MEMORANDUM

Tetra Tech, Inc.

10306 Eaton Place, Suite 340

Fairfax, VA 22030

phone 703-385-6000

fax 703-385-6007

TO: Paul Shriner and Jan Matuszko, EPA

FROM: John Sunda (SAIC) and Kelly Meadows

DATE: March 25, 2010

SUBJECT: Water Balance, Flow Reduction, and Optimization of Recirculating Wet Cooling 

Towers

Introduction

Tetra Tech and SAIC were tasked with developing documentation to support regulatory options 

that may require a facility to retrofit to closed-cycle cooling. This memo discusses the reduction 

in flow that can be expected, ways to optimize those reductions, and estimated the additional 

costs that will be incurred to optimize the cooling towers.

Estimation of Flow Components in Recirculating Wet Cooling Towers

Closed-cycle cooling systems significantly reduce the volume of cooling water withdrawals. 

However, there is still a need for some water to be withdrawn; make-up water replaces losses to 

the system. The water balance in and out of a recirculating wet cooling tower is defined by the 

following equation:

Make-up = Evaporation + Drift + Blowdown

The make-up flow volume is typically controlled by water level monitors in the cooling tower 

basins which control the make-up water pumps to ensure that a sufficient depth of water is 

maintained in the cooling tower basin to allow for proper operation. As such, the volume of the 

make-up withdrawals is driven by the volume of the three components of water exiting the 

recirculating water system (i.e., the right hand side of the above equation). Each of these is 

discussed in detail below.
- 2 -

Evaporation

The amount of evaporation is driven by the amount of heat that is transferred to the cooling 

water in the exhaust steam condensers. The amount of this heat is a function of the power 

generation rate and the efficiency of the boiler and the generating system. In a typical coal-fired 

steam boiler, 75% to 90% of the heat energy derived from the fuel is converted to steam energy

(Dbal et al 1995). The component of the steam energy that is not converted to electricity in the 

turbines will exit the system through the cooling water system. The heat exiting through the 

cooling water system is transported to the towers through an increase in the temperature of the 

cooling water passing through the steam condenser. For any given power plant output level, the 

circulating cooling water flow rate will determine the temperature difference between the 

condenser inlet and outlet. 

At the cooling tower end of this system, the heat that exits the system leaves through a 

combination of evaporation of water and an increase in the sensible temperature of the air 

passing through the system. In conventional wet cooling towers, the majority of the heat exits 

the system through evaporation. The evaporation rate can be estimated using the following 

equation:

Evaporation (gpm) = Recirculation (gpm) x ∆T (F) x Evaporation Factor

Table 1 below shows evaporation factors provided by two technical sources plus the value that is

equivalent to a tower where 100% of the heat exits the tower via evaporation. While 100% 

evaporation is possible, it would only occur when the ambient air has low humidity and is as 

warm (or warmer) than the hot water entering the tower. The mechanical draft cooling towers 

engineering evaporation estimation factors shown in Table 1 are equivalent to conditions where

roughly 80% of the heat exiting is via evaporation. The actual proportion of heat exiting the 

tower through evaporation at any given time will vary depending on tower design, the amount of 

air flow, the water temperature and meteorological conditions such as wet bulb temperature and

dry bulb temperature. Differences in these factors will affect the evaporation rate (and thus the 

make-up volume) by only a modest amount however, since conventional towers are designed 

such that most of the heat exits via evaporation. Non-conventional designs such as hybrid plume 

abatement towers will have a lower proportion of heat exiting through evaporation and thus a 

lower make-up water volume.

