In view of the problems existing in the installation of fresh air filters, installation of filters in exhaust section, installation of air return ports, pressure control settings, and air volume settings, the economical and effective methods and ideas are put forward for clean air conditioning systems.
At present, the cleanliness level of many hospitals is emphasized unilaterally in the design process, while the energy saving factors in the operation and maintenance process are neglected, resulting in high investment and operation cost of the clean operation Department. On the basis of ensuring pollution control, how to make the purification system design reasonable and energy saving? The author makes an analysis and Discussion on this issue for the reference of colleagues.
1. Determination of Air Supply Volume
Before the publication of the technical specification for hospital clean operation Department (hereinafter referred to as "specification"), the design of clean air conditioning system in operation room has basically been carried out in accordance with the design standard of industrial cleanroom, such as "code for design of clean workshop".
This kind of design adopts the concept of "whole room dilution and purification" (as shown in Figure 1). Although uniform downward air flow can be obtained, self-purification ability is strong, and personal purification settings can be simplified, there are two problems: 1. large power consumption, large occupancy area, difficulty in noise control of wind system; 2. high cost of construction and maintenance, difficulty in lamp layout, and difficulty in plugging leakage of high-efficiency filters, for example: The required air volume of 36m is 32400 m /h to 45360m/h (section wind speed is 0.25m/s to 0.35m/s). Under 1000 level, the concentration of bacteria under the airflow is not ideal in the turbulent flow of the concept of "whole room dilution and purification". In view of the above problems, referring to the German WEISS clean air conditioning system concept, in the two aspects of air volume calculation and airflow organization, it breaks through the design concept of industrial cleanroom, and introduces the design concept of reducing total air volume, strengthening local air supply, and adopting the vertical unidirectional flow and focusing on the area of the operating bed. This method has the advantages of convenient installation and maintenance, and large investment cost reduction. Low power consumption, less occupied area and so on.
For example: a 36m hundred level, the air inlet area is 2.4m * 2.4m, and the air volume is 11340m /h, which is only 40% of the industrial cleanroom.
2. Setting of fresh air section
Some air conditioning systems usually have three levels of filtration: the first stage is located at the return air inlet, the second level is in the system positive pressure section, and the third level is located at the end of the system.
In my opinion, the filtration effect of this three stage filtration is unstable in 100 grade, because in China, there are some problems in medium efficiency filter, such as filter material, variety and low performance, which can not effectively protect the high efficiency filter. In this design, if a certain grade does not match, the replacement period of the three stage filter will be unreasonable, resulting in poor overall filtering effect.
Therefore, the problem of fresh air filtration should be given full attention. Fresh air is often mixed with air-conditioned air without independent filtration. The result is that life expectancy, medium efficiency and high efficiency filter (reference www.bacclean.com) are shortened, frequent replacement, the cost of transportation and maintenance of the system is increased, and even the normal use of operation room is affected. This is because before the mixing of fresh air and return air, the air dust concentration of fresh air is too different. Even after initial treatment, the dust concentration of fresh air is about 70 times higher than that of 100,000-grade air-conditioning return air in the same particle size range, which is tens of thousands of times higher than that of 100,000-grade air-conditioning return air in the same particle size range, so that the medium-efficiency and even high-efficiency filters do not have enough protection.
In order to solve this problem, an independent initial effect and intermediate effect filter is installed in the fresh air passage to make the fresh air mix with the return air after two stages of filtration. At this time, the mixed fresh air and the return air are close to the dust concentration in the same particle size range, which really plays the role of protecting the intermediate effect and high efficiency filter. Moreover, the cleaning and replacement of the primary and intermediate effect filter of the fresh air filter set is more convenient. Compared with the replacement of high efficiency filter, it has less investment and easy maintenance. The method has been put into use and achieved ideal results.
3. Setting of exhaust filter
At the cleanliness, the air outlet should be set above the head of the operation table. According to the regulation, the air volume of each row is not less than 200m/h. Each fan is equipped with a separate exhaust fan, and the primary, middle and sub high efficiency filters should be set up before the exhaust fan. This is often neglected. The hospital's clean project is only a small number of primary filters, and the consequences are not as good as the fresh air units. During the shutdown period, the outdoor air will directly pollute the clean air through the air outlet. The indoor temperature and humidity will change quickly, and the dust particles will increase. The self purification time will be prolonged before the next use, and the life of the filter will be shortened, and the energy will be wasted.
