JPH0239708B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Field of Industrial Application The present invention relates to the degree of superheating of a refrigeration system equipped with an electric valve equipped with a pressure reducing mechanism such as a thermoelectric expansion valve, a reversible electromagnetic proportional valve, and a pulse type electric valve. Regarding measurement methods.

(B) Prior art As a method for controlling the degree of superheating using a thermostatic expansion valve, the degree of superheating is affected by the pressure loss of the evaporation pressure of the heat exchanger on the user side, and the degree of superheating is affected by the deviation of the measured value from the set value, for example, within 1 degree or less. If the pressure loss is equal, an internal pressure equalization temperature type expansion valve is used because the pressure loss does not affect superheat control, but if it is 1 degree or more, the pressure loss and superheat become large and the target value of superheat cannot be determined. Therefore, a method using an external pressure-equalizing temperature-type expansion valve is used. If the above deviation exceeds a certain range, the measured value of the degree of superheat will be the set value + the pressure loss value, and the suction gas will be overheated and the logarithmic average temperature will rise, so it is necessary to correct the pressure loss with an external pressure equalization type. occurred.

Even if these temperature-type expansion valves have the same pressure reduction capacity, the measured value of the degree of superheat is different. Therefore, it is necessary to select and use either an internal pressure equalization type or an external pressure equalization type, and what is more, the measured value is the pressure Since the pressure is calculated as follows, there is a drawback that it is necessary to convert this pressure into temperature to obtain the target value.

(c) Purpose of the Invention The purpose of the present invention is to calculate the degree of superheat to be controlled by expressing the pressure loss of the evaporation pressure of the heat exchanger on the user side of a refrigeration system in terms of temperature.

(d) Structure of the Invention A method for measuring the degree of superheat in which the target value of the degree of superheat is measured by subtracting the evaporation temperature in the case where the pressure loss does not affect the degree of superheat control from the suction temperature in the case where there is a pressure loss.

(e) Embodiments of the invention Reference numeral 1 shown in FIG.
A heat source side heat exchanger 3, an electric valve 4 equipped with a pressure reduction mechanism,
It is constructed by connecting a plate-fin type user-side heat exchanger 6, etc., which are forcedly ventilated by a blower 5, in a ring through piping, and seals a refrigerant of, for example, R22, and compresses, condenses, liquefies, and depressurizes this refrigerant. , forming the well-known refrigeration cycle of evaporation. 7 is a sensor that detects the evaporation temperature ET of the refrigerant, and 8 is a sensor that detects the suction temperature ST of the refrigerant.The temperature signals from these two sensors are sent to the controller main body (not shown), and the control signal G from this main body is used. Then, the degree of opening and closing of the electric valve 4 is adjusted.

The electric valve mentioned above is the ``bimetallic heat-responsive valve with electric heating means'' introduced in Japanese Patent Publication No. 58-7869, and the monthly newspaper ``Refrigeration'', Volume 56, No. 641 (Showa
This is a "thermoelectric expansion valve" introduced on pages 60 to 64 of the March 1956 issue, and the control signal is applied to the heating device that serves as the energized part to displace the bimetal and move the valve body up and down. It operates in the direction.

FIG. 2 shows a Mollier diagram for the above-mentioned refrigeration system. In FIG. 2, 9 is a saturated vapor line, 10 is a saturated liquid line, 11 is a critical point, A to C ₁ are isobaric lines 12 having pressure P ₁ and temperature ET, and C ₁ to D ₁ are evaporation processes represented by isobar lines 12. The compression process is represented by the isentropic line 13, the condensation and liquefaction process is represented by the isobaric line 14, and the isenthalpy line 15 is represented by E _- A.
In the depressurization process expressed by , this pressure enthalpy diagram shows that there is almost no pressure loss at the evaporation pressure _P
Moreover, even if it occurs, it is ideal because it does not affect superheat degree control. The degree of superheat SH ₁ at this pressure enthalpy is expressed by a width of _{1 1} . Furthermore, 1
6 to 19 are isothermal lines, and the ideal suction temperature ST is represented by point _C1 on isothermal line 19.

However, in the refrigeration system 1, the type of refrigerant,
Pressure loss occurs in the evaporation pressure due to the evaporation temperature, the length of the piping, etc., and the pressure generally decreases. Conventionally, it has been difficult to detect the suction temperature ST at this time using only the sensor 8. .