Table 1

Wet Cooling Tower Evaporation Factors

Source Evaporation 

Factor

Percent of Total Heat 

Exiting Tower As 

Evaporation

Marley 0.0008 78%

NPCI 0.00085 82%

100% Evaporation 0.00103 100%
- 3 -

Drift

Drift (aka windage) is the small proportion of the recirculating cooling water that leaves the 

tower as fine droplets entrained in the exiting air flow. Drift is typically estimated as a 

percentage of circulating water flow and will vary with tower design. Drift is different from 

evaporation in that it is not responsible for removing heat from the system, but can be 

responsible for removing some of the dissolved solids that build up in the recirculating cooling 

water that otherwise would exit through the blowdown. A change in the drift rate at a tower 

maintained at a specific cycle of concentration (see below) will affect the blowdown volume but 

not the make-up water volume.

Table 2 below presents drift estimation rates for different types of cooling tower designs without 

drift eliminators and for those with drift eliminators.

1

 

Table 2 

Cooling Tower Drift Factors

Tower Type Drift Estimation Factor*

Natural Draft 0.3 to 1.0%

Mechanical Draft 0.1 to 0.3%

Mechanical Draft Tower with 

Drift Eliminator

0.005%

Mechanical Draft Tower with 

High Efficiency Drift Eliminator

0.0005%

* Drift (gpm) = Recirculation (gpm) X Factor

Source (Engineering Tips 2009)

Blowdown

Of the three components that comprise the make-up water volume requirements, blowdown is 

the one component that is completely under the control of the cooling tower operator. The 

blowdown is the component used to control/prevent the build-up in the dissolved and suspended

solids in the recirculating water. Theoretically, it can range from 0% to 100% of the condenser 

cooling water flow (minus drift and evaporation). The latter condition (i.e., 100%) describes a 

cooling tower operating in the helper mode with no recirculation. 

Since nearly all make-up water sources will contain some dissolved solids, a tower operating 

with 0% blowdown would experience a continuous build-up of dissolved solids in the 

recirculating water as dissolved solids are left behind by the evaporating make-up water. This 

build-up would increase until the concentration becomes so high that the amount of solids lost in 

the drift equals the amount coming in through the make-up water. Usually before that happens, 

the build-up of dissolved solids in the system will reach saturation concentrations for certain 

components, resulting in the precipitation of solids as scale, suspended solids, and sludge. These 

solids can create an array of operational problems including the plugging of piping and tower 

media, a reduction in the efficiency of heat exchange surfaces, and an increase in metal corrosion

 

1 Note that engineering costs for the revised Phase II rule included drift eliminators for all cooling tower 

installations.
- 4 -

due to anaerobic conditions beneath the deposited layer of solids. Corrosion may also increase 

due to higher salt content of the water. 

There are no upper limits for the blowdown volume, and some systems may operate at relatively 

high blowdown rates in order to completely avoid dissolved solids-related problems or to 

increase turbine efficiency by providing supplemental cooling by operating the system in 

essentially a partial once-through mode.2This provides cooler water to the condensers whenever 

the source water temperature is below the tower effluent temperature, which is most often the 

case.

For any given make-up water quality and tower system design, cooling tower manufacturers and 

treatment chemical vendors can evaluate what should be the acceptable upper operating limit for 

the concentration of the mix of dissolved solids present. The acceptable upper limit is not fixed 

and can be adjusted upward through the use of treatment chemicals. Rather than defining such 

upper limits in the form of a maximum concentration, this limit is often expressed as a multiple 

of the make-up water concentration. The ratio of the dissolved solids concentration of the more 

concentrated recirculating water to the dissolved solids concentration of the make-up water is 

called the cycle of concentration (COC). 

The recommended maximum cycle of concentration is directly related to the quality of the makeup water and can be modified by use of water treatment chemicals. A make-up water source 

with high dissolved solids (e.g., saltwater) or high hardness will tend to result in the need to 

operate at a lower COC, even with the use of treatment chemicals. Towers that operate at a COC 

near the upper operating limit have a greater potential for increased operating and maintenance 

costs due to higher chemical costs or increased equipment maintenance costs due to the higher 

potential for corrosion and scale buildup. 

