Industrial cooling systems

APPLICATION NOTE
INDUSTRIAL COOLING SYSTEMS
Dr. Hugh Falkner
May 2018
ECI Publication No Cu0117
Available from www.leonardo-energy.org

Publication No Cu0117
Issue Date: May 2018
Page i
Document Issue Control Sheet
Document Title: Application Note - Industrial Cooling
Publication No: Cu0117
Issue: 03
Release: Public
Content provider(s) Hugh Falkner
Author(s): Hugh Falkner
Editorial and language review Bruno De Wachter (editorial review)
Content review: Guido Magneschi (DNVGL)
Document History
Issue Date Purpose
1 June 2007 Initial publication
2 October
2011
Update for adoption into the Good Practice Guide
3 May 2018 Development of an entirely new Application Note on the same topic
Disclaimer
While this publication has been prepared with care, European Copper Institute and other contributors provide
no warranty with regards to the content and shall not be liable for any direct, incidental or consequential
damages that may result from the use of the information or the data contained.
Copyright© European Copper Institute.
Reproduction is authorized providing the material is unabridged and the source is acknowledged.

Page ii
CONTENTS
Summary ........................................................................................................................................................ 1
Introduction.................................................................................................................................................... 2
Overview of Industrial Cooling requirements ................................................................................................. 3
Selecting a cooling system......................................................................................................................................3
Psychrometry of air ................................................................................................................................................3
Operation of the cooling water recirculation loop.................................................................................................4
Minimizing the cooling load ...................................................................................................................................5
Alternative uses for the waste heat .........................................................................................................5
Critically assess the required cold water temperature ............................................................................5
Regulating the flow through the heat exchangers...................................................................................5
Open-circuit Recirculation systems..........................................................................................................5
Cooling Tower operation and optimization..................................................................................................... 7
Evaporative cooling towers ....................................................................................................................................7
Energy and water consumption..............................................................................................................................8
Counterflow evaporative cooling towers ...............................................................................................................8
Crossflow evaporative cooling towers..................................................................................................................10
Dry Air Cooling Systems........................................................................................................................................11
Plant Optimization........................................................................................................................................ 14
Plant Optimization - Fans .....................................................................................................................................14
Speed control of the cooling tower fan..................................................................................................14
Speed control of the fan in multiple tower systems ..............................................................................15
Fan selection and maintenance..............................................................................................................16
Plant Optimization - Pumps..................................................................................................................................16
Multiple pump control ...........................................................................................................................16
Preferential use of best performing pumps ...........................................................................................17
Pump selection.......................................................................................................................................17
Non-return valves operation..................................................................................................................17
Plant Optimization - Drives...................................................................................................................................18
Motors....................................................................................................................................................18
Transmissions.........................................................................................................................................18
Operational and Management Cost Savings ................................................................................................. 19

Page iii
Water balance and billing.....................................................................................................................................19
Water Treatment..................................................................................................................................................19
Total dissolved solids control ...............................................................................................................................20
Sump Heater controls...........................................................................................................................................20
Monitoring and Targeting.....................................................................................................................................20
Operator training..................................................................................................................................................20
Action Checklist ............................................................................................................................................ 21
Minimizing the heat load .......................................................................................................................21
Cooling tower .........................................................................................................................................21
Cooling tower fans .................................................................................................................................21
Circulating pumps...................................................................................................................................21
Water management ...............................................................................................................................21
Energy management ..............................................................................................................................21
References.................................................................................................................................................... 22

Page 1
SUMMARY
The starting point for a review of an industrial cooling system should be to see what options there might be for
minimizing the heat load, and then to see if there are any alternative uses for the waste heat produced. Once
the demand has been reduced, attention can then be given to optimizing the cooling system to run efficiently.
Evaporative cooling systems are the most popular type found in industry. This Application Note explains how
they work and the energy and water saving opportunities that they may present. For both evaporative and dry
air cooling systems, variations in ambient air conditions and process loads, means that they will spend much of
their time working at part load operation. On/off and variable speed control of the system fans and pumps can
give large energy savings, but the selection of methods depends on the detailed design of the cooling plant.
Care also must be taken to also ensure that the system will work satisfactorily at partial load.
Water treatment and selection, and maintenance of cooling tower fill are important for effective and reliable
operation, and have direct impact on energy use. Regular monitoring of the system will ensure that any
changes in performance can be identified and remedial measures taken.
This Application Note makes suggestions of well proven techniques to save energy, that vary from simple
maintenance tasks to operational and equipment changes that will require the input of a specialist.

