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Shifting Currents

Among the many complexities of operating a supermarket, perhaps the one most taken for granted is keeping the building at a comfortable temperature and humidity. With shoppers continuously entering and leaving a store, outside air invariably enters the premises, bringing with it whatever temperature and humidity are in the area. Moreover, stores with deli, bakery and meat/seafood departments use ovens

Among the many complexities of operating a supermarket, perhaps the one most taken for granted is keeping the building at a comfortable temperature and humidity.

With shoppers continuously entering and leaving a store, outside air invariably enters the premises, bringing with it whatever temperature and humidity are in the area. Moreover, stores with deli, bakery and meat/seafood departments use ovens that need to be ventilated, pulling air out of the store.

As a result, supermarket energy and maintenance personnel face the challenge of compensating for the shifting air currents in the building so that the net effect is a stable and comfortable environment for shoppers and employees — especially those near the front of the store.

The typical heating, ventilation and air conditioning (HVAC) strategy used by many food retailers is to configure the air conditioning and heating unit to bring in additional outside air in order to generate a slight positive pressure in the store that will “offset the air filtering into the front of the building or the loading dock area,” explained Jonathan Perry, director of energy and maintenance, Farm Fresh, Virginia Beach, Va., a 45-store division of Minneapolis-based Supervalu.

That is the strategy Perry has used at Farm Fresh stores for many years. However, over the past 16 months, Perry has introduced a radical new air distribution design in three new stores that he regards as a significant improvement on the status quo. He plans to employ the new design, which he developed, in new Farm Fresh outlets, including two that are being constructed.

Perry described the new design, as well as the factors that led to its development, at the Food Marketing Institute's Energy & Technical Services Conference, held Sept. 9-12 at the Denver Marriott Tech Center.

Unlike the traditional approach to air treatment in supermarkets, Perry's new design creates a “neutral” airflow, with little or no unwanted air entering or treated air leaving the store. As a result, the three stores where the design is in place “are the most comfortable stores we have,” said Perry. “You can't feel a strong wind at the front of the store. Someone can smoke a cigar in the vestibule and you can stand two feet inside the store and not smell anything.”

Compared with a building with slight positive air pressure, a building with neutral airflow saves Farm Fresh money, said Perry. That's because positive pressure causes some treated air to leave the building — a waste of resources on a calm day when not much air is coming in. And on windy days, the positive pressure is not enough to offset “the average winds in most areas, let alone wind gusts,” he said.

Perry suspects that the new design saves energy as well, though he has not been able to measure that to date. “By not bringing in additional outside air to pressurize the store, you don't have to run motors to treat more air than you need to,” he said. He hopes to conduct scientific measurements of energy usage.

Unfiltered outside air also brings with it the occasional bug — a most unpleasant occurrence for a supermarket. This, too, has been reduced under Perry's new design. “Our sanitary inspector raves about the system for low fly counts,” he said. Perry plans to do a formal test of the design's impact on fly reduction as well.

Perry's new design was several years in the making. He started the process in 1997, when, as director of energy, he was among those directed to remove the inner doors at the entrance to stores, thereby eliminating the vestibules and leaving one set of entrance doors. The intent was to create a more “open feel” at the entrance, but Perry was concerned that it would be harder to maintain comfortable store conditions without a vestibule and a second set of entrance doors.

To compensate for the absence of inner doors, Perry and his colleagues decided to increase the supply of outdoor air to the stores' main air handling units “to give the store a little more ability to resist the infiltration [of air] at the front,” he said. They also stepped up “housekeeping,” replacing doors with bad seals and repairing any holes or cracks in the walls. “In the worst stores, we installed air curtains over the front door, mainly for use in the winter,” he added.

These measures helped keep energy bills from going up too much and held customer complaints to a minimum. However, store associates, especially at the front end, “complained loudly and constantly during the peak summer heat and the winter cold,” said Perry.

In 2000, Perry became director of both energy and maintenance. The merger of the two departments under his direction led him to start “thinking about the building envelope holistically,” he said.

Farm Fresh's stores, like many supermarkets, have been configured so that “supply air” — air treated by the air conditioning or heating units — is distributed via long ducts to the front of the store. “Return air” — air that has been used in the store and needs to be brought back to be treated again — is channeled via short ducts to the back of the store.

Under this conventional design, the return air “actually sets up an air pattern that assists in pulling outdoor air through the store when the front doors are open,” Perry said.

With Perry's new design, implemented in the three new stores over the past 16 months, he essentially reversed the traditional setup. Instead of moving return air to the back of the store, Perry channels it via long ducts to the front, where it “collides” with air coming in through the entrance door, effectively “canceling an infiltrating wind,” he said.

The combination of “reverse return air” and incoming air is sucked up through a “capture door,” which delivers the air via fabric ducts back to the main air handling unit for re-treatment. (The capture door is also the inside open door through which shoppers walk to enter the store.) Supply air, meanwhile, is delivered via short ducts to the back of the store.

This scenario represents a departure from the standard supermarket design, Perry said. “I'm the only one who's done it this way.”

He received technical guidance for the project from BRR Technologies, Morehead City, N.C., which supplies his air handling unit and a plenum that gathers air inside the capture door. “They gave me a good reality check,” he said. Perry commended upper management at Supervalu and Farm Fresh for allowing him to develop the new system.

BRR, which has applied for a patent on the design (with Perry as inventor), has started marketing the system via Hill Phoenix, Conyers, Ga.

Another change Perry made in his new design is to air-condition the motor room rather than using an exhaust fan, which might pull air from the store. He also installed double air-lock doors separating the sales floor and the back room so that “wind can't blow straight through the building,” he said.

Perry uses one main air handling unit in the new stores rather than multiple units. “I believe circulating air and mixing wide ranges of air is more effective than heating and cooling that same air in small local zones,” he said.

The new stores also use treated outside air in their exhaust hoods rather than untreated “makeup air.” Down-blast fans are employed to channel warm air from the ceilings down to colder areas of the stores. And Perry made sure all new stores were tightly sealed.

Unlike most retailers, Farm Fresh employs its own engineers and does its own HVAC installations. As a result, the cost of installing the new design was close to what a traditional design has cost, Perry said. He acknowledged there may be a “slight up-charge” for the new design, which may require a little more ductwork.

Fred Young, Western regional manager for HVAC supplier Seasons-4, Douglasville, Ga., who attended Perry's presentation at the FMI Energy & Technical Services Conference, told SN that Perry “has done something that I think is going to change the industry.”

Young, an HVAC veteran who said he is familiar with supermarket requirements, has long believed that air balancing in supermarkets is poorly done, and often affects the quality of frozen food. “[Perry's] methodology gives better control — though not total control — of outside air,” he said. “This makes it much easier to keep air from coming into the building.”