New Air Conditioner Conquers All Climates, Saves Up To 90% Energy

Jun 22, 2010 by Bill Scanlon
NREL senior engineer Eric Kozubal examines a prototype air flow channel of the DEVap air conditioner, which he co-invented. DEVap, which stands for desiccant-enhanced evaporative air conditioner, is a novel concept that uses membrane technology to combine the efficiency of evaporative cooling and the drying potential of liquid desiccant salt solutions. The graph superimposed on the photo shows shows how hot humid air, in red, changes to cool dry air, in blue, as the air passes through the DEVap core. Credit: Pat Corkery

Ah, the cool, refreshing feel of air conditioning on a sweltering summer day. Ugh, the discomfort when those energy bills in July, August and September come due — $200, $400, $600 or more.

Feel miserable, or dig deep into your wallet — not much of a choice for the 250 million Americans who live in climates where heat, humidity or both are a Catch-22 for three to 12 months a year.

A soothing solution may be on its way, thanks to a melding of technologies in filters, coolers and drying agents.

The U.S. Department of Energy's National Renewable Energy Laboratory has invented a new air conditioning process with the potential of using 50 percent to 90 percent less energy than today's top-of-the-line units. It uses membranes, evaporative cooling and liquid desiccants in a way that has never been done before in the centuries-old science of removing heat from the air.

"The idea is to revolutionize cooling, while removing millions of metric tons of carbon from the air," NREL mechanical engineer Eric Kozubal, co-inventor of the Desiccant-Enhanced eVaporative air conditioner (DEVap), said.

"We'd been working with membranes, evaporative coolers and desiccants. We saw an opportunity to combine them into a single device for a product with unique capabilities."

Hot and Humid Climates are Tricky

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.

This illustration shows how the DEVap cooling core uses water and liquid desiccant to draw in outside air, exhaust some of that air and return cool, dry air to the area being cooled. DEVap's integrated evaporative component and its desiccant drying process offer improved dehumidification and, thus lower costs and much lower energy usage.

Cooling Requires Temperature Drop and Less Moisture

Cooling comes in two forms — sensible cooling, which is a temperature drop, and latent cooling, which comes from pulling the moisture out of the air.

One intriguing product already on the market in arid, temperate climates is the Coolerado cooler. It differs from a typical evaporative cooler by never increasing the moisture content of the supply air. It provides cool air through indirect evaporative cooling. Indirect evaporative systems use a purge air stream that removes heat from the product or supply air stream that is then directed into a building.

That way, the Coolerado can cool the air all the way to the wet-bulb temperature.

"It's a big improvement on evaporative cooling because it doesn't add moisture and still gives you cold air," Kozubal said. However, in a humid climate, it still does not provide cold air or humidity control.

DEVap: Liquid Desiccants, Permeable Membranes

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.

Because of the complexity of desiccant cooling systems, they have traditionally only been used in industrial drying processes. Inventing a device simple enough for easy installation and maintenance is what has impaired desiccant cooling from entering into commercial and residential cooling markets.

These graphs show the savings possible with DEVap in a warm, dry climate such as Phoenix, if natural gas is the source of energy.

To solve that problem, the NREL device uses thin membranes that simplify the process of integrating air flow, desiccants, and evaporative cooling. These result in an air conditioning system that provides superior comfort and humidity control.

The membranes in the DEVap A/C are hydrophobic, which means water tends to bead up rather than soak through the membranes. Imagine rain falling on a freshly waxed car. That property allows the membranes to control the liquid flows within the cooling core. "It's that property that keeps the water and the desiccant separated from the air stream," Kozubal said.

"We bring the water and liquid desiccant into DEVap's heat-mass exchanger core," Kozubal said. "The desiccant and evaporative cooling effect work together to create cold-dry air."

The air is cooled and dried from a hot-humid condition to a cold and dry condition all in one step. This all happens in a fraction of a second as air flows through the DEVap air conditioner. The result is an air conditioner that controls both thermal and humidity loads.

DEVap helps the environment in many ways. DEVap uses 50 percent to 90 percent less energy than top-of-the-line refrigeration-based air conditioning.

Because DEVap uses salt solutions rather than refrigerants, there are no harmful chlorofluorocarbons (CFCs) or hydrochlorofluorocarbons (HCFCs) to worry about. A pound of CFC or HCFC in refrigerant-based A/Cs contributes as much to global warming as 2,000 pounds of carbon dioxide. A typical residential size A/C has as much as 13 pounds of these refrigerants. The release of this much refrigerant is equivalent to burning more than 1,300 gallons of gasoline, or driving over 60,000 miles in a 2010 Toyota Prius. That's based on the Environmental Protection Agency's fuel efficiency rating for the 2010 Toyota Prius and on the standard of 19.5 pounds of carbon dioxide for every gallon of gasoline burned.