Page 2
INTRODUCTION
An unavoidable byproduct of many industrial processes is waste heat, which must be safely removed and
dissipated to the environment by a dedicated cooling system. Unfortunately, these cooling systems are often
seen as a free facility, with the true costs of operation often being overlooked. Even a thermal load of 60
MWth can cost over 1 M€ per year to remove from a site.
This Application Note gives an overview of the design and operation of common types of industrial cooling
systems, showing how energy savings in excess of 10% can frequently be found without significant investment.
Improved operation and maintenance can also improve cooling plant performance and reliability, and lead to
reduced water consumption
1
.
The cooling systems described in this Application Note are found in many high heat producing applications,
most commonly:
 Removal of heat from exothermal reactions in chemical reactors
 Cooling of large industrial plant, such as air compressors
 Cooling of high temperature products, such as steel production
 Cooling of condensers for power generation (though large power plants use single pass water cooling
systems and natural draft towers, which need special considerations that are outside the scope of this
Application Note)
In addition, many of the considerations for the optimization of cooling towers used in industry are also very
relevant to the condenser cooling found on larger chiller systems, such as those of building air-conditioning
systems.
1
ISO16345:2014 “Water-cooling towers -- Testing and rating of thermal performance” gives in depth
information on how the performance of cooling towers can be assessed, and gives useful insights on the
factors that impact performance.

Page 3
OVERVIEW OF INDUSTRIAL COOLING REQUIREMENTS
SELECTING A COOLING SYSTEM
The selection of cooling system will depend on a balance of many factors. These include factors related to the
local environment, such as:
 Variation of dry and wet bulb temperatures around the year.
 Availability and quality of water for use in the cooling process.
 Temperature set-point of process cooling water.
 Danger from localized fog caused by steam plumes from evaporative cooling systems.
 Available footprint and height restrictions.
 Local noise restrictions.
 Local wind conditions and the location of nearby buildings or industrial processes.
As well as process-related factors, such as:
 Quantity and variation of heat to be dissipated.
 Costs of chemical treatment to prevent corrosion, scaling and biological growth.
 Risk of people coming into contact with spray carrying legionella bacteria.
 Capital, operations and maintenance costs.
For the range of industrial processes considered in this Application Note, the choice is between different types
of evaporative or dry air water recirculation cooling systems. For very large plant, such as power generation
stations, a single pass system with discharge of warmed water back to source is common.
PSYCHROMETRY OF AIR
For dry air and evaporative cooling systems, the properties of the ambient air are critical for determining the
cooling ability of the system [1]. Three temperatures are of interest when considering cooling tower operation:
 Temperature of the warm water entering the cooling tower
 Temperature of the cold water exiting the cooling tower
 Approach temperature of the air
The temperature drop between the warm water entering the tower and the cold water exiting is known as the
temperature range. This is typically in the range 6 – 10°C. The difference between the cold water return
temperature and the temperature of the air is known as the approach temperature. This should ideally be as
small as possible.
The dry bulb temperature is the temperature of dry air, and is relevant where sensible heat transfer is the
underlying mechanism, such as for dry air coolers. An approach temperature of around 12°C is typically
achievable for these systems.
For evaporative cooling systems, the capacity of the air to hold additional evaporated water is an important
factor. The wet bulb temperature is a measure of the degree of saturation of the air, which takes into account
dry bulb temperature, relative humidity and air pressure. It is the lowest temperature to which water can
theoretically be cooled, taking into account the additional cooling from the latent heat used in the transition of
water from liquid to gas when it is evaporated. The lower the degree of saturation, the more moisture it is
capable of holding, and so the greater the cooling potential. An approach temperature of around 4°C is
achievable for these systems.

Page 4
The wet bulb temperature is lower than the dry bulb temperature, except when the air is fully saturated, at
which point the two values will be the same.
Table 1 shows the end (exit) temperatures achievable by dry and wet systems in a variety of temperature
conditions, showing clearly the lower temperatures achievable by evaporative systems.
Country, city Temperature (°C)* Temperature
difference
(°C)
End temperature (°C) T (Wet – Dry)
systems (K)Dry bulb Wet bulb Dry
system
Wet
system
Greece, Athens 36 22 14 48 26 22
France, Paris 32 21 11 44 25 19
Portugal, Lisbon 32 27 5 44 31 13
Ireland, Dublin 23 18 5 35 22 13
Belgium, Brussels 28 21 7 40 25 15
Germany, Hamburg 27 20 7 39 24 15
* Statistically only 1% of the maximum temperatures are above this data.
Table 1 – Achievable cooling of dry air and evaporative cooling systems in different locations. Adapted from
IPPC BREF (Table 1) [2] .Illustrative only, based on a 4K (dry air) and 12K (evaporative) temperature approach.
OPERATION OF THE COOLING WATER RECIRCULATION LOOP
Figure 1 shows the high level design of a cooling water loop, where heat is transferred from the process to the
cooling circuit through heat exchangers. The now warmed up water leaving the heat exchanger then enters
the cooling tower (or another type of water-to-air heat exchanger), where it is cooled by the airflow. This cold
water exits the cooling tower, and is then pumped back to the process heat exchangers. As below, it is
common for a cooling system to serve many parallel heat exchangers serving different processes. Valves, that
might be manual or automatic, should adjust the flow in each arm to suit the required flow.
Figure 1 – Schematic of a cooling tower system with multiple heat loads.

