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Scant months after the Great Blackout of 2003, the Audubon Society unveiled in Los Angeles a demonstration site of a prime solution to the problems of the shaky electric grid and the relentless demand for electric power: solar-absorption air conditioning, a technology that runs completely on the free energy of the sun.

The Audubon Society has chosen Los Angeles's Ernest Debs Regional Park, northeast of downtown L.A. and overlooking the Pasadena Freeway (the first freeway built in the United States), as the site of the organization's first urban nature center. The $15.5-million park project will create the Los Angeles Audubon Nature Center on a 16-acre parcel, which will house nature exhibits, an amphitheater and a hummingbird garden, within the refurbished 282-acre Debs Park, which will enjoy a new network of hiking trails leading up from the old freeway and other new features. If successful, the Audubon Los Angeles Nature "Discovery Center" -- a 5,026-square-foot facility devoted to ecological experience, enjoyment and education -- will be followed by some two dozen new urban nature centers in other cities nationwide. The Nature Center represents about a third of the park project's cost.

The use of a fully solar-powered air conditioning system in a new urban nature center meets several goals of today's broadbased environmental movement, including the encouragement of clean energy technologies and a greater big-city presence that brings nature to people who cannot easily leave the cities to travel to nature. The Audubon Nature Center, according to the solar AC system's designer, James Bergquam of Bergquam Energy of Sacramento, will be the first completely solar-cooled building in southern California and one of only a handful in the world, the others being in Sacramento (where Bergquam has built two demonstration systems), Germany, Japan and China.

The new $90-thousand, 10-ton Los Angeles system utilizes an 800-square-foot array of 408 Chinese Sunda vacuum tube solar collectors, six-and-a-half-foot (2,000 mm)-long and nearly four-inch (100 mm)-diameter glass tubes, each enclosing a copper heat pipe and an aluminum nitride absorber plate (with a selective coating) that absorb the solar radiation. The Sunda tubes operate on a heatpipe principle: low-pressure water always present inside the tubes is heated to a vapor that flows up to the copper condenser section of the tube, a sleeve that protrudes from the condensor section of the internal heat pipe. This heats water flowing through the manifold that connects all of the tubes, transferring thermal energy from the collectors to the 1,200-gallon insulated high-temperature hot water storage tank. When the stored water reaches a minimum of 180 degrees F. (it can reach 192 degrees F.), hot water from the tank is pumped through the generator in a Yazaki 10-ton single-effect absorption chiller. A lithium bromide salt solution in the chiller boils and produces water vapor as a refrigerant that subsequently is condensed; its evaporation at low pressure produces the cooling effect in the chiller. This is transferred to the interior of the Audubon Nature Center by chilled water that is pumped through the evaporator in the chiller and then through fan coil units in the building. The internal air in the building is blown across the coils that contain the chilled water, providing the interior cooling.

The system also will provide space heating in the winter on any days cool enough to require that, and hot water throughout the year. The 10-ton absorption cooling system costs approximately $90,000 or $9,000 per ton.

The third main component in the system is a Marley cooling tower.

For the chiller, the nominal generator temperature is 190 degrees F., the cooling water inlet temperature is 85 degrees F., and the chilled water outlet temperature is 48 degrees F.

A small amount of electricity is required to run the pumps that move the chilled water and hot water, and run the fans -- and this too is completely solar-powered, with some of the electricity from the new center's 25-kilowatt (kW) solar-photovoltaic system (more than 200 crystalline-PV panels) and battery bank that also powers the building's lights and electrical equipment.

