The smart way to filter costs
Evolution in cleanroom filtration continues to move forward at an increasingly fast pace. We have recently seen new PTFE (Teflon) media for non-boron outgassing ultra low penetration (ULPA) filters, new chemical filtration for airborne molecular contamination (AMC) control and most recently, fan filter units with 'smart' filtration (smart FFUs). FFUs are becoming more and more popular due to the flexibility this style of filtration device affords cleanroom designers, owners and operators. Traditional central air handling units (AHUs) in combination with lay in high efficiency particulate air (HEPA) filters or even ULPA filtration is becoming a thing of the past. These systems are somewhat cumbersome to adjust and in general have very little flexibility when compared to their FFU counterparts. One of the driving factors moving operators towards FFU filtration is the fact that these systems provide versatility never seen before in cleanroom fabs. Firstly, there are the standard alternating current (AC) powered FFUs, which can have the speed control for the fan (and hence the airflow) adjusted from either the top of the unit or from inside the cleanroom. Other options include gel or gasket seal, HEPA or ULPA filters, particulate/chemical pre-filters, various voltages such as 115V, 230V and 277V, aerosol dispersion mechanisms and attached troffer lighting. There are basically three components to an FFU: the motor, the housing and the filter. Design improvements are focused around these three areas. For example, some motors are more electrically efficient than others; some housings are less expensive; some filters are manufactured in ISO 9001 facilities, others are not. The most significant improvements have come from the motor manufacturers. Initially, the improvements were in AC fan motor electrical efficiencies, whereby some motor manufacturers lowered energy usage by increasing motor efficiencies. Graph 1 indicates the difference in energy efficiency (cost to operate) between two different motors. Motor A is more cost effective from an energy savings standpoint. More recently, FFUs have taken an even greater cost conscious direction. These smart FFUs have a number of new features and benefits over their old style AC counterparts. First, these units are powered on direct current (DC), which reduces energy consumption by as much as 50% when compared to AC powered units. Secondly, these DC or electronically commutated (EC) fan motors can be monitored and adjusted either individually or together using a computerised control interface. By controlling the rpm of the fan motor and hence the airflow of the FFU, the operator has complete control over the systems at all times. Some of these new EC motors have a built in 'smart chip' that detects changes in resistance to airflow through the filter and consequently increases the rpm of the motor to maintain airflow at the originally designed settings. Owing to the longevity or life cycle of most HEPAs and ULPAs in the cleanroom genre, this feature is becoming less attractive as the payback cycle is too long to be economically justified. In addition, this style of motor is not as electrically efficient as others currently on the market. While it is an improvement over the older AC powered units, they are being made obsolete by an even newer 'smart system' motor. Graph 2 compares the energy usage of the 'smart chip' motor to the smart system motor. The smart system motor uses considerably less energy. Another area where the smart FFU excels is with its programmable calendar. This is where the real energy savings can be realized. For example, if a cleanroom fab is producing product on the first shift only, the FFUs can be programmed to power down to a lower rpm during those times when the cleanroom is not in use. If the first shift runs from 8am until 5pm, the computer signals the FFUs to operate at the appropriate rpm and airflow during that time and slow down from around 5:30pm until 6am the following morning. Weekends, holidays and scheduled shut downs can also be programmed into the calendar function. The theory supporting energy savings via a programmable FFU calendar is that of the 'cube law' for fans. This law basically states that if a fan's speed is turned down by 10%, the energy savings for that fan is roughly 30% during this down cycle. Over the course of a year, the savings realized from this energy conservation feature can be tremendous. Energy efficiency is only one aspect of the savings offered by smart FFUs. The DC motors (electronically commutated) are not only far more energy efficient, they also generate far less heat. This translates into capital cost savings for reduced air conditioning equipment to maintain proper temperature control plus additional energy cost savings for reduced cooling requirements during operation. One of the drawbacks of the original FFUs was the noise level of the fans – sound levels above 65dB were typical. Improvements in fan efficiency and sound attenuating features have contributed to units with significantly lower sound levels. Units operating at 50dB and below are now available. These advances in cleanroom technology, most notably with smart FFUs, have resulted in energy savings, cost savings, design flexibility and operating control for cleanroom designers, owners and operators. Further advances with smart FFUs are already in the development stages.
For further information contact Scott Moore at Airguard, tel: +1 502 969 2304; fax: +1 502 961 0930
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