Page 5
MINIMIZING THE COOLING LOAD
ALTERNATIVE USES FOR THE WASTE HEAT
Dissipating heat to atmosphere is inherently wasteful, and so the preference is to reclaim value from the heat
stream by finding an alternative use. On most sites which produce large amounts of waste heat, there is little
demand for additional heat, and so uses off site should be considered. For example, greenhouse horticulture
and space heating is sometimes supplied by power station condenser cooling water. However, on many
systems the production of waste heat is much lower during the colder seasons, making it hard to find a cost
effective match.
Organic Rankine Cycle based power generation [3] could be considered, but the economics will be limited by
the temperature of the waste heat, and the variation in quantity of heat produced over the year. For more
information ORC, see the LE Application Note “Sustainable Heating and Cooling”.
On more complex energy intensive sites that have several different processes, a PINCH [4] approach can be
used to move waste heat energy between processes with different thermal heating/cooling requirements. For
example, a finished chemical product might require cooling from 120°C to 40°C, where some of this
temperature drop can be achieved by using heat exchangers to pre-heat an earlier stage of the process. This
use of waste energy will reduce the net cooling demand on the cooling towers.
CRITICALLY ASSESS THE REQUIRED COLD WATER TEMPERATURE
The starting point for optimizing the energy performance of a cooling system is to understand the actual cold
water return temperature needed by the process heat exchangers to sufficiently cool the process loads. The
origin of this set point should be critically reviewed in conjunction with the plant operators. Suspiciously
rounded target temperatures, such as 30.0°C, or systems where records show that the return water
temperature drifts with ambient, or other non-process conditions, are indications that further investigation
could be useful. The cost of cooling means that just a small increase in required return temperature can lead to
big savings.
REGULATING THE FLOW THROUGH THE HEAT EXCHANGERS
Control valves should be fitted to heat exchangers to vary the flow to match demand, and to allow isolation
when not in use. These controls commonly include, such as:
 Time-switches.
 Load sensors.
 Thermostats.
The use of a Variable Speed Drive to vary the pump speed will save energy by reducing flow as the total
demand varies.
OPEN-CIRCUIT RECIRCULATION SYSTEMS
At some industrial sites, the water will also be used for cleaning or direct cooling of products, meaning that it
will pick up debris that needs to be removed. An example of this is in steel rolling mills, where the water is also
used for slab de-scarfing, tank washdown and direct slab cooling, (figure 2).
To avoid subsequent damage to the pumps and other components, the spent water is captured in scale pits,
from where it is pumped by the scale pit pumps to a clarifier tank for further cleaning. It is then pumped
through a filter by the clarifier pumps, and then through the cooling tower. The mill supply pumps finally
supply the cooled water back to the mill processes.

Page 6
This system means that the water is pumped three times on each passage around the cooling loop.
Consequently, minimizing the required water has an even larger associated reduction in total pumping energy.
Figure 2 – Simplified schematic of the water supply in a steel rolling mill, showing multiple pump stages used in
circulating the water around the supply and cooling loop [5].

