A well structured slideshow by Steve Lowe, PE for the Hampton Roads, VA Chapter of ASHRAE. Presentation explains how to apply cooling towers including the basic cooling tower principles, design considerations, and construction issues. For more information on any cooling tower issue in Colorado, New Mexico, Wyoming, Montana, Utah, Nevada, Idaho, or the western Dakotas, contact: Mountain States Engineering and Controls 1520 Iris Street Lakewood, CO 80215 303.232.4100 Phone 303.232.4900 Fax Email: info@mnteng.com

2.  Stephen Lowe
 ASHRAE Hampton Roads Chapter Past President
 AECOM Design – Mechanical Engineering Discipline
Manager, Virginia Beach Division
 Professional Engineer Commonwealth of Virginia  Professional Engineer – Commonwealth of Virginia,
NCEES
 BSME – University of Virginia, 2002
 Sheet metal fabricator, equipment installer, refrigeration
service technician during high school and college
C l i E i f P Consulting Engineer from 2003 – Present

3. OverviewOverview
 Introduction
 Cooling Tower Basics
 Principles of Operation
 Types of Cooling Towers
 Common Applications
 Design Considerations
 Selection CriteriaSelection Criteria
 Open Piping and Pumping Systems
 Water Quality
 Tower Location
 Ancillary Systems Ancillary Systems
 Construction Issues
 Constructability, Quality Control and Startup
 Rating and Certification
L L d Lessons Learned
 Conclusion
 Resources
 Questions and Discussion

4. Cooling Tower Basics
 Principles of Operation
 Cooling Via Evaporation – depends on Wet Bulb
TemperatureTemperature
 Design Dry Bulb Temperatures commonly exceed 95 deg
F: poor delta T for cooling processes
D i W b lb h l d F Design Wet bulb much less: ~80 deg F
 Use a process that depends on WB to take advantage of
greater delta Tg
 Evaporative effect is a change of state and thus a large
transfer of energy occurs relative to the required mass
flowflow

5. Cl d Ci i
Open Cooling Tower
Closed Circuit
Cooling Tower

6. Cross Flow Arrangement Counter Flow Arrangement

7. Cooling Tower Basics
 Common Applications
 Power Plant Steam Condensation
 Process Cooling
 HVAC Heat Rejection
 Chiller Condenser Heat Chiller Condenser Heat
 WSHP Loop Heat
*We will be focusing on open, cross flow cooling towers for
chiller condenser heat rejection for the remainder of the j
presentation.

8. Basic HVAC Cooling To er ApplicationBasic HVAC Cooling Tower Application

9. Design Considerations
 Design Considerations
 Selection Criteria
 Open Piping and Pumping Systems
 Water Quality
 Tower Location Tower Location
 Ancillary Systems

10. Design Considerations
 Selection Criteria
 Process (Chiller Condenser) Temperature Requirements
 Hot Water Temperature (HWT): Temperature of water entering the p ( ) p g
tower
 Cold Water Temperature (CWT): Temperature of water leaving the
tower
 Tower Range: HWT – CWT
 Lower CWT generally results in higher Chiller Efficiency
 Flow Rate or Capacity
 Ambient Conditions
 Evaporation (or Entering) Design Wet Bulb (EWB)
 Approach: CWT ‐ EWB
 Lower approach generally results in a larger tower

11. Design ConditionsDesign Conditions

12. Design ConditionsDesign Conditions
YESNO YES

13. Design Conditions
 Use Evaporation Design WB for selection of
evaporative equipment
U f % % % di i i h d i  Use of 0.4%, 1%, or 2% condition is up to the designer
based on specific application and design firm practice
 A 2 degree F margin of safety is recommended to  A 2 degree F margin of safety is recommended to
account for recirculation (rule of thumb – further
analysis is required for the specific application)y q p pp
 Condenser water delta T depends on many factors
such as the process that is cooled and optimization of
h i the pumping system

14. Design Considerations
 Open Piping and Pumping Systems
 Cooling tower pumping application troubles are
ll l d f h f ll i igenerally related to one of the following issues:
 Incorrect Pump Head Estimation
 Pump Cavitation Pump Cavitation
 Air Introduction to Pump Suction
 Improper Bypass Configuration/ControlImproper Bypass Configuration/Control

15. Design Considerations
 Open Piping and Pumping Systems
 Pump Head Estimation
l l f h h Determine actual static lift height
 Determine impact of siphon draw: either break the siphon or
design to maintain it.
 Determine friction head
 Pipe
 Equipment (condenser tower spray nozzle etc ) Equipment (condenser, tower spray nozzle, etc.)
 Components (valves, strainers, etc.)

