DEMYSTIFYING

SOLID DESICCANT
DEHUMIDIFICATION
By: David Schurk, National Sales Manager, Innovative Air Technologies
Copyright 2024. Innovative Air Technologies All rights reserved.

No part of this training manual, including text, imagery, graphics, or photos, may be reproduced,
distributed, or transmitted in any form or by any means, including photocopying, recording, or
other electronic or mechanical methods, without the prior written permission from Innovative
Air Technologies, except in the case of brief quotations embodied in critical reviews and certain
other noncommercial uses permitted by copyright law. For permission requests, contact Innova-
tive Air Technologies.

Prepared by: Summer Neal, Marketing Manager, Innovative Air Technologies

Prepared for: Innovative Air Technologies

Innovative Air Technologies

16200 Georgia Peach Avenue
Covington, GA 30014
770-788-6744

www.dehumidifiers.com
 Innovative Air Technologies

TABLE OF CONTENTS
*If you are viewing this document in a digital format, please note that this Table of Contents features interactive links; click on the Section you would like to see & you will be taken to it.

Introduction .................................................................................... 4
Desiccant Dehumidifier ................................................................ 5
What is a Desiccant? .................................................................... 6
Components of a Solid Desiccant Dehumidifier .................... 8
Process Air Stream ........................................................................ 9
The Desiccant Wheel ................................................................... 10
Reactivation Air Stream ................................................................ 12
Solid Desiccant vs. Refrigerant-based Dehumidification ...... 13
Conclusion ....................................................................................... 14
Appendix .......................................................................................... 15

Demystifying Solid Desiccant Dehumidification Training Manual. Innovative Air Technologies. © 2024. All rights reserved. 3
 Innovative Air Technologies

INTRODUCTION
Solid desiccant dehumidifiers are utilized in removing
humidity from the air to create and sustain comfortable,
healthy, and productive indoor environments.
Most desiccant dehumidifiers function primarily the same way, they remove water from the air in its molecular
state, using the vapor pressure differences between the air and the desiccant surface to attract and hold, or
oppositely release that moisture.

Perhaps in the past you have been led to believe that solid desiccant dehumidification is too complex and
confusing to understand. Or maybe you thought that solid desiccant dehumidification is inefficient, overly
expensive, and should only be applied in extreme cases where it must be used. We hope the information
we share in the following pages will put these misconceptions to rest. As you read, you will see that solid
desiccant dehumidification is an energy-efficient, sustainable, and cost-effective solution for almost any
environment requiring the removal of moisture. It is truly a thermodynamically-eloquent dehumidification
option when properly applied.

Figure 1.1: Innovative Air Technologies IDP Desiccant Dehumidifier with packaged DX cooling

4 Demystifying Solid Desiccant Dehumidification Training Manual. Innovative Air Technologies. © 2024. All rights reserved.
 Innovative Air Technologies

DESICCANT DEHUMIDIFIER
Typical Unit Design

8
PROCESS AIR SIDE
7 1. React Fan
2. Process Air Inlet*
1 3. Process Air Filter
4. Pre-Cooling Coil
& Bypass Damper
5 5. Desiccant Wheel (Rotor)
6. Process Air Fan
2 4 6 7. Process Air Outlet
8. PLC Touch Screen
3

Figure 1.2a: Solid Desiccant Dehumidifier, Process Air side view

15
12
16 REACTIVATION AIR SIDE
10. React Air Inlet
11 13 11. React Filter & Heater
10 12. Process Air Outlet
13. Desiccant Wheel (Rotor)
14. Pre-cooling Coil
15. React Air Outlet
14 17 16. React Fan
17. Process Air Inlet*

Figure 1.2b: Solid Desiccant Dehumidifier, Reactivation Air side view

* Process air inlets are unobstructed, this unit/image is for display purposes only.

Demystifying Solid Desiccant Dehumidification Training Manual. Innovative Air Technologies. © 2024. All rights reserved. 5
 Innovative Air Technologies

WHAT IS A DESICCANT?
A desiccant is a hygroscopic material,
further defined as a substance which
has a high affinity for moisture.
Solid desiccants work on the principle of adsorption, which relates
to individual water molecules “sticking” to or adsorbing to the
desiccant’s surface. If the desiccant material used has a large internal
surface area, then lots of water molecules may be adsorbed. Solid
desiccant materials should withstand being saturated with water
molecules and avoid changing into a liquid form.