Page 7
COOLING TOWER OPERATION AND OPTIMIZATION
EVAPORATIVE COOLING TOWERS
Evaporative cooling towers are popular because they are usually lower cost, have a smaller footprint and
require less energy than dry air systems. But they do require more maintenance, and the growth of legionella
bacteria needs to be managed. In addition, a typical tower will be designed to lose about 1.5% of the water to
evaporation. This loss needs to be replaced on an ongoing basis by make-up water. The water will also need
regular chemical dosing to maintain water quality.
There are two principal types of evaporative cooling towers; counterflow and crossflow. Both work on the
same thermodynamic principle. Towers are commonly made from galvanized steel and/or fibre re-inforced
plastic, with some older tower designs still using wooden walls. Large cooling towers may be constructed on
site out of concrete.
It is common to find several cooling towers installed in parallel to make up the required capacity. This gives
many options for part load control, and makes maintenance easier to schedule. The differing pressure:flow
characteristics of the crossflow and counterflow systems mean that in multiple tower systems, the two types
should not be mixed.
Cooling tower fill is essential for operation (figure 3), as it maximizes the air:water interface and transit time,
hence maximizing the amount of evaporation that can take place as the water falls through tower. Modern fill
usually consists of hexagonal tubes created from multiple pre-formed PVC sheets, with fine ridges (flutes) built
into the walls to direct the water on circuitous routes to the bottom. The fill will have an optimum air:water
flow ratio of around 3:1.
For dirtier water, coarser flutes are used, but at the expense of heat transfer capability. Where entrained dirt is
a big issue, some counterflow systems just use a direct spray of water into the cooling tower with no fill.
For extremely dirty water, descending fill bars are used, where the water falls and splashes from one bar to the
next. The reduced surface area of these droplets compared with film flow means that performance is not as
good.
Figure 3 – Cross section through PVC film fill for counterflow cooling towers
2
.
2
Diagram taken from http://www.towercomponentsinc.com/operation-film-fill.php

Page 8
ENERGY AND WATER CONSUMPTION
Electricity consumption of the fans and pumps, and water consumption in evaporative cooling systems, varies
between different designs and operating conditions. By way of illustration, tables 2 and 3 show annual costs
based on running a 60 MWth cooler at 3,000 h full load equivalent per year.
Item kW/ MWth kW
Assumed cost
(€/kWh)
Total annual cost of
electricity for 3,000 h
full load equivalent
Electricity - Pumps 15 900 0.12 €324,000
Electricity - Fans 5 300 0.12 €108,000
Table 2 – Illustrative annual cost of water in an evaporative cooling tower (see table 3.3 in [2] for derivation of
kW/MWth figure), where MWth is the nominal cooling load.
Item m3
/h / MWth m3
/h
Assumed cost
(€/m3
)
Total annual cost of
water for 3,000 h full
load equivalent
Water 2 120 2.0 €720,000
Table 3 – Illustrative annual cost of water in an evaporative cooling tower (see table 3.6 in [2] for derivation of
m
3
/h / MWth figure).
COUNTERFLOW EVAPORATIVE COOLING TOWERS
In counterflow cooling towers, the water is first pumped to the top of the tower, from where it is sprayed
downwards onto the fill (figure 4). The fan induces a vertical counterflow of the air from underneath the fill.
As the water moves through the fill under gravity, a small proportion of the water is evaporated. The
remaining cooled water then falls into the cold water sump, from where it is then returned to the cooling loop.
For best operation, each flute should have equal air:water flows. However, the circular pattern of standard
nozzles means that this is difficult to achieve. This means that some flutes will have a poor air:water ratio, and
so will not work at their optimum. Bounceback of spray hitting the cooling tower walls can also cause a more
localized air:water imbalance around the cooling tower edge.

Page 9
Figure 4 – Schematic of a counterflow cooling tower.
Figure 5 – Spray pattern of standard nozzles in a counterflow evaporative cooling tower, showing an uneven
water flow distribution.
Nozzles that produce a pattern that is closer to a square are also available, and should be considered for new
or retrofit installation.
Low water pressure operation could reduce the spray pattern diameter. This leads to wide water:air ratio
variations across the fill, limiting the pressure range over which the tower can work effectively. Some nozzles
have integral valves that close the nozzle if the supply pressure is too low (figures 6 and 7).
Figure 6 – Impact on the spray pattern of a counterflow evaporative cooling tower with insufficient pressure.
[6]

Page 10
Figure 7 – Uneven water flow pattern across fill at times of insufficient pressure.
High pressure nozzles that have a wider spray pattern mean that the separation between nozzles and the top
of the fill can be minimized. If specified at design, this can decrease pumping energy and tower capital costs. If
retrofitted, the additional fill increases the effectiveness of heat transfer, since heat transfer within the flutes
is around ten times more effective than that in the freefall zone above.
CROSSFLOW EVAPORATIVE COOLING TOWERS
In crossflow evaporative cooling towers, the water is pumped to a distribution pan at the top of the tower,
where it falls through nozzles in the base onto the fill below, (figure 8).
Figure 8 – Schematic of a crossflow cooling tower.
An advantage of this system is that the nozzle head is fixed by the depth of water in the distribution pan, and
so a greater turndown flow ratio is possible than on counterflow systems with varying nozzle water pressure
On crossflow systems, the depth of water in the redistribution deck varies with the flow. The depth of water in
the distribution deck is typically 6” at rated flow. Very low water flows should be avoided, as it can lead to icing

