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.
Cooling towers and HVAC systems in general can be massive consumers of energy, simply due to their size and operation. As discussed in a previous entry, insulating concerns such as scaling, fouling, and microbiological activity can greatly increase the energy required for effective cooling. It has been documented that a fouling layer of just 0.001 inches can increase the required power to achieve cooling by 10% (ASHRAE 1998). Since side stream filtration continuously filters the circulating cooling water, contaminants such as suspended solids, organic particles, silt, and others are constantly being removed from the system. Effectively removing waterborne particulates lowers the probability that fouling, scaling, and microbiological growth will occur, improving efficiency and lowering energy consumption (PNNL 2012). A DoE study conducted at the Oak Ridge National Laboratory (ORNL) found that their side stream filtration system reduced suspended particles in the cooling water by greater than 99% (US DoE FEMP 2014). In the case of the Chattanooga study, potential energy savings are further increased with the use of Pathex® in an Aqua-Stream™ side stream filter by continuously killing a high percentage of waterborne bacteria, further lowering the likelihood of insulating activity within the cooling system.
A 2013 evaluation conducted at a ten-story hotel in Washington, D.C. documented the effects of side stream filtration using Pathex® on cooling system operating efficiency. Performance was measured by the change in water temperature (ΔT) between the inlet and outlet flows in the cooling tower system, with gains in heat transfer (increasing ΔT values) showing improved system performance. Data was collected over the first eleven weeks after installation. As shown in Figure 1, the heat transfer was initially calculated at 2.5°F and improved to 10.1°F over the course of the evaluation.
The increase in the ΔT variable is significant in that a cooling system’s efficiency is directly related to its ability to extract heat. The antimicrobial action of Pathex® in a side stream filter helps improve and maintain effective operation in cooling systems, ultimately resulting in savings on energy and operating costs.
In the next post, we will look at the relationship between cooling system efficiency and water consumption.