JPH1089779A - Air conditioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air conditioner which can maintain high freezing capacity under wide driving conditions in the conditioner having a refrigerant circuit for supercooling main flow refrigerant by heat exchanging the main refrigerant with a bypass flow refrigerant. SOLUTION: A refrigerant circuit 1 has a main circuit 6 in which refrigerant sequentially flows in order a compressor 2, a condenser 3, a supercooling heat exchanger 10, a motor driven expansion valve 4 for constituting a first expansion mechanism, an evaporator 5, and a bypass circuit 11 branched from the circuit 6 between the condenser 3 and the valve 4 and in which the refrigerant sequentially flows a capillary tube 12 for constituting a second expansion mechanism and a supercooling heat exchanger 10 to combine with the circuit 6 at a suction side of the compressor 2. The main flow refrigerant passing an outlet of the evaporator 5 is controlled by the valve 4 to become predetermined superheat degree irrespective of the state of the bypass flow refrigerant passing a bypass side outlet of the exchanger 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an air conditioner. More specifically, the present invention relates to an air conditioner including a refrigerant circuit that performs heat exchange between a mainstream refrigerant and a bypass flow refrigerant to supercool the mainstream refrigerant.

[0002]

2. Description of the Related Art As shown in FIG. 3, a refrigerant circuit 310 of this type of air conditioner includes a compressor 302, a condenser 30
3. Double-tube heat exchanger 310 for supercooling, electric expansion valve 3
04, a main circuit 306 having an evaporator 305, a four-way switching valve 309, and an accumulator 308 in this order, and a branch point 3 between the condenser 303 and the supercooling heat exchanger 310.
At 41, the main circuit 306 branches, passes through the capillary tube 312 and the subcooling heat exchanger 310, and at the junction 342 near the inlet of the accumulator 308, the main circuit 30
6 and a bypass circuit 313 (shown by a dashed line) that joins the known bypass circuit. As the refrigerant, a single refrigerant such as HCFC (hydrochlorofluorocarbon) 22 is used. The refrigerant discharged from the compressor 302 is condensed by a condenser (for example, radiates heat to outdoor air) 303 and is separated into a mainstream refrigerant flowing through a main circuit 306 and a bypass refrigerant flowing through a bypass circuit 313 at a branch point 341.
The mainstream refrigerant is supercooled in the subcooling heat exchanger 310 by heat exchange with the bypass-flow refrigerant after passing through the capillary tube 312, and then decompressed by the electric expansion valve 304. Then, the mainstream refrigerant is evaporated by an evaporator (for example, absorbing heat from indoor air) 305, and the four-way switching valve 309 and the accumulator 3 that performs gas-liquid separation
08 to the compressor 302. On the other hand, the bypass flow refrigerant is depressurized by passing through the capillary tube 312 and then evaporated by heat exchange with the main flow refrigerant in the supercooling heat exchanger 310. Thereafter, the bypass refrigerant flows into the junction 3 near the inlet of the accumulator 308.
At 42, it merges with the mainstream refrigerant.

[0003] By supercooling the mainstream refrigerant with the subcooling heat exchanger 310 in this way, the refrigeration effect of the mainstream refrigerant can be increased as compared with a case where supercooling is not performed. In addition, since the volume flow rate of the mainstream refrigerant is reduced by branching the bypass flow from the flow of the refrigerant, as shown in a pressure-specific enthalpy diagram (hereinafter, referred to as a “Ph diagram”) in FIG. The pressure loss ΔP in the evaporator 305 and the suction-side pipe of the compressor 302 can be reduced (for comparison, the pressure loss ΔP when supercooling is not performed (basic circuit))
₀ is shown in FIG. ). Therefore, the refrigeration capacity of the system can be improved. FIG. 5 (b)
The portions indicated by A, B, and C in the drawing correspond to the states of points A, B, and C near the junction 342 in the refrigerant circuit 301 in FIG. As can be clearly understood from FIG. 5C, which is a partially enlarged view of FIG. 5B, the bypass refrigerant reaching point A and the mainstream refrigerant reaching point B merge to form a state at point C. Is obtained.