Page 11
in cold weather, and to enhanced scaling. Dams, or nozzle cups, can be used to restrict the active nozzles and
hence fill at times of low water flow, (figure 9).
Figure 9 – Use of nozzle cups and a dam to vary active zones with water flow on a crossflow redistribution deck.
DRY AIR COOLING SYSTEMS
Dry air coolers work by the transfer of heat by convection from radiator cooling fins to moving air (figure 10). A
fan is used to increase air flow and hence heat removal.
Because there is no water loss, the operational water make-up and chemical dosing costs are negligible. This is
a major operational advantage over evaporative cooling towers. As water is only required to fill the system
once, they are ideal for sites where water is not always available. Because the water is not in contact with the
air, the risk of legionella bacteria is low, making these systems popular where people are at risk of inhaling
airborne water droplets.
A wider range of mediums can be used as a cooling fluid because the system is closed. There will also not be
the visible plume sometimes seen coming from evaporative cooling towers, which is a benefit in locations
where fog development is a risk.
However, because these systems rely on convection cooling only, they do not benefit from the latent heat
cooling of evaporation. As a result, they require more surface area. They are generally more expensive than
evaporative cooling systems.

Page 12
Figure 10 – V-type dry air cooler.
The cooling matrix is built of an assembly of copper pipes inserted through aluminium fins to help heat
dissipation (figure 11). Air is then sucked through the fins to enhance heat transfer. It is usual for large arrays
to be built from multiple small fans. The fan power required is higher than for a comparable evaporative
system, and so this type of plant may also be noisier.
Dry air coolers are often sold as packaged units with multiple fans (figure 12). These can be controlled
sequentially or by speed reduction, with substantial energy savings possible through speed reduction at times
of low cooling duty. Brushless DC motors are popular, resulting in a high-energy efficiency both at full and at
reduced flow.
Figure 11 – A heat exchanger detail showing copper pipes with aluminium fins.

Page 13
Figure 12 – Multiple fan dry air cooling unit, which might be vertically or horizontally mounted.
Periodic cleaning is required to ensure that the cooling fins do not get blocked, which is a particular risk in
dusty industrial environments.
Some dry air coolers include a water spray onto the fins for adiabatic cooling. In this way, almost free
additional cooling within 6°C of the wet bulb temperature can be gained when ambient conditions are
favourable.
Only a small amount of water will be used, but is designed to be completely evaporated. These systems are
therefore only applicable where there is water available. A drain point is required to drain of water in the
distribution pipes at the end of operation.
De-scaling of water might be required depending on water properties, and incoming water can be disinfected
using UV sterilization units.

Page 14
PLANT OPTIMIZATION
PLANT OPTIMIZATION - FANS
SPEED CONTROL OF THE COOLING TOWER FAN
Cooling systems are designed to provide a maximum cold water temperature at specified ambient and load
conditions, but will spend much of their time working at a much lower duty.
At these lower duties, sufficient cooling can still be achieved with reduced airflow. This can be done by
installing a Variable Speed Drive (VSD) using temperature feedback to vary the speed of the fan. In this way,
the required set-point return water temperature can be maintained (figure 13).
Since the power consumption of a fan varies with the cube of the speed, even just a 20% reduction in fan
speed will theoretically almost halve the power consumed.[7].
Pnew = 0.8
3
x Poriginal => Pnew = 0.51 x Poriginal.
Where Poriginal is the original power consumption when it was running at full speed, and Pnew is the reduced
power consumption.
Figure 13 – Installation of a VSD to regulate the fan speed, using a temperature sensor to maintain return
water temperature. [8]
The VSD also gives a controlled increase of speed during start up, which reduces the mechanical stress, as well
as the peak currents when starting high inertia axial fans. The VSD will have internal losses, and will slightly
increase the losses in the motor, but these losses are small in comparison to the potential energy savings. The
typical increase in motor losses when driven by a VSD is approximately equivalent to the loss reduction
achieved through a downgrade of half of an IE motor efficiency class [9].

