That partnership was made possible by a Department of Energy program that sought novel high-efficiency technologies to independently control temperature and humidity levels in buildings. The products are called desiccant air-conditioning systems, and two manufacturers that worked with ORNL are commercializing units much sooner than might be possible without the program.
"The idea behind this effort was to have industry and individuals with good ideas work with ORNL to stimulate research and development to integrate desiccant systems with conventional vapor compression technology," said Jim Sand, a researcher in ORNL's Engineering Science & Technology Division.
While conventional vapor compression air-conditioning systems do a great job of cooling, they are not designed to handle temperature and humidity loads separately. As a result, people tend to set thermostats to lower settings to offset the relatively high humidity. Compounding the problem is that oversized compressors are frequently installed to dehumidify the incoming air. Furthermore, to meet humidity requirements, vapor-compression systems are often operated for long cycles at low temperatures, which reduces their efficiency and may require reheating the very cold dehumidified air to achieve some degree of comfort.
"Obviously, when you have this going on in thousands of buildings across the country, it wastes a lot of energy and puts an unnecessarily high burden on the electric grid," Sand said. "So part of DOE's interest in desiccant air-conditioning systems is in reducing that load while allowing people to be more comfortable in healthier environments."
Also at work are new American Society of Heating, Refrigerating and Air-Conditioning Engineers requirements that call for increased use of outdoor air and more dehumidification in commercial buildings. Greater use of outside air and lower humidity help improve indoor air quality and combat mold and mildew problems common in many parts of the country.
ORNL's involvement in the program was a natural, Sand said, because the lab has expertise in such areas as instrumentation and controls, desiccant equipment, vapor compression technology and systems integration. Another key capability is in thermally driven systems, which use waste heat instead of electricity to provide cooling and dehumidification.
While there are different approaches to designing a desiccant system, the basics are the same in that these systems remove moisture from air, then cool the air using either evaporative cooling or the cooling coils of a conventional air conditioner. Moisture is then removed from the desiccant with heat provided by waste heat, natural gas or electricity. Thus, the desiccant is constantly being regenerated.
In addition to making conditions a lot more comfortable for millions of people, DOE hopes desiccant systems capture increasingly greater shares of the commercial air-conditioning market. With a market share of 15 percent, for example, carbon dioxide emissions could be reduced by up to 18 million tons. Carbon dioxide, considered a greenhouse gas, is increasing in the atmosphere each year and is thought to be a major factor in climate change.
In part because of the program, one of the partners, SEMCO, has already introduced an active desiccant-vapor compression hybrid rooftop unit. SEMCO is based in Columbia, Mo. And a partnership with Trane and Charles Cromer of the University of Central Florida has resulted in the Trane Active Cromer Cycle system, which is expected to be on the market by the end of the year or in early 2005.
A third partner, the team of Kathabar of Somerset, N.J., and AIL Research, is developing a system with greater risk but potentially greater payback, Sand said. Field demonstrations are scheduled for this summer, and commercial production could begin within 18 months.
Other ORNL researchers involved in the project are Bob DeVault, Ed Vineyard, Abdi Zaltash, Randy Linkous and Andrei Petrov. The National Renewable Energy Laboratory is also collaborating with ORNL.
ORNL is managed by UT-Battelle for the Department of Energy. Funding for the project was provided by DOE's Office of Energy Efficiency and Renewable Energy.