United States
Environmental Protection
Industrial Environmental Research
Research Triangle Park NC 27711
EPA-600 7-80-078
April 1980
Wet/Dry Cooling
Tower Test Module

R&D Program  Report


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                                          April 1980
Wet/Dry Cooling Tower
          Test Module

                D.M. Burkart

        Southern California Edison Company
                P.O. Box 800
           Rosemead, California 91770
              Grant No. R805220
           Program Element No. INE624
        EPA Project Officer: Theodore G. Brna

     Industrial Environmental Research Laboratory
   Office of Environmental Engineering and Technology
         Research Triangle Park, NC 27711
                 Prepared for

        Office of Research and Development
             Washington, DC 20460


     In February  1978,  a ten-member group of utilities, public
agencies,  and private  concerns, with Southern California Edison
Company acting as Project Manager, began the field testing of a
single cell wet/dry cooling tower  (capable of cooling the waste
heat  from a  nominal  15 MWe  of  generation)  at a  generating
station located  in San  Bernardino, California.  The objectives of
the test program were to:

             1.    Determine the water  conservation  aspects of
                  a  wet/dry cooling  tower in an arid  climate.

             2.    Determine  the  operational  characteristics
                  of a  wet/dry cooling tower.

             3.    Develop  and  verify  a mathematical model
                  of the  wet/dry cooling tower.

     The test program  was successful  in achieving  the stated
goals  of  determining  the water  conservation characteristics,
determining the  operational characteristics,  and  developing and
verifying  a mathematical model  of a  wet/dry  cooling tower.

     Reduction of the  data revealed that the wet/dry  tower could
save  approximately  19% of the water normally  evaporated  by an
evaporative  cooling tower at  the San Bernardino  Generating
Station without  significantly  affecting  the normal plant perfor-
mance.  This degree of water  conservation must be considered to
be  very  good given the conditions of  operation.   It  is  also
indicative of the great potential  of  wet/dry cooling  for achiev-
ing significiant water  conservation when the system is optimized
with that  goal in mind.

     During the  testing period of eighteen months  there were
several operational problems, the most notable  being sticking wet
and dry section dampers, which resulted  in design modifications
and revised maintenance and operational  procedures.

     The mathematical model  was developed under EPRI  contract by
PFR Engineering  (Systems,  Inc.,  and was  verified  by  field test
data obtained  from the  project.

                         TABLE OF CONTENTS


    Abstract                                                   ii

    List of Figures                                            iv

    List of Tables                                              v

    Acknowledgements                                           vi

1.  Introduction                                                1

2.  Conclusions and Recommendations                             7

3.  Operating History                                           8

4.  Test Results                                                9

5.  Mathematical Model                                         18


     A.  Operational Characteristics                           20

     B.  Method of Determination of Heat Rejection
         Rate and Evaporation Rate                             35

     C.  Uncertainty Analysis                                  37

     D.  Test Instrumentation                                  39

     E.  Description of Damper Control System                  47

     P.  Test Plan                                             49

     G.  Table of Conversion Factors                           51

                        LIST OF FIGURES


  1     San Bernardino Generating Station Plot Plan             2
  2     Operational Schematic of Ecodyne Wet/Dry Cooling Tower  4
  3     Dry Section Performance                                10
  4     Wet Section Performance, Hot Water Temp. = 96P        n
  5     Wet Section Performance, Hot Water Temp. = 94F        12
  6     Wet Section Performance, Hot Water Temp. = 92F        13
  7     Wet Section Performance, Hot Water Temp. = 90F        14
  8     Wet Section Performance, Hot Water Temp. = 88F        15
  9     Evaporation Rate                                       16
A-l     Damper Linkage (photograph)                            21
A-2     Structural Support Member (photograph)                 22
A-3     Damper Blades (photograph)                             24
A-4     Biological Growth in Hot Water Basins (photograph)     26
A-5     Floating Scum in Hot Water Basins (photograph)         27
A-6     Top View of Hot Water Basin                            29
A-7     Example of Finned-tube Fouling (photograph)            30
A-8     Workman Cleaning Finned Tubes (photograph)             32
A-9     Results of Finned-Tube Cleaning (photograph)           33
A-10    Effect of Finned-Tube Cleaning (photograph)            34
D-l     Wet/Dry Cooling Tower Anemometer Locations             4o
D-2     Wet Bulb Temperature and Velocity Map of Stack,
          "All Wet"                                            42
D-3     Wet Bulb Temperature and Velocity Map of Stack,
          50% Wet/505? Dry                                      43
D-4     View of Top of Stack showing Psychrometer Location     44
D-5     Wet/Dry Cooling Tower Instrumentation Schematic        46
E-l     Damper Control as a Function of Demand                 48

                         LIST OP TABLES

  1     Average Site Meteorological Conditions
A-l     Typical Wet/Dry Cooling Tower
          Circulating Water Quality


     The  author  acknowledges the  time  given and  patience  shown
by the  active  members  of  the Coordinating Committee:   John  Bartz
of EPHI,  Ted Brna  of EPA, Alex Mailer of  DWR,  Al  Ward of Tucson
Electric, Rudy Alleman of Battelle, Cal  Singman of  LADWP,  Harry
Bishop  of WEST,  and  John  Lipnicke  of  Ecodyne;  during the  testing
period  and  the preparation of this report.  A  special thanks  is
given to  the personnel at the San  Bernardino Generating Station,
especially Jack  Severn and Mike Varvis,  who, many  times, bailed
the project out  of  trouble.   Work  done by Ron  Moore  of Environ-
mental  Services  Corporation,  Dave  Stackhouse of Ecodyne,  and  the
SCE Shop  and  Test  Department  in helping to calibrate  the  tower
instrumentation was invaluable.

     Finally,   a  word  of  gratitude is  given to Bill  Vanderford
who worked long,  hard,  and often alone  to  keep  the project

                         1.  INTRODUCTION


     During 1976, a  ten  member co-operative was formed for  the
purpose of constructing and  testing a wet/dry cooling tower.   The
membership of this group  is  as  follows:

       Southern California Edison Company
       Tucson Electric Power Company
       Department of  Water and Power of  the  City of Los  Angeles
       Ecodyne Corporation
       Electric Power Research  Institute  (EPRI)
       Western Energy Supply and Transmission  Associates  (WEST)
       United States  Department of Energy
       United States  Environmental Protection Agency
       State of California Department of  Water Resources
       State of California Energy Commission

     Southern California  Edison Company was designated as  Project
Manager of the Wet/Dry Cooling  Tower Test Module (Wet/Dry  Tower).
Onsite construction  commenced in April 1977 and was completed in
December 1977.   The  test program  commenced  in February 1978  and
was completed in July 1979.


     The objectives of the test program were as follows:

     1.  Determine the operational characteristics of a
         wet/dry cooling tower in an actual  generating  station

     2.  Develop a  mathematical  model  of  the wet/dry cooling
         tower and verify it with actual  data.

     3-  Determine  the  water conservation aspects of  a wet/
         dry  cooling  tower  operating in  an arid  climate.


     The  Wet/Dry Tower  was  sited  at the  Southern California
Edison Company's San Bernardino Generating Station located in San
Bernardino, California.   The generating  station consists  of  two
60  MW oil/ gas  fired units cooled by  two 10-cell  evaporative
cooling towers.  The layout  of the station is shown  in Figure 1.
The Wet/Dry Tower is  situated near  the north station  cooling
tower  with a  portion of the  plant circulating  water  being  by-
passed  from that tower  to  the Wet/Dry  Tower  by a  small circu-
lating pump.   The water  is  returned  to  the north tower basin by
gravity flow from the Wet/Dry Tower basin.


                                        station fence
                                 Wet/Dry Tower

cooling towers
                        Unit 2
turbir es
                        Unit 1
 Figure  1.   San  Bernardino  Generating Station Plot Plan

     The average meteorological conditions recorded at the  site
during the test period  are as follows:


                          Jan   Feb   Mar   Apr   May   Jun

Mean High     Dry Bulb(F) 63    66   68    73    78      85
Temperature   Wet Bulb(F)  52    53   53    56    59      61

Mean Low      Dry Bulb(F)  38    40   43    47    51      55
Temperature   Wet Bulb(F)  35    36   38    40    42      45

                          Jul   Aug   Sep   Oct   Nov   Dec

Mean High     Dry Bulb(F)  95    94   91    81    71      64
Temperature   Wet Bulb(F)  64    64   63    59    55      54

Mean Low      Dry Bulb(F)  60    61   58    51    43      39
Temperature   Wet Bulb(F)  49    50   49    45    40      36


     As seen  in Figure 2, the  Wet/Dry Tower (manufactured by
Ecodyne  Corporation)  is  essentially a crossflow evaporative
cooling tower  below  with  a crossflow water-to-air surface  heat
exchanger on top.   The water  flow path  is  from the hot water
basin  atop the tower  down  through the finned-tube dry  section
directly onto the splash-fill wet  section.   The air flow  path is
parallel  through both the wet and dry sections with air  flow
being  controlled independently  to  each  section  by  dampers.  The
amount of heat rejected  by  either the wet  or dry sections is
controlled by these  dampers.  It is possible to operate the tower
in  the all-wet  or all-dry modes, or  any combination of  the  two,
by opening or closing  the  dampers.