Page 15
SPEED CONTROL OF THE FAN IN MULTIPLE TOWER SYSTEMS
For larger cooling requirements making use of multiple cells or towers, switching these on and off individually
is a traditional way to match the cooling power to the demand. This can give useful energy savings, but the
energy savings can be much larger by keeping all cells running and slowing down the fans. In this way, the heat
transfer surface area is maintained at a maximum, with the energy savings coming from the reduction in fan
speed. [6]
The airflow produced by the fan is proportional to the fan speed, with cooling capacity falling as the speed
falls. But because the fan power is proportional to the speed cubed, the specific fan power (kW/l/s) required
for the same total flow is now much less.
Figure 14 – Running three cooling tower fans at 2/3rds speed theoretically uses less than half the energy of two
fans running at full speed.
In the example shown in figure 14, 3 towers at 2/3 flow will give the same airflow as 2 towers at full flow,
(table 4). But the theoretical total energy consumption will now be just 45% (=100 x 89/200).
Fan Operation Flow (% of single fan rated
power)
Power (% of single fan rated
power)
2 Fans at full speed 200% 2 x 100% = 200%
3 Fans at 2/3rds speed 200% 3 x (2/3)3
x 100% = 89%
Table 4 – Energy savings from running multiple fans at reduced speed.
This is a very effective way to save energy, providing that the cooling tower can work satisfactorily at this
reduced airflow. Historically, variable pitch blades or two speed motors have been used to adjust the fan duty,
but their lower cost and other advantages have made VSDs popular in this application.

Page 16
FAN SELECTION AND MAINTENANCE
Particularly for new cooling towers it is worth checking that a high efficiency design has been selected and that
it is working within its ideal zone of operation. The blades should also be kept clean to maintain efficiency.
PLANT OPTIMIZATION - PUMPS
MULTIPLE PUMP CONTROL
For open evaporative systems, there is significant static head, which limits the potential energy saving from
speed reduction. In addition, for counterflow towers, nozzle performance depends critically on pump pressure
and hence rotational speed. This means that there is limited scope for varying the pump speed as a means to
reduce the energy requirement
Instead, flow can be varied by switching on and off individual pumps in multiple pump systems. A common
energy saving opportunity is to review the control strategy of such pump banks in order to minimize the
number of pumps operating.
The system operating point with 1 and 2 pumps in use is shown in figure 15. When the second pump is
switched on, the total flow will increase by an amount that depends on the shape of the system curve. For a
system that has static head only and no friction, the flow would double. But for a real life system which does
have friction, the increased flow will give rise to an increase in friction head. This means that 1) despite having
two pumps, the flow has not doubled, 2) the pressure is higher than was originally needed, which represents
wasted energy, and 3) the pumps will be working at new operating points with different efficiencies (figure
16).
In this example, the pumps are selected for best performance when two are running. But it is also possible to
specify pumps that have optimum efficiency when just one pump is running. This enables the system to be
designed to have the lowest specific energy consumption when supplying the most common flow demand.
It is not unusual to find excess pumps running after they were used to overcome a short term peak in demand,
and were not switched off again afterwards. A PLC can be used for automatic sequencing of the pumps in
response to varying demand.
Figure 15 – Control of multiple pumps on a counterflow cooling system.

Page 17
Figure 16 – Change in the working point and hence efficiency of an individual pump as the number of pumps
used is varied.
PREFERENTIAL USE OF BEST PERFORMING PUMPS
Measurement of the electricity consumption and water flow of the different pumps will give the specific
energy consumption (kWh/m
3
) of each pump. By measuring the pump performance at different flows, its Best
Efficiency Point (BEP) can be found. The best performing pumps can then be given preference when
sequencing pump operation. This also gives information on the number of pumps at which the system will be
the most efficient.
PUMP SELECTION
The circulation pumps should be chosen to be high efficiency designs, with a working range close to their Best
Efficiency Point (BEP). For larger pumps, it can be worth periodically checking their efficiency using an in situ
pump efficiency test method. The gradual decrease in efficiency can then be monitored and the pump
refurbished or replaced as necessary.
NON-RETURN VALVES OPERATION
Non-return valves are important to ensure that pressurized water does not recirculate through the unused
pump back to the suction side of the operational pumps (figure 17). Also, if they do not open fully, then this
throttling will reduce the delivered water and increase the specific energy consumption of that pump.
Figure 17 – Arrangement of multiple pumps and non-return valves on large cooling system [8].
It is usual, but not essential, for all the pumps in parallel systems to have identical characteristics.

