ASHRAE Journal - April 2024 - 8

LETTERS
Avoiding Wet, Moldy AHUs in
Food Manufacturing
I previously worked for two food
manufacturing and marketing
companies, and I edited the chapter
on microbiology in the ASHRAE
Handbook for a few years in the late
1990s and early 2000s. Every month
I look forward to reading ASHRAE
Journal.
The article " Avoiding Wet & Moldy
AHUs in Critical-Care Facilities "
by David Schurk, Life Member
ASHRAE in the November 2023
issue of ASHRAE Journal caught my
attention, since I encountered this
in many food plants, especially those
handling flour. It was hard to avoid
flour depositing on wet cooling
coils and creating very moldy ones.
These were very hard to clean as
required in food plants, and almost
as important as in medical facilities,
though for different reasons.
For food safety and quality, food
manufacturing and mold don't go
together.
Daily coil cleaning was one
solution, but very costly. Later I
learned about ultraviolet (UV)
lighting used in HVAC and water
treatment in Europe. We installed
UV lighting in a few of the worst
moldy air-handling units (AHUs),
shining them on the moldy coils in
a food processing plant with much
mold. I requested that the plant
Quality Assurance department, who
had initially asked for a solution to
moldy coils, send me a report on the
condition of coils. About a month
after the installation of UV lighting,
they sent a few pictures. The coils
looked as shiny as when they were
newly installed.
From then on, I recommended
8
UV lights for AHUs wherever mold
could be an issue. The clean coils
should be more energy efficient as
well. I learned UV lighting could
be beneficial not just for health
and food safety but also for energy
efficiency. We did not measure
energy efficiency post installation,
but experience indicates that it
should have improved.
In conclusion, one could look
into using UV lighting to fight
mold in AHUs instead of the very
innovative method described in the
article. I left the active practice of
engineering 16 years ago, so I would
like to hear and learn from current
practitioners in this area.
Godan Nambudiripad, P.E.
Life Member ASHRAE,
Burnsville, Minn.
SCHURK RESPONDS
Thank you for reading and
responding with real-world trials
and tribulations of microbial
contamination on wet cooling
coils. While I have also worked in
food processing environments,
mold growth on cooling coils is
independent of the application and
directly related to the condensation
of moisture (when air is chilled to its
dew-point temperature) on the coil's
cold surface.
Microbial
and biological
growth within
health-care HVAC
systems is an
ongoing issue
of considerable
concern, for
both patients
ASHRAE JOURNAL ashrae.org A P R I L 2024
and staff in these environments.
Some health-care applications use
ultraviolet germicidal irradiation
(UVGI) systems installed at
the cooling coil as a proactive
measure in helping reduce the
growth of biohazards on wet AHU
components. Unfortunately, staff
is often taxed to the point where
maintenance may be negatively
impacted. I've seen how this can
affect the timely replacement
of UV-C bulbs, which are then
extended beyond their useful
service life. I've also witnessed deep
cooling coils, typically six rows or
more, where the UV-C light emitted
to treat the coil cannot reflect and
refract deeply enough through
tightly spaced fins to keep inner-coil
surfaces sanitized.
One of the benefits of desiccant
dehumidification positioned
upstream of a post-cooling coil is
entering air has been desiccated and
its latent load removed. This allows
the coil to cool the air sensibly and
always remain dry-no water, no
mold. Mentioning this in my article
was to demonstrate yet another
advantage of using desiccant
dehumidification in critical-care
hospital environments, where it
can serve to make major impacts
in indoor air quality and energy
efficiency. I agree that UVGI, when
properly applied and maintained,
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ASHRAE Journal - April 2024

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