Contents. Feature Articles. Special Sections. 6 Data Sheet 73 CTI Licensed Testing Agencies 74 CTI ToolKit. Departments

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3 The CTI Journal (ISSN: ) PUBLISHED SEMI-ANNUALLY Copyright 2008 by The Cooling Technology Institute, PO Box 73383, Houston, TX Periodicals postage paid at Houston, Texas. MISSION STATEMENT It is CTI s objective to: 1) Maintain and expand a broad base membership of individuals and organizations interested in Evaporative Heat Transfer Systems (EHTS), 2) Identify and address emerging and evolving issues concerning EHTS, 3) Encourage and support educational programs in various formats to enhance the capabilities and competence of the industry to realize the maximum benefit of EHTS, 4) Encourge and support cooperative research to improve EHTS Technology and efficiency for the long-term benefit of the environment, 5) Assure acceptable minimum quality levels and performance of EHTS and their components by establishing standard specifications, guidelines, and certification programs, 6) Establish standard testing and performance analysis systems and prcedures for EHTS, 7) Communicate with and influence governmental entities regarding the environmentally responsible technologies, benefits, and issues associated with EHTS, and 8) Encourage and support forums and methods for exchanging technical information on EHTS. LETTERS/MANUSCRIPTS Letters to the editor and manuscripts for publication should be sent to: The Cooling Technology Institute, PO Box 73383, Houston, TX SUBSCRIPTIONS The CTI Journal is published in January and June. Complimentary subscriptions mailed to individuals in the USA. Library subscriptions $20/yr. Subscriptions mailed to individuals outside the USA are $30/yr. CHANGE OF ADDRESS Request must be received at subscription office eight weeks before effective date. Send both old and new addresses for the change. You may fax your change to or vmanser@cti.org. PUBLICATION DISCLAIMER CTI has compiled this publication with care, but CTI has not Investigated, and CTI expressly disclaims any duty to investigate, any product, service process, procedure, design, or the like that may be described herein. The appearance of any technical data, editorial material, or advertisement in this publication does not constitute endorsement, warranty, or guarantee by CTI of any product, service process, procedure, design, or the like. CTI does not warranty that the information in this publication is free of errors, and CTI does not necessarily agree with any statement or opinion in this publication. The entire risk of the use of any information in this publication is assumed by the user. Copyright 2008 by the CTI Journal. All rights reserved. Contents Feature Articles 8 Tracking Molybdate in Cooling Water Vadim B. Malkov 26 The Cost of Noise Robert Giammaruti 34 Architectural Enclosure Influences on the Performance of Field Erected Counterflow Cooling Towers Toby Daley 42 Improved Calcium Phosphate Control for Stressed Systems Gary Geiger 54 Evaluate Your Cooling Tower Richard J. DesJardins 64 Seismic Qualification of Cooling Towers by Shake-Table Testing Panos G. Papavizas Special Sections 6 Data Sheet 73 CTI Licensed Testing Agencies 74 CTI ToolKit Departments 2 Meeting Calendar 4 View From the Tower 6 Editor s Corner 6 Multi Agency Press Release see page...26 see page...8 see page...34 CTI Journal, Vol. 29, No. 2 1

4 CTI Journal The Official Publication of The Cooling Technology Institute Vol. 29 No.2 Summer 2008 Journal Committee Paul Lindahl, Editor-in-Chief Art Brunn, Sr. Editor Virginia Manser, Managing Editor/Adv. Manager Donna Jones, Administrative Assistant Graphics by Sarita Graphics Board of Directors Dennis Shea, President Jess Seawell, Vice President Mark Shaw, Secretary Randy White, Treasurer Gary E. Geiger, Director Robert (Bob) J. Giammaruti, Director Richard (Rich) Harrison, Director Chris Lazenby, Director Frank Michell, Director Ken Mortensen, Director FUTURE MEETING DATES Committee Annual Workshop Conference July 6-9, 2008 February 8-12, 2009 Hyatt Regency, Orange County The Westin, Riverwalk Garden Grove, CA San Antonio, TX July 12-15, 2009 February 7-11, 2010 Marriott Hotel The Westin Galleria Colorado Springs, CO Houston, TX Address all communications to: Virginia A. Manser, CTI Administrator Cooling Technology Institute PO Box Houston, Texas (Fax) Internet Address: CTI Journal, Vol. 29, No. 2

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6 View From The Tower The winter is gone and spring is here. If you build, inspect, test, maintain, treat or operate a cooling tower, summer is fast approaching so this is peak activity time preparing for full operation. The CTI as well is gearing up for the July Committee Workshop in California. The Annual Conference commitment deadlines for the Committee Workshop are fast approaching. Committee chairs are preparing meeting agendas and catching up on details in preparation for the Committee Workshop. It is a busy time for CTI Staff, Board of Directors and yours truly. It is time to reflect for a moment on where CTI is at and where the organization is headed. The CTI Annual Conference was very successful with excellent technical papers, technical panel presentations, owner/ operator seminar, and our training seminar. A great deal of work was also completed during the committee meetings. The addition of working technical meetings at the Annual Conference has increased the face to face time of all our committees. This means that the important work of writing, reviewing or brainstorming new CTI Standards and Guidelines are progressing at a faster pace. The utilization of the new committee organization format has brought about increased participation from Manufacturers, Suppliers and Owner/Operators. As with Denny Shea any organization it is time to look forward to the next question. How can we meet our commitment to the Cooling Tower Industry better? The CTI standing and working committees are working on the future but they need your help. The CTI is in constant need of new ideas and new directions to venture into so we can grow. In the short time since assuming the Presidency, I have had several members offer ideas and suggestions about what they see as needs that the CTI can fill. We would also like to hear about areas where CTI is not fulfilling it obligations. This past year we surveyed the CTI membership to begin the process of understanding the needs of our members. I would like to invite anyone reading this Journal to help CTI by providing input to CTI through your Company Representative, Board of Directors, CTI Office, or myself. It is only through your input and ideas that CTI can meet the objectives of our organization. I hope to see everyone in California for some fun and hard work Denny Shea President 2008/2009 REDWOOD DOUGLAS FIR 24 Hour Service on Your Lumber and Plywood Requirements COMPLETE FABRICATION AND TREATING SERVICE FROM OUR OPELOUSAS, LA PLANT 4 GAIENNIE LUMBER COMPANY BOX 1240 OPELOUSAS, LA (FAX) Member CTI Journal, Vol. 29, No. 2

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8 Editor s Corner The CTI program for thermal certification of cooling towers, and soon for evaporative condensers, is a remarkable program. The program is based on CTI STD-201. From the beginning of the existing program in the early 1990 s, it has grown from a few companies in the United States to 16+ companies with certified lines from Europe, Asia and the Americas. There are 38+ lines certified. More are added on a regular basis, so the numbers quoted above are likely to understate the actual by the time of printing this journal. The CTI certification program is now recognized by both the State of California Energy Commission (in Title 24), and by the US Department of Energy (via its requirement for states to adopt ASHRAE 90.1 or more stringent energy efficiency standards). The CTI certification program is effectively required by law for open and closed circuit cooling towers on air-conditioning applications in the United States. The program is run by Tom Weast, the CTI Certification Administrator. Tom has done a magnificent job of applying his personal integrity and strong work ethic, not to Paul Lindahl Editor-In-Chief mention his legendary skill in keeping costs down, to build a credible and rapidly growing program. CTI owes Mr. Weast a substantial debt of gratitude for the hard work and perseverance applied to getting us where we are with the program. We anticipate continued growth of the certification program as the green initiatives across the new-building construction industry raise concerns for energy efficiency, and validation of that energy efficiency. This is the role that STD-201 plays in CEC Title 24 and ASHRAE STD Carbon footprint concerns are directly related to energy consumption as well. If you have a chance to talk to Tom Weast, take the opportunity to thank him for a very fine job. Respectfully, Paul Lindahl Editor-in-Chief CTI Journal Data a Sheet Introducing a new company, BOLToutlet.com. This company is dedicated to supplying a wide range of cooling tower related hardware, to the cooling tower manufacturer. The owner has been in the hardware business for twenty-nine (29) years and is a second generation of buying and selling industrial hardware. BOLToutlet.com has a program that will bring the best quality and competitive pricing directly to you. They can offer a complete line of cooling tower related bolts, nuts, washers, nails and other products. See their advertisement on page 67. For Immediate Release Contact: Chairman, CTI Multi-Agency Testing Committee Houston, Texas, 1 - May The Cooling Technology Institute announces its annual invitation for interested drift testing agencies to apply for potential Licensing as CTI Drift Testing Agencies. CTI provides an independent third party drift testing program to service the industry. Interested agencies are required to declare their interest by July 1, 2008, at the CTI address listed. Please advise if you have any questions. 6 CTI Journal, Vol. 29, No. 2

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10 Tracking Molybdate in Cooling Water Vadim B. Malkov (Hach Company), Blaine Nagao (ChemCal, Inc.), Steve Dumler (H2TrOnics), Phil Kiser (Hach Company) Abstract Molybdate-based chemicals have been used as corrosion inhibitors in cooling tower systems for several years. Although they provide superior performance, levels of molybdate have been reduced because of large price increases and certain local regulations. It has become more necessary to control molybdate levels to optimize performance versus cost and compliance in corrosion inhibition. A new on-line analyzer has been developed that can measure molybdate as molybdenum (Mo 6+ ) with minimum maintenance. This analyzer can be used to monitor remotely when connected to a data acquisition system with web-based reporting component. Three of these complete systems have been evaluated for several months at beta-testing sites in Texas. Comparisons have been conducted versus bench tests. This paper will discuss results of current testing and some features of the web-based monitoring system with graphs and charts illustrating its performance. Introduction The main purposes of this study were to validate performance of a newly developed process analyzer in real-life conditions when the instrument is maintained solely by customers, and also to determine suitability of the analyzer to application for monitoring Molybdate tracer concentration in cooling water. A secondary goal was to validate projected life time of the colorimeters equipped with new polymeric light pipes. The method employed by the analyzer is a simple and well-known colorimetric method based on use of reaction between pyrocatechol and molybdenum in aqueous solutions (A.I. Busev, Analytical chemistry of Molybdenum, p.202, Ann Arbor Humphrey Science Publishers, London 1969). Pilot version of this analyzer underwent vigorous field testing in spring of 2005 and met all advertised technical specifications (Table 1). However, the testing revealed a short projected life time for the colorimeter. In order to address the discovered issue, an extensive search for new materials and following laboratory testing was undertaken. New polymer implemented for molding light pipes serving to provide unobstructed path between light source (an LED) and photo detector, showed very good stability during one-year-long test (Figure 1) and the colorimeter projected life time was calculated to be minimum of 5-7 years. One limitation of the tested polymer was its relatively high cost; therefore, it was decided to find less expensive materials suitable to the application. Vadim B. Malkov A strategic partnership was developed with a company providing industrial clients with comprehensive service for cooling towers. The company was presented by H2TrOnics Inc. and ChemCal, Inc., which are parts of the same organization. The present field testing was conducted utilizing their customer base, as well as their existing electronic system allowing for remote monitoring of various parameters of cooling water. The system also allows direct interaction with econtrollers over the internet, which enables a degree of control of the treatment processes. The discussed process instrument was named Hach MO42 analyzer. Experiment The present β-test was started on 12/30/2006 at one industrial site in Dallas, TX (Dallas-1). Second MO42 was installed at Cooling Tower #1 at the power plant of University of Texas (UT) in Austin, TX on 01/23/2007, and the third instrument was installed at another industrial facility in Dallas, TX on 04/17/2007 (Dallas-2). The installations are shown in Figures 2-4 below. Initially colorimeters of the tested instruments were equipped with the light pipes made from a cheaper polymer - Sylgard 184 (a registered product of Dow Corning Corporation). However, this silicone rubber had some potential limitations for the application indicated in the data sheet susceptibility to moisture, although it was supposed to be reversible. Nevertheless, the testing was conducted in order to prove or disprove this material s suitability. Eventually, in April of 2007, new colorimeters equipped with light pipes made from more expensive, but proven material (discussed in Introduction) were installed on all three analyzers and the â-test was continued and finished. Reagents and Standards Existing Hach MO42 reagent (p/n ) was used in the test and no standards were involved, because the analyzer did not require calibration. Procedure The analyzers were installed as parts of control panels including several other sensors monitoring various parameters of cooling water. The instruments were set to work unsupervised in the industrial environment. Two bottles of the reagent should provide one month of uninterrupted work and colorimetric cell manual cleaning was to be done by the operators on either monthly basis or as required by their maintenance protocols ma output was used to connect each analyzer to monitoring controller that transmitted the data to a secure server. Then processed data are available for end users through the service provider s web site. The web based application provides access to data generated by all sensors (econtroller), all logs (Operator and Service), and all bench test results manually entered into the system. The system also has statistical tools to display the data in 8 CTI Journal, Vol. 29, No. 2

