Water Efficiency Management Guide
Mechanical Systems
EPA 832-F-17-016C
November 2017

Mechanical Systems
The U.S. Environmental Protection Agency (EPA) WaterSense® program encourages property
managers and owners to regularly input their buildings' water use data in ENERGY STAR® Portfolio
Manager®, an online tool for tracking energy and water consumption. Tracking water use is an
important first step in managing and reducing property water use.
WaterSense has worked with ENERGY STAR to develop the EPA Water Score for multifamily
housing. This 0-100 score, based on an entire property's water use relative to the average national
water use of similar properties, will allow owners and managers to assess their properties' water
performance and complements the ENERGY STAR score for multifamily housing energy use.
This series of Water Efficiency Management Guides was developed to help multifamily housing
property owners and managers improve their water management, reduce property water use, and
subsequently improve their EPA Water Score. However, many of the best practices in this guide
can be used by facility managers for non-residential properties.
More information about the Water Score and additional Water Efficiency Management Guides are
available at www.epa.qov/watersense/commercial-buildinas.

Mechanical Systems Table of Contents
Background	1
Sirigle-Pass Cooling...																												 1
Cooling Towers				1
Boiler and Steam Systems	5
Understanding Mechanical System Water Use	6
Seasonal Comparison																												 7
Electric Power Use	8
Chiller Tonnage..																														 9
Maintenance Best Management Practices	10
Retrofit and Replacement Options		 11
Single-Pass Cooling	11
Cooling Towers and Boilers																										 12
Water Savings Calculations and Assumptions	14
Single-Pass Cooling	14
Cooling Towers			15
Boilers																																		 16
Additional Resources	17
Appendix A: Summary of Water Efficiency Measures and Savings	A-1
November 2017
Water Efficiency Management Guide

Mechanical Systems
Mechanical systems are frequently utilized to provide heating (of water as well as living
spaces) and cooling for multifamily properties. They typically fall into two categories—
centralized and decentralized systems. Centralized mechanical systems provide heating
and cooling from a central location, such as a mechanical room or utility penthouse. These
systems are more common in mid- and high-rise multifamily properties. Centralized
mechanical systems can include cooling towers, boilers, and steam systems, each of which
uses water as the heat transfer medium. As a result, the use of water for building heating
and cooling can be significant, and using sound management practices is a good
opportunity for water savings.
Decentralized mechanical systems treat each unit of a multifamily property as its own
space, as if each unit were a stand-aione singie-famiiy residence. Decentralized
mechanical systems are common in low- and mid-rise multifamily properties, since they
typically have lower initial purchase and installation costs. Decentralized systems do not
typically use process water, so these systems are not the focus of this water efficiency
management guide.
Single-Pass Cooling
When looking to reduce mechanical system water use, facilities should try to eliminate
single-pass cooling or recirculate the water used for single-pass cooling. Single-pass
cooiing systems use water to remove heat and cool specific pieces of equipment, such as a
condenser or air conditioning unit. However, after the water is passed through the
equipment, it is typically discharged to the sewer, rather than being recooled and
recirculated. In some cases, single-pass cooling can be the largest water user at a facility,
using approximately 40 times more water to remove the same heat load than a cooling
tower operating at five cycles of concentration. Most types of equipment cooled with single-
pass water can be replaced with air-cooled systems.
Cooling Towers
By design, cooling towers use significant
quantities of water. Cooling towers dissipate
heat from recirculating water that is used to
cool chillers, air conditioning equipment, or
other process equipment. After assessing
whether single-pass cooling can be eliminated
or recirculated, property managers should
focus on ensuring that cooiing towers are
properly maintained to minimize the need for
make-up water.
Water leaves a cooling tower system in
several ways: evaporation; blowdown or bleed-
off; drift; and leaks or overflows.
• Evaporation is the primary function of a cooling tower and is the method that removes
heat from the cooiing tower system. The quantity of evaporation is not typically targeted
for water efficiency, as it is responsible for the cooling effect. Improving energy
efficiency within the system that uses the cooling water will, however, reduce the
November 2017
Water Efficiency Management Guide