In general, cooling tower treatment chemical vendors will evaluate the water chemistry and 

associated costs for various COC levels and will select an optimal operating COC and treatment 

chemical dosage. As the COC is increased, there will be an increase in chemical dosage and at 

the same time a decrease in the amount of chemicals lost in the blowdown. This optimal COC 

will usually involve financial and operating considerations that strike a balance between the 

variations in treatment chemical dosage and cost, the limits of the ability of treatment chemicals 

to prevent problems associated with scale formation, corrosion and biofouling, and the benefits 

of using less water. In cases where there are significant costs associated with obtaining source 

water and disposing of blowdown, these costs may provide additional incentive to set the optimal 

COC to higher values and thus reduced make-up water volumes. A cooling tower treatment 

chemical vendor3indicated that most power plants practice minimal treatment chemical use,

often operating well below the optimal COC, primarily because of the relatively low cost of 

obtaining make-up water and disposal of blowdown. 

A general rule of thumb for most towers is that calcium hardness in the recirculating water 

should be limited to 350 to 450 ppm unless treatment chemicals are used. Other limiting factors, 

 

2

In other words, a facility could only recirculate a portion of the heated circulating water through a cooling tower 

and back to the condenser; the remaining portion would be discharged as if it were once-through cooling water.

3 Keister, Timothy. ProChemTech International Inc.
- 5 -

such as silica, phosphate, and process contaminants should be considered as well (Harfst, 2008). 

Saltwater can be concentrated to about 55,000 ppm TDS in cooling towers with no serious 

scaling problems without pH adjustment (Nelson, 1986). The ratio of this 55,000 ppm to a 

typical seawater concentration of 35,000 ppm results in a calculated COC of 1.57, and so a COC 

for full strength seawater of 1.5 is a reasonable value to use for systems requiring minimal use of 

treatment chemicals. Estuarine and tidal waterbodies that contain some combination of saltwater 

and freshwater or brackish water will be able to operate at somewhat higher COC values. The

recommended COC values for saltwater systems range from 1.5 to 2.0.

In general, the higher the COC, the greater the reduction in make-up withdrawals, as less water is 

blown down. Appendix A shows cooling tower flow balance components for a 100,000 gpm 

cooling tower for cycles of concentration ranging from 1.1 to 10.0 and for temperature rises

across the condenser (∆T) ranging from 10 to 30 F. The percent flow reduction values represent 

the intake water flow reduction that would occur if this recirculating system replaced a oncethrough cooling system with the same condenser cooling water flow rate. Table 3 below shows 

the percent flow reduction values for the different values of COC and ∆T based on the data in 

Appendix A. 

Table 3

10 15 20 25 30

1.1 90.7% 86.0% 81.3% 76.6% 72.0%

1.2 94.9% 92.4% 89.8% 87.3% 84.7%

1.5 97.5% 96.2% 94.9% 93.6% 92.4%

2.0 98.3% 97.5% 96.6% 95.8% 94.9%

3.0 98.7% 98.1% 97.5% 96.8% 96.2%

4.0 98.9% 98.3% 97.7% 97.2% 96.6%

5.0 98.9% 98.4% 97.9% 97.3% 96.8%

6.0 99.0% 98.5% 98.0% 97.5% 96.9%

8.0 99.0% 98.5% 98.1% 97.6% 97.1%

10.0 99.1% 98.6% 98.1% 97.6% 97.2%

Evaporation Rate = T x gpm x 0.00085 (82% of heat loss is evaporation)

Drift Rate = gpm x 0.0005/100 (high efficiency drift eliminators)

Delta T (o

Cycles of F)

Concentration

Calculated Percent Flow Reduction

Figure 1 presents a graph of the data in Table 3 for ∆T = 10, 20, and 30 F. This data shows that 

the change in percent reduction in make-up water volume diminishes rapidly as the COC exceeds 

a value of about 5.0 and becomes nearly asymptotic at a value of 10.0. The COC and ∆T are 

primary factors driving the percent flow reduction of retrofit cooling towers.

