Since its installation in 1996, the existing chiller had been riddled with problems, including compressor failures, excessive noise, and significant oil in the refrigerant.
EL CAJON, Calif. - The county of San Diego's East County Family Resource Center is part of the Health and Human Services Agency and offers self-sufficiency services for a better quality of life for all individuals and families in San Diego County. Many different programs utilize the 22,000-square-foot facility, which was constructed in the 1970s, so keeping the cooling system working is a top priority.
The center had a new 88-ton air-cooled chiller with two reciprocating compressors installed as part of a 1996 upgrade, but that retrofit didn't go as smoothly as planned. Numerous problems kept occurring over the years, including continually failing compressors, excessive noise, and significant amounts of oil in the refrigerant.
In April 2005, one of the reciprocating compressors failed again, and the replacement cost was estimated to be $12,800. Instead of once again replacing the failed component with another reciprocating compressor, the chiller was retrofitted with one R-134a, 80-ton, oilless, centrifugal Turbocor compressor. Ever since the changes were made, the chiller has been running smoothly
The center relied on mechanical time clocks to turn the chiller on and off. As part of the energy efficiency upgrade, a new building automation system was installed.
TIME FOR SOMETHING NEW
One of the reasons why there were so many problems with the chiller was the fact that it had no controls, said Ben Erpelding, PE, CEM, engineering manager, San Diego Regional Energy Office (SDREO). "The compressors would short-cycle and experience high condensing temperatures. When one of the compressors failed again last year, we needed to get cooling quickly. If we'd had the money, it would've been ideal to replace the whole chiller. That wasn't an option, though, so we went with the Turbocor retrofit."
Fortunately, Erpelding's department had already been researching the Turbocor compressor, so they had data to convince the county of San Diego that this new component would solve their problems. They explained that Danfoss' Turbocor compressor is completely oil-free and its magnetic bearings provide essentially frictionless operation, which reduces noise and vibration. The compressor weighs 80 percent less than a traditional compressor, and it also has an integrated variable frequency drive (VFD) that provides better part-load efficiency, according to the company.
All these factors result in a boost in energy savings by as much as 30 to 50 percent, plus elimination of oil management hassles. Erpelding outlined the energy calculations and potential maintenance savings, and the county realized the return on investment with a Turbocor compressor would be very favorable. As a result, the local expert on Turbocor retrofits, Tom Shaw of Alpha Mechanical, San Diego, was brought in to install the new compressor and also convert the existing chiller to R-134a.
Shaw, who has been retrofitting chillers with Turbocor compressors for about three years, noted that the long operational hours and part-load conditions at the center made the facility a perfect candidate for a Turbocor retrofit. Indeed, with the temperate climate in San Diego, chillers run at part load for all but 1 percent of the year.
A new LonWorks building automation system (BAS) was also installed, replacing the mechanical time clocks that were used to control the equipment previously. As part of the DDC retrofit, the economizers were fixed, electronic actuators were installed, and CO2 sensors were placed in the return air duct of each air handler.
"The BAS now controls everything in the building from lighting to cooling, which really helps with the energy savings," said Erpelding. "Another benefit is when an employee complains of being too hot or too cold, the maintenance guys can make changes to the system right from their desks without having to run over there."
Figure 1. The costs of the compressor retrofit at the Family Resource Center. (Click on the chart for an enlarged view.)
LESS NOISE, MORE SAVINGS
The center is located in a residential neighborhood, and the old compressors were very loud. Previously when the system cycled on, several commented that the compressors sounded like they were screaming. With the new Turbocor compressor, noise is a thing of the past. "Now the condenser fans are louder than the compressor," said Erpelding.
In addition, the retrofit is saving the center money on energy costs, and the county of San Diego is on track to recoup the $22,485 cost of the compressor upgrade within three years (See Figure 1). According to multiple spot measurements taken before the retrofit, the existing chiller with the reciprocating compressors consumed 1.4 kW/ton. Based on 15-minute interval data collected between January and October 2006, the variable-speed chiller with the new Turbocor compressor consumes an average of 0.86 kW/ton.
Other energy upgrades were made to the chiller as well, including the installation of an electronic expansion valve (EXV), and a variable frequency drive to control the two condenser fans.
During the first year of operation, the county saved $16,960 from the entire energy upgrade. Based on the measurement and verification data, the Family Resource Center stands to benefit $8,000 to $8,500 in annual energy savings from the new compressor technology. The new Turbocor compressor is keeping the East County Family Resource Center comfortable while consuming approximately 39 percent less energy over the pre-retrofit reciprocating unit (based on 2006 data).
The entire retrofit went very smoothly, said Erpelding. In fact, maybe it went a little too well. "The chiller worked really great right away. After everything was done, instead of people complaining it was hot, they were actually complaining it was too cold. That was an easy one to fix," he said. And since then, the chiller has run nonstop (except for a transformer failure this summer) - even through 110-plus degree days - allowing the center to serve the needs of the community virtually without interruption.
Publication date: 11/13/2006