Building and Process Parameters that Influence the Ventilation System
The building parameters generally do not influence the target levels and the ventilation system in industrial ventilation. The process influences the ventilation system in many different ways, and these are described in the respective chapters (Chapters 5, 7, 8, 10, 13, and 14). However, many buildings exist where the building parts, and also the equipment used, may influence the ventilation system and therefore also the target levels.8 Naturally, the number of floors and the building height influence the ventilation design. This should not change the target levels. Emissions from surfaces and the tightness of walls, roof, and floor can also be of importance. Other parameters are also involved. For example, the size of the windows influence the temperature inside; and light walls and floors diffuse vibrations from machinery and fans and do not store any heat, but thick walls store heat. This changes the temperature variation and makes control of the temperature more complex. Doors that do not close make temperature and airflow control difficult, surface materials can adsorb contaminants and act as secondary emission sources, and so on.9
Normally there are no exceptional demands on buildings. For target levels II (good industrial level) and III (general industrial level), there is a great possibility that the building’s performance influences the ability to maintain the specified levels. For levels IV (minimum industrial level) and V (nonoccupied zone), the influence from the building on the maintenance of these levels is normally negligible. Target level I (special rooms) always demands careful design, taking into account all possible mechanisms that may influence; the environment.
The building parameters have varying importance depending on whether they affect the occupied zone or the nonoccupied zone, just as the process has different influences on these zones. For the nonoccupied zone it is of little significance if a high contaminant concentration is achieved, since no person will be in that zone. However, there could be some limits depending on the equipment or control systems situated in this zone. Since the size and location of the occupied zone can change during the building’s use, it is necessary to be very cautious. To treat the whole volume as an occupied zone is a conservative and safe measure.
There are many different types of equipment that are not directly connected to the process. One example is elevators, which can influence the ventilation system both when moving and when standing. In addition to the need for ventilation of the elevator, elevator shaft, and machine room, the moving elevator can induce airflows that change the air distribution and airflows in different parts of the building.
The influence of the building on the ventilation system, and indirectly on the target levels, can take many forms. There are, e. g., emissions from the materials that demand increased airflow rates and also door and window open-
Ings that influence the airflow distribution. These influences can sometimes differ between operating and nonoperating times.
The emissions of gases and vapors (and particles) from surfaces (both building materials and equipment) are easy to define in theory but can be very difficult to quantify in practice. There are many contaminants that can be generated, which makes it necessary to define the levels for a few, which are to be chosen from data from suppliers or from contaminants known to be generated by used materials.10
Adsorption by surfaces is normally of little significance, except when the adsorbed material can change the performance of the surface (e. g., its strength through corrosion) or when the adsorbed contaminants can be reemitted to generate new contaminants.
Leakage through walls, floors, and ceilings must be taken into account for contaminants (gases, vapors, particles, moisture, etc.) and leakage between building parts for air (with contaminants). Leakage from the ground of water vapor or radioactive gases is better prevented by construction measures than by ventilation measures. It is possible to use ventilation to diminish the influence of these parameters, but that could be unnecessarily expensive. Infiltration of radon depends on the pressure difference between the inside and outside, and by avoiding unnecessary high pressure differences it is possible to keep radon infiltration low.
Incoming radiation from the sun is dependent on the size, type, placement, and shading of windows (and placement of the building), and the subsequent heating or cooling of surfaces can change the air distribution in the room.
In general, it is mandatory to have some kind of partition between different parts of a building because of fire risks and regulations. These partitions can easily change both the airflow rate and the air distribution if proper preventive measures are not taken.
The influence of the sewage and the waste-handling systems on air quality must be taken into account, since both odorous and toxic gases may be emitted from these systems to the ventilation system.
Placement of the building in relation to wind directions and surrounding activities, such as other industrial plants and their exhausts and neighboring roads, can be important for the performance of the ventilation system and thus also for the possibility of keeping to the target levels. Trees and bushes generate bioaerosols that may enter the ventilation system.11
The location of the ventilation system’s different parts can also have some consequences. For example, one common fault is the placing of the air intake in the wake of the building or downstream from the air outlets. The locations of air intakes should be decided by the ventilation designer in connection with the building designer, but there are other parameters beside the outlet air that may change the quality of the incoming air. Lorry quays and transport openings in the building can be difficult to move and may require another place for the air intake. (They may also change the air distribution, depending 011 wind directions and velocities.) The placement of the air intake is more important if natural ventilation is used in some part of the building.
The energy distribution system used for the building could influence the possibilities of maintaining the target levels. This is due to the influence on the ventilation system or because the energy system requires some separate target levels, e. g., for tightness between some rooms in the building or for emission rates of contaminants to the building’s interior or surroundings. The choice of heating/cooling distribution through the floor or ceiling affects the air distribution and normally also the temperature distribution in the building. The contaminant distribution can also be changed.
The different target levels can interfere with each other depending on the process, climate, and building. For example, the target level for some contaminant’s concentration could demand a flow rate such that it is nearly impossible to keep to the target levels for air velocities. In such cases it is necessary to first look for another solution for the ventilation system (including local ventilation) and then to evaluate the different target levels against each other. This could result in changes of one or more of the target levels. If this situation occurs, the whole system (process, building, protection, etc.) must be carefully reviewed to find an appropriate solution to accomplish the main task, which normally is to manufacture a product.
Building parameters influencing the ventilation system are reviewed in Table 6.22. “Large” means that the building parameter usually has large influence on the ventilation system’s performance. “Variable” means that the building parameter’s influence usually varies depending on other building or ventilation variables. “Small” indicates that the building parameter usually has little influence on the ventilation system’s performance. The numbers refer to the required target levels presented in Section 6.4. For instance, if the target level is II (good industrial level), the tightness of the building has a large influence on the ventilation system’s performance. On the other hand, with target levels III (general industrial level) to V (nonoccupied zone) the influence of tightness on the ventilation system’s performance is usually limited.
TABLE 6.22 Simplified Table of Building Parameters that Influence the Ventilation System
Numbers refer to the target level classes presented in Fig. 6.10.
The distribution given in the table should, as for Table 6.21, be used only as a guide, not for designing. There are many cases where one parameter of the building system can have a large influence on the performance of the ventilation system, even when there are low demands on the target levels.
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