JP3232852B2 - Superheat control device for air conditioner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superheat control apparatus for an air conditioner capable of optimally controlling superheat at low cost.

[0002]

2. Description of the Related Art Conventionally, there is an outdoor unit in an air conditioner capable of controlling the degree of superheat as shown in FIG.
This air conditioner is a multi-room air conditioner, and the outdoor unit 1 is connected to a plurality of indoor units (not shown) provided in a plurality of rooms (A room, B room, C room, D room). It is connected.

[0003] The outdoor unit 1 has a gas side refrigerant pipe 4,
The four-way switching valve 3, the compressor 2, the outdoor heat exchanger 5, and the liquid-side refrigerant pipe 6 are connected to form a refrigerant circuit. Are connected in parallel via a header 7 to the liquid-side refrigerant pipe 6 on the side opposite to the outdoor heat exchanger.
On the other hand, four gas-side branch pipes 10, 10,... Are connected in parallel via a header 9 to the anti-four-way switching valve side of the gas-side refrigerant pipe 4. It is interposed the first electric expansion valve EV ₀ capable of controlling the valve opening to any degree in the liquid-side refrigerant pipe 6. Then, interposed liquid receiver 11 between the first electric expansion valve EV ₀ and header 7, the operation has been the outdoor unit 1 by volume change of the indoor units are power and indoor unit capacity Extra liquid refrigerant due to unbalance is stored. Furthermore, the liquid side branch pipes 8, 8, the second controllable valve opening to any degree in ... electric expansion valve EV _1,
..., it is interposed the EV _4.

The outdoor unit 1 having the above-described structure operates as follows by switching the four-way switching valve 3 to a position indicated by a broken line and circulating a refrigerant as indicated by a solid line arrow during heating. That is, in the stable period after the start of the heating operation, the thermistor 12
The deviation E is calculated by the equation (1) based on the outdoor heat exchanger outlet temperature “T ₁ ” detected by the thermistor 13 and the low-pressure saturation temperature “T ₂ ” detected by the thermistor 13. Then, the calculated deviation E is the opening control of the first electric expansion valve EV ₀ so that E = 0, the outlet side of the outdoor heat exchanger 5 (i.e., the suction side of the compressor 2) The superheat control is performed so that the superheat of the low-pressure gas refrigerant is constant (SH). E = (T ₁ −T ₂ ) −SH (1) where SH: superheat degree target value (for example, 5 ° C.)

[0005] When the superheat degree control is performed, if the capacity of the indoor heat exchanger in one of the indoor units connected to the outdoor unit 1 is low, the gas side refrigerant pipe 4 The pressure of the refrigerant inside increases, and the compressor 2 is damaged or the high-pressure switch HPS is activated to start the protection operation.

Therefore, when the condensing temperature of the indoor heat exchanger in the indoor unit in which the indoor heat exchanger having a small capacity is installed exceeds a predetermined temperature, the electric motor for driving the compressor 2
The compression capacity of the compressor 2 is reduced by lowering the rotation frequency (not shown). Then, further, when the condensation temperature of the indoor heat exchanger in the indoor unit is also the rotational frequency of the compressor 2 is led to the lower limit value is not lowered to a predetermined temperature, the bypass circuit 14 by opening the solenoid valve SV _B A part of the high-pressure and high-temperature gas refrigerant discharged from the compressor 2 via the compressor 2 is returned to the suction side of the compressor 2 to reduce the circulation amount of the refrigerant and reduce the compression efficiency of the compressor 2.

[0007]

As described above, the outdoor unit 1 in the conventional air conditioner capable of controlling the degree of superheat has the refrigerant pressure on the high pressure side when the low capacity indoor heat exchanger is connected. In order to prevent the abnormal rise of the compressor 2, a bypass circuit 14 for returning a part of the refrigerant discharged from the compressor 2 to the suction side of the compressor 2 is required.

Accordingly, an object of the present invention is to provide a superheat degree control device for an air conditioner which can prevent a rise in pressure of a high pressure side refrigerant when a low capacity indoor heat exchanger is connected without providing a bypass circuit. To provide.