     The  dry section  tubes are   1  inch  O.D.,  constructed of
copper-nickel  with  aluminum  fins rolled  on the tubes.  The
overall diameter of  the finned  tubes  is  2.25 inches; there are 11
fin  spirals  per inch,  and the  total  length  of the tubes is 19
feet,  3  inches.  There is a  total  bare tube  surface  area of
approximately  20,000  square  feet.   Operationally, water  flows
into  the  tubes from the  hot  water basins  through flow  control
nozzles.   The  flow  control nozzles are  of  a unique design which
causes the water to spiral  down the  interior wall of  the tube,
* English  system units rather than metric have been used through
  this report because the English system remains the standard in
  the  utility industry  for which this  report is intended.   A
  conversion table is included as  Appendix G.


                           WARM DRY
                       Figure 2

            Operational Schematic of Ecodyne
                 Wet/Dry Cooling Tower

creating a film flow condition which significantly increases the
heat transfer  coefficient  over conventional axial flow.   There
are 7  basins  per  side  (14  in  total)  with 273  finned  tubes per
basin.   The  flow to each  basin is individually controlled by
butterfly valves.

     The water  exits  the tubes through nozzles  which  spray the
water  directly  onto  the splash fill in the  wet section.   Fixed
positon air intake louvers  are  provided to prevent splash leakage
out  of the  wet  section.    The  wet section is  29  feet  high.

     The dampers  are actuated  by  motor  drives  which  are located
on the fan deck at the  top  of the  tower.  The drive elements pass
through the  deck  to  torque  tubes which  connect to  the dampers.
The damper positioning  is accomplished by a unique damper control
system which automatically controls the distribution of air flow
between the wet and dry  sections based on the exiting cold water
temperature.   A complete description of the damper control system
is found in Appendix  E.

     Air flow is  provided  by a 28  foot  diameter fan  which has 8
blades.  The  fan is powered by  a 250 horsepower  motor and runs at
a constant 135 RPM.   The  blades are manually adjustable for
pitch angle.


     As can be  seen from Figure 1,  the Wet/Dry  Tower is situated
as a  side-stream  process to the  station's  main cooling towers.
During normal  testing,  the Wet/Dry Tower has a water flow of
approximately 20% of the total circulating water flow.  Combined
with the  fact  that the main towers have  a larger cooling  range
and a  lower approach than  the Wet/Dry Tower, this results in the
Wet/Dry Tower having little  effect  on the condenser circulating
water  exit temperature  (cooling  tower inlet water temperature).
During the summer months this causes no difficulty as the cooling
tower  inlet temperature  is sufficiently high enough to allow the
tower  to  develop  a full range  of cooling,  but  in the winter a
problem does  exist.   Because  of  the lower  approach  and larger
range  of the main towers,  the cooling tower  inlet temperature is
too low to allow the  Wet/Dry Tower to develop a  full range in the
all-dry cooling mode.   During  the winter the station  condensers
typically operated with a backpressure in  the range of  1.1 to 1.4
inches HgA (mercury,  absolute).   A backpressure of  4  to 4.5
inches  HgA would  have been  required in  order  to allow a normal
cooling  range  in the all-dry  cooling mode.   Operating at  such
high backpressures solely for the  purposes  of this test could not
be economically justified.

     This  limitation did  not  present  serious  difficulties in
defining the dry section parameters, but  did limit the  simulation


of normal winter operation.


     Possibly the  most important result of the test program was
the development and verification of the mathematical model.  This
will be very  valuable  in future site selection and preliminary
engineering.   Unfortunately, the model at this  time is limited to
this particular design of wet/dry cooling tower, which somewhat
limits its  usefulness.   It  is  anticipated  that additional im-
provements will be made to the model a result of the data  taken
during the test program,  resulting in a  more flexible predictive

     The  major  goals  of  the  program  were  achieved  and wet/dry
cooling has been  shown to  be an effective and viable method of
achieving  water conservation at  an inland generating station
(approximately 19% during the test program).  However, during the
test  period  several areas  of investigation, the most notable
being the measurement of the  individual wet and dry section air
flow rates,  had to be abandoned as unproductive.

     The  eighteen month  period  of field operation revealed two
deficiencies  which will require  further rectification before
this  design of wet/dry  cooling  could  be recommended without
reservation for commercial  operation.   The major  concern lies
with  the  sticking air control dampers;  this  problem renders
automatic  control  of  the  tower impossible.   As discussed in this
report, it is  recommended  that  several  improvements  be made in
order to  assure reliable  operation:

     1.   Redesign  of the  damper  drive linkages.    Although
          this  is already being done  by  the  manufacturer,
          it  will  be necessary  to field test  in order to  prove
          the design.

     2.   New motor  drives  should be selected  to  provide more
          starting torque.

     3.   The drive  linkages for the damper blades  should be
          positioned  on both  ends of  the  blades rather than on
          one end  only  as is presently done.

     The  other deficiency lies  with the  fouling of  the dry
section  finned tubes.   Ecodyne  has presented  and  proved one
method of cleaning which is labor intensive  and  expensive.  Some
type  of permanently mounted  cleaning  system which would provide
the  option for reduced  manpower must now  be developed.   This
would  allow  an evaluation of the  site  to be made, taking into
account  such  factors  as   expected  cleaning frequency, site
remoteness, cost  of labor,  and  capital  expense  of  the  permanent
system, yielding the  most economical method of cleaning.

                        3.  OPERATING HISTORY

     On February  6,  1978, testing was initiated and on July  23,
1979,  the  test program was  completed.   During the 532 day test
period, the Wet/Dry Tower was  available  for  testing 80.3% of  the
period.  Additionally,  due  to a labor strike  which required  the
reassignment of some SCE  technical  and managerial  personnel,  the
Wet/Dry Tower was unmanned a major portion of the  period from  May
1, 1978, through July 30,  1978.  During  this  period no  testing was
performed although data was  collected automatically on an hourly

     The unavailability of  the Wet/Dry  Tower  can  be broken down
into the following categories:

     Sticking Dampers                           10%
     Biological Growth in  Hot Water Basins        1%
     Instrumentation Failures                     5%
     Fan Drive Shaft Bearing Failure              8/?
     Recalibration and Relocation
       of Instrumentation                        J6%

     The problems encountered  with  sticking  dampers and biologi-
cal  growth  in the hot  water basins are  discussed in  detail in
Appendix  A.   The fan drive shaft bearing  failure was  due to
faulty maintenance.   The  instrumention  failures occurred solely
with the data acquisition  and storage systems.   The recallbration
is discussed in Appendix D.

     Because of these problems, most notably  the sticking dampers
and  instrumentation  failures,  the test plan  was not followed
in its entirety  as  is detailed in Appendix F.   However,  the
primary objectives of the  test  plan wera  met.

                       4.  TEST RESULTS


     Figure  3  shows  the dry  section  performance  in degrees
Fahrenheit of water cooling  (dry  section  range  of  cooling)  as  a
function  of  the temperature difference  between the inlet  hot
water  temperature  and  the inlet  air dry-bulb  temperature at  a
constant water-air mass  flow ratio.   Two distinct sets of  data
are plotted,  data taken with the finned tubes heavily fouled and
data  taken after  cleaning  of the  tubes (see  Appendix A).   A
marked  difference  between  the  two is  obvious.   The  data  taken
with the finned tubes heavily fouled  were all taken within a two
month  period and,  therefore, do not reflect  any function of
fouling with  relation to  time.  By calculation,  the air-side heat
transfer coefficient was  found  to be  ^5% higher  for  the  clean
tubes over the  fouled tubes.  The  data taken with the clean tubes
were taken during a short  period of time and cannot be considered
complete.   However, the  greatly  improved  agreement between this
data and the performance  predicted by  the mathematical model is
very encouraging.