Page 18
PLANT OPTIMIZATION - DRIVES
MOTORS
The induced draft fan motors are mounted within the airstream, and must consequently be rated for the warm
and humid atmosphere.
High efficiency motors should be specified as standard. In many countries, motors of the high performance IE3
efficiency class are now the only ones available. Retrofit of working motors with new high efficiency motors is
unlikely to be economic, but when an older motor needs replacing anyway, the economics of upgrading to a
higher efficiency motor are usually attractive [10]
TRANSMISSIONS
The rotational speeds of standard induction motors are too high for cooling tower fans, and so a belt drive or
gearbox transmission are needed for the fan to operate correctly.
Wedged Drive belts are commonly used where the fan shaft and motor shaft are in the same orientation. As
they become slacker with use, internal energy losses will increase, and so they should be periodically re-
tensioned. As the belts wear, the sheaves (pulleys) will also wear and will require replacement. On drives
where there are several drive belts in parallel, it is important that they are equally tensioned. Where it is
practical, toothed belts are a good alternative that have much lower internal losses.
Gearboxes are used where the fan shaft is at 90° to the motor shaft. These have internal losses that vary by
type and also with the load. They also require periodic lubrication.
New direct drive motors are now available that are designed specifically for evaporative cooling tower fans,
which avoid the need for a separate transmission [11]. These give much higher efficiencies and will also
produce less noise. The maintenance requirement is less, and alignment is also simpler. However, care should
be taken that the fan supports can withstand the total weight of the motor in the centre of the tower.

Page 19
OPERATIONAL AND MANAGEMENT COST SAVINGS
WATER BALANCE AND BILLING
A typical evaporative cooling tower is designed to lose about 1.5% of water flow to evaporation, which should
be reflected in the amount of make-up water required. If make-up water is more than this, then it indicates
losses through either drift, leakage or blowdown. This is costly in terms of water, energy and chemicals.
 Drift is spray or mist that is blown out of the cooling tower. Drift eliminators are boards that are
positioned to reduce airborne drift, but should be checked to ensure that they are functioning well. On
the best installations drift eliminators will keep drift to 0.001 – 0.005%. This airborne drift is distinct from
the plume of pure steam that is sometimes seen over cooling towers. Careful selection and maintenance
of drift eliminators is important to minimize the pressure drop, and the corresponding additional fan
energy required to overcome this.
 Blowdown is necessary to maintain the right chemical balance of the water. Minimising the amount of
water lost through blowdown is described in the next section.
 Leakage can occur anywhere in the system.
Any water that does not return to drain should not be included in the sewage charge. Fitting an approved
meter to the make-up water supply can be used to support a reduced waste water bill.
WATER TREATMENT
For evaporative systems that require ongoing filling with make-up water, regular dosing will be needed to
maintain effective and safe operation:
 Corrosion inhibitors for reducing rusting.
 Scale inhibitor chemicals are needed to reduce the build-up of scale from minerals such as calcium,
magnesium and silica carbonate in the water. Scaling can be a particular problem in flutes subject to
regular on/off cycling.
 Biocides to reduce the growth of biological film.
In addition, dirt, leaves, paper and other organic waste can be blown into evaporative systems. These larger
suspended solids can be removed by filtering.
Legionnella Pneumophilla bacteria is found in many systems and must be controlled in line with local legal
requirements and guidelines
3
. It can become a hazard where the water temperature in all or some part of the
system may be between 20–50 °C; there are deposits that can support bacterial growth, such as rust, sludge,
scale and organic matter; and where it is possible for water droplets to be produced and dispersed.
Closed systems also require treatment, but because a regular input of fresh make-up water isn’t required, the
costs will be much lower.
3
The regulations published by the United Kingdom Health and Safety Executive give a good overview of the
approach that should be taken to managing legionella bacteria. [12]

Page 20
TOTAL DISSOLVED SOLIDS CONTROL
As the pure water evaporates from the cooling tower, the Total Dissolved Solids (TDS) of the remaining water
will increase, with fresh make-up water bringing in additional minerals. Periodic blowdown of a proportion of
the volume of water in order to maintain TDS at an appropriate level is therefore important. Without accurate
monitoring of actual TDS levels, blowdown is likely to remove more water and chemicals than is actually
needed.
On-line TDS monitoring reduces water use by only initiating blowdown when a defined TDS level has been
reached, greatly reducing the cost of replacing water and chemicals unnecessarily sent to drain. Systems that
can work satisfactorily with a higher TDS peak concentration will require less blowdown. Specialist advice and
training is recommended to specify and maintain a chemical dosing and blowdown regime appropriate to the
system. The equipment and processes are very similar to those used for blowdown of boiler water.
SUMP HEATER CONTROLS
Evaporative cooling towers have a sump to collect the cooled water, which could freeze in low ambient
temperatures. A heater will be fitted to prevent this happening.
The heater controls should be checked to ensure that it switches the heater on and off at the required
temperatures. If the switch off temperature is too high, then excess energy will be used in heating the water to
this temperature.
MONITORING AND TARGETING
Ambient temperature and cooling demand will be important factors in influencing electricity and water
consumption. Separate meters for the electricity and water used by the cooling system are recommended to
enable consumption to be measured on a regular basis. This will enable any variations from the norm to be
identified and their cause traced. There may be genuine reasons for variances, in which case a comparison of
water and electricity use with other influencing factors can give much deeper insights into system
performance. Comparisons should be made over whatever time period is relevant, which might be different
for a batch or continuous process.
OPERATOR TRAINING
It is important that the staff operating the cooling system are aware of the high electrical, water and chemical
costs of the plant that they control. Very often they have little idea of the costs of the regular decisions that
they make, and have not been given the knowledge to understand how they can make changes to operating
procedures in order to make useful energy savings. It is vital to involve the Production Department (and any
other customers of the cooling system) in any changes in operating procedures.