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12 different formats (Trend Reports) and to compare various parameters to each other. The system provides end customers with very convenient tools for monitoring and controlling their cooling towers remotely from any computer connected to the internet using their unique user ID and password. All data used in present report were collected using this system. Results and Discussion Light Pipes β-test The test of two analyzers (Dallas-1 and UT sites) containing light pipes made from the first tested silicone material lasted for several months (January April) and revealed in general positive results. Main parameter that the customers were interested in was the accuracy, which was expressed in tracking of the bench test results. Bench analysis for molybdate (as Mo 6+ ) was conducted by the operators using Hach Method #8169 according to their laboratory protocols and procedures. Results of the tracking for both sites/ analyzers are presented in Figures 5 through 7 below. Some additional explanations are provided in the titles for corresponding figures. Blue lines on the provided charts represent trends built based upon the bench test results, and as seen from the Figures 5 and 6 the tracking was very good and it made the customers very confident in the instrument. The third instrument started working at Dallas-2 facility just a few days before the colorimeter was replaced, therefore the collected data was considered not representative and was not taken into account. Based on previously acquired knowledge about the instrument performance (discussed in the Introduction), Reference Counts data were collected and analyzed in order to prove acceptable light pipes life expectancy. The reference counts were found in the instrument s menu, manually recorded by the operators on a regular basis (daily through weekly), and then entered into the system. Several following figures below show the reference counts trends reflecting cleanliness of the sample and/or the colorimetric cell, and most importantly the downward trend of the counts values during prolonged time. The deep drop in the counts (circled on Fig. 7) was explained by a dirty cell and following maintenance, which brought the counts back to normal. Based on the slope (Fig. 8) and assuming that the decay rate remained the same regardless of the LED intensity level, the projected life time for these light pipes would be approximately days, which is not acceptable. Removing the outliers makes the slope even steeper. Similar behavior was observed at another β-site (Fig. 9, 10). According to the displayed slope (Fig.10), life expectancy for this colorimeter would be even worse than at the Dallas-1 site. Observed trends for the reference counts basically disproved Sylgard 184 as the material suitable for the application. Apparently, increased sensitivity to moisture/humidity indicated in the manufacturer s data caused some irreversible changes in the light pipes and the observed downward trend has confirmed that. The β-test was continued with new colorimeters equipped with light pipes made out of the more expensive polymer (further called OE4500), which had been tested in Environmental Chamber at Hach Company and proved itself very well. This part of the β-test started on 4/20/07 at Dallas-1 and Dallas-2 sites and on 4/25/07 at UT in Austin, TX. The procedure of the test did not change, thus main information was collected from comparison between bench analysis and MO42 readings as well as the reference counts trends. Since this silicone material had been extensively tested in the lab and environmental chamber, the decision was made to run a shortened β-test. The test results are presented in two groups similarly to the first test results comparison between MO42 readings vs. bench test results and analysis of the reference counts trends (Fig ). It is necessary to mention that the customers consciously used data averaging feature of the analyzer, and therefore, MO42 readings sometimes showed smoother curves than the bench test (Fig. 12). Nevertheless, as seen from Figures 11 13, tracking between bench analyses and MO42 readings was very good and the customers expressed very high level of confidence in the analyzer. At the time of testing the instruments at Dallas-2 and UT sites were used for monitoring only, while the MO42 at Dallas-1 was initially used for partial control of the corrosion inhibitor feed pump. The partial control was accomplished by allowing the controller to base load the tower with corrosion inhibitor at a rate of approximately 80 percent of the theoretical demand. In May 2007, the analyzer was allowed a greater portion of control. The increased level of control resulted in a greater than 20 percent increase in the number of inrange test results as recorded by the on-site operators and the chemical service representatives. The greater control was accomplished by reducing the base loading of corrosion inhibitor and allowing the controller to use the instrument data for a much larger portion of the feed. Feed was on/off control based with a deadband of approximately 0.01 ppm. Growing confidence in the instrument has led to the customers desire to use the other instruments for control of the feed pumps, too. The feedback was received through both the strategic partner and directly from the end users during visiting of the β-sites. When asked about spikes or drops in MO42 readings, customers normally explained it by some maintenance performed on either cooling towers or the analyzers. As seen from all data (Fig. 5, 6 and 11 13) there were not many such situations during the entire test, and apparently, it never affected operation of the towers, therefore the customers never complained. Analysis of possible interfering factors, such as Temperature, ph, Oxidation-Reduction Potential (ORP), Alkalinity, Hardness, iron and copper ions concentration, which might have caused the spikes, or drops, or otherwise a discrepancy between the results, did not reveal any significant or even observable interference. Some examples of such analysis are presented and discussed in the end of this report (Interference Analysis). Next several figures (Fig ) show the trends of the reference counts and comparison with MO42 readings. Drops in the reference counts visible on the charts usually occur due to either dirty sample or the colorimetric cell and do not cause adverse effect to the concentration readings. This conclusion comes clear from a cross-comparison between graphs for each β-site, because it is necessary to see all data: reference counts, MO42 concentration readings and bench test results simultaneously (Fig ). 10 CTI Journal, Vol. 29, No. 2

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14 Separate analysis of the reference counts trends presented in figures and comparison with previously accumulated data on the OE4500 light pipes life expectancy (discussed in Introduction) confirmed previously established 5-7 years time span, which was considered sufficient for this product (see Figure 17). Interference Analysis Several examples of trend analyses for potential interference from other monitored/controlled parameters of the cooling water are presented below. Main parameters analyzed for possible interference were identified to be the Alkalinity, Hardness, Temperature, ph, and ORP of the treated water. Concentrations of disinfectants as well as iron and copper ions present in the sample have also been analyzed from the interference point of view. Explanations for conducted analyses are mostly provided in the titles for corresponding figures below. All data have been obtained from the monitoring system over the internet. Bromine (generated from reaction between sodium bromite and chlorine) is used as disinfectant at this cooling tower (Dallas-1). The disinfectant may not be strong enough to prevent bio-growth (see Fig. 2 overflow pipe). Chlorine in form of hypochlorite is used as disinfectant at Dallas-2 site and there was no bio-film found in the instrument sample preparation system (see Fig. 4 overflow pipe). It is interesting to discuss disinfection of cooling water in some more details. As seen from figures 22 and 23 above as well as from Figures 2 and 4, different disinfectants might change oxidationreduction potential (ORP) of the sample in a different manner and some disinfectants might not be strong enough to prevent biogrowth in the system. However, other factors such as increased corrosion ability of chlorine should be taken into account, therefore application of one or another disinfection agent at specific sites should be thoroughly considered. At UT in Austin, TX chlorine dioxide is used for disinfection (Fig. 24) and as expected it prevents formation of the bio-growth very well, however, it might cause slight interference to the Molybdate analysis (MO42) as shown in figures below. As seen in Figure 25, measured molybdate concentration dropped every time the disinfectant was injected in system that reflected in the spikes of ORP, however, the injections did not affect bench analysis results. According to the customer, the observed drops in first MO42 readings right after the injections were ~ ppm (outside the specified repeatability), while recorded values were lower ( ppm) due to engaged signal averaging feature. Because ph of the water is always alkaline (Fig. 21), it is assumed that ClO 2 is converted into chlorite ions fairly fast, therefore the interference might be caused by molecular chlorine dioxide existing in the system in concentration ~ 0.2 ppm (customer s bench test results DPD bleaching method) during the injections (Fig. 26). It is necessary to mention that after change of the main PCB (software) and the colorimeter, the momentary drops in measured Molybdate concentration (MO42) disappeared (Fig. 27). This observation leads to conclusion that the momentary drops in MO42 concentration readings outside of the specified precision (±0.03 or 3%, whichever is greater) was possibly caused not by chemical interference, but either electronic or optical response to the presence of volatile compounds such as chlorine dioxide. This phenomenon has not been seen at the other β-sites using chlorine or bromine for disinfection. There was no direct correlation found between MO42 readings and sample conductivity (Fig. 28, 29). This actually indicated that the Molybdate tracer concentration cannot be simply monitored by conductivity of the sample, although conductivity provides valuable feedback about other parameters of cooling water. Some correlation was observed between molybdate concentration and concentrations of iron and copper ions in the sample determined intermittently by the bench testing, however, no interference was found (Fig. 30, 31). In the same time, no correlation was observed between MO42 and data obtained from newly implemented corrosion meters for Mild Steel (MS) and Copper corrosion (Fig ). Corrosion rate of the metals is expressed in Mills per Year MPY and reflects presence of the corresponding ions in the sample. The observed inconsistency may be attributed to the trending provided for bench test results by the software and therefore should be disregarded. Follow Up Study Performance of the beta-units was recently checked and it was found that in onc case the instrument helped to identify and repair a mechanical break down of one of the protected systems at a Dallas site. The instrument started showing multiple spikes in molybdate concentration that was not captured by regular bench testing Figure 36. By a coincidence the bench testing was performed at times when the system was working properly (see the marked areas on the chart, Fig. 36) and the malfunctioning went unnoticed for some time. After the problem was discovered and mechanical issue causing chemical to back up in the header was fixed, the system returned to normal operation. Conclusions Analysis of all data accumulated on MO42 performance during two β-tests along with extensive in-lab and environmental chamber testing has shown that the analyzer will perform to the advertised specifications in cooling water applications. The instrument will be suitable for both Molybdate Tracer (~0.5 ppm) and Molybdate Inhibitor (~3 ppm) applications (concentrations as Mo 6+ ). The study has found no interfering factors in cooling water Molybdate Tracer application. The electronic system providing easy access to all data allows for efficient remote data monitoring and analysis, as well as allows controlling the cooling water parameters from any computer over the internet. Acknowledgement The authors wish to thank the operators and managers of the facilities where the study was conducted for their help and patience. The special thanks go to Kevan Decker (University of Texas), and David McDougall (Dow Corning) for their ongoing understanding and support. 12 CTI Journal, Vol. 29, No. 2

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16 Figures and Tables Fig. 1 Reference counts showing rate of decay of the colorimeter. Average slope = -9.6 ± 7.4 (based on calculations for each month of testing and the LED intensity level). Fig. 5 Dallas-1: Results of tracking between MO42 and Molybdate bench testing (blue) from the β-test start through 4/20/07 when the colorimeter and main PCB were replaced Table 1. Molybdate Process Analyzer Technical Specifications Fig. 6 UT: Results of tracking between MO42 and Molybdate bench testing (blue) from the β-test start through 4/25/07 when the colorimeter and PCB were replaced. Fig. 2 MO42 installed at Dallas-1 industrial site. Fig. 3 MO42 installed at UT Power Plant. Fig. 4 MO42 installed at Dallas-2 industrial site. Fig. 7 Dallas-1: Trend analysis for Reference Counts (blue) vs. Molybdate concentration (MO42). 14 CTI Journal, Vol. 29, No. 2

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18 Fig. 8 Dallas-1: Reference counts trend for colorimeter equipped with first tested silicone light pipes (LED level 1). Fig. 11 Dallas-1: Results of tracking between MO42 and Molybdate bench analyses (blue) since the new colorimeter was installed on 4/20/07. Fig. 9 UT: Trend analysis for Reference Counts (blue) vs. Molybdate concentration. Deep drops in the counts were explained by a dirty cell. Following maintenance brought it back to normal. Fig. 12 Dallas-2: Results of tracking between MO42 and Molybdate bench analyses (blue) since the new colorimeter was installed on 4/20/07. Fig. 10 UT: Reference counts trend for colorimeter equipped with first tested silicone light pipes (LED level 1). Fig. 13 UT: Results of tracking between MO42 and Molybdate bench analyses (blue) since the new colorimeter was installed on 4/25/ CTI Journal, Vol. 29, No. 2

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20 Fig. 14 Dallas-1: Reference Counts trend for colorimeter equipped with OE4500 light pipes. Fig. 17 Reference counts and life expectancy analysis for all three analyzers equipped with OE4500 light pipes. Average slope = -6.5 ± 16.5 (both negative and positive outliers removed). Fig. 15 Dallas-2: Reference Counts trend for colorimeter equipped with OE4500 light pipes. Fig. 18 Dallas-1: parallel trends for MO42 (blue) and Alkalinity readings obtained from the analyzer and bench testing (Alkalinity). No interference observed. Fig. 16 UT: Reference counts trend for colorimeter equipped with OE4500 light pipes. Fig. 19 Dallas-1: parallel trends for MO42 (blue) and Total Hardness readings obtained from the analyzer and bench testing (Hardness). No interference observed. 18 CTI Journal, Vol. 29, No. 2

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22 Fig. 20 Dallas-1: parallel trends for MO42 (blue) and Temperature ( F) readings obtained from the analyzer and temperature sensor. The temperature has fluctuated within F (20-28 C) window that fit into the ideal sample temperature range (17-27 C). No interference observed. Fig. 23 Dallas-2: parallel trends for MO42 readings (blue) and ORP readings. No interference observed. Fig. 21 UT: parallel trends for MO42 (blue) and ph readings. No interference observed. Fig. 24 UT: MO42 (blue) and ORP readings obtained through econtroller. Chlorine dioxide is used as disinfectant at this cooling tower. 20 Fig. 22 Dallas-1: parallel trends for MO42 (blue) and Oxidation-Reduction Potential (ORP) readings. No interference observed. Fig. 25 UT: an example of momentary negative interference of ClO 2 injections (blue) to MO42 readings (circled areas). CTI Journal, Vol. 29, No. 2

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24 Fig. 26 UT: Molybdate (MO42, blue) and Chlorine Dioxide concentration trends. No direct interference observed. Fig. 29 UT: Molybdate concentration (blue) vs. Conductivity. No correlation observed. Fig. 27 UT: No interference to MO42 readings (red) after the replacement of the PCB and colorimeter. Fig. 30 UT: Comparison between MO42 readings (blue) and bench test results for Iron concentration 22 Fig. 28 Dallas-1: Molybdate concentration (blue) vs. Conductivity. No correlation observed. Fig. 31 UT: Comparison between MO42 readings (blue) and bench test results for Copper concentration. CTI Journal, Vol. 29, No. 2

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26 Fig. 32 UT: Comparison between MO42 readings (blue) and Mild Steel corrosion trend (MPY). Fig. 35 Dallas-2: Comparison between MO42 readings (blue) and Copper corrosion trend (MPY). Fig. 33 Dallas-2: Comparison between MO42 readings (blue) and Mild Steel corrosion trend (MPY). Fig. 36 Mechanical failure captured by the analyzer at one of the Dallas sites Fig. 34 UT: Comparison between MO42 readings (blue) and Copper corrosion trend (MPY). 24 CTI Journal, Vol. 29, No. 2

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28 The Cost of Noise Robert Giammaruti Hudson Products Corporation Jess Seawell Composite Cooling Solutions, LLC ABSTRACT Today, owner/operators, OEM s and suppliers are facing lower and lower near and far field noise limits with respect to their equipment. However, lost in this race to see who can out quiet who is the impact of cost. Specifically the cost of noise with respect not Robert Giammaruti only to fans, but the fan mechanical/structural parts as well This paper will look at two specific applications, one a bank of induced draft air-cooled heat exchangers and the other being a set of field erected cooling tower cells. In both case studies, the cost of lower and lower near and far field noise will be evaluated with respect to the fan and mechanical and structural components. INTRODUCTION We will look at two case studies here, the first being a 11 bay bank of Air-Cooled Heat Exchangers (ACHEs) and the second being a 8 cell counter flow Cooling Tower (CT). Before getting into the descriptions of the equipment, we will review the assumptions that went into this analysis. The following assumptions apply to both systems unless otherwise noted: The total airflow and static pressure delivered by the fans is maintained as noise is reduced. Noise reduction is achieved solely by speed reduction of the fans and modification of the fans to different blade counts and blade types. No other noise abatement devices were considered and standard motors, gears or drives were employed. Near and far field noise predictions are for fans only. No attempt was made to assess noise generated by the drive/ gear systems, motors or waterfall (cooling tower only). Inlet conditions and tip clearances of the fans remained constant. ACHE near field noise were predicted one meter below the ACHE bank center with all the fans running CT near field noise were predicted between cells 4 and 5 along the centerline of the towers, two meters above the deck level, with all the fans running. Far field noise for both the ACHE and CT were predicted at 100 meters perpendicular to the long side of the units, 2 meters above the ground. The noise correlations used were the same for both the ACHE and CT systems. No additional bays or cells have been added plot area remains constant. Heat transfer surface remained constant. CT water flow remained constant. 26 Jess Seawell Tolerance on near and far field Sound Pressure Level (SPL) and Sound Power Level (PWL) noise predictions are +/- 2 db(a). Tolerance on cost estimates is +/-10% to 15%. Additionally the authors wish to emphasize that, with respect to cooling towers, only fan noise spectrum and reduction was considered here and this paper does not attempt to address the higher frequency water noise. While fan noise can be analyzed without changing the overall system resistance, water noise reduction/suppression requires adding attenuators to the inlet and/or outlets of the cooling tower. These attenuators increase the overall system resistance (i.e. increases motor power draw) and thus add a level of complexity that, while important, was outside the scope and purpose of this paper. However, the authors do agree that the subject of cooling tower water noise should be addressed in the future as a separate paper. Finally, it is acknowledged that other design options are available for noise reduction such as ACHE/CT redesign or other low noise technologies. But as with water noise, our scope here is solely limited to fan noise reduction. AIR-COOLED HEAT EXCHANGER DESCRIPTION The base design air-cooled heat exchanger (ACHE) described in this paper (Figures 1 and 2) is a grade mounted, carbon steel induced draft item built to the API-661 Standard (Reference 1). The ACHE has a thermal duty of 29.3MW (100 Million Btu/hr) cooling light gasoline from 60.3C (141F) to 37.8C (100F) at an ambient design temperature of 32.2C (90F). The item consists of 11 individual bays with 12.2 m (40.0ft) long 25.4 mm (1.0 in) OD carbon steel tubes with extended surface. The extended surface consists of extruded aluminum fins 15.9 mm (0.625 in) high fins spaced at 10 fins per inch. The tubes are spaced in an equilateral tube pitch of 63.5 mm (2.5 in). The individual bays are 4.98 m (16.34 ft) wide with an overall item with of 54.8 m (179.8 ft). Height from the bottom of the tube bundle frame to grade is 2.74 m (9.0 ft). The base mechanical fan drive systems consists of 25 HP, 60 HZ, single speed motors, synchronous belt speed reduction, and 3.96 m (13 ft) fiberglass reinforced plastic (FRP) fans with 4 blades. Each bay has two mechanical drive systems with the entire item containing twenty-two such systems. Figure 1. Induced air-cooled heat exchanger front (inlet) view CTI Journal, Vol. 29, No. 2

