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University of Texas Arlington secures stimulus funding to replace chillers with new high-efficiency units

Thanks to stimulus funding, The University of Texas Arlington has commissioned two new high-efficiency chillers that will serve the main campus cooling loop and provide annual energy savings of nearly $200,000. The University opted to replace two 3,000 TR chillers, which were charged with HCFC-22 refrigerant, in order to meet the reliability requirements of the research facilities. The Johnson Controls-manufactured replacements were two new 3,000 TR, high-efficiency, YORK model YK-EP centrifugal chillers charged with HFC-134a refrigerant, which has zero ozone-depletion potential and no phase-out date. The chiller replacement project is one of six major projects on the UT Arlington campus funded by the Texas State Energy Conservation Office (SECO).

“The University is in an exciting period of growth, with a number of major projects underway across the campus," said Larry Harrison, Director of UT Arlington Mechanical Operations and Grounds. The University opened the 234,000-sq-ft Engineering Research Building in January and is developing more than 20 acres at the College Park District, including the 6,500-seat College Park Center and a mixed-use residential and retail center called College Park.

"With the University's advanced research facilities, it is extremely important that we have highly reliable and dependable chillers," Harrison said. "We simply cannot afford any downtime, and in those rare cases when there is downtime, we need to get back online as quickly as possible."

The YK-EP chillers feature compressor drivelines with industrial-grade open motors, which mean less downtime. If a motor failure occurs, the chiller can be brought back online much faster and at a reduced cost, when compared with chillers that utilize hermetic motors.

How it works
The YORK YK-EP chiller operates much the same as the YK single-stage chiller. The only exception is a small economizer loop to compress partially expanded gas to extend capacity and improve efficiency.

Step 1. Evaporator—Liquid refrigerant (R-134a) flows into the evaporator and is distributed for contact to a bundle of tubes that carry the chilled liquid for the system. The low-pressure liquid refrigerant absorbs heat from the chilled liquid causing the refrigerant to boil. The boiled refrigerant rises to the top of the tube bundle as vapor and passes through a mesh pad that prevents liquid-refrigerant droplets from being drawn into the compressor.

Step 2. Primary compressor—The refrigerant vapor that has passed through the mesh pad is drawn up to the compressor. Centrifugal compres¬sion is used to pressurize the refrigerant and develop flow. The high-pressure refrigerant vapor is then discharged from the compressor to the condenser.

Step 3. Condenser—The high-pressure refrigerant vapor is distributed across a bundle of tubes carrying cooling liquid in the condenser. The high-temperature and high-pressure refrigerant vapor rejects heat to the cooling liquid that is passing through the tubes. The cooling liquid will generally later reject its heat to the environment in a cooling tower. When the refrigerant vapor gives up its heat to the cooling liquid, it condenses on the outside of the tubes and drips down to the sub-cooler. The liquid refrigerant passes through the sub-cooler where it rejects a little more heat to the cooling liquid as the refrigerant temperature is reduced.

Step 4. Expansion and economizer—
The refrigerant liquid from the condenser is partially expanded to a pressure intermediate to the evapora¬tor and condenser. The partially expanded two-phase refrigerant is separated to liquid and vapor streams in the economizer. The liquid stream is expanded a second time to repeat the cycle in the evaporator. The vapor stream is drawn out of the economizer by the economizer compressor. Note that the quality of refrigerant delivered to the evaporator as a result of economizing extends the refrigerating effect of the flow through the evaporator and primary compressor.

Step 5. Economizer compressor—The economizer compressor draws the refrigerant vapor from the economizer. The efficiency benefit of the cycle is a result of not having to compressor this gas over the full head of the chiller system. As in the primary compressor, centrifugal compression is used to pressurize the refrigerant and develop flow. The high-pressure vapor refrigerant is then discharged from the economizer compressor to the condenser.

The benefits realized by UT Arlington as a result of installing the YK-EP chiller were summarized by Bill Blair of Texas Air Systems, sales agent for Johnson Controls, "The YK-EP chillers were the best option for UTA because of their high efficiency at both design and off-design conditions, and the reliability provided by their open motors."

TDIndustries, a mechanical contractor in north and southwest Texas, helped secure funding for the project from SECO, targeting money that is designated for state projects that meet specific payback criteria. For the balance of the funding, UT Arlington and TDIndustries entered into a performance contract, whereby the energy savings would pay for the improvements. The savings for the entire project are projected to be over $1.1 million a year.

Barry Whaley, TD Account Executive, said: "Our project at UT Arlington addresses not only energy-cost reduction through equipment replacement, but also the University's need to upgrade its infrastructure to provide increased systems reliability. Other elements of the project will help the University save energy by providing our Continuous Commissioning services over the life of the program - insuring the persistence of the projected savings."

In addition to the two new YK-EP chillers, the main plant at UT Arlington includes two 2,000 TR YORK model YK centrifugal chillers and one 3,400 TR YORK model YD centrifugal chiller, all with proven track records of dependability.

For more information, visit
Johnson Controls Inc.; TDIndustries; or University of Texas—Arlington.

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