Mechanical Systems
Water Sense
evaporative load on the tower, thus saving water in addition to energy. Regardless of
cooling tower operating efficiency, approximately 1.8 gallons of water are evaporated
for every ton-hour of cooling.
•	Blowdown or bleed-off is performed to remove high concentrations of dissolved solids
(e.g., calcium, magnesium, chloride, silica) from the cooling tower system. As water
evaporates, the dissolved solids remain behind, and the concentration of total dissolved
solids (TDS) in the cooling tower water increases. High concentrations can cause scale
to form or can lead to corrosion, leading to system inefficiencies and degradation. The
concentration of TDS is controlled by removing (i.e., bleeding or blowing down) a
portion of the water that has high TDS concentration and replacing it with make-up
water (e.g., city water, collected rainwater, collected air conditioner condensate), which
has a lower concentration of TDS. Blowdown can be initiated manually or automatically,
depending on your cooling tower's control method. The quantity of blowdown is dictated
by the "cycles of concentration" achieved by the tower. More detail on cycles of
concentration are discussed later in this document.
•	Drift is the small quantity of water that can be carried from the cooling tower as mist or
water droplets. If not managed properly with drift eliminators, drift volume can vary from
0.05 percent to 0.2 percent of the flow rate through the cooling tower. This might not
sound like a lot, but in most towers, the flow rate through the cooling tower is in the
range of 120 gallons to 180 gallons per ton-hour. Drift loss without proper control could
therefore be 0.24 gallons to 0.36 gallons per ton-hour, which adds up over an entire
cooling season. Installing drift eliminators can reduce drift loss to less than 0.005
•	Leaks or overflows should not occur in a properly operated cooling tower, but they do
happen. Most plumbing and building codes require an overflow alarm be installed so
that an alarm is activated when water is flowing into the overflow drain.
The amount of water needed by the cooling tower is dictated by the amount of water that is
lost through evaporation, blowdown, drift and leaks.
Cooling Tower Water Use (Make-Up) = Evaporation + Blowdown + Drift +
See Figure 1 on page 3 for an illustration of the water being recirculated, added to, or lost
from a cooling tower.
Equation 1. Cooling Tower Make-Up Water (gallons)
November 2017
Water Efficiency Management Guide

Mechanical Systems
Figure 1. Cooling Tower System
Evaporated Water
Circulated Cooling Water
Drift Loss
Make-Up Water
Cooling Tower
Efficient drift eliminators and effective leak/overflow detection should minimize water losses
from drift and leaks. If that is the case, make-up water for a well-managed cooling tower is
essentially only based on evaporation and blowdown rates.
Equation 2. Cooling Tower Make-Up Water With Negligible Drift and Leaks (gallons)
Cooling Tower Water Use (Make-Up) = Evaporation + Blowdown
A key parameter used to evaluate cooling tower operation is cycles of concentration
(sometimes referred to as "cycles" or "concentration ratio"). The cycles of concentration are
the ratio of the concentration of IDS (i.e., conductivity) in the blowdown water divided by
the conductivity of the make-up water.
Equation 3. Cooling Tower Cycles of Concentration Based on Conductivity
Cycles of Concentration = Conductivity (TDS) of Blowdown Water +
Conductivity (TDS) of Make-Up Water
Since TDS enter the system in the make-up water and exit the system in the blowdown
water, the cycles of concentration are also approximately equal to the ratio of volume of
make-up water to blowdown water.
Equation 4. Cooling Tower Cycles of Concentration Based on Water Use
Cycles of Concentration = Make-Up Water + Blowdown Water
To use water efficiently in the cooling tower system, the cycles of concentration must be
maximized This is accomplished by minimizing the amount of blowdown required, thus
reducing make-up water demand. The degree to which the cycles can be maximized
depends on the water chemistry within the cooling tower and the water chemistry of the
make-up water supply. As cycles of concentration are increased, the amount of TDS that
stays within the system also increases.
November 2017
Water Efficiency Management Guide

