Metro Nashville District Energy System

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What is the Metro Nashville District Energy System?

History

The Metro Nashville District Energy System is a facility that provides heating and cooling to many of the buildings in Downtown Nashville. District Energy systems are very important to many metropolitan areas around the nation, including those in New York City, Washington D.C, and Chicago. Nashville’s own District Energy System, which wasn’t known as the Metro Nashville District Energy System at the time but Nashville Thermal Transfer Corporation, was among the first built in the United States, and began its service in February, 1974. District Energy Systems all provide heating and cooling services. Nashville, actually, became the first city in the world to use solid waste to power both heating and cooling. The energy made from burning waste made steam which could heat downtown buildings, or make chilled water for cooling. The facility also could generate electricity for buildings, due to the $36 million expansion it underwent from 1984 to 1986. The Metro Nashville District Energy System currently provides heating and cooling, alone, to 42 buildings.

Until 2003-2004, Downtown Nashville relied on the Waste-to-Energy, Nashville Thermal Transfer Corporation, or NTTC, facility for heating and cooling purposes, rather than the not-existing Metro Nashville District Energy System. The Metro Nashville District Energy System replaced it as it was determined that the cost of disposal at the Nashville Thermal Transfer Corporation was high and the facility’s operations were unreliable. Despite the multiple expansions and updates to the NTTC, it struggled to meet pollution restrictions and remain profitable. In mid-December 2003, the Metro Nashville District Energy System came into operation and by January 2004 was able to fully serve its customers. Later, the old NTTC facility was then torn down to make room for other developments near the property.

Before the Metro Nashville District Energy System came to be, as mentioned before, the NTTC used solid waste, from trash, and burned it to cool and heat buildings. Instead of using this method, the Metro Nashville District Energy System instead uses natural gas and electricity to produce steam and chilled water. The steam and chilled water is then distributed through a series of underground pipes to about 42 individual buildings in the downtown area, with the chilled water circulating at a rate of up to approximately 42,000 gallons per minute [11]. These buildings don’t require boilers, furnaces, chillers or use fuel or electricity in water heaters; the MNDES does that work for them. This is known as a fossil fuel system. Currently, many big name facilities use the plant for their heating and cooling systems. Examples are places like, Bridgestone Arena (the home of our Nashville Predators), The Schermerhorn Symphony Center, The Ryman Auditorium Mother Church of Country Music, and even the Tennessee State Museum and Archives [12]. The Metro Nashville District Energy System also utilizes a back-up system of stored propane, to maintain natural gas even in the event of a natural gas shortage, interruption, or unforeseen event [13]. This has allowed customers to maintain their heating and cooling since its conception. [14]

The Metro Nashville District Energy System was built with a few focuses in mind, and those being:

1. To be visually attractive and environmentally friendly.
2. To keep costs reasonable and predictable for customers.
3. To use the most modern and reliable equipment.
4. And, to be long lasting and contribute to Nashville’s growth and economic development.

Sustainability

Regarding sustainability, the Metro Nashville District Energy System's pollution output is relatively low when compared to that of the other large number of facilities that make their home in Nashville. This can be attributed to the modern and new equipment that is much safer for the environment than the burning of waste was before. Burning waste in waste to energy plants can be a big contributor to both environmental and health problems [17]. The burning of waste in waste-to-energy plants, though better than allowing waste to pile up in landfills, as landfills produce methane, a more potent gas than CO2 [5, 18], waste-to-energy plants are much worse than those that use natural gas, producing more CO2 per megawatt hour [19]. Burning waste, which is done in waste-to-energy plants, releases chemicals, like heavy metals, dioxins (a carcinogen) and furons, and acid gases. These harmful particles can only be controlled to an extent [17, 19] and at times enter people and animals, entering our food chain and causing people illness. Some of these chemicals can cause cancer, neurological damage, and even disrupt many bodily systems, like the reproductive system, the respiratory system, and the thyroid system. It also goes against recycling, encouraging the continuation of burning waste [17]. The release of carbon-dioxide from burning waste also contributes to climate change, further affecting our environment. By switching to natural gas, the MNDES effectively reduces the scope of its impact on the environment through its carbon footprint.
The equipment of the MNDES allows for much of the chilled water and water used for steam to be recycled; a large percent of it actually. As of right now, nearly 100% of the chilled water supplied to customers for cooling is returned and recycled, while 70 percent of the water used for steam is returned and recycled [14]. This is an incredibely large amount and demonstrates the Metro Nashville District Energy System's attempt at being sustainable. The MNDES is also made up of one plant, rather than several small plants, maximizing their energy use, further increasing their sustainability. Nearly 100% of the steam and chilled water they deliver is available for use, while smaller in-building boilers and cooling systems normally need 50% more energy to receive the same benefits the MNDES provides. The Metro Nashville District Energy System's efforts are something not too overlook. The recent levels of pollution output that the Metro Nashville District Energy System has released can be found on the United State's Environmental Protective Agency's (EPA's) Website, with data going back since 2011. Compared to 2011, its emissions have been rising, but have remained decreasing since 2013. When comparing the Metro Nashville District Energy System’s emissions, in 2019, on the EPA website with other facilities, it’s apparent that they are relatively lower than other facilities, especially those within Nashville, only reaching approximately 31,000 metric tons of CO2 emitted [20] as compared to Tennessee's average 312,500 metric tons of CO2 emitted [21].

Metro Nashville District Energy System's Methods

As stated before, the Metro Nashville District Energy System has gone through a multitude of ways to reduce their pollution and greenhouse gas output, with a few key ones being the opening of the facility and destruction of the Nashville Thermal Transfer Corporation. Metro Nashville District Energy System features a system using chilled water, steam, and electricity to provide heating and cooling, rather than utilizing waste burning techniques like the Nashville Thermal Transfer Corporation did. Burning waste is a poor, alternate way to provide heating and cooling services, releasing many chemicals and greenhouse gases into the air [17, 19]. By switching to the steam, electricity, and chilled water service, the MNDES was able to provide much more energy in a more cost-effective, and energy conserving way.