Conventionally, the flow rates of the mainstream refrigerant and the bypass refrigerant have been adjusted by changing the throttle amount of an electric expansion valve 304 provided in a main circuit 306. Specifically, the temperature Tc detected by the temperature sensor 332 at the condenser outlet
And the temperature Te detected by the temperature sensor 333 at the evaporator inlet.
As shown in FIG. 4, a target temperature Td (target) = f (Te, Tc) at the outlet of the compressor is set as a function f. The function f is a known function adapted to a basic circuit that does not perform supercooling (having only the main circuit 306 without the bypass circuit 313). Then, the temperature sensor 331 at the compressor outlet (discharge pipe) is controlled by control means (not shown).
Is the actual discharge pipe temperature Td detected by the target temperature Td.
The throttle amount of the electric expansion valve 304 is adjusted so as to be (target). That is, the discharge pipe temperature Td is equal to the target temperature T.
When it is lower than d (target), the electric expansion valve 304
When the discharge pipe temperature Td rises above the target temperature Td (target), the electric expansion valve 304 is controlled to open to control the mainstream refrigerant flow rate. I try to increase. On the other hand, the amount of restriction of the capillary tube 312 provided in the bypass circuit 313 (determined by the size of the tube) is as follows.
° C and a room temperature of 27 ° C (hereinafter referred to as “cooling standard condition”. Throughout this specification, the temperature means dry-bulb temperature (DB)) and the refrigerating capacity (coefficient of performance COP). Is set to be the maximum. That is, when the mainstream refrigerant is saturated at the outlet of the evaporator 305 under the cooling standard conditions, the supercooling heat exchanger 3
The bypass-side outlet temperature of 10 is set to be the saturation temperature of the refrigerant (the bypass-flow refrigerant becomes saturated).

[0005]

However, in the above-mentioned system, the following problems occur when the operating conditions change.

[0006] For example, under an operating condition in which the outdoor temperature is lower than the cooling standard condition, as shown in the Ph diagram of FIG.
The differential pressure in the refrigeration cycle becomes smaller (Fig. 6 (b)
S1). In this state, the temperature difference between the mainstream refrigerant and the bypass refrigerant flowing through the subcooling heat exchanger 310 is reduced, and the amount of heat exchange in the subcooling heat exchanger 310 is reduced. The state A of the bypass refrigerant flowing through the bypass outlet of the exchanger 310 shifts to the wet side (S
2). Then, since the discharge pipe temperature Td of the compressor 302 decreases (S3), the electric expansion valve 304 is controlled to close so that the discharge pipe temperature Td is prevented (S4). As a result, the flow rate of the mainstream refrigerant decreases, the state E of the mainstream refrigerant passing through the outlet of the evaporator 305 shifts to the superheat side, and the flow rate of the bypass refrigerant increases. The state A of the bypass flow refrigerant passing through the outlet shifts more and more to the wet side (S5). As a result of such a vicious cycle in refrigerant flow control, the refrigeration capacity of the system is reduced (S6).

[0007] On the other hand, when the operating condition is such that the outdoor temperature is higher than the cooling standard condition, as shown in the Ph diagram of FIG.
The differential pressure in the refrigeration cycle increases (Fig. 7 (b)
S11). In this state, the temperature difference between the mainstream refrigerant passing through the supercooling heat exchanger 310 and the bypass refrigerant increases, and the amount of heat exchange in the supercooling heat exchanger 310 increases. The state A of the bypass refrigerant flowing through the bypass outlet of the exchanger 310 shifts to the superheat side (S12). Then, since the discharge pipe temperature Td of the compressor 302 rises (S13), the electric expansion valve 304 is controlled to open so as to prevent it (S14). As a result,
The flow rate of the mainstream refrigerant increases, and the state E of the mainstream refrigerant passing through the outlet of the evaporator 305 shifts to the wet side, and the flow rate of the bypass flow refrigerant increases, passing through the bypass-side outlet of the supercooling heat exchanger 310. The state A of the bypass flow refrigerant further shifts to the superheated side (S15). As a result of such a vicious cycle in refrigerant flow control, the refrigeration capacity of the system is reduced as in the above case (S16).