 
Figure 1

Cooling Tower Percent Flow Reduction for Various Delta T and COC Values 

70.0%

75.0%

80.0%

85.0%

90.0%

95.0%

100.0%

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0

COC (1.1, 1.2, 1.5, 2, 3, 4, 5, 6, 8, 10)

Percent Flow Reduction

Delta T = 10 F

Delta T = 20 F

Delta T = 30 F
Chemical Requirements Costs of Operating at Higher Cycles of Concentration

A major component of cooling tower and cooling system maintenance involves measures taken 

to control biological growth, corrosion, and the build-up of deposits on metal surfaces and tower 

media. These deposits can consist of biological growth, solids contained in the make-up water, 

solids cleaned from the air, and solids that precipitate out of solution. The most damaging metal 

corrosion is the result of localized pitting which occurs under surface deposits. Additionally, 

deposits on heat transfer surfaces result in a reduction of overall system power generating 

efficiency and the growth of certain microorganisms such as Legionella can create a human 

health hazard. 

Control of suspended solids in recirculating cooling water systems can include pretreatment of 

make-up water as well as side-stream filtration of a portion of the recirculating water. However, 

such measures are often cost prohibitive for large cooling systems. In some locations, dust 

entrained from the air can be a major source of solids in the system. Certain BMP provisions to 

control dust, such as better control of ash piles and suppression of dust from roads and coal piles, 

may be helpful.

Chemical treatment of cooling water generally serves the purposes of prevention and control of 

one or more of the following:

 Biological fouling

 Scale formation

 Solids deposition

 Corrosion

Treatment for control of biological fouling is almost universally practiced in both once-through 

and recirculating systems. Biocides are often injected on an intermittent basis, and so the 

amount used is not as dependent on the cooling water system input and output flows as are other 

chemicals that must be maintained at a constant dosage in the recirculating system. Thus, while 

some change in the amount or type of biocide used may occur when converting from oncethrough to recirculating cooling towers or when changing the cycles of concentration of a 

cooling tower, the change should not significantly alter treatment costs for biocides use. For 

many power plants, including those that currently use cooling towers, chemical treatment with 

biocides such as chlorine (including possible dechlorination of the effluent) is the only chemical 

addition that is associated with cooling water use. For many cooling towers, the operators 

generally operate the towers at a COC low enough to avoid serious solids- and scale-related 

problems. Problems not related to biofouling are dealt with using a non-chemical maintenance 

approach such as periodic system cleaning to deal with solids and cathodic protection, and

ultimately equipment replacement to deal with corrosion. 

Recirculating systems operating at higher cycles of concentration will develop correspondingly 

higher concentrations of the dissolved solids, hardness, and alkalinity in the make-up water,

which can result in problems with respect to scale formation. The formation of calcium 

carbonate scale is the result of a reaction of calcium hardness with alkalinity. One of the 

simplest treatment methods for control of calcium carbonate scale is the addition of acid (such as 
- 8 -

sulfuric or hydrochloric acid) to the make-up water, which reduces the alkalinity. In this 

treatment method, enough acid is injected into the make-up water to reduce the total alkalinity to 

50 to 100 ppm and maintain the pH of the cooling water within the range of 6.8 to 7.5 (Harfst, 

2008). However, treatment with acid must be carefully controlled to prevent an excessively low 

pH, which could lead to corrosion problems and involves the risk of onsite storage of large 

quantities of a hazardous material.

Another common treatment chemical useful for preventing scale formation is phosphonate.

Phosphonate controls scale by adsorption onto crystal surfaces disrupting the crystalline structure 

of calcium carbonate. A typical dose of phosphonate for a cooling tower operating with a COC 

in the range of 3-6 would be 2-4 ppm (Keister 2009). The term “dose” as used here is the 

concentration that must be maintained in the recirculating water. As such, the rate of chemical 

addition associated with any dosage will be dependent on the rate of depletion, such as loss 

through blowdown, drift, and degradation.