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30 Figure 2. Induced air-cooled heat exchanger side view COOLING TOWER DESCRIPTION The base CT described in this paper is an 8 cell, in line, induced, mechanical draft cooling tower (Figures 3, 4 and 5) designed to the applicable CTI standards and guidelines (References 2,3). The tower structure is constructed with fire retardant FRP structural components and incorporates 304 SS hardware for all structural and mechanical connections. The roof deck is FRP with a non-skid surface applied. The interior and exterior casing is 12 oz fire retardant (FR), FRP casing. The tower includes two FR, FRP stairways, one at each end of the tower and one FR-FRP ladder and cage, located in the center of the tower. Cell size is m x m (48 ft x 48 ft), with 1.83 m (6 ft) of low fouling PVC film fill that is bottom supported. The drift eliminators are PVC, cellular type, 0.40 mm (0.015 in) thick; with a maximum allowable drift rate of % of design flow. The tower design flow is 401,254 L/min (106,000 GPM) total with entering hot water of 37.8 C (100 F), exiting cold water of 29.4 C (85 F) and a design wet bulb temperature of 25.6 C (78 F). The base mechanical fan drive systems consists of 250 HP, 480 VAC, 60 HZ, single speed motors, double reduction gear reducers, composite drive shafts and 10 m (32.8 ft), FRP fans with 9 blades. The FR-FRP fan stacks are velocity recover type design, 10 m (32.8 ft) in diameter and 3.05 m (10 ft) in height. Controls consist of low oil level cut off switches and vibration switches with manual and remote reset features mounted on the gear reducer. The tower is installed on a customer supplied concrete basin with a basin depth of 1.22 m (4.0 ft). Figure 5. Cooling tower end view CASE 1 AIR-COOLED HEAT EXCHANGER Table 1 lists the common operating parameters of all the ACHE fans studied. Table 2 lists the base case fan condition along with the lower noise options listed in order of decreasing noise. Table 1. ACHE fan-operating parameters. Figure 3. Cooling tower front view Figure 4. Cooling tower top view Table 2. ACHE fan-operating conditions in order of decreasing noise. As one can see from Table 2, the fan speed was lowered to approximately 50% of the base design while the fan shaft power remained fairly constant. Fan speed was varied in approximately 10% increments by a combination of drive ratios and motor speeds to achieve the required noise reductions. Multiple fan selections were performed for the STD, VLN and ULN fans types as applicable to achieve the overall most cost effective solution at that particular 28 CTI Journal, Vol. 29, No. 2

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32 speed. Cost increases were estimated for fan Cases 1 through 8 taking into account changes (if any) in fan, motor, drives, mechanical structure and fan rings. The cost increase estimates were then plotted against the near and far field SPL noise predictions as shown in Figure 6 below. Figure 6. ACHE bay cost increase vs. near and far field SPL The overall ACHE cost per bay significantly increases as noise is decreased with the lowest noise option increasing the per bay cost by approximately 35%. Given the non-linearity of the data (a general 3 rd order polynomial was used to trendline the data) one can see that the cost increase accelerates faster for a relative steady decrease in noise. Put another way, the first 10 db(a) of far field noise reduction increased the overall cost per ACHE bay by about 4% from the base design. However the next 10 db(a) increased the cost 20% from the base design. The majority of this increase is related to the fan and depending on the type of fan (VLN or ULN See Figure 7 for a general size comparison) will range from 70 to 90% of the total increase. This is shown below in Figure 8 where the costs increases are plotted as a function of fan sound power level. Figure 8. Percent cost increase split between fans and mechanicals the total cost increase as noise is reduced. However, every situation is unique and the owner/operator is encouraged to investigate all possibilities with the OEM/Supplier. CASE 2 COOLING TOWER Table 3 lists the common operating parameters of all the cooling tower (CT) fans studied. Table 4 lists the base case fan condition along with the lower noise options listed in order of decreasing noise. Table 3. Cooling Tower fan-operating parameters. Figure 7. Size comparison of standard noise (foreground), very low noise (middle) and ultra low noise (back) fan blades The variance shown in Figure 8 is simply a function of the design points chosen. For example, at the 92.7 db(a) SPL point, nearly 30% of the cost increase is due to non-fan components due to the fact that the fan, in this instance, did not change as the speed was reduced. However, when looked at in total, this combination of fan, motor, drives and so forth provided the least amount of overall cost increase. Another factor is the fan material. Aluminum fans tend to be less costly than FRP fans and will move the cost split more towards the non-fan components. A good rule of thumb is that the fan will account for approximately 70% (Aluminum) to 85% (FRP) of 30 Table 4. Cooling Tower fan-operating conditions in order of decreasing noise. As one can see from Table 4, the fan speed was lowered to approximately 60% of the base design while the fan shaft power remained fairly constant until Cases 6 and 7. Here the lower efficiencies of the ULN fans significantly increased the required fan shaft power. This is not uncommon for these types of fans as the goal is normally lowest possible noise, not power optimization. It should be noted here that it is highly unusual for a client to accept 300HP motors and in most cases, additional cells or other methods will be employed by the CT OEM to stay at or below 250 HP motors. However, for the purposes of this analysis we have assumed that the client will accept the larger motors. CTI Journal, Vol. 29, No. 2

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34 Fan speed was varied in approximately 10% increments (Base Case to Case 4) by a combination of gear ratios and motor speeds to achieve the required noise reductions. Cases 5, 6 and 7 were the lowest speeds possible for the given CT operating conditions. Multiple fan selections were performed for the STD, LN, VLN and ULN fans types as applicable to achieve the overall most cost effecting solution at that particular speed. Cost increases were estimated for fan Cases 1 through 7 taking into account changes in (if any) fan, motor, gears, mechanical structure and fan stacks. This cost increase estimates were then plotted against the near and far field noise predictions as shown in Figure 9. The overall CT cost per cell significantly increases as noise is decreased with the lowest noise option increasing the per cell cost by approximately 30%. Given the non-linearity of the data (a general 3 rd order polynomial was used to trendline the data) one can see that the cost increase accelerates faster for a relative steady decrease in noise. Put another way, the first 10 db(a) of far field noise reduction increased the overall cost per CT cell by about 9% from the base design. However the next 3.4 db(a) increased the cost 28% from the base design. Figure 9. CT cell cost vs. near and far field SPL The majority of this increase is usually related to the fan and, depending on the type of fan, will range from 20 to 80% of the total increase. This is shown below in Figure 10 where the costs increases are plotted as a function of fan sound power level. Figure 10. Percent cost increase split between fans and mechanicals The variance shown in Figure 10 is simply a function of the design points chosen. For example, at the db(a) SPL point, nearly 80% of the cost increase is due to non-fan components due to the fact that the fan cost, in this instance, did not increase that much relative to the speed reduction. In this case, it was the gear driving the cost increase, as it was necessary to move up to the next box size. However, when looked at in total, this combination of fan, motor, gears and so forth provided the least amount of overall cost increase. A good rule of thumb is that the fan will account for approximately 60% of the total cost increase as noise is reduced. However as mentioned in Case 1, every situation is unique and the owner/operator is encouraged to investigate all possibilities with the OEM/Supplier. SUMMARY As presented in the two cases herein, the cost of noise, in this case lower noise, significantly impacts the cost of an ACHE or CT depending on how low and where the noise guarantee points are located. And while significant near and far field noise reductions is achievable (in these cases without adding ACHE Bays or CT Cells), as the curves show, the increase in cost is not a linear function but rather a 3rd order polynomial that accelerates quickly as one reduces the noise levels. While this analysis is far from exhaustive, the authors hope this paper provides the reader with some perspective in the realm of ACHE and CT fan noise. As the old adage goes there are no free lunches with the same being true here. However, in this instance, the cost of lunch will probably increase rapidly compared to what you receive in return. REFERENCES 1. American Petroleum Institute, Air-Cooled Heat Exchangers for General Refinery Service, API Standard 661, Sixth Edition, February Cooling Technology Institute Standards 111,131, 136, 137 and Cooling Technology Institute ESG CTI Journal, Vol. 29, No. 2

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36 Architectural Enclosure Influences on the Performance of Field Erected Counterflow Cooling Towers Toby Daley Composite Cooling Solutions, L.P. Abstract Architectural enclosures for cooling towers are not new phenomena. Ideal clearances are provided by manufacturers to achieve the rated performance. However predicting the tower capability when the clearances are less than ideal can be complex. This paper will present a study of an architectural louver enclosure and its influence on the performance of the tower when less than ideal clearances are achievable. Introduction Locating a cooling tower inside of an enclosure is not a new idea. It has been the goal to hide the cooling tower from sight especially on architecturally sensitive projects. As a result, architectural concrete cooling towers were introduced. Utilization of these towers has created some very remarkable and impressive architectural structures that blend in with the building. As construction costs increased for concrete towers in the 1970 s and 1980 s a new type of tower constructed of Pultruded fiberglass was introduced. It was designed to replace concrete construction. The Pultruded fiberglass tower provided the durability and longevity of concrete but substantially less in weight. The additional benefit was the ability to create an architecturally pleasing tower which would not require a screen wall or enclosure. Thousands of concrete towers have been constructed since the 1940 s and architectural fiberglass towers from However, the vast majority for HVAC and architectural applications are still enclosed in some type of a surround or enclosure wall. The types of towers range from factory assembled to field erected and crossflow to counterflow and metal to wood to fiberglass. The purpose of the enclosure is to make the tower disappear and/or provide sound attenuation. However, in most cases the pursuit of hiding the tower overrides the basic need of a cooling tower which is to receive and discharge the required air volume in a uniform pattern. In the past ten to fifteen years HVAC cooling tower applications have grown in size in response to chiller manufacturers supplying larger chillers. Thus, it is not uncommon today to see massive central district cooling plants approaching 650,000 tons in capacity and utilize large field erected counterflow cooling towers. They are limited in available real estate and located in populated areas and subsequently the towers are located on the roof of the plant and must be enclosed. Sound is an issue in many locations and sound attenuators are often added to the inlet and discharge which adds additional air blockage to the tower. In most cases the roof is also limited in space and thus the space for the cooling tower is con- Toby Daley stantly shrinking. The end result is the tower is placed in a location that is usually not free from influences caused by obstructions. This paper will present some fundamental considerations involved which should be addressed when placing a cooling tower in an enclosure and the potential influences on performance if not properly addressed. Types of Enclosures Depending upon the type of facility there are two basic types of enclosures or a combination of the two. Basic Types of Enclosures Solid Wall The tower is completely surrounded by a solid wall. Porous Wall The tower is completely surrounded by a wall that air can pass through. Solid Wall Enclosure - A solid wall enclosure can only receive air from above. Thus, the cooling tower is discharging air into the same air space that the tower is trying to pull air into the air inlets. The obvious problem with this type of installation is the tendency for the discharge air to recirculate into the air inlets and thus degrading the thermal performance. If the enclosure wall is higher than the top of the fan stack then the recirculation influence is much greater. This would be most prevalent when cross winds and/ or inversions are occurring. Porous Wall Enclosure This enclosure can be constructed of limitless materials and shapes. When a cooling tower is placed in this enclosure the air is drawn both through the louver wall and vertically from above the tower. The following lists the most basic types. Basic Types of Porous Wall Enclosures Architectural Concrete Wall This type is usually a geometric pattern of openings built into a wall. The entire wall can be porous or it can be a combination of porous and solid. Architectural Louver Panel Wall This type is usually constructed of commercially available panels comprised of blade type louvers. The panels can be oriented in an exhaust or intake configuration. The intake configuration is used when air is entering the enclosure. The exhaust configuration is used when air is discharged or venting an enclosure. Depending upon the size of the project and the local structural design parameters the panels can require a substantial amount structural steel framing for support. 34 CTI Journal, Vol. 29, No. 2

37 Perforated Screen Wall This type of panel is constructed of a perforated material which may be combined with free open areas to create the architectural effect. This type of enclosure will also require structural framing to provide support for the screen. Solid Wall Enclosure When rating or selecting a tower for placement within a restricted enclosure there are three basic influences that must be considered. Basic Influences on Performance Net Free Open Area The net free open area of the air pathway to the air inlets of the tower must be taken into account. Blockage Resistance in air flow can exist due to enclosure structural framing, external walkways, common header piping, valves, and pumps. These block the air path and increase the inlet velocity, pressure, and cause mal-distribution of air. Clearances The clearance between the tower air inlet and the enclosure wall determines how the air volume will be balanced between the air approaching from above the tower and / or the air approaching through the porous wall. Architectural Louver Wall Perforated Metal Screen Enclosure Free Open Area, Blockage and Clearances The following sketch presents a typical installation where the tower is located in a restricted environment. The Impact on Thermal Performance can occur in two ways. Type of Influence Increased Pressure Drop The tower as located could possibly not have an ambient air inlet pressure as a starting point. Thus, additional system pressure prior to the air inlet was not included in the tower design. This would translate to not being able to achieve the required air flow for the tower. CTI Journal, Vol. 29, No. 2 35

