Evaluation of the Aqua-Stream™ Side Stream Filter with Pathex® Antimicrobial Filter Media Part 6: The Economics of Side Stream Filtration
Summary of Study:
Beginning in October 2016, AS Filtration, LLC conducted a year-long study to document the effectiveness of a non-oxidizing biocide within a side stream filter on the cooling tower system of a four-story office building in Chattanooga, Tennessee. AS Filtration installed an Aqua-Stream™ side stream filter, utilizing their unique Pathex® antimicrobial filter media, on the 400-ton cooling tower system in operation at the office building. The goal of this study was to analyze the effects of the Aqua-Stream™ and Pathex® on bacteria, energy use, water use, and overall equipment/maintenance costs.
Side stream filtration offers savings in energy and water consumption, as well as maintenance and equipment costs. The formula used by the Pacific Northwest National Laboratory in the paper “Side Stream Filtration for Cooling Towers” is applied below to simulate the annual energy cost for a 400-ton cooling tower, similar to the one at the Chattanooga site:
A/C tonnage x kW/ton x load factor x hours of operation/year x cost/kWh = energy costs per year
The cooling tower at the Chattanooga site is a 400-ton tower, this example assigns a 50% operating efficiency, a typical 70% load, 3,500 operating hours per year (roughly 40% of the year), and an energy cost of $0.11 per kWh (the actual cost per kWh at the location during the study, according to supplied records). Using these values, the approximate annual operating cost of $53,900 for this cooling tower is calculated as follows:
400 ton x 0.5 kW/ton x 0.7 load factor x 3,500 hours/year x $0.11/kWh = $53,900/year
The Pacific Northwest National Laboratory anticipated the side stream filter to result in a minimum energy savings of 10%, or $5,390 per year. Also, the frequency of required blowdown was expected to decrease, allowing water to be utilized by the cooling tower roughly 33% longer, saving 228,000 gallons per year. Using a combined water cost of $7 per thousand gallons, the actual average cost at the location, this decrease in water demand would result in water cost savings of $1,596 annually. It was also expected to cut required maintenance in half, leading to a conservative estimate of $2,160 of savings per year. All chemical treatment was removed for the study, relying only on the Aqua-Stream™ and Pathex® for water treatment, saving approximately $1,500 per year in chemicals. In total, the installation of this side stream filtration system on a properly maintained cooling tower would result in an estimated savings of $10,646 annually (PNNL 2012).