A common treatment chemical useful in controlling solids deposition is polyacrylate. 

Polyacrylate acts as a dispersant and is very effective at controlling solids with particle sizes of 2 

microns or less. For cooling towers operating with a COC in the range of 3-6, a typical dose of 

polyacrylate would be 4-5 ppm (Keister 2009)

As a cooling tower’s water efficiency is increased by increasing the cycles of concentration, a

point will be reached where treatment chemicals may become necessary, and the dosage will 

increase as the COC increases beyond that point. This may also result in an increase in costs for 

more frequent monitoring of tower water quality and control of blowdown rates. However, the 

associated reduction in blowdown volume will also result in a reduction in the rate of chemical 

lost from the system. Treatment chemical vendors are able to evaluate the variation in chemical 

costs associated with these tradeoffs and recommend the optimum level that minimizes chemical 

and other operating costs while also minimizing risks. One treatment chemical vendor said that 

the optimum level for most industrial cooling towers is at a COC ranging between 3 and 6, with 

the lower end being applicable to systems with high hardness make-up water (Keister 2009).

Estimated Costs for Modifications to Operate Cooling Towers at Higher Cycles of Concentration

Operating at higher COCs in the range of 3 to 6 or higher for freshwater systems and 1.5 to 2.0 

for saltwater systems requires more precise control and monitoring of the blowdown rate and use 

of additional treatment chemical to control solids and scale. The following added costs may be 

necessary:

 Capital costs for a make-up flow meter and control system;

 Capital costs for chemical feed systems for up to two chemicals such as polyacrylate and 

phosphonate;

 O&M costs for additional chemical treatment; and

 O&M costs for additional labor for system maintenance, monitoring, and laboratory

analysis.
- 9 -

To illustrate these additional costs and to estimate scalable cost factors for the increased costs of 

operating at a higher COC, an example cooling tower configuration was developed. In this 

example, chemical treatment is assumed to include a scale inhibitor such as phosphonate for both 

saltwater and freshwater systems, plus a solids control chemical such as polyacrylate for 

freshwater systems. While these chemicals serve as examples for cost estimation purposes, other 

chemicals may be substituted where appropriate with little change in costs (Keister 2009B). 

All costs are assumed to be linear and are expressed in dollars/gpm of recirculating flow. The 

costs are based on a nominal system with the following design:

 A recirculating flow rate of 100,000 gpm

 A ∆T of 15 F

 A COC of 4.0 for freshwater systems and 1.5 for saltwater systems

Table 4 below provides the corresponding design data for a 100,000 gpm recirculating flow 

cooling tower.

Table 4

Chemical Cost Design Assumptions for a 100,000 gpm Cooling Tower

COC = 4.0 COC = 1.5

Make-up (gpm) 1,700 3,825

Blowdown (gpm) 425 2,550

Polyacrylate Dosage (ppm) 3.0 3.0

Phosphonate Dosage (ppm) 4.5 4.5

Additional Labor (hrs/day) 1.0 1.0

Capital Costs

Capital costs for the make-up control system and chemical feed system in the example cooling 

tower are based on the following costs:

 Flow meter for 1270 gpm make-up piping costs $4,000 or $2.80/gpm (Keister 2009);

 Chemical feed system costs $3,000 per chemical;

 Installation costs are 100% of total equipment costs; and

 Other indirect and direct costs including controls, electrical, engineering, site preparation, 

contingency, and allowance are 100% of total installed costs.

