First, the determination of the amount of air supply
Before the publication of the "Technical Specifications for the Construction of Hospital Cleansing Department" (hereinafter referred to as "Specifications"), the design of clean air conditioning systems in hospital operating rooms in China has basically been designed in accordance with industrial clean room design standards such as "Clean Plant Design Specifications". . This type of design adopts the concept of “full room dilution and purificationâ€. Although it can obtain uniform downward airflow, it has strong self-cleaning ability and can simplify the personal purification. However, there are two problems: First, large power consumption, large occupied area, and wind system. The noise control is difficult; the second is the high cost of construction and maintenance, the difficulty in arranging the lamps, and the difficulty in plugging high-efficiency filters. For example: a 36m2 class 100 operating room, the required air supply is 32400m3 / h ~ 45360m3 / h (section wind speed is 0.25m / s ~ 0.35m / s); in the operating room below 1000, the "full room The concentration of bacteria in the turbulent flow of the concept of dilution and purification is not ideal. In view of the above problems, refer to the German WEISS operating room clean air conditioning system concept, in the operating room air volume calculation and airflow organization, break through the industrial clean room design ideas, introduce the reduction of total air volume, strengthen local air supply, air supply mode adopts vertical unidirectional flow The focus is on the design concept of the operating bed area, which has the characteristics of convenient installation and maintenance, greatly reduced input costs, reduced power consumption, and small footprint. For example: a 36m2 class 100 operating room, the air outlet area is 2.4m × 2.4m, the air supply is 11340m3 / h, only 40% of the aforementioned industrial clean room.
Second, the setting of the new wind section
Some operating room purification air conditioning systems usually have three levels of filtration: the first stage filter is located at the return air outlet, the second stage is located in the system positive pressure section, and the third stage is located at the end of the system. In the 100-level operating room, the filtering effect of this three-stage filtration is unstable, because in China, the medium efficiency filter has the filter material, the variety is less, and the performance is low, which cannot effectively protect the high-efficiency filter. In this design, if the setting of one level does not match, the replacement period of the third-stage filter will be unreasonable, resulting in poor overall filtering effect. Therefore, the filtration problem of fresh air should be paid full attention. The fresh air is often directly mixed with the air-conditioning return air without independent filtering treatment. As a result, the initial effect, medium efficiency, high efficiency filter life is shortened, frequent replacement, system operation and maintenance The cost is increased and even affects the normal use of the operating room. This is because before the fresh air and the return air are mixed, the air dust concentration of the two is too different. If the fresh air is treated with the initial effect, the dust concentration is in the same particle size range as the 100,000 air conditioner return air. It is about 70 times larger than the tens of thousands of times of the dust concentration in the range of the same level of airflow, so that the medium efficiency and even the high efficiency filter are not adequately protected. In order to solve this problem, the fresh air is filtered through two stages and then mixed with the return air by installing a separate primary effect and medium efficiency filter on the fresh air passage. At this time, the mixed fresh air and return air are in the same particle size range. The concentration is relatively close, which really plays a role in protecting the medium-efficiency and high-efficiency filter. Moreover, the cleaning and replacement of the primary and intermediate-effect filters of the fresh air filter unit are more convenient, and the investment is less and the maintenance is simpler than replacing the high-efficiency filter. This method has achieved the desired results when it is put into use.
Third, the exhaust filter settings
In the clean operating room, the air outlet should be arranged above the head of the operating table. According to the "Specifications", the exhaust volume of each operating room is not less than 200m3/h. Each operating room is equipped with a separate exhaust fan, and the primary, middle and sub-high efficiency filters should be installed in front of the exhaust fan. We sometimes have access to the hospital clean operating room project, only a few are equipped with primary filter, the consequences are the same as the new fan group does not have a filter, during the operation of the operating room, the outdoor air will directly pollute the clean air through the exhaust port In the room, the temperature and humidity in the room change rapidly, and the dust particles increase, resulting in prolonged self-cleaning time before the next use of the operating room, shortening the life of the filter and wasting energy.
