First, the specification

1. 1 Cleanroom Air Conditioning System Specifications

With the development of the economy and the improvement of living standards, the requirements for cleanrooms in the fields of electronics, pharmaceuticals, food, bioengineering, and medical care have become higher and higher, and the clean technology has also developed. It integrates technology in construction, construction, decoration, water supply and drainage, air purification, HVAC, and other aspects. According to the People's Republic of China Standard GBJ73-84 "Code for the Design of Clean Houses," the main technical indicators related to the air conditioning system are:

1. Air cleanliness:

Grade ≥ 0.5 micron dust particles per M3 air ≥ 0.5 micron dust particles per M3 air

Level 100 ≤ 35×100

1000 grades ≤35×1000 ≤250

10000 grades ≤35×10000 ≤2500

100000 grade ≤35×100000 ≤25000

2. Temperature and humidity:

(1) Satisfy the production requirements;

(2) When the production process has no temperature and humidity requirements, the cleanroom temperature is 20-26°C and the humidity is less than 70%;

(3) The temperature of personnel purification room and living room is 16-28°C.

3. Clean room positive pressure:

The clean room must maintain a positive pressure. The static pressure difference between different grades of clean room and between the clean area and the non-clean area shall not be less than 4.9 Pa. The static pressure difference between the clean area and the outdoor area shall not be less than 9.8 Pa.

In addition, there are technical requirements for air volume, wind speed, etc. In short, the cleanliness of the various indicators are very strict, so it is necessary to make precise control.

1. 2 Significance of Automatic Control of Clean Room Air Conditioners

In modern commercial and industrial buildings, there are many air-conditioning systems, and automation management is an important guarantee for making it safe and well-functioning. At the same time, air-conditioning energy consumption generally accounts for more than 40% of total energy consumption. Therefore, air-conditioning energy-saving is an important means of energy conservation. This is especially true for clean rooms. The use of air-conditioning automatic control products will produce the following series of benefits:

First of all, as the air-conditioning system achieves automatic monitoring, it can make the system run more safely and maximize comfort. For the clean room, it becomes a necessary condition for ensuring production.

In addition, due to the realization of automated monitoring, it can meet the various technical indicators of the system's safe operation and ensure the system, while maximizing energy-saving control, in line with the increasingly prominent energy-saving and environmental protection needs. Relevant information shows that after adopting an air-conditioning automatic control system, it can save 10% of the annual operating expenses of air-conditioning system equipment. The more optimistic estimate is that it can reach 15%-30%. The investment in air-conditioning automation products accounts for less than 0.5% of the total investment of the entire building or plant, and the investment recovery time is short.

At the same time, due to the realization of automatic control and management of equipment, personnel maintenance can be reduced, personnel costs can be saved, the overall management level can be improved, the occurrence of unexpected accidents and equipment damage can be reduced, thereby bringing potential benefits.

1. 3 clean room air conditioning control system function price

The Excel 20 Chinese version controller is a member of HONEYWELL's advanced Excel 5000 controller family. It is especially suitable for air conditioning control of cleanrooms such as operating rooms and cleanrooms, in accordance with the national standards for "clean room construction acceptance specifications", "clean plant design specification", and "production ventilation and air conditioning design specifications", and comprehensive consideration of the above The internal connection of each system, we built a complete clean room air-conditioning automatic control system with Excel 20 as the core, it has the following characteristics:

1. Constant temperature and humidity proportional integral control

2. Indoor remote start and stop air conditioning

3. Indoor temperature setting

4. Critical fault (fire) alarms and interlocks

5. Non-critical fault (filter plugging / air overheating) alarm and interlock

6. Prevention of air supply condensation/winter freeze protection in summer

7. Boot sequence and interlocking.

8. Custom start and stop time programs.

Below, its composition, working principle, etc. are described in detail.

II. Composition of Automatic Control System for Cleanroom Air Conditioning

2. 1 analog meter automatic control

The automatic control system composed of analog controller (also called analog control instrument), sensor, actuator and controlled object is shown in Figure 2-1. This is a block diagram of single-loop control system. Because of its mature theory, simple structure, low investment, easy adjustment and other factors, it has been widely used in air conditioning, cold and heat sources, and water supply and drainage systems.

The general analog controller is electrical or electronic, only the hardware part, without software support. Therefore, it is relatively simple during adjustment and commissioning. Its composition is generally a single loop control system and can only be applied to small-scale air conditioning systems. From the perspective of development trends, it has been adopted less frequently and will not be further explained here.

