JPS6356465B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of controlling a refrigeration system, and particularly to a method of controlling the degree of superheat.

Conventionally, the system shown in the system diagram of FIG. 1 has been known as a general refrigeration system.

As shown in FIG. 1, the refrigerant compressed by the compressor 1 is condensed and liquefied by the condenser 2. As shown in FIG. The refrigerant sent out from the condenser 2 is supplied to an evaporator 4 via an expansion valve 3. The refrigerant vaporized by the evaporator 4 is returned to the compressor 1 again. This refrigerant return line is provided with a temperature sensing cylinder 5 for detecting the refrigerant temperature at the outlet of the evaporator 4.
The temperature sensing tube 5 is associated with the opening control drive section of the expansion valve 3. Normally, the above-mentioned expansion valve 3, evaporator 4, and temperature-sensitive tube 5 are installed in a freezer 6, which is a heat load of the evaporator 4.

In the refrigeration system configured in this way, the evaporator 4
When the refrigerant supplied to the freezer 6 is vaporized, the heat of vaporization cools the air, which is the cooling medium inside the freezer 6. Fluctuations in the amount of heat load on the evaporator 4 are handled by controlling the refrigerant flow rate using the expansion valve 3 to control the amount of evaporation in the evaporator 4. The refrigerant flow rate is controlled by the temperature sensor 5 in the evaporator 4.
This is done by detecting the temperature of the outlet refrigerant and operating the opening degree control drive section of the expansion valve 3 so that the degree of superheating becomes a constant value. In this way, the freezer 6
The internal temperature is controlled to the desired temperature.

The degree of superheat is a main parameter of the refrigeration effect, and it is known that the optimum degree of superheat that maximizes efficiency changes depending on the equipment characteristics of the evaporator 4 and the expansion valve 3, or load conditions such as heat load and evaporation temperature. An actual measurement example is shown in FIG. In FIG. 2, the horizontal axis shows the degree of superheating SH, and the vertical axis shows the heat load Q. The lines in the figure indicate the characteristics of the optimum degree of superheating at a constant evaporation temperature, where the line shows an example where the evaporation temperature is high and the line shows an example where the evaporation temperature is low. The region with a low degree of superheating bordering on the line is called the unstable region (A), and the region with a high degree of superheating is called the stable region (B). When operated in the unstable region (A), a liquid return phenomenon of the refrigerant and a hunting phenomenon of the expansion valve occur, both of which are undesirable for the refrigeration system. In addition, although the above-mentioned phenomenon does not occur when operating in the stable region (B), the degree of superheating is too high, so the effective heat transfer area of the evaporator 4 decreases, and the amount of refrigerant discharged from the compressor 1 decreases. This may lead to a decrease in the efficiency of the refrigeration equipment, resulting in a lack of refrigeration capacity.

However, the degree of superheating SH in the conventional example shown in FIG. 1 cannot be changed in response to changes in heat load, etc., as shown in FIG. The superheat degree was set to a constant value by adjusting the superheat degree adjusting screw. Therefore, if the superheat degree SH is set too close to the optimum superheat characteristic, it will enter the unstable region (A) depending on changes in load conditions such as heat load, so even if the load conditions change, it will not be in the stable region. In order to operate within (B), the superheat degree must normally be set to SH with a sufficient safety factor, resulting in inefficient operation.

Additionally, a thermoelectric expansion valve has been proposed that detects the refrigerant temperature at the inlet and outlet of the evaporator using a temperature sensor and controls the temperature difference between them to be constant. However, since the degree of superheating must be set to a constant value in advance, it has the same drawbacks as mentioned above.

An object of the present invention is to provide a method for controlling the degree of superheat of a refrigeration apparatus, which can control the degree of superheat to an optimal value according to equipment characteristics and load conditions.

The present invention includes a first stroke in which the expansion valve is throttled to a predetermined opening degree when a change in the load condition of the evaporation temperature or heat load amount is detected or a given command, and a refrigerant temperature at the outlet of the evaporator is adjusted at predetermined intervals. A second step of detecting the rate of change, a third step of counting the number of times the rate of change has reached a predetermined rate of change or more, and determining whether the counted value in a certain number of cycles has reached a predetermined value or more. and when the judgment is negative, the expansion valve is opened by a certain amount, and then the second to fourth steps are performed.
A fifth step in which the steps are repeated, and when the judgment in the fourth step is affirmative, the opening degree of the expansion valve is reduced by a certain amount, and then the temperature difference between the outlet refrigerant temperature and the refrigerant evaporation temperature in the evaporator is detected. and a sixth step of setting the temperature difference as the optimum degree of superheat, and by controlling the expansion valve based on the optimum degree of superheat, correction control is performed to the optimum degree of superheat according to the equipment characteristics and load conditions. The aim is to achieve stable and highly efficient operation.