Accordingly, an object of the present invention is to provide an air conditioner having a refrigerant circuit for supercooling a mainstream refrigerant by exchanging heat between the mainstream refrigerant and a bypass flow refrigerant, over a wide range of operating conditions. To provide an air conditioner that can maintain high refrigeration capacity.

[0009]

In order to achieve the above object, an air conditioner according to claim 1 comprises a compressor, a condenser,
A main circuit for flowing a refrigerant in the order of a supercooling heat exchanger, an electric expansion valve and an evaporator constituting a first expansion mechanism, and a branch from the main circuit between the condenser and the electric expansion valve. A refrigerant circuit including a capillary tube forming an expansion mechanism of No. 2 and a bypass circuit for flowing a refrigerant in the order of the supercooling heat exchanger and merging with the main circuit on the suction side of the compressor. The heat exchanger performs heat exchange between the mainstream refrigerant flowing through the main circuit and the bypass refrigerant flowing through the bypass circuit after passing through the capillary tube,
In the air conditioner for subcooling the mainstream refrigerant, regardless of the state of the bypass refrigerant flowing through the bypass side outlet of the supercooling heat exchanger, the main expansion refrigerant passing through the outlet of the evaporator is determined by the electric expansion valve. Is controlled so that the degree of superheat is increased.

In the air conditioner of the present invention, the main expansion refrigerant passing through the outlet of the evaporator is controlled by the electric expansion valve regardless of the state of the refrigerant flowing through the bypass on the bypass side of the subcooling heat exchanger. Since the control is performed so as to be a predetermined superheat degree (typically, the superheat degree is zero (saturated state)), the operation condition deviates from the cooling standard condition, that is, the operation condition where the outdoor temperature is lower than the cooling standard condition or the cooling standard condition Even under the operating condition in which the outdoor air temperature is higher than that, the vicious cycle in the refrigerant flow rate control unlike the related art does not occur. Moreover, since the capillary tube provided in the bypass circuit is a fixed throttle, the highest point of the refrigerating capacity of the system appears almost when the mainstream refrigerant passing through the outlet of the evaporator is saturated. Therefore, high refrigeration capacity is maintained over a wide range of operating conditions.

[0011] The air conditioner according to the second aspect is the first aspect.
Wherein the temperature sensor detects the outlet temperature (Tc) of the condenser, the inlet temperature (Te) of the evaporator, and the discharge pipe temperature (Td) of the compressor, and the temperature sensor detects the temperature. Outlet temperature of the above condenser (Tc)
And calculating a target temperature (Td (target)) of the discharge pipe of the compressor with respect to the basic circuit including only the main circuit based on the inlet temperature (Te) of the evaporator, and calculating the target temperature (Td (target)) of the refrigerant circuit. The target temperature (Td (target)) is set so that the mainstream refrigerant passing through the outlet of
A discharge pipe target temperature calculation unit for performing correction in accordance with the difference (Tc-Te) between the outlet temperature of the condenser and the inlet temperature of the evaporator; and the discharge pipe temperature (T
a main electric valve control unit that adjusts the throttle amount of the electric expansion valve so that d) becomes the corrected target temperature (Td ′ (target)) by the discharge pipe target temperature calculation unit. And

In the air conditioner according to the present invention, the discharge pipe target temperature calculating section calculates the outlet temperature (Tc) of the condenser detected by the temperature sensor and the inlet temperature (Tc) of the evaporator.
e), the target temperature (Td (targe) of the discharge pipe of the compressor for the basic circuit consisting of only the main circuit
t)) is calculated. Furthermore, the discharge pipe target temperature calculation unit
The difference between the outlet temperature of the condenser and the inlet temperature of the evaporator with respect to the target temperature (Td (target)) so that the mainstream refrigerant passing through the outlet of the evaporator of the refrigerant circuit is saturated. Correction is performed according to (Tc-Te). Then, the main motorized valve control section controls the electric expansion valve so that the discharge pipe temperature detected by the temperature sensor becomes the corrected target temperature (Td ′ (target)) by the discharge pipe target temperature calculation section. Adjust the aperture amount of. As a result, the mainstream refrigerant passing through the outlet of the evaporator is saturated regardless of the state of the bypass refrigerant flowing through the bypass-side outlet of the subcooling heat exchanger.

