JPH081337B2 - Refrigerant control device for refrigeration system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control system for an expansion valve of a heat pump type refrigerating apparatus, which has a compressor, a condenser, an expansion valve, and an evaporator as main components. In particular, the present invention relates to a method of controlling the opening degree of the expansion valve depending on the degree of superheat of gas discharged from the compressor.

[Conventional technology]

Conventionally, as a method of controlling the opening degree of the expansion valve according to the refrigerant superheat degree on the high pressure side of the refrigeration cycle, No. 55-143470 has been proposed. The expansion valve is opened and closed according to the difference with the high-temperature side saturated refrigerant temperature. In this way, the saturation temperature in the condenser is detected as the saturation temperature on the high pressure side, and no consideration has been given to the detection of the saturation temperature in the refrigerant discharge part of the compressor. Further, no consideration was given to the calculation method of the opening / closing control of the expansion valve. Further, as another conventional example, the one in which the expansion valve opening degree is controlled according to the superheat degree on the suction side of the compressor is disclosed in JP-A-49-128350 and JP-A-59-1918.
No. 54 or JP-A-59-205559, but there is no description of a method of controlling the expansion valve by the superheat of the discharge gas.

[Problems to be solved by the invention]

The above-mentioned prior art does not consider the method of detecting the degree of refrigerant superheat in the refrigerant discharge portion of the compressor. That is, in the prior art, the refrigerant temperature Tc of the condenser is detected as the saturation temperature on the high pressure side, the temperature Td of the discharge pipe of the compressor is detected, and the expansion valve is controlled according to the temperature difference (Td-Tc). Was there.

Therefore, first, when the connecting pipe between the compressor and the condenser is long, the saturation pressure in the condenser decreases due to the pressure loss in the connecting pipe portion, and the saturation temperature also decreases. in this way,
The degree of superheat of the discharged refrigerant, which is detected and calculated, changes depending on the length of the pipe, and there is a problem that an accurate degree of superheat at the compressor discharge portion cannot be obtained.

An object of the present invention is to accurately detect the superheat degree of discharged refrigerant,
An object of the present invention is to provide a control method that controls the expansion valve opening degree by making the set superheat degree correspond to the detected superheat degree, stabilizes the superheat degree of the discharge gas, and operates the refrigeration system efficiently.

[Means for solving problems]

The above-mentioned purpose is to provide a branch pipe with one end closed in the discharge pipe section near the compressor, and cool the branch pipe to condense the discharge gas in this branch pipe, and to adjust the saturation temperature corresponding to this discharge pressure. The superheat degree of the discharge refrigerant is detected accurately at the discharge gas temperature and the detection saturation temperature, and the expansion valve is controlled by comparing the detected superheat degree with the set superheat degree.
Taking into consideration the temporal change of the above difference and the temporal integration result,
Stabilize the refrigeration system by optimizing the constant of superheat control of the discharge gas and controlling the valve opening in the closing direction if the above superheat is lower than the set superheat and opening the valve if it is higher. Is achieved.

[Action]

The discharge gas atmosphere of the compressor is provided with a branch pipe whose one end is closed, and by cooling the branch pipe, the discharge gas is cooled and condensation occurs. By providing the temperature sensor in the region where condensation occurs in the branch pipe, it is possible to detect the accurate saturation temperature corresponding to the pressure of the discharge gas atmosphere portion. The degree of superheat of the discharge refrigerant is detected by the detection saturation temperature and the discharge gas temperature, the detected degree of superheat and the set superheat degree are compared, and the expansion valve opening is controlled so that the degree of superheat of the discharge refrigerant becomes almost constant. The amount of circulating refrigerant is controlled. Therefore, the expansion valve opening can eliminate the abnormal closing operation of the expansion valve from the transient state after the start of the refrigeration system to the steady state, and the expansion valve control during the startup operation at the start of the refrigeration system. Is optimized.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 shows the structure of the refrigeration cycle of the present invention. In FIG. 1, 1 is a compressor, 2 is a condenser, 3 is an evaporator, 4 is an electrically driven expansion valve, 5 is a discharge gas pipe of the compressor, and 6 is a compressor.
Is a branch pipe whose one end is closed and the other end is open to the discharge gas pipe 5, 7 is a first sensor for detecting the temperature of the branch pipe 6, 8 is a second sensor for detecting the temperature of the discharge gas, and 9 is The control device 10 detects the temperature Teat of the first sensor 7 and the temperature Td of the second sensor 8, calculates the degree of superheat SHd (= Td-Tsat), and drives the opening of the expansion valve 4, 10 is the intake It is a gas pipe. The tip of the branch pipe 6 is attached to the suction pipe 10 so that heat can be exchanged.

