Clean room automation system solution

First, the specification

1. 1 Clean Room Air Conditioning System related specifications

With the development of the economy and the improvement of living standards, the requirements for clean rooms in the fields of electronics, pharmaceuticals, food, bioengineering, and medical care are getting higher and higher, and clean technology is also developing. It combines technology in all aspects of technology, construction, decoration, water supply and drainage, air purification, and HVAC. According to the People's Republic of China standard GBJ73-84 "Clean Factory Design Code", 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

100 level ≤ 35 × 100

1000 level ≤ 35 × 1000 ≤ 250

10000 level ≤ 35 × 10000 ≤ 2500

100000 class ≤ 35 × 100000 ≤ 25000

2. Temperature and humidity:

(1) Meet production requirements;

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

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

3. Clean room positive pressure:

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

In addition, there are technical requirements for air volume, wind speed, and the like. In short, the indicators in the clean room are very strict, so it is necessary to carry out precise control.

1. 2 The significance of self-control of air conditioning in clean room

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

First of all, due to the automatic monitoring of the air conditioning system, the system can be operated more safely, and the comfort level is greatly improved. For the clean room, it is a necessary condition to ensure production.

In addition, due to the realization of automatic monitoring, it can meet the various technical indicators of the system safe operation and guarantee system, while Zui realizes energy-saving control to a large extent, in line with the increasingly prominent energy-saving and environmental protection needs. Relevant information shows that the use of air-conditioning automatic control system can save 10% of the annual operating costs of air-conditioning system equipment. A more optimistic estimate is that it can reach 15%-30%. The investment in air-conditioning self-control products accounts for less than 0.5% of the total investment in the entire building or plant, and the investment recovery time is short.

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

1. 3 clean room air conditioning control system function simple price

The Excel 20 Chinese version controller is a member of the advanced Excel 5000 controller family of HONEYWELL. It is especially suitable for air conditioning control in clean rooms such as operating rooms and clean workshops. It is in accordance with the National Standards for Cleanroom Construction Acceptance Specifications, Cleanhouse Design Specifications, and Ventilation and Air Conditioning Design Specifications. Intrinsic to each system, we built a relatively complete clean room air conditioning automatic control system with Excel 20 as the core, which 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) alarm and interlock

5. Non-critical faults (filter blockage/supply overheating) alarm and interlock

6. Prevent air supply condensation in summer/antifreeze in winter

7. Boot sequence and interlocking, etc.

8. Customize the start and stop time program, etc.

In the following, the composition, working principle, etc. will be described in detail.

2. Clean room air conditioning automatic control system

2. 1 automatic control of analog instruments

The automatic control system consisting of analog controller (also known as analog control instrument), sensor, actuator and controlled object is shown in Figure 2-1, which is a block diagram of the single loop control system. Due to its mature theory, simple structure, low investment, easy adjustment, etc., it has been widely used in air conditioning, cold and heat sources, water supply and drainage systems.

Generally, the analog controller is electrically or electronically, only the hardware part, and no software support is required. Therefore, it is relatively simple in the process of adjustment and commissioning. Its composition is generally a single-loop control system, which can only be applied to small-scale air conditioning systems. In terms of development trends, it has been used less and will not be further explained here.

2.2 computer control system

Due to the development of computer technology, control technology, communication technology and image technology, the application of microcomputer control technology in the automatic control of refrigeration and air conditioning is becoming more and more popular. After introducing the microcomputer, the traditional control system can make full use of the powerful arithmetic operation, logic operation and memory functions of the computer, and use the computer command system to compile the software that conforms to the control law. By executing these programs, the microcomputer 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. Repeating these three steps will cause the entire system to be controlled and adjusted according to the given rules. At the same time, it also monitors the controlled variables and equipment operating status, faults, etc., over-limit alarm and protection, and records historical data.

It should be said that computer control is incomparable in terms of control functions such as accuracy, real-time, reliability, etc., which cannot be controlled by analog control. More importantly, the enhancement of management functions (such as alarm management, history, etc.) brought about by the introduction of computers is simply impossible for 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-sized air conditioning systems, computer control has dominated.

2.2.1 Direct digital control

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

The CPU in the DDC controller runs very fast and has as many input/output ports (I/0) as it is configured. Therefore, it can control multiple loops at the same time, which is equivalent to multiple analog price ratios.

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 the management functions are as concentrated as possible. Its basic structure is shown in Figure 2-3. It is connected by a central station, a substation, an on-site sensor and a communication channel.

The substation is the above DDC controller with micro processing as the core. It is distributed in the field of each controlled device of the whole system, and is directly connected with the sensors and actuators in the field to realize the detection and control of the field devices. The central station implements 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 completed by the substation or DDC controller.

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

3. 1 air purification

In a general clean room system, an air filter is used for air treatment. Normally, after installing the primary and intermediate filters, the air cleanliness can reach 10,000. High-efficiency filters should also be installed in the clean rooms for ultra-clean requirements. In this way, the air cleanliness can be higher (such as 100 or even higher).

When the filter is used for a long time, the dust deposited on the filter material will gradually increase, which will increase the airflow resistance and affect the operation of the entire air conditioning system. Therefore, the engineering should automatically detect and alarm the airflow resistance of the filter. The differential pressure method is usually used to measure the differential pressure Pd before and after the filter, and the differential pressure signal is displayed and alarmed according to the set differential pressure limit for timely cleaning or replacement.

4. 2 temperature control

3.2.1 Control of primary heating

The primary heating of the air, also known as preheating, is used to heat fresh air or to mix fresh air with a return air. One heating is generally only used in areas where the winter is very cold, to prevent the fresh air from being saturated with a return air, to achieve water mist or ice formation. One heating is also applied to a super clean air conditioning system where mixing is not allowed to change.

When steam or hot water is used for heating, temperature control is generally implemented by adjusting the valve opening degree of steam or hot water; when electric heating is used, temperature control is realized by controlling the heating electric power through the thyristor power controller. 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 return air mixing section. The purpose of the secondary heating is to ensure the supply air temperature or the temperature in the air-conditioned room in the case of relative humidity requirements. The control method is basically the same as that of one heating.

The three heatings are refined and heated, usually in the heating section for fine-tuning the temperature during high-precision temperature control. Its control should be implemented according to the above principles according to the specific conditions.

3.3 humidity control

3.3.1 Humidification treatment and control

In the clean room air conditioning project, the humidification operation is generally carried out during the winter or during the transition season. There are many ways to humidify the air. Switching control or power regulation of steam humidifiers and electric humidifiers is usually used. When steam is humidified, it can be realized by position control of the solenoid valve or continuous adjustment of the two-way control valve according to the humidity control requirement.

3.3.2 Dehumidification (drying) treatment and control

The air cooling and drying process is usually performed by a surface cooler. The two processes of isothermal cooling of the cold treatment of the air. When the humidity is controlled by the air cooler, it is realized by adjusting the flow rate of the refrigerant (such as chilled water) of the air 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 rate to achieve dehumidification (ie, drying) treatment; otherwise, the flow rate is reduced to achieve humidification treatment.

It should be noted that due to the physical properties of air, the control of humidity is relatively complicated and there are many methods. Moreover, the two parameters of temperature and humidity of the air interact with each other during the adjustment process. For some reasons, the indoor temperature is raised, causing a change in the saturated partial pressure of water vapor in the air, and the relative humidity is reduced in the case where the moisture content is constant. Therefore, when one of the parameters is adjusted, it will also cause another parameter to change. For example, in the summer, the air cooler is used for dehumidification adjustment, and when the large cold water valve is opened, the humidity is returned to normal while the temperature is lowered. Therefore, this feature should be fully considered in the design of the process design and automatic control scheme.