38 Mal-distribution of Air If the tower does not have proper clearances or is influenced by blockage then the air entering the tower may not be as uniform as a free field environment under which the tower was rated. The mal distribution can translate into areas of the fill material being bypassed or underutilized. This can cause two problems 1) increased static pressure as a result of high localized velocities and 2) hot water bypass in areas of the fill that are being bypassed. Recirculation A major impact on performance is the recirculation of the discharge air back into the fresh air inlets. Recirculation increases the wet bulb temperature of the air entering the tower. If the tower was designed for a 78 F Inlet Wet Bulb temperature (IWBT) and the recirculation is increasing the IWBT to 80 F then the tower performance capability will still be 100 % based upon the manufacturer s performance curves. However, colder water could be achieved if the recirculation was not occurring. Thus, the energy efficiency of the total system suffers. Recirculation can occur due to wind forcing the discharge air stream to turn back into the enclosure and the tower air inlets. If the clearance between the tower and the enclosure walls is not sufficient, then the greater the downward air velocity next to the wall. The higher this downward velocity compared to the tower discharge velocity, the greater the recirculation tendency. Secondly, the height of the enclosure wall also influences the magnitude of recirculation. If the wall exceeds the height of the stack, then the greater the tendency of mild wind conditions to cause recirculation of the hot discharge air back into the fresh air intakes. Structural Framing for support of the louver wall can present major blockage for the tower air inlet. Architectural Louver Selection- The architectural louver should be selected with consideration of the tower type and available clearance. If the tower is located less than the manufacturers recommended distance from the louver wall then the louver can directly impact the tower performance. It is often the misconception that if you select a louver with a reasonable percent free open area then the tower will be okay. However, an architectural louver can have an acceptable percent free open area but still have an unacceptable pressure drop. The direction of the louver can also impact how the air enters the tower. Improper orientation can cause the air to take multiple turns causing an increase in pressure and potential air mal-distribution. It is important to understand the basis of the louver manufacturer s pressure drop curves. If it is based upon net velocity then the pressure drop should be calculated using the velocity associated with the predicted louver air flow volume and the net free open area. The net free open area should also include reduction for structural framing which blocks the tower air inlet. Additionally, there is a pressure drop curve for an intake or an exhaust orientation. The following is an example of three architectural louvers and the range of variability that can occur when making a selection based upon free open area only. Air Inlet Blockage Due to Structural Framing for Louver Enclosure Roof Top Installation with Louver Wall Enclosure Louver Model B and C are very close to the same free open area but Louver C has a 34% higher static pressure due to its more restrictive shape. Louver A has a velocity pressure coefficient less than louver B but only 37.6% free open area. It has the highest static pressure because of the higher net velocity. Air Balance Equilibrium and Effective Louver Height - When a tower is located in a louvered enclosure the air flow through the air paths will reach an equilibrium point. At equilibrium the actual amount of air that is delivered through the louvers and through the vertical well (the area between the tower and the louver wall) will be established. 36 CTI Journal, Vol. 29, No. 2

39 At equilibrium the effective height of the louver wall will not be the full height of the wall. If, for example, the height of the louver wall is 30 feet only a portion of the wall would be utilized by the air path. This effective louver height is different for each installation and is dependent upon the parameters previously discussed. If you were to expect all of the required air to pass through the louver wall and chose a louver with a free open area of 50% then you would need an effective louver area equal to twice the tower air inlet area to simulate a free field environment. Or the net velocity of the louver wall equals tower air inlet velocity. The following presents net velocity limits based upon experience with architectural louver installations and large counterflow cooling towers and practical clearances that can be achieved. A modeling system was developed which solves for the equilibrium point of the air flow streams for specified distances away from the tower. The tower, enclosure and louver characteristics are entered into the model. The analysis results in a recommended distance from the enclosure wall. The following is the model for the example tower, installation and Louver A. \ Selecting the Proper Distance - Selecting the correct distance to locate the tower from the louver wall influences the tower performance. Whether in a solid or porous wall arrangement the velocity and trajectory of the air approaching the air inlet will determine the uniformity of the air flow in the tower. If the tower has louvers the type of louvers will also influence the trajectory. Tower manufacturers have recommended velocity limits for the well and louver velocity which ultimately defines the required distance. If these distances are achievable then the tower rating is applicable. The following table presents some example of published velocity limits. In this example only 20% to 30% of the air is passing through the louvers. Thus, 70% to 80% of the air is coming from the vertical well. Even if the tower was located closer to the louver wall the air flow would equalize at only 38% to 48% through the louvers and the well velocity would be on the order of 950 to 1100 FPM. Thus, the velocity limits not only influence the tower performance by improved air flow distribution but also by minimizing recirculation resulting from high vertical well velocities. CTI Journal, Vol. 29, No. 2 37

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42 However, if the recommended distance is not achievable then a more complex study involving computational fluid dynamics modeling is required to predict the deficiency in performance. It is not uncommon for the tower capability to be reduced to 85% when it not properly placed in the enclosure. The graph below presents the potential deficiency if the tower and louver are not optimized for the installed clearances. Enclosure Checklist for Field Erected Cooling Towers The following is a recommended checklist when designing an enclosure for a field erected counterflow cooling tower. Select the type of enclosure such as solid, louvered, porous or a combination. Define the space available for the tower and walls that will be solid, louvered or porous. Select the architectural louver type and obtain the % free open area and static pressure curves. Determine the structural framing required for both horizontal and vertical support of the louver wall that needs to be factored into the net free open area. Determine in general the plan for the tower supply and return piping that needs to be factored into the net free open area. Determine in general the plan for access to and around the tower that needs to be factored into the net free open area. Contact the cooling tower manufacturer and provide the above information along with the thermal duty requirements and any special requirements such a specific number of cells, horsepower limits, etc. Request that the tower manufacturer provide you with recommended o Size and quantity of cells for the thermal duty. o Clear distance required from the tower to the enclosure walls. o The predicted capability of the tower if the available space cannot accommodate the required distance. Conclusions In concluding, the performance related influences can often be overlooked when placing cooling towers in restrictive enclosures. The key variables to address are air pathways, velocities, trajectories, clearances, obstructions and recirculation. The prediction of these influences is complex but is predictable using custom analysis techniques. A successful result is dependent upon properly selecting the louvers and tower for optimum performance in the installed environment. If an analysis is not performed then at least consideration should be given to increasing the tower size in an attempt to compensate for these influences. IF YOU BLOCK THE AIR TO THE COOLING TOWER THE THERMAL PERFORMANCE WILL BE IMPAIRED 40 CTI Journal, Vol. 29, No. 2

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44 Improved Calcium Phosphate Control For Stressed Systems Gary Geiger, Caroline Sui Water and Process Technologies GE Infrastructure 4636 Somerton Road, Trevose, PA ABSTRACT Inorganic phosphate is the most widely used mild steel corrosion inhibitor for open recirculating cooling water systems. However, effective control of calcium phosphate precipitation must be maintained both in the recirculating cooling water and at heated surfaces, if corrosion is to be controlled without a loss of heat transfer efficiency. Over the past 30 years notable advances have been made in polymeric dispersant technology that have improved calcium phosphate control. This paper discusses the performance of a recently developed polymer that has shown excellent performance under stressed conditions. Keywords: deposit control, corrosion control, stabilized phosphate, polymer, phosphate, azole, cooling water, cooling tower, high cycle, and stressed water condition INTRODUCTION Cooling water treatment programs must control corrosion, deposition and microbial activity to maintain heat transfer efficiency and avoid premature corrosion failures of process equipment. All three areas of concern are interrelated and must be simultaneously addressed. Excessive steel corrosion will result in flow restrictions and the accumulation of iron corrosion products that impede heat transfer. Soluble iron released at the corroding surface can poison polymeric dispersants, resulting in diminished efficacy and the formation of iron phosphate deposits. Deposits not only impede heat transfer, but also are responsible for premature corrosion failures due to under-deposit corrosion mechanisms. Deposits provide a safe haven for anaerobic bacteria that are responsible for microbiologically influenced corrosion (MIC). Both sessile and plaktonic bacteria control are necessary to prevent slime forming bacteria from establishing biofilms that restrict heat transfer and provide a protective environment for the colonization of anaerobic bacteria. Open recirculating cooling water circuits are typically mixed metallurgy systems containing both carbon steel and copper-based alloys. Electrochemical corrosion of these metals involves both anodic and cathodic corrosion reactions. Metal loss occurs at the anode and oxygen reduction occurs at the cathode. (Oxygen reduction at the cathode is the primary reaction with air-saturated waters operating at neutral to alkaline ph.) For ferrous metals, soluble iron is released at the anode and hydroxide anions are generated at the cathode. For corrosion to proceed, the anodic and cathodic reactions must occur simultaneously and at the same rate. Corrosion protection is achieved by inhibiting either or both reactions. 1 Gary Geiger Inorganic phosphate is the most widely used steel corrosion inhibitor for open recirculating cooling systems. Orthophosphate suppresses both the anodic and cathodic corrosion reactions. High dosages of orthophosphate (12-20 ppm) catalyze the formation of a protective oxide film, that retards the anodic corrosion reaction. 2.3 Orthophosphate restricts electron transfer at the cathode through the formation of an insoluble calcium phosphate film. Orthophosphate-based corrosion programs may include the addition of polyphosphate (pyrophosphate or hexametaphosphate) and/or zinc to enhance cathodic corrosion inhibition and guard against lo- calized corrosion. The use of polyphosphate is favored where discharge restrictions limit or preclude the use of zinc. Like orthophosphate, polyphosphates form insoluble calcium salts at the cathode due to the localized high ph. Corrosion inhibitor programs for mixed metallurgy systems containing both copper and iron alloys will include an azole. Azoles form a protective chemisorbed film on the copper surface and inhibit the cathodic corrosion reaction, although there is some evidence that they also retard the anodic reaction. 4,5 If copper corrosion cannot be adequately controlled, steel corrosion will suffer. As copper corrodes, copper ions enter the bulk cooling water and will plate on carbon steel surfaces forming galvanic corrosion cells. This results in severe localized corrosion (pitting-type) of the steel surface. The commercially available azoles are benzotriazole (BZT) and tolyltriazole (TTA). A proprietary halogen resistant azole (HRA) is also available. 6,7,8 The use of inorganic phosphate for steel corrosion protection requires an effective calcium phosphate precipitation inhibitor to maintain the phosphate soluble in the bulk cooling water and prevent deposition at heat transfer surfaces. Effective polymeric inhibitors/dispersants for calcium phosphate were first developed in the late 1970 s. Since that time, a wide variety of copolymers and terpolymers have been introduced that have expanded the role from calcium phosphate inhibition to particulate fouling control. However, the primary role of the polymeric dispersant in an inorganic phosphate-based program is to prevent calcium phosphate formation. Calcium phosphate demonstrates retrograde solubility with both ph and temperature. At any given level of calcium hardness and phosphate, the dosage of the dispersant is dictated by the temperature of the hottest process equipment and the operating ph range, if scaling is to be avoided. Precise ph control is required to minimize high ph swings and avoid exceeding the control capabilities of the inhibitor. Microbiological (MB) control is extremely important in maintaining efficient and reliable equipment operation. If unchecked, microorganisms can accumulate and form slime deposits on heat transfer 42 CTI Journal, Vol. 29, No. 2

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46 equipment, transfer piping, tower fill and decking, etc., causing a loss of heat transfer efficiency as well as promoting under-deposit corrosion. Some microbes also pose significant health concerns while others can degrade water treatment chemicals. There are numerous approaches for MB control including the use of halogens (chlorine, bromine), organic biocides, (both oxidizing and nonoxidizing), ionization, and UV (electromagnetic radiation). Of these, chlorine is by far the most cost-effective, being far less expensive than non-oxidizing biocides and certain stabilized bromine treatments. Chlorine gas, when dissolved in water, hydrolyzes quickly to form both hypochlorous and hydrochloric acids. The former is also generated when using hypochlorite solutions (bleach) instead of dissolving chlorine gas in water. Hypochlorous acid is a weak acid, which can undergo further dissociation to a hydrogen ion and a hypochlorite ion. While both hypochlorous acid and the hypochlorite ion are oxidizing agents, the former is more germicidal. Its effectiveness is attributed to the ease in which the molecule can penetrate the cell wall of a microorganism. Hypochlorous acid has a similar structure to that of water and can thereby permeate the cell wall. Both hypochlorous acid and hypochlorite ion can degrade organic deposit control agents and corrosion inhibitors. Chlorine tolerant treatment additives can allow the unrestricted use of chlorine for MB control, reducing the costs associated with non-oxidizing biocides. If the organic treatment components (polymeric dispersant, azole) are susceptible to chlorine oxidation, the free chlorine residual must be closely control to avoid excessive treatment degradation. This paper focuses on laboratory generated application data for a recently developed stress tolerant polymer (STP) for neutral ph, high phosphate treatment programs. STP represents the culmination of over 30 years of GE Water & Process Technologies polymer research. LABORATORY SCREENING & POLYMER EVALUATION The advanced scale control chemistry, referred as stress tolerant polymer (STP), was evaluated in the laboratory and compared to a sulfonated acrylic acid copolymer (SAA) and other commercial copolymers and terpolymers, designated polymer A, B, C, and D. The majority of the comparative studies were performed with the SAA polymer since its performance was comparable to that of the other commercially available polymeric dispersants in calcium phosphate beaker studies. The SAA polymer is one of the most widely used commercial calcium phosphate inhibitors. Evaluations were conducted using a static beaker test protocol and a dynamic Bench Top Unit (BTU) protocol. Static beaker tests are designed to be a screening tool that can quantify the relative efficacy of calcium phosphate inhibitors. The BTU is a recirculating system incorporating a heat transfer surface to assess deposition. Both testing methods have been described in prior papers. 9 BTU tests are designed to simulate a severe system condition. Bulk water and heat transfer surface temperatures are controlled, ph is monitored and controlled, and corrosion rates of low carbon steel (LCS) and Admiralty brass (ADM) are measured with test coupons. The BTU is not an evaporative system, so it does not simulate an open recirculating system. The BTU simulates a heat exchanger that is constantly recirculating hot water (120 O F) for cooling. The unit uses a heat exchanger tube fitted with an electrical heater to 44 adjust the surface temperature and a cooling coil to remove excess heat and maintain the temperature of the recirculating water. The system retention time (holding time) is controlled by adjusting the rate of makeup to the water reservoir. Test results using the two methods are discussed in detail in the paper. 1. Static beaker tests A. Calcium Phosphate Inhibition Testing Calcium phosphate inhibition studies were conducted under standard water conditions. The standard test water contained 400 ppm (mg/l) Ca, 100 ppm (mg/l) Mg, 35 ppm (mg/l) M-alkalinity (all as CaCO 3 ), 10 ppm (mg/l) orthophosphate, and the polymer under evaluation. Each solution was adjusted to ph 8.2 and placed in a water bath controlled at 158 O F (70 O C) for a period of 18 hours. The solutions were then filtered through a 0.2 micron filter and the filtrate analyzed for soluble phosphate. Percent inhibition of calcium phosphate was then calculated for each polymer relative to a control sample without treatment. The polymers were evaluated at dosages of 5, 10 and 15 ppm (mg/l). The stress tolerant polymer (STP) was compared to a sulfonated acrylic acid copolymer (SAA) and four other commercially available polymers (A, B, C & D). As shown in Figure 1, the STP polymer was highly effective even at a dose rate as low as 5 ppm. SAA provided greater than 95% inhibition at 10 ppm, while the other commercial polymers gave less than 10% PO4 inhibition at dose rates equal to or less than 10 ppm. These results clearly demonstrated the superior performance of the STP compared to SAA and other commercial polymers. B. Calcium Pyrophosphate Inhibition Testing Pyrophosphate is included in many neutral ph programs to fortify cathodic corrosion inhibition. The use of pyrophosphate is limited by calcium pyrophosphate solubility concerns, similar to orthophosphate. To exploit its properties as a corrosion inhibitor, the pyrophosphate dosage must be adjusted based on the calcium hardness of the cooling water and take into consideration its reversion to orthophosphate. Polyphosphates revert (hydrolyze) to orthophosphate and the degree of reversion is a function of temperature, ph and system holding time. Calcium pyrophosphate inhibition efficacy was evaluated at ph 8.2 with a 400 ppm (mg/l) calcium hardness water containing 10 ppm pyrophosphate (as PO 4 ). The solution was placed in a water bath controlled at 158 O F (70 O C) for a period of 18 hours. The solution was then filtered through a 0.2 micron filter and analyzed for total inorganic phosphate. The percent inhibition was calculated for the STP and SAA polymers relative to a control sample without treatment. The polymers were evaluated at dosages of 5, 7.5, 10, and 15 ppm (mg/l). The degree of reversion of pyrophosphate was determined by measuring the amount of orthophosphate at the end of the test period. Reversion was less than 20% (2 ppm). A comparison of polymer performance demonstrates that the STP polymer provides a greater degree of stabilization than the SAA copolymer. The SAA copolymer was ineffective below a dosage of 10 ppm, while the STP polymer provided nearly complete inhibition at the lowest dosage tested (5 ppm). Figure 2 summarizes the doseresponse data. 2. Bench Top Unit Evaluations The STP and SAA polymers were further evaluated at neutral ph under recirculating, heat transfer conditions in the BTUs. The BTUs CTI Journal, Vol. 29, No. 2

