JPH0545867B2 - - 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 is provided with an alarm function to notify when a change in cooling composition becomes large.

[Conventional technology]

Regarding refrigeration equipment that uses a non-azeotropic mixed refrigerant, which is a mixture of two types of refrigerants with different boiling points, in a single-stage refrigeration cycle, see Refrigeration-Vol.
Volume 56, No. 649, November 1989 issue, pages 892 to 892
The basic structure is well known as described in "Refrigerant and Refrigeration Cycle" on page 903, especially on pages 899 to 901. 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, 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 the above-mentioned known techniques. It is something.

[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, and as shown in FIG. Control may be performed so that the difference between the temperature T ₁ and the refrigerant temperature T ₂ at the outlet of the evaporator 13 is constant, but the problem with such a temperature detection method is that the response speed is slow, and the transition period It is difficult to perform control with good followability, and there is a risk that a hunting phenomenon may occur. On the other hand, as shown in FIG. 9, overheating is carried out so that the difference between the saturation temperature signal T _S corresponding to the suction pressure detected by pressure detector 1 and the suction refrigerant temperature signal T _G detected by temperature detector 2 is constant. Although constant temperature control has the advantage of fast response speed, the composition of the non-azeotropic refrigerant mixture may change due to refrigerant leaks during use, or the mixing ratio may change due to incorrect operation during refrigerant charging. When the temperature drops, the pressure-temperature relationship changes as shown in FIG. 7, so the refrigerant saturation temperature T _S obtained from the output of the pressure detector 1 differs from the refrigeration cycle saturation temperature due to the change in refrigerant composition. This is undesirable because the control point will shift and the operation will result in dampness or excessive superheating. For example, in Figure 7, the initial refrigerant composition is W ₁
At this time, if the pressure calculation circuit that receives the output of the pressure detector 1 is set to output the temperature T ₁ a of the saturated steam line corresponding to the constant pressure P, then in this state the refrigerant composition is W. ₂ , the temperature of the saturated steam line for the same pressure P is T ₁ a
Despite the change from T ₁ b, the pressure calculation circuit
By outputting T ₁ a corresponding to W ₁ and causing a deviation shown by △T = T ₁ b - T ₁ a, if control is performed as it is, the superheat degree will decrease by △T, and the composition in this case If the change is large enough, the compressor may draw in wet refrigerant and cause liquid compression. 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 eliminates the above-mentioned conventional drawbacks and maintains stable operation by providing a mechanism that quickly detects changes in refrigerant composition and issues an alarm. It is an object of the present invention to play a role in promoting the spread of refrigeration equipment having a boiling mixture refrigerant.

[Means for Solving the Problems] Accordingly, the present invention uses a non-azeotropic mixed refrigerant in a refrigeration cycle, and also uses the evaporation pressure and saturation temperature of the non-azeotropic mixed refrigerant filled at an initially set mixing ratio. Based on the relationship, the suction pressure detected by the pressure detector 1 is converted into a saturation temperature signal T _S corresponding to the suction pressure, and the difference between this saturation temperature signal and the suction refrigerant temperature signal detected by the first temperature detector is The refrigeration system is configured to control an electric expansion valve installed in the liquid pipe so that the difference is constant, and the refrigerant temperature is detected close to the saturated vapor line on the low-pressure side to control the refrigerant temperature. A second temperature detector that emits a temperature signal compares the saturation temperature signal corresponding to the suction pressure detected by the pressure detector with the refrigerant temperature signal that the second temperature detector emits, and determines that the difference is within a predetermined range. The refrigeration system is provided with an alarm circuit comprising a comparison calculation means that issues a warning signal when the comparison calculation means is off, and an alarm device activated by the warning signal issued by the comparison calculation means.

[Effect]

The present invention having the above configuration performs refrigerant control 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. As a result of activating an alarm system based on a comparison calculation means that determines that the refrigerant is too large or wet, it is possible to know that there has been a change in the composition of the refrigerant, and to prevent accidents such as seizure or damage to the compressor. It is possible to take measures without delay.

【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 concentrator 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 rotational speed is controlled according to the number of pulse voltages applied to the pulse motor 3M, and the valve is opened and closed 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. By attaching it to a location where refrigerant is present at a temperature close to the saturated vapor line, it is possible to detect the refrigerant temperature T _E near the saturated vapor line.
The temperature sensor 4 is attached to the wall of the heat transfer tube at a location where the liquid phase and the gas phase coexist, for example, slightly upstream from the outlet of the evaporator 13. Next, the controller C, whose structure is schematically shown in FIGS. 2 and 3, includes a central processing unit CPU, arbitrary access memory RAM, read-only memory ROM input ports I ₀ to I ₂ and output ports O ₀ and O ₁ consists of a microcomputer with an input port
A pressure detector 1 is connected to I ₀ , a first temperature detector ₂ and a second temperature sensor 4 are connected to input port I 1, and input elements such as a compressor operation determination signal are connected to input port I ₂ . On the other hand, an amplifier 9 for issuing a control output to the pulse motor 3M is connected to the output port _O0 , and an alarm device 6 is connected to the output port _O1 . The functions of the controller C are clarified by the block diagram shown in FIG. 2 and the flow chart shown in FIG. 4. type expansion valve control means

[hereinafter abbreviated as valve control means] 8 and conversion constant changing means 10. 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.

