A recent retrofit reducing power consumption by 1.6 kWh at the food processing plant of Truitt Bros. Inc. (Salem, OR) is resulting in annual energy savings of over $70,000/yr and a payback of less than two years.

The 59% total energy reduction is due to the cold storage area re-design of consulting engineer, Rob Morton, P.E., vice president of Cascade Energy Engineering in Portland.  At the request of Truitt’s long-time refrigeration contracting vendor PermaCold Engineering of Portland, Cascade performed an energy audit revealing many energy inefficiencies at the 30-yr-old facility. The audit recommended new industrial doors from Rite-Hite Doors, a new Frick, 263-hp compressor, a Logix centralized refrigeration control system, evaporator coil rezoning, and other new technology changes such as Rockwell Automation VFDs.

Truitt, a third-generation, family-owned food processor that produces shelf-stable entrees, side dishes, and desserts for a wide variety of companies, embarked on the ambitious project because of its penchant for environmental concerns, energy efficiency, and superior employee working conditions.

MULTIPLE INCENTIVES

Several incentives made this comprehensive, $470,000 retrofit possible, including an energy incentive of $151,000 from the Energy Smart Plan program of non-profit electric cooperative, Salem Electric; an energy incentive from federally mandated wholesale power provider, Bonneville Power Administration; and an Oregon Business Energy Tax Credit of 35% of the total project cost prorated over a five-year period.  The incentives were critical in achieving the total retrofit that Morton, Truitt plant engineer Dean Pemble, and PermaCold’s vice president Randy Ceiloha all envisioned.

The incentives were contingent on performance results consisting of power monitoring on the compressor, one-time measurements of several evaporator fan speeds correlated with input power, and the control system history. Morton’s conservative projection of 1.2 million kWh was surpassed by more than 400,000 kWh annually, data shows.

OPENING THE DOOR TO SAVINGS

Since Morton’s recommended mechanical system improvements wouldn’t be as effective without eliminating the large amount of heat infiltration due to an existing slow-moving door separating the 54,000-sq-ft, -10°F freezer and an 18,000-sq-ft, 32° cooler area, a key step of the project was specifying an Iso-Tek™ cold storage industrial door from Rite-Hite Doors.  “As energy prices rise, doors are becoming a bigger part of energy retrofits and refrigeration system efficiencies,” said Morton. “Manually operated doors, slow-moving doors, or worse yet, strip curtains in poor condition, are all big energy losers.  Besides energy losses, moisture infiltration can be a safety hazard source in the freezer.”

Illustrating Morton’s point is the fact that replacing Truitt’s previous slow rigid door/strip curtain combination with state-of-the-art door technology plus installing VFDs on six evaporator coils produced a 29% energy reduction in the freezer alone. 

Much of the efficiency improvement was due to the Iso-Tek’s 3-in.-thick insulation that requires no energy-consuming panel defrost system, opens and closes at a comparatively quicker rate of 84-in./sec and has flexible, impactable hinged panels that can take a hit and resist damage. “Doors are always subjected to damage in industrial environments that have forklifts, so durability and seals are key issues,” Morton added. “Also, the infiltration might be in check, but large energy losses could result from constant door defrosting. We’ve seen doors that consume 30 to 60 kW continuously in defrosting, which can add up to as much as $25,000/year in energy costs.”

BEYOND THE DOORS

Besides doors, increasing compressor efficiency was also critical. Decades of plant expansions and modifications had created a compressor assortment consisting of two rotary vane booster compressors, a high-stage screw compressor, and two high-stage reciprocating compressors all controlled electro-mechanically with glycol-cooled oil coolers. Morton consolidated the compressor requirements into the 263-hp economized screw model with a VFD.  Screw compressors don’t truly get more efficient during unloading, but a VFD can keep them fairly consistent, according to Morton. 

Now with the better control characteristics of the new Frick compressor, Logix control system, and the rezoned evaporator, suction pressures are the equivalent of 15° to 20° higher than the old system and discharge pressures float just above the ambient wetbulb temperature. “Increasing the suction pressure and lowering the condensing pressure has made the compressor even more efficient on a kW/ton of refrigeration basis,” said Morton. “The old screw compressor operated at part-load very inefficiently because as it unloaded, the capacity dropped off quickly, but the power consumption didn’t,” said Morton.