The air conditioning system of operating room requires controlling indoor temperature, temperature, dust, bacteria, harmful gas concentration and airflow distribution, ensuring the fresh air quantity needed by indoor personnel, and maintaining reasonable airflow direction indoor and outdoor. The most important is to control the concentration of bacteria in the room in order to prevent surgical wound infection and improve the success rate of the operation. Compared with the air conditioning requirements of general buildings, the system should have the following characteristics:
(1) Purification and sterilization of air;
(2) Controlling the airflow and wind speed in each region;
(3) To ensure the reasonable flow direction and pressure distribution between different regions;
(4) To ensure the necessary temperature and humidity for medical treatment;
(5) Exhaust and harmful gases are discharged to ensure fresh indoor air.
A good operating room air conditioning system is not only to meet the requirements of a single index, but also to achieve the goal of "sterile environment protection system" in an all-round way, eliminating all possible risks of post-operative infection in the whole operation process.
The formation of modern operating room has a history of more than 100 years, and the earliest one-way flow clean operating room in the world has been more than 30 years. Clean operating room has developed rapidly since the 1960s. The development of clean air-conditioning system in operating room and the progress of related scientific research are closely related to different national standards, design ideas and technical measures. From fresh air supply to return air application, from overall laminar flow system to local displacement device, from centralized large-scale system to centrally controlled hybrid system, operating room vacancy Various types of air conditioning systems have their own merits. Here are the air conditioning system models and ideas adopted by operating rooms in different countries.
2 Common air conditioning systems in operating rooms abroad
2.1 air conditioning system model for operating room
Most of them are centralized large-scale systems in the United States. There are roughly two types. In the early 1960s, according to the 1959 ASHRAE guidelines, fresh air system has 8 to 12 ventilation times per hour, room temperature 25.6 C, relative humidity 55%. Indoor exhaust air collects into the exhaust manifold, and then discharges after heat recovery using total heat exchanger.
Another type of system was built in the 1970s. Indoor air is allowed to circulate. The number of ventilation increases to 25 times per hour. Fresh air is at least 5 times per hour. Generally, the return air is taken to the maximum. In order to control each room separately, the operating rooms in general hospitals generally adopt the terminal reheat mode of single air duct system, which can flexibly implement the opening, stopping and temperature and humidity regulation.

French operating room system is representative in Europe, similar to the United States in the early stage, using a fresh air system or a one-way flow pattern in the whole room. Joubert et al. developed a new system in the late 1970s, which combines the common purification air-conditioning system and one-way flow system. After several improvements, the air-conditioning system of the present Qiubert operating room was formed. In the system, three-stage fan is used to increase the self-circulation of indoor air, so as to increase the number of ventilation and reduce indoor bacterial concentration.

The number of clean operating rooms in Japan is second only to that in the United States, far larger than that in Europe. The development of the system is deeply influenced by the western countries. Now it has gradually formed its own characteristics, namely, the so-called mixed operating room, which takes the whole operating department and each operating room as the control object at the same time.
The layout of the German surgical department emphasizes the operating room unit, which includes the operating room and the anterior room. An operation department consists of multiple operation units and other auxiliary rooms. This layout ensures that the operations are carried out independently and without interference. However, the whole operation Department requires a large air supply, and the flow direction of airflow is difficult to control because of too many divisions. Therefore, Germany adopts a combination of local and overall control, that is, each clean operation unit adopts an independent air conditioning system, and a unified positive pressure air supply system. During the working period of the operating department, the two systems operate simultaneously; during the working period of some operating rooms, only the independent air conditioning system and the positive pressure air supply system of these operating rooms need to be operated; during the non-working period, only the positive pressure system needs to be operated. In this way, the normal operation of the operating room can be guaranteed easily and effectively, and the gradient pressure difference distribution of the whole operating department can be maintained all the time. Positive pressure air supply is provided by positive pressure (fresh air) units, and the air conditioning air supply of each operating room unit is handled by an independent air conditioning box with fresh air.
In the non-centralized air supply system of each operation unit, airtight valves are installed in the return air and exhaust air pipelines of each room. When the air conditioning box and exhaust fan of each room are closed during the non-working period, the airtight valves are closed to prevent the return air and exhaust air system from being poured into the single positive pressure air supply, which makes it difficult to maintain the normal positive pressure air flow direction. 2.2 Reasonable Air Distribution
Reasonable indoor air flow can prevent the accumulation of bacterial particles and remove them quickly, effectively protect key areas. Indoor airflow is divided into turbulent flow and laminar flow. The turbulent flow is both upward and downward return. The upper air outlets are arranged in different positions, including side, oblique and top feeding. Later, most of the airflow is delivered over the operation area, and the lower two sides are returned. It is considered that this kind of up-send and down-return has the best effect. The clean effect of laminar flow has been recognized unanimously, but its cost is high. In Europe, partial laminar flow has been developed, such as air bath system, roof air supply unit with air curtain, and laminar flow hood with envelope or curtain.