Mechanical Systems
Facilities often employ a water treatment vendor
to monitor the cooling tower, add chemicals to
the system to control scaling and chemical
buildup, and maximize the cycles of
concentration. Critical water chemistry
parameters that require review and control
include pH, alkalinity, conductivity, hardness,
microbial growth, biocide, and corrosion inhibitor
levels. Controlling these parameters allows water
to be recycled through the system longer,
thereby increasing cycles of concentration.
Controlling blowdown using an automatic system
provides a better opportunity to maximize cycles
of concentration, as the TDS concentration can
be kept at a more constant set point. For guidance, Table 1 indicates maximum
concentration for parameters in cooling tower water, as suggested by the U.S. Green
Building Council.1
Table 1. Maximum Concentrations for Parameters
in Cooling Tower Water
Maximum level
Calcium (as CaCCb)
1,000 parts per million (ppm)
Total Alkalinity
1,000 ppm
Silica (Si02)
100 ppm
Chlorine (CI)
250 ppm
Conductivity (TDS)
2,000 |jS/cm
Equation 3 and Equation 4 on page 3 can also be used to determine if there is a leak,
overflow, or excessive drift. Since the equations assume that the water lost to drift and
overflow is negligible, if cycles of concentration are calculated using both equations, and
the results from Equation 4 are higher than that from Equation 3 by more than 10 percent,
the cooling tower might be losing water due to one of these malfunctions.
As discussed previously, approximately 1.8 gallons of water are evaporated for every ton-
hour of cooling, regardless of tower efficiency. However, the quantity of blowdown (and
subsequently make-up water) is dependent on the tower's cycles of concentration. As
shown in Figure 2 on page 5, the greater the cycles of concentration, the less blowdown is
1 U.S. Green Building Council. Cooling tower water management (WEc51. www.usabc.ora/crediis/we5
November 2017
Water Efficiency Management Guide

Mechanical Systems
Water Sense
Figure 2. Cooling Tower Water Use per Ton-Hour Cooling (gallons)
ro 0.0
O 3.0
2 2.5
x 2.0
0 1.0
£ 0.5
2 2.5 3 3.5 4 4.5 5 6
Cycles of Concentration
10 15
Make-up A Blowdown )( Evaporation
Property managers can also consider alternative sources of water, such as condensate
from air conditioners or rainwater, for cooling tower make-up to significantly reduce the
demand for potable water. This is explained in more detail in the Retrofit and Replacement
Options section below.
Boiler and Steam Systems
Boiler and steam systems can be used in multifamily properties for space and water
heating. Hot water boilers are used to provide hot water for bathing, laundry, dishwashing,
or similar operations. Hot water boiler distribution systems can be open or closed. Open
systems provide hot water to end uses, such as bathing and laundry, and closed systems
are used for building heating. Because water efficiency isn't a primary concern for hot water
boiler systems, they are not discussed in this section.
Steam boilers, such as water-tube boilers or fire-tube boilers, generate steam by burning
fuel (i.e., gas or oil) and indirectly or directly heating water within the boiler system, thus
generating steam. As steam is distributed throughout the property, its heat is transferred to
the ambient environment and, as a result, condenses to water. This condensate is either
discharged to the sewer or captured and returned to the boiler for reuse. If the condensate
is discharged to the sanitary sewer, most codes require it to be cooled to an acceptable
temperature before discharging (usually between 120°F and 140°F). The hot condensate is
typically tempered with cool water to meet the temperature discharge requirements.
Some properties might have access to a steam utility or district steam. Ensuring that there
are no onsite leaks in these instances will conserve water within the system and reduce
utility costs for steam.
From a water efficiency standpoint, installing and maintaining a condensate recovery
system to capture and return condensate to the boiler for reuse is the most effective way to
reduce water use. Recovering condensate:
•	Reduces the amount of make-up water required.
•	Eliminates or significantly reduces the need to add tempering water to cool condensate
before discharge.
November 2017
Water Efficiency Management Guide

Mechanical Systems
Water Sense
•	Reduces the frequency of blowdown, as the condensate is highly pure and adds few to
no additional TDS to the boiler water.
•	Saves energy, since the hot condensate being returned to the boiler requires much less
energy to reheat to produce steam again.
If you obtain steam from a steam utility or district steam, condensate recovery and return is
likely cost prohibitive. Instead, identify whether there are opportunities for onsite reuse of
Similar to how TDS build up in a cooling tower as water is evaporated, TDS also
accumulate in the boiler system as water is converted to steam. If the concentration of TDS
gets too high, the TDS can cause scale to form or can lead to corrosion, causing boiler
inefficiency or malfunction. As with cooling towers, the concentration of TDS is controlled by
blowing down a portion of the water within the steam system. Some boiler operators
practice continuous blowdown by leaving the blowdown valve partially open, requiring a
continuous feed of make-up water (and potentially a continuous stream of tempering water
as well for sewer discharge). This practice can waste a lot of water and subsequently
energy, since the water being sent down the drain is hot water at near boiling temperatures.
Proper control of boiler blowdown water is critical to ensure efficient boiler operation and
minimize make-up water use. Insufficient blowdown can lead to scaling and corrosion, while
excessive blowdown wastes water, energy, and chemicals. The optimum blowdown rate is
influenced by several factors, including boiler type, operating pressure, water treatment,
and quality of make-up water. Generally, blowdown rates range from 4 to 8 percent of the
make-up water flow rate, although they can be as high as 10 percent if the make-up water
is poor quality with high concentrations of TDS. Work with a trained water treatment vendor
to identify your boiler's ideal operating conditions and to establish a management approach
that minimizes water and chemical use.
The amount of make-up water required for a boiler is based on the condensate lost from the
system and the amount of blowdown.
Equation 5. Boiler or Steam System Make-Up Water Use (gallons)
Boiler Water Use (Make-Up) = Condensate Losses + Blowdown
Understanding Mechanical System Water Use
In order to evaluate mechanical system improvements and their associated savings, it is
important to first understand how much water is being used.
Dedicated make-up and blowdown meters can track cooling tower and boiler water use and
allow property managers to document actual savings. Installing and monitoring a dedicated
meter or submeter for properties' cooling tower and boiler make-up and blowdown lines is
by far the most effective way of determining mechanical system water use and verifying if
the desired cycles of concentration are occurring in each system.
For cooling towers in particular, there are several other methods that can be used to
estimate water use, if a submeter is not an option for your property. However, they are less
November 2017
Water Efficiency Management Guide

