Benchmarking, resequenced chiller controls serve up success for Atlanta data center
As one of the largest commercial real estate firms in the southeastern United States, Childress Klein oversees and services nearly 40 million sq ft of office, industrial, retail and residential properties. Ensuring that building controls and mechanical systems are efficient is a critical part of the firm’s commitment.
“We take very good care of our tenants, our building owners, and our properties,” said Jack Kennedy, director of engineering services for Childress Klein in Atlanta. “If the systems are not tweaked and working as well as they can, we’ll have uncomfortable tenants and we’ll pay excessive utility bills.”
In one single-tenant, 13-story commercial office building in the Atlanta area, Childress Klein faced challenges with higher than normal energy consumption. They began searching for a solution that would help them identify energy savings and improve comfort.
The building houses a mission critical data center, which requires 24/7 operation and support. Two 350-ton centrifugal chillers in the building’s main plant provide chilled water to the building, with a third 120-ton air-cooled rooftop chiller that was being used only for emergencies. The building also has an air handler on each floor and a plate-frame heat exchanger.
Because of the round-the-clock operation requirements, the 350-ton chillers were operating 24 hours a day, even though the building load was not constant during that time. Running the chillers more often than needed was inefficient and resulted in high utility costs. It also caused a draft effect in the building.
Childress Klein consulted with Trane to identify ways to save energy and reduce operating expenses. Trane used energy modeling and benchmarking to help Childress Klein analyze how the building was consuming energy and made recommendations for conservation measures.
“By using Trane Energy Optics to analyze the raw interval data from the utility company, we were able to map exactly how the building operates under certain conditions and use that information to come up with the strategy we implemented with Childress Klein,” said Jeff Kellner, energy services account manager with Trane.
A strategy was devised to utilize the rooftop chiller — previously used only for emergencies — on evenings and weekends when there is a lighter load on the building. Because the rooftop chiller is smaller and consumes less energy, using it during light load conditions offered significant energy savings.
Rather than complete major pipe renovations on the building to achieve this, the rooftop chiller was incorporated into the daily operation sequence of the building using the existing equipment and mechanical systems. This was accomplished by converting the facility from constant-flow to variable primary flow technology and adding pressure independent control valves to the air handlers.
A critical part of this process was the addition of two Trane® AdaptiView™ panels to each of the 350-ton centrifugal chillers. The panels provide access to the more efficient variable flow technology so staff can control the amount of refrigeration the chillers produce based on actual building load and conditions.
“With the AdaptiView panel facility staff are able to vary the water flow and control the chiller in a different way,” said Kellner. “This is a more efficient way to distribute the water throughout the facility and connect the load of the building to the production and use of chilled water — using the chilled water in a more efficient way.”
The panels also give pressure ratings that are used to make decisions on air pressure control and provide insight on which chiller is the most efficient to run at any given time based on the active tonnage data the panels collect.
“The AdaptiView panel tells us when we’re below a set tonnage so we can change our energy strategy to use the smaller rooftop unit,” Kennedy said. “The information we are able to receive through the panel helps us determine the most cost-efficient method to cool the building.”
The panels allow Childress Klein to get more accurate control of the chillers and to deploy strategies in the building that otherwise would not be possible. They also provide details on trends happening with the chillers over a particular period, such as amperage drawn and chiller and condenser water temperature.
The touchscreen provides real-time information on chiller operation, energy use, and system performance — showing the flow and how pumps are running, temperature setpoints, chilled water return temperature, and more.
“We virtually can check every part of the chiller and verify what’s happening, how it’s working, when it began, when it stopped,” said Juan Bedoya, general maintenance engineer for Childress Klein.
One of the main objectives for Childress Klein in managing the building for its client is ensuring proper comfort levels.
“It’s the number one thing we do when we’re here, and it all starts with the chillers,” Muraco said. “Luckily, with the AdaptiView we can monitor all that from the screen. The AdaptiView on the one chiller can tell us when it’s ready to pull on the other chiller.”
With the panels the building operators know immediately that the building is being cooled at the proper level. If there is a problem with bringing the other chiller online, the AdaptiView interfaces with the BAS and sends an alert to help ensure system reliability.
Childress Klein saw significant energy savings and a payback of less than three years. In addition, Childress Klein saved tens of thousands of dollars in annual energy and reduced the building’s environmental footprint.