Page 21
ACTION CHECKLIST
MINIMIZING THE HEAT LOAD
 Critically assess the basis of the specified return water temperature. Can it be raised – even a little?
 Take steps to reduce the heat load that needs dissipating. This might involve a review of the set-
points for the cooling loads, checking the selection and operation of controls, and cleaning of heat
transfer surfaces.
 Can the waste heat be re-used, for example in the heating of other processes on or off site, or for
power generation?
COOLING TOWER
 Check the type and condition of the fill, and clean or replace as necessary.
 Check that the water flow across the fill has acceptable variation.
 Consider the use of alternative spray nozzles to give an improved spray pattern.
 Check that the nozzles are not broken or blocked.
 If fitted, valves should be adjusted to provide a more even flow across the nozzles.
 Check the operation of drift eliminators. In particular, look for scaling or biological growth that might
be restricting air flow.
 Check the operation of sump heater controls
 For crossflow designs, check that the sump water level is above the bottom of the fill, otherwise it will
offer an alternative way to bypass where it is required.
 Clean the cooling fins of dry air cooling systems to enhance air flow.
COOLING TOWER FANS
 Consider installing VSDs to vary the speed of the fans.
 Replace motor and transmission with high efficiency integrated direct drive motor/inverter.
 Clean the fan blades to maintain efficiency.
 Upgrade older fans on evaporative cooling towers to higher efficiency designs.
CIRCULATING PUMPS
 Check proper operation of non-return valves.
 Sequence the pump control to match the flow to instantaneous demand.
 Assess performance of each pump to decide on priority pumps when sequencing.
 Measure pump efficiency over time to decide the best time to replace or repair.
WATER MANAGEMENT
 Use automatic Total Dissolved Solids (TDS) monitoring and blowdown control to minimise make-up
and to dose the use of chemicals.
 Fit a water meter to the make-up water inlet to monitor usage.
ENERGY MANAGEMENT
 Upgrade failed low efficiency motors to high efficiency types
 Install electricity and water meters to enable ongoing review of system performance.
 Train the operators to be aware of energy efficiency aspects during plant operation.

Page 22
REFERENCES
1 Cooling Tower Performance TR-017, SPX Cooling Technologies, 2016. spxcooling.com/pdf/TR-017.pdf
2 Integrated Pollution Prevention and Control (IPPC) – Reference Document on the application of Best
Available Techniques to Industrial Cooling Systems. European Commission December 2001.
3 Cu0155 AN Sustainable Heating and Cooling v1, Leonardo Energy, 2013.
4 Introduction to Pinch Technology, Linnhoff March, 1998. https://www.ou.edu/class/che-design/a-
design/Introduction%20to%20Pinch%20Technology-LinhoffMarch.pdf,
5 Reducing Water Pumping Costs in the Steel Industry, GPG170, ETSU, 1996.
6 Variable flow over cooling towers TR-014, SPX Cooling Technologies, 2017.
http://spxcooling.com/library/detail/variable-flow-over-cooling-towers
7 Saving energy With Cooling Towers, Frank Morrison, Ashrae Journal, Feb 2014.
http://www.corecontrolsdfw.com/documentation/2014Feb_034-041_Morrison.pdf
8 Based on an example in “Industrial Cooling Water Systems”. Good Practice Guide 225, 1999.
9 IEC 60034-30 standard on efficiency classes for low voltage AC motors.
10 Cu0104 Application Note – Electric Motor Asset Management, 2015.
11 ABB Industrial cooling direct drive motor and VSD packages, 2015.
http://search-
ext.abb.com/library/Download.aspx?DocumentID=3AUA0000179912&LanguageCode=en&DocumentPar
tId=&Action=Launch
12 Legionnaires’ disease: Technical guidance Part1: The control of legionella bacteria in evaporative cooling
systems, UK Health and Safety Executive, 2013. http://www.hse.gov.uk/pubns/priced/hsg274part1.pdf

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