The Pacific Northwest National Laboratory, in the paper "Side Stream Filtration for Cooling Towers" (PNNL, 2012), estimates that substantial energy and water savings can be achieved through the use of a side stream filter on a cooling system. This study predicts a minimum energy savings of 10% and a decrease of blowdown frequency that allows water to be used up to 33% longer before discharge is needed. Side stream filtration with Pathex antimicrobial filter media enhances these benefits by killing and controlling waterborne coliform bacteria in the cooling system. Contact AS Filtration to learn more!

Thermal conductivity is significantly affected by fouling, a thin insulating layer or film that accumulates on heat transfer surfaces. In fact, a fouling layer of just one thousandth of an inch (0.001") increases system power requirements by 10%. Fouling can be caused by biofilm or suspended solid particles that settle on heat exchangers. Side stream filtration with Pathex antimicrobial filter media addresses the suspended solids that contribute to fouling, as well as the bacteria that support biofilm formation. Contact AS Filtration to discuss implementing Pathex and improving heat exchanger performance at your facility.

Outbreaks of the potentially deadly Legionnaires' disease have become an increasingly common occurrence in recent years. According to USA Today, reports of Legionnaires' disease cases have increased by more than five times since 2000. A significant number of these cases are found to have originated in cooling towers with high levels of Legionella bacteria. Testing has shown that filtration through Pathex antimicrobial filter media can reduce levels of Legionella by more than 98%.

Contact AS Filtration and learn how to combat waterborne bacteria using Pathex at your facility!

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.

Conclusions:
The Aqua-Stream™ side stream filter, using Pathex® antimicrobial filter media, proved successful during the year-long study in Chattanooga. The goal of a side stream filter on a cooling tower is to treat the water in such a way that operation is more efficient, both financially and in terms of cooling effectiveness. Bacterial presence in the Chattanooga cooling system was consistently lowered throughout the year to levels significantly below industry standards, commonly exceeding the performance demanded by the cooling industry. As the presence of bacteria encourages the proliferation of other concerns like scaling, fouling, and microbiologically influenced corrosion, its removal results in improved operational efficiency (PNNL 2012). Additionally, the removal of chlorine chemical treatment for the year suspended the corrosive action of oxidizing biocide treatments. The negative environmental impacts of chemical use were also halted. Finally, the financial savings from the use of a side stream filter were estimated to be $10,646 per year, including a savings of approximately 228,000 gallons of water, using the Pacific Northwest National Laboratory formula for a comparable, properly maintained 400-ton cooling tower.

The use of the Aqua-Stream™ side stream filter and Pathex® antimicrobial filter media from AS Filtration™ successfully controlled waterborne bacteria and provided exceedingly beneficial results for the year-long study in Chattanooga. The side stream filtration system would reasonably be expected to continue to improve the condition and operation of the cooling tower system, with minimal maintenance requirements. Several side stream filters utilizing Pathex® have been in continual operation for nearly a decade, with proper maintenance and backwashing, and continue to operate as designed for the control of bacteria in cooling systems. Given the proven benefits of the Aqua-Stream™ side stream filter with Pathex® antimicrobial filter media, its continued use on the Chattanooga cooling tower system would result in ongoing financial savings and improved operational efficiency for many years to come.

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.

Economics:
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).

Contact AS Filtration to find out more about using the Aqua-Stream™ and Pathex® at your facility!

Maintenance and Equipment:
Cooling towers are inherently dirty systems due to their operation and being open to the environment. As explained in a previous entry, cooling towers harbor a constantly increasing amount of contaminants and impurities. Traditionally, this build up would require the cooling tower to be shut down, drained, and the layers of sediment and other deposits to be manually removed. It is not uncommon for a properly maintained cooling tower to undergo this cleaning twice a year, costing extra in downtime, labor, lost water from draining and refilling the system, and additional cleaning chemicals (PNNL 2012). Side stream filtration, by constantly “cleaning” the water within the cooling tower, provides for considerably longer periods of operation between shutdowns for required maintenance actions, drastically reducing the annual cooling tower maintenance costs. In a study at the Oak Ridge National Laboratory, annual maintenance requirements for a 400-ton cooling tower with a side stream filter were 80% less than a comparable tower not using side stream filtration. In this example, the cooling tower with a side stream filter took half a day to be cleaned out by a vacuum truck, while the non-filtered tower took two and a half days to clean (US DOE FEMP 2014).  In addition, keeping the system cleaner extends the life of the equipment, meaning cooling towers and their components can be used longer before needing replacement or maintenance.