17. Design Considerations
 Open Piping and Pumping Systems
 Pump head estimation errors can cause:
bl Unstable pump operation
 Unstable condenser flow at the chiller
 Admission of air into the pump inletp p
 Energy waste due to need for extensive throttling
 Many wasted hours and headaches finding the problem!

18. Design Considerations
 Open Piping and Pumping Systems
 Pump cavitation is the flashing (boiling) of the working
fluid (water) into a vapor due to excessively low suction
d i ft f d ith i i t d ti i t th pressure and is often confused with air introduction into the
pump suction.
 Net Positive Suction Head (NPSH) is the measure of suction
pressure pressure.
 The required suction pressure for a particular pump is
indicated NPSHR and is published as a curve on the pump
selection chart.
 The suction pressure available to the pump in a particular
system is indicated NPSHA and must be calculated by the
engineer.
If NPSHA NPSHR it ti ill If NPSHA < NPSHR, cavitation will occur.

19. NPSHA Example Calculation

22. Design Considerations
 Open Piping and Pumping Systems
 B & G Cooling Tower Pumping and Piping Manual has 4
l i th ti i irules concerning the pump suction piping:
1. Leave the suction Line Alone!
2. Place the pump below tower pan water levelp p p
3. Avoid “above the pump” air traps in the suction line
4. Avoid fine mesh, high pressure drop strainers in the suction
lineline

23. Design Considerations
 Open Piping and Pumping Systems
 Air admittance to the pump inlet is typically caused by:
 Tower pan vortexing
 Tower pan drain down
 Incorrect bypass arrangementyp g

24. Design Considerations
 Open Piping and Pumping Systems
 Tower pan vortexing is caused by excessive velocity in
th t it i i d b t ll d bthe tower exit piping and can be controlled by:
 Do not excessively oversize the pump
 Maintaining tower exit pipe size for a minimum of 10 pipe g p p p p
diameters
 Increase pan depth
 Provide a vortex breaker in the tower pan Provide a vortex breaker in the tower pan
 Install tower on the equator

25. Design Considerations
 Open Piping and Pumping Systems
 Tower pan drain down is caused by insufficient water
d th t fl d th t it i i d b id d depth to flood the tower exit piping and can be avoided
by:
 Correctly sizing the makeup water liney g p
 Evaporation Rate
 Blowdown Rate
 Providing a check valve to keep the piping system flooded on  Providing a check valve to keep the piping system flooded on
pump shut down
 Properly isolating tower cells in multiple cell installations

26. WRONGWRONG
Condenser and a significant
portion of the piping system will
drain pack to pan on pump
shutdown. Pan may flood and shutdown. Pan may flood and
chiller could start with a dry
condenser.
CORRECTCORRECT
Condenser will remain flooded
on pump shutdown. Minimal
system volume will drain to pan
on shutdown, therefore pan p
should not flood.

28. WRONG
Bypass connected to pump
i i i i suction piping can cause air
introduction to pump inlet and
unstable pump operation.
CORRECT
B di h i t b i ith Bypass discharging to basin with
balancing valve set equal to
discharge nozzle pressure drop
will result in constant pump
head and flooded pump suction.p p

29. CORRECT
Separate operators allow valves to maintain
WRONG
Linked valves will result in unstable flow.
a constant total flow as both valves
modulate.

30. Bypass Configuration Example

31. Design Considerations
 Water Quality
 Removal of Solids
 Chemical Treatment
 Consult a chemical treatment professional for your specific
applicationpp
 Biological Contamination
 Minimize drift
 Site towers away from air intakes
 Avoid piping designs that result in stagnant water
 Chemically treaty

32. Design Considerations
 Water Quality
 Removal of Solids
 What’s that floating in the basin????g
 Whatever it is, it has a good shot at ending up inside your chiller!!!!