Based on the above assumptions, the capital costs for upgrading a recirculating cooling tower 

system to operate at higher COCs is $43,000 for freshwater and $55,000 for saltwater for a 

100,000 gpm system or $0.43/gpm and $0.55/gpm, respectively. This is a relatively small onetime cost item representing about 0.2% of the capital cost of an average difficulty cooling tower 

system.4

 

4 Using the EPRI cooling tower design and costing model, which assigns costs on various factors, including an 

assessment of the difficulty (easy, average, or difficult) for the tower retrofit.
- 10 -

O&M Costs

O&M costs consist primarily of the cost of treatment chemicals and added labor for monitoring 

and maintaining the system and conducting laboratory analysis of cooling water samples. It is 

assumed that the power plants have an onsite wet chemistry laboratory and maintenance staff and 

that these labor cost will only require an incremental increase in labor hours. O&M costs are 

based on the following assumptions:

 Cost of biocide treatment will not change significantly;

 Amount of treatment chemical added is equal to dosage times the volume lost to 

blowdown plus 10% to account for degradation;5

 Average unit cost of treatment chemicals is $4.00/lb6of active ingredient;

 Total added labor is 1.0 hour/day per 100,000 gpm of recirculating water (based on BPJ); 

and

 Labor rate is $54/hr based on the $41.1/hr labor rate used in the Phase II cost modules 

adjusted for inflation from 2002 to 2009 dollars.

Table 5 shows the resulting costs for a 100,000 gpm cooling tower.

Table 5

Estimated Increase in O&M Costs for Optimized Operation of Cooling Towers

COC = 4.0 COC = 1.5

Chemical Costs $61,000 $148,000

Labor $20,000 $20,000

Total $81,000 $168,000

Unit Costs/gpm $0.81 $1.68

Based on the above methodology, these costs can be considered as representative of the added 

costs to operate at higher COCs on a broad scale, but actual costs will vary based on site-specific 

water quality conditions. The average of these two values is $1.25/gpm and is nearly equal to 

the non-power-related net increase in O&M costs derived from the EPRI model that was used in 

calculating cooling tower costs for the revised Phase II rule development. The exact details of 

EPRI’s cost methodology are not known (i.e., which cost elements are included and what 

assumptions were used, but given that they are intended to be representative of past experience, 

it is reasonable to assume that the EPRI costs are based on the current practice of operating at 

lower COC values with minimal treatment using biocides. Thus, the above costs represent the 

incremental increase in O&M costs that should be added to cooling tower retrofit costs as well as 

for existing plants required to operate at higher values of COC. The COC that can be achieved 

with such a chemical treatment scheme will be dependent on the quality of the make-up water,

but at a minimum should be in the range of 3-6 for freshwater systems and 1.5 to 2.0 for 

saltwater systems.

 

5 Based on conversation with Timothy Keister, ProChemTech International Inc.

6 Approximate average based on estimated chemical cost of $3.44/lb and $4.25/lb active ingredient for phosphonate 

and polyacrylate, respectively. These costs are adjusted upward using a 40% markup and 5% tax from purchase 

costs reported by a chemical vendor of $2.34 and $2.89, respectively (Keister 2009).
- 11 -

Cooling Tower Media

Cooling tower media serves the purpose of increasing the interaction of water and air by slowing 

down the rate at which water drops through the tower and by increasing the surface area of the 

air/water interface. There are generally two kinds of media: splash fill and film fill. Splash fill 

consists of material that intercepts water droplets and redirects (splashes) them as they move

down through the tower. Film fill is composed of thin corrugated plastic sheets upon which the 

water flows as a thin film. Film fill tends to produce a more efficient heat transfer, but is more 

susceptible to plugging by solids and requires the initial spray system to be capable of providing 

a more uniform distribution of water droplets. Thus, while film fill may be more efficient it is 

also more likely to experience operational problems requiring maintenance. 

