Hindering Hazardous
Cooling Tower-borne Pathogens
Anti-microbial option reduces risk of Legionnaires’
Disease in chiller/cooling tower applications
A new Center for Disease Control & Prevention
(CDC) study involving 196 cooling towers nationwide
found that 84% contained Legionella DNA,
indicating that the dangerous bacteria that causes a severe,
even fatal type of pneumonia were present or had
been at some point. This means the real question is not
“if there will be another outbreak” but merely “where
and when” it will occur.
“During 2000–2014, passive surveillance for legionellosis
in the United States demonstrated a 286% increase
Arkansas Surgical Hospital
in reported cases per 100,000 population,” stated the
CDC website. The CDC also estimates that about 5,000
cases of Legionnaires’ disease are now reported each
year in the U.S. and keeping Legionella out of water
systems in buildings, with cooling towers a noted risk, is
critical in preventing infection.
In response, heat, ventilation and air conditioning
(HVAC) contractors are now pairing chillers and high
performance plastic cooling towers with new anti-microbial
options that significantly reduce the infection risk.
Controlling Pathogen Growth
Throughout the U.S. and most of the world, the mainstay
of large cooling systems remains the traditional
HVAC combination of chillers, air handlers and cooling
towers. Cooling towers have a long history of effective
use in expelling heat from the water used in many commercial
and industrial applications that involve chillers.
However, it is well established that, under typical operating
conditions, cooling towers can propagate Legionella.
The design of many cooling towers creates pockets
where water may stagnate, a condition that can lead to
microorganism development.
This has recently led ANSI/ASHRAE to publish its
Standard 188, Legionellosis: Risk Management for
Building Water Systems, which documents new risk
standards and requirements for the design of new buildings
and the renovations to existing structures.
Del Williams
Technical Writer
“All facilities with HVAC or process cooling systems
need to be aware of Legionnaires’ disease and handle
any concerns about it,” explained Rick Hill, Facilities
Director at Arkansas Surgical Hospital, a physicianowned
hospital specializing in joint and spine surgery in
Central Arkansas. “There have to be good procedures in
place to prevent or control it.”
When it was time to replace an air cooled chiller at
Arkansas Surgical Hospital, Steve Keen, President of
Powers of Arkansas, the HVAC contractor responsible
for the hospital project, recommended and installed a
water cooled chiller, paired with an advanced cooling
tower with unique anti-microbial properties.
“Legionella is always a concern for HVAC systems
using a cooling tower and anywhere you have water exposed
to the atmosphere,” said Keen. “The Delta Cooling
Towers’ anti-microbial properties will help prevent that
type of growth and exposure to patients and staff.”
Delta Cooling Towers, which pioneered the HDPE
(high-density polyethylene) plastic cooling tower in the
1970s, recently introduced a line of towers constructed of
anti-microbial resin, which is fully compounded into the
base cooling tower structural material and casing. The
cooling tower fill and drift eliminator are also made from
anti-microbial PVC.
The anti-microbial resin contains wide-spectrum additives
that operate on a cellular level to continuously
disrupt and prevent uncontrolled growth of microorganisms
and biofilm within the cooling tower. Efficacy tests
were performed by Special Pathogens Laboratory, who
tout themselves as “The Legionella Experts®.”
To avoid problems of stagnant water leading to pathogen
growth, experts recommend that cooling tower designs
feature a sloped
basin and/or basin
sweeper system.
While some cooling
tower manufacturers
now market a tower
with an anti-microbial
fill (the medium over
which the hot water
is distributed as it is
being cooled), a better
option is to have a
cooling tower featuring
the fill, structural
casing and sump all
composed of anti-microbial
material.
“We decided that
Delta Cooling Tower
16 ICM/November/December 2017