3.4 Positive pressure control

China's national standards stipulate that between different levels of clean rooms should be greater than 4.9Pa, and between clean areas should be greater than 9.8 Pa. The structure of the clean room is basically determined. During operation, maintaining a 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 damper or return air door.

3.5 Other control and air conditioning energy saving

For the clean room, in addition to the above-mentioned technical indicators that must be guaranteed, there are also some requirements for safety and energy conservation. Combining years of engineering practice, there are mainly the following aspects.

3.5.1 Fan Fault Alarm

Determine whether the fan is working properly by detecting the wind flow status of the fan. If the fan stops due to motor burning or loose belt, etc., it should immediately alarm? lt;BR>3.5.2 fan frequency conversion control

In order to maintain a stable positive pressure in the clean room or a certain fresh air/return air ratio, variable frequency control can be implemented for the number of revolutions of the machine (motor). Practice has proved that the frequency conversion control is better than the simple damper opening adjustment control, and can greatly save power consumption. Because in the air conditioning system, the fresh air / return transport accounts for a large proportion of the power consumption. The damper control actually realizes the change of the airflow through the throttling device (ie, the damper).

3.5.3 Water pump frequency control

In the case of a pump-to-one adjustment system, it is better to use a variable frequency speed regulation (water pump rotation number) to achieve flow control than to use a throttle device (ie, a regulating valve). This method is not only reflected in the better control effect, but also in the substantial saving of power consumption.

3.5.4 Energy saving procedures

Energy-saving control becomes a reality due to the application of computer control systems. That is to say, in addition to the above-mentioned energy-saving control means for the process characteristics of the air-conditioning system, the computer control can also realize such as coma control, night cycle, night wind purification, start-stop, zero energy zone and the like. Of course, for a particular clean plant, its energy-saving procedures should be compiled according to its specific conditions to achieve energy-saving effects.

Fourth, the air conditioning control system equipment configuration

The devices that implement the air conditioning automatic control system include controllers, sensors, and actuators. As before, the mainstream control system has changed from analog control to computer control. Here, the device that realizes direct digital control and DDC control is briefly introduced.

4. 1DDC controller

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

The EPROM has a standard program; the Excel-enabled DDC controller is a DCP intelligent substation specified by the Chinese national standard. The programming of each controller is stored in its own memory. The Excel 20 contains a 16-bit microprocessor i80186 that can control 16 physical points (ie, 16 detectors, switches, actuators can be connected).

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

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

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

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

Digital Output Module (DI): 4 relay outputs

The start/stop of the switch can be controlled by the time schedule to start and stop. Flexible time plan zui 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, large transmission distance: 200 m;, NTC20K. Environmental requirements: --35 ° C to 60 ° C, 5% RH to 95% RH, electrical wiring: 2X 1.5MM2, should be shielded with line power, outdoor temperature sensor C703F, effective temperature range: -20 ° C to 50 ° C; Zui large 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 temperature sensor C7031C, effective temperature range : -20 ° C -50 ° C, Zui large transmission distance: 200 meters

4.4 hot and cold water valve and driver, proportional integral electric valve

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

4.5 Steam heating / humidification valve and driver

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

4.6 electric damper driver

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

4.7 air pressure difference switch

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

4.8 air pressure difference gauge and differential pressure transmitter

1. Micro differential pressure gauge 2000 series:

On-site display: pointer display; measurement range: zui section 0-60 Pa;

2. Micro differential pressure transmitter MODT30

Measuring range: zui small 0-25 Pa output signal: 4-20MA input signal: air pressure difference, working 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 meter 477 (with temperature display):

Range: zui small 0-1000 Pa; working temperature: 0-50 ° C; accuracy: 50% FS; power supply: 9V alkaline battery;

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

Range: zui small 0-1000 Pa; working temperature: 0-40 ° C; accuracy: ± 3% FS; power supply: 9V alkaline battery;

4. Portable Digital Particle Counter:

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

5 calculation modes;

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