A Chilling Retrofit for a Food Processor
The 59 percent total energy reduction is due in part to the cold storage area redesign by consulting engineer Rob Morton, P.E., vice president, Cascade Energy Engineering, Portland, Ore. At the request of Truitt’s refrigeration contracting vendor PermaCold Engineering of Portland, Cascade performed an energy audit revealing energy inefficiencies at the 30-year-old facility. The audit recommended state-of-the-art industrial doors from Rite-Hite Doors, a new Frick 263-hp compressor, a centralized refrigeration control system, evaporator coil rezoning, and other new technology changes such as variable-frequency drives (VFDs).
Truitt is a third-generation family-owned food processor that produces shelf-stable entrees, side dishes, bases, and desserts for a variety of companies from restaurants and businesses to health care establishments and retailers. The company embarked on the project because of its penchant for environmental concerns, energy efficiency, and good employee working conditions.
“Many times a client will do just a few project improvements because only so much money is available,” said Morton, who specializes in industrial refrigeration consultation. “However, Truitt did everything, which creates a total synergy among the 10 improvements we recommended.”
Several incentives made this comprehensive, $470,000 retrofit possible:
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. “This was one of the larger incentive plans we’ve done and I would say its success really created a win-win situation for both Truitt and us,” said Jeff Lewis, member services supervisor, Salem Electric.
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. Final data of recorded power consumption reductions revealed that Morton’s conservative projection of 1.2 million kWh was surpassed by more than 400,000 kWh annually.
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-square-foot, -10°F freezer and 18,000-square-foot, 32° cooler area, a key step of the project was specifying an Iso-Tek™ cold storage industrial door from Rite-Hite.
“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, can be 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 percent energy reduction in the freezer alone.
Much of the efficiency improvement was due to the Iso-Tek’s 3-inch-thick insulation that requires no energy-consuming panel defrost system, opens and closes at a comparatively quicker rate of 84 inches per second 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.”
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 electromechanically with glycol-cooled oil coolers. Morton consolidated the compressor requirements into the 263-hp economized screw model with 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 compressor, 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 wet bulb temperature. “Increasing the suction pressure and lowering the condensing pressure has made the compressor even more efficient on a kW per 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, whose company specializes in industrial energy efficiency.
Compressor consolidating, plus replacing the glycol loop and its energy-consuming pumps with a thermosyphon passive heat exchange method, saved 13 percent in the project. The thermosyphon method uses natural convection instead of pumps to reject oil heat from the compressor.
Morton’s audit also revealed that the original configuration of dual evaporators in three zones presented defrost and energy inefficiencies. Poor defrost and temperature controls coupled with a lack of capacity control for the rotary vane booster created a situation where suction pressures and space temperatures pulled down to inefficient levels. “Rezoning evaporator coils is a very unusual recommendation in energy retrofit work because it involves so much repiping and valve work,” said Morton.
Additionally, all evaporator zones received fan VFDs. Besides the energy savings, the lower fan speeds have also reduced wind chill factors in the freezer and increased employee indoor air comfort.
For more information, visit www.ritehite.com.
Publication date: 04/02/2007