It’s a mouthful, but desiccant-enhanced evaporative (DEVap) air conditioning may soon provide you with a superior climate control system consuming a small fraction of the electricity used by today’s most efficient, conventional air-conditioning equipment, releasing far less carbon dioxide in the process, and cutting costly peak electrical demand by an estimated 80% to boot.
As the name implies DEVap air conditioning combines two apparently contradictory technologies: dehumidification and evaporative cooling. The system pulls moisture out of the air by blowing it across a liquid desiccant--a water-absorbing material (diluted lithium chloride)--that draws vapor out of the airstream, dehumidifying it. In the second stage, this dry air is tempered by an advanced, indirect evaporative cooling system. Unlike a conventional evaporative system that cools air by evaporating water into it, this system brings the airstream only into thermal contact with an airstream that blows over a moistened surface. The natural heat exchange between the adjacent airstreams (moist and dry) pulls heat out of the dry air, cooling it.
Even if you don’t follow the technical description, the bottom line is a system that dehumidifies air and then cools it using only the electricity required to run two small fans. If deployed in a climate like Phoenix, where the air is naturally dry most of the year, the system will use approximately 90% less energy than a conventional, high-efficiency system while delivering equivalent or greater cooling capacity. In a humid climate like Houston’s, where the latent load will require high levels of dehumidification, DEVap air conditioning will still save approximately 35%.
But direct energy savings is only the beginning. DEVap air conditioning solves the most vexing problem for air condition engineers by efficiently separating latent (dehumidification) from sensible (temperature) loads. Unlike a conventional system that must cool to dehumidify, DEVap air conditioning can do one or the other, or both. In other words, dehumidify without cooling and cool without dehumidifying, allowing you to set individual thresholds for latent and sensible loads without compromising efficiency for comfort. In some climates, such as Seattle, building owners could benefit from combining dehumidification with heating, explains Jason Woods, a lead researcher on DEVap air conditioning with NREL.
Woods believes that a commercial building application of this technology will come to market in about five years, and a residential version may be available in as early as ten. When commercialization begins, DEVap is estimated to cut peak electrical demand by nearly 80% in all climates, saving billions of dollars in investments and operating costs for our nation’s electrical utilities, according to NREL. The laboratory estimates that initially, rooftop units using the patented DEVap design will cost about 30% more than competing models, but the energy savings should yield a payback period of less than three years.
Another benefit with using water as refrigerant, it eliminates all of the negative environmental effects associated with many of today’s conventional refrigerants. You can obtain the latest NREL report on DEVAP air conditioning at: http://www.osti.gov/bridge.