2.2 Computer Control System

Due to the development of computer technology, control technology, communication technicians, and image technology, the application of microcomputer control technology in the automatic control of refrigeration and air conditioning is becoming more and more common. After the introduction of the microcomputer, the traditional control system can make full use of the computer's powerful arithmetic operations, logic operations, and memory functions. Using the computer command system, the software that complies with the control laws can be compiled. The microcomputer executes these programs and can control and manage the controlled parameters, such as data acquisition and data processing.

The computer control process can be summarized into three steps: real-time data acquisition, real-time decision making and real-time control. Repeatedly repeating these three steps will allow the entire system to be controlled and adjusted according to the given rules. At the same time, it also monitors the monitored variables, equipment operating status, and faults, over-limits alarms and protections, and records historical data.

It should be said that computer control is incomparable in terms of control functions such as accuracy, real-time performance, reliability, etc. that analog control cannot be controlled. More importantly, the enhancement of management functions (such as alarm management, history records, etc.) brought about by the introduction of computers is beyond the reach of analog controllers. Therefore, in recent years, in the application of automatic control of refrigeration and air conditioning, especially in the automatic control of large and medium air conditioning systems, computer control has dominated.

2.2.1 Direct Digital Control

The so-called in-digital control is based on micro-maneuvering, and the sensor or transmitter or the output signal in the system is directly input to the microcomputer without analog instrumentation, and the micro-computer is directly processed by the pre-programmed process. The control method of the drive actuator, referred to as DDC (Direct Digital Control), is called a direct digital controller, or DDC controller for short.

The CPU in the DDC controller runs fast, and it has more input/output ports (I/0) configured. Therefore, it can control multiple loops at the same time, which is equivalent to the characteristics of multiple analog prices.

2.2.2 Distributed Control System

The distributed control system Total Distributed System is abbreviated as TDS. Compared with the traditional computer control methods in the past, its control functions are as scattered as possible, and management functions are concentrated as much as possible. The basic structure is shown in Figure 2-3. It is connected by central stations, substations, on-site sensors and communication channels.

The substation is the above-mentioned DDC controller with microprocessing as its core. It is distributed on the site of all controlled devices in the entire system, and is directly connected with sensors and actuators on the site to realize the detection and control of field devices. Central station realizes centralized monitoring and management functions, such as centralized monitoring, centralized start-stop control, centralized parameter modification, alarm and record processing. It can be seen that the centralized management function of the distributed control system is completed by the central station, and the control and regulation functions are performed by the substation or DDC controller.

Second, the realization of clean room air-conditioning automatic control system

3. 1 air purification

In a typical clean room system, an Air Filter is used for the air treatment. Under normal circumstances, the air cleanliness can reach 10,000 levels after installing the primary filter and the intermediate filter. In addition, high-efficiency filters should be installed for the cleanliness required for cleanliness. In this way, the cleanliness of the air can be even higher (eg 100 or even higher).

When the filter is used for a long time, the dust attached to the filter material will gradually increase, which will increase the airflow resistance and affect the operation of the entire air conditioning system. Therefore, in engineering, the airflow resistance of the filter should be automatically detected and alarmed. Differential pressure method is usually used to measure the pressure difference Pd before and after the filter, and the differential pressure signal is displayed and alarmed according to the set differential pressure limit, so that it can be cleaned or replaced in time.

4. 2 temperature control

3.2.1 One-time heating control

Air heating, also known as preheating, is used to heat fresh air or a mixture of fresh air and return air. The first heating is generally only used in areas that are very cold in winter to prevent the fresh air from mixing with a return air to reach saturation and produce water fog or ice. One heating is also applied to an ultra-clean air-conditioning system where the mixing is not allowed to change.

When steam or hot water is used for heating, the control valve opening for controlling steam or hot water is generally used for temperature control; when electric heating is used, the thyristor power controller controls its heating power to achieve temperature control. The principle is shown in Figure 3-2.

3.2.2 Control of secondary heating and tertiary heating

The secondary heating of the air is usually after the surface cooler or after the secondary air return mixing section. The purpose of the secondary heating is to guarantee the supply air temperature or the temperature in the air-conditioned room under the condition of relative humidity. The control method is basically the same as the one-time heating.

