November 5, 2003—While displacement ventilation has the potential to improve indoor air quality and save energy, it has not been widely used in the United States, reports ASHRAE.
But its potential for use is great, due to existence of large core offices in many U.S. buildings that are isolated from the external climate and that need cooling.
A 10-step guideline for use by designers in designing displacement ventilation systems is featured in a book from ASHRAE. System Performance Evaluation and Design Guidelines for Displacement Ventilation] is the result of an ASHRAE research project by Qingyan Chen, Ph.D., professor of mechanical engineering, Ray Herrick Laboratories, Purdue University, West Lafayette, Ind., and Leon Glicksman, Ph.D., professor of building technology and of mechanical engineering, Massachusetts Institute of Technology.
“Our results show that displacement ventilation systems can provide a thermally comfortable indoor environment at a high cooling load through careful design,” Chen said.
Displacement ventilation is used mainly in Scandinavian countries. Many U.S. cities have higher temperatures in summer than those in Scandinavian cities, and U.S. offices may have more lighting and equipment that produces more heat. Therefore, the cooling load could be higher.
With displacement ventilation, warm contaminants rise to the ceiling, the contaminated air is extracted, and fresh, cool air is supplied at floor level.
“The indoor air quality is better if the contaminant sources are associated with the heat sources, such as computers, people and equipment,” Chen said. “This is because the thermal plumes from the heat sources will bring the contaminants to the upper part of the room where exhausts are located. The displacement ventilation system can also save energy but requires a separate heating system if it is applied to building perimeter zones.”
The cost of System Performance Evaluation and Design Guidelines for Displacement Ventilation is $59 ($47, ASHRAE members). To order, contact ASHRAE Customer Service at 800/527-4723 or visit the ASHRAE Bookstore.
