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District Energy BenefitsDistrict energy is an energy-efficient, environmentally sound method of heating and cooling buildings. |
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District energy systems produce steam, hot water or chilled water at a central plant using fuels such as biomass (plant materials), natural gas, oil or coal. The steam or water is then piped underground to individual buildings within a defined area for heating, cooling or industrial use. A district energy system is:Reliable. Building owners and managers can count on district energy systems since energy professionals operate around-the-clock and have backup systems readily available. Most district energy systems operate at a reliability rate of 99.999 percent, according to the International District Energy Association. Energy efficient. When steam, hot water or chilled water arrives at a customer's building, it is 100 percent efficient at the door, compared with 80 percent or lower efficiencies when burning natural gas or fuel oil. In addition, a district energy system can use the "waste heat" that results from burning fuel to produce electricity at a power plant. The system then becomes a combined heat and power (CHP) system—generating both electricity and heat for customers. This more than doubles a power plant's fuel efficiency and also lowers the emissions typically associated with standard electrical production. Less energy is used, resulting in less sulfur dioxide and carbon dioxide being expelled into the environment. Environmentally sound. A district energy system enables building owners to conserve energy, improve operating efficiency and protect the environment. With district energy, building managers no longer need to burn fuels or store or use refrigerants on-site, so the site is safer and more environmentally sound. Instead, fuel and refrigerants are used at district energy plants. These systems employ strict emission controls, resulting in air quality benefits. Fuel flexible. District energy systems have the flexibility to use a variety of fuel sources in larger, more economical volumes, reducing the impact of supply and price variations. By closely managing its fuel purchases, a district energy system can mitigate the impact of an increasingly volatile fossil fuel market. This results in stable rates and lower energy costs for its customers. Easy to operate and maintain. District energy is worry-free heating and cooling delivered directly to a customer's building—ready to use. Customers do not need boilers or chillers, so there is less maintenance, monitoring and equipment permitting. District energy customers also eliminate the need for fuel deliveries, handling and storage so there are fewer safety and liability concerns for employees and building occupants. Comfortable and convenient. Building occupants can be both comfortable and satisfied, no matter what the outdoor temperature. District energy service is available whenever a building needs heating or cooling. In addition, a district energy system reduces vibrations and noise problems that could annoy building occupants and frees up building space. Cost-effective. Since buildings using district energy service don't need boilers or chillers, building owners reduce their upfront capital costs and their ongoing operating, maintenance and labor costs. That means less financial risk and a far better return on investment—plus the elimination of principal and interest payments, property taxes associated with new boiler and chiller installation, costly insurance and annual maintenance contracts, and costs associated with operation of boilers and chillers. District HeatingDistrict Energy St. Paul, an Ever-Green Energy affiliate, currently provides heating service to more than 185 buildings and 300 single-family homes, representing more than 31 million square feet of building space, or about 80 percent of Saint Paul's central business district and adjacent areas. Buildings connected to a district heating system do not need boilers and auxiliary equipment, freeing up valuable space for other uses. Each building has its own heat exchanger and control valve, which transfers thermal energy from the district heating system water to the building's heating system water. Cooler water is then returned to District Energy's main plant to be reheated and circulated once again to buildings connected to the system. District CoolingDistrict Cooling St. Paul, an Ever-Green Energy affiliate, currently provides air-conditioning service to more than 95 downtown buildings, representing more than 18.5 million square feet of building space or about 60 percent of Saint Paul's central business district. Buildings connected to a district cooling system do not need chillers or cooling towers, eliminating the use of ozone-depleting chlorofluorocarbon (CFC) refrigerants. Chilled water is produced at a central plant and piped underground to buildings in the downtown business district. Once used in customer buildings, the water is returned to the central plant to be rechilled and then recirculated through the closed-loop piping system. A 2.5-million-gallon chilled water storage tank was constructed in 1994 to store chilled water produced at night, using off-peak electricity, for daytime distribution to downtown Saint Paul district cooling customers. A second chilled water storage tank, which holds 4 million gallons of water, began operating in spring 2003 at a new district cooling plant located in the northeast section of downtown Saint Paul.
The use of chilled water storage: |
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