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DEVap: An Energy-Saving Air Conditioning Design

17 June 2010 7,854 views 7 Comments

I like to set my home thermostat at around 80 degrees during the summer when friends and family aren’t around because I can’t stand to be cold.  I’m always freezing at work because the people who make decisions about temperature tend to be ample-waisted males of the suit-wearing persuasion who would rather have their fingernails pulled out one at a time than break a sweat.  I used to have a personal heater at my desk to counteract the effects of the arctic blast aimed roughly at the top of my head, but the heater voided the warranty on our cubicles so I had to take it home.  Now I drink hot water and wear scarves and sweaters all summer in Texas, where today for example, it is 103 degrees outside.

Unless it suddenly becomes socially acceptable for the thermally blessed to wear tank tops and shorts to the office, I think it’s safe to assume that air conditioning will continue to enjoy widespread use – despite the fact that it accounts for 5 percent of the 40 quadrillion British Thermal Units expended annually in American buildings (according to the U.S. Energy Information Administration).  Those of us who enjoy high surface area to volume ratios and poor circulation often point out the high cost in resources and dollars of setting the temperature low in hot weather, and so it’s with a bit of a pained smile that I will relate the following very good news, which completely undermines my argument:

Researchers working at the U.S. National Renewable Energy Laboratory (NREL) in Golden, CO, have developed “a new air-conditioner design that they say will dramatically increase efficiency and eliminate gases that contribute to global warming” (Savage).  The air conditioner utilizes the principles of indirect evaporative cooling paired with a desiccant to further absorb moisture. 

Image credit: Pat Corkery 

Here’s how the desiccant-enhanced evaporative, or DEVap, air conditioner works.  A polymer membrane coated with both a teflon-like substance that repels liquid water and a desiccant divides the air flowing through the system into two streams.  The membrane has pores about 1 micrometer to 3 micrometers in diameter; these are large enough for water vapor to pass through but too small for the desiccant to sneak across.  The desiccant draws moisture from the airstream, leaving dry but warm air.  Indirect evaporative cooling takes place in a secondary chamber, chilling the other half of the divided airstream.  As the air in the second chamber grows cooler and wetter it cools the dividing membrane, which in turn cools the first airstream, and out of the machine comes cool, dry air.  The process uses up to 90 percent less energy, depending upon the humidity of the air that goes into the system at the start (Source: NREL).  

Image Credit: NREL

NREL’s liquid desiccant takes the form of a 44% salt by volume solution of lithium chloride or calcium chloride (aka road salt).  The corrosiveness of the salt “requires that metal be eliminated from the hardware. What’s particularly attractive is that it replaces the chlorofluorocarbons that are used as the refrigerant in traditional air conditioners. Those CFCs can easily leak, and every kilogram of them provides the same greenhouse gas effect as about 2,000 kilograms of carbon dioxide” (Savage).  When the desiccant has absorbed too much water it can be heated to boil off the excess moisture.  The system could take advantage of waste heat from industrial processes, or gather heat from solar energy that might otherwise go to waste. 

NREL plans to hand off the design to industry for commercialization in about five years, which sounds like a long time –  but you might just think of it as until the next World Cup plus one year. Another bonus is that the system has been designed to replace existing systems without many changes, meaning that it would be an air conditioner upgrade rather than an infrastructural overhaul.  Either way, it looks like I’ll be wearing sweaters in June for a long time…


This post is all about water.


“Energy Saving A/C Conquers All Climates.” NREL.  06/11/10.  Accessed 06/17/10.  URL.

Savage, Neil.  “An Energy-Saving Air Conditioner.” Technology Review. 06/17/10.  Accessed 06/17/10.  URL.

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  • DEVap: An Energy-Saving Air Conditioning Design | ARCHITERIALS | airdeveloper.com said:

    […] Read more here: DEVap: An Energy-Saving Air Conditioning Design | ARCHITERIALS […]

  • sam said:

    “I used to have a personal heater at my desk to counteract the effects of the arctic blast aimed roughly at the top of my head, but the heater voided the warranty on our cubicles so I had to take it home.”

    Did you heater not also kill the power supply of your computer, once upon a time?

  • Alli Dryer (author) said:

    You are correct sir.

  • jarrol said:

    —“NREL’s liquid desiccant takes the form of a 44% salt by volume solution of lithium chloride or calcium chloride (aka road salt). The corrosiveness of the salt requires that metal be eliminated from the hardware”—
    perhaps Liquidmetal Technologies can provide a perfect solution for the corrosiveness issue.

  • jarrol said:

    normal evaporative cooling is generally not effective in a high humidity climate like miami…will this technology be effective there?

  • ahmed said:

    currently chinese introduced adsorption chillers that save upto 90% of your cooling bill. not only that it is extremely low maintenance as it does not have a compressor and uses some sort of gell the apparently cools hot water! and it also cna be used as a heater in winter! i think time is comming that europeans will have to start copying the chinese.

  • Steven said:

    What’s not clear is, now does the dessicant dry out and continue to absorb water? What takes away the water?

    In traditional evaporative coolers (“swamp coolers”) the water absorbs heat and evaporates, and is replaced by more water. But there’s no incoming stream of dessicant.

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