Commercial Refrigeration Basics

General

  • Chilling liquid for process cooling (common in the food processing industry) and possibly to make hot water (to provide heat for air handler heating or reheat. Supermarkets routinely use this last concept).
  • Chilling brine to freeze an ice sheet (e.g., a hockey arena).
  • Heat pump systems (please see the separate section covering heat pumps in more detail)...

Refrigeration is only a means to an end. In most cases, that end is the preservation of foods. Refrigeration is often a significant steady use of year-round electricity since this equipment runs even when the building is unoccupied. Therefore, it is usually cost effective to install the most efficient refrigeration practical. Consequently, the utility's representatives welcome the opportunity to work closely with energy customers during the early planning stages to help them understand their options.

Typical System

Food service requires refrigerators to meet a variety of needs. Many of these are self-contained and the refrigeration system is of the conventional air-cooled type. Some use ice for display purposes. The typical types are:

Commercial Refrigeration

Reach-in Refrigerators

These are larger commercial versions of the typical household refrigerator. They are for medium (32 to 45°F) and low (0 to -10°F) temperature ranges. Most are self-contained; however remote refrigeration systems are used where cabinets are in a hot or otherwise unfavorable location, where the noise or rejected heat would be objectionable, or in other special conditions. Shelves, tray slides, and other interior accessories are designed to increase food holding capacity or to improve operational efficiency.

Roll-in Cabinets

These differ from reach-in units in that the inside floor is about the same level as the room floor, so wheeled racks of food products can be rolled into or out of the cabinet interior. Cabinet doors are full-height with drag-gaskets on the bottom and interiors have no shelves.

Walk-in Coolers & Freezers

Similar to reach-ins, they are factory made larger versions designed to store foods and other perishables in larger quantities and for longer time periods. Dissimilar foods should be stored in separate rooms because they require different temperatures and moisture conditions, to avoid odors from some foods being absorbed by others.

Large facilities may have up to four rooms. One for fruits and vegetables; one for meats and poultry; one for dairy products; and one at 0°F for frozen foods.

Recommendations/Energy Services Opportunities

Many restaurants come and go relatively frequently based on service and fads and demographic changes. Many employ used equipment to reduce first cost. Be alert to expansion needs and the potential replacement of old inefficient equipment with new, improved units.

Energy Use Information

Refrigeration - Basic Cycle Concepts

Heat energy always flows naturally from a higher to a lower temperature level. That is, hot areas naturally cool off and cold areas naturally warm up. Therefore, moving heat from a lower to a higher temperature requires the input of work (or heat), usually to create a pressure differential in the cycle refrigerant.

The refrigerant (acting as a heat transfer fluid) is used to transfer heat energy from a lower temperature to a higher temperature. The refrigerant is evaporated at a temperature lower than the desired temperature in the freezer or cooler. The condensing temperature of the refrigerant is increased by compression so that it can either be rejected to the environment or recovered as useful heat. The basic refrigeration cycle, with all steps combined, is shown below.

  • Step One, Evaporation: Liquid refrigerant at a sufficiently low pressure is brought into contact with the heat source (the medium to be cooled). The refrigerant absorbs heat and boils, producing a low-pressure vapor. The heat exchanger used for this process is called the evaporator.
  • Step Two, Compression: The compressor raises the pressure of the refrigerant vapor, normally using an electric motor drive. This increases the temperature at which the vapors will condense to a temperature above the temperature of the heat sink. Most common compressors are reciprocating (piston and cylinder) or screw (looking much like an old meat grinder) compressor designs.
  • Step Three, Condensation: The high-pressure refrigerant gas now carrying the heat energy absorbed at the evaporator, plus the work energy from the compressor, enters the condenser. Since the refrigerant's condensing temperature is higher than that of the heat sink, heat transfer will take place, condensing the refrigerant from a high-pressure vapor to a high-pressure liquid.
  • Step Four, Expansion: The condensed liquid's pressure is reduced (called "throttled") to the lower pressure evaporator using a valve, orifice plate or capillary tube device. In actual practice, the condenser cools the refrigerant a bit more, sub-cooling it below the condensing temperature. This is an important efficiency improving attribute to the cycle, since it reduces the amount of refrigerant liquid that has to evaporate (it is called flashing at this stage in the cycle) to a gas in the expansion valve to reduce the pressure and temperature of the liquid entering the evaporator. This reduction in flash gas is important to improve system performance.

    Links to Related Topics

    Basic Cycle Concepts
    Basic Refrigeration Principles
    System Selection
    Refrigeration Applications and Calculations
    Ice Makers
    Operation and Maintenance