DENNIS R. HELDMAN DALE A. SEIBERLING FOOD ENGINEERING RESEARCH LABORATORY Using Off-Peak Power Rates to Reduce Refrigeration Costs

Introduction Challenge -- Managing a refrigerated warehouse during periods of increasing energy costs Can operating costs be controlled through effective and managed use of off-peak energy rates? Frozen food quality and shelf-life is sensitive to elevated and fluctuating storage temperatures Can changes in frozen food temperatures and quality during periods when a refrigeration system is not functioning be predicted?

Objectives Overall -- to evaluate the relationships between storage temperatures and frozen food shelf-life Specific – 1. to review factors with influence on the temperature of air in the warehouse 2. to translate changes in warehouse air temperature into changes in frozen food temperature 3. to predict changes in frozen food temperature into losses of product quality and shelf-life

Frozen Food Quality Quality Attributes of Frozen Foods 1. Texture – impacted primarily by ice crystal size 2. Color, flavor, nutrients – impacted primarily by temperature dependent reactions 3. Changes in all attributes are influenced by amount of water in liquid state at any temperature

Frozen Food Shelf-Life Shelf-life is reduced by any temperature above -18 ᵒC (-0.4 ᵒF) during storage and distribution.

Warehouse Air Temperature Factors with influence on air temperature in the warehouse 1. Refrigeration system; on or off 2. Insulation of walls, ceiling and floor 3. Openings to air outside storage space 4. Total volume within warehouse 5. Amount of frozen product in warehouse

The Refrigerated Storage Space Frozen Product Volume Vs.

Walls, Ceiling and Floors Fundamental energy transfer Effects from solar radiation Walls and Ceilings  Insulation values  Highly investigated materials Floors  Need attention  Flow under for product  Higher energetic cost Concrete Recirculated air

Warehouse Air Temperature Changes when refrigeration system is not functioning Air temperature increases more rapidly on a smaller volume warehouse 2. Good insulation reduces rate of temperature increase 3. Rate of temperature rise is tempered by larger quantities of frozen product 4. Frequency of openings to outside warmer air causes air temperature to increase

Air Temperature as Function of Warehouse Volume

Air Movement Complex in nature  CFD Modeling Adding variability  Storage regime  Tertiary package Making universal  Simulation tangible to warehouse managers Ho, S. H., Rosario, L., & Rahman, M. M. (2010). Numerical simulation of temperature and velocity in a refrigerated warehouse. International Journal of Refrigeration, 33(5), 1015–1025.

Product Temperature Factors influencing the product temperature when refrigeration system is not operating – 1. Difference in air temperature as compared to the product temperature 2. Air movement over product surfaces 3. Percent of space occupied by frozen product 4. Configuration of product in warehouse space 5. Product properties

Frozen Product Storage Configuration Tertiary structure Secondary structure  Bulk material  Packaged goods Open configuration not good for system down time

Frozen Product Temperature as Function of Location

Frozen Product Quality Factors influencing product quality when refrigeration system is not operating – 1. Product temperature and all factors influencing product temperature 2. Sensitivity of frozen food quality to temperature changes 3. Location of product within storage and product configuration

Sensitivity of Frozen Foods Food CategoryShelf-LifeEAEA Seafood20050 Vegetables40060 Fruit35064 Meat21565 Poultry23075 Ice Cream300100

Frozen Food Quality The loss of frozen food shelf-life is accelerated by the following: 1. An increase in the product temperature 2. Location of product near an interface of warm air and frozen product 3. Configuration of frozen product stacking with more product surface area exposed to warm air 4. Frozen food quality attributes with greater sensitivity to changes in temperature

Frozen Food Shelf-life as Function of Location

A Warehouse Management System A Program for Reducing Warehouse Energy Costs While Maintaining Product Quality A. Inputs – 1. Total capacity of the warehouse; volume of space 2. Portion warehouse space occupied by product 3. Insulation quality 4. Air movement within the warehouse 5. Sensitivity of product quality to temperature 6. Local energy rates; both peak and off-peak; $/kWh 7. A proposed number of hours per 24 hour period that the refrigeration is not operating

Warehouse Management System Outcomes from System – 1. The cost savings for energy due to defined peak rate periods of refrigeration system down time 2. The number of days with the defined refrigeration system down time before a defined loss of frozen food shelf-life is evident

Summary A management system for estimating potential cost savings due to refrigeration system down-time during peak energy costs without significant loss of frozen food shelf-life has been proposed. The system is based on the capability to predict changes in air temperature, frozen food temperature and product shelf-life during a period when the refrigeration system is not functioning.