results in increased resistance to air flow
and a loss in thermal efficiency. AFT is
designed to keep the air conditioning
coil clean and free of bio-contaminants,
including viruses, bacteria and bio-film.
Robert Axon, director of UV Technology
Global, explains that AFT uses a ‘nonionising’
field created using low power
alternating current. This can destroy
airborne bacteria, viruses and volatile
organic compounds as they pass through
its destructive electron field.
He says: “AFT is scientifically proven to
reduce particulate and airborne pathogens
to less than 0.1 micron without the use
of inefficient, energy consuming passive
filtration. Depending on the filtration
installed, AFT can reduce your HVAC
system energy footprint by over 50%.”
INHERENT RISKS
While acknowledging that coils can be
cleaned in several ways, Betts believes
they all have inherent risks. He says, for
example, that soft brushes will remove
surface dust, but they can also drive
dust between coil fins, exacerbating the
contamination problem, and hose washing
using low-pressure water flow tends only
to remove surface debris from the fins.
With typical chemical and low-pressure
HVAC – COIL & FILTER CLEANING
washing, meanwhile, the chemicals are
left to soak into the debris, which is then
rinsed off with a low-pressure hose. Betts
again: “This is more effective than the first
two options, but not too environmentally
friendly.” Besides, coil cleaning is only half
the job. Panel and cartridge filters in a
HVAC system also need to be changed,
ideally every 90 days, according to Intrieri. It
has been estimated that air indoors is 70%
more polluted than outside air. Poor indoor
air quality is said to be among the top public
health risks.
This is where HVAC air filters come in.
They trap and hold a wide range of particles
and contaminants. There are several
benefits to changing air filters, including
healthier indoor air, increased efficiency
(and money savings) because the HVAC
system isn’t working as hard, and increased
longevity of the HVAC system with fewer
system failures. It’s also environmentallyfriendly,
because if the system is working
harder, it uses more energy, electricity and
more greenhouse gases are produced.
Of course, prevention is better than
cure, and that is why Betts advocates a
physical barrier between HVAC coils and
the outside air – external filter screens.
For Intrieri, there are advantages and
drawbacks to using screens. “In some
applications, they can work if they’re
installed correctly, as long as they’re
not decreasing the airflow to the point
where it’s starving the coil. If the airflow
is diminished getting to the coil, the
motor inside the air handler is going to
compensate and work harder which will
increase energy usage.”
However, according to Betts, by creating
a static charge that attracts and traps
airborne particulates, air intake screens
prevent sensitive components and cooling
and condensing coils from contamination
without restricting airflow. He says: “Our
business is about keeping the coils and
filters clean. Disposable air handling unit
filters, which protect the internal coil, get
less efficient with face loading; 16,000
panel filters would fill eight shipping
containers with landfill debris because they
cannot be recycled. We can make them last
up to 60% longer between changes.”
He claims that air intake screens extend
the time between external coil cleans, don’t
alter the discharge pressure, maintain
efficiency, reduce environmental impact of
chemical cleaning and mechanical damage,
and are easy to see when dirty.
An analysis of coil cleaning methods by SpeedClean
Coil cleaning method Positives Negatives
Aerosol sprays • Inexpensive • For inside use only
• Allows user to apply the chemical easily but not rinse it
• Many sprays claim self-rinsing or no-rinse formulas. What this normally means is the chemicals
stay on the coils until enough condensate is built up to eventually rinse the coils clean. This can
make for an even more clogged coil until the rinse is finally achieved
• Leaves harsh chemicals on sensitive aluminium coils for extended periods of times
Garden hose • Easily available & simple to use • Doesn’t yield much pressure
Pressure washer • High water pressure – effective
for removing dirt and debris
build-up
• Can only be used outside
• Coil fins can bend or flatten easily
• Too much power can crush coils flat
Pump sprayer • Good for applying harsh
chemicals and/or acids
• Simple to use
• Can be used inside and outside
• Not designed to flush out coils or wash away debris
• User may struggle to keep the pressure going consistently
• Applying chemicals is really only 30% of a coil cleaning job; pressure and flow to clean the coil
are far more important
May 2019 www.operationsengineer.org.uk 19
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