When it comes to home comforts, few inventions can beat the air conditioner for its ability to help us tolerate the dog days of summer. The problem is, when it comes to energy-guzzlers, few inventions can beat the air conditioner.
But the National Renewable Energy Laboratory has invented a new air conditioning system that uses 50 to 90 percent less energy than the best available units. The Desiccant-Enhanced eVaporative air conditioner -- DEVap -- combines membranes, evaporative cooling and liquid desiccants in a way that has never been done before.
NREL mechanical engineer Eric Kozubal, who co-invented the system, says the goal is to revolutionize cooling while removing millions of metric tons of carbon from the air. It cools and dries the air in one step. Evaporative cooling, blowing air across a wet surface to promote evaporation, has long been used in swamp coolers, as Technology Review notes. The DEVap takes it a step further, dividing air into two streams that are separated by a polymer membrane.
Water passes through one airstream, making it cooler and wetter. The cooler air cools the membrane, which cools the air on the other side, without making that side any more humid.
Another process dries the air, making the system effective even in humid locales -- a big step toward reducing refrigeration-based air conditioning, which is used in most of the country and is responsible for about 5 percent of the nation's energy consumption.
The DEVap uses a liquid desiccant, a solution of lithium chloride or calcium chloride, which is about 44 percent salt by volume. Most people know desiccants as those little packets of yellowish balls that come in boxes of shoes or new clothing.
In the DEVap, another membrane separates the desiccant from the rest of the air, and allows water vapor to pass through its micrometer-sized pores. The desiccant pulls moisture from the airstream, leaving dry, warm air. Then, in a second channel, water evaporates to cool a second airstream, which cools the first, dry airstream. The result is cool, dry air.
The idea of combining evaporative cooling with desiccants isn't new -- it's just that nobody has figured out how to do it cheaply and efficiently until now.
The process uses much less energy than a traditional air conditioner, and doesn't rely on any refrigerants, which produce chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFC). That also helps the environment, because a pound of CFC or HCFC in refrigerant-based A/Cs contributes as much to global warming as 2,000 pounds of carbon dioxide, NREL says.
so when can I buy one?
First as an ME, I want to say good job, and I hope it pans out to be a robust product.
However, how do they remove the excess moisture from the desiccant? I work in an industry that uses desiccants (albeit the low tech ones) a lot and we have to bake-out our desiccant to re-use.
I wonder what the delta T is for the cooling. This is one of the problems with the tank-less water heaters. If you live in a cold climate, the system needs some sort of auxiliary heating to get the water temperature up. Similarly, heat pumps with-out auxiliary heating do not work well when it gets really cold either.
Well it won't be "removing millions of metric tons of carbon" per se, but it certainly will "prevent" it.
But I don't think we can just use calcium chloride or lithium chloride just like that. These substances are mildly toxic to people and may have their own environmental consequences as well. A few good tests are needed and possible improvements to compensate.
Overall, it's a good device and would be a nice upgrade to our homes. I just hope it can handle the same workload.
Ugh, how can you have such an great article with no working prototypes to show or an ETA. I want to know when this may hit the market! .. sounds awesome though, hope it really works like said here. I'm all for improving current technologies to be both greener and apparently cheaper too? can't get better then that.
"These substances are mildly toxic to people and may have their own environmental consequences as well"
So is Clorox and a myriad of other products we use in our homes already.
Calcium chloride is already used in many different ways in industy: as a dessicant; swimming pool additive; road de-icer; water treatment; fire extinguisher; blast furnaces; fabric softeners; additive in plastics; additive in concrete.
It is also considered safe by both the EU and US as a food additive (estimates put average consumption at 160-345mg/day), where it is used in things such as: sports drinks; preservative in canned vegetables; pickles (reducing soium be keeping saltiness); caramel in chocolate bars (prevents freezing); tofu; making brie and stilton cheeses; brewing beer.
And it has uses as a pharmacuetical for things like: treating hypocalcemia (direct intravenous injection); treating black widoe spider bites, and others; treatment of hives; magnesium intoxication; cardiac resucitation, particularly after open-heart surgery; lower dangerous levels of potassium.