First, the principle of the present invention will be explained using FIG. 3.

FIG. 3 shows an example of the temporal change in the evaporator outlet refrigerant temperature T _B and the evaporation temperature T _A of the refrigerant in the evaporator at that time as the degree of superheating is reduced. In the illustrated section t ₁ , the refrigerant flow rate is small relative to the heat load and all of the refrigerant evaporates, and the refrigerant is superheated and the outlet refrigerant temperature T _B reaches the temperature inside the freezer. Next, as the refrigerant flow rate is increased, T _B stably decreases in section _t2 , and the difference between T _B and T _A , that is, the degree of superheat SH, is stably reduced for a while. When the refrigerant flow rate is further increased, T _B fluctuates unstably as shown in section t ₃ , and finally a relatively regular periodic hunting phenomenon occurs as shown in section t ₄ , and the liquid It can be seen that the state returns and enters the unstable region.

The present invention was made by focusing on the fact that when the refrigerant flow rate is increased, a phenomenon occurs in which T _B fluctuates unstablely before the liquid returns, as shown in FIG. It is something. In other words, the superheat degree correction command is given at regular intervals or when changes in heat load, evaporation temperature, etc. are detected.
Once the expansion valve opening is brought to a close state, the opening is gradually increased to increase the refrigerant flow rate, and at the same time, the change state of the outlet refrigerant temperature T _B is detected and a predetermined unstable change state is established. The difference between T _B and _TA just before the difference is determined as the optimum degree of superheat SH ₀ , and the expansion valve is thereafter controlled based on this optimum degree of superheat SH ₀ .

The present invention will be explained based on illustrated embodiments.

FIG. 4 shows a system configuration diagram of a refrigeration system to which the method of the present invention is applied. In the figure, the same reference numerals as in the conventional example shown in FIG. 1 indicate the same parts and the same functions.

As shown in FIG. 4, an evaporation temperature sensor 7 is provided inside the evaporator 4 to detect the evaporation temperature of the refrigerant. An outlet temperature sensor 8 is provided on the outlet pipe of the evaporator 4 to detect the outlet refrigerant temperature. Temperature signals from these temperature sensors 7 and 8 are input to an expansion valve control device 9. The expansion valve control device 9 includes an input section 9a, a calculation section 9b, and an output section 9c. Further, an electric heater 10 is attached to the temperature sensing cylinder 5. The amount of heat generated by the electric heater 10 can be controlled by the output section 9c, and by controlling this amount of heat, the degree of opening of the expansion valve 3 is controlled.

Note that the evaporation temperature sensor 7 may be installed not only inside the evaporator 4 but also on the connecting pipe between the expansion valve 3 and the evaporator 4 as long as the evaporation temperature sensor 7 can accurately detect the evaporation temperature of the refrigerant. In the case of a large capacity, the pressure loss in the evaporator 4 is large, so that the saturated steam temperature also varies depending on the position within the evaporator. Therefore, the evaporation temperature sensor 7 is located at the evaporator 4 as a position where the evaporation temperature corresponding to the refrigerant pressure can be correctly detected.
It is desirable to provide it at an intermediate position. Furthermore, the outlet refrigerant temperature sensor 8 may be installed at any position as long as it is a refrigerant pipe extending from the evaporator 4 outlet to the compressor 1.

The operation of the embodiment configured as described above will be explained below with reference to FIG.

Figure 5 shows the procedure for controlling the degree of superheating, and the series of operations shown in the diagram are performed in response to a degree of superheating correction command given at fixed intervals or when changes in heat load, evaporation temperature, etc. are detected. . Note that the superheat degree adjusting screw of the expansion valve 3 in this embodiment is set in the expansion valve closing direction, and when the amount of heat generated by the electric heater 10 is small, the temperature of the temperature sensing tube 5 is lowered and the expansion valve 3 is closed. is set to be in the closing direction.

As shown in FIG. 5, the process starts when a superheat degree correction command is input (step 101), and although not shown, the expansion valve 3 is throttled to a predetermined opening degree.
Next, the output of the electric heater 10 is controlled to P ₁ ,
The opening degree of the expansion valve 3 is increased (stroke 102). itinerary
At 104, take in the outlet refrigerant temperature T _BN and
In step 105, the rate of change △T = T _BN - T _BN-1 is calculated from the previously measured outlet refrigerant temperature T _BN-1 , and in step 106, the magnitude is determined from the predetermined rate of change △Ts (for example, 2.5°C). are doing. If ΔT>ΔTs, 1 is added to the count value M (step 107), and if ΔT≦ΔTs, the count value M is not changed (step 108). After such calculation is completed, a predetermined period Θ ₁ (for example, 1 minute)
After waiting for the elapsed time (step 109), the next T _BN+1 is fetched and the above calculation is repeated. After repeating i times (for example, 10 times) in this manner, in step 110, the magnitude of the count value M and a predetermined count value L (for example, 4 times) is determined. Here, if the count value M is M<L, it is determined that the refrigeration system is not experiencing the hunting phenomenon, and in order to further increase the refrigerant flow rate, the output of the electric heater 10 is controlled to _{P2, which} is increased by a predetermined amount Po. (Step 112),
Step 103 of waiting for the predetermined time Θ ₂ to elapse (step 113)
The count value M is reset, and the arithmetic and control operations described above are repeated.

