Maximize cooling tower efficiency by improving water quality.
All PIM content was independently developed and reviewed to be vendor-, product-, and service provider-neutral.
Managing the concentration of dissolved solids in the water recirculating through a cooling tower can lead to significant water savings.
Project Talking Points
- Depending on the climate, cooling towers can account for up to 25 percent of a facility’s total water consumption.
- Water is lost through cooling towers in four possible ways: (1) evaporation, (2) drift, (3) blowdown (i.e., water discharged from the system, typically to a drain), and (4) basin leaks or overflows. Makeup water must be added to replace lost water and maintain an appropriate concentration of dissolved solids.
- Dissolved solids must be kept at an appropriate level of concentration to avoid scaling, biological growth, and corrosion.
- In many cases, the amount of blowdown for a cooling tower is greater than necessary, resulting in wasted water. This performance improvement measure (PIM) focuses on reducing the blowdown rate by decreasing the amount of makeup water needed to keep solids dissolved. The key is to optimize cooling tower efficiency by finding the right balance between water consumption and concentrations of chemicals and solids in the water.
Triple Bottom Line Benefits
- Cost benefits: Reducing water consumption reduces water and sewer costs. As well, less water used means less water treated, so chemical treatment cost is also reduced.
- Environmental benefits: Reducing the amount of water consumed also reduces the amount of treatment chemicals required, which in turn results in a lower volume of chemicals discharged to the waste stream and the environment.
- Health and safety benefits: Saving money on wasteful and unnecessary tasks saves resources that can be used to accomplish the real mission of the hospital. Supporting water quality and conservation contributes to environmental stewardship and healthy communities.
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- Adjust the cooling tower blowdown rate to maintain total dissolved solids (TDS) at levels recommended by manufacturer specifications. Or, as a rule of thumb, adjust the rate so the system maintains five concentration cycles (the ratio of TDS in the blowdown water compared to TDS in the makeup water). Consult a water treatment specialist to determine a regimen based on the quality of your makeup water and the maximum number of concentration cycles your system can sustain. A water treatment regimen depends on the quality and characteristics of the local water supply (e.g., hard water has more dissolved solids than soft water). Make sure the treatment specialist understands that saving water, without compromising system safety, is your priority.
- Consider installing a conductivity controller to automatically adjust blowdown. The controller will provide makeup water only when the conductivity of the discharge water exceeds a setpoint. Install with a data logger to track system performance.
- Consider installing flow meters on makeup and blowdown lines. Either install them with a data logger or be sure to include regular readings in your scheduled maintenance inspections. Use the data to calculate actual cycles of concentration and compare them with your target number. The data will also be useful for identifying and tracking system leaks and other maintenance issues. Check with your local water utility, as they may be able to source or provide ”deduct” meters which can factor, and then credit back, the amount of water that evaporates from tower operation.
- Identify additional opportunities offered by retrofit strategies to reduce cooling tower water consumption. Examples include:
- Sidestream filtration, which uses external filters to remove sediment from the tower sump. This can be effective in areas subject to dusty atmospheric conditions.
- Automated chemical feed systems, which monitor conductivity. These systems allow precise regulation of chemicals in the makeup water.
- Explore alternatives to chemical treatment, including ozonation, ionization, and UV systems. Contact a representative of your cooling tower manufacturer to review planned system upgrades and to confirm system performance parameters before you begin the work. Some components of the strategies listed can be obtained through the original equipment manufacturer.
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Regulations, Codes and Standards, Policies
- The Uniform Plumbing Code and the International Plumbing Code are the basis for plumbing system regulation in most local building codes. The applicability of local building codes often depends on the size or scale of a retrofit.
- You may also need to consult ASHRAE standards for water-saving improvements to HVAC systems and equipment.
- Due to the urgency of water conservation in California, the state leads the way in terms of regulation. Reference documents include the Water Conservation Act of 2009 and the 20x2020 Water Conservation Plan.
Cross References: LEED
- LEED for Existing Buildings: Operations + Maintenance
- Water Efficiency Credit 4.1: Cooling Tower: Chemical Management
- Water Efficiency Credit 4.2: Cooling Tower: Non-Potable Water Source Use
- LEED for Healthcare: New Construction and Major Renovations
- Water Efficiency Credit 4.2: Cooling Towers
- LEED for Existing Buildings: Operations + Maintenance
Cross References: GGHC
- Operations: Facilities Management Credit FM 2.1-2.5: Potable Water Use Reduction: Total Building Reduction
- Operations: Facilities Management Credit FM 2.8: Potable Water Use Reduction: Cooling Tower: Non-Potable Water Source
- Operations: Facilities Management Credit FM 4.1: Building Operations & Maintenance: Staff Education
- Operations: Facilities Management Credit FM 4.2: Building Operations & Maintenance: Building Systems Maintenance
Cross References: EEP
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- Alliance for Water Efficiency, general water conservation info
- Cooling Technology Institute. The CTI website contains educational and technical materials with a mission “to advocate and promote the use of environmentally responsible Evaporative Heat Transfer Systems (EHTS), cooling towers, and cooling technology.”
- North Carolina Department of Environmental and Natural Resources, Water Efficiency Manual for Commercial, Industrial and Institutional Facilities
- U.S. Department of Energy, Federal Energy Management Program
- Cooling Towers: Understanding Key Components of Cooling Towers and How to Improve Water Efficiency
- Water Efficiency Best Management Practices: BMP #10 - Cooling Tower Management
- Optimize Operations
- Engineering/Facilities Management
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