Instructions for Retrofit Cost Analyses

November 2008 

EPRI, in collaboration with a number of participating utilities, is assembling information

to develop an estimate of the costs to the industry associated with widespread retrofit of 

power plant cooling systems from once-through cooling to closed-cycle cooling. The

aim of this effort is to obtain information from as many plants as possible, currently

equipped with once-through cooling, and from this sample to extrapolate to a national

estimate of closed-cycle cooling retrofit costs. 

To expedite the collection of information from the plants, a simplified methodology has 

been developed which is to be provided to each plant in the form of an ExCel spreadsheet 

for organizing the required information and making basic calculations necessary to 

estimate the capital and operating costs associated with a cooling system retrofit. A set of 

instructions accompanies the spreadsheet. 

A few general comments intended to clarify the approach and request follow: 

Approach: 

1. The cost estimates which results from this methodology are in no sense a 

substitute for site-specific engineering budget estimates. 

2. The capital cost estimates are developed in two steps: 

• Step 1: Three separate cost number are calculated for each unit based 

solely on the circulating cooling water flow rate of the existing oncethrough cooling system. These three costs are considered to be 

representative of an “Easy” (lowest cost), “Average” (intermediate cost) or 

“Difficult” (highest cost) retrofit. The costs per gpm of circulating cooling 

water flow rate for each category were determined in a survey of more 

detailed retrofit cost estimates from 50 plants. The methodology and 

results of this survey are described in detail in Reference 1. 

• Step 2: A wide range of site, plant and neighborhood characteristics are 

identified and examined for the purpose of making a qualitative judgment

as to where in the range of “Easy” to “Difficult” the particular unit would 

be expected to fall. 

3. In addition to the project capital cost of the retrofit, there are other costs to be 

considered. These include 

i. Higher cooling system operating costs 

ii. Higher maintenance costs 

iii. Plant performance penalty costs. 

These estimates of these costs are estimated in the spreadsheet based on

general guidance or rules-of-thumb for cooling tower size, typical performance 

and power requirements as well as local meteorological conditions and expected 

power plant operating profiles. 

1
4. Capital and operating costs are aggregated on a common basis by amortizing 

the capital costs for mid-range economic assumptions and remaining plant 

life. 

Request for information: 

Using the attached instructions and spreadsheet, please provide the following 

information. 

• Fill out Worksheet 1, 2 and 3 completely 

• Review Worksheets..... to ensure that all the relevant “automatic” 

calculations have filled in and to determine whether the default 

values given on the worksheets seem appropriate for your plant. 

Adjust the default values as seems appropriate. 

• Review all the qualitative information requests in Worksheets and

add descriptive comments and identifiers as appropriate. 

• Provide all drawings, maps, regulatory information as requested in 

the Instructions for each Worksheet.

• Provide in tabular form 

o Plant operating profiles (Worksheet 13) 

o Source water temperature (Worksheet 11) 

o Ambient temperature and wet bulb data 

(Worksheet 11) 

 in as much detail as possible. 

The Spreadsheet worksheets are set up for a maximum of 10 units per plant which 

should be adequate for nearly all cases. If a plant has more than 10 units, two separate 

spreadsheets can be used. 

Please return the filled out worksheets and the requested supporting documents by 

January 1, 2008. The spreadsheet should be sent to: 

Dave Bailey – dbailey@epri.com and John Maulbetsch (Independent EPRI Contractor) 

maulbets@sbcglobal.net

The following material consists of explanatory material for, and instructions for the use

of the accompanying ExCel spreadsheets to determine the costs of closed-cycle wet 

cooling system retrofits. 

Comprehensive retrofit cost estimates must include: 

• Initial capital cost of the retrofit itself

• Additional operating power costs 

• Additional O&M costs 

• Plant performance penalty costs 

• Assorted additional miscellaneous costs 

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The accompanying ExCel file {Retrofit_Cost_Analyses.xls} contains 14 worksheets for 

compiling and organizing the required information and for executing many of the 

required calculations for developing a cost estimate. 

Descriptions of the individual worksheets and instructions for filling them out are

provided below. 

Worksheet 1: Plant Information

Worksheet 1 asks for general location and contact information for the plant and is

essentially self-explanatory. 

