Energy Systems Group (ESG) was awarded a Guaranteed Energy Savings Act (GESA) contract for the Department of Corrections, State Correctional Institution Dallas (SCI-Dallas). The project evaluated central utilities, wastewater treatment, lighting, and water conservation. We were employed by ESG to provide an investment-grade energy audit and associated Energy Conservation Measures (ECMs) for SCI-Dallas’ central heating utility and wastewater treatment plants respectively. We identified 15 ECMs, of which 7 were selected for full design and implementation, at a cost of $11M, with annual energy savings of $1.8M. The selected ECMs replaced SCI-Dallas’ existing coal with new natural gas and oil-fired boilers, and modified their wastewater treatment plant to improve sludge dewatering. A total project cost of $19.9M, with annual energy savings of $2.25M, results in a total energy savings of $34.5M over the next 15 years.
SCI-Dallas’ heating, domestic hot water, cooking, and laundry needs were served by a central steam plant utilizing coal and oil boilers. SCI-Dallas’ plant was operating year-round to serve the 2,000+ inmates and 600+ employees on-site daily. The existing coal boilers were oversized for SCI-Dallas’ current steam load demand and could not be operated efficiently much of the year, forcing SCI-Dallas to rely on their oil boilers. Furthermore, new environmental emissions regulations would require significant upgrades to the coal boilers in order to comply.
We evaluated the 30 year life cycle costs of the following four primary heating options to calculate a net present value (NPV):
- Convert existing coal boilers to natural gas boilers
- Install new natural gas boilers
- Upgrade existing coal boilers to pass environmental regulations
- Decentralize plant with natural gas condensing boilers in each building
The decentralized option presented the lowest NPV, but SCI-Dallas was not comfortable abandoning their central plant, so they chose to go with the 2nd lowest NPV and install new natural gas boilers, which will provide $1.8M in energy savings annually for SCI-Dallas.
SCI-Dallas has a .45MGD biological process wastewater treatment plant (WWTP) on-site. In the baseline year, SCI-Dallas produced and shipped out for disposal over 1.4MG of sludge. An estimated 1.5% of this sludge was solids. We recommended and designed sludge process improvements to reduce the liquids in the sludge, thus reducing the cost to dispose of the sludge. An abandoned clarifier was modified and turned into a sludge thickening tank; cartridge membranes were added to existing aerated digesters to increase the volume of solids in the sludge to 3%. The sludge reduction will result in a 34% annual savings or $83,000 in sludge disposal fees.