San Diego stays cool with chilled water system
More than 2 million square feet of space in the heart of San Diego — including hotels, theaters and shopping centers, such as the 900,000-square-foot Horton Plaza — receive chilled water for air conditioning via a 2.5-mile subterranean District Cooling System, which is owned by San Diego Power & Cooling Co.
Operated as a private utility, the power and cooling company is small in physical size but provides significant benefits to San Diego’s Central Business District through its delivery of dependable, cost-saving and environmentally friendly thermal energy to some of the downtown areas largest users of air conditioning.
The company produces chilled water in its downtown San Diego plant and pumps chilled water to buildings in a 50-block central business district via an underground network of 24-inch welded steel pipes.
The water is recycled so it can be chilled and used again.
The San Diego system is identical in all but size to the highly successful District Cooling Systems in Berlin, Boston, Copenhagen, Geneva, Paris, San Francisco, Stockholm and Tokyo.
Just this past year, a similar system became operational in downtown Chicago, where temperatures soared above 100 degrees regularly during the summer heat wave of 1995. (The new District Cooling System in Chicago has won kudos for Unicom Thermal Technologies, a subsidiary of Unicom Corp., parent company of Commonwealth Edison.)
Such shared systems have become the preferred source of thermal energy in so many of the world’s most sophisticated cities because “as an alternative to the production of chilled water by separate on-site water chilling plants in major buildings, a District Cooling System is far more efficient, economical, dependable and friendly to the environment, which means healthier,” says Steven Mueller, president of the power company.
For example, the chilled water delivery system all but eliminates the use of chlorofluorocarbons, or CFCs. Because they are suspected of damaging the earth’s ozone layer, the production of CFCs, commonly used in office building air conditioning systems, has been outlawed.
Also eliminated on a building-by-building building basis is the potential risk of Legionnaires’ Disease and the costly need to chemically treat cooling water to avoid accumulation of the responsible bacteria.
But cost-effective energy and competitive edges are not the only economic benefits of a District Cooling System. On-site chilling plants are extremely expensive propositions when it comes to the equipment, installation, maintenance, operations and replacement. And to comply with the Clean Air Act of 1990, all but the newest buildings in the downtown area will have to replace their CFC-refrigerant R-11 chilling plants — at a cost of up to several hundreds of thousands of dollars per building — by the end of the decade.
This convergence of environmental legislation and big-ticket expenditures leads some to predict that energy customers will turn to District Cooling Systems instead of installing expensive new equipment.
And, independent chilling plants in most large buildings are equipped to deliver about twice peak summer demand to protect against failure.
“We call this ‘preventive overbuilding,”‘ Mueller says. “The practice is to build a chilling plant to twice what the peak demand will be July through September to assure that you can meet the demand. The problem is that such a system also costs twice as much in electricity and maintenance the other nine months of the year.”
Koll Center, a 350,000-square-foot office tower designed to use the system, includes a 500,000-gallon water storage tank in its basement. The building takes chilled water from the utility at night, when rates are lowest. The customer uses the water during the day, when rates are highest. Koll Center’s thermal storage system paid for itself rapidly and offers the lowest cost service per square foot in the downtown area.
Taxpayers still pay for the equipment, operations, maintenance, repair and replacement of environmentally questionable individual chilling plants, while the private-sector owners of comparable facilities are cutting both expenses and risks.