Desiccant Dehumidification Equipment and Components
ASHRAE Technical Committee 8.12

Scope of TC 8.12

TC 8.12 is principally concerned with solid and liquid desiccant dehumidification equipment, its performance, application engineering, related load calculations, commissioning, operation, and maintenance. The committee is also concerned with the integration of desiccant equipment and components into other systems and with fundamental abstracts of heat and mass-transfer as they relate to desiccant materials and compounds.

[Our scope does not include desiccants used for contamination control in refrigerant systems (TC 3.3), or desiccants used in the operation of either absorption cooling equipment (TC 8.3), or air-to-air enthalpy heat exchangers (TC 5.5).]


The ASHRAE Handbook is published in a series of four volumes, one of which is revised each year, ensuring that no volume is older than four years.

The Handbook can be purchased at the ASHRAE Bookstore by clicking on this link.

TC 8.12 is responsible for the following handbook chapters:

FUNDAMENTALS: Sorbents and Desiccants
Sorption refers to the binding of one substance to another. Sorbents are materials that have an ability to attract and hold other gases or liquids. They can be used to attract gases or liquids other than water vapor, which makes them very useful in chemical separation processes. Desiccants are a subset of sorbents; they have a particular affinity for water.

HVAC SYSTEMS AND EQUIPMENT: Desiccant Dehumidification  and Pressure-Drying Equipment
Dehumidification is the removal of water vapor from air, gases, or other fluids. There is no pressure limitation in this definition, and sorption dehumidification equipment has been designed and operated successfully for system pressures ranging from subatmospheric to as high as 6000 psi (40 MPa). In common practice, dehumidification usually refers to equipment operating at essentially atmospheric pressures and built to standards similar to other types of air-handling equipment. For drying gases under pressure, or liquids, the term dryer or dehydrator is normally used. This chapter mainly covers equipment and systems that dehumidify air rather than those that dry other gases or liquids. Both liquid and solid desiccants are used; they either adsorb water on the desiccant’s surface (adsorption) or chemically combine with water (absorption).

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Technical committees develop and sponsor technical sessions at the winter and annual conferences. Information about their future technical program is discussed at each TC meeting and at the TC’s Program Subcommittee meeting.

ASHRAE publishes papers and transactions from presentations at its conference events. In addition, ASHRAE records most of the seminar sessions from its conferences on DVD. These DVDs are ideal for use at chapter meetings, in university courses, or company lunch and learns. Products available from the most recent conference may be found here.


Technical Committees are responsible for identifying research topics, proposing research projects, selecting bidders, and monitoring research projects funded by ASHRAE. Information about their specific research program is discussed at each TC meeting and at the TC’s Research Subcommittee meeting.

TC 8.12 co-sponsors the following research project (with TC 8.10, Mechanical Dehumidification Equipment and Heat Pipes; TCs 1.12, Moisture Management in Buildings, & TC 5.5, Air-To-Air Energy Recovery)

1712-RP: Development of the ASHRAE Design Guide for Dedicated Outdoor-Air Systems

This design guide will help practicing HVAC engineers design dedicated outdoor-air systems that minimize energy use, maximize indoor environmental quality, and balance life-cycle cost with environmental impact.


ASHRAE writes standards for the purpose of establishing consensus for: 1) methods of test for use in commerce and 2) performance criteria for use as facilitators with which to guide the industry. ASHRAE publishes the following three types of voluntary consensus standards: Method of Measurement or Test (MOT), Standard Design and Standard Practice. ASHRAE does not write rating standards unless a suitable rating standard will not otherwise be available. ASHRAE is accredited by the American National Standards Institute (ANSI) and follows ANSI's requirements for due process and standards development. Standards may be purchased at the ASHRAE Bookstore.

TC 8.12 is cognizant for these standards:
Standard 139: Method of Testing for Rating Desiccant Dehumidifiers Utilizing Heat for the Regeneration Process
Standard 174: Method of Test for Rating Desiccant-Based Dehumidification Equipment

Other Activities

TIP: If MTG involvement add here otherwise leave blank.

Include other activities, such as MTG involvement, into this section.


ASHRAE Technical FAQs are provided as a service to ASHRAE members, users of ASHRAE publications, and the general public. While every effort has been made to ensure their accuracy and reliability, they are advisory and provided for informational purposes only, and in many cases represent only one person’s view. They are not intended and should not be relied on as an official statement of ASHRAE. Technical questions not addressed may be submitted to the ASHRAE Technical Services department at

In addition to the ASHRAE FAQs, TC 8.12 has developed answers to these questions:

Question: Who's allowed to make presentations and suggest desiccant-related topics for seminars, forums and symposia at ASHRAE meetings?
Answer: Anybody and everybody. Just let us know what you are interested in presenting, or what you'd like to hear more about, and we'll put the information into one of our programs. Contact us through the Chair of our Program Subcommittee.

Question: How can I find a list of manufacturers of desiccant dehumidification equipment?
Answer: Because ASHRAE is a technical society rather than a trade organization, we don't publish such lists. You might get useful results by typing "Desiccant Dehumidifiers" or "Desiccant Dehumidification" into one of the usual internet search engines.

Question: What sort of moisture removal performance could I expect from a desiccant dehumidifier compared to a mechanical dehumidifier.
Answer: An accurate answer depends upon the exact hardware you are comparing. Performance of both desiccant and mechanical dehumidifiers varies widely, because the equipment is usually optimized for a specific application and operating range. In general, as the required dew point goes down, economics begin to favor desiccants over cooling-based dehumidifiers. Conversely, higher dew points tend to favor cooling-based dehumidifiers.

Question: How can I figure out which kind and what size desiccant dehumidifier will meet my need?
Answer: The most certain and reliable decision-making process begins with your clear definition of the need: How dry must the space or the air stream be made, and what happens if it does not meet that level of dryness? If you know the answers to those questions, most manufacturers can ask you more questions which will guide you to a cost-effective equipment selection. But without the answers to those questions, any equipment selection will be uncertain. For a more complete understanding of the variables governing equipment selection, we suggest the ASHRAE Humidity Control Design Guide