‘Cool it, sunshine’

 

BY BOB “hot rod” ROHR,

contributing writer

 

What a great way to put solar energy to work, keeping people and places cool. Think about when we need cooling the most. Generally the hottest, sunniest days present the highest cooling loads to our buildings. What a great match-up for solar energy: leverage the energy for heating in the winter months, and cooling during the summer. The buzz is in the air and products are showing up on the market to accomplish this on commercial and residential levels.

 

But thinking about it, we actually do solar cooling on a very large scale now. Most of our largest solar power generation sites are located in the sunniest and warmest locations. Solar power plants, Nevada #1 & # 2  supply the Las Vegas area with electrical power via cps (concentrated power solar.) A new thermal solar power plant is coming on-line in Arizona. Nellis Air Force base in Nevada has one of the largest PV arrays in North America. Individual businesses are adding large solar arrays to help power lighting and cooling loads. So in an indirect way, solar cooling already is in place. In fact some of our solar power generation stations have been running non-stop since the 1980s.

 

New technology is being implemented to store the super heated fluids from cps. One way to do this is to park the thermal energy in brine solution or a salt bed. This would allow the thermal energy to be used in the evening hours. Six-hour storage is already on-line, seven-hour is on-line in Europe and 12-hour storage is in the design stages for North America generation stations. Wind-powered energy is coming on-line at a strong rate in the United States, too. Large wind farms are up and running in the sunbelt states. Canada, with about the same land mass as the United States, is looking into wind energy to provide power to their 32 million people and export excess wind energy to American consumers.

Solar roofing and facades could supply on-site energy to power small cooling loads. Check out this “solar tree” from Italy. It powers a ground source heat pump housed inside the structure.

 

If this technology excites you, consider subscribing to Sun & Wind Energy magazine. Check it out at www.sunwindenergy.com. It is now a monthly subscription and they keep a finger on the pulse of these technologies worldwide.

Solar heating and cooling was installed in 2006 at Cochise College in Arizona. Parabolic trough collectors, 6,800 square feet of them, collect and store the thermal energy at 260° - 280°F in a 7500-gallon tank. Abengoa Solar, a Spanish company, built and installed the system. The system heats and cools the building winter and summer. Energy Concepts provided a 60-ton ammonia cycle absorption chiller.

 

Abengoa Solar will build the world’s largest solar power system near Gila Bend Arizona, able to supply 70,000 homes. (www.abengoasolar.es/en/our_projects/usa/arizona/index.html)

 

Other schools are looking at solar as a means to provide energy. Los Angeles Community College is planning to have all nine campuses off the grid and produce its own power. More and more building owners are looking at alternate energy.

Cooling homes with equipment powered by solar thermal panels is getting a lot of attention. Three technologies are being developed. Many of us are familiar with absorption cooling. Absorption chillers use a thermal compressor instead of a mechanical one. This is the technology used in RV refrigerators, for example. Small IP bottles typically power refrigerators on the rv. Large-scale absorption has been around for many years. Cities like New York — with district steam — actually run large commercial cooling projects with their district steam infrastructure.

 

Thermafrost of Canada is working on a small two Kw cooling unit, based on an ammonia salt solution.

 

Adsorption chillers (ADCH) are also being studied. Adsorption uses water as the cooling medium, and silica gel, in some cases, as the adsorbent. Germany and Japan seem to be taking the lead on developing these products. On the residential side, InvenSor of Germany has adsorption cooling units in the 5- 50kw range currently available. These are said to work with a fluid temperature in the range of 113°F, well within the reach of solar thermal flat panels. (www.invensor.com)

Climate Well of Sweden has 150 or so cooling units installed on single-family residences in Spain. They are expected to double their installations this year.

 

Open sorption is yet another technology being developed. This method cools the air, not fluid. One advantage of DEC (desiccant and evaporation) is the low 120°- 210°F driving temperature requirements. Www.ecn.nl has some good reading on this principle of cooling.

 

The Australian research institute CSRIO also is looking at DEC and expects to have a system for single-family homes to provide heating, cooling and SDHW.

 

On the home front, Solargenix has two parabolic trough systems providing cooling to homes in North and South Carolina. (www.solargenix.com)

 

You may recall the Servel gas- and kerosene-powered refrigerators, dating back to 1923. Incorporated in Indiana their slogan, “Serving Electric,” was shortened to Servel. For more than 30 years, Servel designed and built refrigerators. At the 1939 World’s Fair, it displayed the “All Year.” This was a residential gas air conditioner. In 1941, the two millionth Servel refrigerator was produced. During WWII, Servel built wings for the P-47 Thunderbolt. In the mid-60s, Servel introduced an air-cooled ammonia/gas fired chiller that could be used for ac or process cooling. The Robur Group of Italy took over the Servel gas air conditioning division in 1991. Robur Corporation was born in the United States with the purchase of the product line and manufacturing facility. In 1999, Robur introduced Servel chillers with a 30% performance increase due to their gax absorption technology. Watch for this company to be a player in solar-powered chillers and cooling equipment. (So we Americans are no strangers to this technology.)

 

Solar Panels Plus and a handful of other companies had some solar cooling equipment on display at ASHRAE/AHR this year in Chicago. Nice!

 

Solar cooling is still a bit more expensive than current methods. I think we will see this price drop as more manufacturers work to develop the equipment. Solar absorption cooling has been researched for 20 plus years now. It has been proven to be workable, but economics thus far have prohibited large-scale acceptance and use. I feel the new administration will do a lot to drive this technology to the mainstream over the next few years.

 

There is a huge advantage to being able to leverage solar thermal arrays for a year around load. The economics pencil out so much better when a consistent load is available. Maybe it’s time to breakout the old Servel refrigerators and power them with solar. These are interesting times for the solar cooling technologies. Hvac and hydronic contractors (roofers? electricians?) would be well served to stay abreast of solar cooling technology. This is the growth industry, my friend.