The type of fill can affect the air pressure drop across the media, which in turn affects the air 

flow rate through the tower. Within the different types of media are numerous design 

modifications that could result in tradeoffs between system efficiency, maintenance costs and the 

potential for operational problems. For example, a film fill with smaller channels may be more 

efficient than one with larger channels because of the greater water surface area, but may also be 

more prone to plugging with solids, which could result in lowered efficiency and higher 

maintenance costs. Decisions regarding selection of fill type and design must take into 

consideration the expected tower efficiency, water quality, spray system design requirements, the 

control measures to be employed both chemical and physical, and expected maintenance 

requirements. Use of film fill in towers where solids control is not adequate may result in a 

requirement to periodically clean the towers to remove the solids, and under worst-case 

situations the tower media may become so plugged that the media must be completely replaced.
- 12 -

References

Carney, Barbara. Feeley, Thomas J. McNemar, Andrea. NETL Power Plant water research 

Program. EPRI Advanced Cooling Technology workshop. July 9, 2008.

Daniels, David. M&M Engineering Associates, Inc. Put a Lid on Rising Chemical Costs. 

POWER Magazine. September 15, 2008. (http://www.powermag.com/issues/features/1347.html

DOE EIA. Electric Power Industry Overview- Electric Power Generation. Accessed on June 17, 

2009 at website: http://www.eia.doe.gov/cneaf/electricity/page/prim2/chapter3.html

Drbal , Lawrence F. Boston, Patricia G. Westra, Kayla L. Black & Veatch. Power Plant 

Engineering. 1995.

Engineering Tips. Chemical Process Engineering FAQ – Cooling Tower – How to calculate 

cycles, blowdown, evaporation, make-up. Accessed on October 20, 2009 at website: 

http://www.eng-tips.com/faqs.cfm?fid=1152

Harfst, William F. Enhanced Cooling Tower Maintenance Saves Water. Maintenance 

Technology. October 2008.

http://www.mt-online.com/article/1008-Enhanced-Cooling-Tower-Maintenance-Saves-Water

Keister, Timothy. ProChemTech International Inc. Log of telephone conversation with John 

Sunda. SAIC regarding technical, treatment chemical usage, and cost issues regarding the impact 

of increasing cycles of concentration (COC) in cooling towers August 25, 2009.

National Productivity Council of India (NPCI). Guide Book 3 – Energy Efficiency in Electric 

Utilities. Chapter 7 – Cooling Towers. No Date. Accessed on March 25, 2009 at website: 

http://www.em-ea.org/Guide%20Books/book-3/Chapter%203.7%20Cooling%20Tower.pdf. 

Nelson, John A. Marley Cooling Towers. Cooling Towers and Saltwater. November 5, 1986.

http://spxcooling.com/pdf/CTs-and-Salt-Water.pdf
- 13 -

Appendix A

Delta T

Circulating

water

Make-up 

Water Blowdown

Evaporati

on

Evapratio

n % of 

Circ. Drift

Cycles of

Conc

Make-up

% of Circ.