As our solid desiccant of choice, we use silica gel which is a common

material used for the purpose of removing water vapor from the
air. It is economically priced, commercially available, chemically inert,
odorless, nontoxic, and noncorrosive. Viewing it through a microscope
would reveal a massive internal network of passages and crevices.
It is the porosity of its
structure that in part allows REMEMBER:
it to adsorb and hold up to Solid desiccant dehumidification
Figure 1.3: Silica gel beads removes water from the air in its
40% of its dry mass in water.
molecular state.

The desiccant never becomes wet.

This is a benefit for solid desiccant

dehumidification as it is not limited
by cold coil surfaces which can
frost or freeze liquid condensate.

Figure 1.4: Pre-cooling coil, see Figures 1.2a #4 & Figure 1.2b #14

6 Demystifying Solid Desiccant Dehumidification Training Manual. Innovative Air Technologies. © 2024. All rights reserved.
 Innovative Air Technologies

Dehumidification achieved by the adsorption of water colder to lower the air’s leaving temperature, therefore,
molecules marks an important distinction between condensing more moisture.
desiccant technology and that of refrigerant based air-
conditioning. In the more traditional refrigerant-based As mentioned, solid desiccant dehumidification removes
system, warm air passes through a cold cooling coil and water from the air in its molecular state based on vapor
its sensible temperature is reduced as heat is absorbed. pressure deferential. Water is never condensed in the
Depending on the surface temperature of the coil, and traditional sense, nor does the desiccant ever become
the leaving temperature of the air, latent heat may also wet. This is a benefit of solid desiccant dehumidification
be removed forming liquid condensate which lowers as it is not limited by cold coil surfaces which can frost
the air mixture’s moisture content. It is important to or freeze liquid condensate. This allows solid desiccant
understand that traditional refrigerant based systems like dehumidification to produce leaving air dew-point
this are designed primarily to cool the air sensibly, with temperatures as low as -80°F (-62°C) or less, and to
the dehumidification, or removal of moisture, being a maintain environments at single digit relative humidities
byproduct. if required. There are many stringent environmental
applications where desiccant dehumidification is the only
In these systems, if the air requires deep dehumidification, solution that will work.
the cooling coil surface temperature must be made

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 Innovative Air Technologies

COMPONENTS OF A SOLID
DESICCANT DEHUMIDIFIER
The heart of a solid desiccant dehumidifier is its desiccant wheel (or rotor) which is centered between two opposing
and isolated air streams. The process airstream consists of the air which is to be dehumidified, and the reactivation
airstream removes the moisture which has been adsorbed into the desiccant during the dehumidification process. It
is this airstream which “dries” the wheel and allows for consistent, continuous, and uninterrupted dehumidification.

Flow Diagram
React Fan Heat Source Filter
React Air Outlet
React Air Inlet
Humid air
Outside Air
ducted outside

Process Air Inlet

Process Air Outlet
Outside or
Dry Space Air
return air

Filter Process Fan

Rotating Desiccant Wheel

Figure 1.5: Innovative Air Technologies Dessicant Dehumidification Flow Diagram

Process air inlet

photo of filters opening and
damper photo

Figure 1.6: Process Air Filter, see Figure 1.2a #3 Figure 1.7: Process Air Inlet*, see Figure 1.2a #2, & Figure 1.2b #17
*Process air inlets are unobstructed, this unit/image is for display purposes only.

8 Demystifying Solid Desiccant Dehumidification Training Manual. Innovative Air Technologies. © 2024. All rights reserved.
 Innovative Air Technologies

PROCESS AIR STREAM

Let us take a closer look at what a solid desiccant dehumidifer looks like, and discuss how it works...

Starting on the process side’s air inlet and working in the direction of airflow, we see the dehumidifier pictured in this
manual has been built to provide 100% outdoor ventilation air to the building, with an air opening and motorized
damper located on the rear of the unit. It would also include a hood assembly if this unit were to be located outdoors.
IAT could also provide an additional return air opening and motorized damper if building air is to be returned, and this
section would then be referred to as an air mixing box.

Our next component in the direction of airflow is some type of air filter. It can be any type or efficiency specified by
the end user. The higher the MERV rating, the more efficient it is at extracting smaller sized particles from the entering
airstream. This not only helps keep downstream componentry clean, but may also safeguard the health, comfort, and
productivity of occupants, or ensure the quality of a particular process occurring in the indoor space.

As we continue our journey, we see a pre-cooling coil and drain pan,

which has been positioned upstream of the desiccant wheel. This
Pre-cooling is pre-cooling coil could be either chilled-water or direct-expansion,
depending on the specific project requirements. Pre-cooling is
sometimes necesary sometimes necessary, particularly in 100% outdoor air applications
as a method to lower the
or in extremely hot and humid environments, as a method to lower
temperature of the process air the temperature of the process air prior to entering the wheel. As
prior to entering the wheel. silica gel is hygroscopic, this decreases the desiccant’s surface vapor
pressure so it can more deeply adsorb moisture, helping produce
extremely low leaving air dew-point temperatures if necessary.

