Prime Air Products Company
Prime Air Products Company Case Study:
SG America Cross Contamination

www.SGAmerica.com

January 2011

Cross-Contamination by Desiccants in Heat Wheels

A study of ION-exchange material and 3A molecular sieve concludes that ION-exchange material is a better choice as a desiccant concerning cross-contamination by desiccant transfer for energy recovery wheels.

Introduction:

Ventilation is an essential technology required to improve indoor air quality (IAQ). It is required in almost all building codes and it is of course the subject of ASHRAE Standard 62. Ventilation without heat/energy recovery increases the building seasonal air-conditioning for either cooling or heating load. Exhaust or relief air is used to discharge indoor CO2 and other air pollutants to the outdoors. Enthalpy wheels provide an important opportunity towards achieving acceptable indoor air quality while reducing the HVAC energy requirement.

Desiccant materials such as silica gel, molecular sieves and ion-exchange materials are used to transfer humidity from one air stream to the other. As is the case in all heat exchange devices, according to the Law of Thermodynamics, warm flows to cool and according to the corollary rule, wet flows to dry. The air stream with the warmer temperature, comparing supply and exhaust air streams, is cooled and the other air stream is warmed. Similarly, the humid air stream is dehumidified while the other air stream is humidified.

Cross-Contamination:

During the past few years, the industry has learned that cross-contamination between the two air streams has happened by the co-adsorption of water vapor and airborne contaminants. This is because gaseous substances with offensive odors or harmful health affects can also be adsorbed by desiccants. A study was undertaken to determine which desiccant performed better concerning cross-contamination of internally generated air contaminants.

Among conventional desiccant materials, 3A molecular sieve is expected to provide good selective adsorption characteristics by excluding the adsorption of contaminants that have a diameter greater than 3 Å . Modified ION-exchange resins also have good absorbability for water vapor and are also selective concerning co-adsorption. Seibu Giken has successfully developed an enthalpy wheel using an ion exchange resin to achieve a low cross-contamination. This product has been applied in ventilation service successfully for more than ten years.

In the study, odor transfer tests for typical contaminants such as ammonia, carbon dioxide, formaldehyde and propane were carried out using two enthalpy wheels which were compared to each other. Both wheels are commercially available. One uses 3A molecular sieve and the other uses an ION-exchange resin.

Test Set-up:

All experiments and calculations were conducted in accordance with ANSI/ASHRAE Standard 84-2008 “Method of Testing Air-to-Air Heat/Energy Exchangers” and ANSI/ARI Standard 1060-2005 “Performance Rating of Air-To-Air Heat Exchangers for Energy Recovery Ventilation Heat Equipment”.

Enthalpy Exchange Effectiveness:

The enthalpy exchange effectiveness of both wheels were investigated and compared. Although the ION-exchange resin wheel was slightly thinner than the wheel using 3A molecular sieve, the enthalpy performance of the desiccants was within 2% points of each other. Given the uncertainty analysis of the test loop apparatus this indicates that the two samples have essentially the same enthalpy effectiveness.

Cross-Contamination:

It was found that the ION-exchange enthalpy wheel showed two to six times less cross-contamination than the 3A molecular sieve wheel for all contaminants tested in this study. Conversely, the 3A desiccant caused more cross-contamination than did the ION-desiccant.

Request Report and Paper:

For a full copy of our report cover and the Study results published by the Journal of Chemical Engineering of Japan authored by Akio Kodama of the School of Mechanical Engineering, College of Science and Engineering, Kanazawa University please send a request to Sales@SGAmerica.com. To qualify, please include your complete contact information.

Seibu Giken America

2929 Park Drive

Owatonna, MN 55060

507-214-2715
For more information on SG America products Click HERE.