From the Association of Water Technologies (www.awt.org) Cooling Water Management.PDF
To minimize the carbon-footprint, water usage and environmental impact of HVAC
cooling systems and process cooling systems, generally by optimizing the control of water
chemistry, and specifically by:
o minimizing water usage, including using non-potable makeup water where available;
o maximizing energy efficiency through maintaining clean heat-transfer surfaces;
o extending the life cycle of equipment by controlling corrosion and mechanical deterioration of materials;
o reducing carbon footprint of facilities personnel by integrating cooling water data mining into building management systems;
o and favoring materials and processes friendly to the environment and operator safety.
OPTION 1. Water Systems Management Program (1 point)
Develop and implement a water systems management program for the cooling tower
(meant to include all types of evaporative cooling equipment) and associated water
systems. Address best environmental practices for heat transfer efficiency, equipment
reliability, asset life expectancy, maintenance costs, minimization of water and energy
inputs, hygiene risks, safety, and environmental impact. Such a program should also
address the use of peer-reviewed, proven equipment suitable for pretreatment, plus
inhibitor treatments for control of scales and deposits, corrosion (including microbial
induced corrosion), and fouling (including biofouling). All equipment and treatment
methods should be appropriate for the specific makeup water source. Additionally, the
water systems management program should address equipment maintenance issues, layup,
and regular technical support services from a qualified professional, certified by an
independent third party. Required technical support services will include training of
operating personnel, inspection of treatment pumps and other feed systems and control
devices, regular water testing and interpretation of results, and periodic technology and
Improve water efficiency by minimizing water system bleed-off and system losses. To
accomplish this include in the system the following: water meters on makeup water line
and on the bleed-off; a conductivity controller on the recirculating water; and automatic
controls to adjust the bleed-off rate. Maximize energy efficiency by ensuring the
cleanliness of all heat transfer surfaces through additives that control corrosion, deposits
OPTION 2. Non-potable Water Source Use (1 point)
Use makeup water that consists of at least 50% non-potable water, such as harvested
rainwater, harvested storm water, air-conditioner condensate, swimming pool filter
backwash water, pass-through (once-through) cooling water, gray water, foundation drain
water, municipally reclaimed water, steam condensate, treated industrial wastewater, or
any other appropriate on-site water source that is not naturally occurring groundwater or
surface water. All non-potable, recycled, or reused waters will require pretreatment (such
as filtration, oxidation, and/or disinfection) before being suitable as an alternative source
of cooling system makeup.
Have a measurement program in place that meters makeup water quantities used from nonpotable
sources as well as potable sources. Meters must be calibrated within the
manufacturer’s recommended interval if the building owner, management organization or
tenant owns the meter. Meters owned by third parties (e.g. utilities or governments) are
Utilize bleed-off for on-site irrigation, when permitted and appropriate.
OPTION 3. (2 points)
Achieve both Options 1 and 2.
BENEFITS AND ISSUES TO CONSIDER
Water-cooled systems utilize the natural cooling effect from evaporation of water to
remove heat from buildings or processes. Proper stewardship minimizes water
consumption while maximizing energy efficiency in the cooling of the building or process.
Water-cooled systems are more energy efficient than alternatives, such as air-cooled,
consequently requiring less electricity in their operation.
Water usage in cooling tower systems consists of three types: evaporation, bleed-off, and
losses. Evaporation is the principal mode of cooling and is both intended and desirable.
Bleed-off is necessary to avoid excessive buildup of minerals and other solids that enter
the system. In minimizing bleed-off, it must be controlled in conjunction with the water
treatment program so that the minerals and solids do not precipitate and deposit in the
system. The control parameter recommended is conductivity, and that parameter should be
used to control the amount of bleed-off by use of an automated bleed controller. Using a
constant bleed-off rate or periodic manual bleed is not recommended, as this practice
wastes water and may compromise the useful life of the equipment.
Losses are largely avoidable if facility staff are trained to identify them. Proper
maintenance can reduce problems with overflowing basin, leaking seals, splash out onto
surrounding areas, excessive drift, and back-flooding. Staff should also be trained to
inspect and adjust ball float valves periodically, check drain valves for proper closure and
sealing. Improper pipe configurations, especially in systems that have undergone many
additions, are common sources of large, unseen losses. Environmentally sound best
practices call for constant attention to water losses, not just from cooling tower systems,
but from all water systems in the facility.
