ASHRAE Journal - November 2023 - 36

TECHNICAL FEATURE
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eliminate the necessity for installing
and maintaining energy-intensive
UV-C lights for this same
purpose. Keeping wet
cooling coils clean is
important, but it can be
a recurring expense,
which negatively
impacts overall cost
of ownership.
3. External AHU
and ductwork surfaces
may be maintained at
higher temperatures
because the air being
conveyed through them
doesn't need to be deeply cooled
to also dehumidify it. Conveying
cold, saturated air to reheat boxes will
challenge insulation to prevent condensation on metal
exteriors. Desiccant dehumidification can lessen the
risk of surface condensation and possibly reduce the
cost for the construction, materials and insulation of
these components.
4. Keeping cooling coil surfaces free of biofilm
contamination maintains design cooling coil
performance, pressure drop and heat transfer
efficiency. Various guidance suggests this has the
potential for a savings in energy of between 10%
and 25%.12
5. Lowering indoor relative humidity can easily
be accomplished with desiccants. Reducing space
relative humidity may allow for maintaining a
higher indoor dry-bulb temperature, which can
foster superior levels of occupant comfort and
satisfaction.13 This will also lower the temperature
difference between the indoors and outdoors,
reducing space heat gain to garner energy and
operational cost savings. Maintaining lower indoor
relative humidity also helps reduce the probability of
mold growth both interstitial to building materials
and on indoor surfaces and helps mitigate its concern
from occupant exposure.
6. If low-cost or no-cost waste heat (cogeneration,
heat recovery, etc.) can be used for the desiccant
regeneration process, operating costs for
dehumidification can be reduced to a mere fraction
36
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of any competing technology. Recovery strategies
incorporated to recoup reactivation air heat can
provide substantial energy and utility cost savings.
7. Central cooling plants may be allowed to operate
at higher refrigerant evaporator temperatures,
reducing compressor lift and increasing chiller
efficiency. This can considerably reduce HVAC energy
use and lower utility bill costs.
8. Desiccant dehumidification can decouple latent
load requirements from refrigerant-based central
plants, freeing up additional cooling capacity that can
be used elsewhere or for future facility expansion.
This also unloads cooling towers, reducing water
and chemical treatment, resulting in capital and
operational cost savings.
9. Applying desiccant dehumidification properly
can reduce or eliminate the need for costly reheat
energy. When air is " over-cooled " to properly dry it, it
is often necessary to add heat back into the airstream
to warm it to a temperature suitable for achieving
occupant comfort. Reheat can account for up to 65%
of a large hospital's natural gas energy consumption.
Conclusion
The engineering controls outlined in this article are
intended to positively impact both the performance
and hygiene of air-handling systems by improving
a building's indoor air quality, helping protect
exposed occupants from airborne and surface source
contaminants and improving building sustainability.
While desiccant dehumidification may be more
familiar to those engineers working in settings
that require precise control of relative humidity
or dew-point temperature, such as in aerospace,
pharmaceutical, food processing, cleanroom,
laboratory, semiconductor manufacturing and other
industrial applications, it is certainly applicable
for less demanding yet still critical environments,
including hospitals and others. Traditional
refrigerant-based cooling technologies are usually
incapable of achieving the dew-point temperatures
required to achieve the psychrometric outcome and
operational benefits detailed in this article.
Desiccant dehumidification, when properly
applied, installed and operated, can help any indoor
environment (particularly those deemed critical)
achieve a more productive, energy efficient and
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ASHRAE Journal - November 2023

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