Traditional air conditioners use a lot of electricity to run the refrigeration cycle, but DEVap replaces that refrigeration cycle with an absorption cycle that is thermally activated. It can be powered by natural gas or solar energy and uses very little electricity.

This means that DEVap could become the most energy efficient way to cool your house whether you live in Phoenix, New York, or Houston.

NREL has patented the DEVap concept, and Kozubal expects that over the next couple of years he will be working on making the device smaller and simpler and perfecting the heat transfer to make DEVap more cost effective.

Eventually, NREL will license the technology to industry, "We're never going to be in the manufacturing business", said Ron Judkoff, Principle Program Manager for Building Energy Research at NREL. "But we'd like to work with manufacturers to bring DEVap to market and create a more efficient and environmentally benign product."

Explore further: Eye implant could lead to better glaucoma treatment

More information: Thermally driven air conditioning - www.nrel.gov/dtet/thermal_air_cond.html

Provided by National Renewable Energy Laboratory

4.3 /5 (44 votes)

Related Stories

Keeping cool using the summer heat

Jan 23, 2009

(PhysOrg.com) -- While most Australians are taking care to shield themselves from the harsh summer heat, scientists from the CSIRO Energy Transformed Flagship are working on ways to harness the sun’s warmth ...

Staying Cool Shouldn't Burn a Hole in Your Wallet

Jul 07, 2006

Air conditioning costs don't have to take a big bite out of a family's budget during the dog days of summer, says a Purdue University expert on refrigeration and air conditioning. There are a number of practical and inexpensive ...

NIST helps heat pumps 'go with the flow' to boost output

Jan 23, 2008

Air-source heat pumps typically deliver 1 1/2 to three times more heating energy to a home than the electric energy they consume. This is possible because heat pumps move heat rather than convert it from a ...

UC Davis challenge produces a better air conditioner

Aug 14, 2009

The first certified winner of the UC Davis "Western Cooling Challenge" is Coolerado Corp. of Denver. Recent federal tests showed that their five-ton commercial rooftop unit should be able to air-condition a typical big-box ...

Recommended for you

3D printed nose wins design award

7 hours ago

A Victoria University of Wellington design student is the New Zealand finalist for the James Dyson Award 2014 for his Master's project—a 3D printed prosthetic nose.

Engineering the Kelpies

8 hours ago

Recently, Falkirk in Scotland saw the opening of the Kelpies, two thirty metre high horse head sculptures either side of a lock in a new canal extension.

Technology on the catwalk

8 hours ago

Summer days bring thoughts of beach picnics, outdoor barbecues and pool parties. Yet it only takes the buzz of one tiny mosquito to dampen the fun.

Dismantling ships and the trajectory of steel

9 hours ago

Tell me how you dismantle a ship, and I'll tell how a region can prosper from its steel! This could be the motto of this master's cycle at ENAC during which the projects of two civil engineering students ...

User comments : 14

Adjust slider to filter visible comments by rank

Display comments: newest first

Sustainabilian
4 / 5 (2) Jun 22, 2010
This development sounds fantastic and may prove to be an important advance toward reducing our need for fossil fuels. But how long is it likely to take to make these new air conditioners available commercially and secondly to result in a significant reduction in energy usage?
Tuppu
not rated yet Jun 22, 2010
Can it be used to heating? I'm living in very cold country, so this inventment would save lot of energy. Normal straight electric heating system in new 100 m^2 house uses 10 - 20 MWh in one year.
fleem
5 / 5 (1) Jun 22, 2010
Dust is already a big problem even for conventional cooling. It seems this would need far better filtering and filter maintenance to protect the salt because, unlike a conventional evaporator coil, you can't just spray it with a hose to clean it--it would wash away the desiccant salt. Still, it'll have some cool applications.
Bob_Kob
1 / 5 (1) Jun 23, 2010
I guess you would just have to replace the salt periodically.
bottomlesssoul
not rated yet Jun 23, 2010
I guess you would just have to replace the salt periodically.
I notice that there is no mention of recycling the desiccant. How is the water finally purged? I expect the cooling efficiency isn't so special when this is accounted for.

Still, if in the end it's the same efficiency as CFC technology this would be a great new replacement.
Neurons_At_Work
5 / 5 (1) Jun 23, 2010
I've been following this sort of technology for at least twenty years, in one form or another. The earliest I recall was a Japanese system that actually ran the salt solution over black corrugated metal plates mounted to the roof in direct sunlight to drive off the collected moisture.
The desiccant is indeed recycled, first pulling moisture out of the airstream and going from a strong to a weak solution in the process, then being pumped through a gas-fired boiler to drive off the collected water. They've been trying to use solar for years, but the required temperature vs. cost could never be satisfied. It is fundamentally a fascinating system, both efficient and safe, using only a suitable heat source, pumps, fans, and a brine solution, but no compressor or high-pressure refrigerant. Incidentally, I live in Phoenix and so am intimately familiar with the 'joys' of conventional 'swamp cooling' in the middle of August. I really wish they'd perfect this- 300/month electric bills suck.
Neurons_At_Work
5 / 5 (1) Jun 23, 2010
Can it be used to heating? I'm living in very cold country, so this invention would save lot of energy. Normal straight electric heating system in new 100 m^2 house uses 10 - 20 MWh in one year.


