1 Selection of ventilation rate
《化工采暖通风和空调调节设计规范》规定化验室房间的更小换气量一般在6 次/h~8 次/h。 ASHRAE 规定验室内的整体换气次数应由下列风量之决定：从局部排风设备或其他房间排风所排出的总风量；带走房间热负荷所需的制冷风量；更小换气次数需求。在使用情况下，实验室的更小换气次数应维持6 次/h~10 次/h。
According to the code for design of heating, ventilation and air conditioning in chemical industry, the minimum air exchange rate of laboratory room is generally 6 times / H ~ 8 times / h. According to ASHRAE, the overall air change rate in the laboratory shall be determined by the following air volume: the total air volume discharged from the local exhaust equipment or other rooms; the cooling air volume required to take away the heat load of the room; and the minimum air exchange rate requirement. Under the condition of use, the minimum ventilation rate of the laboratory should be maintained at 6 times / H ~ 10 times / h.
In general, the room ventilation rate > 10 times / hour is considered to be appropriate. However, when there are analytical equipment with high heat load in the laboratory, or there is a large amount of local exhaust in the room, the air exchange rate may need to be increased accordingly. There are fume hoods in the wet chemical room and a large number of heating furnaces in the heating room. The calculation method of fume hood is referred to the design code for chemical heating, ventilation and air conditioning regulation for light, moderate or dangerous hazardous substances. Under the condition that the indoor ceiling has air supplement, the minimum suction surface speed of the operation port of the fume hood is 0.5m/s. For the utilization rate of fume hood, when the number of fume hood is more than 2, the simultaneous utilization rate of 60% ~ 70% should be taken. Heating furnace is to maintain the furnace heating temperature of the heat balance law to calculate the required exhaust air volume. Through the above, the total safe ventilation can be calculated. In addition, the air volume of air conditioning calculated by the load is compared with the minimum air change frequency of 10 times, and the maximum value of the three is taken.
2 air supply and exhaust forms
"Code for design of heating, ventilation and air conditioning regulation of chemical industry" stipulates that when the exhaust air volume of the laboratory is large, outdoor fresh air supplement system should be set up and the fresh air load should be included.
According to the code for architectural design of scientific laboratory, each exhaust device should be equipped with an independent exhaust system. All exhaust devices in the same laboratory should share one exhaust system. The laboratory that uses exhaust system continuously during working hours should be equipped with air supply system, the air supply volume should be 70% of the exhaust air volume, and the air supply should be purified according to the process requirements. For heating areas, the supply air should be heated in winter. The air supply should not damage the normal operation of the laboratory exhaust device.
ASHRAE stipulates that all gases discharged from the chemical laboratory should be directly discharged out of the room, and can not be recycled. Therefore, unless the chemical laboratory also has cleaning requirements, it is necessary to keep the negative pressure relative to the adjacent area. Whether to choose 100% fresh air supply system should be an important part of laboratory risk assessment.
Each unit of the laboratory is equipped with an independent exhaust system, which is installed on the roof. Due to the toxic, corrosive and high temperature gas produced in the wet chemical room and heating room, fresh air treatment must be adopted. For example, the general laboratory for computer analysis and the constant temperature and humidity room for material testing, 100% fresh air supply system is not the only choice. Because of the different process functions of the laboratory, fresh air ventilation or fresh air treatment is not necessary. To meet the process can only be the first, 100% fresh air is for the environment of fume hood, and for the general laboratory circulating air treatment can meet the requirements, it is not necessary to 100% fresh air. Moreover, in the air-conditioning environment with fresh air, the energy consumption is very high.
3 room differential pressure
According to the code for design of heating, ventilation and air conditioning in chemical industry, the relative negative pressure should be kept in the laboratory.
ASHRAE stipulates that all gases discharged from the chemical laboratory should be directly discharged out of the room, and can not be recycled. Therefore, unless the chemical laboratory also has cleaning requirements, it is necessary to keep the negative pressure relative to the adjacent area.
In fact, this provision should be based on the specific object of implementation. In this project, the constant temperature and humidity room needs strict temperature and humidity control range, which should be designed as positive pressure. Because if it is designed as negative pressure, the air in the adjacent area will enter. On the one hand, it may damage the control precision of temperature and humidity; on the other hand, if the polluted air enters, it may also cause safety problems. For wet chemical room and heating room, it is necessary to design negative pressure in order to prevent toxic, corrosive and high temperature gases or volatiles from spreading to the room or even other areas. The office area of the laboratory building should always maintain positive pressure relative to the corridor and laboratory. The air flow in the laboratory should flow from the low-risk area to the high-risk area, and finally to the outdoor through various fume hoods or heating equipment.
4 control system
The control should integrate the above items, which can meet the requirements of room pressure, room pressure difference, ventilation rate, temperature and humidity and other aspects of the laboratory, and reduce energy consumption. There are many chemical pollution sources, especially harmful gases, which are harmful to human health. But at the same time, energy is often consumed, so the requirements of laboratory ventilation control system are from the early constant air volume, bistable, variable air volume system to the latest adaptive control system. The so-called most safe and comfortable environment, and the most energy-saving way is not too extravagant. The system responds quickly to ensure personal safety, accurately controls the balance of air supply and exhaust and indoor pressure with the highest accuracy to provide maximum stability. Try to reduce the user's early investment and reduce the user's expenses in operation, energy consumption and maintenance.
ASHRAE stipulates that on the one hand, the laboratory control adjusts the temperature and humidity control of the equipment; on the other hand, it monitors the safety facilities to protect the staff, which system is used only