A new refrigerated and frozen food distribution facility in Connecticut maximizes energy savings through careful design and tight equipment control.

The use of variable-frequency drives (VFDs) on condenser fan motors enables the system to maintain optimum condensing pressures while minimizing compressor horsepower.

Burris Logistics, based in Milford, Del., operates a network of frozen food warehousing and distribution systems in the eastern United States. In late 2007, the company decided that it needed to build a new warehouse - its 17th - to serve BJ's Wholesale Club and the northeast public refrigerated warehouse market. Burris Logistics teamed up with Jacksonville, Fla.-based Stellar, a design, engineering, construction and mechanical services firm, to design and build the new  260,000-ft2refrigerated and frozen food distribution facility in Rocky Hill, Conn.

"We've used Stellar exclusively in nine projects out of 10 since 1987," says Joe Morris, vice president of engineering for Burris Logistics. "They approach each project differently, focused on our needs and specific requirements. They understand how to implement new, innovative designs and technologies to achieve energy savings and increased safety."

Stellar provided a range of services for the project, including real estate acquisition, land use and permitting, design, engineering, construction, refrigeration, insulation, roofing and HVAC.

The warehouse, which was completed in August 2008, includes a 92,000-ft2-10°F (-12°C) freezer; a 20,000-ft2convertible room (with temperatures ranging from -20°F to 35°F [-29 to 2°C], depending on the product); a 4,000-ft2ice cream room; a 15,000-ft2meat freezer; a 31,000-ft2dairy/deli cooler; and a 15,000-ft2produce area. The facility also includes 46,000 ft2of dock space, 13,000 ft2of support and utility areas, and 24,000 ft2of office and welfare areas. Several sustainable features were incorporated into the facility, including 100-percent storm water retention (all storm water is absorbed into the ground on the property); a white roof to reflect heat; an energy-efficient refrigeration system; and a control system that manages utility load consumption.

Figure 1. Using just one evaporation coil per penthouse with a total of 12 penthouses allows the system to achieve greater efficiency across the different temperature zones.

A More Efficient Penthouse

The facility required five different temperature zones ranging from -20 to 58°F (-29 to 14°C) to store products such as frozen food, dairy, deli meat and produce. To address these needs, Stellar implemented a central ammonia refrigeration system with an individual penthouse design.

In a standard penthouse system, a number of evaporators are located in a single housing, or penthouse, on the facility's roof. For the Burris Logistics facility, Stellar designed the system to achieve greater efficiency across the different temperature zones by using just one evaporation coil per penthouse, with a total of 12 penthouses (figure 1). The units were equally spaced among the different temperature zones.

For each penthouse, Stellar installed two temperature transmitters - one in the supply airstream and one in the return airstream. All evaporator fans are equipped with variable-frequency drives (VFDs) to modulate the fans' speeds based on the temperature. To control each penthouse, the control system averages readings from two different temperature transmitters at regular intervals and, in response to the average value, either speeds up, slows down or turns off the fans completely to regulate the temperature. In total, 24 temperature transmitters are located throughout the refrigerated rooms. According to Joe Moores, senior project manager with Stellar, this design offers better control compared to older, more traditional systems and has produced significant energy savings for Burris Logistics.

In addition to addressing the varying temperature requirements, the complex system also controls humidity, with humidification zones incorporated according to the respiration rate of certain products. In addition, ethylene scrubbers were implemented to maintain the ethylene concentration at a level that meets the plant's requirements without affecting the produce.

Figure 2. Three-dimensional drawings of the system allowed Burris Logistics to review all the components and actively participate in the design process.

Additional Equipment Controls

In addition to using VFDs on the evaporator fans, Moores explained that Stellar also installed VFDs on the condensers' fan motors. Older condenser fan designs run based on pressure, thereby causing the motor to draw a substantial amount of amperage. The VFD-driven system maintains optimum condensing pressures while minimizing compressor horsepower. Using a VFD on fan motors also reduces maintenance on fan motors and belts.

The VFDs are tied to the control system and operate based on a floating-head-pressure-control strategy, in which the head pressure is allowed to "float" to a lower level when permitted by ambient conditions, to reduce the load on the compressors. By monitoring the outside dry bulb and wet bulb readings, an optimum pressure is targeted, and the condenser fans vary to achieve that pressure.

Stellar also used motorized valves to control the liquid feed into the vessels, which operate at different pressures. The use of these motorized valves, along with the smart control system, has made for tighter vessel control and a much more consistent operating pressure in each vessel.

"The valves can react more quickly and precisely to system changes compared to the solenoid-controlled valves that are used in most facilities, thereby further enhancing overall system efficiency," Moores says.

One other area in which Stellar and Burris Logistics were able to reduce energy consumption was in the facility's ice cream room, which had the lowest temperature requirement of the entire facility.

"Rather than running our entire freezer at a lower temperature, which would have required more brake horsepower per ton of refrigeration, we decided to design the ice cream room as a separate unit, completely independent of the central ammonia system," says Morris.

The -20°F (-29°C) 4,000-ft2ice cream room uses an environmentally friendly alternative refrigerant - R-404A - and has its own computerized controls that are monitored from the plant's common system.

Burris Logistics' 260,000-ft2 refrigerated and frozen food distribution facility in Rocky Hill, Conn., is designed to maximize energy savings.  

Throughout the project, communication and collaboration were key. When designing the refrigeration system, Stellar developed three-dimensional drawings of the entire system that allowed Burris Logistics to review all the components, including compressors, vessels, piping and control groups (figure 2). When opened with the right software, the drawings permitted a virtual "walk-through" of the facility.

"The 3D perspective was a great tool in the early design and layout stages of the equipment and piping of the machine room," Morris says. This review process allowed Burris to suggest changes to the design in order to accommodate proper access and maintenance, and it also ensured that the project managers had a comprehensive picture of what the system would look like once it was installed.

"Although the facility has only been in operation since mid-July, we believe its energy consumption is either equal to or less than Burris' similar facilities that are 35,000 ft2smaller," Morris says. "We're extremely happy with the performance of this facility and believe the energy savings we're seeing are due to Stellar's design."

For more information from Stellar, call (800) 488-2900, e-mail jmoores@stellar.net or visit www.stellar.net. For more information about Burris Logistics, visit www.burrislogistics.com.