The mysterious workings of Stanford’s energy services are all in a day’s work for Robert Reid, energy services manager. But every day cars and bikes unknowingly roll right over an enormous underground tank where water is cooled and pumped out around the Farm for air conditioning. With the sun bearing down, Stanford thought we should learn just what goes on in the chilled-water and ice plants.
It works the graveyard shift.
Built in 1999 to augment the cooling capacity of the older chilled-water plant, the Stanford Ice Plant was, at the time, the third largest of its kind in the world. Ice is created during the night—when electrical rates are lowest. It melts into chilled water during the hottest part of the day, then gets piped wherever air conditioning is needed.
Ice Ice Baby.
The ice collects on 360 miles of one-inch steel tubing. “We have chillers cooling a glycol solution similar to antifreeze in your car,” Reid says. “You run that solution through the tubes, exposing the outer surface of the tube to very cold temperatures, and the water surrounding the tubes freezes. We actually ‘grow’ ice on the outside of these tubes to a depth of about 2.5 inches.”
Talk about a deep freeze.
The stacks of tubing are stored in a four-million-gallon, 25-foot-deep tank five feet below the Jordan Quad parking lot. “The ice storage allows the primary advantage of being more compact storage,” says Reid. A stratified water storage tank with the same capacity would have to be 125 feet—or 10 stories—deep.
The numbers are chilling.
Refrigeration is measured in tons, and one ton of refrigeration equals 12,000 British Thermal Units. One BTU is the amount of energy required to change one pound of water one degree Fahrenheit. The Ice Plant can store 120,000 tons of refrigeration, the equivalent of 160,000,000 ice cubes. Stanford’s normal peak summer demand is 24,000 tons per hour, or the amount of energy needed to cool 10,000 single-family homes.
It beats clipping coupons.
By creating ice when electrical rates are low and then “burning” it during the hottest part of the day, the Ice Plant saves Stanford roughly $500,000 per year and decreases Stanford’s peak electrical demand by 8 megawatts.
Who’s first in line at the drinking fountain?
Every load of chilled water produced is ranked and a computer system assigns where it will be sent. Hospital areas supporting human life get top priority, then animal life safety, followed by telecommunications and central computer systems, then labs in which long-term research could be disrupted. Next come classrooms. “The first people to get cut off are what we call ‘occupant comfort’—which includes all the administrative buildings,” Reid says. “It’s one thing being in your office when it’s 85 degrees, and it’s another thing being in a big lecture hall with 400 people.”
Last summer’s heat wave was a series of unfortunate events.
The only times the system can’t handle all of Stanford’s demands are on the hottest 10 to 15 days a year when cooling is needed into the night and the ability to make ice is thwarted. Last year the Bay Area endured two weeks of three-digit temperatures; area cities set numerous high-temperature records. Just before that, Reid says, two pieces of equipment unexpectedly failed. “We had a construction project that was not quite complete that had a fair amount of the plant out of service. So, that combination of events made that heat wave a very difficult time,” Reid says. “For another $20 million we could solve the problem, but to spend $20 million to solve a problem that may occur 10 to 15 days a year . . . that’s a tough one.” It’s cool—when the heat became unbearable, we “occupant comfort” folk got to go home early.