Mechanical Systems
Water Sense
These calculation methods provide approximations of cooling tower water use and suggest
the magnitude of potential savings. Remember that all of the components of the cooling
tower system must be optimized in tandem in order to realize maximum water savings and
efficient operation. Additionally, human behavior plays an important role in minimizing water
use; property managers, operations staff, or water treatment vendors should identify and
quickly repair leaks, regularly monitor meters and controllers, and verify cycles of
Seasonal Comparison
By comparing the amount of water used during the actual cooling season to other times of
the year, you can determine the amount of water used in a cooling tower throughout the
year. For example, if you only operate your cooling towers from April through September,
monthly water use should be higher in those months and lower/more constant from October
through March. The difference between those two periods will be approximately equal to
your property's total annual cooling tower water use.
Note, however, that if other sources use water seasonally (e.g., landscape irrigation in the
summer), this method may be less effective, as distinguishing between seasonal uses is
impossible using billed water use information alone.
Table 2 represents water usage data for a sample property, pulled from monthly water utility
bills. This information is illustrated in Figure 3 to the right of Table 2.
Table 2. and Figure 3. Example Monthly Property Water Use
Water Use (gallons)
Baseline use
(non-cooling tower)
/// / ^
* ^ *	* 
Mechanical Systems	nPA ™
Water Sense
To estimate cooling tower water use, subtract this estimated annual baseline water use
from the metered total presented in Table 2.
890,000 gallons/year - 660,000 gallons/year = 230,000 gallons used for irrigation per year
If you have other seasonal water uses (e.g., landscape irrigation), but have a separate
submeter that monitors the water used for these systems, you can subtract the submetered
water used by these other sources from the total seasonal water use estimated from this
method. In this example, if the irrigation system operates during a similar season (April
through September) and the dedicated irrigation submeter indicated 80,000 gallons used
for the year, subtract that amount from the 230,000 gallons of seasonal water use.
230,000 gallons - 80,000 gallons = 150,000 gallons use for cooling tower make-up per year
This same methodology can be used regardless of the cooling season in your area. Simply
average the monthly water use across the number of months that the property is not
utilizing its cooling towers. Then follow the same steps to estimate your seasonal water
Electric Power Use
If your property's chiller has a dedicated electric meter (not associated with other equipment
such as pumps and fans), you can determine its annual energy use. Using the chiller's
rated efficiency (kWh per ton hour), you can deduce the number of ton-hours of cooling that
your chiller has provided throughout the year. Per the American Society of Heating,
Refrigeration and Air-Conditioning Engineers (ASHRAE), cooling tower tons are
approximately equal to 1.25 times the chiller tons, since ancillary equipment such as pumps
and fans contribute additional heat load. Therefore, if chiller tons are known, that tonnage
should be multiplied by 1.25 to obtain cooling tower tons.
An electric meter indicates the chiller system used 600,000 kWh in one year, and the chiller
is rated at 0.5 kW per ton (based on the chiller nameplate or other product literature on the
chiller). Therefore, cooling ton-hours for the system are expressed as follows:
Total chiller ton-hours = 600,000 kWh 0.5 kW per ton = 1,200,000 ton-hours
Chiller tons need to be converted into cooling tower tons by multiplying by 1.25.
1,200,000 chiller ton-hours x 1.25 = 1,500,000 cooling tower ton-hours
Using Figure 2 on page 5, you can determine your cooling tower's water usage based on
your annual cooling tower ton-hours and your tower's cycles of concentration. For example,
if your cycles of concentration are currently 2.5, then 3.0 gallons of make-up water are
required for each ton-hour. Therefore, your cooling tower's total water use would be:
3.0 gallons per ton-hour x 1,500,000 cooling tower ton hours = 4,500,000 gallons
November 2017
Water Efficiency Management Guide