The three heatings are also fine heating, which is usually a heating section for fine-tuning the temperature when the temperature is controlled with high precision. The control should be implemented according to the specific conditions described above.

3.3 Humidity Control

3.3.1 Humidification and Control

In the cleanroom air-conditioning project, humidification operations are generally performed during the winter or during the transitional season when the air is dry. There are many ways to humidify air. Switch control or power regulation of steam humidifiers and electric humidifiers are commonly used. Steam humidification, according to the humidity control requirements, can be achieved through the position control of the solenoid valve or the continuous adjustment of the two-way control valve.

3.3.2 Dehumidification (drying) treatment and control

The air cooling and drying process is usually done with a surface cooler. The table is cooled by two processes of iso-humid cooling for air treatment. When using a surface cooler for humidity control, it is achieved by adjusting the flow of refrigerant (such as chilled water) in the surface cooler. When the humidity is higher than the required value, the flow rate of the cold water valve can be increased to increase the flow, and the dehumidification (i.e., drying) process can be realized; otherwise, the flow rate can be reduced to achieve the humidification process.

It should be noted that due to the physical properties of air, the control of its humidity is relatively complicated and there are many methods. Moreover, the two parameters of air temperature and humidity influence each other during the adjustment process. If, for some reason, the room temperature rises, the saturated partial pressure of the water vapor in the air changes, and the relative humidity decreases when the absolute moisture content is constant. Therefore, when one of the parameters is adjusted, another parameter will also change. For example, in the summer, a defrosting control is performed using a surface cooler, and when the large cold water valve is opened, the humidity is normalized and the temperature is lowered. Therefore, this feature should be fully taken into account in the design of process design and self-control schemes.

3.4 Positive Pressure Control

According to China's national standards, clean rooms of different grades should be greater than 4.9 Pa, and clean areas should be greater than 9.8 Pa. The structure of the clean room is basically determined. During the operation, maintaining positive pressure can be achieved by controlling the amount of fresh air or return air. This is achieved by controlling the opening of the new or return air door.

3.5 Other Control and Air Conditioning Energy Saving

For the clean room, in addition to the technical indicators indicated above, there are some requirements for safety and energy saving. Combined with years of engineering practice, there are mainly the following aspects.

3.5.1 fan fault alarm

The wind status of the fan is determined to determine whether the fan is working properly. If the fan stops due to the motor burned or the belt is loose, etc., it should be immediately alarmed. lt;BR>3.5.2 fan frequency control

In order to maintain a stable positive pressure or a certain ratio of fresh air/return in the clean room, variable frequency control can be performed on the number of revolutions of the machine (motor). Practice has proved that variable frequency control is better than simple damper opening adjustment control, and can greatly save power consumption. Because in the air-conditioning system, the fresh air/return transmission accounts for the largest proportion of electric energy consumption. The throttle control actually changes the air flow through a throttling device (ie, a damper).

3.5.3 Frequency Control of Pump

In the case of a pump-to-one regulation system, the use of variable frequency speed control (water pump revolutions) to achieve flow control is preferred over throttling devices (ie, regulating valves). This approach is not only reflected in the better control results, but also reflected in the substantial savings in power consumption.

3.5.4 Energy Saving Program

Due to the application of computer control systems, energy-saving control has become a reality. That is, in addition to the above-mentioned energy-saving control methods for the air-conditioning system process features, the computer control can also achieve such as enthalpy difference control, night cycle, night air purification, the best start and stop, zero energy zone. Of course, for a specific clean room, its energy-saving procedures should be compiled according to its specific conditions in order to achieve the best energy-saving effect.

Fourth, air conditioning control system equipment configuration

The devices that implement the air-conditioning automatic control system include controllers, sensors, and actuators. For example, the former mainstream control system has been transformed from analog control to computer control. Here, a brief introduction to direct digital control of both DDC-controlled devices is presented.

4. 1DDC controller

Power supply: 24; Power consumption: 45 Protection standard: Backup battery: 3V lithium battery; LCD display: 4 lines × 16 amps

The standard program is located in the EPROM; the Excel capable DDC controller is a DCP intelligent substation specified by the Chinese national standard. Each controller's programming is stored in its own memory. Excel 20 contains 16-bit microprocessor i80186 can control 16 physical points, (that is, connect 16 detectors, switches, actuators).

