Facing an impending electricity-rate increase, officials for the city of Marshall, Texas, knew they needed to update aging, inefficient HVAC equipment in city buildings for the city to continue to operate in a fiscally and environmentally responsible manner.
In January 2010, the city entered into a $1.1 million performance contract with Schneider Electric. The energy-management specialist conducted a comprehensive audit of equipment in city buildings, including City Hall, Marshall Convention Center, Marshall Public Library, the Center for Applied Technology, the police and fire station, and multiple community centers.
City Hall, which was constructed as a bank in 1972 and renovated in 1994, was experiencing particularly high utility costs. The chiller and boiler, which were more than 20 years old, were running 24 hr a day, seven days a week. The annual maintenance cost for the chiller alone was $20,000 to $30,000. Compounding the problem, most of the pneumatic thermostats had exceeded their operational life, and many were not located for optimal comfort control.
The 100-ton chiller was replaced with an efficient and quieter 80-ton Trane CGAM scroll chiller, which features improved fan-staging logic for low-ambient starting capability.
The inefficient cast-iron, noncondensing boiler was replaced with an AERCO Benchmark 1.5 low-nitrogen-oxide condensing boiler that reclaims heat energy that otherwise would be exhausted through the flue and uses it to further heat boiler water, reducing overall fuel usage.
Air handlers and pumps were retrofitted with Altivar 61 variable-speed drives from Schneider Electric. The drives regulate the delivery of ventilation air and chilled water to maintain building temperature, reducing energy consumption and improving comfort.
Lastly, ductwork was reconfigured to match HVAC zones with room partitions and city departments.
With these retrofits, City Hall's utility bill was reduced by approximately 50 percent.
Citywide Building Automation System
The city had been relying on individual employees to control heating and cooling through unlinked thermostats. With that method of control, many buildings' HVAC systems ran constantly, even when the buildings were unoccupied. To remedy the situation, the building contractor installed Schneider Electric TAC Vista software, Schneider Electric TAC Xenta controllers, and Viconics VT7600 series thermostats, which provide advanced monitoring and scheduling capability in eight city buildings.
“While some of our city buildings had newer heating and cooling systems, there was never an element of control within these facilities …,” City Manager Frank Johnson said. “Upon installation of the building automation system, not only did we see improvement in associated operational costs, but hot/cold complaints dropped considerably, and we're now able to troubleshoot problems from one central location, allowing our maintenance staff to focus their time and effort on other building projects.”
Slated to be completed in October 2010, the facility and HVAC upgrades were finalized a month ahead of schedule. During the nine-month installation, the city realized energy savings totaling $39,082. The first two months following project completion, the city saved $24,242 more, for total energy and utility savings of $63,324.
The project, which included a large-scale lighting retrofit, will save 1,145,800 kwh of energy annually, which is equivalent to 2,688,788 driving miles avoided or 32,862 trees planted.
“With these retrofits, we were able to make large-scale improvements to our HVAC systems and provide greater staff and visitor comfort in our city buildings …,” Johnson said. “As a result, the city of Marshall is now running in a more efficient, environmentally conscious manner, and we will continue to make improvements in the future.”
Information and photographs courtesy of Schneider Electric.