1. As run energy efficiency of Cooling Towers
D.Pawan Kumar

2.  Therm al perform ance of an evaporative tower is prim arily
d epend ent upon the entering air wet bulb tem perature (WBT)
and relative hum id ity (RH ).
 The entering WBT is an ind epend ent variable that d ictates
cooling tower selection.
 It is both the theoretical lim it to the leaving cold water
tem perature and the only air param eter involved in cooling tower
selection.
 The d ifference between the WBT and the tower leaving or cold
water tem perature (CWT) is called the approach tem perature or
the approach.
 Approach tem peratures generally fall between 5 to 20 F.
 The d ifference between the tower leaving or hot water
tem perature (H WT) and the CWT is called the range
 Cooling tower effectiveness is the ratio of range (achieved
value)and range plus approach (achievable value
theoretically).H ighest effectiveness value is d esirable.
 Sim ultaneous achievem ent of m axim um Range, Capacity and
E ffectiveness with lowest input energy need s are d esirable
attributes of a cooling tower in operation.

4.  We get higher cooling water temperature
than design
 Higher Cooling water temperature means
higher back pressure for a steam turbine,
higher heat rate, higher cost of generation.
 Higher cooling water temperature means
poor efficiency and performance of diesel
generating sets, air compressors,AC
plants,furnaces and process equipment.

5.  Is it giving the capacity,
range,effectiveness, as per design?
 Cooling tower may not be subjected to the
design conditions in as run conditions.
 To assess the as run performance, also
refer to cooling tower performance curves.

6.  They are drawn for a flow variation of
80-120 %
 They are drawn for a WBT variation of +/-
5 deg.C with respect to design value
 They are drawn for a cooling range
variation of +/- 20%

7.  The factors the tower can be assessed for,
include:
• Heat load(capacity),
• Cooling water flow,
• Fan Power,
• Cooling Range, approach, and effectiveness.

8.  Cooling Towers normally do have spare
cells by design:
• Examine if operation of spare cell would
beneficial
• Careful analysis of various operational costs
and
performance data would help optimize

9.  Return water distribution system to ensure:
• uniform hot water flow to all the cells
• Clean nozzles
• Splash bars in original location
• All fills in place and in clean condition
• Air inlet is clear of obstructions.
• Fans are operating at design condition
• Operating cells only get water inflow

10. Water losses include evaporation, drift (water entrained in discharge vapor),
and blow down (water released to discard solids).
Drift losses are estimated to be between 0.1 and 0.2% of water supply.
Evaporation Loss = 0.00085 x water flow rate x (T1-T2)
Blow down Loss = Evaporation Loss/(COC-1)
where cycles of concentration (COC)
is the ratio solids in the circulating water to the
solids in the make-up water
Total Losses = Drift Losses + Evaporation Losses + Blow down Losses

11. Cooling Water Treatment:
With increasing costs of water, increase Cycles of Concentration
(COC) would help to reduce make up water requirements
significantly.
Drift Loss in the Cooling Towers:
drift loss minimization to as low as 0.003 – 0.001% by change
in drift eliminator shapes & opting for more efficient designs.
Cooling Tower Fans:
Adoption of fans (lightweight, efficient designs)with better
aerodynamic profile with optimum, twist, taper for achieving fan
total efficiency as high as 85–92 %desirable.
Cooling Tower loads:
Segregation of high temperature (like furnace cooling) and
temperature sensitive loads is desirable for better overall
efficiency.
Condition of Nozzles and Fills
Upkeep of Nozzles and fills is crucial for efficiency and capacity
management

12.  Optimizing fan operations desirable through
on-off controls or multi speed fan motors,
automatically adjustable pitch fans, variable
speed fan drives.
 Adoption of varying combinations in L/G ratio
for optimum cooling tower performance
during summer, monsoon and winter times
desirable, to achieve highest cooling tower
effectiveness alongside capacity
simultaneously.
 Adoption of on-line conductivity monitoring
with optimized blow-down and makeup water
management desirable.

13. THANK YOU