Reducing the Regulatory Burden with Low Charge
In an effort to meet those needs, Evapco, a Maryland based designer of ammonia refrigeration equipment and systems, has developed a lowcharge ammonia package system, called Evapcold. The first two units were installed in June at a 30,000-square-foot freezer facility in Ogden, Utah.
Unlike traditional stick-built ammonia systems, the lowcharge ammonia package units use less than five pounds of ammonia per ton (lbs/TR). Each 70 TR package at the Utah facility contains only 290 pounds of ammonia for a total charge of 580 pounds for the two units. By comparison, a traditional stick-built field-erected ammonia system contains 3,500 pounds or more of ammonia.
“The lower quantity of ammonia was the driving force behind this product because of regulatory pressures,” said Kurt Liebendorfer, vice president at Evapco. “First, this is safer because you’re using less ammonia. In designing and building the system, we paid attention to the codes and regulations, including IIAR standards, along with the operator, human safety and offsite benefits of low-charge.”
One of the lessons learned during extensive research and development was the importance of finding the proper balance of how much ammonia to remove from the low-charge unit while maintaining the required reliability and performance, which was affected when too much ammonia was removed. It was determined that two to five pounds per ton of ammonia is a suitable range for the various model sizes applied to freezer applications. “That is where we found the correct balance of reducing the ammonia significantly but still retaining the right amount to effectively deal with the difficult operating conditions that industrial systems are expected to handle,” Liebendorfer said.
Using these guidelines, the units were able to handle varying conditions, such as convertible rooms, and perform hot and cold starts and temperature pull-down while providing essential liquid management and compressor protection. In the case of the Utah facility, the unit was started in June, when the ambient temperature was 100 degrees. The units ran at 45-degree room temperature for one month while construction of the building was completed, at which time the units then easily pulled down the freezer to minus-10 and also minus-20 degrees.
“The system is able to pull down the building in a hot-start condition because the units have a robust liquid management system for that scenario,” Liebendorfer said. “This also represents the ability of the units to reliably and automatically restart after a power outage.”
The water-cooled system also maximizes energy efficiency with variable frequency drives (VFDs) on all motors. Because the system is entirely self contained, energy consumption can be measured at the main power feed. Energy management software is also part of the control system. The Utah facility is saving 20 percent annually in kilowatt consumption compared to a baseline stickbuilt installation of a single-stage economized recirculated liquid ammonia system.
In addition, each unit’s screw compressor utilizes a VFD to provide superior part-load efficiency that improves overall system efficiency. Optional VFDs on the evaporator fans have also been shown to improve efficiency when running below maximum capacity. Each unit is rated at 60 TR for peak conditions but is capable of providing 70 TR at maximum capacity by speeding up the compressor to 4,000 RPM.
Energy efficiency was enhanced by eliminating the long piping runs found in typical ammonia systems, which cause pressure and temperature losses and the compressors to operate at lower suction temperatures. The package units reduced these pressure and temperature losses because they eliminate the long piping runs and are internally piped. This also means that the compressors correctly run at their design suction temperature.
The case study showed a third benefit through reduced installation costs. The low-charge ammonia packages are internally piped, insulated and wired, which reduces labor required for refrigeration and electrical contractors. The packages also eliminate the cost of constructing or expanding the central machinery room. “The machinery room is part of the package design. The rule of thumb for the building cost of an average, traditional machinery room is $1 million, so that savings can be passed on to the facility owner,” Liebendorfer said.
Liebendorfer noted that the savings is optimized if the architect designs the facility properly for these new packaged systems. The general contractor must also account for the additional roof weight of the package units in the design of the building’s structural support steel. A package of this size requires more localized roof support than traditional stickbuilt installations, but if this is accounted for in the building design the cost impact is minimal. It should also be noted that one size does not fit all; Evapcold units cover spaces from 5,000 to 35,000-square-feet per unit.
“What this will mean for the ammonia refrigeration industry is a growth in applications where these lowcharge ammonia packages can be installed in food and beverage processing facilities using different versions and configurations,” Liebendorfer said.
