Pressurizing with dust collectors: Making the right decision

Indoor air quality: Choosing positive or negative pressure is a multi-faceted decision

05/20/2013


Figure 1: A cartridge dust collection pressurizing system is installed on the roof of a maintenance building in the harbor of a European coal power plant to prevent ambient coal dust from entering the building. The unit is installed in front of a ventilatPressurization is a well-known ventilation technique in which a positive or negative atmospheric pressure is maintained in an isolated or semi-isolated environment. A clear way to illustrate this principle is the example of the healthcare industry, where pressurization has been used for many years for infectious disease control.

A patient with an immunodeficiency disorder will typically be housed in a positive pressure isolation room, which maintains a flow of air out of the room, thus protecting the individual from contaminants and pathogens which might otherwise enter. Conversely, a patient with a contagious disease will be housed in a negative pressure isolation room, which maintains a flow of air into the room to keep the infection from spreading to other patients and healthcare workers.

In industrial settings, positive pressure (known as “inflating the building”) is similarly used to keep particulate or gaseous contaminants out of a room, creating an air barrier between the outside and the inside. If you walk into a positively pressurized environment and open the door from outside, you will feel the “whoosh” of air escaping due to the higher pressure of the air inside the room. This is the desired effect when you are trying to protect the contents of the room from dirty outdoor air conditions, from dust or fumes generated by an adjacent production process, or even from excess humidity that might seep in through walls or other openings. Offices, labs, and electrical and server rooms in industrial facilities are especially prone to dust infiltration that can create unpleasant working conditions while causing problems with critical equipment, especially electronics.

Conversely, in a pharmaceutical facility where potent compounds are used, negative pressure may be applied—sometimes in conjunction with containment systems—to prevent the dust generated in a manufacturing space from cross-contaminating other areas of the plant.

Figure 2: A 16-cartridge dust collector pressurizes and ventilates a compressor room in a power generation plant in South America. Wall louvers allow for air exchange and are calibrated to maintain a specific pressure inside the facility. Courtesy: CamfilTo guard against cross-contamination and maintain desired air quality during either positive or negative pressurization, proper air filtration is a necessary component of the process. High-efficiency HVAC filters (ASHRAE-grade or HEPA filters) are the most common solution, but cartridge-type industrial dust collectors can offer an effective and sometimes overlooked alternative for applications where dust loads are extremely heavy and filter life is prohibitively short.

Pressurizing with dust collectors is applicable to many industries, including cement and lime production, metal and coal mining, pharmaceutical processing, grain processing, or potentially anywhere that high volumes of dust are generated. Areas that are most commonly protected through pressurization include:

  • Control rooms
  • Clean rooms
  • Compressor rooms
  • Offices
  • Quality control labs
  • Substations
  • Electrical equipment and motor control center (MCC) rooms
  • Server rooms  

Deciding when to pressurize

Figure 3: Dust collection system is used to pressurize a control room at a gold mine. The collector is connected to a ducting system in a very similar configuration as if an air conditioning unit performed the same function. Courtesy: Camfil APCHow does a plant engineer decide whether pressurization is a good choice? The decision can’t be based solely on the volume of dust to be controlled, because other factors come into play such as the type of dust, conditions inside and outside the space, and what (or whom) you are trying to protect.

If there is nothing much of value inside the space, pressurization may not be worth the expense. But if you are protecting electrical equipment that costs $100,000 from damage or from creating a safety hazard due to contact with dust, it will be worth investing in a $20,000 pressurizing system to protect that equipment. Similarly, if workers in an office area are exposed to unhealthy levels of dust or fumes, you will want to keep the area clean to protect occupants against the well-known health hazards associated with dirty indoor air and comply with OSHA regulations for exposure. Not only will you be in compliance and preserve their health, but morale and productivity will also be enhanced.

Climate considerations might also impact your cost analysis. In the tropics, if you inject large amounts of warm, moisture-laden air from outside to pressurize a building, the additional air conditioning load could be cost-prohibitive. However, in colder climates or during winter season, you can take advantage of the “free cooling” and use your pressurizing system for conditioning, saving substantially on air conditioning costs required to keep servers and electrical equipment from overheating.

Return on investment should typically be less than two years for pressurization to be cost-effective, and field experience shows that the payback is often much faster. Though as stated before, in many cases the main justification is to guarantee a certain air quality in a space to protect something or someone valuable. The technology is best applied to new construction, expansion, or renovation projects. Retrofitting of existing facilities, while possible, can be more costly and complex depending on the setup and location. 


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