• The contact person should be someone capable of answering (or of identifying 

other staff capable of answering) a broad range of questions about turbine and 

cooling system design and operation, plant site layout and constraints and 

pertinent environmental constraints at the site. 

• The plant inlet water flow should reflect the maximum water intake to the 

plant for all purposes. It must be entered in units of “gallons per minute” 

(gpm). If it is normally available in other units, common conversions are 

• 1 mgd (million gallons per day) = 694.4 gpm 

• 1 cfs (cubic feet per second) = 448.4 gpm 

Worksheet 2: Unit Information

Worksheet 2 asks for unit-specific information for each unit at the plant. There is the 

possibility for confusion in the case of combined-cycle plants since some companies 

designate the combustion turbine and steam turbine portions of combined-cycle plants 

with different unit numbers while others a assign single unit number to the entire 

combined-cycle unit. 

For the case of simple cycle combustion turbine units, only information under “All unit 

types” is required. For combined-cycle units, the gross capacity of the steam turbine is 

desired in addition to the total (CT’s + steam turbine) capacity. The condenser cooling 

water flow refers to the steam condenser cooling water flow only. 

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4

Worksheet 1: Plant Information

Plant Name

Owner(s)

Operating Company

Location

Street

City

State

Zip Code

Latitude

Longitude

Elevation

Contact person

Name

Title

Phone

E-mail

Plant Capacity, net (MW)

Plant Water Intake 

Flow, gpm

PLANT INFORMATION
Worksheet 2: Unit Information 

Unit 12 345 6 7 8 9 10

Unit Type (1)

For all unit types

Unit Capacity, gross (MW)FuelYear on lineCapacity factor, %

2006

2002 - 2006 Average

For steam units

Condenser cooling water

Flow, gpm

For combined cycle units

Steam turbine capacity, gross (MW)Condenser cooling water

Flow, gpm

(1) Unit type: CT (Combustion turbine); S (Steam cycle); CC (Combined-cycle)

UNIT INFORMATION

Worksheet 3: Capital Cost Information

Worksheet 3 calculates a range of initial retrofit capital costs based on the results of a 

survey of 50 plants conducted by Maulbetsch Consulting in 2002. The only input 

required is the condenser circulating water flow rate for each unit. The spreadsheet will 

return three costs for each unit classified as “Easy”, “Average” or “Difficult” retrofits.

The judgment as to which category best describes the situation at the individual plant and 

unit will be based on qualitative, descriptive information as requested in subsequent 

worksheets. These are: 

• Worksheet 4: Tower size 

• Worksheet 5: Site characteristics 

• Worksheet 6: Drift calculations 

• Worksheet 7: Neighborhood characteristics 

• Worksheet 8: Alternative water sources. 

Worksheet 3: Range of retrofit costs 

Retrofit Project Cost Estimates

Enter data

Plant: 0 Automatic calculation

Unit No. Circulating Water Flow

(gpm) Easy Average Difficult

1 0 1 $0 $0 $0

2 0 2 $0 $0 $0

3 0 3 $0 $0 $0

4 0 4 $0 $0 $0

5 0 5 $0 $0 $0

6 0 6 $0 $0 $0

7 0 7 $0 $0 $0

8 0 8 $0 $0 $0

9 0 9 $0 $0 $0

10 0 10 $0 $0 $0

Plant Total $0 $0 $0

Circulating Water Flow Rates Range of Retrofit Cost Estimates

Degree of Difficulty Unit No.

Worksheet 4: Tower size

Worksheet 4 returns the tower size as number of cells and the length and width of the 

tower footprint as a function of circulating water flow rate and a number of default 

assumptions listed on the worksheet. These are: 

Flow rate per cell: 10,000 gpm 

Cell dimensions: 50’ x 50’ 

Basin dimensions: Extends 4’ beyond tower in all directions 

These default values may be changed to accommodate individual design preferences. 

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The primary arrangement is in-line. The number of cells is rounded up to the nearest 

integer. 

Back-to-back tower arrangements may be considered if the in-line arrangement is too 

long to be sited any where on the plant property. The worksheet also returns dimensions 

for back-to-back arrangements. In this case, if the number of cells calculated for the inline tower is odd, it is increased by +1 to have an even number of cells. 

