What Are the Different Types of Room Ventilation?

Full ventilation, also called dilution ventilation, is to ventilate the entire room. The principle is to use a certain amount of clean air to enter the room, dilute the indoor pollutants so that their concentration reaches the permitted concentration in sanitary regulations, and discharge the same amount of indoor air with pollutants to the outside. ^[1]

(1) Natural ventilation

Natural ventilation that relies on heat or wind pressure is a widely used method.

(2) Mechanical ventilation

The method of making the air flow through the action of the fan, causing the room to ventilate.

(3) Natural and mechanical ventilation

Somewhere in between.

The system that uses machinery to implement comprehensive ventilation is divided into a mechanical air supply system and a mechanical exhaust system. For a certain room or area, there are several system combinations:

(1) There are both mechanical air supply system and mechanical exhaust system;

(2) Only mechanical exhaust system, outdoor air naturally infiltrates by doors and windows

(3) Combination of mechanical air supply system and local exhaust system;

(4) The mechanical air supply system is combined with the mechanical exhaust and local exhaust systems;

(5) Combination of mechanical exhaust system and air conditioning system;

(6) The combination of mechanical air supply system and air-conditioning system, or the task of comprehensive ventilation by air-conditioning system.

1. In a room that emits heat, humidity, and harmful gases, when the source is scattered or not fixed and local exhaust cannot be used, or it is still difficult to meet the hygienic requirements, local ventilation should be used or supplemented.

2. In addition to local exhaust, production plants that emit heat, steam and harmful gases at the same time, or only release harmful gases with a density lower than air, should be fully or naturally ventilated in the upper zone. Ventilation is less than once per hour. When the room height is greater than 6m, the exhaust air volume can be calculated as 6m / h per m of floor area.

3. Comprehensive ventilation includes natural ventilation, mechanical ventilation, or a combination of natural ventilation and mechanical ventilation. When designing, natural ventilation should be used as much as possible to achieve the goals of energy saving, investment saving and noise interference avoidance. When natural ventilation is difficult to ensure hygiene requirements, mechanical ventilation or a combination of mechanical ventilation and natural ventilation can be used.

4. To set up a production room with central heating and exhaust air, the possibility of natural air supply should be considered first. For a comprehensive exhaust system with less than 2h air changes or a local exhaust system that operates less than 2 hours per shift, a mechanical air supply system can be omitted to compensate the exhaust air volume. When the natural wind supply can not reach the indoor sanitary conditions, production requirements or technical and economic reasons are not reasonable, a mechanical air supply system should be installed.

5. For clean rooms, when the surrounding environment is poor, the supply air volume should be greater than the exhaust air volume to ensure the positive pressure of the room. For rooms that generate harmful gases, in order to avoid polluting adjacent rooms, the supply air volume should be less than the exhaust air. Volume to ensure negative room pressure. The general supply air volume can be 80 ~ 90% of the exhaust air volume.

6. When calculating the air balance and heat balance for the comprehensive ventilation in winter, the following factors should be considered according to the specific conditions:

(1) For a short period of time, the temperature can be reduced or the exhaust air can be discontinued. The exhaust air can be ignored in the calculation of air heat balance;

(2) Inlet air for comprehensive ventilation that dilutes harmful substances shall be calculated using the temperature of the heating outdoor in winter to eliminate waste heat and humidity. 7. For comprehensive ventilation, the temperature may be calculated using the outdoor ventilation in winter.

When calculating the heat dissipation of processes and equipment, the following principles should be followed:

(1) Winter

Calculated according to the heat dissipation of the process equipment of the minimum load shift;

Infrequently dissipated heat will not be counted;

For regular but unstable heat dissipation, use the hourly average.

(2) Summer

Heating according to the heat dissipation of the process equipment of the maximum load shift;

Frequent and unstable heat dissipation, heating according to the maximum value;

It should be considered when the day-to-day heat dissipation is large. ^[2]

(1) Fully ventilated intake and exhaust air should avoid the air containing a large amount of wet, hot or harmful substances from flowing into the place where there is no or only a small amount of wet, hot or harmful substances. Generally speaking, the air inlet should be as close to the work place as possible, and the air outlet should be as close as possible to the source of harmful substances or areas with high concentrations of harmful substances;

(2) When the hygienic conditions required in the workshop are higher than the surrounding sanitary conditions, keep the room at a positive pressure.

(3) In a fully ventilated room, the inlet airflow should be evenly distributed to reduce eddy currents and avoid the accumulation of harmful substances in local operating places;

(4) The relative positions of the air inlets and the air outlets are properly arranged to prevent the incoming air flow from being discharged directly to the outside without being polluted, forming a short circuit of the air flow. ^[3]

Full ventilation is to ventilate the entire room. The fresh air sent into the room is used to dilute the concentration of harmful substances in the room below the allowable concentration of national health standards. At the same time, the polluted indoor air is discharged directly or after purification treatment. Go into the outdoor atmosphere. Full ventilation can improve the indoor environment of the entire room, but it consumes a large amount of wind and wastes energy.

Local ventilation is to use local airflow, so that the place where people work is not polluted by harmful substances, so as to create a good local working environment. Local ventilation has the advantages of good ventilation effect and saving air volume. It is suitable for large workshops, especially high-temperature workshops with a large amount of waste heat. It is used when comprehensive ventilation cannot guarantee that all parts of the room reach a suitable level. However, the local ventilation design needs to be accurately calculated, otherwise the degree of ventilation cannot be guaranteed.