[0013] The air conditioner according to the third aspect is the first aspect.
, The outlet temperature of the condenser (Tc), the inlet temperature of the evaporator (Te), the discharge pipe temperature of the compressor (Td), the outdoor air temperature (To), and the indoor air temperature (Tr). Based on the temperature of the condenser and the temperature of the outlet of the condenser (Tc) and the temperature of the inlet of the evaporator (Te) detected by the temperature sensor. The target temperature (Td (target)) of the discharge pipe is calculated, and the target temperature (Td (target)) is set so as to saturate the mainstream refrigerant passing through the outlet of the evaporator of the refrigerant circuit. A discharge pipe target temperature calculation unit for performing correction in accordance with the difference (To-Tr) between the outdoor temperature and the indoor temperature detected by the temperature sensor, and the discharge pipe temperature (Td) detected by the temperature sensor is used as the discharge pipe target. The above by the temperature calculation unit Positive after the target temperature (Td '(ta
rget)), characterized in that a main electric valve control unit for adjusting the throttle amount of the electric expansion valve is provided.

In the air conditioner of the present invention, the discharge pipe target temperature calculating section may calculate the outlet temperature of the condenser (Tc) and the inlet temperature of the evaporator (Tc) detected by the temperature sensor.
e), the target temperature (Td (targe) of the discharge pipe of the compressor for the basic circuit consisting of only the main circuit
t)) is calculated. Furthermore, the discharge pipe target temperature calculation unit
The difference between the outlet temperature of the condenser and the inlet temperature of the evaporator with respect to the target temperature (Td (target)) so that the mainstream refrigerant passing through the outlet of the evaporator of the refrigerant circuit is saturated. Correction is performed according to (Tc-Te). Then, the main motorized valve control unit controls the discharge pipe temperature (Td) detected by the temperature sensor to the corrected target temperature (Td ′ (target)) by the discharge pipe target temperature calculation unit. Adjust the throttle amount of the electric expansion valve. As a result, the mainstream refrigerant passing through the outlet of the evaporator is saturated regardless of the state of the bypass refrigerant flowing through the bypass-side outlet of the subcooling heat exchanger.

[0015]

Embodiments of the present invention will be described below in detail.

FIG. 1 shows a refrigerant circuit 1 including a main circuit 6 and a bypass circuit (shown by a broken line) 11 of an air conditioner according to one embodiment.

The main circuit 6 includes a compressor 2, a condenser 3, a double-tube heat exchanger 10 for supercooling, an electric expansion valve 4, which constitutes a first expansion mechanism, an evaporator 5, and a four-way switching valve. 9 and an accumulator 8 in this order. The bypass circuit 11
Branching off from the main circuit 6 at a branch point 41 between the condenser 3 and the subcooling heat exchanger 10, passing through the capillary tube 12 and the subcooling heat exchanger 10 constituting the second expansion mechanism,
It joins the main circuit 6 at a junction 42 near the inlet of the accumulator 8. The subcooling heat exchanger 10 exchanges heat between the mainstream refrigerant flowing through the main circuit 6 and the bypass refrigerant flowing through the bypass circuit 11 after passing through the capillary tube 12. In other words, the mainstream refrigerant is supercooled with a simple circuit configuration using the bypass refrigerant flowing through the capillary tube 12.

The air conditioner is provided with a discharge pipe target temperature calculating section 26, a comparing section 27 and a main motorized valve control section 23 for controlling the electric expansion valve 4. The temperature sensors 32, 33, 31, 38, and 39 detect an outlet temperature Tc of the condenser 3, an inlet temperature Te of the evaporator 5, a discharge pipe temperature Td of the compressor 2, an outdoor air temperature To, and an indoor air temperature Tr, respectively.
Further, a pressure sensor 40 mounted on the inlet side of the accumulator 8 detects the pressure on the suction side of the compressor 2. These temperature sensors 32, 33, 31, 38, 39
Since the pressure sensor 40 and the pressure sensor 40 are generally provided in an air conditioner, there is no need to add them.

