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Dehumidification in Industrial and Building Applications

A. Bhatia, B.E.


Course Outline

Dehumidification is the process of removing moisture content from the airspace. It is vital for creating a comfortable indoor environment and to protect product integrity in a variety of industries, including pharmaceuticals, food, chemical and bulk powders.

Often the limit for the risk of damage from humidity is around 55-60%RH. To eliminate the moisture problem at a reasonable cost, the designer needs to know how much moisture is present, how did it get in the facility and how to select the proper dehumidification system? This 4-hr course material provides a basic introduction to the principles involved in controlling humidity.

The course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

At the conclusion of this course, the reader will:


Intended Audience

This course is aimed at students, engineers, designers, architects, facility managers, H &S professionals, supervisors, technical and sales representatives and anyone who wants a basic understanding of humidity control.


Course Introduction

Humidity levels around 40-50%; during the summer are ideal for the comfort of people, pets, and property. Dehumidifiers make living and working spaces more comfortable and help protect property from the ravages of excessive moisture by reducing the humidity. Dehumidification systems find wide application in manufacturing operations and processes. Only few materials tolerate the exposition to high atmospheric humidity for a longer period of time. Most of them will be ruined. Examples are: iron will corrode, salt and fertilizers will get lumpy, wood and textiles will go moldy and rot, cardboard boxes will lose their firmness and sustainability. If at storage and warehousing of goods (paper, textiles, furniture, steel products, ammunition, etc.) you do not provide a sufficiently low level of humidity, you risk that the goods get damaged with great loss of value as a result.

There are basically two types of dehumidification: cooling based systems and desiccant systems. Cooling-based systems extract moisture in a liquid state by using coils to cool the air to a saturation state. In contrast, desiccant systems directly extract moisture from the air in a vapor state. To properly size a dehumidification system, one has to have a basic understanding of psychrometrics.

This course reviews the above criteria in detail.

Course Content

The course content is in a PDF file Dehumidification in Industrial and Building Applications. You need to open or download this document to study this course.


Course Summary

Buildings in hot/warm and humid climates, with high space latent loads, high outside air ventilation rate, low interior space humidity requirement or stringent humidity control, will need dehumidification. Broadly there are two types of commercial dehumidifiers; both differ substantially as regards mode of operation, price, and efficiency, and in this way also as regards the field of application.

1) Refrigerant Dehumidifiers - Refrigerants work on the basis of condensation and are most effective above 68ºF and 40% RH, (relative humidity). They may be used below these conditions; however icing of the coils may be a problem. Some units have hot gas bypass systems that allow these to be used down to 33ºF. When operating in conditions that are hard to control, you may consider using a desiccant.
2) Desiccant Application -When the required dewpoint is low, or when very low RH levels are needed, desiccant-based dehumidification is often a more cost-effective alternative. In desiccant system, a turning wheel impregnated with desiccant material absorbs moisture. Once it collects the moisture, the wheel turns so that it's in a stream of heated air (about 250 degrees). That air dries out the wheel so it can again collect moisture.

To eliminate the moisture problem at a reasonable cost, the designer needs to know how much moisture is present, how did it get in the facility and how to select the proper dehumidification system? Following steps are followed in the sizing of dehumidification systems:

1) Eliminate the incoming water source
2) Remove excess moisture using water extraction principles
3) Use the science of psychrometry to determine type and amount of equipment needed for job.
4) Install type and amount of equipment needed for job (air-movers, dehumidifiers, etc.)
5) Repeat testing of moisture and RH until structure is dry

If you use too little dehumidification, materials dry too slowly, increasing the chances of secondary damage; if you use too much, you may waste your client's money.

Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

Take a Quiz

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.