     Figures  4,  5>  6,  7  and 8 show  the  wet section  performance
in  degrees Fahrenheit of water cooling  (wet section  range of
cooling) as a function of the temperature difference  between the
inlet  hot  water  temperature  and  the  inlet air wet bulb tempera-
ture  at a constant inlet hot  water temperature and  constant
water-air mass  flow ratio.  Both the  performance predicted by the
mathematical  model and the measured  performance are  shown.   The
predicted  performance is very  close  to  the  measured,  never
varying more than +3% or -7%.  For the mathematical model, water
flow rate and inlet hot water temperature  are  input values, which
means  that the calculated cold water  temperatures never  varied
from these measured by  more than + 3% or -7%.

     Figure  9  shows the  evaporation rate of the  Wet/Dry Tower
as  a  percentage  of the Inlet water flow rate per degree Fahren-
heit of  the  wet  section  range  of  cooling.  The evaporation  rate
is  a  function  of  the  difference  between the wet  section inlet
water  temperature  and  inlet  wet  bulb  temperature  at a constant
wet bulb  depression.   Both  the predicted evaporation rates and
the  measured  evaporation   rates  are  shown.   Correlation is
acceptable with  the predicted ranging  from -H% to  -19%  of the
measured rate.

     The data  used in  preparing  these curves were obtained  from
carefully controlled  tests in order  to minimize error.   Data
were  taken both at  constant air flow  rates  with varying water
flow rates and at constant water  flow rates  with varying air  flow


4J  5





          Lines of constant
          water to air mass
          flow ratio

                                      1.0 water-air  ratio A
                                      1.4 water-air  ratio 
                                     Lines  are  performance
                                     predicted  by mathe-
                                     matical  model and
                                     points are measured
                         r                   t                    i
    10                  20                  30                  40

    AT (Wet Section Hot Water  Temperature-Wet Bulb Temperature) F

         Figure 4.  Wet Section  Performance,  Wet Section
                    Hot (Inlet)  Water Temperature = 96F



c 12-
0  8
w  2-
           Lines of constant
           water to air mass
           flow ratio

                                        1.0 water-air
                                        1.4 water-air
ratio A
                                         Lines are performance
                                         predicted by mathe-
                                         matical model  and
                                         points are measured
    10                  20                  30                   40

    AT  (Wet Section Hot Water Temperature-Wet  Bulb  Temperature)0?
             Figure  5.  Wet  Section  Performance.  Wet Section
                        Hot  Water  Temperature  =  94F





        Lines of constant
        water to air mass
        flow ratio

                                     1.0 water-air ratio  A
                                     1.4 water-air ratio  Q
                                   Lines  are  performance
                                   predicted  by mathe-
                                   matical  model and
                                   points are measured
     AT (Wet Section Hot Water Temperature-Wet  Bulb Temperature) F

               Figure 7.  Wet Section Performance,  Wet
                          Section Hot Water  Temperature -



0) bO


*~~ O


S-S Q)

(U cfl
Pd C

O 4->
4J 0)
rt oo
               Lines of constant wet bulb depression (dry bulb temp. - wet bulb  temp.)
                   NOTE:  Lines are  evaporation rates predicted by mathematical
                          model and  points  are measured evaporation rates


                                                            30F Depression  0
                                                            20F Depression  &
                                                            10F Depression  0
                         AT  (Wet Section  Hot  Water Temperature-Wet Bulb Temperature), F
                                            Figure  9.   Evaporation Rate

     Data collected  hourly  by the  data  acquisition system were
used  to analyze  the  Wet/Dry Tower operational modes  during
varying atmospheric  conditions.   During  the  one-year  period of
operation from July  1, 1978, to June 30,  1979,  the dry section
dampers were  open  41%  of the time,  creating  a water savings of
13%.   Because of  the  fact  that  the Wet/Dry Tower  was  down for
repairs and relocation  of  instrumentation during a large period
extending  from October to  December 1978,  this is not  a true
measure of the potential water savings.   Based  on the performance
of  the  Wet/Dry Tower and the atmospheric conditions during that
period, it  is estimated that the potential water savings during
that period would  be  approximately  19%.   An even  more significant
water  savings  could  have been achieved  had  it been possible to
develop a full range  of  cooling in the all-dry  cooling mode
during  the winter months  (see Limitations of Test Facility for a
full discussion).


     One of the unknowns when this program began was the amount
of  air leakage which  could  be  anticipated  through the dampers.
One method  which  was tried to measure the leakage was holding a
totalizing anemometer  in  various  locations  near the  closed
dampers for a specific period of time.   The  repeatability  of data
using  this method was  very  poor.   After  several  other trials, it
was concluded  that the air  flow  rate due to leakage was  too low
to  be measured by direct means.

     The entering and  exiting water  temperatures  of both  the wet
and dry sections were  then  examined.  In the case  of the  all dry
cooling mode  with the  wet  dampers closed, it  was found that a
large,  easily  measured  differential  existed between  the entering
and exiting water temperatures in the wet section.   This tempera-
ture  differential   indicated a  significant  air leakage.   By
calculation,  it was  determined  that the  air leakage through the
wet  dampers  must  have  been approximately 8 to  9% of the  total
measured air  flow through  the tower  in  order to cool the  water
by  that amount.   In  all,  15 different cases were examined with a
low leakage rate of  8.3% and a high of 9.1%.

     The consistency of these results allow a comfortable  predic-
tion of the leakage  in  the wet dampers,  but unfortunately  this is
not  the case  for  the  dry dampers.   The  temperature  differential
that  exists  in the  dry section  with the dry  dampers closed was
quite  small,  in most  cases  being  less  than the accuracy of  the
instrumentation.   However,  since  the design  of the wet  and  dry
dampers is  identical,  it should  be reasonable  to assume  that  the
leakage per unit  area  of damper would  be nearly the same.   The
area  of the wet  dampers is 2474 ft2 and  of  the  dry dampers 1622
ft2.   This then  would correspond  to a  dry damper  leakage  rate
of  approximately 5 to  6% of the total air flow through the tower.


                      5. MATHEMATICAL MODEL

      As  previously stated,  one of  the  three objectives of  the
 test program was  the development  and  verification  of a mathe-
 matical  model  of  the Wet/Dry  Tower.   PPR Engineering  Systems
 Inc.,  of Marina del Key,  California,  was  selected  to  provide  the
 analysis in the form  of  a computer program.*  The analysis  was
 performed  separately  for  the wet  and dry  sections  with the  water
 condition  at the exit  of the dry section used  as input to  the  wet
 section.   Each section is treated as a crossflow  tower which is
 divided  into  a grid  of  small increments  in both  the  water flow
 direction  and air flow direction.

      As  the wet and dry sections  are  both  served by a common  fan
 system,  neither the  total  air flow  through  the  system nor  the
 distribution  of air between  the  wet and  dry sections  is known.
 The  program incorporates  several  convergence calculation loops*
 enmeshed in each other, which determine the above  unknowns.   The
 total air  flow and  its  distribution  between the wet and  dry
 sections are  initially assumed to allow a first set  of  calcula-
 tions to be made.

     The calculation procedure  determines  the amount  of heat  and
 mass  transferred and  the pressure  drop  in each section for  the
 assumed  flows.  The pressure  drop over each major  element in  the
 flow path is determined including the tube bundle, the fill,
 dampers, louvers  and any  turns  encountered by  the air.    The
 heat  transfer  in the  dry  section  and the heat and mass  transfer
 in the  wet section are calculated  on the  basis of the physical
 principles of  the  transfer process  combined with  empirical data
 for the properties  of the fill.

     The first convergence  loop checks  whether the air  side
 pressure drop from  the inlet  to the  tower  to  the exit  of the  fan
 is identical for both  the wet  and dry sections.  If the pressure
 drop  comparison is not  within 1%  convergence  tolerance,  a  new
 split of the flow distribution is  assumed,  and the  calculation is
 repeated until convergence.  An outer convergence loop determines
 the  total  air  flow rate  that  corresponds  to  tower air pressure
and the fan characteristics.

     Verification of  the  mathematical model  was  done with  two
fan  pitch  angles,  13 and  17, at various damper  settings,
 including all-wet,   all-dry, and 50/&-wet/50#-dry.   Because of  the
difficulties experienced with sticking dampers (se=j Appendix  A),
less  useful data were  obtained at  the intermediate  damper setting

*PFR Engineering  Systems,  Inc.  A  Computer  Program for the
      Performance  Simulation  of Wet/Dry Cooling  Towers.  Marina
      del Ray,  CA.  1977. 48pp.


complete discussion of  the  correlation  of  predicted  and actual
performance  is  found  in  Test Results.    Briefly,  however,
with the  exception of the  dry  section, correlation of actual
data with predicted  results  fell within  acceptable  limits.
Additional testing  showed the extreme fouling  of  the finned tubes
to be  the  chief  contributing  factor to  the poor correlation of
the dry section  data, and  also  pointed out a weakness of  the
mathematical  model, the  need  to provide a  dry  section fouling
factor.   PFR has  agreed  to  make the necessary modifications to
the program to  provide this factor.

