JPH08121916A - Suction pressure-estimating method - Google Patents

Abstract

PURPOSE: To reduce the cost of a suction pressure sensor by estimating the suction pressure of a compressor based on a saturation pressure at an installation part of a temperature sensor in a lower pressure side refrigerant flow passage and an estimated value of pressure loss. CONSTITUTION: The suction pressure during cooling operation is estimated with a controller 151 based on formulas I Pe=α1×Te+α2 in the case of Te<T0, II Pe=α3×Te+α4 in the case of Te>=T0, and III ΔP=α5×F<α6> where Pe stands for saturation pressure, Te for detected values of temperature sensors 113, 204 and 205, and their minimum values are adopted. ΔP stands for a pressure loss from the position of an adopted temperature sensor to the inlet of a compressor, F stands for a rotary speed of a compressor motor, and α1 to α6 stand for coefficients, and α5 varies with the mounting position of an adopted temperature sensor or a line of a gas pipeline 121. The suction pressure during heating operation is also estimated based on the formulas I, II and III, in this case, Te stands for a detected value of a temperature sensor 112, ΔP stands for a pressure loss from the position of the temperature sensor 112 to the inlet of the compressor. The rotary speed of the motor of the compressor is computed so that the estimated suction pressure may be within a set range, thereby a motor rotary speed controller 152 controls the compressor motor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting the suction pressure of a refrigeration cycle.

[0002]

2. Description of the Related Art A conventional air conditioner is disclosed in JP-A-60-14032.
As described in the publication, a suction pressure sensor is provided at the compressor inlet, and the compressor capacity is controlled so that the suction pressure reaches a set value.

[0003]

The prior art has a problem that the cost of the product increases because an expensive suction pressure sensor is provided.

Further, if the suction pressure sensor fails, the capacity of the compressor will be abnormally reduced or abnormally increased, and the electric input will increase due to insufficient cooling capacity or overload operation of the compressor. .

An object of the present invention is to reduce the cost of the product, diagnose the failure of the suction pressure sensor, and back up when the suction pressure sensor fails.

[0006]

A temperature sensor, which is less expensive than a suction pressure sensor, is provided in a low pressure side refrigerant passage of a refrigeration cycle, and means for estimating a pressure loss from a temperature sensor installation portion to a compressor inlet portion is provided. .

[0007]

[Function] The saturation pressure of the temperature sensor installation portion can be calculated by the temperature sensor provided in the low pressure side refrigerant passage, and the pressure loss from the temperature sensor installation portion to the compressor inlet portion can be estimated by the pressure loss estimation means, and the saturation pressure calculated value The compressor suction pressure can be estimated by subtracting the estimated pressure loss value from.

Further, it is possible to determine the failure of the suction pressure sensor by using the suction pressure estimated value.

Furthermore, if the suction pressure sensor fails,
By using the estimated suction pressure, the compressor capacity can be controlled normally.

[0010]

FIG. 1 shows an embodiment of the present invention.

The outdoor unit 100 includes a compressor 105 whose motor rotation speed is variable, a four-way valve 106, an outdoor heat exchanger 101,
It is composed of a subcooler 111, an outdoor fan 103, a check valve 110, a capillary tube 109, an accumulator 104, a temperature sensor 112, a controller 151 and a motor rotation speed controller 152. The indoor unit 200 includes an indoor heat exchanger 201, an expansion valve 202, an indoor fan 203, and temperature sensors 204 and 205. Outdoor unit 100
The indoor unit 200 and the indoor unit 200 are connected by a gas pipe 121 and a liquid pipe 122. The signals from the temperature sensors 112, 204, 205 are input to the controller 151.

Next, the operation during the cooling operation will be described.

First, the flow of the refrigerant will be described. The solid arrows in the figure indicate the direction of refrigerant flow.

The refrigerant discharged from the compressor 105 passes through the four-way valve 106 and enters the outdoor heat exchanger 101 where it is heat-exchanged with the outdoor air sent by the outdoor fan 103 and condensed. After that, the condensed refrigerant flows into the subcooler 111 without passing through the check valve 110 because the flow is blocked by the check valve 110, and is heat-exchanged with the outdoor air sent by the outdoor fan 103 to be supercooled. Becomes the liquid refrigerant. The supercooled liquid refrigerant is slightly decompressed by the capillary tube 109, becomes a two-phase refrigerant of liquid gas, exits the outdoor unit 100, enters the liquid pipe 122, and is sent to the indoor unit 200. Indoor unit 2
The two-phase refrigerant entering 00 is further decompressed by the expansion valve 202, enters the indoor heat exchanger 201, is heat-exchanged with the indoor air sent by the indoor fan 203 and is evaporated, and the indoor air is cooled. Then, the evaporated refrigerant exits the indoor unit 200, enters the gas pipe 121, and is sent to the outdoor unit 100. The refrigerant that has entered the outdoor unit 1 is sucked into the compressor 105 through the four-way valve 106 and the accumulator 104, compressed, and then discharged again. During cooling, three temperature sensors 204, 205 and 113 are used to estimate the suction pressure, and the temperatures detected by the temperature sensors 204, 205 and 113 have the three patterns shown in FIG. 2 depending on operating conditions. Pattern 1 indicates that the saturated refrigerant flows up to the position of the temperature sensor 113. Pattern 2 indicates that the saturated refrigerant has flowed to the position of the temperature sensor 205, and the refrigerant is overheated on the downstream side. Pattern 3
Indicates that the saturated refrigerant has flowed to the position of the temperature sensor 204, and the refrigerant is overheated on the downstream side.

Next, a method of estimating the suction pressure during cooling will be described. The estimation is performed by the controller 151.

The suction pressure is estimated by using Equations 1, 2 and 3.

[0017]

When Te <T0, Pe = α1 × Te + α2 (Equation 1)

[0018]

## EQU2 ## When Te ≧ T0, Pe = α3 × Te + α4 (Equation 2)

[0019]

(Equation 3)

In the equation, Pe is the saturation pressure and Te is the detection value of the temperature sensor, and the lowest value of the three temperature sensors is adopted.
ΔP is the pressure loss from the temperature sensor position to the compressor inlet, F is the rotation speed of the compressor motor, α1 to α6 are coefficients, and α5 is the mounting position of the temperature sensor to be used and the gas pipe 1
It depends on the length of 21.

Next, the operation during the heating operation will be described.

First, the flow of the refrigerant will be described. The dashed arrow in the figure indicates the direction of refrigerant flow.

The refrigerant discharged from the compressor 105 passes through the four-way valve 106, enters the gas pipe 121, and enters the indoor unit 200.
Sent to. The refrigerant that has entered the indoor unit 200 is an indoor heat exchanger.
Entering 201, the heat is exchanged with the indoor air sent by the indoor fan 203 to condense, and the indoor air is warmed. After that, the refrigerant is decompressed by the expansion valve 202, becomes a two-phase refrigerant of liquid gas, enters the liquid pipe 122, and is sent to the outdoor unit 100. The refrigerant that has entered the outdoor unit 100 passes through the check valve 110, enters the outdoor heat exchanger 101, is heat-exchanged with the outdoor air sent by the outdoor fan 103, and evaporates. The evaporated refrigerant is sucked into the compressor 105 through the four-way valve 106 and the accumulator 104, compressed, and discharged again.
When heating, the temperature sensor used to estimate the suction pressure is 112
Temperature sensor.

Next, a method of estimating the suction pressure during heating will be described.

The suction pressure is estimated by using Equations 1, 2 and 3 as in the case of cooling. Pe in the formula is saturation pressure, Te
Is a detection value of the temperature sensor 112. ΔP is the pressure loss from the position of the temperature sensor 112 to the compressor inlet, F is the rotation speed of the compressor motor, and α1 to α6 are coefficients.

Here, a method of calculating the saturation pressure Pe of the equations 1 and 2 will be described. The relationship between the temperature and the pressure in the saturated state of the refrigerant is a curve as shown by the solid line in FIG. It is difficult to obtain the saturation pressure from the detected temperature using such a saturation curve. Therefore, it was decided to approximate it by a broken line like a broken line and to obtain it by a linear equation. T0 represents the temperature at the bent point of the broken line.

The motor rotation speed of the compressor is calculated so that the suction pressure thus estimated falls within the set range, and the signal is sent to the motor rotation speed controller 152, and the motor rotation speed controller 152 causes the compressor to rotate. Control the motor.

Another embodiment of the present invention is shown in FIG.

FIG. 4 shows an outdoor unit 100 and two indoor units 20.
0,300 are connected in parallel. Outdoor unit 100
Is a compressor 105 whose motor rotation speed is variable, a four-way valve 1
06, outdoor heat exchanger 101, expansion valve 102, outdoor fan 103, receiver 107, accumulator 104, temperature sensor 113, pressure detector 108, controller 151
And a motor rotation speed controller 152. The indoor unit 200 includes an indoor heat exchanger 201, an expansion valve 202, an indoor fan 203, and temperature detectors 204 and 205. The indoor unit 300 includes an indoor heat exchanger 301, an expansion valve 302, an indoor fan 303, and temperature detectors 304 and 30.
It is composed of 5. The outdoor unit 100 and the two indoor units 20
A gas pipe 121 and a liquid pipe 122 are connected to 0 and 300. Temperature sensor 112, 204, 205, 30
The signals of 4,305 and the signal of the pressure detector 108 are input to the controller 151.