The most significant aspect of fully solar-powered air conditioning is its capability of providing the service most in demand on the very hot days that most tax the electricity grid without using the grid: interior cooling. The same high solar insolation and hot weather that makes air conditioning the greatest contributor to peak electricity demand (and the occasional subsequent brownouts and blackouts) provides the greatest amount of energy to the solar AC technology. "The matter of peak-load power demand should be a top priority of every politician following the wake-up call of the big blackout of 2003," suggested Ken Bergquam, a member of the Bergquam Energy team, as he looked down from the nature center's roof as he and two colleagues neared the completion of the Audubon installation. The unique aspect of the solar air conditioning system is that it displaces 15 kilowatts of peak demand for a 10-ton system. The comparative advantage over an electric compression HVAC system is that the energy is paid for upfront as part of the package; therefore, the Center is not affected by rising peak-demand energy cost. The Audubon Center's electric energy cost rates are fixed for the life of the system -- the energy is free. The system uses only .4 kW per ton of electricity to operate compared to the 1.6 kW-per-ton electricity consumption of compressor-type air conditioning -- very significant since air conditioning consumes 40 to 60 percent of the energy used in buildings. An added bonus: the solar panels provide added insulation to the roof, while also reducing the air conditioning load by 20 percent and extending the life of the roof.

Les Hamasaki, president of SUN Utility Network of Los Angeles, the western-U.S. distributor of Sunda Tubes, whose strategic alliance with Bergquam brought the solar AC technology to Audubon's attention, elaborated, "Peak-load demand is the critical part of assuring reliable energy supply, and air conditioning is the critical part of peak demand. The only thing connected to the grid here at the Audubon Center is the water, necessary to conform to the local fire regulations. The key to energy security is distributed, onsite self-generation; this will make our state and country more independent from rising energy costs and will lessen the load on the electric grid. The public sector should be an integral part of the overall 21st-century strategy of solar energy as the backstop of the traditional electricity grid.

"Solar thermal, especially used for air conditioning, should have a buydown rebate similar to the solar electric photovoltaic buydown program. When comparing the cost of solar-electricity versus solar-thermal air conditioning, one producing electricity and the other displacing the electric load, solar AC would come out as more cost-effective even without rebates," Hamasaki continued. He has proposed to the Los Angeles Department of Water and Power that solar air conditioning, since it displaces peak load demand, should receive the same rebates as photovoltaics. "The same 15-kW photovoltaic system would cost approximately $150,000 or $10 per watt installed. The 15-kW displacement achieved by use of solar AC costs approximately $90,000. With a $6,000-per-kW rebate, or 80% of the installed cost, the system would cost only $18,000."

Bergquam Energy in Sacramento has used other kinds of solar collectors for solar HVAC applications, including a 1,600-square-foot array of flate plate solar collectors driving a 10-ton single-effect absorption chiller on a 10,000-square-foot commercial building, in continuous operation since 1985, and a 1,200-square-foot array of parabolic trough, one-axis tracking collectors driving a 10-ton single-effect absorption chiller on an 8,000-square-foot commercial building, installed in 1995 on a contract with the California Energy Commission (reinforced since 1998 by the addition of a 1,100-square-foot array of direct-flow 336 vacuum-tube collectors). Bergquam's experience with these collectors has demonstrated that the direct-flow vacuum tube solar collectors are the superior technology for solar HVAC applications, offering a combination of high-efficiency, simplicity and freeze and over-temperature protection. Flat plate collectors generally are not suitable in these applications, due to their low efficiencies, and because their freeze protection is expensive and/or not reliable. Parabolic trough collectors have high enough efficiencies, but their tracking mechanism is an added expense, and there are maintenance and service requirements for both the tracking device and keeping the reflecting surfaces clean. A nice feature of the vacuum tubes is that they can be removed and replaced without affecting the operation of the array.

The Audubon Nature Center has just received from the U.S. Green Building Council (www.usgbc.org) the highest -- i.e., the greenest -- 'Platinum' LEED rating for "Leadership in Environment and Environmental Design." The Audubon Nature Center in Los Angeles is a U.S. Green Building Council LEEDTM (Leadership in Energy & Environmental Design) 'Platinum' building, because it is 100% solar-powered, uses 80% less water than a conventional building of the same size, incorporates an on-site waste water treatment system, and utilizes other sustainable technologies, strategies and designs, including passive solar "bioclimatic" architecture. The Audubon Center is located at 4700 North Griffin Avenue in Los Angeles (use the Ave. 43 exit of the 110 Freeway between downtown Los Angeles and Pasadena).

Reprinted from Heating, Ventilation, Air Conditioning & Refrigeration News (www.HVACRNews.com), December 2003.