CN100362294C - The Control Method of Screw Cooling Precision Air Conditioning System - Google Patents

Abstract

The invention discloses a control method of a screw cold water precision air-conditioning system, which comprises a compressor, a condenser, a drying filter and an evaporator which are connected with the compressor in sequence, a chilled water outlet pipe and a chilled water return pipe which are arranged on the condenser, and a PLC controller, wherein a temperature sensor for detecting the return water temperature of the chilled water is arranged on the chilled water return pipe, the output end of the temperature sensor is connected with the input end of the PLC controller, an electromagnetic valve for controlling the running state of the compressor is arranged in the compressor, the output end of the PLC is connected with the input end of an electromagnetic valve arranged in the compressor and is controlled by the PLC in combination with PID programming, the energy of the screw cold water precise air-conditioning system can be automatically adjusted, and the freezing return water temperature of the central air-conditioning system can be accurately controlled within a set range.

Description

The Control Method of Screw Cooling Precision Air Conditioning System

technical field

The invention relates to a chilled water supply system in the field of heating, ventilating and air-conditioning, in particular to a method for controlling a screw chilled water precision air-conditioning system using a PLC controller.

Background technique

At present, in the field of existing commercial air conditioners, most of the screw-cooled precision air conditioners are controlled by single-chip microcomputers. Since the single-chip microcomputer control system must be used in conjunction with peripheral electronic circuits, it is difficult to control the programmed single-chip microcomputer without changing the hardware. The program in the single-chip microcomputer is modified again, which makes the controller lose flexibility for the widely used screw-cooled precision air-conditioning system.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned defects in the prior art, and provide a control method that can automatically adjust the energy of the screw-cooled precision air-conditioning system and effectively reduce the frequent start-up of the compressor.

In order to achieve the above object, the technical solution provided by the present invention is as follows: provide a control method for a screw-cooled precision air-conditioning system, the screw-cooled precision air-conditioning system includes a compressor, a condenser connected to the compressor in sequence, and a dry filter , the evaporator, the chilled water outlet pipe and the chilled water return pipe arranged on the condenser also include a PLC controller, and the chilled water return pipe is provided with a temperature sensor for detecting the return temperature of the chilled water, the temperature sensor The output end is connected with the input end of the PLC controller, and a solenoid valve for controlling the operating state of the compressor is arranged in the compressor, and the output end of the PLC controller is connected with the input end of the electromagnetic valve arranged in the compressor. The compression ratio of the compressor is controlled by controlling the position of the slider in the compressor, including the following steps:

a. Detect and restore each output component to its original state, and start the machine;

b. Detect the temperature of the return water of chilled water, and convert the temperature of the return water of chilled water into a current analog signal of 4-20mA through a temperature sensor, and can also be converted into a voltage analog signal of 0-10V or 2-10V;

c. The current analog signal or current analog signal is fed back to the PLC controller. After the PLC controller detects the signal, it compares the temperature signal sensed by the temperature sensor with the temperature signal set by the user, performs PID difference calculation, and outputs the corresponding The digital signal makes the solenoid valve set in the compressor act, and its calculation formula is as follows:

Where: T is the actual temperature _Tset is the set temperature

If T>T _set +2°C, the compressor starts with a minimum load of 25%, that is, the "compressor" starts with 25% of the full load as the "minimum load"; runs for 25 seconds, and the compressor automatically loads to 50 %; After running for 30 seconds, if T>T _set , the compressor enters the standby state, if T>T _set +3°C, the compressor loads to 75%, if the two conditions are not met, the compressor stabilizes at 50% Running; when T>T _set +3°C is detected at a certain moment, the compressor loads to 75%, after running for 30 seconds, if T>T _set +1°C, the compressor returns to 50% state, if T>T _set +4°C, the compressor is loaded to 100% load, if the two conditions are not met, the compressor runs stably at 75%; when T>T _set +4°C is detected at a certain moment, the compressor is loaded to 100%, After running for 30 seconds, if T>T _set +2°C, the compressor returns to 75% status, otherwise the compressor runs stably at 100%.

The compressor is a screw compressor, and a plurality of electromagnetic valves for adjusting the operating state of the compressor are arranged in the compressor.

The effective effect of the control method of the screw-cooled precision air-conditioning system of the present invention is: through the PLC controller combined with the PID difference calculation, the automatic energy adjustment of the screw-cooled precision air-conditioning system can be realized, and the central air-conditioning system can be refrigerated and returned to the water accurately. The temperature is controlled within the set range, and through the adjustment of the temperature difference, it can effectively reduce the frequent start of the compressor, so as to ensure the stability of the refrigeration source of the central air conditioning system and prolong the service life of the unit. The control of the system is very flexible, and the hardware can not be changed. Under this condition, as long as the control software of the system is modified, the system can be adapted to the requirements of different usage environments.

The control method of the screw-cooled precision air-conditioning system of the present invention will be further described below in conjunction with the accompanying drawings and embodiments:

Description of drawings

Fig. 1 is the front view of the screw-cooled precision air-conditioning system of the control method of the screw-cooled precision air-conditioning system of the present invention;

Fig. 2 is the control logic diagram of the control method of the screw-cooled precision air-conditioning system of the present invention;

Fig. 3 is a control circuit diagram of the control method of the screw-cooled precision air-conditioning system of the present invention.

Detailed ways

The following is the best embodiment of the control method of the screw-cooled precision air-conditioning system of the present invention, which does not limit the protection scope of the present invention.