During operation, the refrigerant discharged from the compressor 2 is condensed by a condenser (for example, radiating heat to outdoor air) 3, and the main refrigerant flowing through the main circuit 6 at a branch point 41 and the bypass refrigerant flowing through the bypass circuit 11 Divided into refrigerant. The mainstream refrigerant is supercooled by heat exchange with the bypass-flow refrigerant after passing through the capillary tube 12 in the heat exchanger 10, and then decompressed by the electric expansion valve 4. Then, the mainstream refrigerant is evaporated by an evaporator (for example, absorbing heat from indoor air) 5, and is sucked into the compressor 2 through a four-way switching valve 9 and an accumulator 8 for performing gas-liquid separation. On the other hand, the bypass-flow refrigerant is depressurized by passing through the capillary tube 12 that provides a predetermined throttle amount, and is then evaporated in the heat exchanger 10 by heat exchange with the mainstream refrigerant. Thereafter, the bypass-flow refrigerant merges with the mainstream refrigerant at a junction 42 near the inlet of the accumulator 8.

By supercooling the mainstream refrigerant in the heat exchanger 10 as described above, the refrigerating effect of the mainstream refrigerant can be increased as compared with a case where supercooling is not performed. In addition, since the volume flow of the mainstream refrigerant is reduced by branching the bypass flow from the flow of the refrigerant, the supercooling is not performed as shown in FIG. 5B (see FIG. 5A). , The pressure loss ΔP in the evaporator 5 and in the suction-side pipe of the compressor 2 can be reduced. Therefore, the refrigeration capacity of the system can be improved.

In this air conditioner, the adjustment of the throttle amount of the electric expansion valve 4 is performed as follows.

First, the discharge pipe target temperature calculator 26 calculates
The outlet temperature T of the condenser 3 detected by the temperature sensors 32 and 33
c and the main circuit 6 based on the inlet temperature Te of the evaporator 5.
The target temperature Td (target) of the discharge pipe of the compressor 2 for the basic circuit consisting only of the above is calculated. That is, the condenser 3
F between the outlet temperature Tc of the evaporator 5 and the inlet temperature Te of the evaporator 5
The target temperature of the discharge pipe Td (target) = f (Te,
Tc) is set. As already mentioned, this function f is known.

Further, a discharge pipe target temperature calculating section 26
Is the difference between the outlet temperature of the condenser 3 and the inlet temperature of the evaporator 5 with respect to the target temperature Td (target) so that the mainstream refrigerant passing through the outlet of the evaporator 5 of the refrigerant circuit 1 is saturated. Correction is performed according to (Tc-Te). Specifically, a correction value α is added to the target temperature Td (target) to calculate a new target temperature Td ′ (target) = Td (target) + α. How to obtain the correction value α will be described later.

Then, the comparing unit 27 is provided with the temperature sensor 3
1 (Td−Td ′ (targe) between the actual detected discharge pipe temperature Td and the corrected target temperature Td ′ (target).
t)), and the main motorized valve control unit 23 calculates the difference (Td
-The throttle amount of the electric expansion valve 4 is adjusted so that -Td '(target)) becomes zero. As a result, the subcooling heat exchanger 1
The mainstream refrigerant passing through the outlet of the evaporator 5 can be saturated regardless of the state of the bypass refrigerant flowing through the bypass-side outlet 0.

Therefore, the standard cooling condition (the outdoor temperature is 3
Operating conditions at 5 ° C and room temperature outside of 27 ° C)
That is, even under the operating condition in which the outdoor temperature is lower than the cooling standard condition or the operating condition in which the outdoor temperature is higher than the cooling standard condition, it is possible to prevent the conventional vicious circulation in the refrigerant flow control from occurring. In addition, since the capillary tube 12 provided in the bypass circuit 11 is a fixed throttle, the highest point of the refrigerating capacity of the system appears when the mainstream refrigerant passing through the outlet of the evaporator 5 is almost saturated. Therefore, according to this air conditioner, it is possible to maintain a higher refrigerating capacity as compared with the related art over a wide range of operating conditions.

