branching/collecting units, as well as the size of the heat exchanger, due to an unnecessary increase in the number of circuits. In addition, of the total number of refrigerant tubes, by setting the proportion accounted for by the one-circuit portion and the two- to four-circuit portions within the range from 7 to 30 % in accordance with the capacity of the heat exchanger, while maintaining the pressure loss within an appropriate range both during cooling and heating, it is possible to prevent, during heating, the deterioration of the heating COP due to the deterioration of the heat transfer coefficient caused by the proportion accounted for by the one-circuit portion and the two- to four-circuit portions falling below 7 % and by a decrease in the flow rate of the refrigerant that is made liquid-rich due to an increase in the number of circuits, and, during cooling, on the other hand, it is possible to prevent the deterioration of the cooling COP due to the deterioration of the heat transfer coefficient caused by the proportion accounted for by the one-circuit portion and the two- to four-circuit portions exceeding 30 %, thus increasing the pressure loss of the refrigerant that has expanded by being vaporized due to a decrease in the number of circuits; therefore, it is possible to maintain a high COP by setting the heat transfer coefficient and the pressure loss of the refrigerant in the optimal ranges both during cooling and heating, which makes it possible to ensure a high enough heat exchange performance, and therefore, heating performance, in a heat exchanger employing HFO refrigerant.
With an air conditioner of the present invention, even if HFO refrigerant, which is a low-GWP refrigerant, is employed as the refrigerant, by employing the above-described heat exchanger as an indoor heat exchanger, it is possible to enhance the heat exchange performance by maintaining a high COP by setting, both during cooling and heating, the heat transfer coefficient and the pressure loss of the refrigerant within the appropriate ranges; therefore, by suppressing the deterioration of the heating performance, it is possible to ensure substantially equivalent air conditioning performance to that of air conditioners employing R410A refrigerant.

{Brief Description of Drawings}

{Fig. 1} Fig. 1 is an external perspective view of an air conditioner according to an embodiment of the present invention.
{Fig. 2} Fig. 2 is a schematic diagram showing an example configuration of refrigerant tube circuits of an indoor heat exchanger provided in an indoor unit of the above-described air conditioner.
{Fig. 3} Fig. 3 is a table showing example settings of the refrigerant tube circuits of the heat exchanger described above.
{Fig. 4} Fig. 4 is a graph showing the relationship, in the above-described heat exchanger, between circuit proportion and the COP and pressure loss during heating.
{Fig. 5} Fig. 5 is a graph showing the relationship, in the above-described heat exchanger, between circuit proportion and the COP and pressure loss during cooling.

{Description of Embodiment}

An embodiment according to the present invention will be described below with reference to Figs. 1 to 5.
Fig. 1 is an external perspective view of an air conditioner 1 according to this embodiment of the present invention, and Fig. 2 is a schematic diagram showing an example configuration of refrigerant tube circuits of an indoor heat exchanger of an indoor unit of the air conditioner 1.
The air conditioner 1 is a separate-type air conditioner and is provided with an outdoor unit 2 and an indoor unit 3. The outdoor unit 2 is installed at an appropriate outdoor location, and, in addition, the indoor unit 3 is installed on an indoor wall surface or the like via a mounting plate 4; the outdoor unit 2 and the outdoor unit 3 are connected by an indoor-outdoor connecting pipe 5, signal lines (not shown), and so forth to form a single unit, and the operation thereof is controlled via a remote controller 6.
As is known, the outdoor unit 2 accommodates outdoor equipment installed therein, such as a compressor, an outdoor heat exchanger, an outdoor blower, a four-way valve, an expansion valve, an outdoor controller, and so forth, and the indoor unit 3 accommodates indoor equipment installed therein, such as an indoor heat exchanger, an indoor blower, an indoor controller, and so forth. The compressor, the outdoor heat exchanger, the four-way valve, the expansion valve, the indoor heat exchanger, and so forth are sequentially connected by means of pipes via refrigerant pipes, including the indoor-outdoor connecting pipe 5, thereby forming a known refrigeration cycle which is a closed cycle. Also, the interior of the refrigeration cycle is filled with a required amount of R1234yf refrigerant (HFO refrigerant) which is a low-GWP refrigerant having a low Global Warming Potential (GWP).
In addition, the indoor unit 3 takes in indoor air from an intake grill 7 that is provided at a top face thereof (and/or a front face), blows out this air into an indoor space from a vent 8 by means of the blower, after the temperature thereof is adjusted by cooling or heating the air by means of an indoor heat exchanger 9 (see Fig. 2), thus supplying this air for indoor air conditioning. As shown in Fig. 2, the indoor heat exchanger 9 is divided into a plurality of heat exchangers which are disposed in the indoor unit 3 in a stacked manner so as to form two layers each at the front side and the rear side thereof in the front-to-back direction.