Charley, a British surgeon, has finalized the first laminar flow device known as the "green house" in Britain. Through continuous improvement, the present Chaley super-clean air supply system has been formed. Its central outflow area is surrounded by a fence with a distance of about 2m from the lower edge of the fence, which is equivalent to shortening the air outlet to the operating table. The one-way flow pattern of airflow can be well maintained without increasing the velocity of air supply. Esdorn, Berlin University of Technology, Germany, has developed a dedicated air supply unit for the operating room, which forms a displacement flow in the operating area. Because of its dramatically reduced air supply volume, remarkable energy-saving effect, and can well meet the requirements of indoor noise. This air supply device can maintain a low turbulence displacement air flow, but also can form a stable air flow. The device has a large area, generally 3 m x 3 m. Because the velocity of air supply is small, it is easy to be disturbed by the heat source (such as people and lamps) below and the transverse air flow in the room, so the air nozzle is set in the center of the ceiling to support the weak vertical downward air flow. At the same time, the flow is maintained by the temperature difference of air supply, which should be strictly controlled. If the temperature difference of air supply is too small, the air supply can not reach the operating table; if the temperature difference of air supply is too large, the clean area will be reduced. Some devices can also change the wind speed by adjusting the perforation rate of the air supply orifice plate. This air supply ceiling unit requires other equipment in the operating room (such as operating lights and closed doors), the quality of the operator, the understanding and cooperation of the clean technology, the air distribution and the relationship between the air volume and the return air and the exhaust air. In order to facilitate transportation and installation, Trox developed a modular air supply unit for operating room. Unlike laminar flow devices in Britain, fencing is not allowed around German air supply devices. Japan emphasizes comprehensive laminar flow technology, requiring that the air supply surface should not be less than 75% of the ceiling.
2.3 Positive Pressure Control
Generally, it is realized by controlling the fresh air volume or the relationship between fresh air and return air, combined with the means of automatic control. In order to emphasize that the whole operation Department is a safeguard system, Germany has developed an independent positive pressure air supply system and applied a mechanical air volume regulator to stabilize the air volume, which improves the stability.
2.4 Suitable air filtration system
Good configuration of filtration system can effectively ensure indoor sterile environment and prolong the service life of end filter. Although it has been proved that 99.9% of all bacteria in hospitals can be filtered by filters with 90-95% colorimetric efficiency (equivalent to sub-high efficiency filters in China) as early as the 1980s, the newly revised hospital ventilation standards in various countries generally have the tendency to improve the filtration efficiency. The application section of the 1999 version of ASHRAE manual stipulates that three-stage filtration must be used in the air-conditioning system of clean operating room, requiring that the DOP efficiency of the terminal air filter should not be less than 99.97%. Generally, two-stage filtration is allowed in operating room, and the DOP efficiency of the terminal filter should not be less than 90%. The 1998 edition of "Hospital Air-conditioning Equipment Installation" The Guidelines for Accounting and Management have also been revised accordingly. Compared with the 1989 edition, the specific changes are shown in Table 1. Obviously, this trend of change is not based solely on the effect of bacteria filtration, but should be said that the idea of "comprehensive safeguard system" has been widely accepted by all countries. Differences in filter efficiency requirements between 1998 and 1989 Guidelines for the Design and Management of Hospital Air Conditioning Equipment are shown in Table 1.
Area name end filter efficiency (%)
Class I, Class II and Class III
98 edition High Clean Area Clean Area Quasi Clean Area
89 Version of Highly Clean Zone A Clean Zone B
DOP Efficiency of 98 Version > 99.97 DOP Efficiency > 95 Colorimetric Efficiency > 90
89 edition of counting method efficiency > 99.97 colorimetric efficiency > 90 colorimetric efficiency > 80
2.5 Humidity Control in Clean Operating Department
Improper indoor humidity control will not only increase the number of human bacteria, but also provide nutrients for bacterial reproduction. Cooling and dehumidification followed by reheating are widely used in foreign countries to control humidity effectively, but the energy consumption is high. Then some energy-saving measures are taken, such as using waste heat, heat recovery devices, etc. The latest closed-loop heat recovery system uses the heat of fresh air to reheat the system. Recovery heat is generally unstable, and auxiliary electric heaters or steam heaters are often added.