The answer is no, unfortunately. But, I would search for anything other than electric heat--the most inefficient form there is. If it's very cold, conventional heat pumps are out, but you might consider a geothermal heat pump, although they are pricey. Also, gas heat is cost-effective in many areas--more so than oil, in my opinion. Another thought is using one or more 'trumbe walls'. This is a passive heating technique. Also, solar thermal air or water systems with a large heat storage medium like river rock in an insulated pit can also reduce your heating costs, as long as you have substantial cloud-free conditions. Think outside the box, and do your research, and you might just find something that works within your budget and level of expertise...
xponen
not rated yet Jun 23, 2010
I guess you would just have to replace the salt periodically.
I notice that there is no mention of recycling the desiccant. How is the water finally purged? I expect the cooling efficiency isn't so special when this is accounted for.

"The membranes in the DEVap A/C are hydrophobic, which means water tends to bead up rather than soak through the membranes. Imagine rain falling on a freshly waxed car. That property allows the membranes to control the liquid flows within the cooling core." -mentioned in the article.
GSwift7
2.3 / 5 (3) Jun 23, 2010
"making the device smaller and simpler and perfecting the heat transfer to make DEVap more cost effective"

Don't get excited. If this thing costs thousands of dollars, and saves me five hundred dollars a year on electricity and needs replaced every couple years then I can't use it.

If this technology even gets close to being actually feasable, then you'll see an entirely different sort of news release than this one. You'll hear an announcement that company XYZ has announced the construction of a new production facility and plans to begin production by the XYZ Quarter of XYZ year. With current government subsidies for green appliances, they must not even be close to the point where this thing will work, or they would be making them already.

You have to read between the lines, but my guess is that it costs too much and doesn't last long enough. It may even need constant adjustment and maintenance in order to work well, and who wants to have to work on the A/C all the time?
xponen
not rated yet Jun 23, 2010
Don't get excited. If this thing costs thousands of dollars, and saves me five hundred dollars a year on electricity and needs replaced every couple years then I can't use it.

"Advanced liquid-to-air contactors have been developed that contain the desiccant without mist eliminators. This is a critical advance that eliminates the maintenance traditionally associated with liquid systems, making possible their broad application as packaged systems. These contactors further improve on the industrial state-of-the-art in that they can be mass manufactured, provide the same dehumidification at a fraction of the pressure drop, and incorporate independent cooling and dehumidification in one air-conditioning component to simplify and reduce the cost of the system."- another article.

I'm optimistic. I don't think it require a constant maintenance or is expensive. They said; this thing can be mass produced.
jimbo92107
not rated yet Jun 23, 2010
This doesn't appear to be a fragile or expensive technology. If their efficiency numbers are real, then it should be produced.
DaveGee
not rated yet Jun 26, 2010
We should all remember this is all being done by a government agency of researchers and as they stated above "We're never going to be in the air conditioner manufacturing business"...

I find this a positive. Remember, government run/sponsored agencies have never been known for producing the most cost-effective solution and I'd be very surprised if the talent they have at their disposal are suitable to be entrusted with 'getting the costs down'.

After all, that's what the private sector is supposed to be for... and in their statement it's quite clear they are making plans to get this out to the private sector under some form of licensing agreement. My only wish is this technology is made available to all interested parties... Which I'm expecting to be the case. I just don't wanna see 'insert some AC giant' being the only one invited to the party.
DaveGee
not rated yet Jun 26, 2010
Actually.... I'd be much more comfortable if the companies that do get involved aren't 100% AC manufactures. Somehow I'd be somewhat skeptical of 'Carrier' or another 'ac is ALL we do' being put in charge of this... Call me a conspiracy crackpot if you must but I could see 'old stalwarts' being less than enthusiastic about a total reboot on the AC market.
Shootist
1 / 5 (2) Jun 27, 2010
Actually.... I'd be much more comfortable if the companies that do get involved aren't 100% AC manufactures. Somehow I'd be somewhat skeptical of 'Carrier' or another 'ac is ALL we do' being put in charge of this... Call me a conspiracy crackpot if you must but I could see 'old stalwarts' being less than enthusiastic about a total reboot on the AC market.


It seems the "creative destruction" mechanism of highly regulated Capitalism is broken. But be of good cheer, all the large multi-nationals, like BP and GE, are firmly behind cap and trade.

You gotta wonder why.