[Solid line curve/L ₁ ]
From, for arbitrary access memory RAM in advance,
Temperature conversion constants corresponding to each pressure value are memorized, and each time pressure is detected, the necessary conversion constants are read out, and temperature conversion calculations are performed to convert to the corresponding saturated steam line temperature. There is. Note that the arbitrary access memory RAM stores the P-T curve for the mixed refrigerant with the initial setting mixture ratio.
In addition to conversion constants based on L ₁ , there are several P-T curves with various mixing ratios in the vicinity as parameters.

A conversion constant based on [broken line curve L ₂ ] is stored, and this conversion constant can be retrieved when necessary. When the pressure-temperature conversion means 7 outputs the saturation temperature signal T _S corresponding to the suction pressure in this way, this signal T _S and the suction refrigerant 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. Compares the detected refrigerant temperature signal T _E and issues a warning signal and change command signal if the difference is outside a predetermined range.
A warning signal is input to the alarm device 6, and a change command signal is input to the conversion constant changing means 10. The warning device 6 to which the warning signal has been input issues a warning for a predetermined time period to warn that the composition of the refrigerant in the refrigeration cycle, that is, the mixing ratio, is significantly deviated from the set condition. In addition, the conversion constant changing means 10 to which the change command signal is inputted changes the conversion constant determined from the P-T curve corresponding to the mixed refrigerant having the changed mixing ratio.
A change command is input into the pressure-temperature conversion means 7 so as to be read from the RAM. 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 sensor 4 is output, and the operation is not stopped due to a change in refrigerant composition, but the initial conditions are changed following this composition change. It is possible to automatically change the temperature and then continuously perform the refrigeration operation by controlling the degree of superheat. In addition, in order to change the solid line curve L ₁ to the broken line curve L ₂ in Fig. 5 and extract the changed constant from this curve, if the saturation pressure-temperature relationship is limited to the target operating temperature range, lnP = a-b/T, p: Absolute pressure, T: Absolute temperature a, b: Since it is expressed by a constant determined by the refrigerant, the constant a,
All you have to do is change b, but in reality, omitting the detailed calculation process and just showing the results, b=lnP+A/B-1/T a=B・b-A However, A=a ₁ b ₂ −a ₂ b ₁ /b ₁ −b ₂ and B=a ₁ −b ₂ /b ₁ −b ₂ , and it is sufficient to store the values of A and B. Note that a and b are constants for one component refrigerant, and a ₂ and b ₂ are constants for the other component refrigerant. The 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 (a), the timer is cleared (b) and the compressor 11 starts operating. If (c), the timer starts counting (d), and from this point on, the suction pressure P, suction refrigerant temperature T _G , and refrigerant temperature T _E are detected (e). Then, the valve control means 8 controls the electric expansion valve 3 to maintain a constant degree of superheating (f), and determines whether or not it is in steady operation (g). As time passed (ch),
Compare T _S and T _E by comparison calculation means 5 (li),
Clear the timer when the temperature difference is within the specified range
(b) Then repeat the same procedure again. On the other hand, when the temperature difference deviates from the predetermined range and becomes large, the alarm device 6 is activated for a certain period of time, for example, 30 seconds, and the conversion means 10 is activated, and constants a and b corresponding to the detected pressure are activated. After calculating and storing it in RAM (1), clear the timer (2) and repeat the same procedure again. In addition, as a judgment (g) 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, the timer is cleared (b) as it is assumed to be in an unstable state due to a transient period or for other reasons, and the operation is restarted from the initial state. Further, if the load fluctuation is not large and the predetermined period is about 10 minutes, it can be considered as steady operation, so the determination (g) as to whether 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 superheated 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. 6,
It may be a device added to the heat exchanger 14 that performs heat exchange between the suction refrigerant and the high-pressure liquid refrigerant, and of course other modified devices may 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 Changes in the composition of the refrigerant are detected and an alarm is issued if the degree of change is large, so appropriate measures can be taken to prevent unforeseen situations such as the compressor being damaged by abnormal overheating or liquid compression. Therefore, it is possible to provide a refrigeration system that is highly safe and reliable.

[Brief explanation of drawings]

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 structural diagram and flow diagram of a control circuit. FIG. 5 is a conceptual diagram for explaining the calculation of pressure-temperature conversion, FIG. 6 is a circuit diagram of an apparatus according to an example of the present invention, and FIG. 7 is a relationship between the composition and temperature of a non-azeotropic refrigerant mixture. 8 and 9 are circuit diagrams of conventional refrigeration equipment. 1...Pressure detector, 2...First temperature detector, 3
...Electric expansion valve, 4...Second temperature detector, 5...
... Comparison calculation means, 6... Alarm device.

Claims (1)

[Claims] 1 Based on the relationship between the evaporation pressure and saturation temperature of the non-azeotropic mixed refrigerant used in the refrigeration cycle and filled with the initially set mixing ratio,
The suction pressure detected by the pressure detector 1 is converted into a saturation temperature signal T _S corresponding to the suction pressure, and the difference between this saturation temperature signal T _S and the suction refrigerant temperature signal T _G detected by the first temperature detector 2 is calculated. This is a refrigeration system that controls an electric expansion valve 3 installed in a liquid pipe so that the difference is constant, and detects a refrigerant temperature close to the saturated vapor line on the low pressure side and issues a refrigerant temperature signal _TE . Second
The temperature detector 4 compares the saturation temperature signal T _S corresponding to the suction pressure detected by the pressure detector 1 with the refrigerant temperature signal T _E emitted by the second temperature detector 4, and determines that the difference is a predetermined difference. A refrigeration system characterized by being provided with an alarm circuit consisting of a comparison calculation means 5 which issues a warning signal when the comparison calculation means 5 deviates from the range, and an alarm device 6 which is activated by the warning signal issued by the comparison calculation means 5.