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48 were conducted under standard and stressed cooling water conditions. The standard water composition and operating parameters are shown in Table 1. The cooling treatment contained 15 ppm (mg/ L) orthophosphate, 3 ppm (mg./l) pyrophosphate (as PO 4 ), and 1.2 ppm (mg/l) Halogen Resistant Azole (HRA), unless specified otherwise. The treatment program is designed for a near neutral ph range ( ). High levels of inorganic phosphate were used to ensure excellent steel corrosion protection. This was necessary to preclude the possibility of iron poisoning of the polymer due to excessive corrosion. Polymer dosages were varied based on test conditions and the polymers used. The test duration was 7 days. Samples were taken from the sump daily for water chemistry characterization including turbidity, ortho-po4 and ICP analysis of both filtered (F) and un-filtered (UF) samples. At the end of each BTU evaluation, the corrosion coupons and heat exchanger tube were visually inspected for deposits. Coupon corrosion rates were determined by a weight loss method. A. Polymer Dosage Requirements As A Function of ph And Temperature Testing was directed at determining the minimum polymer dosage required to control calcium phosphate precipitation in the recirculating water and prevent deposition on the heat transfer surface. Maintaining phosphate solubility is necessary to ensure steel corrosion protection. Table 2 provides a summary of the data. Studies performed at standard conditions, over a ph range of (Tests1-8) demonstrate the superior dose-response performance of the STP polymer over that of the SAA copolymer. Although the SAA copolymer provided excellent scale control, the STP polymer achieved the same level of performance at a much lower dosage (33-50%). At ph 7.2, 4 ppm (mg/l) SAA was required while only 2 ppm STP ppm (mg/l) was needed. As the ph increased from 7.2 to 7.8 the polymer requirement increased significantly. Calcium phosphate deposition control was achieved with 18 ppm (mg/l) SAA vs.12 ppm (mg/l) STP, at ph 7.8. The effect of ph on calcium phosphate solubility in relation to the polymer requirement is clearly evident in these studies. As the calcium phosphate super-saturation increases with ph, higher levels of polymer are required to control scaling. Good ph control is necessary to minimize ph swings that lead to scaling. In the absence of good control, the polymer dosage must be increased when the ph exceeds the upper level of the ph control range. Alternatively, the phosphate dosage must be reduced or the cycles of concentration decreased. The relative performance of the two polymers was further investigated at the ph 7.2 water condition with heat exchanger tube surface temperatures from 130 O F (54.4 O C) to 160 O F (71.1 O C). Increasing the surface temperature from 130 O F required a slight increase of the STP dosage from 2 to 3 ppm (mg/l) at 140 O F (60 O C), and to 4 ppm (mg/l) at 160 O F to maintain calcium phosphate scale control (Test 1, 10 & 12). The SAA copolymer controlled phosphate deposition at the 140 O F condition at a dosage of 6 ppm, but was unable to maintain the heat transfer surface free of deposits at 160 O F at 8 ppm. B. Impact of ph Upset On Calcium Phosphate Deposition Control The ability of the STP and SAA polymers to recover from a loss of acid feed was evaluated under standard conditions. Testing was initiated at a ph of 7.2 and the ph incrementally increased to 7.9 to simulate the loss of acid feed. The ph was then decrease back to The ph excursion was limited to ph 7.9 to avoid calcium carbonate precipitation/deposition. The soluble orthophosphate (0.2 micron filtrate) was monitored to track calcium phosphate inhibition efficacy. The STP and SAA polymers were applied at 4 and 8 ppm (mg/l), respectively. Previous testing demonstrated that these dosages were sufficient to prevent both bulk water precipitation and deposition of calcium phosphate at ph 7.4. Figures 3 & 4 provide a summary of the data. Precipitation of calcium phosphate occurred when the ph exceed 7.4. This was not unexpected based on the previous ph doseresponse testing (Table 2). The loss of phosphate from the recirculating water was nearly identical for both polymers when the ph was increased to 7.9. Soluble orthophosphate levels decreased from an average of 16 ppm to 8 ppm, indicating a complete loss of precipitation control. However, as the ph was decreased from 7.9 back to 7.4, the soluble orthophosphate increased to its initial value with the STP treated system, but not with the SAA treated system. Soluble phosphate levels remained at 14 ppm with the SAA polymer and did not increase with time, indicating continued loss of phosphate. All of the phosphate (16 ppm) was recovered with the SAA polymer when the ph was decreased to 7.2 and an additional 8 ppm polymer was added. Figure 5 provides a visual record of the comparative deposition performance of the two polymers. As can be seen, calcium phosphate deposition is significantly less with the STP copolymer. Calcium phosphate precipitation and deposition resulted in a significant decrease in the active polymer. The active (free) SAA copolymer level decreased from an initial value of 8 ppm to 2 ppm as the ph increased from 7.4 to 7.9, while the STP dosage decreased from its initial value of 4 ppm to 1 ppm. Polymer loss is attributed to adsorption on calcium phosphate particulate in the circulating water and on surface deposits. Under actual field operating conditions the appropriate response to an alkaline ph excursion would be to increase the polymer dosage. However, the STP polymer offers a significant degree of protection compared to the SAA polymer when the ph drifts out of the control range. The necessity of increasing the polymeric dispersant dosage when the calcium phosphate super-saturation is exceeded was evaluated at standard condition with the SAA copolymer. Testing was performed over a ph from 7.2 to 7.8. Automatic polymer control was used to continuously maintain the active SAA dosage at a constant 4 ppm, i.e., the dosage necessary for the ph 7.2 condition. Calcium phosphate control was monitored by measuring the soluble phosphate maintained in the circulating water. As can be seen for Figure 6, the soluble phosphate level decreased with increasing ph, even though the SAA copolymer dosage was held constant. The heat transfer surface was covered with a uniform calcium phosphate deposit. This study clearly demonstrates that the polymer dosage must be adjusted as the calcium phosphate super-saturation increases. Merely maintaining a constant active polymer residual without regard for the stresses that affect calcium phosphate solubility will result in deposition. C. Comparison of Halogen Stable and Conventional Treatments Testing in the presence of a free chlorine residual compared the corrosion and deposit control efficacy of two treatment programs under standard water conditions, at ph 7.2. The treatments only CTI Journal, Vol. 29, No. 2

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50 differed in the polymer and azole used for copper alloy control. The SAA containing program contained 4 ppm SAA and 3 ppm benzotriazole (BZT). The STP program used 2 ppm STP and 1.2 ppm halogen resistant azole (HRA). Both programs utilized the 15 ppm ortho-po 4 / 3 ppm pyro-po 4 blend for steel corrosion protection. Systems were continuously chlorinated to maintain a free chlorine residual of 0.5 to 1.0 ppm. Chlorination was initiated 24 hours after the start of the test to ensure initial passivation of both the steel and brass metallurgy. Performance of the STP program was excellent with coupon corrosion rates averaging <0.5 mpy for low carbon steel and <0.2 mpy for Admiralty brass. The difference between filtered and unfiltered orthophosphate levels (delta PO4) averaged 0.3 ppm. The coupons and heat exchanger tube at the end of the study were free of deposits and corrosion. See Figure 7. The conventional program using SAA and BZT experienced slight, uniform calcium phosphate deposition on both the corrosion coupons and heat exchanger tube. The difference between filter and unfiltered orthophosphate levels averaged 0.6 ppm, indicating that the polymer was preventing precipitation from the recirculating water. Corrosion rates average 0.6 mpy for low carbon steel and 0.2 mpy for Admiralty brass. Slight pitting corrosion occurred on the heat exchanger tube. The increase in deposition experience during chlorination is attributed to the effects of corrosion (i.e., soluble iron generation) and not degradation of the polymeric dispersant. Chlorine is a strong oxidizing agent that accelerates the cathodic corrosion reaction. The SAA/BZT treatment was modified by increasing the SAA dosage to 8 ppm to address the deposition experienced at the 4 ppm level. At the higher polymer dosage the calcium phosphate scale was completely eliminated, but localized corrosion of steel surfaces increased significantly. Both the low carbon steel coupons and heat exchanger tube experienced severe pitting-type corrosion. The coupon corrosion rates averaged 1.4 mpy for low carbon steel and 0.6 mpy for Admiralty brass. Elimination of the calcium phosphate deposits left the metal surfaces more susceptible to chlorine-induced corrosion (Figure 8). The studies performed with the SAA copolymer demonstrate that calcium phosphate films can provide some corrosion protection. However, this barrier film technology is not practical since the rate of deposition cannot be controlled in systems having equipment with a wide range of heat loads (surface temperatures). D. Evaluation of a Pyrophosphate-Based Corrosion Program Evaluation of STP as a calcium pyrophosphate scale inhibitor was conducted at standard conditions with a modified corrosion program. The 15 ppm orthophosphate/3 ppm pyrophosphate blend was replaced with 18 ppm pyrophosphate (as ppm PO 4 ). STP was applied at 10 ppm. Low polymer dosages were not evaluated, since the purpose of this study was to verify the precipitation inhibition studies. The pyrophosphate program provided excellent corrosion performance. Steel coupon corrosion rates averaged 0.5 mpy and heat exchanger tube was free of localized corrosion. STP prevented both calcium pyrophosphate precipitation in the circulating cooling water and scaling of the heat exchanger tube. The difference between filtered (0.2 micron) and unfiltered total inorganic phosphate levels was less than 0.2 ppm. 48 CONCLUSIONS 1. The stress tolerant polymer (STP) is an excellent inhibitor for both calcium orthophosphate and calcium pyrophosphate. 2. STP provides superior calcium phosphate control with near-neutral ph, inorganic phosphate-based programs under heat transfer conditions. 3. The polymer dosage must be adjusted for increases in calcium phosphate super-saturations due to alkaline ph excursions. 4. STP provides a significant margin of safety during high ph excursions 5. The excellent corrosion and scale control performance of the phosphate-based program employing STP and a halogen resistant azole (HRA) is attributed to the chlorine stability of the additives and their superior inhibition properties. ACKNOWLEDGEMENTS The authors would like to acknowledge the support of GE Water and Process Technologies Cooling Research and Technical Marketing teams and to acknowledge the technical assistance of Lisa Larks, Julie Davis, John Mahurter, Gloria Tafel and Debby Arnold for their involvement with laboratory testing of the STP polymer development. REFERENCES (1) Betz Handbook of Industrial Water Conditioning, Ninth Edition, 1991, pp (2) R. C. May, G. E. Geiger, D. A. Bauer, A new Non-Chromate Cooling Water Treatment Utilizes High Orthophosphate Levels Without Calcium Phosphate Fouling, Corrosion/80, Paper No. 196, 1980 (3) W. F. Beer, J. F. Ertel, Experience With High Phosphate Cooling Water Treatment Programs, Corrosion/85, Paper No. 125, 1985 (4) Hollander, O.; May, R. C., Corrosion, 1985, Vol. 41, pp (5) T. Notoya, G. W. Poling, Boshuku Gijutsu, 1981, Vol. 30, p. 381 (6) D. W. Reichgott, et.al., U.S. Patent #5,772,919, Methods of Inhibiting Corrosion Using Halo-Benzotriazoles, June 30, 1998 (7) L. Cheng, R. C. May, K. M. Given, A New Environmentally- Preferred Copper Corrosion Inhibitor, Corrosion/99, Paper #101, 1999 (8) R. C. May, L. Cheng, K. M. Given, P. R. Higginbotham, Application of a New Corrosion Inhibitor for Copper Alloys at the Harris Nuclear Plant, Power Conference, December, 1997 (9) S. M. Kessler, N. T. Le, Performance of a New Paper Mill Supply Treatment Program, Materials Performance, Vol. 36, No. 8, 1997, pp CTI Journal, Vol. 29, No. 2

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56 Evaluate Your Cooling Tower By Richard J. DesJardins Cooling Tower Consultant It is the purpose of this paper to show a few simple methods to determine the best way to arrive at the most economical cooling tower selection for a project. Low first cost may not be the best method for selecting a cooling tower. Power consumption for pumps and fans, the cost of the basin, piping and electrical equipment, and the choice of tower layout should often be This paper evaluates options of present worth value, annual cost and capitalized costs of revenue streams, projected life span, return on investment, depreciation, taxes, general administrative expenses, insurance requirements and the cost of power, and it provides comments on the proper choice of decision making formulas. It is well known that only a few specific items are needed to select a cooling tower, such as the water flow rate, the hot water temperature, the cold water temperature, and the wet bulb temperature. Generally, when we are called for a selection, the engineers and purchasing agents contacting us are sophisticated enough to know these basic requirements. One can only hope they have considered what one degree colder water would do to the overall plant capability and profitability. Also, it is not always the most economical to choose the highest recorded wet bulb temperature. It is usually desirable to investigate the optimum balance between the cost of the cooling tower and the heat exchangers or other equipment it is cooling. The concept of alternate design temperatures is presented here just to provoke thought on the possibilities and the effect they may have on the overall plant economics. Although these are important concepts they will not be detailed in this paper. In reality we often really need more than just the temperatures and flow rate. We need to know what power is worth, and this becomes a major stumbling block since the engineer and purchasing agent probably have not discussed it with management or even mentioned to management that power will be consumed as well as generated or it is needed to make a product. The reactions we get are from denial to what you are talking about? Why do you need to know that? We need to know it because it may make a big difference on the price or the plot space required. There is a natural tendency to take bids and pick the low price. That may or may not be the best approach for your project. There may be a very significant long term savings for the project if the economics of operation and cost of capital are investigated. Why evaluate? First, the need for the analysis and the effect that it can have should be demonstrated. Many of the projects proposed for cogeneration, ethanol or other chemical plants and refineries just happen to Richard J. DesJardins the deciding factors. Optimization of tower design con- ditions related to other equipment such as heat exchangers and condensers is discussed. fall in a size where many different types of cooling towers are available. These can range from crossflow to counterflow, from packaged factory assembled towers to the small or large field erected towers. A great variety of products are available for your consideration: almost too many. Larger power plants can be air cooled, either by direct or indirect steam condensation, or water cooled with mechanical or natural draft cooling towers, and to a lesser extent, rivers and the oceans. Refineries, high rise air conditioning and other projects usually use cooling towers. Evaluating a power project, as compared to evaluating a chemical or refinery project, often requires a major adjustment in conceptualizing for both project engineers and managers. For a high rise office building the cost of energy is necessary to retain the tenants. In a refinery electrical consumption is often considered a cost of producing the product. In the power industry electricity is the product. It may be a surprise that cost of operating the central plant in a high rise building complex can be one-third of the total cost of operation of the entire building. Current politics regarding greenhouse gasses has stirred considerable pressure to reduce our energy requirements. More than ever it is necessary to look at all of the equipment in the plant or building cooling loop to try to make improvements. Power consumed in operating a power plant is obviously nonproductive. You can either use it, or you can sell it. For some cogeneration projects the power consumed is purchased from the local utility and the power generated is sold to your client. The two can be at different rates. There are significant variations on the method of establish-ing a power contract, and it is not the intent of this paper to evaluate the various contracts. We are more concerned with the effect on selection of equipment and plant layout and how they might affect the project. What is energy worth? Energy rates can be found on the internet. Energy Information Administration (EIA) posts rates for residential, commercial, industrial and transportation categories monthly for every state. April 2007 kilowatt-hour rates (cents per kw-hr) for a few locations are tabulated below: State Commercial Industrial All Sectors Connecticut Hawaii Missouri Idaho U. S. average In addition to the $/KW charges there can be demand charges to offset the peak power requirements the plant may need for hot days or other conditions. However, we are not talking pennies. Here are examples of power consumption over time using the U. S. average cost of industrial power (unadjusted for inflation-8,000 hours per year). 54 CTI Journal, Vol. 29, No. 2