Percent

Reduction

deg F gpm gpm gpm gpm gpm Xc/Xm

10 100,000 9,350 8,499 850 0.9% 0.5 1.1 9.3% 90.7%

15 100,000 14,025 12,750 1,275 1.3% 0.5 1.1 14.0% 86.0%

20 100,000 18,700 17,000 1,700 1.7% 0.5 1.1 18.7% 81.3%

25 100,000 23,375 21,250 2,125 2.1% 0.5 1.1 23.4% 76.6%

30 100,000 28,050 25,500 2,550 2.6% 0.5 1.1 28.1% 72.0%

10 100,000 5,100 4,250 850 0.9% 0.5 1.2 5.1% 94.9%

15 100,000 7,650 6,375 1,275 1.3% 0.5 1.2 7.7% 92.4%

20 100,000 10,200 8,500 1,700 1.7% 0.5 1.2 10.2% 89.8%

25 100,000 12,750 10,625 2,125 2.1% 0.5 1.2 12.8% 87.3%

30 100,000 15,300 12,750 2,550 2.6% 0.5 1.2 15.3% 84.7%

10 100,000 2,550 1,700 850 0.9% 0.5 1.5 2.6% 97.5%

15 100,000 3,825 2,550 1,275 1.3% 0.5 1.5 3.8% 96.2%

20 100,000 5,100 3,400 1,700 1.7% 0.5 1.5 5.1% 94.9%

25 100,000 6,375 4,250 2,125 2.1% 0.5 1.5 6.4% 93.6%

30 100,000 7,650 5,100 2,550 2.6% 0.5 1.5 7.7% 92.4%

10 100,000 1,700 850 850 0.9% 0.5 2.0 1.7% 98.3%

15 100,000 2,550 1,275 1,275 1.3% 0.5 2.0 2.6% 97.5%

20 100,000 3,400 1,700 1,700 1.7% 0.5 2.0 3.4% 96.6%

25 100,000 4,250 2,125 2,125 2.1% 0.5 2.0 4.3% 95.8%

30 100,000 5,100 2,550 2,550 2.6% 0.5 2.0 5.1% 94.9%

10 100,000 1,275 425 850 0.9% 0.5 3.0 1.3% 98.7%

15 100,000 1,913 637 1,275 1.3% 0.5 3.0 1.9% 98.1%

20 100,000 2,550 850 1,700 1.7% 0.5 3.0 2.6% 97.5%

25 100,000 3,188 1,062 2,125 2.1% 0.5 3.0 3.2% 96.8%

30 100,000 3,825 1,275 2,550 2.6% 0.5 3.0 3.8% 96.2%

10 100,000 1,133 283 850 0.9% 0.5 4.0 1.1% 98.9%

15 100,000 1,700 425 1,275 1.3% 0.5 4.0 1.7% 98.3%

20 100,000 2,267 566 1,700 1.7% 0.5 4.0 2.3% 97.7%

25 100,000 2,833 708 2,125 2.1% 0.5 4.0 2.8% 97.2%

30 100,000 3,400 850 2,550 2.6% 0.5 4.0 3.4% 96.6%

10 100,000 1,063 212 850 0.9% 0.5 5.0 1.1% 98.9%

15 100,000 1,594 318 1,275 1.3% 0.5 5.0 1.6% 98.4%

20 100,000 2,125 425 1,700 1.7% 0.5 5.0 2.1% 97.9%

25 100,000 2,656 531 2,125 2.1% 0.5 5.0 2.7% 97.3%

30 100,000 3,188 637 2,550 2.6% 0.5 5.0 3.2% 96.8%

10 100,000 1,020 170 850 0.9% 0.5 6.0 1.0% 99.0%

15 100,000 1,530 255 1,275 1.3% 0.5 6.0 1.5% 98.5%

20 100,000 2,040 340 1,700 1.7% 0.5 6.0 2.0% 98.0%

25 100,000 2,550 425 2,125 2.1% 0.5 6.0 2.6% 97.5%

30 100,000 3,060 510 2,550 2.6% 0.5 6.0 3.1% 96.9%

10 100,000 971 121 850 0.9% 0.5 8.0 1.0% 99.0%

15 100,000 1,457 182 1,275 1.3% 0.5 8.0 1.5% 98.5%

20 100,000 1,943 242 1,700 1.7% 0.5 8.0 1.9% 98.1%

25 100,000 2,429 303 2,125 2.1% 0.5 8.0 2.4% 97.6%

30 100,000 2,914 364 2,550 2.6% 0.5 8.0 2.9% 97.1%

10 100,000 944 94 850 0.9% 0.5 10.0 0.9% 99.1%

15 100,000 1,417 141 1,275 1.3% 0.5 10.0 1.4% 98.6%

20 100,000 1,889 188 1,700 1.7% 0.5 10.0 1.9% 98.1%

25 100,000 2,361 236 2,125 2.1% 0.5 10.0 2.4% 97.6%

30 100,000 2,833 283 2,550 2.6% 0.5 10.0 2.8% 97.2%

Assumed Evaporation Rate 0.00085

Assumed Drift rate 0.000005

Cooling Tower Flow Calculations