                           APPENDIX A

     The  number of  operational  problems  encountered was  small-
however, correction of the problems proved to be quite  difficult!
Three  specific problems  (sticking  dampers,   biological  fouling,
and  finned  tube fouling) accounted for all  abnormal maintenance


     The most  significant  problem was that  of  sticking  dampers,
which  rendered automatic control of the Wet/Dry Tower impossible!
Sticking was first noted in  the  wet  section  dampers  in May  1978
less  than  5 months  after  the Wet/Dry Tower  commenced operation
and only 3 months after the tower began continuous  operation.   At
that  time a design  deficiency  was  noted in  the  linkages that
connect the  damper  panels  to the torque  tubes  (see  Figure  A-l).
The O.D. of  the  shoulder bolt and the I.D.  of  the metal  linkage
bushing  were  nearly identical  and  did not  allow  room  for the
fiber  bushing  which  was to  fit  between  them.  This resulted  in
galling which  appeared to  be  causing  the  sticking.   New  linkages
were  supplied  by the  manufacturer and installed,  but within a
short  period   the sticking  resumed in  the  wet section  dampers.

     After a careful review,  it was concluded by the  manufacturer
that the sticking was due to  a misalignment of the  damper panels.
Additionally,  it was found that  the  torque tube universal  joints
contained hollow pins which were falling out, causing a situation
where  the dampers were being  partially opened by the  torque  being
transmitted through the U-joirit  dust cover.  Following these
repairs,  the Wet/Dry Tower operated  for  a short period  withaut
sticking before the  tower  was  shut dov>n for  recalibration of the

     When the  Wet/Dry Tower resumed  operation,  the  south dry
section dampers  jammed  in  the mid-range  position.    Individual
damper blades  were impacting  both  structural  support members and
structural bolts.  The  solution was providing  additional clear-
ances between the dampers and the structural  support  members, and
removal of some bolts (see  Figure A-2).

     Immediately after  the  tower was  returned to service,  the wet
section dampers began sticking again.   At  this point, a panel was
loosened  from  the torque tube and an attempt  was rade  to  actuate
It manually.   It took  two men  to move  the damper  through its
complete  range  of  motion.    Penetrating oil  was then applied  to
the 38 pivot points in the panel with the result that  the damper
could be  moved  easily with  one hand.   With this  knowledge, several
linkage arms were removed and sent  to  the  manufacturer  for analy-
sis.   Extensive corrosion between the  brass bushing and the  stain-


        Figure A-l

Damper Linkage with Linkage
     Shoulder Bolt and
   Bushing Shown Circled

       Figure A-2

Structural Support Member
    with Bolt Removed
     and Clearances
     "Chipped" Away

less steel linkage pin was discovered.   The  solution  to this will,
at  a minimum, require  the complete  redesign of  the  linkages.

     Currently,   redesigned  linkages  have been  installed  in the
Wet/Dry Tower, and an operational test  of approximately 3 months
is underway.  Results of  that test will be  issued as an addendum
to this test report.

     It  is  important to  note, however,   that  unless  the new
linkages  are  completely   successful,  "additional  redesign  of the
dampers will  be  required  in  order  to  make  them  suitable  for a
commercial utility application.   As can be  seen in Figure A-3, a
heavy deposit of scale has already built up on the damper blades
after only 18 months  of operation.  Considering the  good quality
of  the  circulating  water  at  the  Wet/Dry  Tower (Table  A-l), the
reliability of the  linkage pivot  points with the poorer quality
water typical of the  Southwest  is questionable.  The use of some
form of  either  sealed or    pressure-lubricated joints may  ulti-
mately be required.   Additionally, the  present method of driving
the  dampers  from only one  side  only appears  inadequate;  an
arrangement of  driving  from  each  side of  the  dampers  would be
much more suitable for reliable operation.  This would result in
the torque being  transmitted  directly  through  the area where the
sticking occurs,  rather than being reduced by  the  twisting of the
flexible blades  as the torque is  transmitted  along the length of
the  blade. Finally, the size of  the motor drives,  which is
presently 1/4  horsepower, should  be significiantly  increased to
provide more starting torque.

     In  mid-summer  of  1978,  after approximately  six  months  of
operation, a heavy  build-up  of  biological  growth  was observed  in
the hot  water  basins (Figure A-4).   The majority of  the  growth
occurred  at  the  end  opposite  the  hot water distribution  piping
where  the lowest water velocities  occur.   A  secondary  problem,
the buildup  of  a  foamy scum floating on  the  surface, was  also
observed  in  the  same  area  (see Figure A-5).   The  growth  is  pri-
marily algae,  not  tenacious  in  its adherence,  and easily  removed
with a garden  hose  stream of water.   In  fact,  it  is  this  quality
which  created  the  worst problem;  the algae would break  off  in
chunks and block the flow control nozzles.

     In  investigating  this  problem,  a large quantity  of  sawdust
was discovered to be  layered in with  the algae.   The  presence  of
the sawdust  is  due  to standard operating procedure   at  the San
Bernardino  Generating Station;  sawdust  is  added to  the  circu-
lating water to  stop  small  condenser leaks temporarily.   It  is
probable that the  presence of the sawdust acts to  accelerate
biological  growth  by supplying nutrients, but the  growth would
most  likely  still  be present and  result in operational problems


     Figure A-3

Damper Blades Showing
  Heavy Deposition
      of Scale

                           TABLE A-l



Total Hardness as CaC02                      100-150 nig/1

Total Alkalinity as CaC02                    200-300 mg/1

Total Dissolved Solids                       300-400 mg/1

Electrical Conductivity                      500-700 umhos

pH                                           8.2-8.7

Calcium                                      35 - 55 mg/l

Magnesium                                    4-8 mg/1

Sodium                                       50 - 120 mg/1

Potassium                                    4-6 mg/1

Sulfate                                      30 - 70 mg/1

Chloride                                     10 - 50 mg/1

Nitrate                                      5-15 mg/1

      Figure A-4

Build-up of Biological
 Growth in Hot Water

   Figure A-5
Floating Scum in
Hot Water Basins

without  the sawdust.

     A  review of  the  station's water  quality  control revealed
that  chlorine is  used  as the  only  form  of biological control.
The injection of chlorine is made near the  inlet of  the condenser
for a period of 30 minutes per eight-hour shift, and the level of
residual  chlorine  is  maintained below  0.5  pprn  at the condenser
outlet.  By the time the chlorine travels nearly 1000 feet to the
tower, its concentration level is far too low to be  effective for
biological control.

     By  trial  and  error  the  following  steps  were discovered to
be  effective  in controlling the  problem.  Removal of  three
flow control  nozzles  in  the  outboard  row,  one  from each corner
and one from the middle (Figure A-6),  significantly  increases the
water flow  rate in the  otherwise  stagnant outboard  area.   The
benefits from  this are  threefold:   (1)    slower build-up of
growth,  (2)  lessening  of flow  control  nozzle pluggage,  and (3)
elimination of the  build-up of  floating scum.  Additionally, the
individual basins are  shock treated  with sodium hypochlorite on a
quarterly basis by isolating  the  basin  from  hot water  flow,
adding two gallons  of  the  sodium hypochlorite, and  "soaking" for
a period  of one  hour.   The basin is drained and then thoroughly
rinsed before  returning  to service.   This  process  is performed
one basin at a time with the tower in operation.


     Fouling  of the  finned  tubes   in the dry  section  became
obvious after a  few months of operation and grew steadily worse
throughout the  test program.    In discussions with  the manufac-
turer,  it became apparent that although a fouling factor was used
in  determining  the heat  transfer  area  required,  no one had
anticipated  the degree  of fouling  which  occurred (see  Figure
A-7).   In fairness, the San Bernardino site is possibly a little
unusual in that besides being  situated  on a  dirt and loose gravel
field,  the Wet/Dry  Tower is  also located  near  the  northern and
eastern  fence of  the  station.  The  land  on the other  side of
these  fences  is agricultural  and  is disked and  plowed  several
times  a  year, which puts  a considerable amount  of dust into the
air.  Also,  a high degree of pollen  and  insects  exist  in the
area.   However,  dust,  pollen  and insects  are factors  which will
exist  to  some degree at  most  sites  located in the Southwest and
as such must  be accounted for  in future design.