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58 Do you select a big tower or a little tower? The cooling tower doesn t set the heat load. The plant sets the heat load, and in order to do the cooling duty you can be provided with a big tower that does not use much power or a little tower that uses a lot of power. The tower can be tall with little plot space or short with a lot of plot space with resulting variations in pumping costs. The fans can be efficient or cheap. The variations can be dramatic. However, they can all be designed to do the same required cooling duty. So, which one should be selected? Selecting the evaluation tools It is not believed necessary to be sophisticated, at least in the early stages of the project. You need to establish the cost of power consumption which may well be the same as the selling price for your locality or the value in your power contract. Next, it is necessary to consider the cost of capital, which can be considered your overall corporate cost of capital, the cost of borrowing money for this project, the inflation rate plus a percent or so, or the marginal return that you could get on your money if you did not invest it in the project at all. Third you need to establish the duration of the analysis. It is also necessary to consider variations on how the equipment will be used. There are several methods of analysis which can be used. The method used (present worth, annual cost, or capitalized cost, discounted cash flow rates of return, payout period, or present worth combined with a capital recover, etc.) does not make much difference in the final analysis. Annual cost and capital cost methods make use of levelizing techniques, which employ present worth analysis either directly or indirectly. Management sometimes prefers the annual cost method because they can relate it to flow of funds, As will be demonstrated later it is necessary to adjust the initial cost of capital to include a return on the investment you are making and to account for annual fixed expenses. The adjustments need to be brought to present worth values and compared to the energy consumption to get a true comparison of one alternative to another. The method used for analysis probably has more to do with the personality of management than the actual method used. What is important is to get the understanding that some consideration must be made for the perpetual conflict between capital cost and power consumption. Once the necessary information is obtained the easiest methods to use to evaluate equipment is a combination of capital recovery factor and present worth. This paper will explain the process to obtain that information and reduce it to a few simple factors that can be used to facilitate the analysis of which cooling tower or tower component is best for your plant. What is the evaluation period? Are you going to operate the plant for a full 30 years, and you will be the owner? Have you signed a power agreement for 30 years but you re really an investor looking to make a quick buck and take advantage of the current tax laws. Maybe you really plan to unload the plant to somebody else in about 5 years so they can write it up again and start the depreciation all over. Are you a tax paying 56 entity or are you part of a public institution that has no tax advantages? How many hours a year do you expect the project to operate considering downtime for maintenance? That new high rise building in downtown is supposed to last well over 100 years (I saw one in great shape in Brussels Belgium with a corner stone dated 1492), so how long are you going to design yours for? Casinos in Las Vegas are never designed for over 15 years they tear them down and build something bigger. Historically power projects are evaluated over a period of 25 to 30 years with the normal being years of operation. Petroleum and refinery projects are generally evaluated on a 7 or 8 year period with typical economic evaluations being made on 3 to 5 year payouts. Why is this? I guess I wondered why for a long time, and I finally determined in a conversation with one of my banker friends that the banks would only loan monies to a chemical or refinery project for 7 or 8 years, and since it takes 3 or 4 years to build the plant they are only allowed 3 to 5 years to pay it out. If you cannot pay it back in the required payout period, the project is not viable. The banks will not loan you the money. Recent research of projects on the internet and talks with bankers revealed loan durations for power plants and large buildings are about 30 years. Cogeneration, ethanol plants, geothermal and general industry loans appear to be about 10 to 15 years, but there are few solid guidelines. Bankers are looking at the power contract, life of equipment, projection of long term demand for the product and the general business climate before making a decision on loan duration. They want to be sure they get their money back. Projects with long duration evaluations increase the magnitude of the before and after tax affect of capital usage and the cost of power consumption. Your management wants to get a return on their investment, and that may be the deciding factor for evaluation. More will be discussed about this later. Present worth calculation The present worth of a single or multiple future payments (known as cash flows) is the nominal amounts of money to change hands at some future date, discounted to account for the time value of money, and other factors such as investment risk. A given amount of money is always more valuable sooner than later since this enables one to take advantage of investment opportunities. Present values are therefore smaller than corresponding future values. (Wikipedia) Calculating the present worth of a stream of income or expenses is simple. PW = C [1-[1+(r/100)] -n ]/(r/100) PW = Present worth of a stream of payments or expenses. r = annual interest rate in percent C = Capital expenditure. n = number of years The choice of interest rate (r) can vary depending on the consideration for risk. It could be the prime rate, loan rate, corporate weighted average cost of capital, minimum return on capital, inflation rate plus a premium, or other risk adjusted value. For example the present worth factor for $1 for 20 years at 7% interest is: PW = 1 [1-[1.07] -20 ] / (0.07) = 10.6 What is the cost of capital? The first cost is not the only consideration. Many adjustments may be necessary. A few considerations are listed below: CTI Journal, Vol. 29, No. 2

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60 Adjustments to Capital: A Minimum Return on Capital is required if the project is to be successful. Usually this is set as the overall cost of corporate capital which might be from stock, bonds, or loans, and it is often a combination of the weighted average of all three. Income Tax on Return of Capital for the purpose of evaluation of different investments is not the same as for the Internal Revenue Service. The only concern is for the tax on the capital with respect to the minimum acceptable rate of return. If you make more you will pay more, but that should not be part of the decision making process. T = R/1-R ( i+mid-d ) C T = Tax rate in % of Capital R= Income tax rate in decimal format (0.40 +/-) i = minimum acceptable rate of return on investment (0.075) id = depreciation/amortization reserve in % (decimal equivalent) on sinking fund basis d = bank depreciation for IRS in % (say 3.3% straight line- decimal equivalent) C = 1-(B*b/i) [taxable capital] B = Fraction of Capital related to bonds b = interest on bond debt Ad Valorem Taxes (Local or state property taxes) are generally based on an assessed value set as a percentage of the initial plant and equipment total capital cost (say $20 per $100 of total cost). Then the assessed value is taxed at a rate per $100 of the assessed value. The final result might be 1.5 to 2.5% of the initial total capital cost. General and Administrative expenses might be a small percentage of the initial capital cost of a large power plant (maybe 1%) and a larger percentage of a smaller plant where the costs of salaries managers, legal services, advertising, etc. make up a larger percentage of the initial plant cost (maybe 2% or higher) Insurance expenses are often 0.1% to 1% of the initial capital cost of the plant. Depreciation and Amortization (or capital recovery) is the loss due to wear and tear, obsolescence, and other factors that cause the ultimate retirement of the equipment. The minimum acceptable rate of return is the return on investors capital, and depreciation/ amortization is the return of investors capital. This does not need to be the same as the allowable tax rate of depreciation. Think of it as a sinking fund where the amount of a periodic payment increases to the value of the initial cost. A = F [i/(1+i) n -1] A = periodic payment F = accumulated money i = interest rate (%/100) Percentage depreciation = A/capital cost Cost of Capital Example % of Capital Minimum Return on Capital 7.0 Income Tax on Return 2.5 Depreciation/Amortization Reserve 1.0 Ad Valorem Taxes 2.5 Administration General Expenses 1.0 Insurance 0.2 ========= Total annual fixed charge 14.2% Years of evaluation 0 Required return on capital 7% Annual fixed charge 14.7% Present worth factor for $1 for 20 years at 7% PW = 1 [1-[1.07] -20 ]/(0.07) = 10.6 Present Worth of Capital = (0.142)(10.6) * C = 1.50 C Each dollar of capital expenditure today should be considered as $1.50 because it requires having $1.50 on hand today to pay off the equal annual obligation of $0.142 fixed charges. Therefore, the simple adjustment to the first cost of the product or component is to increase the price by the Present Worth of Capital factor. What is the cost of energy? National Average cents per kw-hr = 8.77 Hours per year = 8,000 (there are 8760 hours in a year, but there may be downtime for maintenance or lack of demand for the product) Present worth Factor 20 years at 7% = 10.6 Present worth cost of power = * 8,000 * 10.6 = $7,437/kW = 7,437 * = $5,548 / horsepower If power consumption is tax deductible (estimate 40% total rate State and Federal): Power Cost = 5,548 * 0.6 = $3,330 / HP What components should be evaluated? The cooling tower fans are not the only source of power consumption. The pumping loop through the condenser interconnecting piping and the tower distribution system is often the most critical controlling factor. The fans may not run all the time, but at least one pump probably does. Especially on large projects with flow rates in excess of 30,000 GPM we find the pumping head controls the basic configuration of tower used, such as crossflow versus counterflow and film fill versus splash fill in many instances. Part of the design process might include an investigation to see if it pays to use a taller fan stack. If there are no evaluation factors the only tool to use is an attempt to adjust the height to fully load a motor, and that may not be the correct decision. If evaluation factors are available the cost of the taller fan stack can be compared to the savings in fan power for getting a greater velocity recovery effect. The same can be true for investigating different fill heights, types of fill and drift eliminators, air inlet heights, and various tower configurations. For these reasons evaluation factors should be provided with the request for proposals. Modifications for variations in operating modes, weather and heat loads A review of the actual plant operation for an entire year might indicate that the cooling tower fans will not run at full speed everyday, all day. Winter heat loads for a building will be 30% of summer load while the heat load for a refinery might be the same all year. Cooling too much in the winter might causes problems for a steam turbine. A geothermal plant may be able to use the coldest water it can get all year around. It might pay to run a chiller with colder water down to the point just prior to sucking oil in order to reduce the compressor back pressure, but at that point it is necessary to start shutting down fans, number of cells, number of pumps and 58 CTI Journal, Vol. 29, No. 2

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62 run fewer chillers. Each project should be reviewed to determine the possibility of variations for optimum usage. 33% or 50% pumping capacity will reduce the evaluated pump power, and using ½ speed or VFDs on the fans will reduce the evaluated fan power. Another major consideration is the method of operation to be used. I know of some installations that are operating only in the afternoons on a hot summer day to keep the peaking load down and through this method they have great penalty costs for exceeding maximum allowable meter readings as allocated by the power companies. Maybe this is starting a diesel engine, a gas turbine or diverting steam from an operation, but in many cases it is a justifiable application. For example fans running at half speed will use about 1/5 or 1/6 of the full speed power for half the hours of a year and the cost of fan power can be reduced accordingly. Using the overall power costs calculated above the actual fan power costs for the year can be further reduced: [(4,000 * $3,330) + (4,000 * $3,330 * 1/5)] / 8,000 = $1,980 / HP weighted average fan power cost. Some condenser and heat exchanger pumps are always running, even if the cooling tower fans are turned down for cold weather operation, and the pumping cost must certainly be considered a primary expense of operating the plant. There may be practical limits on turn-down of pumps in cold weather because the cooling tower nozzles may not provide adequate water distribution to prevent freezing in the fill, fouling of the fill or excessive drift due to mal-distribution of the air or water. Maybe only half of the cells or pumps run in the winter. Pumping power (English Units) at 85% pump efficiency can be calculated as: BHP/ft = * GPM (simplified * GPM ) BHP = brake horsepower Ft = foot of pump head GPM = flow rate in gallons per minute Pumping Cost = 50,000 * * $3,330 = $49,950/ft pump head Chances are that the pumps run all the time and fans run 50% of the time. To simplify the presentation the example below uses this assumption. Remember, the object is not trying to evaluate the entire project: rather it is to make rational decisions regarding which cooling tower design options are best. I don t know of any manufacturer who is really thrilled with the possibility of doing the full optimization study for you until you have gone through the preliminary steps. If you go far enough to give them some basic tools to work with they will generally make several selections to help you confirm your optimization. They just don t want to make a hundred selections when you are only going to choose one. At the time of requesting bids you should give the vendor guide lines: cost of fan power cost per foot of pump head concrete basin cost demand cost for electrical connections and controls cost of piping. Although it is not the purpose of this paper to design the tower, the purchaser should realize that sometimes all of the power evaluation cannot be used. There are good practice design standards that should be considered. Some examples are: 1) high fan power evaluation leads to low fan discharge velocities with increased possibility of recirculation, 2) high pump head evaluation leads to low inlet height with high inlet air velocities to the extent air by-passes portions of the fill and the tower does not perform properly, 3) high fan and pump power costs lead to large tower plot areas with light water loadings that cause poor distribution with inadequate wetting of all of the fill surfaces, winter freezing problems, and poor nozzle distribution when one pump is shut off. It is recommended you review the design and your anticipated operating modes with your cooling tower consultant. Analyzing the Bids After the bids are received the first task should be to make sure each selection will perform as required. Equalize the bids for compliance with the specification and then compare power consumption. Premature evaluation is not advised because adjustments to the design may be necessary to assure compliance with the technical specifications. The selections shown in the table below are examples of the variations that can exist. All selections were made for the same thermal duty of flow rate, hot water, cold water, and wet bulb temperatures. The exact conditions are not important for the purpose of this presentation. The object is to show the relative magnitude of costs of energy versus capital expenditure. If you budget too low on capital cost initially funding may not be adequate when you go to buy the equipment. If you budget too high it may kill the project before it gets started. Pump heads shown are for the tower only, and they do not include piping losses or pressure drops of other equipment. For a more detailed analysis you may want to add in the cost of various numbers and sizes of risers and other piping, the cost of VFDs for one or more of the fans, 2-speed motors, wiring and control costs, etc. Evaluation factors are also helpful in considering various tower components. Please note that in the examples given above the fan stack height varies. The energy cost can be used to decide if the present worth savings in fan power due to better velocity recovery from a tall fan stack saves enough to offset the extra cost of the taller fan stack. Changes to motor and starter sizes can also be included. The number of cells may change the piping costs. The ratio of the savings in operating costs and the additional fixed charges should be at least one to one if the client is to break even. Some clients, though, for business reasons may not value the present worth of future savings as much as current capital expenditures. If the capital is not available to start the project it will never get built. Maybe management will apply an additional 1.2 factor on extra capital expenditures for this reason. Decisions like this can be justified if there is a possibility the equipment could be modified in the future. For example, maybe another cell could be added in the future to reduce plant cold water temperatures for increased production after the project has been proven profitable. All of these economic studies will assist in making a selection regarding which type of product to purchase and what its power evaluation should be. However, ultimately the final decision must also include the reliability of the supplier, including reputation or expectation that the product will meet its thermal performance requirements and that the equipment will be suitable for the expected maintenance life of the components of the tower and the life of the tower itself. It is suggested that you condition each vendor s offering to assure that it will meet the design performance requirements before you buy, and that the people evaluating the bids have the expertise and database to tell the difference. After all of that, it is recommended that you test the final product to assure that you received what you asked for. As you consider the concepts of this paper please keep in mind that it can be used just as easily to justify modifications to existing cooling towers as it can for evaluating new towers. Some Engineer/ Constructors have been advising that their clients have been modifying their cooling towers in an effort to reduce energy consumption in order to do what they can to reduce their contribution to 60 CTI Journal, Vol. 29, No. 2