This indoor heat exchanger 9 is a fin-tube-type heat exchanger constituted of numerous plate fins 10 formed of aluminum thin plates and numerous refrigerant tubes 11 formed of copper pipes, and refrigerant is circulated through the numerous refrigerant tubes 11 by being branched to and collected from multiple circuits via a plurality of branching/collecting units 12. The indoor heat exchanger (heat exchanger) 9 in this embodiment is a heat exchanger 9 that is employed in a small air conditioner whose capacity is in the 2-kW to 6-kW class, and copper pipes having a diameter of 6.35 mm are employed as the refrigerant tubes 11.
Note that, in the case of small air conditioners in which the capacity of the indoor heat exchanger (heat exchanger) 9 is in the 2-kW to 6-kW class, in general, air conditioners whose capacity is in the 2-kW to 3.6-kW class use 100-V power as driving power, and air conditioners whose capacity is above the 3.6-kW class and up to 6-kW class use 200-V power as driving power.
Fig. 2 shows a 2.5-kW class heat exchanger 9 whose capacity falls within a range from 2-kW to 3.6-kW class and in which the total number of the refrigerant tubes 11 is 48. More specifically, the configuration of the heat exchanger 9 is such that the total number of refrigerant tubes 11 is 48, that, with regard to the number of branched circuits, one-circuit portions 13A have a total of six refrigerant tubes 11, four-circuit portions 13C have a total of eight refrigerant tubes 11, and six-circuit portions 13D have a total of 34 refrigerants tubes 11; and that the one-circuit portions 13A account for 13 % of the total number of refrigerant tubes 11, and the one-circuit portions 13A and the two- and four-circuit portions 13B and 13C together account for 29 % of the total number of refrigerant tubes 11.
Similarly, the table in Fig. 3 shows example configurations (1) to (4) of the heat exchanger 9 in which the refrigerant tubes 11 are configured in a multi-circuit form.
The multi-circuit example (1) is a heat exchanger 9 whose configuration is such that the one-circuit portions 13A have four refrigerant tubes 11 in total, and the six-circuit portions 13D have 44 refrigerant tubes 11 in total, and that the proportion accounted for by the one-circuit portions 13A is 8 %, and the proportion accounted for by the one-circuit portions 13A and the two- and four-circuit portions 13B (not shown) and 13C is 8 %.
The multi-circuit example (2) is a heat exchanger 9 whose configuration is such that the one-circuit portions 13A have four refrigerant tubes 11 in total, the two-circuit portions 13B (not shown) have four refrigerant tubes 11 in total, and the six-circuit portions 13D have 40 refrigerant tubes 11 in total, and that the proportion accounted for by the one-circuit portions 13A is 8 %, and the proportion accounted for by the one-circuit portions 13A and the two- and four-circuit portions 13B and 13C is 17 %.
In addition, the multi-circuit example (3) is the above-described heat exchanger 9 shown in Fig. 2 as an example.
Furthermore, the multi-circuit example (4) is a heat exchanger 9 whose configuration is such that the one-circuit portions 13A have eight refrigerant tubes 11 in total, the two-circuit portions 13B have 10 refrigerant tubes 11 in total, and the six-circuit portions 13D have 30 refrigerant tubes 11 in total, and that the proportion accounted for by the one-circuit portions 13A is 17 %, and the proportion accounted for by the one-circuit portions 13A and the two- and four-circuit portions 13B and 13C is 38 %.
In Fig. 4, in which the horizontal axis indicates the proportion of the one-circuit portions as well as the proportion of the one-circuit portion and the two- to four-circuit portions, and the vertical axes indicate the heating COP as well as the heating pressure loss, results of analyses are shown regarding the individual relationships between these parameters for the heat exchanger 9 of the above-described multi-circuit examples (1) to (4), and in Fig. 5, in which the horizontal axis indicates the proportion of the one-circuit portions as well as the proportion of the one-circuit portion and the two- to four-circuit portions, and the vertical axes indicate the cooling COP as well as the cooling pressure loss, results of analyses are shown regarding the individual relationships between these parameters for the same heat exchangers 9. In the graphs shown in Figs. 4 and 5, the proportion accounted for by the one-circuit portions and the two- to four-circuit portions sequentially decreases from left to right on the horizontal axis, thus indicating the heat exchanger 9 having a greater number of circuits.
