When you build a freezer you have to heat the earth under the freezer, otherwise freezing temperatures make the earth freeze and the moisture in the earth expands and lifts or heaves the freezer floor.

The systems

There are four underfloor heating systems typically used in the industry, and all have their pros and cons. They consist of air grabbing systems, forced air systems, electric heat, and warm ethylene glycolor oil tubes.

Air Gravity

“The least expensive are the gravity air systems”, according to Ron Vallort of Ron Vallort & Associates Ltd. He explains that in this system, air vent tubes are placed below the subfloor, at least 8 inches in diameter andless than 120 feet in length and typically spaced 5,5 feet apart. The tubes must be sloped so warm ambient air gathers on the high end and any condensation runs down and out the tubes. Both ends of the tubes must be screened and kept free of obstructions, which can be problematic. “we often see installations where the screens have been damaged so that birds and other animals  can build nests in the tubes thereby preventing airflow” comments Vallort. Air gravity can also define a method where the whole building is raised off the ground, according to Marko Dzeletovich, President of Cold box builders, a design/build company that installs all four of the systems.He explains that a structural floor slab supports the racking and product loads, and is constructed so that outside air can pass below a structural slab. Effectively the soil cannot freeze below the slabbecause it is not in contact, so heat cannot be lost from the soil.

Forced Air

Forced air systems are the same as gravity air except air is forced through the system by fans, according to Vallort. Because of the fans, tubes can be much smaller but at least 4 inches in diameter, supplied air should come from warm dry area rather than a cold moisture laden area.

Electric

In this system electrical resistance cables are installed below the insulation and finished floor slab in a mud slab, explains Wooley. Typically the cables are installed in a conduit with access above the floor so that the heating element may be replaced as necessary.The systems are designed to supply the correct amount of heat required for a particular freezing floor, based on its size, shape, operating temperature, and insulation thickness.

Pumped Fluid

Vallort explains that the wet systems have a heated solution circulated through pipe loops installed below the floor insulation and usually encased in a mud slab. Glycol is frequently used, as are other heat transfer fluids. The source of heat is often rejected heat from the refrigeration system.When building large scale freezers, pumped fluid is avery good way to go. It’s free heat and only requires a small pump to circulate the heated fluid. Detecting leaks in the pumped fluid system is difficult but rare. It’s best practice to installe multiple overlapping circuits in the event one of the circuits fails. You will know if one goes down because the pressure will drop immediately. During the construction this needs to be constantly monitored. The great thing is you will know if any damage has occurred before you pour your floor. As build drawings are very important with these systems to show the location of all the circuits.

How to choose the right system

In choosing the right underfloor heating technology for your freezer you have to forts determine what your soil condition is. Ift he soil doesn’t retain water, as in desert climates, or you are building on solid rock, or you have an extremely low water table, you don’t need an underfloor heating system at all, but these are pretty rare conditions. If the freezer is built over a higher water table area, be extra considerate of which system to go with. Since air systems will not be a good choice in this case, and if the water table is high enough, you may consider a structural slab that is raised off the ground entirely, or find another sit.

The key factors in deciding on a system should be: design, installation, life cycle cost and maintenance.

[ΠΗΓΗ:COLD FACTS MAGAZINE]