- THE MAGAZINE
Energy costs can have the biggest impact in the refrigerated and frozen food industry, with up to 25% of electric costs related to refrigeration. During food processing phases, product is often cooked or heated to high temperatures and then quickly frozen for retention. Rapid removal of Btu to quickly freeze or refrigerate cooked food is an energy intensive endeavor. Spiral freezers and plate freezers impose significant refrigeration demand because of their ability to rapidly remove Btu. Once frozen or chilled, the product requires a maintained refrigerated state.
Fortunately, operating behavior and technology can help to control energy use and costs without compromising product quality. Here’s a list of six ways your company can save on energy.
Match compressors to refrigeration load by optimizing compressor sequencing
Compressors are said to be the most energy efficient when they run continuously at maximum capacity. Refrigeration demand can vary widely during the production process, resulting in compressors running at less than maximum capacity. Using an ensemble of different sized compressors that closely match the refrigeration load is ideal.
To maximize efficiency, fully load all compressors except for the one compressor that needs to follow the load. As a general rule, screw compressors are more efficient at maximum capacity than reciprocating ones. However, reciprocating compressors are more efficient than screw compressors as load is reduced. An ideal mix of compressors would include screw ones running at maximum capacity complemented with a reciprocating compressor to follow the varying refrigeration load. Finding the optimum sequencing may take trial and error. Control technology software can help operators achieve the optimum balance.
The installation and use of high-efficiency motors
Motor replacement, while expensive, offers a jump start in reducing energy costs. Motors on compressors, condenser fans and evaporator fans and pumps have extensive run times, so the energy savings accumulates quickly to reduce payback times associated with higher costs of premium motors. Often utility incentives are provided to customers installing high-efficiency motors. A life-cycle cost analysis is helpful in determining justification for motor replacement before the end of the motor’s useful life. High-efficiency motors also generate less heat, therefore minimizing heat gain impact on refrigeration load.
The application of variable frequency drives
Variable frequency drives (VFD) allow fixed-speed motors to operate at varying speeds to control compressor motors, condenser fans and evaporator fans. VFDs can improve efficiency of screw compressors operating at less than maximum capacity. Because of their linear loading and unloading, reciprocating compressors don’t have the same benefit from VFDs. That’s because VFDs are also an excellent measure to reduce energy use of condenser and evaporator single-speed and two-speed motors when refrigeration load is highly variable. VFDs can be used anywhere motors and drives are needed—not just in the food processing arena.
Increase thermal resistance of the refrigeration envelope
The thermal efficiency of the envelope or enclosure of the space being refrigerated impacts energy costs in the same way that insulation and weather-stripping affect home heating and cooling costs. Follow industry code for insulation values of refrigerated space to keep thermal resistance at a maximum. Ensure points of infiltration are sealed.
Minimize heat gain and Btu transfer with rapid closing doors
This technology allows doors of a refrigerated space to open and close as quickly as possible. The main idea is to minimize the amount of Btu transfer when doors are opened. The more a refrigerated space is opened, the more Btu enters that space. For increased energy efficiency, remove Btu and keep them out until the product is shipped. Also, ensure that doors are properly sealed. Inspect for areas of infiltration other than just the doors. Heat-gain sources such as lighting and miscellaneous motors may introduce additional heat and add to the refrigeration load.
High-efficiency lighting and controls
Specialized lighting and controls can help save energy and money. Employees need to be educated about how energy is used in their spaces and how it impacts the bottom line. For example, being aware of how much energy a lit refrigerated room uses can be an eye opener for keeping employees from entering rooms unnecessarily.
Energy savings can be achieved in any area of a company’s refrigerated and frozen food supply chain, with an honest look at what processes and equipment are saving money and which are costing money. Steps like the ones outlined here can have a measurable impact on the bottom line.