Fourth, the setting of the return air outlet
The setting of the return air outlet plays a decisive role in ensuring a reasonable airflow in the clean operating room. In order to make the air supply airflow cover the operating table and not short-circuit the clean airflow, it is required that the return air outlet does not exceed 0.5 m above the ground and the lower end is not less than 0.1 m from the ground. The airflow velocity of the return air inlet should not exceed 2m/s. According to the domestic scientific research results, the unilateral lower return air is used when the operating room width is less than 3m, and the lower return air is used when the operating room is larger than 3m. In the indoor pressure permitting state, the initial air filter should be added to the air return port. Otherwise, in the indoor personnel operation and the pre-operative and post-operative cleaning work, the return air may contain more hair and textile fibers. The fiber is sucked through the return air line. On the one hand, it is easy to make the pipe dust and bacteria. On the other hand, the contamination of the primary filter inside the unit will speed up the replacement frequency of the filter, thereby increasing the maintenance cost.
Fifth, pressure control
The clean surgical department should maintain a positive pressure relative to the surrounding area, and maintain a reasonable airflow direction and an orderly pressure distribution between different areas of the cleanliness level to avoid the impact of outdoor to indoor and low level on high-level environment. Only by ensuring that this gradient pressure distribution is maintained under all conditions (non-surgical) will it be truly effective in reducing the risk of cross-infection in the surgical field.
The positive pressure control is generally realized by adjusting the difference between the supply air and the return air and the exhaust air volume, and combined with the control means. This air volume difference is called the positive pressure permeate air volume, which is assumed by the system fresh air volume, and the positive pressure. The essence is the resistance of the positive pressure to penetrate the air gap through the room. The positive pressure air volume is an unorganized air flow, which penetrates everywhere. Therefore, the more positive pressure air permeate, the smaller the gap in the room, the greater the positive pressure established. Since there are many systems installed in the surgical department, the positive pressure control requirements are high. During the system operation, the positive pressure value will change due to the opening of the door, the dust of the third-stage filter or the outdoor wind speed. As long as any air volume in the air supply, return air, and exhaust air changes, it is possible to destroy the ordered gradient pressure distribution.
Although there are many means of positive pressure control, most of the measures are directed to a single room, it is difficult to control the orderly pressure distribution of the entire surgical department as a whole, and the stability is poor. In order to maintain a stable positive pressure in the room, a mechanical constant air volume device is often installed in the air supply, return air, and exhaust air outlets, and the effect is obvious but the cost is increased. After adopting the clean room air supply and positive pressure control system, the two-position controlled air volume device combines the two systems of fresh air and positive pressure into a new air system, which not only bears the positive pressure air volume of each clean operating room but also undertakes normal operation. With the new air volume, each independent air conditioning unit in each operating room becomes a circulating fan unit, and its air volume change has been independent of the positive pressure distribution in the operating department. Since the fixed air volume device is only installed on the fresh air system branch pipe (the flow rate of the fixed air volume device is much smaller than that of the air supply and return air pipes), the construction cost is lowered.
The whole system operates under different working conditions as follows: When an operating room is normally used, the air conditioner is turned on, so that the two-position controlled constant air volume device on the fresh air branch pipe is adjusted to a high position, and the high-grade fresh air volume (normal fresh air volume) enters. The air volume discharged by the exhaust fan unit is the difference between the fresh air volume and the positive air pressure, and the excess positive pressure air volume permeates the outside to establish a positive pressure. When an operating room is not in use, the air-conditioning mechanism, the dual-controlled constant air volume device on the fresh air branch pipe is adjusted to the low position, the low-range fresh air volume (positive pressure air volume) enters, the exhaust fan group is closed, and the positive pressure air volume permeates the outdoor can still be established. Positive pressure. Because it is delivered through a system, and the orderly gradient pressure distribution in the clean surgical department can be ensured, this effectively ensures the reasonable pressure distribution of the clean surgical department and the directional flow of the airflow. This system has been proved to be very energy-efficient and Effective.
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