Viewing Fig. 4, it is clear that, when the heat exchanger 9 serves as a condenser during heating, it is possible to maintain a high heating COP by enhancing the heat transfer coefficient by decreasing the heating pressure loss, in the range in which the proportion accounted for by the one-circuit portions is from about 5 to 15 % and in the range in which the proportion accounted for by the one-circuit portions and the two- to four-circuit portions is from about 15 to 30 %. This is likely because, during heating, decreasing the proportion accounted for by the one-circuit portions and the two- to four-circuit portions, where the number of circuits involved is low, decreases the flow rate of the refrigerant that is made liquid-rich due to an increase in the number of circuits, and because this deteriorates the heat transfer coefficient, thus deteriorating the heating COP. Therefore, during heating, the above-described ranges are considered to be appropriate ranges for the proportion accounted for by portions having a low number of circuits.
In addition, viewing Fig. 5, it is clear that, when the heat exchanger 9 serves as an evaporator during cooling, cooling pressure loss increases, which decreases the heat transfer coefficient, thus deteriorating the cooling COP, in the range in which the proportion accounted for by the one-circuit portions exceeds about 15 % and in the range in which the proportion accounted for by the one-circuit portions and the two- to four-circuit portions exceeds about 30 %. This is likely because, during cooling, increasing the proportion accounted for by the one-circuit portions and the two- to four-circuit portions, where the number of circuits involved is low, increases the pressure loss of the refrigerant whose volume has expanded by being vaporized via evaporation due to a decrease in the number of circuits, and because this deteriorates the heat transfer coefficient, thus deteriorating the cooling COP. Therefore, during cooling, the above-described ranges are considered to be appropriate ranges for the proportion accounted for by portions having a low number of circuits.
On the other hand, although the above descriptions apply to the heat exchanger 9 employed in the air conditioners whose capacity is in the 2-kW to 3.6-kW class and that is driven by 100-V driving power, in the case of a heat exchanger 9 of one class higher, that is, above 3.6-kW class and up to 6-kW class, because such a heat exchanger 9 is employed in an air conditioner driven by 200-V driving power, the displacement level of the compressor is also increased, and because this increases the amount of circulated refrigerant, in order to cope with this change when configuring an indoor heat exchanger (heat exchanger) 9 in a multi-circuit form, it is also necessary to change the proportions accounted for by the portions having a low number of circuits, namely, the proportion accounted for by the one-circuit portions and the proportion accounted for by the one-circuit portions and the two- to four-circuit portions, respectively.
Now, as described above, in the case of the heat exchanger 9 of above 3.6-kW class and up to 6-kW class, because the amount of circulated refrigerant is increased, although it is necessary to increase the number of circuits involved, it is necessary to ensure a minimum required number of one-circuit portions in order to ensure a high enough performance during heating. The number of refrigerant tubes 11 in this case is two or four, and the appropriate range of the proportion accounted for by the one-circuit portions is from 4 to 8 %.
On the other hand, in consideration of an increase in the pressure loss during cooling, it is desirable to achieve a multi-circuit form by decreasing the number of two- to four-circuit portions as much as possible, except for the minimum number of one-circuit portions required to ensure a high enough heating performance. From these points, when only the minimum number of two- to four-circuit portions required to physically build a multi-circuit form is maintained, the appropriate range for the proportion accounted for by the one-circuit portions and the two- to four-circuit portions is 7 to 15 %, which is approximately half the range for the 2-kW to 3.6-kW class (15 to 30 %).
As above, with the above-described heat exchanger 9, in employing HFO refrigerant, the maximum number of branched circuits among the numerous refrigerant tube 11 is set at six, and, of the total number of the numerous refrigerant tubes 11, the proportion accounted for by the one-circuit portions and the two- to four-circuit portions is set within a range from 7 to 30 % in accordance with the capacity of the heat exchanger 9. By doing so, it is possible to set the heat transfer coefficient and the pressure loss of the refrigerant in optimal ranges both during cooling and heating.
In more detail, among the heat exchangers 9 that are employed in small air conditioners and whose capacity is in the 2.0-kW to 6.0-kW class, with small air conditioners that employ heat exchangers 9 whose capacity is in the 2.0-kW to 3.6-kW class and that are driven by 100-V driving power, of the total number of the numerous refrigerant tubes 11, it is desirable that the proportion accounted for by the one-circuit portions be set within a range from 5 to 15 %, and that the proportion accounted for by the one-circuit portions and the two- to four-circuit portions be set within a range from 15 to 30 %, and, with small air conditioners that employ heat exchangers 9 whose capacity is above 3.6-kW class and up to 6-kW class and that are driven by 200-V driving power, of the total number of the numerous refrigerant tubes 11, it is desirable that the proportion accounted for by the one-circuit portions be set within a range from 3 to 10 %, and that the proportion accounted for by the one-circuit portions and the two- to four-circuit portions be set within a range from 7 to 15 %.