     Another   point  of  consideration  is  that although no  docu-
mentation could be located  as to  the condition of  the  tubes
either when they arrived  at the site  or when they were installed,
a small  sample  section which  was cut for demonstration purposes
does exist.  Examination of that section yielded a light machine
oil coating on the  fins, most likely left there from the rolling


      Center of Tower
inlet, flow
 *^ _^ ^ u, -^ x***' ^ " ^ >*.*^  >^ -x--^>*
 o o o o o o oo oo o
    flow control nozzles removed
Figure A-6. View from top of a hot water basin showing
    location of flow control nozzles removed to
    aid in control of biological growth

 Figure A-7.  Example of
Finned Tube Fouling.  The
  Tube Shown is in the
 Outermost Row (Row 1).

process which attached  the fin to the tube.  The presence of this
oil on  the  fins would very  likely result  in  a faster initial
build-up of  fouling  and possibly a thicker deposit.

     Following the completion of the test program and  the  shut-
ting down of  the  Wet/Dry Tower, a  demonstration cleaning of the
south dry section tubes was  performed  in  order to ascertain the
cost of  periodically cleaning the  tubes.  The  cleaning was per-
formed  by SERMAC  Industrial  Cleaning,  Inc., with an eight-foot
long "lance" which allowed the operator to reach in approximately
five feet into  the  dry section (see Figure A-8).   A  ^5  angle
spray nozzle was used with a  flow rate of 8  gpm, a water tempera-
ture of approximately l40P,  and a water  pressure of 300 psi
eight  inches from  the tip.   Initially a degreasing  agent was
used, but examination  revealed  that hot water  alone was  nearly
as  efficient  in cleaning and greatly  reduced the time required.
Results of   the  cleaning are shown in Figure A-9.   By visual
examination, it appears that in excess  of 90? of the fouling was

     Figure  A-10  shows the effects of the cleaning to a depth of
15  rows of  tubes.  The number  attached to  each tube is its row
number  counting from the outside in, and there are a total  of 25
rows in each basin.  Because this was a demonstration cleaning,
it  was  decided  to clean  only the  exterior half of the south dry
section to  limit cost.   As can  be seen in Figure A-10, good
cleaning was  achieved through Row 9,  but  slight fouling is
observed in  Row 12, which is almost the mid-way  point of the dry
section.  By row 15 the  effects of cleaning are  not observable.
It  is  estimated  that the cost to perform the entire  cleaning job
from both the outside and inside of the two  dry sections would be
approximately $3600.

     Based  upon this experience, it would seem  that  some form of
in-place cleaning  system   should  be  explored  for commercial
applications  of the tower.


           Figure A-8

Workman using eight foot "lance"
to clean finned-tubes.

                Figure A-9

Results of finned-tube cleaning.  View is
from outermost row (Row 1) inward.

                         Figure A-10
        Number^    K* cleaninS Progressing toward center of
show)           n tUbe is the row number,  with row 1 (not
         ing the outmost row away from center of tower.

                          APPENDIX B
                       EVAPORATION RATE
     The method used to calculate the actual heat rejection rate
and evaporation rate of  the  Wet/Dry  Tower is relatively simple.
Based on the data  taken,  a total  tower heat rejection rate can be
calculated for both the water-side (which  loses the heat) and the
air-side  (which gains  the heat).  As is  shown  in Appendix 7.3,
the water-side  calculation  is  the  more accurate  and  is used to
confirm the air-side data for calculation  of  the evaporation rate.
                       Qw=  Mw Cp  (T2  - TI)         (1)
                Qw =  water-side  heat rejection  rate  (Btu/hr)
                Mw =  circulating water  mass  flow  rate  (Ibs/hr)
                CD =  constant pressure  specific heat of water
                T2 =  inlet (hot) water  temperature (P)
                TI =  outlet (cold)  water temperature (P)
 The  air-side heat rejection rate is  calculated as  follows:
                       Qa = Ma (h2 - hi)*            (2)
                Qa =  air-side heat rejection rate (Btu/hr)
                Ma =  dry air mass flow rate (Ibs/hr)
                h2 =  enthalpy of air exiting the cooling tower
                         (Btu/lb  of dry air)
                hi =  enthalpy of air entering the cooling tower
                         (Btu/lb  of dry air)
 por  these  two calculations, T2 and TI are  measured directly
 and Ma, Mw Cp,  h2,  and hi  are determined from tables.
 T~Kreith, Frank.  Principles  of Heat Transfer, International
      Textbook Company,  Scranton,  PA,  2nd  edition,  196?. 620

      The  evaporation rate can  be  determined  using the equation:

                E    = Ma  (Wm2 - Wmi)                (3)


                E    =  evaporation  rate  (Ibs./hr.)

                WHIP  =  weight of moisture per pound of dry air
                       at tower outlet

                Wmi  =  weight of moisture per pound of dry air
                       at tower inlet

      In  this  equation  Wmi  and  Wm2  are determined  by  the
respective  wet and  dry  bulb  temperatures  and are  available in
psychrometric  tables.

      In expressing  the water savings  of a wet/dry cooling tower,
the  evaporation  rate of  the wet  section is  the  critical  para-
meter. If all  of the heat  rejection from the  water to the air is
assumed to be  by release of the latent heat of vaporization (eva-
poration), then  it  can be said that  the evaporation rate varies
directly  with  the  wet section  range  of  cooling  (hot  water tem-
perature  minus cold  water temperature)  for any particular set of
conditons (tower air flow,  tower water  flow,  ambient  air condi-
tions, and tower inlet water temperature).   This  is true  because
the  latent  heat  of vaporization of water  is  nearly constant  for
small changes  of temperature  such  as  is experienced in a  cooling
tower.   From  equation (1)  it  can  be  seen that the wet  section
heat  rejection rate must  vary directly with the wet section range
of cooling,  and  since all heat is  rejected by evaporation,  then
the  rate  of  evaporation  must vary  directly with  the  wet  section
range of cooling.

     Therefore, since  the dry  section (when in  operation)  dis-
places a  portion of  the  wet section range  of  cooling,  the  water
savings may  be expressed as the ratio  of  dry section range of
cooling to the total tower range of cooling.

     Water Savings  = |  "_Tj" x 100                          (4>

     Where      T
                           APPENDIX C
                      UNCERTAINTY  ANALYSIS

     The uncertainty In  the  calculated  parameters  may be deter-
mined by  replacing  the  measured  values  with the measured values
plus the  Instrument errors and solving  for  the total error.  In
the  cases where multiple measurements are made,  the  probable
error of  the instruments  is  determined by  the  method  of  least
squares and  substituted  for  the  instrument error.   Data  taken
from the Wet/Dry Tower  consisted  of  two types:  (1)  data  taken
during  controlled  testing  and   (2)  data  taken hourly  by the
automatic data acquisition system.  Data  taken during controlled
testing are  as  accurate  as  possible, with  all sources of  error
minimized.   The  data  were taken  at steady-state conditions, and
several runs of data were taken within a short  time of each  other
and  averaged in order  to minimize  transients  due to changing
barometric  conditions,  wind,  contact  resistances,  etc.    These
data were  used  for the  verification  of the mathematical model.
The  hourly  data describe the operational  modes  of  the  Wet/Dry
Tower and  were  useful in  estimating  water  savings,  although the
errors  associated  with  these data must be  significantly  higher.
The  accuracy  of  the instrumentation used  at the Wet/Dry Tower  is
as follows:

     Hot and Cold Water Temperature, measured by Resistance
        Temperature Detectors (RTD)                      +_ 0.2P
     Stack Psychrometers                                ~
                    - Wet  Bulb Temperature  (RTD)        + 0.8P
                    - Dry  Bulb Temperature  (RTD)        -f 0.8P

     All  Other Psychrometers
                    - Wet Bulb Temperature  (RTD)        - 0.2F,
                                                        + 0.70F*
                    - Dry Bulb Temperature  (RTD)        + 0.2P
     Water  Plow  Meter                                   + i
     Air  Plow Rate  (Pan Curve from measured Fan KW)     +5%
     Data Acquisition System                           + 0.1*

     The  uncertainty  expected for  the  calculated parameters  are
 as follows:

        Waterside Heat Rejection Rate                  + 4 to   6%

        Airside  Heat Rejection Rate                    + 6 to 10%

        Evaporation Rate                              + 6 to IQ%

        Wet Section Range of  Cooling                   +_ 3 to 5%

        Dry Section Range of  Cooling                   + 10  to  20%


 Where  the  probable  error of each measured value was determined  by
 Peter's  Formula.

           r0  =  '8453  Ivil +  |v2l + 	 + lvnl)*
                n    n-1


         ro =  probable error of the mean

         n  =  number of measurements

         v  =  residual of the observed  value In  relation
              to the mean (I.e., vn = xo - xn)
* Franklin,  Phillip.  Mathematics.  In: Standard Handbook  for
     Mechanical  Engineers, T.  Baumeister  and L.  F.  Marks,  eds.
     McGraw-Hill  Book Company, New York, NY,  6th edition,  1967.
     pp.  2-32  to  2-3^.


