So given these conditions, it will come as no surprise that researchers led by Peter McGrail out of the Pacific Northwest National Laboratory have been working a new porous nanomaterial that improves an existing process used for refrigeration and air conditioning called adsorption chilling.

Image courtesy colmaccoil.com

All refrigerators and air conditioners make the environment cooler by creating phase changes in a refrigerant so that the chemical absorbs heat.  Most familiar air conditioners use electrically driven compressors to mechanically compress the vaporized refrigerant, whereas adsorption chillers use heat to condense the refrigerant. Evaporated refrigerant “adheres to a surface of a solid, such as silica gel. The silica gel can hold a large amount of water in a small space—it essentially acts as a sponge for the water vapor. When the gel is heated, it releases the water molecules into a chamber. As the concentration of water vapor in the chamber increases, the pressure rises until the water condenses” (Bullis). When that happens, heat is absorbed out of the environment and the newly cooled people rejoice!

Image courtesy emissionless.com

Historically, bulky adsorption chillers have been more expensive and far less efficient to operate than chillers that use electrical compressors.  The flip side is that they are cheap to operate and, if you’re an industrial facility or power plant manager who has massive quantities of waste heat lying around, you can practically run them for free. That’s right people: absolutamente GRATIS.

The new material will make it easier to cool smaller buildings with solar water heaters or waste heat from generators by shrinking the hulking adsorption machines by 75% in size and cutting associated costs in half (Bullis).  Size and cost reductions could make adsorption chillers competitive with compressor driven chillers.

The researchers’ nanomaterial consists of “nanoscopic structures that self-assemble into complex three-dimensional shapes. It’s more porous than silica gel, with a larger surface area for water molecules to cling to. As a result, it can trap three to four times more water, by weight, than silica gel, which helps reduce the size of the chiller” (Bullis). The other interesting thing about the material is that it forms weak bonds with water molecules.  This is a good thing because it means less heat is required to free the molecules (or other refrigerants), making the process of adsorbing and desorbing water 50-100 times faster.

While the nanomaterial definitely makes adsorption chilling more attractive, it’s tricky to match the demand for cooling with the production of heat. For example, if you needed to run the chiller when the sun had set because you lived somewhere humid, you might need a heat storage system (and those can be expensive). Still, anytime things get more efficient a little fairy creature gets some wings!

WU XING:

Cited:

Bullis, Kevin. “Using Heat to Cool Buildings.” Technology Review Online. 03/30/11. Accessed 06/29/11. URL.

The material on which I intend to focus today is water in solid form, commonly known as ice.  You may have seen the substance lurking as chunks in your super-large coke, or possibly it has formed, dagger-like, on the eaves of your house in winter.  But did you know that ice can be used to save money on cooling costs all year long?

Image courtesy www.agrichill.com

During normal working hours (9-5) almost everyone uses his or her air conditioning system to cool buildings, which means the demand on the grid is the greatest.  Power companies charge the most money per kilowatt hour at this time of day because it strains the system to meet the demand, and because they can do what they want.

Thermal energy storage (TES) systems take advantage of changes in temperature over the diurnal cycle, storing energy in a thermal reservoir for later reuse.  The systems perform well in commercial and institutional buildings, whose peak energy demand occurs during daytime hours and drops off precipitously at night because everyone has gone home.  The thermal reservoir may be maintained at a temperature above (hotter) or below (colder) than that of the ambient environment, but today I’m writing about ice chiller TES.

Photo courtesy Greensource Magazine

The most widely used form of this technology is in large building or campus-wide air conditioning or chilled water systems. “In this application a relatively standard chiller is run at night to produce a pile of ice. Water is circulated through the pile during the day to produce chilled water that would normally be the daytime output of the chillers” (Source: Wikipedia).  Ice storage systems surprisingly inexpensive; full storage systems are often priced competitively with conventional air conditioning designs.

Baltimore Aircoil Company, out of (you guessed it: Baltimore, MD) is one of the nation’s leading manufacturers of TES systems.  They make ice-chillers “out of serpentine steel tubing that has been galvanized to protect against corrosion. The tubing rests in an R-18 insulated tank and can produce between 237 and 761 ton-hours of ice (one ton-hour equals 12,000 Btu), but much larger custom units are also available” (Greensource Magazine).  The ice chillers take the form of enormous metal-clad boxes (although I’ve seen some systems that get partially set into the ground).  But even though they’re not exactly attractive, if you’re using them they’re probably saving you money and that’s a beautiful thing.

*UPDATE – 07/29/10

I recently heard from another producer of Thermal Energy Storage Systems – CALMAC.  According to a representative, CALMAC’s technology can store renewable energy overnight to reduce next-day cooling costs by 40%.  The technology was recently employed at the Bank of America building at 1 Bryant Park, which acheived a LEED platinum rating.

WU XING:

Ice chillers use frozen water to chill the air, reducing energy consumption.  Therefore, I’ve filed them under Water and Fire.

Cited:

“Ice Chiller Thermal Energy Storage.” Greensource Magazine.  Accessed 07/19/10.  URL.

“The wheel in the sky keeps on turnin’ / I don’t know where I’ll be tomorrow”

Well, okay, I mostly know where I’ll be tomorrow (at the office) but there are a few hours between work and going to sleep tomorrow night that I’m going to play by ear.

Image credit www.moonbeammcqueen.wordpress.com

So now onward to our highly anticipated wheel discussion.  I’m going to assume that the readership of this blog are all pretty fond of wheels due to the fact that wheels make moving things around much easier.  You can use our round and spinning friends to shift people, animals, vegetables, and even minerals.  One thing you might not be using a wheel to move right now is air – but as it turns out, you could be. 

Image credit Airxchange

Airxchange out of Rockland, Mass. has developed an Energy Recovery Wheel designed to supply and humidify/dehumidify fresh air to buildings without simultaneously leaking out all of the inside air that has already been heated or cooled.  “Airxchange energy recovery wheels rotate between the incoming outdoor airstream and the building exhaust airstream. As the wheel rotates, it transfers a percentage of the heat and moisture differential from one airstream to the other. Consequently, the outdoor air is ‘pre-conditioned’ significantly reducing the capacity and energy needed from the mechanical HVAC system.” (Source: Airxchange). 

Images courtesy www.Airxchange.com

LEED and other Green Building protocols award points for increasing natural ventilation in buildings and reducing the energy consumption of HVAC systems.  Airxchange claims that conditioning outdoor air can represent 40% of an HVAC system’s capacity, and that the pre-conditioning ventilation provided by an Energy Recovery Wheel will reduce the load on the system by 70%.  It seems like preconditioning the air with the wheels could make a significant difference.  Does anyone have any experience with the wheels? Hit up the comments!

Airxchange wheels are available in a wide range of sizes for a variety of mechanical systems and come with a five-year warranty. The silica gel desiccant that removes humidity from the air is permanently bonded to the energy transfer media for durability; and cleaning or replacement takes about 15 minutes.  I found a nifty article that explains what’s involved with Energy Recovery Wheel Maintenance.   

WU XING:

I have categorized this under water and fire because it involves dehumidification and air conditioning/temperature changes.

Cited:

“Energy Recovery Wheels.”  Product Roundup.  GreenSource Magazine.  o6/30/10.  Accessed 07/01/10.  URL.

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. 

Cited:

“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.