JPH0157274B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a refrigeration system.

A conventional device of this type is shown in FIG. In the figure, 1 is a sensor that detects the low pressure and force of the refrigerant cycle, 2 is an input conversion device that converts the low pressure and force of the sensor 1 into a mechanical or electrical signal, 3 is a setting device that sets a certain pressure, and 4 is a A set pressure converter 5 mechanically or electrically converts the set pressure of the setting device 3, which inputs the outputs of the input converter 2 and the set pressure converter 4, and converts the low pressure output from the input converter 2 into the set pressure converter 5. A comparator device outputs an output when the pressure becomes lower than the pressure set by the set pressure converter 4, and 6 is a control circuit that stops the compressor or issues an alarm in response to the output of the comparator 5.

Next, the operation will be explained. First, setting device 3,
A set pressure converter 4 sets the set pressure to a certain value. Next, when the refrigeration equipment is operated, when the load is small, the low pressure and pressure decreases, and the low pressure and pressure detected by the sensor 1 and the input conversion device 2 become lower than the set pressure detected by the setting device 3 and the set pressure conversion device 4, and the comparison is made. The device 5 outputs an output, and the control device 6 operates to stop the compressor, thereby preventing liquid back-up operation. Furthermore, even if there is a shortage of refrigerant gas, the low pressure is lowered and the control device 6 operates to stop the compressor in the same way as described above, so that overheating of the compressor can be prevented. However, as this type of device only detects low pressure force, it is possible that the low pressure has decreased due to a decrease in the load, or due to a lack of refrigerant gas, or a combination of these. Since we don't know if the problem has gone down, it takes time and money to investigate the cause. In addition, although the set pressure value can be adjusted, the normal set value is 1 point, so in order to stop the compressor safely, it is necessary to set it to a certain low pressure and force, which can occur due to low load or lack of refrigerant gas. When the low pressure is lowered due to a combination of the above, the ability to operate the refrigeration system below the set pressure is ignored, and as a result, the operating range of the refrigeration system cannot be widened. There was a drawback.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and it detects superheat in addition to low pressure of the refrigerant cycle, identifies low load and lack of refrigerant gas, and outputs it.
The object of the present invention is to provide a control device for a refrigeration system that can have a wide operating range.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2, 7 is a compressor, 8 is a condenser, 9 is a condenser blower 10, an expansion device 11 is an evaporator 12
The evaporator blower 13 is installed at the inlet coil of the evaporator 11, and has a first temperature sensing element that detects the evaporation temperature of the refrigerant or a value equivalent to the evaporation temperature. This is a second temperature sensing element that detects temperature or an equivalent value. In FIG. 3, 15 is an input converter 16 that converts the inputs of the first temperature sensing element 13 and the second temperature sensing element 14 into electrical signals. 17 is a timer device that starts counting from the start of the compressor and outputs the output after a certain period of time; 18 is a calculation device that calculates the converted value and the super heat conversion value; A storage device 19 stores the converted value of low pressure and force, the converted value of super heat, a certain set time, etc., and 19 compares the output data of the arithmetic device 16 and the timer device 17 with the set value of the storage device 18; 16. If the output data of the timer device 17 satisfies the set value of the storage device 18, a comparison device outputs an output corresponding to the set value; 2
0 is a control device that issues a low load alarm, a refrigerant gas shortage alarm, a compressor stop command, etc. based on the output of the comparator 19.

