FAQs

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Hardwall cleanrooms feature a rigid wall structure and are completely enclosed rooms with vents to exhaust air. Available with either single-pass or recirculating air systems, hardwalls hold higher pressure differentials than softwall options, which helps to prevent particulate intrusion. With a recirculating air system, hardwall cleanrooms also offer more control over temperature and humidity than softwalls can. Applications that require negative and positive/negative pressure cleanrooms require hardwall construction. The modular rooms can be disassembled, moved and reassembled if needed.

Softwall cleanrooms are ideal for fast construction and easy expansion. Often called process isolators, these enclosures utilize flexible vinyl curtains to form the room envelope. They are available in virtually any size and the full range of ISO cleanliness classifications. Softwalls are ideal for dust control, sound control, safety, and other operations. Since they usually have an air gap around the perimeter, they can maintain very little positive pressure and no negative pressure differentials. Softwall cleanrooms are ideal for enclosing portable frame systems or for improving laminar flow areas above work spaces. They also can be used to further divide existing cleanrooms to create cleaner inner zones.

The most important factors to consider when constructing a cleanroom are the smallest size of particle that will need to be filtered out and the lowest acceptable particle count. Selecting the appropriate cleanroom classification for the intended use is essential. Building a cleaner room than necessary will greatly increase both construction and operating costs.

Most industries have a default classification that serves as the baseline. For example, in the medical device packaging industry the cleanroom default is ISO 7 (class 10,000). Research in your specific field will provide either a specification or a general classification guideline.

Another important question to consider is how much air needs to be circulated to get the contamination out? A cleanroom is designed to keep the outside environment from getting in, but it’s important to remember that controlling particulate contamination is an ongoing process. Contaminants are generated all the time by people, processes, facilities, and equipment, so they must continue to be removed from the room.

Contamination control requires controlling the total environment. Air flow rate and direction, pressurization, temperature, humidity, and specialized filtration all need to be tightly maintained to remove particles from the cleanroom. The allowable level of contamination is dictated by specifications for the operations being performed. Frequently, companies have found that that a higher classification (less clean, less expensive) cleanroom will meet its needs if staff are garmented to a higher level, and the sources of contamination are understood. The location of return air grills and filtration can even provide cleaner areas within a cleanroom, enabling companies to select a less-expensive option.

A positive-pressure modular cleanroom is designed to protect the environment within the room. Positive-pressure cleanrooms typically use ceiling-mounted, self-powered fan-filter units (FFUs) to force HEPA- or ULPA-filtered air into the room. This creates an internal air pressure greater than ambient pressure, which reduces particulate intrusion around doors, and minor unsealed areas in walls or ceilings.

Wall venting near floor level exhausts cleanroom air with the particles it carries into the external environment and promotes laminar flow of incoming air. The ability to remove particles and create a particulate-controlled environment inside the cleanroom is measured by the number of air changes per hour; the more air changes, the cleaner the cleanroom.

In a given cleanroom, cleanliness can generally be increased by adding more filtered air in the correct locations. Positive pressure can be built with hard walls made of solid plastic or steel, or soft walls made from flexible vinyl strips and curtains. In hardwall cleanrooms, temperature and humidity can be controlled to protect processes and prevent static charges by adding air conditioners, humidifiers, and dehumidifiers.

Negative-pressure modular cleanrooms are designed to keep contaminants generated within the cleanroom from entering the outside environment. A common design uses exhausting air handlers and HEPA filters to remove internal air and exhaust it to a safe location. This exhaust system creates negative pressure inside the cleanroom that draws external air into the room either directly or through filters. A common application for this design is a powder-filling operation. A negative-pressure cleanroom protects the external environment, but not necessarily the area inside the cleanroom.

Positive/negative-pressure modular cleanrooms typically use FFUs to inject clean air into the cleanroom and exhaust contaminated air into a buffer area. An air-handling system then removes slightly more air from the buffer area than is supplied by the FFUs, creating negative pressure with respect to both the cleanroom and the external environment. This negative pressure prevents external particulates from entering the cleanroom and also prevents contaminates from entering the area outside of the room. A positive/negative-pressure cleanroom protects both the cleanroom and the external environment.

The primary difference is in how air is returned to the room. Once the air has been purged from a single-pass cleanroom, that air recirculates through the area outside of the cleanroom and actually helps clean the air there as well. If precise temperature and humidity control are requirements, a recirculating system will ensure that the air won’t escape once it has been conditioned. The decision to use a single-pass or recirculating cleanroom depends more on the required preciseness of the temperature and humidity control than it does on the tightness or control of the particle count.

If a cleanroom needs to maintain a specific temperature but the outside environment around it is at a higher temperature, the cleanroom envelope has to be built to withstand the difference. If this is the case, an R-value in the wall is required to ensure the heat doesn’t transfer through. Because temperature moves with air, in the case of a positive-pressure cleanroom air will be pushed out. To maintain temperature, it’s critical to identify and insulate any areas where temperature can be lost.

If humidity needs to be tightly controlled, the cleanroom will also need to be designed to stop moisture from entering.

Specifying temperature and humidity too narrowly can increase both construction and operational costs. Humidity is relative to temperature, so if the temperature is set at 70 degrees and 50 percent relative humidity, lowering the temperature to 68 degrees would increase the relative humidity to 55 percent. A two-degree temperature decrease results in having to dry that air to get it to a lower moisture content, resulting in higher operational costs.

Modular cleanrooms can usually be installed against existing walls, provided that adequate provisions are made for exhausting air. Both hardwall and softwall cleanrooms generally depend on exhausting air through vents or open spaces at or near the bottoms of walls or curtains. Blocking this exhaust in large areas may create more turbulent airflow in the cleanroom or limit exhausting air. To prevent this, leaving a one- to two-foot clearance between the modular cleanroom and existing room walls is recommended.

Requirements for an environmental room, also known as a critical environment or white room, are similar to those of a cleanroom, although not as stringent. Environmental rooms must be built separately, maintain temperature, and maintain pressurization — making them ideal for applications such as packaging rooms and coordinate measuring machine rooms. Because the requirements aren’t as strict as those of a cleanroom, building and installing an environmental room typically costs less.