[0009]

In order to achieve the above object, as shown in FIGS. 1 and 2, a compressor 2, a four-way switching valve 3, a plurality of indoor heat exchangers 28, 28 are provided.・
..., receiver 11, the electric expansion valve EV ₀ and the outdoor heat exchanger 5
The opening degree of the electric expansion valve EV ₀ in sequential air conditioner comprising linked to the annular air conditioner superheat of the suction side of the refrigerant of the compressor 2 during heating is controlled to be the target value In the superheat degree control device, the plurality of indoor heat exchangers 28, 28,... Detect the respective condensing temperatures, and the respective temperature detected by the temperature detecting units 21, 21,. A temperature determining unit 24 that determines whether the maximum value of each of the condensing temperatures exceeds a predetermined temperature based on the condensing temperatures of the indoor heat exchangers 28, 28,. When the rotation frequency determining unit 25 that determines whether the maximum value of the condensing temperatures has exceeded a predetermined temperature, and when the temperature determining unit 24 determines that the maximum value of each of the condensing temperatures has exceeded a predetermined temperature,
If the rotation frequency of the compressor 2 does not exceed the lower limit based on the determination result of the rotation frequency determination unit 25, a rotation control signal for reducing the rotation frequency of the compressor 2 by a predetermined value is output. , when the rotational frequency of the compressor 2 exceeds the above lower limit value, the opening degree control signal for setting the opening degree of the electric expansion valve EV ₀ lower predetermined opening than the lower limit value during the superheat control , And the control unit 26 resets the superheat target value to a larger value.
And a rotation control unit 19 that receives a rotation control signal from the control unit 26 and controls the rotation frequency of the compressor 2 based on the rotation control signal, and receives an opening control signal from the control unit 26. Te is characterized by having a valve control unit 20 for controlling the opening degree of the electronic expansion valve EV ₀ on the basis of the opening control signal.

[0010]

When superheat control is performed such that the superheat of the low-pressure gas refrigerant on the suction side of the compressor 2 at the time of heating becomes the target value, each indoor heat detected by the temperature detection units 21, 21,. The temperature determination unit 24 determines whether or not the maximum value of the condensation temperature of the exchangers 28, 28,... Has exceeded a predetermined temperature. Further, the rotation frequency determination unit 25 determines whether the rotation frequency of the compressor 2 does not exceed the lower limit value.

When the temperature judging section 24 judges that the maximum value of each of the condensing temperatures exceeds a predetermined temperature, the control section 26 controls the rotation frequency judging section 25.
If the rotation frequency of the compressor 2 does not exceed the lower limit value, a rotation control signal for reducing the rotation frequency of the compressor 2 by a predetermined value is output. Then, the rotation frequency of the compressor 2 is reduced by the predetermined value based on the rotation control signal by the rotation control unit 19, and the compression capacity of the compressor 2 is reduced. On the other hand, when the rotation frequency of the compressor 2 exceeds the lower limit,
By the control unit 26, the opening degree control signal for setting the opening degree of the electric expansion valve EV ₀ lower predetermined opening than the lower limit value during the superheat degree control is outputted. Then,
Opening of the electric expansion valve EV ₀ on the basis of the opening degree control signal is set to a lower predetermined opening than the lower limit value during the superheat degree control. Further, the target value of the superheat is reset to a larger value, and thereafter, the superheat control is performed according to the target value after the reset.

In this way, by increasing the degree of superheat, the apparent capacity of the outdoor heat exchanger 5 is reduced, and as a result, of the indoor heat exchanger 28 among the plurality of indoor heat exchangers 28, 28,. Even when the capacity is extremely low, the abnormally high pressure side refrigerant pressure is suppressed.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments. FIG. 1 is a block diagram of a superheat degree control device for an air conditioner of the present embodiment, and FIG. 2 is a refrigerant circuit diagram of an outdoor unit in an air conditioner whose superheat degree is controlled by the superheat degree control device. Outdoor unit shown in FIG. 2 is basically to remove the bypass circuit 14 which is interposed a solenoid valve SV _B from the refrigerant circuit of the outdoor unit 1 in the conventional superheat controllable air conditioner shown in Fig. 4 arrangement have. Therefore, in FIG. 2, the same members as those in FIG. 4 are denoted by the same reference numerals, and detailed description is omitted.

The configuration of the superheat control device according to the present embodiment will be described below with reference to FIGS. The superheat controller, the rotation control unit 19 for controlling the rotation of the motor 18 for driving the compressor 2, the valve control unit 20 for controlling the opening of the first electric expansion valve EV _0, and detects the temperature of each portion Thermistors 12, 13, 21 that output temperature signals, and output rotation control signals and opening control signals for controlling the rotation control unit 19 and the valve control unit 20 based on the temperature signals from the thermistors 12, 13, 21. Microcomputer
(Hereinafter abbreviated as a microcomputer) 22.