In this way, when the count value becomes M≧L (step 110), it is determined that a hunting phenomenon has occurred (step 114), and the output of the electric heater 10 is reduced by a predetermined amount Po in order to reduce the refrigerant flow rate by one step. The process proceeds to step 117, in which the reduction control is performed (step 115), and the process waits for the elapse of a predetermined time Θ ₂ (step 116). In step 117,
The evaporation temperature T _AO and outlet refrigerant temperature T _BO at that time are taken in, T _AO is subtracted from T _BO in step 118, and this temperature difference is output as the optimum degree of superheat SHo. In this way, one superheat degree correction control operation is completed.

Optimal superheat degree SHo obtained by the above operation
Although not shown in the above procedure, the calculation unit 9
In b, the evaporation temperature T _A and the above-mentioned SHo are added, and in the output section 9 c, the output of the electric heater 10 is controlled so that the outlet refrigerant temperature T _B matches ( _TA + SHo), thereby controlling the refrigerant flow rate. That's what I'm doing.

Therefore, according to this embodiment, the degree of superheating can be controlled to an optimal value according to the device characteristics and load conditions.

Further, according to the present embodiment, optimal superheat degree control can be performed, so that the operation of the refrigeration system can be stabilized and the efficiency can be significantly improved.

In the above-described embodiment, the temperature-sensing tube 5 is attached to the evaporator outlet, but when the output of the electric heater 10 is reduced, the temperature-sensing tube 5 is cooled and the expansion valve is operated in the closing direction. For example, it may be inside the evaporator.

Furthermore, in the above-described embodiment, a temperature-type automatic expansion valve is applied as the expansion valve 3, and the refrigerant flow rate is controlled by controlling the temperature-sensing tube temperature with an electric heater. However, the present invention is not limited to this. . For example, when a well-known thermoelectric expansion valve is used, the heater of the thermoelectric expansion valve can be directly controlled.

Furthermore, in the above-described embodiment, as _a method for detecting an unstable phenomenon in the refrigeration equipment,
Although we have explained how the determination is made based on the change in the outlet refrigerant temperature every time, instead of this, it is also possible to detect the time interval required for a constant temperature change and determine whether it is stable or unstable based on that time interval. It is possible.

As described above, according to the present invention, it is possible to carry out correction control to the optimum degree of superheat according to the device characteristics and load conditions, and to perform stable and highly efficient operation.

[Brief explanation of the drawing]

Fig. 1 is a system configuration diagram of a conventional example, Fig. 2 is a diagram for explaining the optimum degree of superheating, Fig. 3 is a diagram for explaining the principle of the present invention, and Fig. 4 is an application of the present invention. FIG. 5 is a flowchart showing the main operating procedure of the embodiment shown in FIG. 3... Expansion valve, 4... Evaporator, 5... Temperature sensing cylinder,
6... Freezer, 7... Evaporation temperature sensor, 8... Outlet refrigerant temperature sensor, 9... Expansion valve control device, 10
...Electric heater.

Claims (1)

[Claims] 1. In a method for controlling a refrigeration system comprising an evaporator that cools a medium to be cooled by heat of vaporization of an inflowing refrigerant and an expansion valve that controls the flow rate of refrigerant flowing into the evaporator, a superheat degree correction command given a first step in which the expansion valve is throttled to a predetermined opening degree, a second step in which the rate of change in the refrigerant temperature at the outlet of the evaporator is detected at every predetermined period, and the number of times the rate of change reaches a predetermined rate of change or more. a third step in which the count value is counted, a fourth step in which it is determined whether the count value in a certain number of cycles has reached a predetermined value or more, and when the judgment is negative, the opening degree of the expansion valve is opened by a certain amount. After that, a fifth step repeats the second to fourth steps, and if the judgment in the fourth step is affirmative, the opening degree of the expansion valve is reduced by a certain amount, and then the outlet refrigerant temperature and the refrigerant in the evaporator are adjusted. A method for controlling a refrigeration system, comprising: a sixth step of detecting a temperature difference from an evaporation temperature and setting the temperature difference as an optimum degree of superheat, and controlling the expansion valve based on the optimum degree of superheat. .