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-StreamTM and Pathex® on bacteria, energy use, water use, and overall equipment/maintenance costs.

Neglecting to perform preventative maintenance can degrade cooling tower performance and increase the water and energy required to cool effectively. It can also shorten the life of cooling system equipment. Side stream filtration can help reduce required maintenance and lengthen the amount of time in between maintenance actions. Pathex® further enhances the effects of side stream filtration by killing waterborne bacteria and improving overall water quality within the cooling system.

Contact us today for more information and to learn how to use Pathex® at your facility!

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 (Image 1). 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.

Water:
Water is a fundamental component of any cooling tower system, as it is the medium through which heat exchange is achieved.  Cooling tower operation, with side stream filter placement options, is depicted in Figure 1, below. The Aqua-Stream™ filter at the Chattanooga site is located between the pump and heat exchanger (Option 2, below).  As water passes through the heat exchanger, waste process heat is transferred to the cooler water, allowing equipment to operate without overheating. A portion of this hot water is then evaporated in the cooling tower, with the remaining water being cooled for reuse through the heat exchanger.
Cooling towers consume water in two ways: evaporation and blowdown. Evaporation, as seen above, occurs as part of normal cooling tower operation. Because of this, the remaining water retains a constantly growing concentration of dissolved solids. Blowdown manages this issue by purging the water with high concentrations of solids or minerals, often to the sewer system, and refilling the system with clean (usually municipal) water. The longer water can recirculate through the system before blowdown is required, the less water the cooling tower consumes. Side stream filtration helps manage water usage by constantly filtering and removing the suspended and dissolved particles that lead to blowdown. Logically, this translates into water savings, as less make up water is required to operate the cooling tower.

The next entry will examine the maintenance requirements and equipment costs associated with cooling systems and their operation.

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!

Summary of Study:
Starting 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-StreamTM side stream filter, utilizing their unique Pathex® antimicrobial filter media, on the 400-ton cooling tower system in operation at the office building (Image 1). The goal of this study was to analyze the effects of the Aqua-StreamTM and Pathex® on bacteria, energy use, water use, and overall equipment/maintenance costs.

Overview:
Cooling towers are an important part of many large-scale cooling systems. They typically use evaporation to cool process water, so that the water can be reused to extract heat from the system. Given the purpose of cooling towers, they operate much more efficiently when their heat exchange surfaces are clean.

Cooling towers face four primary water treatment issues that can reduce operational efficiency: corrosion, scaling, fouling, and microbiological activity (PNNL 2012).

• Corrosion – can cause premature structural failures; exacerbated by high oxygen levels  and oxidizing biocide chemicals
• Scaling – precipitation of dissolved minerals; has insulating properties that reduce the efficiency of the heat exchange surfaces; requires more work from the system to achieve desired cooling
• Fouling – insulating film formation on heat exchange surfaces affecting performance and energy requirements of the cooling system; causes include process oils, suspended particles, and biologic growth
• Microbiological activity – can be either suspended or formed on system components; strongly insulating, increasing energy requirements; byproducts encourage further microbiological activity/growth     

All of these can negatively affect operational efficiency and are inter-related, such that an increase or decrease in the severity of one can cause a comparable, parallel change in the others (PNNL 2012). These water treatment issues arise for a number of reasons, including water chemistry, suspended and dissolved solids, dust, and bird and insect activity from the open system.

Multiple reputable studies, including several from the Department of Energy (DoE), have shown that side stream filtration can reduce the prevalence of the concerns described above. These studies also examined the benefits of side stream filtration on water usage, energy consumption, maintenance requirements/downtime, and biological control. Side stream filtration using the Aqua-StreamTM and Pathex® antimicrobial filter media allows for all of these benefits of filtration, with the addition of killing and controlling bacteria and biological activity. The Aqua-StreamTM selected for the cooling tower in this study measures 24 inches in diameter and roughly 80 inches in height, with a total footprint of 36 inches by 48 inches (12 ft2), and utilizes approximately 650 lbs (6.5 ft3) of Pathex® media. The filter operates with its own control system, virtually eliminating the need for any maintenance actions. Pathex® antimicrobial filter media does not degrade and is rejuvenated daily by the filter’s control system through a programmed backwash cycle.
 
The next entry will examine waterborne bacteria in cooling systems and the effect of Pathex® on these issues.