First, use natural ventilation conditions.
The above-ground single-row garage can adopt natural ventilation when the parking space is less than or equal to 30 vehicles, the openable door and window area is greater than or equal to 2m2/ vehicle, and the layout is uniform. If the openable door and window area is greater than or equal to 0.3㎡/ vehicle, and the layout is uniform, mechanical ventilation and natural ventilation can be used. When the above requirements cannot be met or natural ventilation cannot meet the requirements, the maximum concentration of CO is less than 30mg/? Standard, mechanical ventilation system should be set up.
The underground garage is located below the outdoor ground, and there are no external windows around it. Only the ramp for cars to go in and out leads directly to the outside. Harmful substances are easy to accumulate beyond the allowable concentration, pollute the air and threaten safety, and are in a relatively closed state. Therefore, the underground garage should be equipped with independent air supply and exhaust systems. When the ramp can be used for air intake, mechanical exhaust and natural air intake are adopted; When the ramp cannot be used for air intake, mechanical exhaust and mechanical air intake are used. The outdoor air outlet should be set in the downwind direction of the building and away from the personnel activity area.
Second, the calculation method of garage ventilation
The ventilation volume of the garage ventilation system shall be calculated according to the following two methods, and the larger value shall be taken:
(1), diluted harmful concentration method. This method is considered to be the most scientific and accurate method to calculate the ventilation of the garage, and it is suitable for all or part of the garage with two or more floors.
(2), garage volume ventilation method. The exhaust air volume shall be calculated according to the air exchange times of not less than 6 times /h, and the air supply volume shall be calculated according to the air exchange times of not less than 5 times/h. When the garage floor is
Among the two calculation methods, the diluted harmful substance concentration method is the most classic one. However, because there are many influencing factors and boundary conditions involved in the actual calculation, it is easy to appear the phenomenon of wide disparity in various calculation results, and the calculation process is complicated, so it is difficult to do the actual calculation. The calculation of volume ventilation frequency method is based on unit volume ventilation index; Because the ventilation of the garage should be related to the emission of harmful substances, not to the garage volume, the emission of harmful substances of vehicles with the same volume may be different, and different dilution effects will be obtained with the same index.
However, the volume ventilation rate method has become a widely used method in China because of its convenient calculation process, simple conditions and simple calculation, but it is unreasonable when used in all or part of double-decker or multi-storey garages. Because of this, it is suggested that all or part of double-deck or multi-storey garages should be used, and the ventilation volume should be calculated by diluting the concentration of harmful substances and the ventilation volume of single-deck garages should be calculated by ventilation volume method. In order to maintain the negative pressure in the garage, the intake air volume of the garage is calculated as 80%~90% of the exhaust air volume.
Three, the garage ventilation design points
1. The layout of the air supply and exhaust ports of the mechanical ventilation system in the garage is of great significance to quickly eliminate harmful substances and keep the garage air fresh. Reasonable tuyere layout and airflow distribution can get twice the result with half the effort. The layout of air supply outlet and exhaust outlet shall meet the following requirements:
(1), air supply outlet and air exhaust outlet shall be arranged to ensure uniform air flow and avoid ventilation dead angle;
(2) The air supply outlet shall be arranged at the upper part of the main passage of the carriage.
2. In the garage mechanical ventilation system with large traffic flow change, it is advisable to set up a CO gas concentration sensor to control the operation of ventilation equipment. When using air duct to supply air, the sensors should be distributed at multiple points; When the induced ventilation system is used, the sensor should be set near the exhaust port.
3. In order to reduce the energy consumption of the ventilation system, multiple fans in the garage ventilation system can be connected in parallel or variable speed fans can be used, and the fan air volume can be reduced by 50% at night or when there are few vehicles.
4. According to the regulation that garages with an area of more than 2000㎡ should be equipped with mechanical smoke exhaust facilities, most underground garages are equipped with mechanical smoke exhaust and air supply systems. In order to save investment and building space, the exhaust and smoke extraction in the garage are allowed to share a system, but for safety reasons, the fire protection requirements should be met first.