In the refrigeration cycle of FIG. 1, the refrigerant discharged from the compressor 1 goes through the discharge gas pipe 5, the condenser 2, the expansion valve 4, the evaporator 3, and the suction gas pipe. Next, FIG. 2 shows details of the branch pipe 6. The branch pipe 6 is attached vertically to the discharge gas pipe 5. As shown in FIG. 2, the refrigerant in the branch pipe 6 is cooled by the suction pipe 10 to lower its temperature, and condensation occurs at a certain position of the branch pipe 6, so that the temperature in the longitudinal direction of the branch pipe 6 is almost constant.ゞ It will be constant. In the branch pipe 6, the liquid refrigerant near the tip of the branch pipe 6 falls, and the dropped liquid refrigerant undergoes a cycle of vaporization due to the discharge gas, and the temperature in the region inside the branch pipe 6 where the liquid refrigerant exists is It will be constant. The first sensor 7 is attached to a region where the temperature of the branch pipe 6 is constant, and the saturation temperature Tsat corresponding to the pressure of the discharge gas atmosphere is detected.

On the other hand, the second sensor 8 detects the discharge gas temperature Td,
The controller 9 opens and closes the expansion valve according to the temperature difference (Td-Tsat), that is, the superheat degree SHd of the discharged gas. Fig. 3 shows the relationship between the superheat degree SHd and the superheat degree and wetness degree on the suction side of the compressor. When the discharge gas superheat degree SHd is small, the suction side is in a wet state containing the liquid refrigerant, and when SHd is large, the suction refrigerant is overheated. The refrigerating capacity is maximized when the superheat of the suction refrigerant is around 0 deg. Therefore, in the example shown in FIG. 3, if the set value of the discharge gas superheat degree SHd is 40 deg, the capacity of the refrigeration cycle can be maximized.

As described above, according to the present embodiment, it is possible to reliably detect the discharge gas superheat degree SHd in the vicinity of the compressor, and by providing an appropriate set value for the discharge gas superheat degree, the refrigeration cycle You can maximize the performance. In addition, if the set value of the discharge gas superheat degree is changed according to the number of revolutions of the compressor, the temperature of the heat medium of the condenser, and the evaporator, the capacity is controlled to the maximum even if the operating state of the refrigeration cycle changes. It is possible.

Further, even when the connecting pipe between the compressor 1 and the condenser 2 is long, according to the present embodiment, there is no influence on the discharge gas superheat degree SHd.

Although FIG. 2 shows the embodiment in which the pipe 6 is cooled by the suction pipe, it is also possible to cool the pipe 6 by the refrigerant from the condenser to the compressor suction portion.

Moreover, if the first sensor 7 is inserted into the pipe 6, the saturation temperature can be detected more accurately.

The means for detecting the saturation temperature corresponding to the pressure of the discharge gas atmosphere and the operation of the discharge gas superheat control have been described above.

Next, a specific example of the opening / closing control system of the expansion valve will be described.

 First, the adjustment amount ΔV of the expansion valve opening is expressed by the following equation.

ε is the discharge gas superheat degree SHd to be detected and calculated and the set superheat degree S
It is the difference in Hdset, and the first term on the right side of the above equation represents the current error, the second term represents the integral value of the error, and the third term represents the differential value of the error. This control method is a so-called PiD control method. The coefficients K ₁ , K ₂ , K ₃ are constants, and these coefficients K ₁ , K ₂ ,
By optimizing K ₃ , the degree of superheat of the discharge gas to be controlled can be controlled stably, and the heat pump refrigeration cycle can be operated stably.

Next, an example of a control method in a transient state such as startup will be described. FIG. 4 shows an operating state after the heat pump device is started. When stopped, the superheat of discharge gas is 0
Therefore, according to the above equation, the correction amount becomes 0, and the signal for opening the expansion valve cannot be output.

