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Facility Audit Report 6 San Leandro WWTF 2.2 Control Systems The treatment plant is controlled by Direct Logic 205 Programmable Logic Controllers (PLCs). The operator interface and historical trending system is Citect SCADA software running on IBM PC compatibles. 2.3 Energy Saving Analysis 2.3.1 Aeration Blower Retrofit The facility SCADA system recorded the entire process data essential to perform the audit for blower replacement: discharge airflow and pressure, electrical current for each blower, and DO. On March 3, 2011, the accuracy of the discharge pressure sensor was verified. On March 17, 2011, at each blower, on-site spot power measurements were made to 1) verify the SCADA current readings were accurate; and 2) establish the power factor of each blower and the ratio of measured current to true power. The individual power factors for each blower were used to convert amperage to power. To establish an annual airflow demand and power baseline, one hour samples of the SCADA airflow data, blower discharge header pressure, blower current and dissolved oxygen were downloaded as a time sequence table for calendar year 2010. The two aeration basins are called A and B. Each basin has its own automatic air control valve, air distribution manifold, and airflow meter. The operators switch treatment from one basin to the other periodically. The 2010 airflow data revealed that Tank B was online (used for treatment) from January 1 to April 14 at 12 noon; while Tank A was offline. Tank A was used for treatment for the remainder of 2010 with Tank B offline. Of the Tank A and B air flow signals, the one that periodically drops to zero indicates the air vented to the offline basin. The airflow signal that always has flow indicates the online basin. The blower discharge pressure sensor was not reading correctly during much of 2010, but as noted above, was verified to be operating correctly by March 2011. Therefore, a three week period of SCADA data, from March 3 to March 17, 2011, was also downloaded using 15 minute intervals to establish the relationship between online basin airflow and system pressure, measured at the blower manifold. The system pressure rises with airflow from increased friction, mainly at the diffusers. The airflow performance baseline analysis treats the online basin air delivery separately from the air sent to the offline basin, since the recommended measure will have them supplied with different blower systems. The online air will be referred to as process air in the discussion of results. The process air comprises the vast majority of energy required, and is given the most attention in the analysis. The time sequence 2010 and 2011 blower baseline data was imported into Microsoft Access 2003 for aggregation into airflow bins. The airflow bins were based on process airflow only. The total power of all three blowers was averaged in each airflow bin to establish the baseline power vs. process airflow for the existing Lamson blowers and control system.