Laboratory clean air conditioning system

In order toClean Operating LaboratoryThe commonly used method to maintain the required parameters such as temperature, humidity, wind speed, pressure, and cleanliness inside is to continuously introduce a certain amount of processed air into the room to eliminate various thermal and humidity interferences and dust pollution inside and outside the clean room. To obtain air with a certain state that is sent into the clean room, a complete set of equipment is needed to process the air, continuously send it into the room, and continuously discharge a portion from the room. This complete set of equipment constitutesClean air conditioning system.

Clean air conditioning systemBasic composition

The clean laboratory air conditioning system is mainly composed of the following equipment

1. Heating or cooling, humidification or dehumidification, and purification equipment;

2. The air conveying equipment and its pipelines that send the processed air into each clean room and circulate it;

3. Provide heat, cold, heat, cold, and their piping systems to the system.

Classification of clean laboratory air conditioning

Clean laboratory air conditioning systems are generally divided into three categories:

1. Centralized: The purification air conditioning equipment required for single or multiple clean rooms in the system is centralized in the computer room, and clean air is distributed to each clean room through air supply ducts.

2. Distributed: Separate purification equipment or purification air conditioning equipment is installed in each clean laboratory within the system.

3. Semi centralized: In this system, there are both centralized purification air conditioning rooms and air treatment equipment scattered in each clean room. It is a form of combining centralized processing and local processing.

People generally name a system based on the cleanliness of each clean room within the system, such as calling it a 100 level purification air conditioning system, a 1000 level purification air conditioning system, etc. Sometimes it is also distinguished based on the properties of the final filter of the system, including high-efficiency air purification systems, sub high efficiency air purification systems, and medium efficiency air purification systems.

centralized

The main characteristics are as follows

1. Concentrate air treatment in the computer room and then deliver it to various clean rooms.

2. Due to the concentration of equipment in the computer room, it is easier to handle noise and vibration.

3. A system controls multiple clean rooms, requiring a high utilization factor for each clean room simultaneously.

4. The clean air after centralized processing is sent into each clean room, achieving different cleanliness levels in each clean room with different ventilation rates and airflow forms.

Centralized is suitable for clean rooms with continuous process production, large clean room areas, centralized locations, and strict requirements for noise and vibration control. There are generally three forms:

1. DC type: All the air processed by the system comes from outdoors, is sent indoors after processing, and then completely discharged outdoors. This system consumes a lot of cold and heat, and has high engineering investment and operating costs. When a large amount of harmful gases are emitted from the clean room and local exhaust cannot solve the problem, this method is adopted.

2. Closed type: The air processed by this system comes entirely from the air-conditioned room itself, in a loop. When no one stays in the clean room for a long time, only for storage or to ensure the normal operation of precision instruments, or for special occasions where fresh air does not need to be obtained from the outside, a closed system can be used. A closed system does not have outdoor fresh air, consumes less cold and heat, but has poor sanitary conditions.

3. Hybrid: This system not only draws in a portion of outdoor fresh air, but also utilizes a portion of return air. Depending on the form of return air, there are primary and secondary return air systems. This system can meet hygiene requirements and is economically reasonable, with a wide range of applications.

decentralized

For some production processes that are single, clean rooms are scattered, and cannot or should not be combined into one system, or where various clean laboratories cannot arrange conveying systems and machine rooms, a decentralized system should be adopted, in which the machine room, conveying system, and clean room are combined together to form a system.

In a decentralized air conditioning system, purification and air conditioning equipment or purification air conditioning equipment is installed on-site in each clean laboratory or adjacent room. Purification air conditioning equipment can be a standardized unit product that has purification function, but the processed air volume is relatively small, often unable to meet the required air volume of high cleanliness cleanrooms. The system processing process is often a return air system.

Due to the requirement of overcoming the resistance of heat exchange coils, channels, and several stages of filters in the fan of purification air conditioning equipment, a high pressure is required. In order to be installed inside the equipment, the volume cannot be very large; If a higher rotational speed is used to achieve the desired pressure, the noise and vibration are also significant. The domestic equipment situation shows that the development of such units is relatively slow.

*In addition to some necessary equipment, clean laboratories should try to set up equipment outdoors as much as possible, and with strict control of personnel numbers, the heat and humidity load of clean rooms is usually smaller than that of ordinary air-conditioned rooms, but the required air volume is larger than that of ordinary air-conditioned rooms, which limits the scope of use of purification air conditioning equipment from another perspective.

In order to solve this problem, local purification equipment such as fans and filter units can be placed in the clean room, or connected to the clean room in adjacent rooms, suites, ceilings, etc., or used as static pressure boxes in adjacent rooms, suites, ceilings, etc., and ordinary air conditioning units can be installed inside for mixed air and air conditioning treatment. Its processing can be regarded as secondary return air.