9 8

7
PROCESS SIDE
5
1. Process Air Inlet
2. Process Filter
4
3. Pre-Cooling Coil
4. Desiccant Wheel (Rotor)
1 3
2 6 5. React Heater
6. Process Air Fan
7. React Air Inlet
8. Process Air Outlet
9. PLC Touch Screen

Figure 1.8: Diagram of Innovative Air Technologies Typical Desiccant Dehumidifier

Demystifying Solid Desiccant Dehumidification Training Manual. Innovative Air Technologies. © 2024. All rights reserved. 9
 Innovative Air Technologies

THE DESICCANT WHEEL

Our next component is the desiccant wheel, also called a rotor. It consists of a circular substrate material, usually made
of fiberglass, aluminum, or ceramic, which is slowly rotated between the two opposing airstreams mentioned earlier.
It is constructed with “fluted” passages through which air can flow. The substrate is impregnated with silica gel (our
desiccant), and as humid process air flows through the wheel in one direction it encounters the desiccant, which is
maintained at an exceptionally low surface vapor pressure. The vapor pressure exerted by the moisture in the air is
higher than that of the silica gel, so based on pressure differential, water molecules move from the air into the silica gel
to be adsorbed and removed.

The desiccant wheel can easily adsorb vast quantities of moisture from the process air, and it bonds these water
molecules tightly into the desiccant material until the wheel is rotated into the opposing reactivation airstream, where
thermal energy (heat) is added, and the wheel is dried. More on reactivation to follow, but it is important to understand
that there is no wetting of any wheel materials or surfaces due to liquid condensation.

Leaving the wheel is process air that has been deeply dehumidified but slightly warmed. The warming of this air is due
to a psychrometric principle called the “latent heat of adsorption.” Any time moisture is removed from an airstream
through a phase change, whether by liquid condensing on a cold cooling coil (latent heat of condensation) or through
adsorption by a desiccant substance, there is an instantaneous conversion of latent-to-sensible heat energy at the rate
of approximately 1,060 BTU per pound (of water removed) which immediately warms the air. This warmed process air
could be sensibly cooled to reduce its temperature, if neccesary.

Figure 1.9b: Front view of

desiccant wheel with chain drive
inside unit, see Figure 1.8 #4

Figure 1.9a: Side view of desiccant wheel see Figure 1.2a #5 & Figure 1.2b #13

10 Demystifying Solid Desiccant Dehumidification Training Manual. Innovative Air Technologies. © 2024. All rights reserved.
 Innovative Air Technologies

IMPORTANT NOTE:
The desiccant wheel is continuously rotating between
Sometimes a small bypass duct and damper are
the process and reactivation sides of the unit. These are
located directly below the wheel. This can be
two opposing and independent airstreams which are
used to blend air passing through the wheel with
internally divided by ducting and a wheel-seal assembly
bypass air which is left unconditioned, providing
which maintains the integrity of the two airstreams,
a downstream mixture which can be controlled
ensuring they do not mix with one another.
to the environmental set-point of the indoor
space, enabling the unit to maintain precise
dew-point temperatures and relative humidities.

From here, the process air enters a fan assembly and is discharged through the end of this unit into field supplied
ductwork which conveys the air to the environment to be controlled. There are several additional components which
can be added to the process air side. A few options might include pre-heating, post-heating, post-cooling, UVC lights,
internal LED lighting, final HEPA filtration, humidification, or anything else a client requires.

Figure 1.10: Process air bypass and fan assembly, see Figure 1.2a #4 & 6

Demystifying Solid Desiccant Dehumidification Training Manual. Innovative Air Technologies. © 2024. All rights reserved. 11
 Innovative Air Technologies

REACTIVATION AIR STREAM

The reactivation air quantity
is a smaller fraction of the
total wheel air flow, typically
between 25% and 33%.
This air may come from the outdoors or from some other
source of clean air, perhaps from within the building itself.
Before entering the desiccant wheel, the reactivation air
is filtered and elevated in temperature. Adding thermal
Figure 1.11a: React Air Inlet,
energy heats the desiccant, increasing its surface vapor
see Figure 1.2b #10
pressure so it is now higher than the vapor pressure of the
reactivation air. This allows the adsorbed water molecules
held tightly in the wheel to break their bond with the silica
gel and be removed. This process is known as “desorption.”