Generally, in a refrigerant device filled with a specified amount of refrigerant, as the load becomes smaller, the low pressure and superheat become smaller. Furthermore, if the load is the same, as the amount of refrigerant charged in the refrigerator decreases, the low pressure force decreases and the superheat increases. FIGS. 4 and 5 show characteristic diagrams according to an embodiment of the present invention. Figure 4 is a characteristic diagram showing the changes in low pressure and force and superheat with respect to changes in refrigerant amount when the refrigeration load of the refrigeration system is constant. , the vertical axis is the evaporation temperature TR of refrigerant R22 and the first
Temperature TE of the temperature sensing element 13 installation part, actual superheat SH of this refrigeration equipment, and apparent superheat ΔT obtained by subtracting the above temperature TE from the temperature TC of the second temperature sensing element 14 installation part (ΔT=(TC) −
(TE)). As you can see in the figure, the low pressure LP = 1.0KG/cm ² where the amount of refrigerant is decreasing
Up to around G, TE tracks well with TR, and ΔT tracks well with SH, which can be converted into actual low pressure force and super heat, respectively. Also, the low pressure LP is 1.0Kg/
When the temperature drops below cm ² G, the actual amount of refrigerant is almost gone and TE approaches the ambient temperature, so it rises rapidly, so TE cannot keep up with TR and ΔT with SH. A temperature rise can be used to determine a refrigerant gas shortage. Note that normally TC≧TE, but in Fig. 4, △
The reason why there is a region where T≦0°C exists is that when the refrigerant gas decreases, the pressure loss of the refrigerant between the position of the first temperature sensing element 13 and the position of the second temperature sensing element 14 increases, and the temperature TC decreases. It is from. Figure 5 is a characteristic diagram showing the changes in low pressure and superheat with respect to load fluctuations in a refrigeration system filled with a specified amount of refrigerant.The horizontal axis is the change in refrigeration load with the standard state being 100%, and the vertical axis is LP. , TR, TE, SH, and ΔT. As can be seen in the figure, the change in refrigeration load
TE closely follows TR and ΔT closely follows SH, and can be converted into actual low pressure force and superheat, respectively, and the state when the refrigeration load is reduced can be detected by changes in TR and ΔT. In this way, as is clear from FIGS. 4 and 5, the detected temperature of the first temperature sensing element 13 follows the evaporation temperature TR of the refrigerant, so from this detected value, the equivalent value of the low pressure can be calculated. can be converted, and the superheat can also be calculated from the apparent superheat ΔT as described above. Note that the low pressure decreases both when the refrigeration load decreases and when there is a shortage of refrigerant gas, and superheat decreases when the refrigeration load decreases and increases when there is a shortage of refrigerant gas, so it seems necessary to detect only changes in superheat. However, in reality, a low load or a refrigerant shortage will not occur unless the low pressure itself decreases, so it is necessary to find a value equivalent to the low pressure based on the low pressure, that is, the detected value of the temperature sensing element 13. For example, even if the superheat is high, if the low pressure is high, it is not a refrigerant shortage but an overload condition. For the above-mentioned reasons, the following data is stored in advance in the storage device 18, taking into account the time period during which the refrigerant cycle is stabilized during a certain period of time when the compressor is started.

(a) 5 minutes after starting the compressor, TE≦-2℃ and ΔT≧
If it is 30deg, it is determined that there is a lack of refrigerant gas.

That is, in Fig. 4, the amount of refrigerant is about 50% of the specified amount, and there is a refrigerant shortage. Also, in Figure 5, TE
At =-2°C, △T≒0°C, so the load is not low.

(b) If TE≧20℃ 5 minutes after starting the compressor, it is determined that there is a complete refrigerant gas shortage.

That is, in Fig. 4, when TE≧20°C, the amount of refrigerant is several percent or less of the specified amount.

Also, in Figure 4, when the amount of refrigerant increases,
TE increases.As shown in Figure 5, TE increases as the refrigeration load increases, but TE never exceeds 20°C.

(c) 5 minutes after starting the compressor, TE≦-2℃ and ∆T≦
If it is 5deg, it is considered that the refrigeration load is small.

That is, in Figure 4, at TE=-2℃, △T
Since the temperature is ≒25℃, there is no shortage of refrigerant. Also, in Figure 5, the load is about 50% of the refrigeration load, which is low.

(d) If TE≦-10℃ immediately after starting the compressor, it is determined that there is a combination of refrigerant gas shortage and small refrigeration load, or the worst condition of each. In addition, the set value -10℃ is the 4th
As is clear from the characteristics in the figure, these are typical values for refrigerators, especially air conditioners, and are only a guideline value, so it is possible to set it to, for example, -5℃, but the setting is another judgment condition mentioned above. Value -2℃
It is important that the value is lower than .