Note that back-to-back towers are built somewhat taller in order to provide the necessary 

air inlet area which is now limited to one side of the cell. This will affect the additional 

pumping power for a given recirculating water flow as the head rise to the hot water 

distribution deck is increased. (See Worksheet 9)

Worksheet 5: Site Characteristics for Judging Degree of Difficulty

The approach to a closed-cycle retrofit used in this analysis is the following: 

The existing once-through cooling system equipment is left intact to the extent possible; 

that is, the condenser, the circulating water pumps and the piping connections to the 

condenser inlet and exit waterboxes are kept the same. Hot water leaving the condenser 

is diverted away from the existing discharge structure and is discharged into a sump. The 

sump serves as the inlet bay for new circulating water pumps which pump the hot water 

through new circulating water line to the hot water distribution deck on top of the cooling 

tower. 

Cold water from the tower basin drains by gravity through a new circulating water line 

back to the intake bay of the existing once-through cooling water pumps. Provisions must 

be made for bringing make-up water to the closed cycle system and for discharging 

blowdown from the system. In some instances, these may be easily integrated into the 

existing once-through cooling intake and discharge structures. In others, new structures 

of the appropriate size and new transport lines may be required. 

A number of factors determine the degree of difficulty and hence the cost. Worksheet 5 

(Site characteristics) identifies the some of the items and the information needed to assess 

the difficulty and provides a place to document the conclusions. 

Tower location....An examination of the site plan determines if open areas of sufficient 

size are available to locate the tower on the plant property. Adjacent property may be 

purchasable. 

Existing structures may have to be torn down and relocated, such as storage sheds, 

parking garages and parking lots, equipment shelters, office buildings, etc. Locations 

with tall structures upwind from the tower are not desirable since they may create 

downdrafts or slow distortions which impair tower performance. 

Tower elevation 

8
The tower should be sited at a higher elevation than the existing cooling system intake 

bay in order to allow gravity return of the cold water. If this is not possible, grading may 

be required to elevate the tower basin. Absent this, a second set of new circulating water 

pumps to return the cold water may be required. 

Interferences 

Underground interferences in the path of the new circulating water lines or at the location 

of the hot water sump and new circulating water pumps may add greatly to the time and 

cost of the installation. 

 

Overhead interferences include transmissions lines. The moist plume and drift from the 

fan stacks of mechanical draft towers should not impinge on transmission lines or plant 

switchgear. 

Excluded areas 

There may be areas on the site reserved for security purposes, storage of hazardous 

materials, turn-around areas for large vehicles, etc. which cannot be relocated or blocked. 

This may be particularly true for nuclear facilities. 

Tie-ins to existing cooling system 

Existing intake/discharge structures are sized for the full recirculating flow rate which is 

much greater (10 to 50 times) than the make-up and blowdown flows from a closed-cycle 

system of the same cooling capacity. They may need to be abandoned 

and replaced with properly sized facilities. In some cases, they can be partially blocked 

to accommodate the lower flows. 

Details of cooling water system circuitry around the condenser are highly variable. The 

general arrangement drawings must be examined with the idea of determining how to 

bring cold water to the pump inlets and diverting condenser discharge to a newly 

constructed intake sump for the new circulating water pumps. The amount of space 

available, the arrangement of existing piping and surrounding structural walls will all 

affect the effort and cost required to convert this portion of the system to closed cycle. 

The new circulating water pumps must be located close to the existing condenser 

discharge area and power must be provided. If there are insufficient on-site auxiliary 

power facilities, they must be provided at additional time, cost and space requirements.

A sump must be provided as an intake bay for the new circulating water pumps. The 

sump must be large enough to provide adequate storage time for the circulating water 

flow (typically several hundred thousand gallons per minute). Finding adequate space for 

the sump may be difficult at many plants. 

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10

Site soil conditions 

Unfavorable soil conditions can add substantially to the cost of the retrofit. Saturated 

soils may require extensive drainage, pumping and the installation of liners to allow 

installation of the circulating water lines, sumps and tower basin. Pilings may be 

required to support heavy structures on unstable soils. 

