Cleanrooms today are made up of various sized environments needing control andmonitoring. From the ballroom style “clean” working areas to the bench-level workspaces, fan-powered clean spaces are required to meet the customer’s requirements. Often, to ease cost constraints, there is a growing placement of higher purity cleanroom minienvironments inside a larger ballroom space. AC fan-powered systems continue to be the major building block in these situations, as costbarriers continue to reduce the appeal of higher efficiency DC brushless platforms. Additionally, recent innovations in AC fan-powered control systems have improved the cost, performance, and efficiency of the AC driven system. This is closingthe gap between the lower cost AC driven FFUs and the more expensive but more efficient DC brushless driven solutions. This article reviews present systems, closed-loop control implementations, and the resulting improved cleanroom systemscapabilities.

Existing Solution Systems Laminar Flow Stations (example)
Most laminar flow stations today do not use closed-loop controls. A typicalsystem is depicted in Figure 1.

The laminar flow hood has one or more filter panels with associated fans for proper air flow and control. The fan speed is set manually to meet the desired criteria (i.e. pressure, air flow). A separate sensor is used to measure the desired criteria providing a readout of the measured value. Setup is often comprised of manually adjusting the air-flow, waiting for the system to stabilize and monitoring the resulting readout until the proper setting is achieved. The flow meter may have an alarm to alert the user if the flow migrates beyondan acceptable range.

In order to optimize the performance of the flow hood and reduce user maintenance, a closed-loop control system would allow the user to set the desired operating point and allow the system to stabilize to the desired setting automatically. An added benefit would be if the alarm system were integrated into the systemto allow for monitoring and notification when the system goes outside an acceptablerange (system out of compliance).

Figure 1: Present Flow Hood

Figure 2: Closed Loop Control Using External Sensors

Figure 3: AirCare VariPhase™ Configuration and Connection

Closed-Loop Control Considerations
The key ingredients of a closed-loop control system can be summarized as follows: