1 design purpose
The air conditioning and ventilation design of infectious disease room, the design purpose mainly has the following points:
(1) Provide a good indoor environment for infectious disease patients.
(2) Ensure that indoor polluted air does not escape outside.
(3) Avoiding airborne cross-infection, reducing and avoiding the risk of healthcare workers contracting infectious diseases.
(4)Effective control of pollution sources:
2 air conditioning system design form
Infectious disease room air conditioning system can be used in variable air volume system, can also be used in a fixed air volume system, it is recommended to use a fixed air volume system.
Variable air volume system (VAV) is an active pressure control strategy, it is through the motorized air volume control valve continuously on the supply air volume or exhaust air volume to maintain the desired pressure.
Active VAV pressure control methods can be categorized into two types: pure differential pressure control (OP) and residual air volume (also known as flow tracking) control (AV).
Constant air volume (CAV) is a passive control method that uses an airflow regulating valve to achieve a desired negative pressure value by balancing the supply and exhaust air, with the supply air being a certain amount less than the exhaust air.
The traditional constant air volume system has the following main characteristics: (1) All the time, the equipment must maintain a constant amount of air supply and exhaust. (2) must be designed according to the full load, to have a large margin to make up for the drop in the performance of the air supply and exhaust system due to filters, etc., continuous full-load operation so that the energy consumption is great.
(3) Due to the fan system, filter system performance degradation or change in the position of the damper, etc., the system often need to re-balance the debugging of the wind, requiring a lot of maintenance. (4) Noise will be on the high side due to high air volume operation at all times.
In order to overcome the shortcomings of the traditional fixed-air volume system differential pressure control, can be used to add a venturi valve fixed-air volume system. By using pressure-independent fixed air volume control device (venturi valve) in the air supply and exhaust duct fixed air volume system, to a certain extent, can take the initiative, dynamic adjustment of the flow rate, to eliminate the static pressure fluctuations caused by the system on the impact of the flow rate, so as to ensure that the flow rate of the constant and the stability of the control.
The number of air changes should be greater than or equal to 12 times / hour, it is recommended that the airflow organization is reasonable on the basis of a single isolation room for a reasonable number of air changes taken as 12ACH, and for double and triple or more isolation ward, it is recommended that the value of about 15ACH.
In order to prevent cross-infection of patients in different rooms in the infectious disease area, the air conditioning system should be used to avoid cross-infection in the form of a reasonable system layout, the outbreak of infectious diseases using the whole fresh air system. In order to set up high efficiency filtration device on the exhaust system to protect the surrounding environment from pollution.
Taking into account the need to meet the negative pressure, the exhaust volume of the room is greater than the room's air supply.
3 ward airflow organization
Airflow organization should try to exclude dead zones, stagnant areas and avoid sending and exhausting short circuits. Send and exhaust air outlet arrangement should make the clean air first flow through the ward may stay in the region, and then flow through the source of infection (mainly refers to the patient) into the exhaust port. In this way, health care workers will not be between the source of infection and the exhaust. The air supply outlet is arranged on one side of the room, the air supply outlet is installed with the ceiling high, opposite to the patient, the exhaust air is discharged from the patient's side, the exhaust outlet is installed with the low, the bottom of the exhaust outlet should be no less than 100mm high above the floor of the room.
Air supply and exhaust have a relative relationship, air supply outlet location and wind speed must have enough energy to dilute the pollutants in the room, and make the patient near the immediate discharge of viruses, reduce their retention in the room time.
The air ducts and air velocity must take into account the patient's feelings to meet the noise requirements, and to avoid making the patient feel uncomfortable airflow (recommended wind speed of less than 0.25m/s).
4 air flow in the ward
Pathogenic factors may spread to other parts of the isolation ward, therefore, the isolation area should be designed to directional airflow. Airflow should flow from clean areas to non-clean areas.
Air flow should be directed from corridors into isolation wards to prevent the spread of contaminants to other areas. Air flow is controlled by a pressure gradient (negative pressure). Air flows from higher pressure areas to lower pressure areas.
5 Pressure gradient
Regional differential pressure control is to ensure that the entire isolation ward in an orderly gradient pressure difference, to achieve the directional airflow from the clean area - semi-contaminated area - contaminated area, in order not to make infectious isolation ward air spread to other places in the hospital, blocking the contamination of other areas, isolation wards must be negative pressure control. Negative pressure control is mainly achieved by making the exhaust air volume greater than the supply air volume within the airtight structure, in order to strictly prevent the leakage of indoor air to the outside, set the buffer room, and require the enclosure to have a certain degree of tightness.
According to the American Institute of Refrigeration "HVAC Design Manual for Hospitals and clinics" book shows that the minimum pressure difference necessary to maintain negative pressure, so that the air flow into the room should not be less than 2.5 Pa, usually take 5 Pa. Buffer room, relative to the wards and restrooms, the amount of air in the buffer room for the clean, so the buffer room air pressure relative to the wards and restrooms. Room air pressure relative to the ward and bathroom should be positive pressure.
Room set differential pressure controller, when the differential pressure is lower than the set value, the pressure alarm occurs, has ensured that the room and adjacent areas of differential pressure, and when the door to enter and exit the room is open, the negative pressure value will be reduced, by the time-delayed signals should be considered enough time for personnel to enter or leave the room without activating the acoustic alarm.
Between the isolation room and the anteroom, a pressure regulator valve is installed to stabilize the negative pressure.
Determination of differential pressure air volume:
5.1 Calculation of infiltration air volume according to ASHRAE Handbook -Fundamentals
In the formula, AL=air leakage area, in.2
=unit conversion,0.186
Qr=air leakage, cfm
ρ=air density, 0.0724lbm/ft3 at normal room temperature
CD = coefficient of permeability,approximately 0.186
=reference pressure difference- for AⅡ,0.01in.w.g
5.2 Calculation of leakage air volume according to the gap method
Sequence - pressure difference air volume required to maintain the clean room pressure difference value, m3/h
-Safety coefficient determined according to the airtightness of the enclosure structure, generally 1.1~1.2;
q-When the clean room is a certain value of pressure difference, its Enclosure unit length gap leakage air volume, m3.(h.m)-1
l=cleanroom enclosure gap length, m.
5.3 air change number method
Domestic and international pressure difference air volume determination, most of the air change number estimate,
6 air filtration
In order to prevent pollution of the environment, exhaust air must be Processing. There are a variety of methods of treatment, such as filtration, ultraviolet disinfection, high temperature disinfection and so on. That is, air filtration is one of the most effective methods. What level of filter is used for exhaust air should be determined according to the degree of harm caused by disease-causing factors.
According to the AIA design guidelines, the filtration efficiency of the primary filter should be not less than 30%, and the filtration efficiency of the intermediate filter should be 95%. The filters should be equipped with differential pressure indicators and prompted to change the filters in a timely manner.
It is believed that after the above introduction, we have a certain understanding of the design of air conditioning and ventilation for infectious isolation ward. Welcome to visit Zhongda Consulting for more information.
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