33. Design Considerations
 Water Quality
 Removal of Solids
h h l d b k Guy with shovel and bucket
 In‐line strainers
 Side stream filters
 Basin sweeping system

34. Design Considerations
 Tower Location
 Visibility
 Sound
 Drift

35. Getting the proper Real Estate
 Location, location, location…
 Cooling Towers are highly visible due to physical size
d land plume
 Need ample clearance to minimize recirculation and
ensure proper performanceensure proper performance
 Low frequency sound emitted from large fans travels
great distancegreat distance
 Drift can mark windows and paint jobs

36. Design Considerations
 Ancillary Systems
 Freeze Protection
 Tower Sump Basin
 Electric
 Steam Injection
 Recirculation
 Piping Piping
 Water Treatment Systems
 Chemical Systems
 Solids FiltrationSolids Filtration
 Control Systems
 Pneumatic operators – will require freeze protection in some
climates
 Large valves require lots of torque – electric operators may need to
be industrial grade

37. Construction Issues
 Constructability, Startup, Quality Control
 There is lots of large piping underneath the tower, make
sure you get plenty of space for itsure you get plenty of space for it
 Consider laying out all of the piping based on a
manufacturer’s particular tower
U h f ’ h kli i  Use the manufacturer’s startup checklist on your site
visit
 Read the installation and operation manual during p g
design; there are lots of options that affect the cost of
the tower. You need to specify them if your application
needs them.

38. Construction Issues
 Ratings and Certification
 Manufacturer’s Rated Performance
 CTI Certification
 Performance Based Commissioning

39. Construction Issues
 Lessons Learned
 Tower Basin Freeze Protection
l d l d l l Direct steam injection is popular in industrial and large scale
HVAC applications.
 Chemical used for boiler feedwater may react with condenser
water chemical treatment resulting in the release of noxious
gases.
 A hot water circulator pump coupled to a heat source can be p p p
used instead.

41. Construction Issues
 Lessons Learned
 Vertical Loop in Suction Piping
d d d h l Tower mounted on grade adjacent to mechanical room
 Cold water pipe exits bottom of basin and passes through
mechanical room wall
 Pipe is the run up the wall to the roof structure to get the pipe
across the room to the pump
 Upon shutdown, the system equalizes and the piping at the Upon shutdown, the system equalizes and the piping at the
roof level becomes air locked
 The pump will require manual priming in order to start

43. Construction Issues
 Lessons Learned
 Flooding Tower on Pump Shutdown
 Tower is mounted on grade adjacent to mechanical room Tower is mounted on grade adjacent to mechanical room.
 There is a significant volume of water located above the tower
basin due to a long horizontal run of hot condenser water pipe
in the mechanical roomin the mechanical room.
 The diverting valve is installed in the horizontal with the
bypass connection facing down.
 Whenever the pump shuts down all of the water in the  Whenever the pump shuts down, all of the water in the
horizontal pipe runs through the diverting valve and back to
the basin.
 The basin overflows in the parking lot resulting in an p g g
unsightly puddle and wasted chemical treatment

44. Construction Issues
 Lessons Learned
 Air introduced to pump suction via bypass

45. Construction Issues
 Lessons Learned
 Air introduced to pump suction via bypass
AIR CAN BE DRAWN INTO
PUMP SUCTION

46. Construction Issues
 Lessons Learned
 Air introduced to pump suction via tower discharge
if ldmanifold

47. Construction Issues
 Lessons Learned
 Air introduced to pump suction via tower discharge
if ldmanifold
MUST ISOLATE TOWER
DISCHARGE

48. Construction Issues
 Lessons Learned
 Flooding hot water pans on manifolded towers

49. Construction Issues
 Lessons Learned
 Flooding hot water pans on manifolded towers
AUTOFLOW VALVE

50. Construction Issues
 Lessons Learned
 Multiple connected towers should have an equalization
liline.
 When adding or replacing towers connected through an
equalization line, design the tower and framing to q , g g
ensure that the existing operating water level is
matched with the new tower.
If i i id ib i i l i f h  If it is necessary to provide vibration isolation for the
tower, the piping system must be isolated from the
tower.

51. Resources
 B & G Cooling Tower Pumping and Piping Manual
 Marley Cooling Tower Company – Cooling Tower
F d lFundamentals
 Baltimore Air Coil Product and Application Handbook
E E i L M l Evapco Equipment Layout Manual
 www.CTI.org
 ASHRAE H db k 8 HVAC S t d  ASHRAE Handbook – 2008 HVAC Systems and
Equipment, Chapter 39

52. Questions?