Posted on June 21st, 2010 by ryan.
Brad was trying to sell me on the idea of using a calcium chloride water feature in Red Bluff to control humidity a few weeks ago, and now it looks like some researchers at the National Renewable Energy Laboratory and used this very idea in what they claim is a radically more efficient method of air-conditioning.
Evaporative coolers are a lower-cost alternative to A/C in dry climates that don’t get too hot or humid — say, Denver, but not Phoenix or Miami. Water flows over a mesh, and a fan blows air through the wet mesh to create humid, cool air.
In humid climes, adding water to the air creates a hot and sticky building environment. Furthermore, the air cannot absorb enough water to become cold.
In Phoenix or Tucson, the evaporative cooler can bring down the temperature, but not enough to make it pleasant inside on a 100-degree day or during the four to eight week moist period known as monsoon season. The cooling bumps up against the wet bulb temperature, the lowest temperature to which air can be cooled by evaporating without changing the pressure. The wet bulb temperature could be 75 or 80 degrees on a mid-summer Tucson day. Typically, evaporative coolers only can bring the temperatures about 85 percent of the way to the wet bulb level.
So, for most of the country, refrigeration-based air conditioning is the preferred way of keeping cool.
The DEVap solves that problem. It relies on the desiccants’ capacity to create dry air using heat and evaporative coolers’ capacity to take dry air and make cold air.
“By no means is the concept novel, the idea of combining the two,” Kozubal said. “But no one has been able to come up with a practical and cost-effective way to do it.”
HVAC engineers have known for decades the value of desiccants to air conditioning. In fact, one of the pioneers of early A/C, Willis Haviland Carrier, knew of its potential, but opted to go the refrigeration route.
Most people know of desiccants as the pebble-sized handfuls that come with new shoes to keep them dry.
The kind NREL uses are syrupy liquids — highly concentrated aqueous salt solutions of lithium chloride or calcium chloride. They have a high affinity for water vapor, and can thus create very dry air.
Sounds like the technical challenge was designing a system which would make the liquid desiccant portion of the system low-cost and reliable.