In the present invention, the expansion valve is forcibly opened by a predetermined amount at the same time as the activation of the heat pump device or after a lapse of a predetermined time after the activation. After the circuit is opened, the opening degree is kept constant for a predetermined time, and the PiD control is performed after the predetermined time has elapsed. That is, the superheat degree of the discharged gas after starting is smaller than the set superheat degree,
Is negative, the expansion valve remains closed and does not open depending on how to select the coefficients K ₁ , K ₂ , and K ₃ . In the present invention, the coefficient K ₃ is increased until the error ε reaches the predetermined width, and the coefficient K ₃ is decreased after the error ε reaches the predetermined width. As a result, after the start-up, when the degree of superheat SHd suddenly decreases,
That is, when the discharge gas temperature rises sharply, the third term in the above equation is positive and the coefficient K ₃ is large, so an opening command is issued to the expansion valve. Therefore, the expansion valve does not have an abnormally small opening after startup. When the error ε has a predetermined width, K ₃ becomes small, and the heat pump device can operate stably.

〔The invention's effect〕

As described above, according to the present invention, it is possible to detect the saturation temperature corresponding to the pressure of the discharge gas atmosphere in the vicinity of the compressor, accurately detect the degree of superheat of the refrigerant discharged from the compressor, and The control can be performed so that the temperature becomes almost the set value, and the performance of the refrigeration system can be efficiently and stably operated. Further, in particular, it is possible to eliminate the abnormal closing operation of the expansion valve from the transient state after the start of the refrigeration system to the steady state, and there is an effect that the start-up operation at the time of startup of the refrigeration system becomes good. .

[Brief description of drawings]

FIG. 1 is a configuration diagram of a refrigeration cycle showing an embodiment of the present invention, FIG. 2 is an enlarged detailed view of a branch pipe portion of FIG. 1, FIG. 3 is a characteristic diagram of the refrigeration cycle, and FIG. FIG. 4 is a diagram for explaining the operating state of FIG. 4 and is a diagram showing the relationship between the elapsed time, the discharge gas temperature, the discharge gas superheat degree, and the expansion valve opening degree. 1 ... Compressor, 2 ... Condenser, 3 ... Evaporator, 4 ... Expansion valve, 5
... Discharge pipe, 6 ... Branch pipe, 7 ... First sensor, 8 ... Second sensor, 9 ... Control device

Claims (5)

[Claims] 1. A refrigerating apparatus comprising a refrigerant circuit formed by sequentially connecting a compressor, a condenser, an expansion valve, and an evaporator, wherein the discharge section of the compressor branches from the discharge section. A first pipe is provided with a branch pipe whose tip is closed, and a first sensor for detecting the saturation temperature of the refrigerant corresponding to the temperature of the refrigerant flowing into the branch pipe is provided in the branch pipe.
A second sensor that detects the temperature of the refrigerant flowing through the discharge portion is provided in the discharge portion of the compressor, and the refrigerant that flows through the discharge portion based on the outputs of the first sensor and the second sensor. And a control means for controlling the valve opening degree of the expansion valve based on the output of the computing means. Refrigerant control device. 2. The difference between the superheat degree (SHd) calculated from the outputs of the first sensor and the second sensor and the set superheat degree (SHd set), the time integration of the error, and the time of the error. The refrigerant control device for a refrigeration system according to claim 1, wherein the valve opening degree of the expansion valve is controlled based on the dynamic change. 3. The control means for controlling the valve opening degree of the expansion valve in the closing direction when the calculated superheat degree is lower than the set superheat degree. Refrigerant control device for a refrigerating apparatus according to paragraph. 4. A coefficient K _{1 for} the difference between the calculated superheat degree (SHd) and the set superheat degree (SHd set), a coefficient K _{2 for} the time integral term of the difference, and a temporal value of the set superheat degree. Coefficient K _{3 for} changes
The refrigerant control device for a refrigerating apparatus according to any one of claims 1 to 3, wherein the expansion valve opening degree is calculated by weighting the. 5. The refrigerant control of the refrigerating apparatus according to claim 1, wherein the opening degree of the expansion valve is held at a predetermined value for a predetermined time after the refrigerating apparatus is activated. apparatus.