Desiccant Research & Development

Efforts to improve energy efficiency in buildings by tightening building envelopes and improving thermal insulation do not address indoor air quality (IAQ) issues or the issue of latent (moisture-related) cooling loads in buildings. Conventional air conditioners are not designed to handle the large ventilation rates needed to provide acceptable IAQ or overcome moisture buildup. The effects of the "sick building syndrome" on public health and productivity and of moisture damage are major incentives to develop energy-efficient space conditioning systems that provide high levels of humidity control.

Desiccants can improve the indoor air quality of all types of buildings. Desiccant cooling systems can be used as stand-alone systems or with conventional air-conditioning. In these systems, a desiccant removes moisture from the air, which releases heat and increases the air temperature. The dry air is cooled using either evaporative cooling or the cooling coils of a conventional air conditioner. The absorbed moisture in the desiccant is then removed (the desiccant is regenerated, or brought back to its original dry state) using thermal energy supplied by natural gas, electricity, waste heat, or the sun. Commercially available desiccants include silica gel, activated alumina, natural and synthetic zeolites, lithium chloride, and synthetic polymers.

Desiccant systems can supplement conventional air conditioners, reducing the need for vapor-compression systems to operate for long cycles and at low temperatures in order to handle temperature and humidity. By working together, conventional cooling systems and desiccant systems can tackle the temperature and humidity loads separately and more efficiently. Heating, ventilating, and air conditioning (HVAC) engineers can then reduce compressor size and eliminate excess chiller capacity.

Desiccant technologies have numerous current and potential applications. For example:

• Supermarkets use them to reduce frost buildup on refrigerated cases and frozen products, extending product shelf life as well as the intervals between expensive, energy-consuming defrost cycles.

• Desiccants contribute to a drier, cleaner, more comfortable environment in schools, hospitals, hotels, office buildings, and stores of all kinds.

Desiccant units are being tested in fast-food restaurants, schools, and elsewhere.

ORNL is also working with researchers at Georgia Tech, Georgia State University, and SEMCO, Inc., on a field study to verify the positive effects of humidity control and continuous ventilation on school IAQ and the health of schoolchildren. To develop baseline data for schools in moderate and hot, humid climates, the researchers are studying four schools in the metropolitan Atlanta area and six in Georgia's coastal region. Some schools in the study have active humidity control and continuous ventilation systems, and some do not. The study will be used to develop recommendations and HVAC design considerations for improving IAQ in schools and other large buildings.

A preliminary report just published summarizes scientific research on IAQ in public buildings, particularly in schools. The report, Causes of Indoor Air Quality Problems in Schools: Summary of Scientific Research, explores the reasons and offers guidance to school boards, school administrators, and local officials on improving IAQ in schools. The report is available as a PDF file.

PDF version of Causes of Indoor Air Quality Problems in Schools: Summary of Scientific Research

(Revised Edition May 2000)

As a result of preliminary marketing analyses performed prior to new product development work, the reports (PDF format) listed below were compiled:

• Desiccant-Based Preconditioning Market Analysis (Phase 1)
• Active Desiccant-Based Preconditioning Market Analysis & Product Development (Phase 2)

Desiccant Humity Control Van

(To spread information about these desiccant systems and to broaden and accelerate their deployment, the U.S. Department of Energy has constructed a mobile exhibit featuring the advantages of desiccant humidity control (DHC Van). It provides a first-hand experience of the comfortable aspects of active humidity control with desiccant systems. The DHC Van is available for display and demonstration at national, regional, and local meetings of trade associations, professional societies, and utility groups. This webiste provides answers to many of the frequently asked questions about hosting the DHC Van and facilitates communications with the potential host.)

http://www.ornl.gov/desiccantvan/

For more information, contact:

James R. Sand
Oak Ridge National Laboratory
P.O. Box 2008, MS 6070
Oak Ridge, TN 37831-6070

Phone Number: (865) 574-5819
Fax Number: (865) 574-9338
E-mail: sandjr@ornl.gov