                           APPENDIX D
                      TEST  INSTRUMENTATION
     During the  early  stages of  the  testing program, extensive
instrumentation was in  place on  the  exterior  of  the  tower for the
determination  of  individual air  flows  through the  wet  and dry
sections.  The instrumentation  consisted  of eight  anemometers per
section  (See  Figure  D-l).   The anemometers  were  propeller-type,
designed to null in a crosswind.

     Attempts to calibrate the  anemometers  were  unsuccessful, due
to  the prevailing west  winds  which  caused erratic readings.
Several  types  of  shielding  were tried with some improvement, but
the  readings  remained  too  erratic  to be of  value.    Trials  were
made  at  other locations, including inside  the tower, but  these
were  also  unsuccessful.   Inside  the  tower,  the  problem was  the
dampers.   Each change in  damper  angle altered the  air  currents
and affected  the anemometer readings.

     Total  tower  air flow  was  obtained  indirectly  from the  fan
motor  horsepower using  a calibrated  air  flow - fan horsepower
curve  for  each fan  blade  pitch angle.   The  curves  were  plotted
from  equal  area traverses which  were performed with the  dampers
in  the all-wet mode,  the  all-dry mode,  and the  50%  wet/50!t  dry
mode.  It  is  estimated that the curve  data are accurate to +_ 5/&.


      Initial  efforts to  calibrate the  Instrumentation monitoring
the stack  exit air temperatures (wet-bulb and dry-bulb) were
unsuccessful,  as demonstrated by an inability to  balance the
air-side and water-side  heat  rejection  rates.   It  is essential
that  the heat  rejection rates balance  within the  error  of the
instrumentation as a  check  of  the  validity  of the  measured exit
air conditions.   Prom these conditions the  evaporation  rate of
the wet  section is  calculated.

      The difficulty lies  in correctly  determining the location
of  the instrumentation under a 28-foot diameter  fan  with various
structural  crossbeams  creating eddys  and localized high velocity
areas.  It was  finally  determined  that  it would be  necessary to
 "map" the stack on a one foot  grid for  both wet-bulb temperature
and air  velocity.

      In  mapping the stack,  it was first  determined  by measurement
 that  the north and south  halves  of  the stack were  symmetrical.
This  allowed  the  mapping of only  one-half  of  the  stack to gain
 the required  results.   The instrumentation, a wet-bulb psychro-
meter and  an anemometer,  were  located  on a moveable  trolley 1.5


A 1  f A
A)  f A
                                                LEGEND:  ANEMOMETER
                 Figure D-l.
Wet/Dry Cooling Tower

Anemometer Locations

feet below the  fan.   The  results  of  the mappings are  shown  In
Figures D-2 and  Figures D-3.

     As a  result  of the  mapping  exercise,  it was  learned  that
placing fixed location  instrumentation in the stack for measuring
exit air conditions  does  not provide optimum results.  Due to the
shifting  of the  air  currents  that occur with  changes  in the
damper  settings,  the  placement  of the  instrumentation (Figure
D-U)  was  a  compromise.  The  locations  were  selected  to  take
advantage of the  symmetry  of  the  stack  while still allowing for
effects such as fouling,  wind,  etc. which  might  affect one side
of the tower more  severely than  another.

     Because  of schedule  and budget restraints, a  more ideal
system  for  this test facility  could  not be installed.   Such a
system  would  consist  of  a  minimum of four  packages, each con-
taining a  psychrometric   station  and  an anemometer,  running on
tracks  in  the  fan stack.  Positioning of  each package would be
controlled by a mini-processor.   Such a system would be  capable
of  performing  an  equal area  traverse of the  stack (based on 10
areas)  every  half-hour.   However,  observations indicated a
repeatable error  of approximately  +_ 0.8F for  the  fixed location
instrumentation in both the wet  bulb and  dry  bulb  temperatures of
the exiting air, which was considered  acceptable.


      All  resistance  temperature detectors  (RTD)  were  calibrated
to  + 0.2F  against an  NBS  calibrated  thermometer.  The data
acquisition  system was calibrated  to + 0.1F.  Both air flow  and
water  flow were recalibrated  by equal area  traverses  with  cali-
brated  Pitot tubes.

      During  this  same time period, it  was determined  that  some
relocation  of  instrumentation  would  be  undertaken  to increase
data  accuracy.   Specifically, two more  ambient weather psychro-
metric  stations were established in addition to the one existing,
ten RTDs  were  placed beneath the  dry section  water discharge to
monitor dry section  cold water temperature,  and  two additional
psychrometric  stations  were  placed in  the stack  (see  STACK
PSYCHROMETRIC MEASUREMENTS  in this Appendix)  for  the  measurement
of  stack exit  air  temperatures.   Eight of  the  sixteen psychro-
metric stations on the  exterior  faces of  the  tower were removed
 to  supply the  needed  instrumentation,  with four  stations  being
 relocated  and four stations  being pirated  to supply eight of the
 ten  required  RTDs.   The  remaining two  RTDs were   purchased.


      As mentioned earlier, some improvements in type  and location
 of  instrumentation were accomplished  in order to  increase  sensi-


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  30.4  27.9  32.J   29.6  31.3  30.0 28.9  23.8

  68.8} <70>.2X7^.6>(7^.5X72>.4)<721.9)(73r9X70,.3> (6^.8)
  33.3   34.2   36.6  35.4  37.9  35.0  40.8  40.4  33.3

K6B.9) (7K 3) (70. 0(70.6) (7^. 3) (7 3^9X74^6) (74^9)( 7^. 3) (68^6)
I  )2*.5   32*   35*.4  36*.6  37*5  36*6  41.3  41*6  39.6  38.3

170.2X72.2X71.4) (71.3) (72.6X73^3X74^9X7^. 5X73^.3X67^.7) (63^.8)

  31*2   32*.l   35*.4  3*.8  3*.2  24*2  2*3  40.0  36*.6  36.6 21.6

[71. 3X71.3) (70.4) (69.4)(71.2) (7 3.1X74.3) (75.1X74.5X69.3X62.8X59^8)

  3*.9   35.4   34.1  35.0  33.3  27.5  31.6  35.8  32.5  41.6 28.3  26.6
                                                                                        Ambient Conditions

                                                                                  wet bulb temperature - 46.5F

                                                                                         Tower Conditions

                                                                                   inlet water temperature - 79.0F
                                                                                   discharge temperature - 66.3F
                                                                                   air flov rate  -  1,240,000 CFM
                                                                                  water flow rate  -  13800 GPM
                                                              3X58.4) '
[70.9)(70,2) (69.6X68.0X70. 3) (71.6) (72.8) (73.5) (74.4)(69. 1X60.8) (61.
 33T7  3279  37*1   35^4  33*3  30TO  3^0  35*8  35*8 40.0  23T3  16*

[71.1X67.8) (70. 2) (68.6X70.1X71.1X72.1X73.2) (74.7X70.4) (61.3) (61^6X60. 2)

 35*4  35*0  33*3   34*1  3K2  27*,!   35.0  36.2  37.5 40.8  38.3  40.8  36.2

 169.1X70 6X70. 2X69. 7X69^9) (70^5X71^6X73^.2X73^.9) (72^6X67^2X69^5) (64^6X58rf.

 33*,3  35*0  33.3   31*6  3I*.6  25*8  36.6  36.6  35.4 39.1  40.8  42.9  41.2  27.'

 (67.3X68.2) (69.1X68.6) (69.5X70.3) (72.0)(73.9X73.4) (73.6) (7^.3X70.7X69.9X6^.6)

 3*.2 3*4  28.3  29.1  300  25.0  35.4  36.6  36.6  36.6  400  28.3  *T.6  50-0

                (67.4X69.4X70.7X72.1) (74.4)(75.1)(74.8) (70^.6X70.4X6^.8X60.8)

       	lf.1  2?.S  18.3  18.7  2*.5  26.2  27.5  29.1  40.0  40-8  3*.l
                                                                                        Calculated  Results

                                                                         mean stack velocity
                                                                         mean wet bulb temperature
                                                                         velocity - weighted mean
                                                                         wet bulb temperature
                                                                         calculated air flow rate
                                                                         water side heat rejection rate
                                                                         air side heat rejection rate
                                                                         heat rejection rate deviation
                                                                                             34 ft/sec.