Conversely, bedrock close to the surface may require blasting and excavation in order to 

place the lines. On some sites, previous usage and spillage may have resulted in 

contaminated soil which, if disturbed, becomes subject to costly clean-up or disposal 

requirements. 

It is difficult to provide rigorous guidance on how the consideration of each of these 

times be translated into the categorization of the project and “easy”, “average” or 

”difficult”. However, if none of the items presents any obvious problems, an “easy” 

retrofit might be 
Worksheet 4: Tower size calculations 

Retrofit Project Tower Size Estimates

Enter data Assumption

Plant: 0 Do Automatic calculation 

not 

erase

Circulating Water Flow

(gpm) # of cells Length Width 

1 0 0 ( - ) Ft. Ft. 2 0 0 1

3 0 0 2

4 0 0 3

5 0 0 4

6 0 0 5

7 0 0 6

8 0 0 7

9 0 0 8

10 0 0 9

10

# of cells Length Width 

( - ) Ft. Ft. 

123456789

10

Circulating Water Flow Rate Information

Tower Size---Back-to-back arrangeme

Unit No.Unit No.

Tower Size---In-line arrangement Unit No.
COOLING SYSTEM RETROFIT ANALYSIS 

Plant: 0 

ADDITIONAL SITE INFORMATION---To determine difficulty of ins

Site description Drawings Available De

Plant site boundaries Existing structures

Type

Location

Ground elevation profiles Underground utilities 

Type

Location

Depth

Areas excluded from consideration as cooling tower location 

Existing cooling system

Schematics/general arrangement drawings

Intake/discharge structures

Condenser inlet/exit piping

Circulating water pumps

Site geology

Saturated or unstable soils

Areas requiring rock excavation

Contaminated soil areas

Worksheet 5: Site characteristics 
expected. If two or three do, “average” is probably appropriate. If more, then “difficult” 

is appropriate. 

Plume and drift considerations 

Cooling towers frequently emit visible plumes during periods of cold weather and all 

towers emit some quantity of drift at all times. The implications of the frequent presence 

of a visible plume and the continuous emission of drift on the cost of and the ability to 

license a cooling tower retrofit depends strongly on the characteristics of the 

neighborhood surrounding the plant. 

Worksheet 6: Neighborhood Characteristics 

This worksheet is used to identify characteristics of the neighborhood in the vicinity of 

the plant and organizes items to consider in determining the likelihood that drift or visible 

plume would raise serious objections to the siting of a cooling tower on the site. 

Visible plumes

Visible plumes can be a problem for safety or aesthetic reasons. Safety issues arise if the 

plume obscures visibility on roadways or at airports. Aesthetic issues can be judged to be 

a problem in scenic areas or in residential areas where residents object. 

Objections to visible plumes can be eliminated through the specification of plume 

abatement towers. However, plume abatement towers can be far more expensive thatn 

conventional towers (a factor of x2 to x3 is likely) and require more fan and pumping 

power. 

Drift

Most modern cooling towers are equipped with drift eliminators which are specified to 

limit drift to 0.0005% of the circulating water flow. Two problems may arise. From a 

regulatory perspective, the dissolved and suspended solids in the drift (TDS and TSS) can 

be categorized as PM10. In some areas, this may be unacceptable or may require that 

offsets be purchased. The costs of offsets can be very high or simply unavailable in some

regions. 

From an environmental effects perspective, drift, particularly if it is high salinity as may 

be the case for saline or brackish water make-up or for towers operating at very high 

cycles of concentration, may cause problems both on-site and off-site. On-site problems

are normally corrosion of downwind equipment and structures requiring high levels of 

continuing maintenance or sometimes premature replacement of equipment. Off-site 

problems are normally related to damage to vegetation, marring of finishes on 

automobiles or other impacts in residential areas. 

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Worksheet 7: Drift calculations

The returns the total drift rate and the associated PM10 emissions rate for a specified 

circulating water flow rate and assumed values of drift eliminator efficiency, source 

water TDS and cycles of concentration. The PM10 emissions rate is determined assuming 

that all the dissolved solids in the drift are classified as PM10. While this is widely 

acknowledged to be a very conservative assumption, it is nonetheless the position taken 

by USEPA in their emissions rule. The cost associated with offsetting the PM10

emissions, if this would be required, must be determined from local information on the 

limits of emissions and the availability and cost of offsets. There is essentially no way of 

reducing the drift rates below the level of 0.0005% of the circulating water flow rate at 

this time. 