Next, a method of obtaining the correction value α will be described.

(I) Various operating conditions deviating from the standard cooling conditions are set, and the difference (Tc-Te) between the outlet temperature of the condenser 3 and the inlet temperature of the evaporator 5 is changed. Then, under each operating condition, the discharge pipe target temperature calculation unit 26 performs compression on the basic circuit based on the outlet temperature Tc of the condenser 3 and the inlet temperature Te of the evaporator 5 detected by the temperature sensors 32 and 33. Temperature Td (target) of the discharge pipe of machine 2
= F (Te, Tc). The actual discharge pipe temperature Td detected by the temperature sensor 31 is compared with the target temperature Td (targ) by the comparison unit 27 and the main motorized valve control unit 23.
The throttle amount of the electric expansion valve 4 is adjusted so as to satisfy (et).
In this case, due to the influence of the bypass circuit 11, the mainstream refrigerant passing through the outlet of the evaporator 5 of the refrigerant circuit 1 shifts from a saturated state to a superheated side or a wet side depending on the operating conditions.

(Ii) Then, the outlet temperature Teo of the evaporator 5 is detected by the temperature sensor 36 at the outlet of the evaporator 5.
On the other hand, the pressure Ps on the suction side of the compressor 2 is detected by the pressure sensor 40 attached to the inlet side of the accumulator 8,
The equivalent saturation temperature Ts of the refrigerant corresponding to the pressure Ps is calculated. Then, the correction value α is obtained by an experiment so as to cancel the difference (Teo−Ts) between the outlet temperature Teo of the evaporator 5 and the equivalent saturation temperature Ts.

FIG. 2 shows various experimental conditions which are different from the standard cooling conditions, and the difference (Tc-Te) between the outlet temperature of the condenser 3 and the inlet temperature of the evaporator 5 is changed. Is shown. In FIG. 2, the symbol □ indicates that the throttle amount of the capillary tube 12 (determined by the size, that is, the diameter and the length) is excessive when the mainstream refrigerant is saturated at the outlet of the evaporator 5 under the standard cooling condition. Heat exchanger for cooling 1
Data points when the bypass-side exit temperature of 0 is set to be in a saturated state are shown. In FIG. 2, the mark “◇” indicates that the throttle amount of the capillary tube 12 is set to the bypass side of the supercooling heat exchanger 10 when the mainstream refrigerant is saturated at the outlet of the evaporator 5 under the standard cooling condition. The data points are shown when the degree of superheat of the bypass flow refrigerant at the outlet is set to be about 4.5 deg. Regardless of which capillary tube is used, the temperature difference (Tc-Te) and the correction value α show a corresponding relationship such that they respectively ride on a certain curve. Therefore, the correction value α for the target temperature Td (target) of the discharge pipe can be obtained according to the temperature difference (Tc−Te). For example, when the former capillary tube is used, when the temperature difference (Tc−Te) is 20 ° C., the correction value α for the target temperature Td (target) of the discharge pipe is obtained as −8 ° C.

The discharge pipe target temperature calculating section 26 calculates a temperature sensor (3) for the discharge pipe target temperature Td (target).
8, 39) detects the difference between the outdoor temperature and the indoor temperature (To
−Tr), the correction may be performed.
That is, when various operating conditions deviating from the cooling standard conditions are set, the difference between the outdoor air temperature and the indoor air temperature is similar to the difference (Tc−Te) between the outlet temperature of the condenser 3 and the inlet temperature of the evaporator 5. (To-Tr) also changes. Then, the temperature difference (Tc
Instead of the temperature difference (To−Tr), the same data as in FIG. 2 may be obtained by an experiment to determine the correction value α. Also in this case, as in the above case, the mainstream refrigerant passing through the outlet of the evaporator 5 is saturated regardless of the state of the bypass refrigerant flowing through the bypass-side outlet of the subcooling heat exchanger 10. be able to. Therefore,
Higher refrigeration capacity than before can be maintained over a wide range of operating conditions.

Although the above has mainly described the cooling conditions specifically, the same applies qualitatively to the use during heating, and the present invention can be used as it is. Also, the present invention
It is effective even when a non-azeotropic mixed refrigerant such as HFC407C or HFC410A is used as the refrigerant.