4. Setting of return air outlet
The setting of the air return port plays a decisive role in ensuring clean and reasonable airflow. In order to make the air supply airflow to cover the operating table, it does not make the clean airflow short circuited. It requires that the air return port does not exceed 0.5m and the lower end is no less than 0.1M, and the air velocity of the return air flow should not be greater than 2m/s. According to the domestic research results, when the width is less than 3m, the single side downward return air is greater than 3m, and the two sides return under the wind.
Under the permissible condition of indoor pressure, the return air outlet should be equipped with an initial or even intermediate effect filter. Otherwise, in indoor personnel operation, pre-and post-operation cleaning, the return air may contain more hair and textile fibers, which are absorbed through the return air pipeline. On the one hand, it is easy to cause dust and bacteria in the pipeline, on the other hand, the pollution of the initial effect filter in the unit will accelerate. The replacement frequency of the filter increases the maintenance cost.
5. Pressure control
Positive pressure should be maintained in the relative surrounding area of the clean operation department, and reasonable airflow direction and orderly pressure distribution should be maintained between different areas of the clean level in the Department to avoid the influence of outdoor on indoor and low level on high level environment. Only by ensuring that the gradient pressure distribution can be kept unchanged under any circumstances (non-operative period), can the risk of cross-infection in the surgical area be effectively reduced. (Refer to Clean Room www.iwuchen.com)
Positive pressure control is generally realized by adjusting the difference between supply air and return air, exhaust air, and combining with control means. This difference is called positive pressure osmotic air flow, which is borne by the fresh air volume of the system. The essence of positive pressure is the resistance of positive pressure osmotic air flow through the room gap. Positive pressure air flow is an unstructured air flow, which permeates everywhere. Therefore, the more positive pressure air flow, the smaller the room gap, the greater the positive pressure established.
Because there are many systems in the operation Department and the requirement of positive pressure control is high, in the operation of the system, the positive pressure value will change due to the opening of the door, the dust accumulation of the third filter or the influence of outdoor wind speed. The orderly gradient pressure distribution may be destroyed as long as any air volume in the supply air, return air and exhaust air changes.
Although there are many means of positive pressure control, most of the measures are aimed at a single room. It is difficult to control the orderly pressure distribution of the whole operation Department as a whole, and the stability is poor. In order to maintain stable positive pressure in the room, mechanical constant air volume devices are often installed in the air supply, return air and exhaust outlets abroad, which have obvious effect but increase the cost. We have developed a clean room air supply and exhaust and positive pressure control system, using a more simple and effective control method. The system uses a two position controlled constant air volume device to combine the two systems of the fresh air and the positive pressure into a set of fresh air systems. It not only assumes the positive pressure air volume of each clean chamber but also assumes the normal fresh air volume, and the independent air conditioning units of each air conditioner become a circulating air unit. Its air volume change has nothing to do with the positive pressure distribution of the surgical department. Because only a constant air flow device is installed on the branch pipe of the fresh air system (the flow rate of the constant air flow device is far less than that of the supply and return air pipes), the cost of the project is reduced.
The whole system operates under different conditions: when a certain unit is in normal use, the air conditioner opens, so that the two position controlled air volume device on the new air branch pipe is transferred to the high position, and the high-grade fresh air volume (the normal fresh air volume) enters. The air volume discharged by the exhaust unit is the difference between the fresh air volume and the positive pressure air volume, and the excess positive pressure air volume penetrates the outdoor area and establishes positive pressure. When a certain unit is not used, the air conditioning unit, the double position controlled air volume device on the fresh air branch pipe is transferred to the low position gear, the low level fresh air volume (positive pressure air volume) enters, the exhaust unit is closed, and the positive pressure air volume penetrated the outdoor area, and a positive pressure can be established. As a result of feeding through a system, and can ensure the orderly gradient pressure distribution in the clean operation Department unchanged, so as to effectively ensure the rational pressure distribution and the directional flow direction of air flow in the clean operation department, this system has proved to be very energy-saving and effective by practice.
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