The reactivation airstream may be heated to somewhere

between 120°F to 285°F depending on how much
regeneration must take place. The warmer the wheel is Figure 1.11b: React Filter,
made, the drier it will become, and the more moisture it see Figure 1.2b #11
can then adsorb from the process air stream. This allows
lower dew-point temperatures to be delivered to the
indoor space.

The thermal energy required for reactivation

can come from various sources including gas,
electricity, steam, or waste heat. If waste heat is
Figure 1.11c: React Heater
available at the temperature necessary, operational Outlet, see Figure 1.2b #11
costs for dehumidification may be virtually free.

From here the reactivation air enters the regeneration

air fan assembly to be discharged outdoors. The air at
this point has been slightly cooled and humidified due to
yet another phase change of moisture in a psychrometric
process known as the “latent heat of desorption.” This air
is loaded with moisture and is at an extremely high dew- Figure 1.11d: React fan,
point temperature. The drier the wheel is made in the see Figure 1.2b #16

reactivation process, the more moisture will be removed

from the wheel and released to the outdoors.

As mentioned, the dehumidification process is continuous,

so if the wheel is turning, the heater is functional, and Figure 1.11e: React Air Outlet,
see Figure 1.2b #15
the fans are moving air, dehumidification is taking place.

12 Demystifying Solid Desiccant Dehumidification Training Manual. Innovative Air Technologies. © 2024. All rights reserved.
 Innovative Air Technologies

SOLID DESICCANT vs.

REFRIGERANT-BASED DEHUMIDIFATION
Traditional refrigerant-based cold-coil systems quickly absorb (remove) the latent heat of condensation, mentioned
earlier, into the cold refrigerant or fluid circulating through the coil, so in effect you never realize that a sensible
temperature rise in the supply air has occured. The desiccant dehumidifier simply leaves this heat in the airstream until
further removal by sensible only
post-cooling, if necessary.

There is a very compelling reason

we may want to leave this
converted heat in the process
airstream; applications needing
lower indoor humidity levels
require the air to be more deeply
dehumidified. With traditional
refrigerant-based air-conditioning,
the only way to accomplish this is
by overcooling the air to reduce its
temperature and moisture content
simultaneously. Many times, the
Figure 1.13: Reheat supply air must be drastically over-
cooled, and then warmed back-up
to a sensible temperature conducive with maintaining comfortable space set-points. These are known as “reheat”
systems and by today’s standards are not an energy-efficient or sustainable option for carbon emission reductions,
particularly when this heat is provided by equipment burning fossil fuel as a prime energy source.

By leaving the converted

sensible heat in the
desiccant’s airstream, it
can be utilized as “heat-
recovery” to help reduce or
eliminate the requirement
for energy intensive reheat.
This is a big sustainability
feather in the cap of solid
desiccant dehumidification
systems.*

*Contact Innovative Air

Technologies for application details
on this important benefit.
Figure 1.12: Desiccant vs. Refrigerant-based dehumidification

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 Innovative Air Technologies

CONCLUSION
Innovative Air Technologies prides itself on using industrial grade
components, including a wheel chain-drive assembly on all our products...
so unlike competing units, there are no belts to slip or break. We also use high quality heaters and fan assemblies
to ensure the utmost in reliability. Our units are built to be robust, maintainable, and user-friendly, and Innovative
Air Technologies always strives to deliver on our promise to provide the best possible desiccant dehumidification
solutions available today.

Short video tutorial

on how a desiccant
dehumidifier works.

Innovative Air
Technologies’ web-based
suite of psychrometric
engineering tools.

David Schurk DES, CEM, LEED-AP,

CDSM, CWEP, SFP, CIAQM, is National
Sales Manager for Innovative Air
Technologies in Covington, GA. He also
serves as an ASHRAE Distinguished
Lecturer, is an ASHRAE Life Member,
and Committee Chair for the ASHE
Sustainability and Decarbonization
Leadership Task Force. He has over 40
years of experience in the design and
analysis of heating, ventilating, and
air-conditioning systems for a variety
of market sectors, with a special
focus on healthcare and aerospace
environmental control and air quality.

Email david@dehumidifiers.com to
schedule training for your team. Figure 1.14: Innovative Air Technologies Rotor Series Desiccant Dehumidifier

14 Demystifying Solid Desiccant Dehumidification Training Manual. Innovative Air Technologies. © 2024. All rights reserved.
 Innovative Air Technologies

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16 Demystifying Solid Desiccant Dehumidification Training Manual. Innovative Air Technologies. © 2024. All rights reserved.
www.dehumidifiers.com | 16200 Georgia Peach Avenue | Covington, GA 30014 | 770-788-6744