That is, this is a region where the low pressure is lower than in (a) and (b) above, and is included in (a) or (b), but in order to protect the compressor, it is not possible to wait until 5 minutes after startup.
For this reason, a timer device 17 in FIG. 3 that generates an output even immediately after startup is provided, and it is possible to check that the output is being generated and that the temperature TE calculated by the calculation device 16 and the temperature TE are stored in the storage device 18. The comparator 19 generates an output on the condition that the relationship with the set value -10°C is TE≦-10°C.

If the data of the arithmetic device 16 and the timer device 17 satisfy the conditions (a) to (d) above in the storage device 18, the comparison device 19 and the control device 20 satisfy the commands (a) and (b), respectively. If the refrigerant gas shortage alarm (c) is satisfied, a low load alarm is issued, and if the condition (d) is met, a compressor stop command is issued.

In the above embodiment, the first temperature sensing element 13 is provided, but the first temperature sensing element 13 may be replaced by a pressure sensing element and the mounting position may be a position that detects the low pressure and force of the refrigerant cycle. In particular, when there is a shortage of refrigerant gas, it follows the actual low pressure and force until the gas is completely exhausted, and it also follows the superheat, allowing for even more precise control. Furthermore, if a microcomputer is used, the input conversion device 15, arithmetic device 16, timer device 17, storage device 18, comparison device 19, and control device 20 are all processed by software, making the circuit configuration easier.

As described above, according to the present invention, low pressure and force in the refrigerant cycle and superheat are detected, low load and refrigerant gas shortage are identified, and an alarm and a command to stop the compressor are issued, so that the problem can be discovered and the cause investigated. This method requires less time and cost, and can be detected with high accuracy, which has the effect of expanding the operating range of the refrigeration equipment.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional control device for a refrigeration system, Fig. 2 is a block diagram of a refrigerant cycle of a refrigeration system according to an embodiment of the present invention, and Fig. 3 is a block diagram of a control system for a refrigeration system according to an embodiment of the present invention. A block diagram of the device, FIG. 4 is a characteristic diagram of low pressure and force, super heat, etc. when the amount of refrigerant changes according to an embodiment of the present invention;
FIG. 5 is a characteristic diagram of low pressure and force, super heat, etc. when the refrigeration load changes according to an embodiment of the present invention. 12... Evaporator blower, 13... First temperature sensing element, 14... Second temperature sensing element, 15... Input conversion device, 16... Arithmetic device, 17... Timer device,
18... Storage device, 19... Comparison device, 20...
Control device, LP...Low pressure force (Kg/cm ² G), TR...
...Evaporation temperature (°C) of refrigerant R22, TE...Temperature (°C) of the installation part of the first temperature sensing element 13, SH...Actual superheat of the refrigeration system according to an embodiment of the present invention,
TC...Temperature (°C) of the installation part of the second temperature sensing element 14,
ΔT...This is the apparent superheat obtained by subtracting TE from TC. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1 A first detection element that detects the evaporation pressure or evaporation temperature of the refrigerant, a second detection element that detects the refrigerant suction temperature of the compressor, and the detection values of the refrigeration cycle from the detection values of these first and second detection elements. A calculation device that calculates a low pressure equivalent value and a superheat equivalent value, and when a predetermined time has elapsed from the start of the compressor, the low pressure equivalent value and superheat equivalent value calculated by the calculation device and the preset low pressure. Compare the set value and the super heat set value, and if the low pressure equivalent value is less than or equal to the first low pressure set value and the super heat equivalent value is greater than or equal to the first super heat set value, or the low pressure equivalent value is equal to or higher than the second low pressure set value, which is set higher than the first low pressure set value, a refrigerant shortage warning control signal is generated, and the low pressure equivalent value is equal to or lower than the first low pressure set value. and if the superheat equivalent value is less than or equal to a second superheat set value that is set lower than the first superheat set value, a low load warning control signal is generated, and the low pressure immediately after the compressor is started. A refrigeration system characterized by comprising means for generating a control signal for stopping the compressor when the pressure equivalent value is less than or equal to a third low pressure set value that is set lower than the first low pressure set value. Control device.