The thermistor 12 includes a low-pressure gas refrigerant pipe 15 connecting the four-way switching valve 3 and the suction side of the compressor 2.
It is provided in. On the other hand, the thermistor 13 is
The refrigerant pipe 16 that connects the refrigerant gas pipe 1 and the low-pressure gas refrigerant pipe 15 via the capillary 17 is provided on the downstream side of the capillary 17. The temperature signals output from the thermistors 12 and 13 are digitally converted by the A / D converter 27 and transmitted to the microcomputer 22. Are connected to the indoor heat exchangers 28, 28,
Are converted into digital signals by an A / D converter 29 and sent to the microcomputer 22.

The microcomputer 22 includes a memory 23 for storing various control information, a temperature judging unit 24, and a rotation frequency judging unit 25.
And a control unit 26. The temperature determination unit 24
Takes in the temperature signals from the thermistors 21, 21,... And determines whether or not the maximum value of the condensing temperature in each of the indoor heat exchangers 28, 28,. I do. On the other hand, the rotation frequency determination unit 25
Based on the current rotation frequency of the compressor 2 and the lower limit of the rotation frequency stored in the memory 23, it is determined whether the rotation frequency of the compressor 2 has exceeded the lower limit. The control unit 26 determines the rotation frequency of the compressor 2 and the first electric expansion valve EV based on the temperature signals from the thermistors 12 and 13 and the determination results of the determination units 24 and 25.
Set the opening at ₀ optimally. Then, a rotation frequency signal for controlling the rotation frequency of the compressor 2 is transmitted to the rotation control unit 19.
And an opening control signal for optimally controlling the opening of the first electric expansion valve EV ₀ is sent to the valve control unit 20. Incidentally, when the latest value of the degree of opening of the set rotational frequency, and the first electric expansion valve EV ₀ of compressor 2 is always stored in the respective regions of the memory 23.

The superheat degree control device for an air conditioner having the above configuration operates as follows to prevent an abnormal increase in the high-pressure side refrigerant pressure when a low-capacity indoor heat exchanger is connected during heating. That is, as in the case of the outdoor unit in the air conditioner capable of controlling the degree of superheat shown in FIG. At this time, the control unit 26 of the microcomputer 22 stores the outdoor heat exchanger outlet temperature “T ₁ ” and the low-pressure saturation temperature “T ₂ ” in the memory 23 based on the temperature signals from the thermistors 12 and 13. Using the superheat target value “SH”, the deviation E
Is calculated. The opening control signal representative of a first degree of opening of the electric expansion valve EV ₀ such that the E = 0 is transmitted to the valve control unit 20, based on the opening degree control signal, the valve control unit 20
Opening is controlled superheating degree control of the first electric expansion valve EV ₀ is performed by. At this time, excess liquid refrigerant due to an imbalance between the capacity of the outdoor unit 1 and the capacity of the indoor unit due to a change in the number of operating indoor units and a change in the capacity of the indoor heat exchanger 28 is stored in the receiver 11. It is done.

Thus, when the superheat degree control is performed, the indoor heat exchanger 2 of a certain indoor unit among the plurality of indoor units connected to the outdoor unit 1 is used.
When the capacity of the indoor heat exchanger 8 is low, the condensation temperature of the indoor heat exchanger 28 increases. Then, the temperature determination unit 2 of the microcomputer 22
4, the condensation temperature "DC" of each indoor heat exchanger 28, 28,... Based on the temperature signal from each thermistor 21, 21,.
The maximum value "MAXDC" of n (n: room number) ") is stored in the memory 23.
When it is determined that the value exceeds the predetermined value “DCA” read from the control unit 26, a rotation control signal for lowering the rotation frequency of the compressor 2 by the predetermined value is sent from the control unit 26 to the rotation control unit 19, and the compression control is performed. The rotation frequency of the machine 2 is reduced. In this way, the pressure increase of the high-pressure gas refrigerant in the gas-side refrigerant pipe 4 is suppressed by reducing the compression capacity of the compressor 2.

Further, even if the rotation frequency of the compressor 2 reaches the lower limit value, the maximum temperature of the condensation temperature "DCn" of the indoor heat exchangers 28, 28,. If it is determined that the value “MAXDC” exceeds the predetermined value “DCA”, the control unit 26 sets the predetermined opening “EV ₀ A” smaller than the lower limit in the normal heating degree control. There is read from the memory 23, the opening control signal the valve control unit 20, such as the opening of the first electric expansion valve EV ₀ to the predetermined opening "EV ₀ a"
And the opening degree of the first electric expansion valve EV ₀ is set to the above “EV ₀ A” which is smaller than the lower limit value in the normal heating degree control. In addition, the control unit 26 controls the memory 23
The superheat degree of the low-pressure gas refrigerant is set high by updating the superheat degree target value “SH” stored in the low pressure gas refrigerant to a larger value “SHA”. Thus, the apparent capacity of the outdoor heat exchanger 5 is reduced, and the pressure increase of the high-pressure side refrigerant is suppressed.

