JPH0545868B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a configuration of a refrigeration system that uses a non-azeotropic mixed refrigerant in a refrigeration cycle and can maintain stable operation without causing abnormal conditions in the compressor even when the refrigerant composition changes significantly.

[Conventional technology]

A refrigeration system has been proposed in which a non-azeotropic mixed refrigerant made by mixing two types of refrigerants with different boiling points is used in a single-stage refrigeration cycle, and the composition ratio of this mixed refrigerant can be changed as necessary. Special Public Service 1986-
It is known from Publication No. 698. That is, a separation device is provided in the middle of the refrigeration cycle to change the composition of the circulating refrigerant between, for example, cooling operation and heating operation. On the other hand, control controls the opening degree of the electric expansion valve installed in the liquid pipe so that the difference between the saturation temperature corresponding to the suction pressure detected by the pressure detector and the refrigerant evaporation temperature of the evaporator is constant. Regarding the system,
As disclosed by Publication No. 51-83258,
This is also known. Therefore, a refrigeration system that uses a non-azeotropic mixed refrigerant in a single-stage refrigeration cycle and allows the composition ratio to be changed, as well as controls the refrigerant with an electric expansion valve and performs refrigeration operation with a constant temperature difference in the evaporator. can be easily constructed using both of the above-mentioned known techniques.

[Problems to be solved by the invention]

In this way, refrigerant control in a single-stage refrigeration cycle using a non-azeotropic mixed refrigerant is possible by differential temperature control using an electric expansion valve. Saturation temperature signal corresponding to pressure
Suction refrigerant temperature signal detected by T _S and temperature detector 2
It is sufficient to control the degree of superheat to be constant so that the difference from _T When the relationship changes as shown in Figure 8, the refrigerant saturation temperature T _S obtained from the output of pressure detector 1 differs from the saturation temperature of the refrigeration cycle, and the control point shifts, resulting in dampness or excessive superheating. This is not desirable as it involves driving. For example, in FIG. 8, the initial refrigerant composition is
Suppose that W ₁ and the pressure calculation circuit that receives the output of the pressure detector 1 at this time is set to output the temperature T ₁ a of the saturated steam line I corresponding to a constant pressure P, then in this state, the refrigerant When the composition changes to _W2 , the temperature of the saturated steam line for the same pressure P is
Despite the change from T ₁ a to T ₁ b, the pressure calculation circuit outputs T ₁ a corresponding to W ₁ , and ΔT=T ₁ b−
Due to the deviation shown by T ₁ a, if control is continued as is, the degree of superheat will decrease by ΔT, and if the composition change in this case is quite large, the compressor may suck in wet refrigerant and cause liquid compression. be. On the contrary, if the composition is changed so that the proportion of refrigerant A becomes smaller, the degree of superheating will increase and the compressor will be heated to a high temperature, resulting in undesirable situations such as overload operation and deterioration of lubricating oil performance. This may lead to In view of the fact that the known technology does not take any measures against changes in refrigerant composition, and may lead to accidents such as compressor burnout,
The present invention overcomes the above-mentioned conventional drawbacks by providing a mechanism for quickly detecting a change in refrigerant composition and modifying the output of a detection signal associated with a pressure detector for obtaining a saturation temperature signal. In addition, it is an object of the present invention to play a role in promoting the spread of refrigeration equipment that can maintain stable operation and has a non-azeotropic mixed refrigerant.

[Means to solve the problem]

Therefore, the present invention uses a non-azeotropic mixed refrigerant in the refrigeration cycle, and uses the suction pressure detected by the pressure detector 1 to calculate the evaporation pressure and saturation temperature of the non-azeotropic mixed refrigerant filled at the initially set mixing ratio. The difference between the saturation temperature signal obtained by conversion by the pressure-temperature conversion means and the suction refrigerant temperature signal detected by the first temperature sensor is determined in advance by the temperature conversion constant corresponding to each pressure value obtained from the relationship. The refrigeration system is configured to control an electric expansion valve installed in a liquid pipe so that the pressure remains constant at a set level.
In addition to the initially set mixture ratio, conversion constants are set for various mixture ratios in the vicinity of the mixture ratio in the temperature conversion means, and a refrigerant temperature close to the saturated vapor line on the low pressure side is detected to generate a refrigerant temperature signal. A second temperature detector compares the saturation temperature signal obtained by the pressure-temperature conversion means and the refrigerant temperature signal generated by the second temperature detector, and if the difference is out of a predetermined range, a correction signal is sent. and a comparison calculation means which is operated by the correction signal which is issued by the comparison calculation means, and which outputs an output for changing the conversion constant to the pressure-temperature conversion means to convert the saturation temperature signal into the refrigerant temperature signal. The refrigeration apparatus is provided with a control circuit comprising a conversion constant changing means for correcting the conversion constant so that the conversion constant is equal to the conversion constant change means.

