Managing Water Consumption in Cooling Systems - a PDH Online Course for Engineers

Managing Water Consumption in Cooling Systems

Course Outline

Cooling water is commonly used to reject heat from a chiller or manufacturing process. Water use for cooling operations can be very high due to a combination of factors including obsolete process technology, poor recycling and reuse practices and poor wastewater treatment.

Water quality in the tower is dependent on makeup water quality, water treatment, and blowdown rate. Optimization of blowdown, in conjunction with proper water treatment, represents the greatest opportunity for water efficiency improvement.

This 3-hour course discusses cooling water conservation, clean water regulations and general methods to reduce water use and costs. This course is based entirely on the guidelines recommended by San Jose Environmental Services Department and is available on their website link www.sanjoseca.gov/ESD/PDFs/cooling.pdf.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of course materials.

Learning Objective

At the conclusion of this course, the student will:

Understand principle of operation of cross-flow, counter-flow, forced draft and evaporative cooling towers;
Understand the relationship between makeup water, drift, blowdown and cycles of concentration;
Understand how to estimate the evaporation rate (water loss) for open recirculating systems;
Understand how to evaluate water savings by increasing cycle of concentration;
Understand the waste water discharge regulations;
Understand the methods to evaluate cooling water systems including their composition, materials, packing etc;
Understand the parameters used to describe the water quality constituents such as pH, TDS, conductivity, alkalinity etc;
Understand the methods to control scale, corrosion, fouling and micro-biological growth through chemical treatment program; and
Understand the diagnostic indicators for cooling systems and learn routine maintenance / monitoring techniques.

Intended Audience

This course is aimed at engineers, designers, facility managers, energy auditors, environmentalists, H &S professionals, O & M personal, technical and sales representatives.

Course Introduction

Water is the primary element of most cooling systems. Cooling tower is heat exchange equipment that pulls heat from air-conditioning systems and other manufacturing processes while using large amounts of water. It works on the principle of evaporation, where small a small portion of the water is evaporated which cools the remaining water.

By their very design, open recirculation cooling systems are prime candidates for high water use and contamination problems. As the water continues to circulate throughout the system, evaporated water exits the system as pure vapor leaving solids behind, which begin to concentrate over time. This concentration of dissolved solids can lead to what is called scale formation. In a cooling system, the concentration of solids in the re-circulated water increases as replacement (make-up) water evaporates leaving behind even more solids. Left unchecked, the system would reach a point where the water could not hold all of the solids in a dissolved state.

The key to the problem lies in effective management of water resources. An integrated approach involving water treatment, source reduction, reuse of process water, effluent treatment, recycling of treated effluent and waste-minimization is required. As far as possible, makeup water shall be used only to replace unavoidable losses.

This course will review above aspects in detail and will provide you a basic understanding of the different types of cooling water systems, treatment processes and the methods to conserve water.

Course Content

In this course, you are required to study the following guidelines recommended by San Jose Environmental Services Department.

Managing Water Consumption in Cooling Systems

Please click on the above underlined hypertexts to view, download or print the documents for your study. Because of the large file size, we recommend that you first save the file to your computer by right clicking the mouse and choosing "Save Target As ...", and then open the file in Adobe Acrobat Reader.

Course Summary

Cooling occurs in a tower by the mechanisms of evaporative cooling and the exchange of sensible heat. The loss of heat by evaporation (approximately 1,000 Btu per pound of water) lowers the remaining water temperature. The rate of evaporation is about 1.2 percent of the rate of flow of the recirculation water passing through the tower for every 10º F decrease in water temperature achieved by the tower.

Blowdown is a term for water that is removed from the recirculation cooling water to reduce contaminant buildup in the tower water. As evaporation occurs, water contaminants, such as dissolved solids, build up in the water. By removing blowdown and adding fresh makeup water, the dissolved solids levels can be maintained to reduce mineral scale build-up and other contaminants in the tower, cooling condensers, and process heat exchangers. Thermal efficiency, proper operation, and life of the cooling tower are related directly to the quality of the recirculating water in the tower.

Drift is a loss of water from the cooling tower in the form of mist carried out of the tower by an air draft. A typical rate of drift is 0.05 to 0.2 percent of the total circulation rate. Reduction in drift through baffles or drift eliminators will conserve water, retain water treatment chemicals in the system, and improve operating efficiency.

Makeup water is water added to the cooling towers to replace evaporative, blowdown, and drift losses. The amount of make-up water added directly affects the quality of water in the systems. The relationship between blowdown water quality and make-up water quality can be expressed as a "concentration ratio" or a "cycle of concentration." The most efficient use occurs when the concentration ratio increases and blowdown decreases.

Water consumption of cooling towers can be reduced significantly by minimizing blowdown in coordination with an integrated operation and maintenance program. Blowdown is minimized when the concentration ratio increases. Typical concentration ratios are 2-to-3, and generally can be increased up to six or more. The maximum concentration ratio at which a cooling tower can still properly operate will depend on the makeup water quality, such as pH, TDS, alkalinity, conductivity, hardness, and microorganism levels.

Scale, corrosion, fouling, and microbial growth are four critical parameters that must be controlled in cooling towers. Minimum blowdown rates must be determined in tandem with the optimum water treatment program for the cooling tower.

As water use and allocation becomes a topic of growing concern around the world, companies will be required to pay greater scrutiny to the ways water is used within their operations. Fortunately, there is a great deal of information and experience in reducing water use in a cost-efficient manner. It is for the companies to adapt these for human and environmental cause.

Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.