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.

Energy:
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.

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.

Bacteria:
As described in the previous entry, controlling bacterial and microbiological presence can help a cooling system operate more efficiently and limit other undesirable issues. A cooling system with bacterial concerns can also be a health issue, harboring pathogenic bacteria such as E. coli and Legionella. These particular bacteria have been known to cause sickness in humans, with Legionella (responsible for Legionnaires’ disease) having caused dozens of fatal infections in the US alone.

Frequently, oxidizing biocide chemicals such as chlorine, chlorine dioxide, and bromine are used to control biological activity. While typically effective, the chemicals are often hazardous to handle, must be constantly replenished, are harmful to the environment, and can accelerate corrosion within the system (GE 2013). The extensive corrosion seen in Images 1 and 2 occurred over only 8 years, the length of time that the cooling tower has been in service. Prior to the installation of the Aqua-Stream™, chlorine was being used to treat the cooling water at the Chattanooga study site. During the year-long study using the Aqua-Stream™ with Pathex® all chemical treatment was suspended. All water samples were taken and analyzed by an independent laboratory. As shown in Image 3, the concentration of waterborne bacteria increased dramatically once the chemical treatment was stopped in mid-October of 2016, quickly approaching the allowable threshold before the effects of filtration were seen.

The combination of the Aqua-Stream™ filter and Pathex® media maintained a reduced bacterial presence via biological control for the remainder of the study. It is worth noting that during the warmer spring and summer months (when the cooling system is being used the most and bacteria thrive) the Aqua-Stream™ with Pathex® consistently maintained cooling system bacteria levels considerably lower than industry standards. Filtration through Pathex® frequently achieved bacteria counts lower than 100 colonies per milliliter (col/mL), and achieved counts as low as 10 col/mL, one one-thousandth of the industry standards set by the Cooling Technology Institute (CTI 2008).

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 188 recommends water treatment plans for a building’s HVAC and water systems to address these issues. Though the standard itself does not have regulatory authority for pathogen control, it is frequently incorporated into building codes. These results demonstrate the suitability of the Aqua-Stream™ filter with Pathex® media as a critical component of a water management plan to meet or exceed the criteria set forth in ASHRAE Standard 188.

The next entry will focus on energy consumption and how it relates to cooling systems and side stream filtration. If you would like to know more or discuss using the AquaStream™ and/or Pathex® at your facility, please contact us!