                                                                                             1,320,400 CFM
                                                                                             1,459,900 BTU/min.
                                                                                             1,647,700 BTU/min.
                                                                                             12.97. (within  error
                                                                                                   of instruments)
                (67.8X69.3) (70^.0) (72^.1) (73^.2) (73.6X73.0X68.6X7J. 2) (66.3X6^. 5)
                 2*8  28.7  25.8  32.1  3*0  36.6  37.5  35.0  36 6  42.1  38.3

                (68.6X68. 9)(71.6)(72. 3X73.4)(73. 7) (71.4) (70.6X71. 7) (64. 7)(60 9)
                 2*0  28.3  25.8  30.0  32.5  35.0  38.3  38.3  35.0  4*.6  4*.5
 2i.2  29.1  23.3  33.3  36.6  35.8  37.9  38.3  37.5  40.8  42.1

(68^.9X69^. 7) (7 1.6) (7 ^.8X72^.9) (7J. 2) (7^.7X7^.8X7^. 3) (69.8) (66.8)

 2*.6  30.4  28.3  3*6  33.3  36.6  38.3  38.3  3*.6  40.0  40.0

(69^.4) (69^.8X72.1X73^.6) (74.2) (7J.9X74.6) (73. 3X69^.0X68. 3) (61.8)

 28.3  30.0  24.1  31.2  3*.5  3*. 2  3*. 3  35.0  3*.0  36.6  3*.6

(69^.2) (70. 5X7y3)(73p.3X75(.5X76>.4X76.3) (73^.5X69. 3X67.8X60.7)
 27.5  32.5  29.1  29.1  25.4  29.1  30.8  31.2  30.0  20.8  30.0

(70^.0) (71.0X71. 5) (7^.6X75^.1X7^. 5) (7^.9X7^.3X69.6X6^.9) (59. 3)

 3*2  31.2  26.6  34.1  36.6  36.6  3*. 1   42.1  4*.6  42.1   3f.6

(70.8X72.2X73.4) (7^.7) (74^. 7X7^. 7)(77(.2X76>.2X70>.a) (6*. 3X5J. 7) i

 37".9  33.7  30.0  36.6  39.6  4*6  42.1   42.5  30.0  41.6   2*. 3 /

(70. 5X72.OX 74.2) (75.2) (75.2) (75.9 (77.5) (75.4) (7U 3) (63.8
 39\6  3f.6  3*6' 38.3  3*.6  40*.8  4f.6   4*6  4*.8  35.0

(71.3X73^.0X75.1X75.4X7^.7X75^.5) (7*.6) (70^.6X66.1X58.8)

 40*.0  38*.3  33.3  36.2  38.3  3*1  40.8   3*3  35.0  2*.  '

(72. 7X73.9) (74. 3X75^.5) (76.1X75.1X70. 7) (65.8)(59.4)

 3*.l  3?.8  3*.6  36*.6  34.1   40.0  4*. 3   38.3  3f. 5
                (73, J)(7
      74..lX7,4X7i.*X74.7) (71.0X68,4X63,2)
      36.6  32.5  34.1  37.5  3.l  36.6  27.5
(72.9) (74.2) (74.OX76.0X7J. 1X71.4X64.1)

 36.6  35.8  33.3  35.0  36.6  40.8  41.6

(71.8) (72.6X7 3. 3) (75.2) (70.4) (61.2)

 3S*.B  3**.6  3^1  33*3  35*.0  tf.O


 3f.5  2?.6  3?.5  3?.3  2?.3

 3*. 3  34*. I  2?.8
                                                                        The numbers  in parentheses are  the wet bulb
                                                                        temperatures  in degrees Fahrenheit.  The
                                                                        remaining numbers are the air velocities in
                                                                        feet per second.   The data was  collected over
                                                                        a four day period which resulted in a range
                                                                        of ambient conditions.   To account for this,
                                                                        the wet bulb  temperatures have  been normalized
                                                                        to the ambient conditions indicated.  The
                                                                        diameter of  the stack is 28.7 feet where the
                                                                        measurements  were taken.
               Figure  D-2.     Wet   Bulb  Temperature   and  Velocity
               Map   of  Stack  During  "All  Wet"  Mode   of  Operation


 37.7  38.7  35.6

 tt.O  42*.8  F
1.475.700 CFM
1.230.000 BTV/nin.
1.312.000 BTU/mln.
6.71  (within error
      of Instruments)
 [69^.5) (67.1) (67^7) (68^.7) (74^4) (75^7) (75^.9) (64rf8) (59rfl) (55^.5) (53^.9) (53^8) (51^2) (49^1)
           IJ.y> VO^.O; \jy,t.i \JJ.JI \jj.7; I^J.O,

34".8  26".7  34*5  38.3  42.7  41.1  35.8  37.3  42~.8  51~6
                 (66,8) (73,5) (74^4) (75.5) (71.9) (66.5) (56^3) (55^3) (53.9) (50.8) (50,1)
                  22*9  28.1  26*7  2/.3  27\9  25.5  35.2  41.8  47.5  44.C  41.3

                 (69,3) (72,2) (74,3) (75,6) (76,0) (73,9) (69,5) (60,5) (5J,2) (50^8) (4^9)
                  24.3  32.6  28.3  25.7  31.3  39.7  41.2  43.8  44.6  43.1  31.7


                  21.6  34*9  32.2  33.1  3.2  .  41.3  40.2  38.7  41.3  43.6

                 (70.8) 171.8) (73.0) (75.0) (77f 0) (72.4) 160.9) (S4.9) 153.4) (52.1) (49.3)

                  22*9  32*7  28.3  36.6  37.3  39.4  39.4  42.7  41.6  43.4  44.6

                 (71^.9) (72.8) (76.4) (77^6) (78.8) (75.3) (65^) (57.2) (54.8) (54.4) (50.1)

                  25.7  38%  34*.7  35*.3  36*7  40^8  40.4  42.7  41.9  43.7  42.2


                  27*4  32*8  30*0  33?3  33*1  36*1  38%  41*1  43*6  41%  39*7

                 (72^9) (73^) (74^2) (73^3) (74^5) (69^4) (59^9) (55^6) (53^1) (50^6) (49^3)

                  35*3  30.1  34.2  24*1  21.7  27.3  34.8  40.0  46.9  40.3  37.3

                  3276  35*6  31T3  39*3  3674  38*5  38T9  43*7  4472  45*8  3770

                 (72^1) (74^8) (75^2) (73^1 (62^) (55^0) (49^1 (49a) (49^) (49^3) (49.1)

                  38.6  39^3  32*1  24Tl  4lTl  43T?  42.6  44*2  36%  4*8  26*:

                 (70^8) (74^) (74.3) (70.3) (61^8) (52.2) (49^8) (50.6) (49.8) (49.4)

                  42%  42%  42*2  36?2  41*3  41*7  43*3  34?7  39Tl  29?9


                  40.0  41.8  39.4  40.2  40.8  42.6  44.7  45.3  43.7 34.

                 (71^8) (72^) (74^) (72^8) (6742) (58^3) (52^6) (50^2) (50^2)

                  35.2  37%  36*2  40.9  38.2  41.7  44.2  41.7  29.6

                 (7149) (73/7) (7^1) (68^) (57.1) (51.1) (50^) (50^)

                  26.4  40.3  35.5  37.0  42.1  42.9  41.7  31.3

                  28*3  37*3  38Tl  41%  44.7  42%  39*9

                  3177  39*6  41.3  4378  4177  40?2


                  38.3  31.7  38.6  41.7  29.7


                  38.6  37.7  31.3
                                                    The niabers In parentheses are  the wet bulb  tempera-
                                                    tures in  degress Farenhelt   The  remaining numbers
                                                    are the air velocities in feet  per aacond    The data
                                                    was collected over a  three day  period which  resulted
                                                    in a range of ambient conditions.   To account for
                                                    thia, the wet bulb temperatures have been normalized
                                                    to the ambient conditions indicated.  The diameter
                                                    of the stack Is 28.7  feet where the measurements
                                                    were taken.
          Figure   D-3.     Wet  Bulb   Temperature   and  Velocity  Map
          of   Stack  During  50%  Wet/50%   Dry  Mode  of  Operation

Figure D-4.
View from top of stack showing location of stack
psychroraeters.   The two tubes shown with each
psychrometer are orificed to provide a weighted
air sample.

tivity or improve data accuracy.   The  discussion  below  reflects
the final instrumentation used for the test results.