Mechanical Systems
Water Sense
Chiller Tonnage
To estimate daily water use for a cooling tower, you will need the tonnage of your chiller
(likely found on the chiller's nameplate) and the cooling tower cycles of concentration. Table
3 provides daily water use for a cooling tower system that operates a full load for 24 hours
per day, based on chiller tonnage and cooling tower cycles of concentration.2
Table 3. Estimated Daily Water Use at Full Chiller Load
Chiller T
The water use levels presented in Table 3 are for 24-hour operations at full load. Most
systems do not operate under these conditions, operating either at less than 24 hours per
day or at a reduced load. Therefore, you will need to incorporate the number of hours and
load that your system operates throughout the year. This can be done by prorating the full
load value in the table. Divide the typical daily operating hours by 24 and multiply this
number by the full load value in the table.
A cooling tower operates at three cycles of concentration, rejecting heat from a 500-ton
chiller that typically operates at approximately 50 percent of full load for 18 hours per day.
The full load daily water use from Table 3 is 27,400 gallons per day. The daily water use
can be calculated:
2 U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE) Federal Energy Management Program (FEMP). Estimating
Methods for Determining End-Use Water Consumption.
energy, aov/eere/femp/estimatina-methods-determinina-end-use-water-consumption	
November 2017
Water Efficiency Management Guide

Mechanical Systems	nPA ™
Water Sense
Full load water use (27,400 gallons) x (0.50 full load) x (18 hours 24 hours)
= 10,275 gallons per day
Consider performing these calculations for each month of the year separately, since the
load on the cooling tower will likely vary depending on weather. For example, a cooling
tower may have a 40 percent load in May and an 80 percent load in August. Add each
month's estimated water use together to estimate your property's annual cooling tower
water use.
Maintenance Best Management Practices
Performing periodic inspections of your mechanical systems will help keep equipment
working and catch water waste before it impacts your water bill. Aim to conduct inspections
at least monthly. Each system type has certain common issues to examine and verify.
Table 4 provides a summary of inspection items that should be performed periodically.
Table 4. Mechanical System Operation and Maintenance Tips
System Type
Check system specifications to determine the minimum water
flow rate required for cooling. If you have a solenoid valve that
shuts off single-pass cooling water when the equipment is
turned off, regularly check operation of the valve to make sure
water is only flowing when heat needs to be removed (i.e.,
when the equipment is running).
A piece of equipment that requires 1
gallon per minute (gpm) of water for
cooling uses 525,000 gallons of water
annually and costs a facility nearly
$5,800 per year at average water and
wastewater rates.3
Cooling towers
Implement a comprehensive maintenance program for your
cooling tower systems.
•	Clean coils, heat exchangers, and condensers of any
scale, biological growth, or sediment.
•	Inspect insulation on chilled water piping and, where
missing, install new insulation.
Maintaining system energy efficiency
and ensuring heat transfer can occur
unimpeded by scale and sediment will
also improve the water efficiency of
your cooling towers.
Cooling towers
Have operations and maintenance personnel read the
conductivity meter and the make-up and blowdown flow
meters regularly and log readings. Check the make-up and
blowdown valves to make sure they cut off the flow of water
cleanly to minimize wasted water from leaks.
Keeping a detailed log of make-up
and blowdown quantities,
conductivity, and cycles of
concentration and monitoring trends
can help to quickly identify problems
and deterioration in performance.
Cooling towers
boiler systems
Cooling tower and boiler systems should be monitored and
maintained by a professional water treatment vendor. Choose
a vendor that can minimize water use, chemical use, and cost,
while maintaining appropriate water chemistry for efficient
scale and corrosion control.
Property managers should read and understand the water
chemistry reports that are provided by the water treatment
vendor when they evaluate the water chemistry of your cooling
tower(s) and boiler(s). Make sure the system characteristics
(e.g., conductivity, pH, cycles of concentration) are within your
target range.
Proper cleaning, maintenance, and
inspections are critical to the health
and safety of building occupants and
the continued effectiveness of the
cooling tower or boiler system. These
efforts can also encourage water and
energy efficiency.
3 Estimated cost of water loss based on an average residential rate of $11.02 per 1,000 gallons for water and wastewater determined from data in American
Water Works Association (Raftelis Financial Consulting), Water and Wastewater Rate Survey (2016).	
November 2017	Water Efficiency Management Guide

