Refrigerated warehousing has a number of important differences from regular dry warehousing. These specialized needs touch all areas of the warehouse environment—the building, equipment and personnel.
A good place to start is the warehouse building itself and the influence of various temperature ranges. As refrigerated warehousing is commonly associated with certain types of food storage and distribution, I will focus in this type of warehousing use.
Refrigerated warehousing is divided into two broad categories: cooler warehouses are designed for above-freezing temperatures and freezer warehouses are designed for below-freezing temperatures.
As a rule of thumb, the colder the temperature ranges you wish to maintain, the more specialized the building and equipment.
As you approach the freezing barrier for low-temperature cooler warehouses (those that should maintain Fahrenheit temperature ranges in the lower thirties), recognize that many of the design characteristics for freezers are a good idea. One example is a heated floor because permafrost below the floor can also form at these temperatures over a prolonged period of time.
Note, as well, that refrigerated storage is found in all parts of North America and design (especially building) features will be different for buildings in the High Arctic as compared to those in Miami.
I am going to divide cooler warehouses into two general categories, chocolate coolers and low-temperature coolers (say for milk and meat products).
Chocolate coolers in their simplest form are air-conditioned warehouses that are designed to stay below a maximum temperature in the heat of summer. Because of the large areas that need to be cooled, supplemental cooling like economizers or roof misting maybe advisable in certain situations to reduce energy consumption.
Economizer systems save energy by using outside air instead of refrigeration equipment to cool the building. Most commonly they take advantage of favourable weather conditions to reduce mechanical cooling by introducing cool outdoor air (usually at night) into a building. The term “free cooling” is used in the HVAC industry to describe savings achieved from a properly working economizer.
Economizers not only save energy, they also decrease wear on the air-conditioning unit and can postpone costly repairs. In early spring and late fall they can also be used to heat the building, using the same principle, prior to or after the onset of full winter lower temperatures.
Generally a regular warehouse building can be used for an air-conditioned warehouse, although better insulation often gives a positive return.
Low-temperature cooler warehousing is similar to freezer warehousing, so I will look at them together.
A freezer warehouse is divided into four sections:
• Incoming adjacent to processing plant
• Combined cooler / freezer
• Incoming / Outgoing loading docks
For product in a processing plant the key issue is to cool it to the warehouse storage temperature.
Two types of freezing processes are usually used. “Contact freezing” costs less to operate and operates with flat hollow plates or slabs through which cooled refrigerants are circulated. Food is placed in direct contact with the plates and is cooled.
“Blast freezing” (flash freezers) is common as well. Batch air blast freezers are mainly used for package products on pallets, as well as loose products. Both of these are done in specialized rooms.
When considering building construction for a freezer there are different needs for each component of the DC: floor, roof, walls, separation between freezer and cooler section, and loading docks (to be addressed in a later column).
The floor in a freezer has a very unusual construction because it is heated beneath the floor. This is done to prevent the freezer envelope extending into the ground and forming permafrost beneath the floor.
The first layer of the slab next to the ground is typically tubing through which is pumped warm glycol to warm the ground underneath the slab. A layer of polystyrene insulation is typically installed that provides a minimum approximate R-20 insulation value to insulate the floor. Finally the concrete slab is poured directly over the insulation. From an energy conservation perspective it is important to construct the freezer as small as possible and proper floor flatness is another important design characteristic.