It is based on the basic CPU module and power supply module, and then any of the following functional modules are set by software according to actual needs:

Analog input and output modules (AL): 7 points, 0~1VDC, 2~10VDC, 420MA;

Analog output module (AO): 3 points, 210 VDC;

Digital input module (DI): 2 points, dry contact;

Digital Output Module (DI): 4 relay outputs

Switching start/stop can be controlled by the time schedule to start and stop it. Flexible schedule can be up to 1 year.

4.2 Temperature Sensor

Indoor temperature transmitter T7412, adjustable set point, effective temperature range: -20 °C to 50 °C, maximum transmission distance: 200 meters;, NTC20K. Environmental requirements: -35°C to 60°C, 5%RH to 95%RH, electrical wiring: 2X 1.5MM2, should be shielded from line power, outdoor temperature sensor C703F, effective temperature range: -20°C to 50°C; maximum transmission Distance: 200 meters, NTC20K, Environmental requirements: -35°C to 60°C, 5%RH to 95%RH, Electrical wiring: 2×1.5MM2, should be shielded with line power, duct type temperature sensor C7031C, effective temperature range: -20°C-50°C, maximum transmission distance: 200 meters

4.4 Hot and Cold Water Valves and Actuators, Proportional-Integral Electric Valves

Including: valve V5011, equal percentage characteristics, electric valve actuator ML7984 or M7421, optional different valve body, suitable for chilled water, hot water medium, DN25-150 grid for choice

4.5 Steam Heating/Humidification Valves and Actuators

Valve V5011, linear characteristics, electric valve actuator M7421, optional different valve body, suitable for steam medium, DN25-150 specifications for selection

4.6 Electric Air Door Drive

Electric air valve ML6184, damper actuator ML6XXX, ML7XXX, ML8XXX, suitable for 0.75M2-15M2 area damper, switch type/discontinuous/continuous type available

4.7 Air pressure difference switch

DPS400, pressure range: 40-400Pa, protection class: IP54, switch capacity: 1.5A/250VAC

4.8 air pressure gauge and differential pressure transmitter

1. Differential pressure gauge 2000 series:

Live display: pointer display; measuring range: minimum section 0-60 Pa;

2. Differential pressure transmitter MODT30

Measuring range: Minimum 0-25 Pa Output signal: 4-20MA Input signal: Air pressure difference, Operating power: 10-35VDC

4.9 Other Testing and Calibration Instruments

1. Portable digital temperature/humidity meter 485-1/2: Range: temperature -30-85°C; humidity 0-100%RH; accuracy: temperature ±0.5°C; temperature ± 2%RH; power supply: 9V alkaline battery; Probe length: 219mm (485-2 type).

2. Portable Digital Pressure/Differential Pressure Gauge Type 477 (with temperature display):

Range: Minimum 0-1000 Pa; Operating Temperature: 0-50°C; Accuracy: 50%FS; Power Supply: 9V alkaline battery;

3. Portable digital anemometer 471 (with temperature display):

Range: Minimum 0-1000 Pa; Operating Temperature: 0-40°C; Accuracy: ±3%FS; Power Supply: 9V Alkaline Battery;

4. Portable Digital Particle Counters:

Hand-held, battery operated; 0.3 or 0.5 micron particles calculated at 0.1FM (cubic feet per minute);

Five calculation modes;

Storage data: 200 groups; RS232/RS485 output; display: 4-line LCD display, 7-bit calculation result;

Zhejiang Sujing Purification Equipment Co., Ltd. is located in Daoshui Town, Shangyu District, Shaoxing City, Zhejiang Province, and is a leading manufacturer of purification equipment in East China. Can provide professional air purification systems for industries such as microelectronics, biomedicine, hospital operating rooms, fiber optic cables, food and beverages, precision instruments, semiconductors, and new material applications in accordance with ISO14644-1, GB50073-2001 national standards, and national GMP regulations. Engineering design, construction, testing and technical services.

The company's main purification table series, air shower series, fume hood series, biological safety cabinet series are widely used in medical and health, electronics, pharmaceuticals, biology, food, agriculture, forestry, animal husbandry and veterinary, inspection and quarantine, aerospace, automotive manufacturing, Precision instruments, universities and research institutes enjoy a high reputation in the domestic and Southeast Asian markets.

Zhejiang Sujing Purifying Equipment Co., Ltd. is dedicated to serving consumers and distributors all over the world. We will provide you with the best quality products, the most humane services, and the lowest price. We sincerely welcome you to join us!

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