The air conditioning unit is actually a small air conditioning system, and its cold source usually uses a compression refrigeration unit. When the capacity is small and flexibility is required, the heat source can use electric heating. Air handling equipment mainly includes evaporators for refrigeration machines, electric humidifiers, and electric heaters.

When the temperature and humidity in the clean room require high control accuracy throughout the year, a constant temperature and humidity unit can be used It can automatically adjust the air temperature to maintain a certain indoor temperature and humidity. When the clean room only requires summer comfort air conditioning, that is, cooling and dehumidification in summer, a cold air unit can be used. The main difference between it and a constant temperature unit is the lack of automatic control (using manual control), electric humidifier, and electric heater.

The above approach of separating the functions of air conditioning and purification not only solves the problem of low heat and humidity load and high air volume in clean rooms, but also makes the system more flexible. Due to the use of suites or ceilings as static pressure boxes, the air circuit section is large and the conveying route is short, which does not require high fan pressure heads for air conditioning units and purification equipment. Therefore, the corresponding noise and energy consumption are also not high Purification equipment can also adapt to the needs of clean rooms, adopting various forms and almost unrelated to air conditioning units This form is widely used in China.

However, the fresh air in this system often only infiltrates through negative pressure generated by the suite or ceiling, which cannot be effectively controlled and cannot meet indoor hygiene requirements. Positive pressure can be established in a clean space by controlling the difference in air supply volume, but negative pressure in the suite does not necessarily cause outdoor fresh air to enter the suite through the fresh air filter. It often infiltrates through other pathways (such as corridors and windows), and the concentration inside the suite is very unstable This not only affects the lifespan of the filter, but may also involve the cleanliness of the clean space, which is a problem that is easily overlooked. For example, the multifunctional clean laboratory of Shanghai Urban Construction Institute has added a sub efficient fresh air purification unit in the suite. Due to its adjustable air volume fan, it can not only maintain positive pressure inside the suite and stabilize the air concentration inside the suite; And the major feature of the distributed purification air conditioning system for preservation is its flexibility and simplicity. It can meet the different air supply requirements of different rooms. When the indoor heat and humidity load changes, the regulating system responds quickly and does not affect the inlet parameters of other rooms. The clean space is small and single, making management more convenient and ensuring cleanliness. In addition, the absence of conveying pipelines and machine rooms saves energy consumption, as well as thermal losses and pollution along the way, reducing auxiliary land occupation. In addition, the air conditioning unit has a small volume, requires less on-site installation work, and is easy to operate and use, without the need for specialized skilled operators.

Semi centralized

Semi centralized is a system form that combines centralized air treatment with local treatment. It has both the advantages of a decentralized system where each clean room can return air locally to avoid back and forth transportation, and a centralized system where fresh air is supplied to each clean room as needed after air conditioning treatment to a certain state, which is beneficial for controlling clean air parameters. With the development of production technology, people have different requirements for clean rooms. People hope to achieve zone control of different cleanliness levels in a clean laboratory.

Therefore, there are two main forms of use for semi centralized and semi clean air conditioning systems, which are introduced as follows:

（1） End devices with heat and moisture treatment capabilities: When the cleanroom is in the following situations, a semi centralized end device with heat and moisture treatment capabilities can be considered

1. When the clean room of the system has a high heat and humidity load;

2. There is a significant difference in load between each clean room;

3. Or the usage time of each clean room may vary;

4. Or avoid mutual contamination between clean rooms.

Due to the heat and humidity treatment capabilities of indoor units, the indoor temperature and humidity can be adjusted according to the requirements of the unit (i.e. end devices). For example, using this system in hospitals can avoid cross infection between operating rooms and meet their different sterile requirements. The temperature and humidity in the operating room can be adjusted by the end device according to the nature of the surgery, the doctor's requirements, and the patient's feelings. However, such air conditioning systems have low control accuracy and poor uniformity in temperature, humidity, and concentration fields. For larger end devices, the primary air can also be directly sent into the fan coil unit, which mixes with the return air and enters the room through the coil unit. Due to the fact that there is only one air supply outlet indoors, it avoids the interference of primary air on the local parallel flow area of the end device.

（2） End devices with pure purification function

The terminal device system with simple purification function is widely used in semi centralized air conditioning systems. Most renovation projects adopt this form. When purifying the original ordinary air conditioning system, filter equipment can be added to the original air conditioning system, such as adding filter boxes at appropriate positions in the air supply ducts, adding filters to the air supply ports in each room, or replacing the original system filters. This forms a pure purification end device system. The end device plays a role in self circulation and self purification indoors, and is an auxiliary means for indoor cleanliness. When adjusting the air volume of the end devices or changing the number of end devices turned on, different levels of cleanliness can be achieved indoors.