While there is little evidence in the literature suggesting that off-site drift damage has 

ever been a serious problem at tested sites, it is likely that attention to drift in siting 

hearings would lead to extended and costly objections which may or may not be 

eventually over come. 

Worksheet 6: Neighborhood characteristics 

Rural/

remote

High

density/

urban

Commercial Residential Other

General character of neighborhood (1)

Descriptive notes

(1) Check all that apply

Type

Distance

from plant, 

miles

Residential neighborhoodHigh traffic roadwayAirportSchoolsRetirement communityHospitalsPlaces of worshipScenic areas

Coastline

National Park

Other

NEIGHBORHOOD FEATURES/FACILITIES

NEIGHBORHOOD CHARACTERISTICS

Name, Identifier or Description
Worksheet 7: Drift calculations 

Retrofit Project Cost Estimates

Plant: 0 

Unit No. Circulating Water Flow Drift Rate PM 10

(gpm) gpm tons/year

1 02 03 04 05 06 07 08 09 0

10 0

Drift eliminator efficiency 0.0005%Source water TDS 500Cycles of concentration 5

DRIFT CALCULATIONS

Assumptions:
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Alternative water sources 

The normal assumption is that the make-up water for the retrofitted closed-cycle cooling 

system will be drawn from the same water source that supplies the existing once-through 

cooling system. Similarly, the cooling tower blowdown is assumed to be discharged to 

the waterbody that the once-through cooling water was returned to. In a limited number 

of situations, this may not be the case. 

Make-up alternatives: 

For example, for coastal plants using ocean water for once-through cooling, the salinity 

of the drift from a cooling tower with seawater make-up may be sufficiently high that the 

calculated PM10 emissions would exceed regulatory limits and require offsets which may 

not be available. In that case, with no options for reducing drift rates, lower salinity 

make-up sources would have to be considered. Options could include reclaimed 

municipal waste water, groundwater, irrigation drainage, produced water, mine drainage 

or perhaps others. 

Worksheet 8: Alternative Water Sources 

This worksheet identifies these water sources and requests information on availability, 

amount, water quality, distance of source from plant and some information on the 

neighborhood through which the supply and return lines would have to be installed and 

any local regulatory impediments to the use of the water. 

Similarly, cooling tower blowdown may not be permitted to be discharged to the same 

receiving water as the once-through cooling was returned to. While this would be 

expected to be a rare situation, increased salinity, the presence of different water 

treatment chemicals or other reasons may pertain. 

Such restrictions may require the installation and operation of additional water treatment 

processes up to and possibly including zero liquid discharge equipment and associated 

solids disposal. If this were the case, the costs could be comparable to those for the 

cooling tower itself. To determine what might be required, local aqueous discharge 

regulations must be reviewed and interpreted. 

Worksheet 8: Alternative water sources 

Characteristics

Municipal

reclaimed

water

Groundwater Irrigation drainage Produ

wate

Available to plant (1)

Quantity available, mgd

Water quality

pH

TSS, ppm

TDS, ppm

Other

Distance from plant, milesNature of area betweensource and plantRegulations affecting use

(1) Check all that apply

ALTERNATIVE WATER SOURCES
Additional operating power costs 

Additional operating power costs are those associated with the additional pumping power 

and fan power required for the operation of the cooling tower and the circulating water 

loop between the condenser and the tower. These costs are calculated in Worksheets 9 

and 10. 

These worksheets are automatically filled and activated by entering the circulating water 

flow rates for each unit in Worksheet 3. 

Worksheet 9: Pumping Power 

The results in Worksheet 9 (Pumping power) also require information about elevation 

changes on the site, the sizing of the circulating water lines, the circulating water pump 

efficiency and the pump motor efficiency. Default values for these quantities are 

displayed on the Worksheet and can be changed if desired to better reflect the situation at 

the individual site or project designer preferences. 