     Figure  D-5  depicts  the  location of  the  psychrometric  sta-
tions,  hot  and  cold water  temperature  detectors,  and other
instrumentation situated  on the  tower.   The  location of  the
ambient weather stations  is shown on Figure 1.  In all cases,  100
ohm  platinum  resistance  temperature  detectors  (RTD) were  used.

     Water  flow measurement created  some  difficulties which
should  be noted.   Initially,  both  inlet and  outlet  flow  was
measured by turbo-probe flowmeters.  However,  it  was discovered
that the sawdust which the  station  personnel  routinely add to the
circulating system  to plug  small  condenser  leaks,  also worked
well  for plugging  the flowmeters.  After some trials,  it was
determined that  the  flowmeters  were  inoperable.   A differential
pressure  cell  was  then  installed  to  monitor  the total  developed
head  of  the circulating  pump and  a calibrated head - flow curve
was  developed  from  a  series of equal' area  traverses   performed
with a Pitot tube at varying  flows.

     While  this  method  of flow measurement  proved adequate, it
was not totally satisfactory, particularly when  it  was discovered
that  the  differential pressure  cell had to be recalibrated every
time  the  pump was  shut down.   Finally,  with the  cooperation of
EPRI  an  "Annubar"  flow  measuring  device was installed  which has
performed flawlessly and maintains  an error of +1%.

  Inlet Water Flow
     Dry Sectiort
                I   .
                     /////////  \\\\\\v\\
(Dry Section
        Outlet Water Flow
                                           LEGEND .-
                                    Water temp,  detector
                                    Flow detector
Figure D-5.  Wet/Dry Cooling Tower Instrumentation Schematic

                          APPENDIX E
     The damper  control system  of  the Wet/Dry  Tower controls
the distribution of  air  flow  between the wet and dry  sections.
The temperature  of  the  cold water  exiting  the  tower  serves as
the control element.   When the  cold water temperature is at
setpoint (which  in  this case was 78P)  or within the  deadband
(1.5F above or  below the  setpoint),  no  demand signal  is  issued
to  the  control  system and  the  dampers  remain in their  current
positions.   In  order  to provide  stability  and  prevent  "hunting"
of  the  system,  a thermal time delay  relay  (agastat)  is  located
between  the demand signal and  the control  system.   It  was
discovered  that  a   5-minute setting  on  this agastat was  suffi-
cient  to  allow  the  cold water temperature  to  stabilize  after  a
change  in damper settings.  Additionally,  another agastat is
provided  to limit  the  period  of time  the  control system  may
actuate the dampers  after  each  5-minute  time  delay.   A 3-second
setting provided  11 degrees  of damper movement,  which  gave
sufficient  change without  encountering  "over-shooting."   Figure
E-l  shows  the basic  damper operation as a  function of demand.
A  key to understanding the operation  is  the fact  that  inter-
locks  are  provided  to  prevent  the  operation of  either  the wet
or dry section  dampers unless  the  other  section  dampers  are
either  fully  open or fully closed.    On  a  typical cool day, the
operation of  the  dampers  might be  as  depicted in Table  E-l.
                         TABLE E-l
A)  12 Midnight  to  8:00 AM -

                   8:00 AM -

                  10:00 AM -

                  10:30 AM -

                  12  Noon -

                   6:00 PM -

                   7:30 PM -

                   8:00 PM -

                  11:00 PM -
Dry Dampers
Wet Dampers
Dry Dampers
Wet Dampers
Dry Dampers
Wet Dampers

Dry Dampers
Wet Dampers

Dry Dampers
Wet Dampers
Dry Dampers
Wet Dampers
Dry Dampers
Wet Dampers
Dry Dampers
Wet Dampers
Dry Dampers
Wet Dampers
                                           10056  Open
                                           Fully Closed

                                           10056  Open
                                           Begin to Open

                                           10056  Open
                                           .Complete Opening

                                           Begin to Close
                                           10056  Open

                                           Complete Closing
                                           10056  Open

                                           Begin Opening
                                           10056  Open

                                           Complete Opening
                                           10056  Open
                                           100J6  Open
                                           Begin Closing
                                           100%  Open
                                           Complete Closing

                 DRY DAMPERS
         0 -
               WET DAMPERS
     (closed) (A
                                                                                    co W
                                                                                    V P
                                                                                    O o
OT *T>
o _*.
p. g;
0 ^

                                                                           (P C

                                                                           ct (p
                       Figure  E-l.   Damper  Control as a Function of Demand


                           APPENDIX  P
                           TEST PLAN

     The objectives  of the  test  program,  as  stated  earlier  in
this report, were as follows:

     1.  Determine the  operational  characteristics  of a wet/dry
         cooling tower operating in an actual  generating station

     2.  Determine  the  water conservation aspects  of a wet/dry
         cooling tower operating in  an arid climate.

     3.  Develop a mathematical model  of the wet/dry cooling
         tower and confirm it with actual test  data.

     The first  objective  was  achieved merely  by operating  the
Wet/Dry Tower,  but the remaining two objectives  required  a  test
plan to follow in order to assure success of  the program.

     To simplify the plan it is broken into test blocks;  however,
because of  the  need to obtain data  over a wide  range of  ambient
conditions,  the test  blocks  were  repeated  throughout the  test


     1.  Confirm fan characteristics

     2.  Confirm pump characteristics

     3.  Determine velocity and temperature distribution of stack
         exit air  (see discussion in STACK PSYCHROMETRIC MEASURE-
         MENTS  in  Appendix D)

     4.  Confirm uniform  distribution of  water  to  cooling tower
         (This  was  accomplished by balancing the flows in the two
         risers  and then equalizing the levels  of  the hot water

     5.  Determine air  velocity distribution entering the Wet/Dry
         Tower  (see discussion in  AIR  PLOW  MEASUREMENTS in
         Appendix  D).

     6.  Calibrate instrumentation  within  limits  (See Appendix C)


     These  tests were  run  at  several constant water flow rates.
Air flow was varied by  changing the pitch  angle  of  the  fan and by
varying the dampers.



     These tests were run at two constant air flow rates corres-
ponding to fan pitch angles of 13  and 17.   Water flow rate was
varied  by use of a valve at  the discharge  of the circulating
water pump.

                           APPENDIX G




Plow Rate:


1 inch = 2.5*1 centimeters
1 foot (ft) = 0.305 meters (m)

1 ft2 = 0.093 m2

1 horsepower = 1.3^1 kilowatt

1 inch Hg. = 0.013 atmospheres
1 psi = 0.068 atmospheres

1 CFM = 0.472 liters/sec
1 gpm = 0.063 liters/sec

1 ft/sec = 0.305 m/sec

1 P = 0.556 C
   to convert from  F to  C use this formula
                                 >C =
                                   - 5(P -  32)

                                TECHNICAL REPORT DATA
                         (Please read Instructions on the reverse before completing)
                                                      3. RECIPIENT'S ACCESSION-NO.
Wet/Dry Cooling Tower Test Module
            5. REPORT DATE
             April 1980
                                                      6. PERFORMING ORGANIZATION CODE

D.M. Burkart
Southern California Edison Company
P.O. Box 800
Rosemead,  California  91770
            10. PROGRAM ELEMENT NO.
            11. CONTRACT/GRANT NO.

            Grant No. R805220
 EPA, Office of Research and Development
 Industrial Environmental Research Laboratory
 Research Triangle Park, NC 27711
15. SUPPLEMENTARY NOTES jERL-RTP project officer is Theodore G. Brna, Mail Drop 61
16. ABSTRACT The report gives results of an evaluation of the engineering performance
of a single-cell wet/dry cooling tower (about 25 MW) in an 18-month field test at
San Bernardino, CA. Test objectives included determination of the water  conserva-
tion and operating characteristics, and verification of a mathematical model for the
wet/dry cooling tower.  The crossflow tower had parallel air flows through the wet
and dry sections, and dampers which regulated air flow to allow cooling in either
section, or any combination of the two. Without significantly affecting normal plant
performance, the wet/dry cooling tower  could save about 19% of the water normally
avaporated annually by  an all-wet tower at the test site.  Greater savings could have
Deen achieved by accepting some loss of  plant efficiency during the winter  months.
rhe mathematical model developed for the tower was verified by test results.
Although some operational problems developed during testing, the major goals of the
test program were  achieved.
                             KEY WORDS AND DOCUMENT ANALYSIS
                                          b.IDENTIFIERS/OPEN ENDED TERMS
                        c.  COSATI Field/Group
Pooling Towers
iVater Conservation
Mathematical Models
Pollution Control
Stationary Sources
Wet/Dry Cooling
Operating  Characteris-

 Release to Public
19. SECURITY CLASS (This Report)
20. SECURITY CLASS (This page)
EPA Form 2220-1 (9-73)