Mechanical Systems	nPA ™
Water Sense
Table 4. Mechanical System Operation and Maintenance Tips
System Type
Boiler and
steam systems
Regularly check steam traps and steam and hot water lines for
leaks. Implement a boiler tune-up program on a quarterly or
annual basis to maintain system efficiency.
In a steam system that has not been
maintained for three to five years, the
Department of Energy (DOE)
estimates that between 15 and 30
percent of steam traps have failed—
thus allowing steam to escape the
Boiler and
steam systems
Use a handheld conductivity meter so that boiler blowdown
can be initiated only once the conductivity exceeds its target
range. Better yet, install a permanent conductivity meter that
automatically controls blowdown.
Switching to an automatic control
system can reduce a boiler's energy
use by 2 to 5 percent and reduce
blowdown by as much as 20 percent.
Boiler and
steam systems
When condensate is discharged to the sanitary sewer, most
codes require it to be cooled to an acceptable temperature
(usually between 120°F and 140°F) before discharging. The
hot condensate is typically tempered with cool water to meet
the temperature discharge requirements. Install and maintain
a thermostatic valve that only applies tempering water when
the effluent exceeds the specified setpoint temperature. Check
valves periodically to make sure they're only flowing when
steam blowdown is occurring or condensate is draining.
Installing a thermostatic valve
eliminates the constant flow of
tempering water.
Boiler and
steam systems
During summer months, consider shutting down boiler
systems that are primarily used for space heating. If you have
multiple boilers that provide hot water and/or space heating,
shift the heating load as necessary to optimize the most
efficient boilers under certain operating conditions.
Shutting down your boiler system will
reduce the water and energy required
to maintain the system in standby
mode. Annual maintenance and tune-
ups can also be conducted during this
Retrofit and Replacement Options
Replacing a cooling tower, boiler system, or other mechanical system can be a big
undertaking and requires significant capital investment; however, there are many cost-
effective retrofit and replacement options that can reduce water use and operating costs in
the long run.
Single-Pass Cooling
If you have equipment that uses single-pass cooling water, the most effective way to reduce
mechanical system water use is to replace this equipment with air-cooled models. If
considering air-cooled equipment as a replacement, evaluate the potential energy use of
the equipment to ensure that increased energy use does not offset water cost savings.
However, with rising water and wastewater costs, cost savings can often be achieved.
If you can't eliminate single-pass, water-cooled equipment, consider modifying it to
minimize water used for cooling. Options to consider include:
4 DOE Advanced Manufacturing Office. Energy Tips: STEAM. Inspect and Repair Steam Traps.
November 2017	Water Efficiency Management Guide

Mechanical Systems
•	Modify equipment to recirculate the cooling water. This can be achieved by
installing a closed-loop recirculation system that will reuse the water instead of
discharging it. The recirculation system can be connected to a dedicated air-cooled,
point-of-use chiller or other heat sink that can reject heat so that the cooling water can
be reused.
•	Install a solenoid valve. A solenoid valve can shut off single-pass cooling water when
the equipment is turned off or when there is no heat load present.
Cooling Towers and Boilers
Recommended retrofit options for cooling towers and boilers are similar. Installing meters,
improving controls, and supplying the systems with high quality water will help improve
water efficiency and allow you to better manage your system. More information is provided
•	Install flow meters on make-up and blowdown lines, if not
already present. Regularly monitor and record meter readings
so you can identify trends. Consider connecting meters to a
building automation system or building management system
so that meter readings are automatically recorded and can
alert you to any spikes in water use. Contact your local water
or wastewater utility to determine if installing a blowdown
meter could make you eligible to receive a sewer charge
deduction, since water that is evaporated is not being sent to
the sewer.
•	Install a conductivity controller to automatically control
blowdown. Conductivity controllers continuously measure the
conductivity of the cooling tower or boiler water and will
initiate blowdown only when the conductivity set point is
exceeded. Working with your water treatment vendor,
determine the maximum cycles of concentration that the
cooling tower and boiler can sustain without risk of scale
buildup or corrosion, then program the conductivity controller to the associated
conductivity set point necessary to achieve that number of cycles.
•	Automate chemical feed systems. In addition to controlling blowdown based on
conductivity, an automated chemical feed system can also regulate chemicals (e.g.,
biocides, scale inhibitors, corrosion inhibitors) that are being added to your cooling
tower or boiler system.
•	Talk to your water treatment vendor about pretreatment or side-stream filtration.
To increase cycles of concentration, consider pretreating make-up water to remove or
neutralize minerals and impurities. Potential pretreatment technologies include water
softeners, water conditioners, reverse osmosis systems, or demineralization. As an
alternative for cooling towers, install a rapid sand filter or high-efficiency cartridge filter
on a side stream taken from the cooling tower basin. This system can filter out sediment
and minerals from the basin water.
•	Install a condensate recovery system. For steam boilers, condensate can be
recovered and returned to the boiler for reuse. This feature can save substantial water
and energy. Not only is less boiler make-up water needed, but because less
condensate is being sent to the sewer, tempering water is also reduced.
Cooling tower make-up meter.
November 2017
Water Efficiency Management Guide

