Principles of Air Cooling

The preferred method for using air as the heat transfer medium is what is known as “forced-air cooling”. The name is misleading to some extent, in that the air is not forced into the cartons by positive pressure, but rather is drawn through them by negative pressure. The effectiveness of forced-air cooling is dependent on container design. It is widely used and adaptable to many types of fruits, vegetables and flowers.

Principles of Forced-air Cooling

The simplest form of forced-air cooling uses a portable blower. Two rows of stacked containers or palletized produce are lined up on either side of the blower inlet. The open area between the containers is covered with a canvas or plastic tarp, sealing the top and back of the stacks. The blower, of a high air volume design, is then started and it directs the air away and upward from the containers, forming a slight pressure differential inside the container stack interior. This negative pressure pulls air though all openings equally. In this simple system the air is chilled by the storage room refrigeration system. If already cooled produce is in the room, sufficient refrigeration power must be available to ensure that the room air does not warm up to an undesirable degree, causing damage to the produce that has already been cooled.