These are some of the things it already used for, and I would say it is pretty safe- unless you rub the anhydrous form on your skin or eat it. But there are so many things we have used for such a long time that require similar precautions. Some of the things that should be ingested are gasoline, Clorox, anti-freeze, and deadly nightshade (okay, so that one isn't that common). And there are a bunch of things you don't want on your skin for very long, like gasoline, Clorox, potassium, sodium, or fire. And don't breathe chlorine gas, phosgene, too much carbon monoxide, gasoline vapours, or water. It all takes common sense.
I do think this is a really "cool" idea (pun intended) and, as usual, wish that the neat things I read about had more information about timeframes for production, commercial viability, and eventual cost. But it's still great reading about it.
Everyone have a great day!
I googled NREL, which turns out to be a "think tank", which is never going to manufacture anything, but say that they will license it in the "future".
Here is a link with a more complete description straight from them.
I love this kind of inventions that are clearly going in the right direction. I really think we will ultimately save the planet through such innovations!
This is just an evaporative cooler combined with dessicants. They're not that uncommon and they've been around since medieval times in one form or another.
The specific heat of vaporization for water is 2.26 MJ/kg. If the air is at less than 100% relative humidity water may evaporate and in doing so cool the air.
If the air is close to saturated with water vapour on the other hand you can't cool the air as much as you want. Adding a lot of water to air has implications for mold growth and other nasties so there are limits to how high you want the relative humidity to go.
This system uses dessicants to suck some humidity out of the air before putting it back in by evaporating water; this way you can use evaporative cooling even when the air is very humid.
It takes energy to get water back out of the desiccants. It would be a waste to use electricity to produce heat, so it probably comes from burning gas. This is the energy they are comparing to the electricity consumed by an electrical heat pump.
If you live in a place like California, you probably don't need the desiccant but water use may be an issue(it's not that huge; it's in the single or low double digit gallons per day range). If you live in a place like Florida you definitely need the dessicants(and a lot of energy to bake the water out of the dessicants).
Note that there also are a couple of indirect evaporative coolers on the market. These never add moisture to the intake air.
Indirect evaporative cooling first takes in air and cools it by evaporating water; then they pass this cool humid air through a counter-flow heat exchanger. This heat exchanger heats the humid air back up and exhausts it outside the building simultaneously as it cools intake air and brings it into the house or appartment.
We absolutely need better cooling tech for future automobiles. I can just imagine how turning on the A/C in the middle of a hot Texas summer is going to suck the juice out of an electric car.
Coolerado has this one beat already and without cumbersome desiccants. They are on the market and performing even as we speak. They have achieved temperatures below wet-bulb and approaching dew point with the Maisotsenko Cycle. A distinct technology from two-stage or indirect evaps. This will be the ac of choice in dry climates soon.
Another A/C unit that cools / cheaper better than the average A/C unit only runs after dark during the cool of the night. The cold is stored as frozen water. Then the building is cooled during the day by runing air around the ice.
Plus several companies now offer solar panels to go with their A/C units to generate their own electric power adding zero CO2 to air to power the A/C unit.
After living in ElPaso for several years, about 3 days a year were so humid as to be uncomfortable. Office buildings mainly run refrigerated air, homes use 'swamp coolers', in general.
Out there a solar powered desiccant dryer would be really appropriate. Just something that doesn't take some of our otherwise stored power (in whatever form, gas, electric, etc) to provide the heat to dry the desiccant. And it would be a double win if the water could be retrieved in liquid form (not just boiled off into the air -- water is a commodity to be conserved in the desert).
I just purchased some 'solid desiccant' sold at WalMart to keep closets dry (we don't live in the desert now). You un-seal the package, put it in your closet or where ever you normally have a 'closed space' and it will remove a cup or two of water over the next month or so, without additional power. I would just like to find a good way to 'recycle' the desiccant without throwing it in my oven for several hours.
I could see real benefit to their methodology. When I moved to West Texas, I was really surprised as to how effective 'swamp buckets' were in cooling a house (open the window in the room you want to be cool, close it in the others!)
Oh on the desiccant, it is 'anhydrous' by nature. Hydrated desiccant is 'used' desiccant and needs to be dried (made anhydrous or 'without water') before it could be used again.
So an effective dryer (especially if it could be solar powered) to capture the water expelled in the process would be a real win!
This is great news for those who are budget conscious. I am grateful we have such scientists ready to tackle and overcome problems. Thank you! :)
Looks like a great new technology. Anything to increase the chances of saving energy especially in our homes is a good thing!
What is the ideal climate for this air conditioner to work efficiently?