With reference to Fig. 1, Fig. 2, Fig. 3, a kind of control method of screw-cooled precision air-conditioning system is provided, and described screw-cooled precision air-conditioning system comprises compressor 1, the condenser 4 that is connected with compressor 1 in sequence, drier filter 6. The evaporator 3, the chilled water outlet pipe 7 and the chilled water return pipe 8 arranged on the condenser 4, an expansion valve 5 is arranged on the pipe connecting the condenser 4 and the evaporator 3, and a PLC controller is also included 2. A temperature sensor 9 for detecting the return temperature of the chilled water is provided on the chilled water return pipe 8. The output end of the temperature sensor 9 is connected to the input end of the PLC controller 2, and a useful The electromagnetic valve used to control the operating state of the compressor 1, the output end of the PLC controller 2 is connected to the input end of the electromagnetic valve arranged in the compressor 1, and the compressor is controlled by controlling the position of the slider in the compressor. compression ratio.

Through the temperature sensor 9 set on the chilled water return pipe 8, the temperature of the chilled return water is converted into an analog signal of 4-20mA and fed back to the PLC controller 2. After the PLC controller 2 detects the signal, the temperature sensor 9 senses the The temperature signal is compared with the temperature signal set by the user, and the corresponding digital signal (0 or 24V) is output to control the solenoid valve action of compressor 1, so as to realize the loading or unloading of compressor 1 and achieve the purpose of automatic energy adjustment.

In the actual operation, the input specific physical variable is converted into a standard variable of 0-10V, 2-10V or 4-20mA, that is, the given value and process variable are standardized into one of 0-10V, 2-10V or 4-20mA an electrical signal between them. After the input electrical signal is calculated by the PLC controller 2, the output is a standard digital quantity of 0 or 24V, which controls the three solenoid valves of the compressor 1 to realize the compressor 1 at 25%, 50%, 75%, and 100%. Operating status. Thereby changing the operating load of the unit and realizing the purpose of automatic energy regulation. Its calculation formula is as follows:

Where: T is the actual temperature _Tset is the set temperature

When the system starts up, after detecting that the sensor and system parameters are normal, the PLC controller 2 compares the chilled water return temperature sensed by the temperature sensor 9 with the return water temperature set by the customer. If T>Tset+2°C (2°C The temperature difference can prevent frequent start and stop of compressor 1 due to temperature fluctuations, the following is similar), then the compressor starts with a minimum load of 25% (25% load is only used for start), that is, "compressor" The "minimum load" is 25% of the full load as the start-up; run for 25 seconds (the default value, which can be modified according to different compressors 1, the following is similar), and the compressor 1 will automatically load to 50% (normal running minimum load); after running for 30 seconds, if T>Tset, compressor 1 enters the standby state; if T>Tset+3℃, compressor 1 is loaded to 75% load; if the above two conditions are not met, the compressor Machine 1 runs stably at 50% load; when T>Tset+3°C is detected at a certain moment, compressor 1 is loaded to 75% load, and after running for 30 seconds, if T>Tset+1°C, compressor 1 returns to 50% % state, if T>Tset+4℃, compressor 1 is loaded to 100% load, if the above two conditions are not met, then compressor 1 runs stably at 75% load; when T>Tset+4 is detected at a certain moment ℃, compressor 1 is loaded to 100% load, after running for 30 seconds, if T>Tset+2 ℃, compressor 1 returns to 75% state, otherwise compressor 1 runs stably at 100% load.

In this way, according to the start-up procedure, the temperature of the chilled water return water is continuously detected → compared → loaded, unloaded, and the automatic energy adjustment function is realized.

Claims (1)

1. A control method of a screw-cooled water precision air-conditioning system, said screw-cooled water precision air-conditioning system comprising a compressor, a condenser connected successively with the compressor, a drier filter, an evaporator, and a chilled water tank arranged on the condenser The outlet pipe and the chilled water return pipe also include a PLC controller, and the chilled water return pipe is provided with a temperature sensor for detecting the return temperature of the chilled water, and the output end of the temperature sensor is connected to the input end of the PLC controller. connection, a solenoid valve for controlling the operating state of the compressor is set in the compressor, the output end of the PLC controller is connected with the input end of the solenoid valve set in the compressor, and the position of the slide block in the compressor is controlled To control the compression ratio of the compressor, it is characterized in that, comprising the following steps: a. Detect and restore each output component to its original state, and start the machine; b. Detect the temperature of the return water of chilled water, and convert the temperature of the return water of chilled water into a current analog signal of 4-20mA, or a voltage analog signal of 0-10V or 2-10V through the temperature sensor; c. The current analog signal or voltage analog signal is fed back to the PLC controller. After the PLC controller detects the signal, it compares the temperature signal sensed by the temperature sensor with the temperature signal set by the user, performs PID difference calculation, and outputs the corresponding The digital signal makes the solenoid valve set in the compressor act, and its calculation formula is as follows:

Where: T is the actual temperature _Tset is the set temperature If T>T _set +2°C, the compressor starts with a minimum load of 25%, that is, the "compressor" starts with 25% of the full load as the "minimum load"; after running for 25 seconds, the compressor automatically loads to 50%; after running for 30 seconds, if T>T _set , the compressor enters the standby state, if T>T _set +3°C, the compressor loads to 75%, if the two conditions are not met, the compressor stabilizes at 50 % running; when T>T _set +3°C is detected at a certain moment, the compressor loads to 75%, after running for 30 seconds, if T>T _set +1°C, the compressor returns to 50% state, if T>T _set +4°C, the compressor is loaded to 100% load, if the two conditions are not met, the compressor runs stably at 75%; when T>T _set +4°C is detected at a certain moment, the compressor is loaded to 100% , after running for 30 seconds, if T>T _set +2°C, the compressor returns to 75% status, otherwise the compressor runs stably at 100%.

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