By increasing energy efficiency, District Energy has achieved significant air quality gains. Sulfur dioxide and particulate emissions, which contribute to acid ruin, have been reduced by 75 percent per unit of end-use energy. Carbon dioxide, the main factor in global warming, has been reduced 50 percent per end-use Btu. With a future expansion of our cogenertion system, we can increase overall energy efficiency, resulting in even greater improvements in air quality.
By converting to a closed loop hot water district heating system, District Energy eliminated 116 million gallons per year of ground water consumption by the old steam district heating system . In the late 1980s, Minnesota banned the use of ground water for building heating and cooling in a gradual process: starting in 1995 and ending in 2010. All of the buildings in downtown St. Paul affected by this legislation have chosen to connect to our district cooling system.
The district cooling system will also eliminate the use of chlorofloururocarbon (CFC) refrigerants in customer buildings. CFCs are manmade chemicals which are destroying the Earth's protective ozone shield. Two of District Energys electric chillers use an ozone-friendly hydrochloroflourocarbon (HCFC) R-22 refrigerant. The newest electric chiller uses R-134a, a refrigerant with zero ozone depleting potential. The two steam absorption chillers run on low-pressure steam exhaust from the cogeneration turbine-generator. Again, absorption cooling has zero ozone depletion potential
District cooling also benefits the environment because it requires less electric energy than individual chiller plants due to efficiencies of scale and better operational practices. With our chilled water storage system, chilled water is produced at night using off-peak electricity and otherwise idle equipment. The chilled water is then pumping out to customer buildings during the day to meet peak cooling demands.
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