Water system management for cooling towers requires investment in a regular,
comprehensive maintenance program coupled with water treatment program technical
support services, in order to save money and energy while increasing the tower’s life
expectancy and reliability. Water meters installed to measure cooling tower make-up and
bleed-off and the application of effective inhibitor programs, help conserve water and
lower operating costs. In addition, conductivity control systems and regular water analyses
with capable interpretation of results provide some of the tools needed to operate and
maintain equipment at higher cycles. Because of the substantial water savings, water
utilities in some locales offer incentives and rebates for the installation of conductivity
meters on existing cooling towers.
Best Management Practices articulate the need for routine measurement and verification of
data sets. This includes metering all make-up sources, system bleed off, as well as
minimizing water usage. Effective implementation of these practices requires the
installation of “smart” controllers capable of properly administering cooling water control
chemistry. To promote water conservation, some systems are supplied with multiple water
sources of variable water quality. In order to allow for efficient program administration,
systems should be equipped with controllers that are programmable via remote access.
Data acquisition can be designed to generate automated system summary reports, alarms,
and preventive maintenance notifications in order to enhance the troubleshooting
capability of facilities personnel. These controllers should have open protocol
communication with building management system through integration platforms giving
building managers/owners the opportunity to administer long-term water efficiency and
conservation objectives. Building management systems are designed to mine data from
multiple sources such as chillers, air handlers, and cooling towers to optimize system
efficiency. Integration into these systems allow for the proper balance of water and energy
conservation, resulting in lower operating expenses.
Water conservation in buildings can also lead to more stable municipal taxes and water
rates. For utility districts that provide potable water, every cubic foot of water recovered
as a result of improving conservation produces more revenue than the same amount
obtained from a new water source for bleed-off, drift loss, and water lost through leaks,
spills or overflows. The amount of water fed into the system to replace what is lost is
referred to as makeup water. With proper cooling system maintenance, water losses can
be kept very low, allowing a project to conserve significant amounts of water. However,
this objective has to be tempered by the need to also conserve energy inputs, heat transfer
efficiency, and equipment life and reliability.
Conductivity controllers that can vary the bleed rate and well-maintained drift eliminators
are long proven means to reduce water loss and conserve resources. A more recent method
is to utilize non-potable water sources for cooling systems, which provides additional
environmental benefits by using water that would otherwise be considered waste.
Potential sources of non-potable water for cooling systems include treated contaminated
groundwater, treated municipal effluent, industrial process water or wastewater, irrigation
return water, and other types of water affected by humans or naturally occurring minerals.
WATER CHEMISTRY AND BIOLOGICAL CONTROL
Engage a qualified water management professional to design and administer a best
practices water management program that meets water conservation and other
environmental objectives. Controlling mineral scales, biological deposits, foulants and
corrosion through the appropriate use of filtration equipment and treatment products helps
maintain water system cleanliness, hygiene, and efficiency, as well as minimizing
microbial growth. Mineral content is typically managed through a combination of bleedoff
and appropriate additives that prevent precipitation of dissolved solids. Effective water
management maintains heat transfer efficiency and reduces the need for bleed-off, thereby
conserving both energy and water.
Outbreaks of Legionnaires’ disease have been associated with ineffective treatment,
maintenance and management practices. ASHRAE Guideline 12-2000, “Minimizing the
Risk of Legionellosis Associated with Building Water Systems”, offers guidance for
developing an effective biological control program.
Consider using corrosion monitoring to ensure that the water management program is
appropriate for all metals in the system. Establish performance metrics to help assess the
effectiveness of a water management program, such as acceptable corrosion rates based on
metal types, and maximum acceptable microbial concentrations.
Maintain treatment records of what products are used, and investigate the use of newer,
environmentally friendly technologies and control solutions, and environmentally
preferred products utilizing the principles of green chemistry. Establishing technical
service schedules will help ensure regular and effective maintenance and program
oversight, including checks for leaks or overflow problems, regular cleaning, and
recalibration of conductivity sensors, ORP meters and the like, per the manufacturer’s