FIG. 3 is a flowchart of the superheat control processing operation performed by the microcomputer 22. Less than,
The operation of the superheat control process in this embodiment will be described in detail with reference to FIG. Under the control of the microcomputer 22,
Four-way valve 3 is set to the broken line position, the opening of the first electric expansion valve EV ₀ is initialized by the valve control unit 20, the rotational speed of the electric motor 18 is initialized by the rotation control unit 19. Then, the refrigerant is circulated by the compressor 2 in the direction of the solid line arrow, and the heating operation is started, and the superheat degree control processing operation is started.

In step S1, it is determined whether or not the heating operation is being performed by referring to a flag in the memory 23, for example. As a result, if the heating operation is being performed, step S2
Otherwise, to step S10. In step S2, the controller 26 controls the outdoor heat exchanger outlet temperature “T ₁ ”, the low-pressure saturation temperature “T ₂ ”, and the superheat degree target value “S”.
H "is taken in, and the deviation E is calculated.
Superheat control is performed based on the value of the deviation E.
Incidentally, when the degree of opening of the first electric expansion valve EV ₀ stored in the memory 23 is updated to the current opening degree. In step S3, the condensing temperature “DCn” of each indoor heat exchanger 28, 28,... Sent from each indoor unit is taken in.
In step S4, the control value "DCA" stored in the memory 23 is read out by the temperature determination unit 24, and the maximum value "MA" of each of the taken-in condensation temperatures "DCn" is read.
It is determined whether or not "XDC" exceeds a predetermined value "DCA". As a result, if it exceeds, the process proceeds to step S5, and if not, returns to step S2 to continue the superheat control.

In step S5, the rotation frequency judgment unit 2
5, the current rotation frequency of the compressor 2 and the lower limit value of the rotation frequency stored in the memory 23 are read.
In step S6, it is further determined whether or not the read current rotational frequency has reached the lower limit. If the current rotational frequency has reached the lower limit, the process proceeds to step S7, and if not, the process proceeds to step S9. In step S7, the control value “EV ₀ A” stored in the memory 23 by the control unit 26.
Is read out, and an opening control signal for setting the opening of the first electric expansion valve EV ₀ to the predetermined opening “EV ₀ A” is output to the valve control unit 20. In step S8, the superheat degree target value stored in the memory 23 is updated to a larger value "SHA", and the process proceeds to step S10.

In step S9, since the current rotation frequency of the compressor 2 has not yet reached the lower limit value, the rotation control signal for decreasing the rotation frequency of the compressor 2 by a predetermined value is sent to the rotation control unit 19 by the control unit 26. Is output. In step S10, it is determined with reference to an external command or the like whether or not to continue the superheat control process. As a result, if the process is to be continued, the process returns to step S1 to perform the superheat control based on the updated superheat target value "SHA", and otherwise terminates the superheat control processing operation.

As described above, in the present embodiment, under the control of the microcomputer 22, when the superheat control is performed during the heating operation, the condensation of the indoor heat exchanger having the minimum capacity in the plurality of indoor units is performed. The temperature “MAXDC” is equal to the predetermined value “D
If CA "is exceeded, first, the rotation frequency of the compressor 2 is reduced stepwise by a predetermined value by the rotation control unit 19 to reduce the compression capability of the compressor 2. Then, the rotation frequency of the compressor 2 is reduced. If the pressure reaches the lower limit, the valve control unit 2
0, the opening degree of the first electric expansion valve EV ₀ is set to a value “EV ₀ A” smaller than the lower limit value in the normal superheat control, and the superheat target value “SH” is set to a larger value “SHA”.
To reduce the apparent capacity of the outdoor heat exchanger 5 by setting the degree of superheat of the low-pressure gas refrigerant high. Thus, by reducing the compression capacity of the compressor 2 and the apparent capacity of the outdoor heat exchanger 5, the pressure of the high-pressure side refrigerant is prevented from increasing when the low-capacity indoor heat exchanger 28 is connected during heating. Thus, the heating operation within the range of use of the compressor 2 is enabled.

The algorithm of the superheat control processing operation according to the present invention is not limited to the flowchart shown in FIG.

