Comfort At Work: Case Study

Cerro La Silla, Chile -- The light gathered by the 3.6-meter telescope atop this parched mountaintop has traveled so far it may be the faint signature of a star that no longer exists. So why, asks Manuel Silva, ruin its journey in the last 15 meters?

This was Silva's problem to solve: Without an adequate cooling system, heat escaping from the telescope dome when it was opened at night would distort the light that had traveled thousands of billions of miles to reach the earth -- much the same as heat waves rising from an asphalt road distort the image of oncoming traffic.

The light-gathering power of four Carrier-cooled telescopes will be combined to create the world's most powerful telescope at Cerro Paranal, Chile.


Silva, an engineer for Interma, Carrier's former distributor and a valued customer in Santiago, solved the problem so effectively he and Carrier Chile have developed a reputation as Chile's telescope cooling experts. The skills he demonstrated at La Silla helped Carrier win the recent contract to cool the world's largest array of telescopes now under construction at Cerro Paranal, about 650 kilometers north of here.

The telescopes at Cerro Paranal will be cooled by three, 23XL screw chillers manufactured in Syracuse, N.Y. Besides their efficiency, the screw chillers also were chosen because of their low vibration levels. As anyone who has used a pair of high power binoculars knows, even small movements are magnified by an optical device. Imagine the multiplication when the object you're looking at is 10 million light years away.



Silva's design for the large La Silla telescope discharges some cool air directly under the telescope's 3.6-meter-wide mirror at floor level; the rest of it flows up through snake-like insulated ducts toward the dome's ceiling.
There are other new Chilean observatories still under bid that have Carrier chillers in their sights, as well, says Alfredo Rodriguez, general manager of Carrier Chile.

Both Cerro La Silla and Cerro Paranal are operated by a consortium of European nations under the umbrella of the European Organization for Astronomy. The ESO, or European Southern Observatories, are located in the Atacama Desert for good reasons. The Atacama is the driest place on earth. The frigid Humboldt Current just off Chile's Pacific coast cools the prevailing westerlies and reduces the air's ability to hold moisture. Once the air is reheated, its relative humidity plunges. The result is more than 300 cloudless nights a year at La Silla and 350 clear nights at Cerro Paranal. And since there are no major cities nearby, there is no haze, no air pollution and no light pollution.

The dirt road to La Silla blends perfectly with the dun-colored plain and the mountain on which the telescopes sit. A herd of shaggy, brown, free-range goats crossing the road would be almost invisible if their hooves didn't create little explosions of dust. There is so little vegetation, you wonder if the goats have somehow learned to eat rocks. The only contrasting colors are black condors circling on thermals in an almost azure sky.

The other contrast is between the desert's rawness and the sparkling mountaintop technology that lets astronomers probe the mind-numbing mysteries of the cosmos. Silva displays a parental concern about the largest of La Silla's telescopes.

"How could we spend so much on a wonderful building and telescope like this and then 'destroy' the information in the last 15 meters?" Silva asks. "My mission was to design and install a system that would keep the air temperature inside the dome the same temperature as it would be outside the dome at night. Only then could the dome be opened without letting heated air escape."

The Atacama may be known for intense sunlight during the day, but radiational cooling at night quickly lowers the outside temperature even in the summer. That's why anyone walking around inside the actual telescope dome is usually wearing a jacket.

The chillers that cool the large La Silla telescope are isolated from the dome to minimize vibration.


The cooling system is designed for the telescope, not for the astronomers," Silva quips. "Of course, all the astronomers work in control rooms outside the dome, so the low temperature doesn't really matter. The control rooms are air conditioned by Carrier, too, so the astronomers have the best of both worlds."

Using historical weather data, the dome's daytime interior temperature is based on projections of what the exterior temperature will be that night. When the dome is opened, Silva says, there is rarely more than a degree or two of temperature difference. That wasn't as easy as it would seem since the distance from the dome's floor to the ceiling is an uninterrupted 15 meters. The temperature difference between floor and ceiling used to be seven degrees Celsius. To reduce temperature stratification, Silva's design discharges some cool air directly under the telescope's 3.6-meter-wide mirror at floor level; the rest of it flows up through snake-like insulated ducts toward the dome's ceiling.

When the Cerro Paranal telescopes begin operation in 2003, astronomers will be able to look further back in time than ever before.


The system, a 30-series chiller from McMinnville, Tennessee and two chillers from Carrier SA in Montluel, France, is operated by digital Carrier Comfort Network controls. The same Carrier Comfort Network also controls the heat exchanger that keeps the oil in the dome's hydraulic system at the right temperature. The hydraulic system moves the telescope and the 30-ton dome itself.

"There's an important difference between the astronomers and our Carrier system," says Silva. "The astronomers only work at night. The air conditioning works always."

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