210.100-IOM (JUL 2021)
Page 43
AcuAir Hygienic Air Units
Maintenance
Calibrating the temperature sensors
Temperature sensors that are out of calibration can affect
both the correct
function and efficient operation of the
hygienic air unit. As part of the routine maintenance pro-
gram, check temperature sensor calibration annually.
The following are two calibration methods.
Ice bath
Cool a cup of water to 32°F using excess ice and agitat-
ing the water for several minutes. Immerse the tip of the
temperature sensor into the 32°F water while the AcuAir
®
controller channel is calibrated to 32°F.
Infrared temperature scanner
Focus the scanner on the tip of the temperature sensor.
Use the temperature reading on the infrared scanner to
calibrate the AcuAir
®
controller input channel.
Figure 50: Temperature sensor
Submerge Tip in Ice Bath or
Focus Infrared Scanner Here
Unit cleaning and sanitation
The AcuAir
®
hygienic unit requires frequent and thorough
cleaning. Consult your chemical supplier when picking the
correct cleaning chemicals.
CAUTION
Disconnect all electrical power before cleaning the
unit.
Before cleaning, uncap any capped drain pipes, and drap
motors with plastic. During cleaning, ensure the following
components are not directly sprayed with water: motors,
damper motors, bearings, pitot tubes, filters, and elec
-
tronic sensors.
NOTICE
High pressure water has the potential to dislodge
caulk and sealing putty. It is important to thoroughly
inspect all seam caulking and electrical conduit seal-
ing putty following a sanitary wash down.
White rust and wet storage stain of
galvanized steel
Many AcuAir
®
rooftop units are purchased with simple mill
galvanized exterior finish.
Galvanizing is the result of ap-
plying a coating of zinc to sheet metal. The zinc coating is
intended to provide long lasting protection of the underly-
ing steel.
Raw zinc, by nature, is reactive and tends to corrode quite
readily when exposed to moisture. To develop the long
lasting protective quality for which it is applied, the zinc
must undergo a sequence of chemical reactions. First the
zinc must react with oxygen to create zinc oxide. Second,
the zinc oxide reacts in the presence of moisture to create
zinc hydroxide. Finally, the zinc hydroxide reacts with CO
2
within dry air to create a thin layer of impermeable zinc
carbonate. The carbonate layer is what forms the long
lasting passive coating that drastically slows down any fur-
ther reaction of the zinc and provides corrosion protection
of the underlying steel. When correctly formed, the zinc
carbonate layer is identified by a dull-gray appearance.
If the zinc coating of new galvanized material is prevented
from thoroughly drying and receiving exposure to CO
2
the
passive carbonate layer is not formed. If the Zinc hydrox-
ide to carbonate reaction does not take place, excessive
zinc hydroxide accumulates as a layer of soft, white, fluffy
product of corrosion. Instead of being dense and protec-
tive, this powdery substance is porous and non-protective
of the substrate material. When the zinc oxide-hydroxide
reaction is allowed to progress, it can rapidly degenerate
the substrate layer of zinc. This buildup of zinc hydroxide
is known as white rust. It is created by small localized
corrosion cells and appears as stain patterns in contrast
to the uniform dull-gray zinc carbonate layer mentioned
previously.
Addressing a light coating of white rust
also known as wet storage stain
Occasionally AcuAir
®
units may arrive on site with patches
of visible zinc hydroxide deposits. In other cases white
patches of the deposit may become visible shortly after
arrival. In either case, because the AcuAir
®
products
are built and are shipped very shortly thereafter, these
hydroxide zones are quite young and any deterioration of
the underlying zinc is insignificant. In most cases the zinc
hydroxide is so light it erodes over time and the preferable
zinc carbonate layer forms naturally with the rain and dry-
ing cycles. However, in a few instances and for cosmetic
reasons it may be necessary to intervene and expedite the
passivation process.
Light coatings of zinc hydroxide can be removed using
readily available cleaning products. A study presented by
the American Galvanizers Association (AGA) suggests the
following five
cleaning products to successfully handle the
task.
Available at any local grocery store:
• Lime juice
• White vinegar
Commercial Cleaners tested:
• Picklex 10G (best solution according to the test – only
available direct from the manufacturer)
• CLR
• Navel jelly rust dissolver - not appropriate for heavy
wet storage stain.
Cleaning white rust
1. Use a nylon bristle brush to apply one of the cleaners
to the affected area.
2. Thoroughly scrub the surface using the nylon bristle
brush, applying water as necessary.
