BAS strategy mixing new and old helps Tennessee university ‘adapt'
June 1, 2007
Tennessee Tech in Cookeville, TN had waited 10 years to renovate its chilled water system. When funding finally came through in 2005, Larry Wheaton, facility engineer, was determined to find long-term solutions to the control and mechanical issues the school had endured for years.
Originally designed as a distributed cooling system, the central plant fed several buildings that had individual chillers. Over time, some of these buildings were added to the central chilled water system when their individual chillers could not meet the CFC regulations of the ‘90s. In addition, some of the remote buildings had their own pumps, while others didn’t. Although each building had existing Andover controls, there was no control strategy to orchestrate efficient operation between the central plant and the buildings on the distribution loop.
Implementing Adaptive ControlThe “cooling deficiency correction program” at Tennessee Tech involved a sizeable investment in new equipment, including a 1,500-ton Trane chiller, three new 350-hp Aurora secondary pumps, and several building pumps. However, Wheaton, and project engineer, Steven Long of I.C. Thomasson Associates knew that new equipment alone would not solve their problems.
“I wanted to tap into TekWorx’ adaptive control technology,” said Long, explaining that TekWorx’ strategy, unlike typical BAS strategies, does not rely on a fixed model. Rather, TekWorx develops adaptive control algorithms based on changing system conditions. Their controls use this information to determine optimal operation points for multiple components (chillers, cooling towers, pumps, etc.) under ever-changing conditions. The result is a reduction in plant-wide kW consumption.
To save installation costs, TekWorx designed the system to take advantage of the existing Andover controls for individual building control. The TekWorx system interfaces with these controls while maintaining central plant control.
“One of the things we really liked about TekWorx was that they didn’t want to redo our entire campus control system. They simply wanted to help us optimize the performance of our chilled water system by integrating their control strategy with what we already had. That alone provides us with a lot of savings,” said Wheaton.
The CEO Does The ThinkingThe Andover units in the buildings control the building pumps based on individual buildings’ differential pressure (DP) values and a setpoint provided by TekWorx. The Andover system transfers building data such as building pump kW and building DP, along with DP values from several transmitters in the distribution loop, to the TekWorx Control & Energy Optimization (CEO) System. The CEO processes this information and calculates the precise operating points for central plant pumps, chillers, VFDs, cooling towers, etc., to minimize hp consumption while still meeting the load. The CEO then calculates which specific building pumps should operate and the associated setpoint for the building. This information is transmitted back to the Andover system like an electronic “workorder.”
“The idea is to look at the whole campus and assess the required flow from the central plant,” said Larry Tillack, TekWorx engineering manager. “For example, if the Andover system says the cooling load has dropped off at a particular building, the CEO determines whether the building pump is still needed. The CEO calculates the setpoint for the speed of the pump for each building and continuously re-evaluates setpoints to minimize kW.”
TekWorx also enables authorized personnel to remotely monitor and adjust the chiller plant operations via the Internet, so troubleshooting is faster and less expensive. It doesn’t attempt to replace an entire BAS; rather it augments a BAS in other ways that save a facility energy.
$75,000 In Utility Cost SavingsTennessee Tech has enjoyed an average ongoing 6% annual reduction in campus wide energy consumption since the cooling deficiency correction program was implemented in 2005. Assuming the chilled water plant accounts for about 25% of overall kW consumption for the campus, this translates to an approximate 25% reduction in kW consumption by the chilled water system alone. This savings can be directly attributed to the cooling deficiency correction program since there were no other changes in consumption or load patterns. Factoring in the substantial increases in electrical costs, the school has avoided approximately $75,000 in utility cost since the project was completed.
The university has benefited from the correction program in other ways. Now that colder water is getting out into the system, dehumidification has improved. This, in turn, has improved IAQ and overall comfort, allowing the university to raise space temperature thermostats by 3°F to 4°, thus saving more energy. ES