[0026]

As is apparent from the above description, the superheat degree control device for an air conditioner according to the present invention includes a temperature detecting section, a temperature determining section,
It has a rotation frequency judgment unit, a control unit, a rotation control unit, and an opening control unit, and when performing superheat control during heating, when the maximum value of the condensation temperature in a plurality of indoor heat exchangers exceeds a predetermined temperature. Meanwhile, if the rotation frequency of the compressor does not exceed the lower limit, the rotation frequency of the compressor is reduced by a predetermined value, while if the rotation frequency of the compressor exceeds the lower limit, the Since the opening of the electric expansion valve is set to a predetermined opening lower than the lower limit at the time of the superheat control and the target value of the superheat is reset to a larger value, the compression capacity of the compressor and the outdoor The apparent capacity of the heat exchanger can be reduced. Therefore, at the time of heating, it is possible to prevent the pressure of the high-pressure side refrigerant from increasing due to the connection of the low-capacity indoor heat exchanger 28, and to perform the heating operation within the usage range of the compressor.

That is, according to the present invention, a low capacity indoor heat exchanger is connected without providing a bypass circuit for returning the high-pressure gas refrigerant from the compressor to the suction side of the compressor. The pressure increase of the high-pressure side refrigerant can be prevented. Therefore, an overheat control device capable of high-pressure control can be realized at low cost.

[Brief description of the drawings]

FIG. 1 is a block diagram of a superheat degree control device for an air conditioner according to the present invention.

FIG. 2 is a refrigerant circuit diagram of an outdoor unit in the air conditioner whose superheat degree is controlled by the superheat degree control device shown in FIG.

FIG. 3 is a flowchart of a superheat control operation performed by the microcomputer in FIG. 1;

FIG. 4 is a refrigerant circuit diagram of an outdoor unit in a conventional air conditioner capable of controlling the degree of superheat.

[Explanation of symbols]

1 ... Outdoor unit, 2 ... Compressor, 3 ...
Four-way switching valve, 5 ... outdoor heat exchanger, 1
DESCRIPTION OF SYMBOLS 1 ... Liquid receiver, 12, 13, 21 ... Thermistor, 18 ... Motor, 19 ...
Rotation control unit, 20 ... valve control unit, 22
... microcomputer, 23 ... memory, 24
… Temperature judgment unit, 25… Rotation frequency judgment unit, 2
6: control unit, 28: indoor heat exchanger, EV
₀ 1st electric expansion valve.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-290456 (JP, A) JP-A-63-180051 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F25B 1/00 F24F 11/02 102 F25B 13/00 104

Claims (1)

(57) [Claims] 1. A compressor (2), a four-way switching valve (3), a plurality of indoor heat exchangers (28, 28,...), A liquid receiver (11), and an electric expansion valve (E).
V ₀₎ and the outdoor heat exchanger (5) the electric expansion valve in a sequential air conditioner formed by connecting in a ring opening of the (EV _0),
In the superheat degree control device for an air conditioner, which controls the superheat degree of the refrigerant on the suction side of the compressor (2) during heating to a target value, the plurality of indoor heat exchangers (28, 28,...) The temperature detectors (21, 21,...) For detecting the respective condensing temperatures, and the condensing temperatures of the indoor heat exchangers (28, 28,...) Detected by the temperature detectors (21, 21,...) A temperature judging unit (24) for judging whether the maximum value of the respective condensing temperatures has exceeded a predetermined temperature, and a rotation judging unit for judging whether the rotational frequency of the compressor (2) has exceeded a lower limit value. When the frequency determining unit (25) and the temperature determining unit (24) determine that the maximum value of each of the condensing temperatures exceeds a predetermined temperature, based on the determination result of the rotation frequency determining unit (25). , The compressor (2)
If the rotation frequency of the compressor (2) does not exceed the lower limit, a rotation control signal for lowering the rotation frequency of the compressor (2) by a predetermined value is output, while the rotation frequency of the compressor (2) is lower than the lower limit. Is exceeded, an opening control signal for setting the opening of the electric expansion valve (EV ₀ ) to a predetermined opening lower than the lower limit in the superheat control is output, and the target of the superheat is set. The control unit (2) resets the value to a larger value.
6), a rotation control unit (19) that receives a rotation control signal from the control unit (26), and controls a rotation frequency of the compressor (2) based on the rotation control signal; 26. An air conditioner comprising: a valve control unit (20) for receiving an opening control signal from (26) and controlling the opening of an electric expansion valve (EV ₀ ) based on the opening control signal. Superheat control device.