As has been described, with this embodiment, in the fin-tube-type heat exchanger 9 configured in a multi-circuit form, the maximum number of branched circuits among the numerous refrigerant tubes 11 is set at six; of the total number of these numerous refrigerant tubes 11, the proportion accounted for by the one-circuit portions 13A and the two- and four-circuit portions 13B and 13C is set within a range from 7 to 30 % in accordance with the capacity of the heat exchanger 9. By limiting the maximum number of branched circuits among the refrigerant tubes 11 to six in this way, it is possible to suppress pressure loss by ensuring a sufficient number of branched circuits and to set the pressure loss within the appropriate range while avoiding an increase in the size of the branching/collecting units 12, as well as the size of the heat exchanger 9, due to an unnecessary increase in the number of circuit.
In addition, of the total number of refrigerant tubes 11, by setting the proportion accounted for by the one-circuit portions 13A and the two- and four-circuit portions 13B and 13C within the range from 7 to 30 % in accordance with the capacity of the heat exchanger 9, while maintaining the pressure loss within the appropriate range both during cooling and heating, it is possible to prevent, during heating, as shown in Fig. 4, the deterioration of the heating COP due to the deterioration of the heat transfer coefficient caused by the proportion accounted for by the one-circuit portions 13A and the two- and four-circuit portions 13B and 13C falling below 7 % and by a decrease in the flow rate of the refrigerant that is made liquid-rich due to an increase in the number of circuits.
Furthermore, during cooling, as shown in Fig. 5, it is possible to prevent the deterioration of the cooling COP due to the deterioration of the heat transfer coefficient caused by the proportion accounted for by the one-circuit portions 13A and the two- and four-circuit portions 13B and 13C exceeding 30 %, thus increasing the pressure loss of the refrigerant that has expanded by being vaporized due to a decrease in the number of circuits.
By doing so, in a heat exchanger 9 employing HFO refrigerant, it is possible to maintain a high COP by setting the heat transfer coefficient and the pressure loss of the refrigerant in the optimal ranges both during cooling and heating, which makes it possible to ensure a high enough heat exchange performance, and therefore heating performance.
On the other hand, with the above-described heat exchanger 9, of the total number of the numerous refrigerant tubes 11, the proportion accounted for by the one-circuit portions 13A and the two- and four-circuit portions 13B and 13C is set within the range from 15 to 30 % in the case of the heat exchanger 9 whose capacity is in the 2-kW to 3.6-kW class, and within the range from 7 to 15 % in the case of the heat exchanger 9 whose capacity is above 3.6-kW class and up to 6-kW class.
As above, by setting the proportion accounted for by the one-circuit portions 13A and the two- and four-circuit portions 13B and 13C within the range from 15 to 30 % in the case of the heat exchanger 9 whose capacity is low, namely, in the 2-kW to 3.6-kW class, and that is designed for air conditioners whose driving power is normally 100 V and by setting the proportion accounted for by the one-circuit portions 13A and the two- and four-circuit portions 13B and 13C within the range from 7 to 15 % in the case of the heat exchanger 9 whose capacity is high, at above 3.6-kW class and up to 6-kW class, and that is designed for air conditioners whose driving power is 200 V, for each case, it is possible to set the proportion accounted for by the one-circuit portions 13A and the two- and four-circuit portions 13B and 13C within the appropriate range in accordance with the capacity, and thus, it is possible to maintain the heat transfer coefficient and the pressure loss within the appropriate ranges.
Specifically, with the heat exchanger 9 of above 3.6-kW class and up to 6-kW class, having a high capacity, because the pressure loss is increased due to an increase in the refrigerant flow rate caused by an increase, in accordance with the capacity, in the amount of circulated refrigerant, by decreasing the proportion accounted for by the one-circuit portions 13A and the two- and four-circuit portions 13B and 13C by a corresponding amount, it is possible to suppress an increase in the pressure loss by optimizing the multi-circuit form by ensuring a minimum number of the one-circuit portion 13A and the two- and four-circuit portions 13B and 13C required to ensure a high enough heating performance or in order to build the circuits.
Therefore, it is possible to ensure a high enough heat exchange performance by maintaining a high COP by appropriately setting the heat transfer coefficient and the pressure loss of the refrigerant in each case in accordance with the capacity of the heat exchanger 9.