In the above-described embodiment, the bypass circuit 11 branches off from the main circuit between the condenser 3 and the supercooling heat exchanger 10. However, the present invention is not limited to this. The bypass circuit branches off from the main circuit between the subcooling heat exchanger 10 and the electric expansion valve 4, and allows the bypass refrigerant to flow in the order of the capillary tube 12 and the subcooling heat exchanger 10. Is also good. In this case, the same operation and effect can be obtained.

[0033]

As is apparent from the above description, in the air conditioner of the first aspect, the electric expansion provided in the main circuit irrespective of the state of the bypass-flow refrigerant passing through the bypass-side outlet of the subcooling heat exchanger. The main refrigerant flowing through the outlet of the evaporator is controlled by the valve so that the superheat degree becomes a predetermined superheat degree (typically, the superheat degree is zero (saturated state)). Even when the operating condition is such that the outdoor temperature is lower than the outdoor temperature or the operating temperature is higher than the cooling standard condition, the conventional vicious circulation in the refrigerant flow control does not occur. Moreover, since the capillary tube provided in the bypass circuit is a fixed throttle, the highest point of the refrigerating capacity of the system appears almost when the mainstream refrigerant passing through the outlet of the evaporator is saturated. Therefore, higher refrigeration capacity than before can be maintained over a wide range of operating conditions.

In the air conditioner according to the present invention, the discharge pipe target temperature calculating section calculates the outlet temperature (Tc) of the condenser and the inlet temperature (Tc) of the evaporator detected by the temperature sensor.
e), the target temperature (Td (targe) of the discharge pipe of the compressor for the basic circuit consisting of only the main circuit
t)), and further, with respect to this target temperature (Td (target)), the outlet temperature of the condenser and the outlet temperature of the condenser so that the mainstream refrigerant passing through the outlet of the evaporator of the refrigerant circuit becomes saturated. Since the correction is performed in accordance with the difference (Tc-Te) from the inlet temperature of the evaporator, the outlet of the evaporator is connected regardless of the state of the bypass refrigerant flowing through the bypass-side outlet of the subcooling heat exchanger. The passing mainstream refrigerant becomes saturated.

In the air conditioner according to the third aspect, the discharge pipe target temperature calculating section calculates the outlet temperature (Tc) of the condenser and the inlet temperature (Tc) of the condenser detected by the temperature sensor.
e), the target temperature (Td (targe) of the discharge pipe of the compressor for the basic circuit consisting of only the main circuit
t)), and further, with respect to this target temperature (Td (target)), the outlet temperature of the condenser and the outlet temperature of the condenser so that the mainstream refrigerant passing through the outlet of the evaporator of the refrigerant circuit becomes saturated. Since the correction is performed in accordance with the difference (Tc-Te) from the inlet temperature of the evaporator, the outlet of the evaporator is connected regardless of the state of the bypass refrigerant flowing through the bypass-side outlet of the subcooling heat exchanger. The passing mainstream refrigerant becomes saturated.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of a refrigerant circuit of an air conditioner according to an embodiment of the present invention.

FIG. 2 shows the correspondence between the difference (Tc−Te) between the outlet temperature of the condenser and the inlet temperature of the evaporator and the correction value α for the target temperature Td (target) of the discharge pipe of the compressor 2 for the basic circuit. FIG.

FIG. 3 is a diagram illustrating a schematic configuration of a refrigerant circuit of a conventional air conditioner that performs heat exchange between a mainstream refrigerant and a bypass flow refrigerant to supercool the mainstream refrigerant.

FIG. 4 is a diagram schematically showing a method of calculating a target temperature Td (target) of a discharge pipe of a compressor from a condenser outlet temperature Tc and an evaporator inlet temperature Te for a basic circuit that does not perform supercooling. It is.

5A is a Ph diagram showing a refrigeration cycle of a basic circuit that does not perform supercooling, FIG. 5B is a Ph diagram showing a refrigeration cycle using the conventional refrigerant circuit shown in FIG. 10, and FIG. It is the elements on larger scale of (b).