The pumping power calculated in Worksheet 9 is only that additional power required for 

the new circulating water line between the condenser and the cooling tower. It is 

assumed that water is delivered to the tower only when the plant is operating and that it is 

the same whether the unit is operating at full or part load. 

The pumping power for the existing once-through cooling circuit will be similar to what 

it was before the retrofit. However, the operating schedule may change. At some plants, 

with once-through cooling, the cooling water flow rate was maintained even when the 

unit was off-line in order to prevent fouling or silting of the intake structure. With the 

closed-cycle arrangement described above, where the intake and discharge structures are 

modified, this would likely not be the case and some pumping power savings might be 

realized. 

In many cases, the need for additional power for the new circulating water pumps and 

fans will require the installation of new on-site, electrical infrastructure such as motor 

control centers, transformers, switchgear, etc. If this is the case for this site, please 

indicate Yes or No and provide a brief description of the nature, size and any difficulties 

associated with locating the equipment on the spreadsheet of separately. 

Worksheet 10: Fan Power 

The results in Worksheet 10 (Fan power) also require information about fan size and fan 

motor efficiency. Default values for these quantities are displayed on the Worksheet and 

can be changed if desired to better reflect the situation at the individual site or project 

designer preferences. 

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The calculations in Worksheet 10 assume that all fans are at full speed whenever the 

plant is operating. During some periods of the year, when the unit is at partial load or the 

ambient wet bulb temperature is well below design, some operators turn off fans to save 

power with little or no effect on turbine performance. However, these operating 

procedures vary widely from plant to plant and are not considered in this analysis. 

In many cases, the need for additional power for the new circulating water pumps and 

fans will require the installation of new on-site, electrical infrastructure such as motor 

control centers, transformers, switchgear, etc. If this is the case for this site, please 

indicate Yes or No and provide a brief description of the nature, size and any difficulties 

associated with locating the equipment on the spreadsheet of separately. 

Additional maintenance costs 

Closed-cycle cooling systems are likely to incur higher maintenance costs than the oncethrough cooling systems which they replace. This is the result of several factors: 

The cooling tower itself requires cleaning, fill and drift eliminator maintenance and, in 

some cases, periodic repacking of the tower. 

The retrofitted system will have additional circulating water pumps, modified intake 

structure, etc. Water treatment may be required for discharge of cooling tower 

blowdown. If zero liquid discharge rules pertain, the costs can equal that of the cooling 

tower. (This seems unlikely at a site currently on once-through cooling.) 

The cost of the additional maintenance in labor, equipment and chemicals is highly sitespecific. However, a range of independent studies (EPA, Burns, Burns and Micheletti) 

have used factored costs ranging from 1 to 3% of the cooling system capital costs. 

Assuming this accounts for approximately 40% of the ”EASY” estimate on Worksheet 4, 

an annual additional maintenance costs may be estimated. This is included in the 

summary cost table on Worksheet 14 using 2% as an intermediate factor. 

Worksheet 9: Pump power calculations 

Retrofit Project Cost Estimates

Enter dat

Plant: 0 Automati

Unit No. Circulating Water Flow Tower Arrangement Line Dia. ∆h3 ∆h4 Total Head Pump P

(gpm) In-line = 1; Back-to-back =2 ft ft ft ft MW

1 0 0.02 0 0.03 0 0.04 0 0.05 0 0.06 0 0.07 0 0.08 0 0.09 0 0.0

10 0 0.0

Pumping power = (Circ. water flow rate x Head rise)/(Pump efficiency x Motor efficiency)Head rise = ∆h1+ ∆h2 + ∆h3 + ∆h4∆h1 = Elevation rise from sump level to pump level∆h2 = Elevation rise from pump to tower site∆h3 = Height of tower hot water distribution deck∆h4 = Head loss through circulating water line to tower∆h1, feet 5∆h2, feet 10∆h3, feet 25 for in-line arrangement∆h3, feet 35 for back-to-back arrangmeent∆h4, feet Calculated assuming circ. water flow velocity Velocity, ft/sec 9