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64 Evaluation factors are also helpful in considering various tower components. Please note that in the examples given above the fan stack height varies. The energy cost can be used to decide if the present worth savings in fan power due to better velocity recovery from a tall fan stack saves enough to offset the extra cost of the taller fan stack. Changes to motor and starter sizes can also be included. The number of cells may change the piping costs. The ratio of the savings in operating costs and the additional fixed charges should be at least one to one if the client is to break even. Some clients, though, for business reasons may not value the present worth of future savings as much as current capital expenditures. If the capital is not available to start the project it will never get built. Maybe management will apply an additional 1.2 factor on extra capital expenditures for this reason. Decisions like this can be justified if there is a possibility the equipment could be modified in the future. For example, maybe another cell could be added in the future to reduce plant cold water temperatures for increased production after the project has been proven profitable. All of these economic studies will assist in making a selection regarding which type of product to purchase and what its power evaluation should be. However, ultimately the final decision must also include the reliability of the supplier, including reputation or expectation that the product will meet its thermal performance requirements and that the equipment will be suitable for the expected maintenance life of the components of the tower and the life of the tower itself. It is suggested that you condition each vendor s offering to assure that it will meet the design performance requirements before you buy, and that the people evaluating the bids have the expertise and database to tell the difference. After all of that, it is recommended that you test the final product to assure that you received what you asked for. As you consider the concepts of this paper please keep in mind that it can be used just as easily to justify modifications to existing cooling towers as it can for evaluating new towers. Some Engineer/ Constructors have been advising that their clients have been modifying their cooling towers in an effort to reduce energy consumption in order to do what they can to reduce their contribution to global warming. The simplified concept of a present worth of capital factor along with the present worth of fan power and pump power is all you need to make an economic analysis of your cooling tower bids. Acknowledgement: 1. Several concepts contained in this paper come from notes and private conversations with Millard Cherry and Paul Leung of Bechtel Corporation during the spring of 1974 in. preparation for a presentation to the Pacific Energy Association in Los Angeles, CA. 2. Cost of energy in various USA locations can be obtained at: 3. Federal Corporation Taxes can be obtained at: 4. State Corporate Income Tax Rates can be obtained at: 62 CTI Journal, Vol. 29, No. 2

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66 Seismic Qualification of Cooling Towers By Shake-Table Testing Panos G. Papavizas, P.E. Baltimore Aircoil Company ports and attachments and the basis of qualification can either be by analysis, testing, or experience data. For the higher level of safety where equipment functionality is vital for the continued operation of critical facilities after earthquakes, the design provisions focus on the equipment itself, as well as the supports and attachments. The basis for qualification in this case is limited to shaketable testing or experience data. Due to the rarity of strong-motion earthquakes and the lack of substantiated seismic experience data for the current generation of equipment, shake-table testing becomes the most reliable method of qualifying equipment functionality. The code-recognized shake-table test protocol, ICC-ES AC156, provides a generic methodology for verifying post-seismic test functionality. It is incumbent upon equipment manufacturers to define the specific functional verification activities that must be conducted as part of the seismic qualification program. The unique functional characteristics of cooling towers necessitate special consideration in developing a test plan that can reasonably and reliably assure post-earthquake functionality. Baltimore Aircoil Company has developed a functional verification methodology as part of a comprehensive seismic qualification program for its products. This methodology and the basis for its development is the subject of this paper. Introduction The seismic design of mechanical equipment is focused primarily on equipment supports and attachments. The intent of the seismic design provisions included in building codes is to reduce the hazard to life posed by the sliding, toppling, or falling of equipment during earthquakes. Typically, the basis for qualifying equipment supports and attachments for this level of earthquake safety (i.e., position retention) is static analysis. This qualification approach, though satisfactory and acceptable for verification of equipment restraint in most applications, is not sufficient for all applications. Mechanical systems often serve vital functions in critical building facilities such as emergency response centers, communication centers, and hospitals. The continued operation of these facilities after an earthquake is partly dependent on the ability of the vital systems, and the equipment within these systems, to function as intended. Failure of equipment to function in these applications Panos G. Papavizas Abstract The design and qualification requirements defined in building codes for active mechanical equipment to resist seismic forces are dependent on the desired level of earthquake safety. For the basic level of safety where the intent is to reduce the hazard to life posed by equipment becoming detached or toppling during an earthquake, the seismic design provisions focus on equipment supcould constitute a hazard to life. The design and qualification of mechanical equipment for this higher level of earthquake safety (i.e., functionality) must reliably assure functionality in addition to position retention. Building codes address this higher level of earthquake safety by requiring the design of equipment itself, in addition to the supports and attachments, to resist seismic forces that are greater than those required for position-retention considerations alone. Though the structural stability and integrity of equipment is directly affected using this approach, functional reliability is only indirectly impacted. It is recognized that this approach may not be sufficient for all types of equipment and for all critical applications. Accordingly, the qualification requirements for active equipment (i.e., equipment with moving or rotating parts) that must function following an earthquake go beyond the requirements for position retention. Functional qualification must be based on experience data or approved shake-table testing. With the rarity of strong-motion earthquakes and the lack of substantiated seismic performance data for the latest generations of equipment, shake-table testing becomes the most reliable way of assuring equipment functionality. The code-recognized shake-table test protocol, Acceptance Criteria for Seismic Qualification by Shake-Table Testing of Nonstructural Components and Systems (AC156), issued by ICC Evaluation Service, Inc., provides a framework for verification of equipment functionality. The test protocol is applicable to all types of equipment including mechanical and electrical equipment. As such, it does not define specific functional compliance tests and activities. It does require the test specifier, which is typically the equipment manufacturer, to provide a detailed description of the equipment functional characteristics. The test specifier must also define all the pre- and post-seismic test functional verification activities to be performed as part of the overall seismic qualification test plan. Cooling towers have unique functional and structural characteristics that must be carefully considered in the development of functional qualification requirements. The challenge for cooling tower manufacturers, and perhaps for the cooling technology industry as a whole, is defining the specific functional verification tests and activities to be conducted as part of an AC156-compliant test program that can reasonably and reliably assure equipment functionality after an earthquake. Baltimore Aircoil Company (BAC) has taken up this challenge in developing a comprehensive seismic qualification program for its products. The functional verification methodology developed by BAC and the basis for its development is the subject of this paper. Background The seismic design provisions for mechanical equipment attached to buildings and other structures have evolved substantially from their initial inclusion in the 1976 edition of the Uniform Building 64 CTI Journal, Vol. 29, No. 2

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68 Code (UBC). The early provisions focused on the attachment of equipment and were largely based on observed equipment damage in prior earthquakes. In later editions of the UBC, though the primary focus of the code was still equipment attachment, the need for greater assurance of equipment functionality in critical applications was recognized and addressed, albeit indirectly. The code required equipment itself to be designed for seismic forces with the assumption that if structural integrity and stability of the equipment are maintained, function and operability are reasonably provided for, although by no means assured (Porush, 1992, p. 27). Shake-table testing as a means of seismically qualifying equipment for building applications first appeared in national seismic provisions in 1985 with the initial publication by the Federal Emergency Management Agency (FEMA) of the National Earthquake Hazards Reduction Program (NEHRP) Recommended Provisions for the Development of Seismic Regulations for New Buildings. However, shake-table testing for functional qualification of mechanical equipment has not been employed to any significant extent outside the nuclear industry. This can be explained in part by the absence of a recognized shake-table test methodology suitable for nonstructural building components. Where tests have been performed for non-nuclear applications, they have been hampered by inconsistent interpretation and translation of the building code seismic provisions into actual test procedures (Gatscher et al., 2003, p.74). Tests so conducted result in uncertain equipment reliability. The test methodology void was filled by the issuance of AC156 in This protocol was developed through collaboration between Schneider Electric, the Building Seismic Safety Council, and the International Conference of Building Officials Evaluation Service, which is now the ICC Evaluation Service, Inc. (Caldwell et al., 2003, p. 449). The most recent edition of AC156 became effective in January, It is suitable for equipment qualification in accordance with the 1997 edition of the UBC and the 2006 edition of the International Building Code (IBC). The AC156 protocol is referenced in the 2003 NEHRP provisions and the American Society of Civil Engineers standard ASCE/SEI 7-05, Minimum Design Loads for Buildings and Other Structures. Current Seismic Qualification Requirements for Critical Equipment The earthquake regulations found in most state and local building codes are based on the International Building Code, the model building code published by the International Code Council (ICC). The NFPA 5000, Building Construction and Safety Code, which is published by the National Fire Protection Association, is used as the basis for earthquake regulations to a much lesser extent and in only a handful of code jurisdictions. Both of these model codes refer to the consensus standard ASCE/SEI 7-05 for seismic design criteria. The seismic design requirements for nonstructural components including mechanical equipment are contained in Chapter 13 of ASCE/SEI All manufactured equipment (i.e., packaged equipment that typically are not custom engineered for specific projects) that fall within the scope of Chapter 13 and are not exempt from the seismic design provisions must be certified and qualified by one of three methods defined in Section These methods are: a. Analysis b. Testing c. Experience data. Critical mechanical components that are required to function after an earthquake are classified as designated seismic system components. These components are assigned a component importance factor, I p, of 1.5 and are themselves required to be designed for seismic forces. Non-critical components are assigned an importance factor of 1.0. The more restrictive qualification requirements for designated seismic system components are contained in Section Specifically, paragraph a. states: Active mechanical and electrical equipment that must remain operable following the design earthquake shall be certified by the supplier as operable based on approved shake table testing in accordance with Section or experience data in accordance with Section Evidence demonstrating compliance of this requirement shall be submitted to the authority having jurisdiction after review and approval by the registered design professional. The requirements for seismic testing are defined in Section This section states in part: testing shall be deemed as an acceptable method to determine the seismic capacity of components and their supports and attachments. Seismic qualification by testing based upon a nationally recognized testing standard procedure, such as ICC-ES AC 156, acceptable to the authority having jurisdiction shall be deemed to satisfy the design and evaluation requirements provided that the substantiated seismic capacities equal or exceed the seismic demands determined in accordance with Section and The experience data requirements are provided in Section , which states: As an alternative to the analytical requirements of Sections 13.2 through 13.6, use of experience data shall be deemed as an acceptable method to determine the seismic capacity of components and their supports and attachments. Seismic qualification by experience data based upon nationally recognized procedures acceptable to the authority having jurisdiction shall be deemed to satisfy the design and evaluation requirements provided that the substantiated seismic capacities equal or exceed the seismic demands determined in accordance with Sections and Clearly, of the three qualification methods only shake-table testing and experience data are recognized and acceptable for functional qualification of critical equipment. There are limitations, however, in the use of experience data. Limitations of Qualification by Experience Observations of buildings and equipment in the aftermath of earthquakes when correlated with recorded ground-motion and building-motion data are an invaluable source of information that can be used to gain an understanding of actual performance during seismic events. This type of reconnaissance information, or experience data, has guided code-writers in developing national seismic provisions to mitigate hazards from future earthquakes, and has revealed to equipment manufacturers the strengths and weaknesses of their equipment designs. Experience data is important for the ongoing development of codes and seismically resistive equipment, but is limited when used as the basis for qualifying the seismic capacity 66 CTI Journal, Vol. 29, No. 2

69 of the current generation of equipment designs for new building applications. The most obvious limitation is that data is relatively rare due to the infrequency of strong-motion earthquakes. Furthermore, experience data that is available likely pertains to equipment designs that are obsolete or that are several generations old. Considering that many equipment manufacturers frequently upgrade and modify their products to gain competitive advantage through differentiation, experience data can become outdated very quickly. Experience data is also relatively difficult to obtain due to the restrictions on access in earthquake damaged areas and the concerns about legal liability. Where access is permitted, groundmotion or building-motion data may not be available making it difficult to determine the actual seismic demand experienced by the equipment. And assuming all the information is available, the substantiated seismic capacity may be so low that it is virtually useless for new applications. To be acceptable as a basis for seismic qualification of equipment, ASCE/SEI 7-05 requires the use of experience data to be based on a nationally recognized procedure. This requirement is necessary to ensure the validity and proper application of the data. One procedure that exists and is used on a regular basis is the Seismic Qualification Utilities Group (SQUG) Generic Implementation Procedure (Eder, 2007). However, this procedure is proprietary to SQUG and is used primarily for qualification of new and replacement equipment in nuclear power plants. No comparable procedure exists for building applications. These limitations by no means preclude the use of experience data, but suggest that for most building applications it is not a viable method for equipment qualification. The limitations also dictate that if this method becomes viable in the future it should be used with extreme care. The more reliable alternative to using experience data for functional qualification is to perform shake-table testing in accordance with AC156. Scope and Purpose of AC156 The stated scope and purpose of the AC156 test protocol is to establish the minimum requirements for the issuance of ICC Evaluation Service, Inc., evaluation reports on seismic qualification shaketable testing of nonstructural components and systems (ICC- ES, AC156, p. 2). ICC-ES is a nonprofit subsidiary of ICC that performs technical evaluations of products to determine code compliance. Evaluation reports are issued by ICC-ES following the review and approval of test data submitted by an applicant to substantiate code compliance. The reports are made available to the public and can be used by engineers, contractors, specifiers, and others, but the primary aim is to aid building officials in the enforcement of code regulations. Building officials can accept or reject ICC-ES evaluation reports as proof of code compliance given that the reports are only advisory. To fulfill the stated scope and purpose, the AC156 test protocol not only clearly defines the test procedure, but also specifies the accreditation requirements for test laboratories and the format requirements for test reports. These requirements must be satisfied for ICC-ES to consider the testing and to issue an evaluation report. However, an evaluation report does not have to be the final outcome of qualification testing in accordance with AC156. CTI Journal, Vol. 29, No. 2 67