That is, the pressure drop due to the pressure loss is from the inlet point A of the user side heat exchanger 6 to the inlet point of the refrigerant compressor 2.
C ₂ , resulting in an evaporation pressure of 12' having a pressure of P ₂ . The degree of superheat SH ₂ in this case is expressed by a width of _{2 2} , and point C ₂ on the isothermal line 18 is on the left side of the isothermal line 19 in the case of no pressure loss, that is, on the lower temperature side. Here, if the intersection of pressure P ₂ and isothermal line 19 is C ₃ , then these two isothermal lines 19 and 18
The temperature difference C ₃ − C ₂ is equal to the temperature conversion value ΔP of pressure loss. That is, the suction temperature ST' at point _C2 includes an error equivalent to the pressure loss. Therefore, at evaporation pressure P ₂ , superheat degree SH ₂
need to be corrected.

In addition, 20 is C ₂ to _{D 2} as the evaporation pressure P ₂ changes.
It is an isentropic line that transfers to .

As mentioned above, the pressure loss of the user side heat exchanger 6 is:
This is due to differences depending on the type of refrigerant and the type of expansion valve used. In order to accurately measure the degree of superheating, in the case of the utilization side heat exchanger 6, it is essential to measure the evaporation pressure, and it is also necessary to quantify the magnitude of the pressure loss.

However, in actual refrigerant superheat control,
When the temperature-converted value ΔP of pressure loss is less than 1 degree, it is considered to be within a range where control is not affected even if it is ignored.

Actual superheat degree control is performed as follows.

That is, when the target value (set degree of superheat) of control is set to 5 degrees, the deviation DEV occurring between the set value of the degree of superheat and the measured value is given by the following equation, and control is performed to eliminate this.

DEV=SH-5 =(ST-ET)-5 = {(ST′+ΔP)−ET}−5 =(ST′−ET)+ΔP−5 ST′: Suction temperature when there is pressure loss.

ET: Evaporation temperature when pressure drop does not affect superheat control.

ST: Ideal suction temperature of the heat exchanger on the user side.
ST=ST'+ΔP ΔP: Value obtained by converting the pressure loss in the heat exchanger on the user side into temperature.

In the above control, correction is required when the value of ΔP exceeds 1 degree, and is ignored when the value of ΔP is less than 1 degree.

When ΔP<1deg, for example, ΔP=0, ST'=-
2.5, ET=-7, (a) DEV={-2.5-(-7)}+0-5 =4.5-5 =0.5 When ΔP≧1deg, for example, ΔP=1.5, ST'=-
3.5, assuming ET=-7 (b) DEV={-3.5-(-7)}+1.5-5 =5.0-5 =0 In addition, correction using ΔP is performed from a microcomputer, etc. as shown by the arrow in Figure 3. input to the controller.
Further, the numerical values of ΔP shown in (a) and (b) above are stored in the program in advance.

Also, the method to cancel ΔP when converting a temperature signal is as follows: V (ET) + ΔP V (ST) - ΔP V (SH) - ΔP [V: voltage value of temperature signal (converted using measured value SH _M )] The method shown in FIG. 3 can be considered.

(F) Effect As described above, the present invention measures the target superheat degree by subtracting the evaporation temperature when pressure loss does not affect superheat control from the suction temperature when there is pressure loss. It produces the effects listed below.

The pressure loss of evaporation pressure can be measured with respect to temperature, and the target value of the degree of superheat can be calculated extremely easily, and the degree of superheat can be easily corrected, making it possible to control the degree of superheat appropriately.

Since there is no need to distinguish between internal pressure equalization type and external pressure equalization type in temperature type expansion valves, the electric valve can be used in a wider range of applications and is easier to handle.

[Brief explanation of drawings]

Figure 1 is a refrigerant circuit diagram of a refrigeration system according to the method for measuring the degree of superheat of the present invention, Figure 2 is a Mollier diagram showing the measured degree of superheat and pressure loss in the refrigeration system, and Figure 3 is a diagram showing the measured superheat degree and pressure loss in the refrigeration system.
The figure is a block diagram illustrating the cancellation of the temperature conversion value of pressure drop.

Claims (1)

[Scope of Claims] 1. In a refrigeration system that supplies liquid refrigerant whose pressure has been reduced by an electric valve to a heat exchanger on the user side, when a pressure loss occurs in the evaporation pressure of the refrigerant that affects superheat degree control, calculation is performed. The degree of superheat SH used for is SH=ST-ET = ST'+ΔP-ET = ST'-ET+ΔP [ST': Suction temperature when there is pressure loss. ET: Evaporation temperature when pressure drop does not affect superheat control. ST: Ideal suction temperature of the heat exchanger on the user side.
ST=ST'+ΔP ΔP: Value obtained by converting the pressure loss in the heat exchanger on the user side into temperature. ] A method of measuring the degree of superheat calculated by the formula.