Pump efficiency 0.85Motor efficiency 0.9Circ. line length, ft 1,000

Pumping Power Calculations

Calculations:Assumptions:
Worksheet 10: Fan power calculations 

Enter data

Plant: 0 Automatic calc

Unit No. Number of cells Fan Power

MW

1 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.0

10 0.0

Calculations:Assumptions:

Fan power = (Number of cells x Fan power)/Motor efficiencyPower per fan 200Motor efficiency 0.9

Fan Power Calculations
Plant performance penalty costs

Retrofitting once-through cooled plants with closed-cycle cooling generally imposes a 

performance penalty on the unit, since the cold water supplied to the condenser from the 

cooling tower is typically at a higher temperature than water that would be withdrawn 

from the local natural waterbody. This is a result of the following considerations. 

1. Cold water from a cooling tower is limited by the ambient wet bulb temperature. 

Typical tower designs deliver cold water about 10oF higher than wet bulb at the 

“1% wet bulb” design point. 1 

2. At times when the wet bulb is lower as it is during colder, drier weather, the

“approach” to wet bulb is higher than 10oF. 

Therefore, the condenser inlet temperature with a closed-cycle system is nearly always

higher than with a once-through cooling system resulting in a corresponding increase in 

the condensing temperature and the turbine backpressure. 

Increased turbine backpressure leads to a higher unit heat rate which results in either 

reduced MW output at a constant firing rate or a higher firing rate to maintain a constant

MW output. In either case, an economic penalty is incurred either as lost revenue or 

increased fuel cost. 

An estimate of the magnitude of the performance penalty can be carried out at varying 

levels of complexity. 

In the absence of any additional information, an annual heat rate penalty of 1.5% to 2% is 

consistent with a number of independent analyses. However, the magnitude of the penalty 

will vary with a number of factors. The most important of these are unit operating 

profile, condenser and cooling tower design, turbine characteristics and site meteorology. 

The following worksheets indicate the information required for a comprehensive estimate

of the performance penalty. 

Worksheet 11: Site Source Water and Ambient Weather Information) 

Worksheet 11 (Site source water and ambient weather information) provides tables for 

entering information on source water temperature and ambient temperature and wet bulb 

temperature in varying levels of detail. Hourly data for source water data for an entire 

year is preferred. However, if this level of detail is not available, an alternate table to 

provide maximum, average and minimum values of source water temperature for each

month is provided. 

Worksheet 12, Table A, requests condenser design information, turbine heat rate 

information2

 and average fuel cost and energy price information. In the absence of 

 

1

 That wet bulb temperature which is exceeded only 1% of the summertime (June through September)

hours (~ 30 hours/year)

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condenser design information, the smaller tables to the left of Table A on the Worksheet 

will use the indicated default values and the maximum source water temperature and the 

1% wet bulb temperature from Worksheet 11 to calculate a “design point” difference in 

turbine backpressure between the two cooling systems. Note that Worksheet 11 contains 

Table A which can accept condenser design information if available. The results 

calculated for the design specifications can then be manually substituted for the default 

values if desired. 

Worksheet 13 (Tables 1 and 2) provide alternate levels of detail for providing the unit 

operating profiles. 

The effect of different tower design choices can be observed by varying the approach 

temperature away from the default value of 10 oF. Limits of 5 oF (larger tower) and 15 oF 

(smaller tower) are suggested. 

Worksheet 14 (Summary) aggregates all the costs in expresses them both as an 

annualized and a life cost.

2

 A manufacturer-supplied heat rate curve would be preferable to these point values if available. 
Worksheet 11: Site source water and ambient temperature data

 Enter data

Plant: 0 Automatic calculation

Water Source Date/Time Temperature, F Month Maximum, F Average, F MSource water temperature 1/1/06 0:00 January

Yearly maximum, F 1/1/06 1:00 February

Yearly minimum, F 1/1/06 2:00 March

Yearly average, F 1/1/06 3:00 April

Ambient temperature 1/1/06 4:00 May

Yearly maximum, F 1/1/06 5:00 June

Yearly minimum, F 1/1/06 6:00 July

Yearly average, F 1/1/06 7:00 August

Ambient wet bulb 1/1/06 8:00 September

1% wet bulb, F 1/1/06 9:00 October

Yearly minimum, F 1/1/06 10:00 November

Yearly average, F 1/1/06 11:00 December

1/1/06 12:00 Annual 0 #DIV/0! 