Mechanical Systems
Another opportunity to reduce water used within your mechanical systems is to utilize
appropriate onsite alternative water sources as cooling tower or boiler make-up water.
Collecting and reusing condensate from air conditioners or rooftop rainwater are iikely the
most suitable retrofit options for sourcing alternative water, particularly if your property
doesn't already have a graywater system installed.
•	Condensate from air conditioning equipment: Condensate is generated when water
vapor comes in contact with an air conditioner's cooling coils, and is commonly
discharged to a drip pan or directly to a floor drain. Condensate from air conditioning
equipment is high quality, cold water that is free of minerals and TDS, making it ideal to
use as cooling tower make-up water. Even better, condensate from air conditioners is
generated in the highest volumes during period of high cooling loads, which mirrors
times when cooling towers are operating the most. Typically, condensate can be fed
directly into the cooling tower basin as make-up water without any treatment, but work
with your water treatment vendor to see if they have any concerns with this approach.
To determine whether condensate capture is a viable in your area, review the Federal
Energy Management Program (FEMP)
Condensate Capture Potential Map.5
•	Rainwater: Rainwater that runs off rooftops
is typically high quality, making it suitable for
many end uses, including cooling tower
make-up, boiler make-up, and irrigation.
Rainwater can be collected from gutters or
roof drains into a storage cistern. Gutter
screens should be used to remove debris.
Similar to condensate, talk to your water
treatment vendor about whether water
treatment is necessary before directing
collected rainwater to your cooling tower or
boiler. To determine rainwater harvesting
potential in your area, review the FEMP
Rainwater Availability Map.6
If you are in the market for a replacement
cooling tower or boiler, first implement energy efficiency measures to reduce cooling and
heating loads, respectively. This may make it feasible to reduce the size of your cooling
tower or boiler, saving money on both the initial purchase and on operating expenses and
improving system energy and water efficiency.
For a new cooling tower, include the following features in your set of requirements.
•	Make-up and blowdown meters (if they're not already installed in your property).
•	Conductivity controller and/or automated chemical feed system.
•	Drift eliminators that reduce water losses to less than 0.005 percent of the cooling tower
flow rate.
•	Overflow alarm.
5	DOE EERE FEMP. Condensate Capture Potential Map. energy.aov/eere/femp/condensate-capture-potential-map
6	DOE EERE FEMP. Rainwater Availability Map, enerav.aov/eere/femp/rainwater-availabilitv-map	
November 2017	Water Efficiency Management Guide
Storage tanks for rainwater collected from roof drains.

