June 30, 2008
Huge Ice Pack Keeps UA Cool: Very Old Principle Helps University Weather Summers
By Tom Beal, The Arizona Daily Star, Tucson
Jun. 30--It's 9:30 a.m. at the University of Arizona's Central Refrigeration Building on East Helen Street. The day is rapidly warming toward triple digits. Time to melt some ice.Plenty is on hand on this Thursday morning. Overnight, the plant's chillers have been pumping 17-degree antifreeze through 156 storage tanks that now hold 23,000 tons of ice.
At another site, at 640 N. Mountain Ave., 49 more tanks boost the ice total to about 30,000 tons.
The ice will be melted throughout the day and the chill transferred to 5.2 million gallons of water that circulates through 7 miles of pipes, collecting heat from 140 buildings on the UA campus.
Keeping campus cool requires chilling that water, and it makes sense to do that when it's not 110 degrees outside. Of course, nighttime is not when you need cooling, so the UA has begun storing its energy in ice.
Thermal-mass storage is not new; in fact, it's one of the oldest forms of heating and cooling. A thick-walled mud adobe home does much the same thing.
Freezing water at night and slowly releasing it during the day saves the university about $423,000 a year in energy costs.
It takes more energy to make ice than to simply cool water in a cooling tower, said Gordon Bush, senior staff technician for the UA's utilities division. But using energy during the day increases the university's "demand charge" from Tucson Electric Power Co.
Using ice to cool the water during peak times also means the UA doesn't have to run its cooling towers and its massive refrigeration units in daytime temperatures, saving energy as well as money, Bush said.
The ice farm and other refinements to the plant made since 2004 removed 375 kilowatts from the plant's electrical load, according to a Facilities Management report.
"It takes a little more energy to make ice than to cool water," Bush said. "If you can offset that, then it's a 'green,' good, viable thing."
Ice plants have been used to condition buildings since the early 1900s, Bush said. It's pretty much the same system used to cool some of Tucson's earliest buildings. Open your home to the cooler night air and let your thick adobe walls suck in the cool. Then lock up tight and let the walls keep the interior space cool throughout those summer days.
"It's exactly the same principle. You're just chilling mass and holding it," Bush said.
An increasing number of homes take advantage of daily temperature shifts, said Al Nichols, a heating and cooling engineer.
Tucsonans with thick walls of rammed earth, adobe or straw bale can use the daily temperature shifts to provide most of their cooling.
Nichols, who now relies on a well-insulated house and efficient cooling at his Civano home and office, said he misses the old days when he'd run his air conditioner for about three hours and let the thick walls of his stuccoed straw-bale home take care of the rest of the day.
Thermal mass allows you to even out shifts in temperature, Tucsonan Rich Michal said.
"Our average temperature swing is in the range of 30 degrees," Michal said. "Anything you can incorporate to take advantage of that phase change is smart."
Michal said Thursday's cooling rain gave him the opportunity to open up his Civano house -- which he built as an experiment in heating and cooling systems -- and store the cool night air in his walls for use throughout the day Friday.
Thermal mass storage gets little respect, said Bob Gilby, whose home at Milagro Co-housing is built from 16-inch adobe blocks and is designed to cool at night.
He recently lost a battle with the state Department of Revenue, which rejected his claim for a tax credit for the purchase of an energy-efficient home, even though his highest electric bill is $80, and he uses no energy to heat and cool his home for most of the year.
Bush, who was project director for the ice farm at the UA, knows the feeling. New technologies such as solar get all the glory, he said, while his low-tech refinements do all the work.
Since Bush's division was assigned by UA Vice President Joel Valdez to trim energy costs eight years ago, it has held those costs constant while adding more than 2 million square feet of office, lab and classroom space, Bush said.
Bush is a proponent of new forms of "green" energy technology, but he said you often can accomplish the same goals by making your existing systems more energy-efficient.
--Contact reporter Tom Beal at 573-4158 or [email protected]
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