Furthermore, in this embodiment, of the total number of the numerous refrigerant tubes 11, the proportion accounted for by the one-circuit portions 13A is set within the range from 5 to 15 % in the case of the heat exchanger 9 whose capacity is in the 2-kW to 3.6-kW class, and within the range from 3 to 10 % in the case of the heat exchanger 9 whose capacity is above 3.6-kW class and up to 6-kW class. As above, by setting the proportion accounted for by the one-circuit portions within the range from 5 to 15 % in the case of the heat exchanger whose capacity is low, namely, in the 2-kW to 3.6-kW class, and that is designed for air conditioners whose driving power is normally 100 V and by setting the proportion accounted for by the one-circuit portions within the range from 3 to 10 % in the case of the heat exchanger whose capacity is high, at above 3.6-kW class and up to 6-kW class, and that is designed for air conditioners whose driving power is 200 V, for each case, it is possible to set the proportion accounted for by one-circuit portions within the appropriate range in accordance with the capacity, and thus, it is possible to maintain the heat transfer coefficient and the pressure loss within the appropriate ranges.
Specifically, at the one-circuit portions 13A, because the pressure loss is increased, both during cooling and heating, due to an increase in the refrigerant flow rate, it is possible to suppress an increase in the pressure loss by decreasing the proportion accounted for by the one-circuit portions 13A by a corresponding amount while keeping only the minimum number of the one-circuit portions required to ensure a high enough heating performance; therefore, it is possible to ensure a high enough heat exchange performance by maintaining a high COP by appropriately setting the heat transfer coefficient and the pressure loss of the refrigerant in each case in accordance with the capacity of the heat exchanger 9.
In addition, because the above-described heat exchanger 9 is employed as the indoor heat exchanger 9 of the air conditioner 1 constituting the refrigeration cycle filled with HFO refrigerant, even if HFO refrigerant, which is a low-GWP refrigerant, is employed as the refrigerant, by employing the above-described heat exchanger 9 as an indoor heat exchanger, it is possible to enhance the heat exchange performance by maintaining a high COP by setting, both during cooling and heating, the heat transfer coefficient and the pressure loss of the refrigerant within the appropriate ranges. Therefore, by suppressing the deterioration of the heating performance, it is possible to ensure substantially equivalent air conditioning performance to that of air conditioners employing R410A refrigerant.
In addition, the present invention is not limited to the invention according to the above-described embodiment, and appropriate modifications are possible within a range that does not depart from the scope thereof. For example, although the air conditioner 1 in which the heat exchanger 9 is employed as the indoor heat exchanger has been described in the above-described embodiment, it is naturally permissible to employ this heat exchanger 9 as an outdoor heat exchanger.

{Reference Signs List}

1: air conditioner
2: outdoor unit
3: indoor unit
9: heat exchanger (indoor heat exchanger)
10: plate fin
11: refrigerant tube
12: branching/collecting unit
13A: one-circuit portion
13B: two-circuit portion
13C: four-circuit portion
13D: six-circuit portion

Claims

A heat exchanger that is a fin-tube-type heat exchanger in which HFO refrigerant is employed, and in which the refrigerant flows through numerous refrigerant tubes (11) by being branched to and collected from multiple circuits, wherein
a maximum number of the branched circuits among the numerous refrigerant tubes (11) is six circuits, and,
of a total number of the numerous refrigerant tubes (11), a proportion accounted for by a one-circuit portion (13A) and two- to four-circuit portions (13B, 13C) is set within a range from 7 to 30%.
A heat exchanger according to Claim 1, wherein, of a total number of the numerous refrigerant tubes (11), the proportion accounted for by the one-circuit portion (13A) and the two- to four-circuit portions (13B, 13C) is set
within a range from 15 to 30 % in the case of a heat exchanger whose capacity is in a 2-kW to 3.6-kW class, and
within a range from 7 to 15 % in the case of a heat exchanger whose capacity is above 3.6-kW class and up to 6-kW class.
A heat exchanger according to Claim 2, wherein, of a total number of the numerous refrigerant tubes (11), the proportion accounted for by the one-circuit portion (13A) is set
within a range from 5 to 15 % in the case of a heat exchanger whose capacity is in a 2-kW to 3.6-kW class, and
within a range from 3 to 10 % in the case of a heat exchanger whose capacity is above 3.6-kW class and up to 6-kW class.
An air conditioner in which a refrigeration cycle is filled with HFO refrigerant, and comprising an indoor heat exchanger constituting the refrigeration cycle, which is a heat exchanger according to any one of Claims 1 to 3.