Mechanical Systems
Water Sense
These features are required by most building and plumbing codes and standards, but
regardless, are encouraged for all new installations to facilitate efficient operation and
management of cooling towers.
For a new boiler system, consider installing multiple small boilers instead of one or two
large boilers. Multiple small boilers offer reliability and flexibility to meet boiler load
fluctuations without compromising efficiency. This also helps limit boiler "short cycling,"
which occurs when an oversized boiler quickly satisfies space heating demands, and then
shuts down until heat is again required. Boilers operate more inefficiently when short
cycling occurs or when the boiler has a low firing rate.7
Water Savings Calculations and Assumptions
The following calculations can be used to estimate water savings from improving the
operation of heating and cooling systems. Some calculations will utilize submeter
information or water use estimates that you've previously prepared based on the
Understanding Mechanical System Water Use section of this guide.
Single-Pass Cooling
Water used for single-pass cooled equipment can be eliminated by replacing existing
equipment with a recirculating system or replacing it with air-cooled equipment. Potential
savings from replacing existing single-pass-cooled equipment with air-cooled equipment
can be estimated by measuring the existing cooling water discharge with a bucket and a
stop watch and determining how often the cooling water flows (e.g., how many hours per
day, how many days per week). In many applications, single-pass cooling water flows
continuously. To estimate potential water savings, use Equation 6.
Equation 6. Water Savings From Eliminating Single-Pass Cooling (gallons per year)
Flow Rate (gpm)
Hours per Day Days per Week Weeks per Year
Total Annual
Water Use
If single-pass cooling is eliminated by replacing equipment with air-cooled models, a
property may see an increase in energy usage. The increased energy use, depending on
how significant, may increase the payback time and decrease replacement cost-
7 DOE Advanced Manufacturing Office. Energy Tips: STEAM. Minimize Boiler Short Cycling Losses.
energy.aov/sites/prod/files/2014/05/f16/steaml 6 cycling losses.pdf	
November 2017
Water Efficiency Management Guide

Mechanical Systems
Cooling Towers
Significant water savings can be achieved by improving the cooling tower management
approach and by maximizing cooling tower cycles of concentration. Tabie 5 shows the
percentage of make-up water savings that can be expected by increasing a cooling tower's
cycles of concentration. For example, increasing cycles of concentration from three to six
can reduce water use by 20 percent. To estimate water savings from improving cycles of
concentration in cooling towers, use Equation 7.
Equation 7. Water Savings From Increasing Cooling Tower Cycles of Concentration
(gallons per year)
Annual Cooling
Tower Water Use
Percent Savings
Based on
Cycles of
Gallons Saved
per Year
Table 5. Percent of Cooing Tower Make-Up Water Saved by Maximizing
Cycles of Concentration
2.0 2.5 3.0 3.5
8.0 9.0 10.0





November 2017
Water Efficiency Management Guide

Mechanical Systems	EPA w
Switching to an automatic control system (i.e., conductivity controller) can reduce a boiler's
energy use by 2 to 5 percent and reduce blowdown by as much as 20 percent. To estimate
water savings, use Equation 8.
Equation 8. Boiler Water Savings From Installing a Conductivity Controller (gallons
per year)
Annual Boiler Percent Savings Gallons Saved
Water Use	per Year
November 2017
Water Efficiency Management Guide

Mechanical Systems
Water Sense
Additional Resources
Alliance for Water Efficiency. Resource Library. Condensate Water Introduction.
www.allianceforwaterefficiencv.org/Condensate Water Introduction.aspx
Alliance for Water Efficiency. Resource Library. Introduction to Cooling Towers.
www.allianceforwaterefficiencv.org/coolinq tower intro.aspx
U.S. Department of Energy (DOE) Advanced Manufacturing Office Resources:
Energy Tips: STEAM. Inspect and Repair Steam Traps.
www.energy.gov/sites/prod/files/2014/05/f16/steam1 traps.pdf
Energy Tips: STEAM. Minimize Boielr Short Cycling Losses.
energy.gov/sites/prod/files/2014/05/f16/steam16 cycling losses.pdf
DOE Office of Energy Efficiency and Renewable Energy (EERE) Federal Energy
Management Program (FEMP) Resources:
Best Management Practice #8: Steam Boiler Systems.
Best Management Practice #9: Single-Pass Cooling Equipment.
Best Management Practice #10: Cooling Tower Management.
Condensate Capture Potential Map.
Cooling Towers: Understanding Key Components of Cooling Towers and How to
Improve Water Efficiency. DOE/PNNL-SA-75820. February 2011.
Rainwater Availability Map.
EPA's WaterSense program. WaterSense at Work. Best Management Practices for
Commercial and Institutional Facilities.
November 2017
Water Efficiency Management Guide

Mechanical Systems
Water Sense
Appendix A: Summary of Water Efficiency Measures and Savings
This appendix can be used to summarize water efficiency measures, upgrades, and
projects that are identified at your property, based on a water assessment and/or review of
this Water Efficiency Management Guide.
Summary of Water Efficiency Measures and Savings
Measure or Project
Name and Description
Projected Annual
Water, Wastewater,
and Energy Cost
Savings ($)
or Project
Cost ($)
Simple Project Payback
Work with cooling tower
water treatment vendor
to increase cycles of
concentration for 2.5 to
Water Cost Savings:












November 2017
Water Efficiency Management Guide