[Effect]

The present invention having the above configuration controls the refrigerant to keep the degree of superheat constant using an electric expansion valve, and also controls the non-azeotropic mixed refrigerant in the refrigeration cycle to change its composition and to change the degree of the change. When the temperature increases, the difference between the saturation temperature signal corresponding to the suction pressure detected by the pressure detector and the refrigerant temperature signal emitted by the second temperature sensor increases beyond the preset range. The comparative calculation means determines that the temperature is too high or the temperature is too wet, and the saturation temperature signal obtained by the pressure detector is changed by comparing it with the refrigerant temperature signal, thereby preventing burning of the compressor. It is possible to continue stable operation without causing damage accidents, and the intended purpose has now been achieved.

【Example】

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a circuit diagram of a refrigeration system according to an embodiment of the present invention, which has a known refrigeration cycle consisting of a compressor 11, a condenser 12, an electric expansion valve 3, and an evaporator 13. The electric expansion valve 3 interposed therein is equipped with, for example, a pulse motor 3M in the valve driving section, as shown in the blocks in FIGS. 2 and 3.
The rotation speed is controlled according to the number of pulse voltages applied to the pulse motor 3M, and the valve is configured to open and close in an adjustable manner. In the refrigeration system configured as described above, the refrigeration cycle is filled with a predetermined amount of a non-azeotropic mixed refrigerant. For example, a mixed refrigerant in which a low boiling point refrigerant R-22 and a high boiling point refrigerant R-114 are mixed in an appropriate ratio is used. . The control circuit that controls the operation of this refrigeration equipment has a pressure detector 1, a first temperature detector 2, and a second temperature detector 4 as input command elements, and also has a pressure detector 1, a first temperature detector 2, and a second temperature detector 4 as input command elements. The motor 3M and the motor for the compressor 11 as controlled objects

It has a controller C provided between it and [not shown]. The pressure detector 1 uses a known pressure sensor that detects suction pressure, converts it into an electrical signal proportional to the pressure value, and outputs it, while the first and second temperature detectors 2 and 4 A known temperature sensor such as a thermistor is used that detects the temperature at a location, converts it into an electrical signal proportional to the temperature value, and outputs it. The first temperature detector 2 is attached to an appropriate location of the suction pipe to detect the temperature T _G of the suction refrigerant, while the second temperature detector 4 detects the temperature of saturated steam on the low pressure side. Attached to a location where a refrigerant with a temperature close to the line exists, the refrigerant temperature near saturated vapor
The second _temperature sensor 4 is installed at a location where the liquid phase and gas phase coexist, for example, on the wall of the heat exchanger tube slightly upstream from the outlet of the evaporator 13. Attach it. Next, controller A, whose structure is schematically shown in Figures 2 and 3, is a central processing unit.

[CPU], arbitrary access memory

[RAM], read-only memory

[ROM] consists of a microcomputer having input ports I ₀ to I ₂ and an output port O ₀ , a pressure sensor 1 is connected to the input port I ₀ , and a first temperature sensor is connected to the input port I ₁ . 2 and second temperature detector 4
The input port _I2 is connected to input elements such as a compressor operation determination signal, and the output port _O0 is connected to an amplifier 9 for issuing a control output to the pulse motor 3M. The functions of the controller C are clearly shown in the block diagram shown in FIG. 2 and the flow diagram shown in FIG. 4. Temperature conversion means 7 and electric expansion valve control means

[hereinafter abbreviated as valve control means] 8. The pressure-temperature conversion means 7 has an arithmetic function that converts the suction pressure signal detected by the pressure detector 1 into a saturation temperature signal T _S corresponding to this suction pressure, and fills with the initially set mixture ratio. The P-T curve shown in Figure 5 shows the relationship between the evaporation pressure P _S and the saturation temperature T _S of the non-azeotropic refrigerant mixture.

Find the temperature conversion constant corresponding to each pressure value from the [solid curve] and store this temperature conversion constant in the arbitrary access memory.

It is stored in [RAM] in advance, and each time pressure is detected, necessary conversion constants are read out, temperature conversion calculations are performed, and the conversion is performed to the corresponding saturated steam line temperature T _S. In addition, arbitrary access memory

[RAM] indicates the P-T of the mixed refrigerant with the initial setting mixing ratio.
In addition to the conversion constant based on the curve, there are several P-T curves using various mixing ratios in the vicinity as parameters.