1/1/06 13:001/1/06 14:001/1/06 15:001/1/06 16:001/1/06 17:00 Month Maximum, F Average, F M

1/1/06 18:00 January1/1/06 19:00 February1/1/06 20:00 March1/1/06 21:00 April1/1/06 22:00 May1/1/06 23:00 June

1/2/06 0:00 July

August

September

October

November

extend for full year December

Annual 72 #DIV/0! 

Wet bulb temperature data

SITE INFORMATION Source water temperature data Ambient temperature data
Worksheet 12: Cooling system and unit design information 

Plant: 0

Enter data

 Automatic calculation

Max. source water temperature, F 0 Unit 12 

Steam condensing temperature, F 27 Condenser design specs.Turbine backpressure, in Hga 0.3 Cooling water flow, gpm 0 0 

Steam flow, lb/hr

Heat load, Btu/hr

1% wet bulb temperature, F 0 Water inlet temp., FSteam condensing temperature, F 37 Water exit temp., FTurbine backpressure, in Hga 0.3 Steam condensing temperature, F

Steam condensing pressure, inHga

Efficiency/heat rate penalties

Output @ design backpressure

Output @ design backpressure + 1 in Hga

Range, F 20 Output @ design backpressure + 2 in HgaTTD, F 7Approach, F 10Fuel cost, $/MMBtu 5Power price, $/MWh 35

Economic factors

Default values

Cooling tower design assumptions

Once-through cooling 

(based on Default values below)

Once-through cooling 

(based on Default values below)

Condenser design assumptions

Table A---UNIT DESIGN/OPERATING INFORMA
Worksheet 13: Unit operating profile; (Table 1---preferred) 

Unit Operating Profile DataPreferred:

Hourly power level for each unit forcorresponding period as source water and ambient temperature data (See Table 1)

Minimum:

Monthly energy output (MWh) for each unit

for same year as source water and ambienttemperature data (See Table 2)

Unit 1 Unit 2 Unit 3 Unit 4 Unit 5

MW MW MW MW MW

1/1/06 0:001/1/06 1:001/1/06 2:001/1/06 3:001/1/06 4:001/1/06 5:001/1/06 6:001/1/06 7:001/1/06 8:001/1/06 9:00

1/1/06 10:001/1/06 11:001/1/06 12:001/1/06 13:001/1/06 14:001/1/06 15:001/1/06 16:001/1/06 17:001/1/06 18:001/1/06 19:001/1/06 20:001/1/06 21:001/1/06 22:001/1/06 23:00

1/2/06 0:00

extend for full year

Table 1 Hourly Power Level--By Unit

Date/Time
Worksheet 13: Unit operating profile; (Table 2---minimum) 

Unit 1 Unit 2 Unit 3 Unit 4 Unit 5 ad

MWh MWh MWh MWh MWh

January

February

March

April

May

June

July

August

September

October

November

December

Table 2 Monthly Energy Output--By Unit

Month
Worksheet 14: Summary 

Maintenance Heat rate penalty

$ $ $ MW $/yr $/yr $/yr $ $ $ 

Easy Average Difficult Easy Average Difficult 

1 $0 $0 $0 0.00 $0 $0 $0 $0 $0 $0 2 $0 $0 $0 0.00 $0 $0 $0 $0 $0 $0 

3 $0 $0 $0 0.00 $0 $0 $0 $0 $0 $0 4 $0 $0 $0 0.00 $0 $0 $0 $0 $0 $0 5 $0 $0 $0 0.00 $0 $0 $0 $0 $0 $0 6 $0 $0 $0 0.00 $0 $0 $0 $0 $0 $0 7 $0 $0 $0 0.00 $0 $0 $0 $0 $0 $0 8 $0 $0 $0 0.00 $0 $0 $0 $0 $0 $0 9 $0 $0 $0 0.00 $0 $0 $0 $0 $0 $0 

10 $0 $0 $0 0.00 $0 $0 $0 $0 $0 $0 

Capital Cost Operating Power

Unit No.

Annualized Cost 

SUMMARY INFORMATION