70 Equipment manufacturers must carefully consider the advantages and disadvantages of pursuing ICC-ES evaluation reports for their tested products before proceeding with a testing program. Generally, for test reports to be considered they must come from accredited laboratories. In special cases ICC-ES will consider reports from non-accredited laboratories as long as on-site assessments are performed to its satisfaction (see ICC-ES, Acceptance Criteria for Test Reports, AC85, for accreditation requirements). Though necessary for the issuance of evaluation reports, these requirements may limit a manufacturer s choice of test facilities and may be prohibitively expensive and burdensome. The evaluation report requirements of AC156 should not dissuade manufacturers from pursuing seismic qualification test programs. The benefits of qualification by testing outweigh the limitations resulting from the absence of an evaluation report. To satisfy the intent of the accreditation requirements, it is advisable and prudent for manufacturers to use test laboratories that are reputable and that have experience performing tests in accordance with AC156. Functional Verification Requirements of AC156 The functional verification requirements of AC156 are intended to be universally applicable to all types of equipment, including mechanical and electrical equipment. The protocol essentially provides a framework within which equipment manufacturers can describe the functional characteristics of their products and define the specific pre- and post-seismic test functional verification activities to be performed as part of the qualification test program. The protocol also provides acceptance criteria for functional verification. Section 4.0 of AC156 details all the information that must be provided by the equipment manufacturer for the unit to be tested, defined as the Unit Under Test or UUT. Specifically regarding the functional requirements, Section 4.4 states: A listing and detailed description shall be provided of the functional and operability equipment requirements and/ or tests used to verify pre- and post-seismic-testing functional compliance. As part of the required information for Section 4.0, the importance factor, I p, must be specified by the manufacturer. This factor establishes the performance level of the equipment. An importance factor of 1.5 indicates that the functionality requirements of the protocol apply. The pre-seismic test functional compliance verification activities must be performed in accordance with Section 6.3. Specifically, Section 6.3 states: Functional and operability requirements and/or tests, as specified in Section 4.4, shall be performed by an accredited testing laboratory to verify pre-test functional performance. Functional testing could be performed at either the test facility or at the UUT manufacturing facility. Test description and results shall be documented in accordance with Section 5.2 (Test Reports). As indicated in the discussion of the scope and purpose of AC156, the accreditation requirements are pertinent when an evaluation report will be sought from ICC-ES. Otherwise, the functional tests should be professionally and competently performed and recorded in the test report. The post-seismic test functional compliance verification requirements are defined in Section 6.7. Specifically, this section states in part: Based upon the specified UUT importance factor in Section 4.3, equipment being qualified must be capable of performing its intended functions after the seismic event. Functionality and operability requirements and/or tests, as specified in Section 4.4, shall be performed on the UUT to verify post-test functional and operational compliance. The acceptance criteria for verification of functionality are defined in paragraph and require the post-test results to be equivalent to the pre-test results. To ensure that the results can be readily interpreted and confirmed, the manufacturer should provide objective pass/fail criteria in the test plan. Paragraph also includes acceptance criteria for basic structural integrity. It is required that the UUT structural system and anchorage are not compromised during the test, though some structural damage such as local yielding is acceptable as long as it does not affect the functionality of the equipment. Repairs to the equipment are allowed as long as they are relatively minor. The example provided in AC156 to illustrate what constitutes a minor repair is replacing a bulb (ICC-ES, AC156, p. 8). Functional Characteristics of Cooling Towers and Qualification Considerations The function of cooling towers, including both open and closed circuit towers, is to reject waste heat into the atmosphere by evaporative cooling. This is accomplished through a complex interaction of the various sub-systems within towers. These sub-systems include the air moving system or mechanical system (i.e., fan, motor, and drive system), the water distribution system (i.e., integral spray pumps, internal piping, nozzles, distribution basins, and collection basins), the heat transfer system (i.e., fill media and/or integral heat exchangers) and the structural system (i.e., support members, bracing, enclosures, and anchorage). These tower sub-systems must remain largely intact after an earthquake for cooling towers to perform their intended function. Therefore, the integrity of these sub-systems must be verified in a comprehensive test and inspection program in order to assure functionality. The most recognized and accepted method of determining the thermal capability of cooling towers is testing in accordance with ATC- 105, Acceptance Test Code for Water Cooling Towers, and its supplement for closed circuit towers, ATC-105S, both of which are published by the Cooling Technology Institute (CTI). Though thermal testing in accordance with ATC-105 could be used to verify cooling tower functionality, it is unnecessary and excessive within the context of seismic qualification. Additionally, when thermal testing is used as the sole means of verification, it may be inadequate to address all the functional characteristics of cooling towers. The primary purpose of thermal performance testing in accordance with ATC-105 is to determine the absolute thermal capability of cooling towers. The AC156 functionality requirements, however, focus on the relative performance of the equipment. As long as the pre-test and post-test functional results are equivalent, the functional compliance requirements of AC156 are satisfied. As an alternative to ATC-105 testing, the functional tests and activities should demonstrate that the various cooling tower sub-systems remain substantially intact and can deliver equivalent pre- and post-seismic test functional results. This approach can reasonably assure 68 CTI Journal, Vol. 29, No. 2

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72 cooling towers will function after an earthquake as well as they would prior to an earthquake. Some of the functional compliance tests and activities must focus on the characteristics of cooling tower sub-systems that an ATC- 105 thermal performance test would not necessarily address, such as mechanical system integrity. Though the ATC-105 code requires an overall condition assessment of mechanical equipment prior to performing a thermal test, this assessment may not assure the continued safe operation of the mechanical system following an earthquake. Other aspects of cooling tower sub-systems that warrant additional consideration are the water containing function of distribution/collection basins and internal piping as well as the structural integrity of the fill media and/or integral heat exchanger in the case of a closed circuit tower. The functional compliance verification methodology developed by BAC includes specific tests and activities that address all aspects of cooling tower function. This methodology is described in the following section. Functional Verification Methodology The functionality of cooling towers after shake-table testing can be reasonably and reliably assured through a comprehensive inspection and test program that focuses on the various internal subsystems of towers. The tests and inspections must verify that: The air moving system is substantially intact and delivers equivalent pre- and post-seismic test air flow. The integrity of the mechanical system is not compromised and that the mechanical components can be operated safely. The water distribution system is substantially intact and delivers equivalent pre- and post-seismic test water flow without significant leaks or drift. The heat transfer system is substantially intact and is not structurally or thermally compromised. The structural system and anchorage are substantially intact with only minor yielding or distortion that does not impact functionality. These criteria can be satisfied by conducting thorough inspections and production-type tests that establish fan/motor performance, demonstrate water distribution, measure vibration characteristics, and assess structural integrity. Specific inspections and tests to be conducted both before and after shake-table testing for open cooling towers and closed circuit cooling towers are provided in Tables 1 and 2, respectively, found at the end of this paper. A similar matrix or outline should be included in the seismic test plan, along with pass/fail criteria suited to the type of tower, to clearly establish the verification requirements. The results of all functional verification tests and inspections should be included in the test report. Test and inspection forms can be developed to facilitate the collection of test data and the interpretation of the test results. The report should also include before and after photographs, including close-up pictures of any post-test damage. The production-type tests listed in Tables 1 and 2 typically would be conducted at the UUT manufacturing facility or research facility since it is unlikely that the shake-table test laboratory has the capability (i.e., hardware, instrumentation, and expertise) to conduct these tests. Therefore, it is critical that the fragility level of the UUT is not exceeded during shake testing so that the UUT can be transported to the functional test facility. This requirement should be communicated to the shake-table lab personnel so that all parties understand the performance expectations. Minor repairs to the UUT are acceptable as long as they are on the same order of magnitude as the example provided in the AC156 protocol. A partial listing of analogous cooling tower-type repairs that should be acceptable to a reviewing authority is provided below: Sealing of minor leaks. Replacement of dislodged water distribution branches or nozzles. Minor retightening of pipe joints. Minor retightening of drive belts. Minor realignment of mechanical components. Replacement of a few dislodged fill packs or drift eliminators. Replacement of a few dislodged louvers or air inlet screens. All minor repairs that occur during testing must be documented in the test report. When conducted as part of a comprehensive seismic qualification program in accordance with AC156, the functional verification tests and inspections listed in Tables 1 & 2 and described herein can reliably assure cooling tower functionality. Certification Requirements Equipment that has been seismically qualified by shake-table testing must be certified by the manufacturer as specified in paragraph a. of ASCE/SEI Currently, there are no specific guidelines in the code for preparing a certificate of compliance, but it is recommended that the following information be included as a minimum for generic building applications (i.e., where the building dynamic characteristics are not known). 1. Name of the manufacturer. 2. Product line covered by the certificate. 3. The code for which compliance was evaluated (e.g., 2006 IBC). 4. Reference to AC156 as the test protocol. 5. Performance level (i.e., I p = 1.5). 6. Certified seismic capacity, defined in terms of the design spectral acceleration parameter at short period, S DS. 7. Installation restrictions, if any (e.g., outdoor, grade level). 8. Product restrictions, if any (e.g., accessories not covered by the certificate) Manufacturers should include the certificate of compliance in their proposal packages. With the seismic qualification basis and the certified seismic capacity clearly defined in the certificate of compliance, equipment specifiers and purchasers can readily determine whether or not the equipment is suitable for their specific project. A certificate of compliance in itself, however, is not sufficient evidence of testing and seismic qualification. All supporting documentation, including the seismic qualification test plan, the test report, and any supporting analyses, must be available for review and approval by the registered design professional and the building official. System Considerations 70 CTI Journal, Vol. 29, No. 2

73 It has been established that cooling towers in designated seismic systems must be designed and qualified to the building code requirements. However, qualification of cooling towers alone does little to assure post-earthquake functionality of the systems within which they operate. All components within these systems and the way that they interact must receive equivalent attention. This system approach to qualification should be directed by the registered professional responsible for the system design. Cooling tower manufacturers can do their part to assure the functional level of earthquake performance in critical systems by satisfying the requirements of the building codes, qualifying their equipment using a methodology similar to the one described herein, and providing sufficient information to the registered professional to facilitate cooling system design. Conclusions Cooling towers classified as designated seismic system components that must operate and function as intended following an earthquake are required to be qualified using either experience data or shake-table testing. Due to various limitations of experience data, the most reliable method of qualification is shake-table testing in accordance with the code-recognized test protocol, ICC-ES AC156. Seismic qualification programs for cooling towers must take into consideration their unique functional characteristics and include specific pre- and post-shake test functional verification activities to reasonably and reliably assure post-earthquake functionality. The methodology developed by BAC and presented herein addresses all aspects of cooling tower function and satisfies the verification requirements of AC156. In the absence of specific functional verification requirements for cooling towers in the AC156 protocol, a companion guideline or standard developed by the cooling technology industry could help ensure that all manufacturers approach functional qualification with equal rigor. Cooling towers qualified by shake-table testing must be certified by the manufacturer. Certificates of compliance must contain sufficient information for specifiers and purchasers to determine the suitability of the equipment for a specific project. Additionally, all supporting documentation must be readily available for review and approval by the registered design professional and the building official. Though functional qualification of cooling towers in critical applications is necessary and important, a focus on the towers alone is insufficient. Cooling tower qualification is just one part of a system approach to assuring the functional reliability of critical systems. References American Society of Civil Engineers. (2006). Minimum Design Loads for Buildings and Other Structures. ASCE/SEI Reston, Virginia: ASCE. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (2007). Heating, Ventilating, and Air-Conditioning Applications ASHRAE Handbook. Chapter 54. Atlanta, Georgia: ASHRAE. Building Seismic Safety Council. (1986). NEHRP Recommended Provisions for Seismic Regulations for New Buildings. Part 1: Provisions (1985 edition). FEMA 95. Washington, D.C.: Federal Emergency Management Agency. Building Seismic Safety Council. (2004). NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures. Part 1: Provisions (2003 edition). FEMA Washington, D.C.: Federal Emergency Management Agency. Building Seismic Safety Council. (2004). NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures. Part 2: Commentary (2003 edition). FEMA Washington, D.C.: Federal Emergency Management Agency. Caldwell, P. J., Gatscher, J. A. (2003). Equipment Qualification for Product Line Families Using a Shaker Table Type Testing Campaign. Proceedings of Seminar on Seismic Design, Performance, and Retrofit of Nonstructural Components in Critical Facilities (pp ). ATC Redwood City, California: Applied Technology Council. Cooling Technology Institute. (2000). Acceptance Test Code for Water Cooling Towers. CTI Code ATC-105. Houston, Texas: CTI Cooling Technology Institute. (1996). Acceptance Test Code for Closed Circuit Cooling Towers. CTI Code ATC-105S. Houston, Texas: CTI Eder, S. J. (2007). Seismic Qualification of Equipment by Analysis. Presented at Symposium on Seismic Regulations and Challenges for Protecting Building Equipment, Components & Operations. October 12, University at Buffalo. Gatscher, J. A., Caldwell, P. J., & Bachman, R. E. (2003). Nonstructural Seismic Qualification: Development of a Rational Shake-Table Testing Protocol Based on Model Building Code Requirements. Proceedings of Seminar on Seismic Design, Performance, and Retrofit of Nonstructural Components in Critical Facilities (pp ). ATC Redwood City, California: Applied Technology Council. ICC Evaluation Service, Inc. (2003). Acceptance Criteria for Test Reports. AC85. Whittier, California: ICC-ES. ICC Evaluation Service, Inc. (2007). Acceptance Criteria for Seismic Qualification by Shake-Table Testing of Nonstructural Components and Systems. AC156. Whittier, California: ICC-ES. International Code Council, Inc. (2006). International Building Code (2006 edition). Washington, D.C.: ICC. International Conference of Building Officials (1976). Uniform Building Code (1976 edition). Whittier, California: ICBO. National Fire Protection Association (2005). NFPA 5000, Building Construction and Safety Code (2006 edition). Quincy, Massachusetts: NFPA. Porush, A. R. (1992). An Overview of the Current Building Code Seismic Requirements for Nonstructural Elements. Proceedings of ATC-29 Seminar and Workshop on Seismic Design and Performance of Equipment and Nonstructural Elements in Buildings and Industrial Structures. (pp ). ATC-29. Redwood City, California: Applied Technology Council. CTI Journal, Vol. 29, No. 2 71

74 Table 1: Open Cooling Towers Table 2: Closed Circuit Cooling TowersReferences 72 CTI Journal, Vol. 29, No. 2

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78 Index of Advertisers Advance Grp Cooling Tower Pvt Ltd AHR Expo Aggreko Cooling Tower Service Amarillo Gear Company... IBC Amcot Cooling Tower... 3 American Coalition for Ethanol American Cooling Tower, Inc... 9 AMSA, Inc... 13, 47 Bailsco Blades & Casting, Inc Bedford Reinforced Plastics, Inc BOLToutlet.com Brentwood Industries ChemTreat, Inc CleanAir Performance Group CTI License Testing Agencies CTI ToolKit Composite Cooling Solutions, LP Cooling Tower Resources Dominion Dynamic Fabricators Emerson Fibergrate Composite Structures Gaiennie Lumber Company... 4 Hesiler Green Howden Cooling Fans... 7 Hudson Products Corporation Industrial Cooling Towers... IFC, 40 Liang Chi Industries Metrix Midwest Towers, Inc Paharpur Cooling Towers & Equipment LTD Power-Gen ProvibTech Rexnord Industries C.E. Shepherd Company, LP Spraying Services, Inc SPX Cooling Technologies... OBC Strongwell... 5 Swan Secure Products, Inc Tower Performance, Inc CTI Journal, Vol. 29, No. 2

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