FIG. 6 is a diagram illustrating a problem in controlling a refrigerant flow rate by a conventional refrigerant circuit under an operating condition in which the outdoor air temperature is lower than a cooling standard condition.

FIG. 7 is a diagram illustrating a problem in controlling a refrigerant flow rate by a conventional refrigerant circuit under an operating condition in which an outdoor air temperature is higher than a cooling standard condition.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Refrigerant circuit 2 Compressor 3 Condenser 4 Electric expansion valve 5 Evaporator 6 Main circuit 10 Supercooling heat exchanger 11 Bypass circuit 12 Capillary tube

Claims (3)

[Claims] 1. A refrigerant in the order of a compressor (2), a condenser (3), a supercooling heat exchanger (10), an electric expansion valve (4) constituting a first expansion mechanism, and an evaporator (5). And a capillary tube (12) that branches off from the main circuit (6) between the condenser (3) and the electric expansion valve (4) to form a second expansion mechanism. The refrigerant flows in the order of the subcooling heat exchanger (10), and the bypass circuit (1) joins the main circuit (6) on the suction side of the compressor (2).
1), and the subcooling heat exchanger (10) includes a mainstream refrigerant flowing through the main circuit (6) and the bypass circuit (2) after passing through the capillary tube (12). 11) In an air conditioner for supercooling the mainstream refrigerant by performing heat exchange with the bypass refrigerant flowing through the bypass refrigerant, the state of the bypass refrigerant flowing through the bypass side outlet of the supercooling heat exchanger (10). Irrespective of the above, an air conditioner characterized in that the main expansion refrigerant passing through the outlet of the evaporator (5) is controlled by the electric expansion valve (4) to a predetermined degree of superheat. 2. The air conditioner according to claim 1, wherein an outlet temperature (Tc) of the condenser (3), an inlet temperature (Te) of the evaporator (5), and a discharge of the compressor (2). Temperature sensors (32, 33,
31) and the main circuit (6) based on the outlet temperature (Tc) of the condenser (3) and the inlet temperature (Te) of the evaporator (5) detected by the temperature sensors (32, 33). The target temperature (Td (target)) of the discharge pipe of the compressor (2) for the basic circuit consisting only of the compressor is calculated, and the mainstream refrigerant passing through the outlet of the evaporator (5) of the refrigerant circuit (1) is saturated. The target temperature (Td (target)) is corrected according to the difference (Tc-Te) between the outlet temperature of the condenser (3) and the inlet temperature of the evaporator (5) so as to be in a state. And a discharge pipe target temperature calculating section (26) for performing the discharge pipe temperature (T) detected by the temperature sensor (31).
a main electric valve control unit that adjusts the throttle amount of the electric expansion valve (4) so that d) becomes the corrected target temperature (Td ′ (target)) by the discharge pipe target temperature calculation unit (26). An air conditioner comprising (23). 3. The air conditioner according to claim 1, wherein an outlet temperature (Tc) of the condenser (3), an inlet temperature (Te) of the evaporator (5), and a discharge of the compressor (2). Tube temperature (Td), outdoor temperature (To) and indoor temperature (T
r) to detect the temperature sensors (32, 33, 31, 38,
39) and the main circuit (6) based on the outlet temperature (Tc) of the condenser (3) and the inlet temperature (Te) of the evaporator (5) detected by the temperature sensors (32, 33). The target temperature (Td (target)) of the discharge pipe of the compressor (2) for the basic circuit consisting only of the compressor is calculated, and the mainstream refrigerant passing through the outlet of the evaporator (5) of the refrigerant circuit (1) is saturated. The target temperature (Td (target)) is corrected in accordance with the difference (To-Tr) between the outdoor temperature and the indoor temperature detected by the temperature sensors (38, 39) so that the target temperature (Td (target)) is obtained. A pipe target temperature calculator (26); and the discharge pipe temperature (T) detected by the temperature sensor (31).
a main electric valve control unit that adjusts the throttle amount of the electric expansion valve (4) so that d) becomes the corrected target temperature (Td ′ (target)) by the discharge pipe target temperature calculation unit (26). An air conditioner comprising (23).