Background

Air-handling units (AHU) in a semiconductor fab perform a critical role: delivering reliable temperature and humidity control to the manufacturing environment. Even slight variations in a fab’s air temperature and humidity can profoundly affect chip quality, and the cost of downtime is extremely high.

Air-handling systems are also among the largest energy consumers in a fab. As a semiconductor fab in the northeastern United States sought ways to reduce their energy consumption, air handlers were a natural place to focus. The project scope included 137 AHU coils; most units had both hot and chill coils.

Solution

Three cleaning methods are commonly used in air-coil cleaning, each with unique benefits and risks:

• High-pressure water: Cleans efficiently but can drive dirt deeper into the coil pack and bend delicate coil fins
• Low-pressure water: Lessens the risk of damaging coil fins but can be less effective at removing dirt and microbial film. May also increase cleaning time and chemical exposure risk for workers.
• Aggressive chemical applications: Removes metal oxides to create a “shiny clean” look but may not fully remove dirt and microbial film. Harsh chemistry can also increase exposure risk for workers and compromise long-term coil life.

To overcome many of these disadvantages, the fab chose Nalco Water’s patented COIL-FLO program, which includes four key features:

• A balanced mix of 500 psi pressure with low water consumption, which reduces the risk of coil damage and cuts disposal volumes
• Low-alkalinity/surfactant cleaner blend minimizes the volume of water and chemistry needed, and reduces risk of driving dirt into the coil pack. In most cases, wash water is sent to the fab’s sanitary or wastewater facility after cleaning.
• Post-cleaning biocide applied to coil surface and drain pan helps prevent quick recurrence of microbial films, lessens corrosion risk and extends time between cleanings
• COIL-FLO cleanings are conducted by trained, qualified service personnel, using appropriate personal protective equipment (PPE) and safety procedures.

In addition, the COIL-FLO program includes the before, after and periodic monitoring of representative AHUs. These steps establish performance benchmarks, quantify operational improvements and energy savings, and confirm the length of the operating life cycle to help confirm a positive return on the customer’s investment.

For this customer, performance of the COIL-FLO program was validated as follows:

1. Eight representative AHUs were identified and surveyed; direct and indirect measurements were taken before cleaning began.
2. After cleaning was complete, direct and indirect measurements were taken on the same AHUs.
3. Based on this representative sample, overall projections were calculated to quantify annual savings.

Results

Air-side chill coil measurements resulted in an average heat transfer improvement of 11.5% per AHU, valued at $69,881 in annual cost savings.

Energy efficiency improved in the fan systems, too, by an average of 17.95% per AHU. For this fab, that translates to estimated annual cost savings of $48,021.

In all, the COIL-FLO program helped this customer achieve 1.22 million kWh per year in energy savings, valued at $117,902, plus a 900-ton reduction in CO₂ emissions. The customer saw a return on their economic investment in just 1.1 years. Note that these values do not include additional savings derived from a reduction in chilled water requirements.

"Energy Savings by Air Coil Efficiency Improvement” originally presented at SESHA (Semiconductor Environmental, Safety & Health Association) Annual Symposium.