The conversion constant based on the [dashed line curve] is stored so that this conversion constant can be retrieved when necessary. In this way, when the pressure-temperature conversion means 7 outputs the saturation temperature signal T _S corresponding to the suction pressure, this signal T _S and the suction cooling temperature signal T _G detected by the first temperature detector 2 are controlled by the valve control. It is input to means 8. The valve control means 8 compares the two signals T _S and T _G and issues a control signal so that the difference matches a preset reference temperature difference. After being amplified, the expansion valve 3
is applied to the pulse motor 3M, so that the opening degree of the expansion valve 3 is automatically controlled so that the difference between the two signals T _S and T _G is constant, that is, the degree of superheat is constant. It is designed to be controlled. On the other hand, the comparison calculation means 5 calculates that the saturation temperature signal T _S corresponding to the suction pressure detected by the pressure detector 1 and the second temperature detector 4 are detected at predetermined intervals, for example, every 10 minutes while the compressor 11 is in operation. The detected refrigerant temperature signal T _E is compared, and if the difference is out of a predetermined range, a correction signal is generated, and this correction signal is input to the conversion constant changing means 6. The conversion constant changing means 6 to which the correction signal is input in this way outputs a change output so that the conversion constant determined from the P-T curve corresponding to the mixed refrigerant having the changed mixing ratio is read out from the RAM. is input into the pressure-temperature conversion means 7. As a result, the pressure-temperature conversion means 7 outputs a refrigerant temperature signal, that is, a second refrigerant temperature signal, which is converted with respect to the detected pressure _P
A signal having a value approximately equal to the refrigerant temperature signal T _E detected by the temperature detector 4 is output, and the initial conditions are automatically changed in accordance with changes in the refrigerant composition, and the degree of superheat is continuously adjusted thereafter. It is possible to perform controlled refrigeration operation. In addition, in order to change the solid line curve in FIG. 5 to the broken line curve and store the temperature conversion constant changed based on this curve, if the saturation pressure-temperature relationship is limited to the target operating temperature range, lnP=a-b/T...○a However, P; Absolute pressure T; Absolute temperature a, b; Since it is expressed as a constant determined by the refrigerant, it is sufficient to memorize the constants a and b based on this. Explain the procedure. When the above formula ○A is transformed, T=b/a-lnP...○B, and if P is detected, T can be found by the formula ○B. By the way, the change from the solid line curve to the broken line curve in FIG.
It is sufficient to determine a and b that satisfy the formula ○A from the detected temperature T, but since there are two unknowns, a and b, this cannot be used alone. Therefore, another conditional expression is required, which can be given by considering the continuity of the change in the pressure straight line, as shown in FIG. In FIG. 6, the straight line L _A is the pressure straight line of the mixed refrigerant, and the straight lines L ₁ and L ₂ are the pressure straight lines of each component refrigerant of this mixed refrigerant, and the constants a ₁ , b ₁ , a ₂ , and b ₂ are respectively
have. In order for the straight line L _A to change continuously from the straight line L ₁ to the straight line L ₂ when the mixing ratio of the mixed refrigerant is changed, it is sufficient to provide some kind of relational expression between the constants a and b. For example, with x as a parameter, a= xa ₁ +

[1-x] a ₂ ...○c b=xb ₁ +

[1-x] b ₂ . . . It can be expressed by ◯ d. Note that x is the relationship of the mixing ratio. Eliminate x from both formulas ○C and ○D and get a=a ₂ +