Next, the operation during the cooling operation will be described.

First, the flow of the refrigerant will be described. The solid arrows in the figure indicate the direction of refrigerant flow.

The refrigerant discharged from the compressor 105 passes through the four-way valve 106 and enters the outdoor heat exchanger 101 where it is heat-exchanged with the outdoor air sent by the outdoor fan 103 and condensed. Then, the condensed refrigerant passes through the expansion valve 102 and the receiver 107, then exits the outdoor unit 100, enters the liquid pipe 122, and is sent to the indoor unit 2 and the indoor unit 3. The respective refrigerants having entered the indoor unit 2 and the indoor unit 3 are expanded valves 202 and 30.
It is decompressed at 2, enters the indoor heat exchangers 201 and 301,
The indoor air is cooled by heat exchange with the indoor air sent by the indoor fans 203 and 303 to evaporate. Then, the evaporated refrigerant exits the indoor unit 2 and the indoor unit 3, enters the gas pipe 121, and is sent to the outdoor unit 1. The refrigerant that has entered the outdoor unit 1 is drawn into the compressor 105 through the four-way valve 106 and the accumulator 104, is compressed, and is discharged again.

Next, a method of estimating the suction pressure during cooling will be described.

The suction pressure is estimated by using the equations (1), (2) and (3) as in the cooling embodiment of FIG. The detected temperature Te is the temperature sensor 113, 204, 205, 304, 3
Use the lowest temperature of 05.

Next, a method of using the estimated suction pressure value will be described.

The suction pressure estimated value estimated from the temperature sensor in the controller 151 is compared with the suction pressure detected by the pressure detector 108, and if both are within a predetermined range, it is judged that the pressure detector 108 is normal. If it is outside the predetermined range, the pressure detector 108 is judged to be out of order and is displayed. Further, when it is determined that the pressure detector 108 is out of order, the suction pressure estimated value is used to provisionally control the compressor.

[0037]

According to the present invention, since the suction pressure can be known even without the suction pressure sensor, the cost can be reduced by the suction pressure sensor.

Further, when the suction pressure sensor is attached, the failure diagnosis of the suction pressure sensor can be performed, and the reliability of control of the compressor and the like is improved.

Further, when it is determined that the suction pressure sensor is out of order, the estimated value of the suction pressure may be used instead of the detection value of the suction pressure sensor to stop the apparatus.

[Brief description of drawings]

FIG. 1 is a system diagram of a refrigeration cycle of an air conditioner showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a detection pattern of the temperature sensor of the embodiment shown in FIG.

FIG. 3 is an explanatory diagram of a method for calculating a saturation pressure.

FIG. 4 is a system diagram of a refrigeration cycle of a multi-room air conditioner showing another embodiment of the present invention.

[Explanation of symbols]

100 ... Outdoor unit, 101 ... Outdoor heat exchanger, 105 ... Compressor, 113,204,205 ... Temperature sensor, 121 ... Gas pipe, 122 ... Liquid pipe, 151 ... Controller, 15
2 ... Motor rotation speed controller, 200 ... Indoor unit, 201 ... Indoor heat exchanger, 202 ... Expansion valve.

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Shinichiro Yamada 4-6 Kanda Surugadai, Chiyoda-ku, Tokyo Inside the Air-Conditioning Systems Division, Hitachi, Ltd. (72) Inventor Kenichi Nakamura 4-Sumita Kanda, Chiyoda-ku, Tokyo 6th Air Conditioning Systems Division, Hitachi Ltd. (72) Inventor Satoru Yoshida 4-6, Sugawadai Kanda, Chiyoda-ku, Tokyo Inside Air Conditioning Systems Division, Hitachi Ltd.

Claims (1)

[Claims] 1. A saturation pressure calculating means for providing a temperature sensor in a low pressure side refrigerant passage of a refrigeration cycle to obtain a saturation pressure of a temperature sensor installation portion from a signal of the temperature sensor, and a temperature sensor installation portion to a compressor inlet portion. And a pressure loss estimating means for estimating the pressure loss of the compressor, and a suction pressure estimating method for estimating the compressor suction pressure by subtracting the pressure loss estimated value from the saturated pressure calculated value.