[a ₁ −a ₂ ]b − b ₂ /b ₁ −b ₂ ...○E is obtained, but if this is added to ○A formula as a conditional expression, a and b can be found from T and P. . Substituting ○H for ○A and rearranging for b, b=lnP+a ₁ −a ₂ ／b ₁ −b ₂・b ₂ −a ₂ ／a ₁ −a ₂ ／b ₁ −b
₂ -1/T...○H is obtained, and after all, using the measured P and T, find b using the formula ○F, and find a from the formula ○E, which can then be determined as the constant a _' of the new straight line L , b′. ○E and ○E both equations can be transformed to make it easier to remember: b=lnp+A/B-1/T......○G a=B・b-A......○C However, A=a ₁ b ₂ - a ₂ b ₁ /b ₁ −b ₂ and B=a ₁ −a ₂ /b ₁ −b ₂ , and therefore it is understood that the values of A and B should be stored. The mode of operation control of the refrigeration system having the above-mentioned configuration is shown in a flow diagram in Fig. 4. When the control operation starts, the timer is cleared, and when the compressor 11 is operating, the timer starts counting, and from this point the suction pressure P and suction refrigerant temperature
Detect T _G and refrigerant temperature T _E. Then, the valve control means 8 controls the electric expansion valve 3 to maintain a constant degree of superheating, and at the same time, it is determined whether or not it is in steady operation. Once this is done, the comparison calculation means 5 compares T _S and T _E , and if the temperature difference is within a predetermined range, clears the timer and repeats the same procedure again. On the other hand, when the temperature difference deviates from the predetermined range and becomes large, the conversion constant changing means 6 operates to calculate constants a and b corresponding to the pressure detected by the pressure-temperature conversion means 7, and After storing it in RAM, clear the timer and repeat the same procedure again. In addition, to determine whether or not it is steady operation,
For example, the refrigerant temperature signal T _E before and after one minute has elapsed
If each value of is within ±0.1℃, it is considered steady,
If not, it is assumed that the timer is in an unstable state due to a transient period or for other reasons, and the timer is cleared and restarted from the initial state. In addition, load fluctuations are not large and the specified period is
If the duration is about 10 minutes, it can be regarded as steady operation, and therefore, the determination as to whether or not it is steady operation may be omitted. Alternatively, a timer may count a predetermined time from startup or unloader control, and thereafter it may be determined that the operation is steady. Preferably, the second temperature detector 4 detects the temperature of the refrigerant at a point where the temperature slightly enters the saturated region rather than the boundary point between the superheated region and the saturated region of the evaporator 13. This is because the refrigeration system always maintains the degree of superheat at an appropriate constant value, and the required area of the superheat region of the evaporator 13 is almost fixed, and the saturated region has a change in latent heat. This is mainly because changes in sensible heat are small and errors in temperature changes do not appear large, which is advantageous. Further, the refrigeration circuit according to the present invention is not limited to that shown in FIG. 1, but for example, as shown in FIG. 7,
A device with an additional heat exchanger 14 that performs heat exchange between the suction refrigerant and the high-pressure liquid refrigerant may also be used, and other modified devices may also be used as long as the refrigerant temperature on the low-pressure side can be detected close to the saturated vapor line. Included.

【Effect of the invention】

The present invention provides a saturation temperature signal T _S corresponding to the suction pressure.
The degree of superheating is controlled by the refrigerant temperature signal _TG and the temperature signal T If a change in refrigerant composition is detected and the degree of change is large, the saturation temperature signal T _S is not the value obtained from the pressure-temperature characteristics based on the initial mixture ratio, but the actual saturation on the low pressure side. After the refrigerant temperature T _E is changed to near the steam line, it is compared with the suction refrigerant temperature T _G and used as a control input element for the electric expansion valve 3. Therefore, if the suction refrigerant is excessively superheated, the electric expansion valve The valve opening degree of No. 3 is further controlled to the open side to lower the superheat degree to the set value, and conversely, when the suction refrigerant is wet, the valve opening degree is further reduced to bring the superheat degree closer to the set value. Therefore, it is possible to continue operation even when the composition of the mixed refrigerant changes without causing abnormal overheating or liquid return, and to maintain a stable state.

[Brief explanation of the drawing]

FIG. 1 is a device circuit diagram according to an embodiment of the present invention;
2 to 4 are control circuit block diagrams,
A schematic structure diagram and flow diagram of the control circuit, FIGS. 5 and 6 are conceptual diagrams and reference diagrams for explaining the calculation of pressure-temperature conversion, and FIG. 7 is a device circuit according to an example of the present invention. 8 is a diagram showing the relationship between the composition and temperature of a non-azeotropic mixed refrigerant, and FIG. 9 is a circuit diagram of a conventional refrigeration system. 1...Pressure detector, 2...First temperature detector, 3
...Electric expansion valve, 4...Second temperature detector, 5...
... Comparison calculation means, 6... Conversion constant changing means, 7...
...Pressure-temperature conversion means.

Claims (1)

[Claims] 1. While a non-azeotropic mixed refrigerant was used in the refrigeration cycle, the suction pressure detected by pressure detector 1 was determined from the relationship between the evaporation pressure and saturation temperature of the non-azeotropic mixed refrigerant filled at the initially set mixing ratio. A saturated temperature signal TS obtained by conversion by the pressure-temperature conversion means 7 using a temperature conversion constant corresponding to each pressure value,
Suction refrigerant temperature signal detected by first temperature detector 2
This is a refrigeration system that controls an electric expansion valve 3 installed in a liquid pipe so that the difference between TG and TG is constant, and the pressure-temperature conversion means 7 is supplied with a mixture ratio as initially set. In addition, a second temperature detector 4 which sets conversion constants at various mixing ratios in the vicinity, detects a refrigerant temperature close to the saturated vapor line on the low pressure side and generates a refrigerant temperature signal TE, and the pressure-temperature converter. The saturation temperature signal TS obtained by means 7 and the refrigerant temperature signal TE generated by the second temperature detector 4
and a comparison calculation means 5 which issues a correction signal when the difference deviates from a predetermined range. On the other hand, it emits an output to change the conversion constant, and the saturation temperature signal TS
A refrigeration system comprising a control circuit comprising a conversion constant changing means 6 for correcting the refrigerant temperature signal TE to be equal to the refrigerant temperature signal TE.