Preventing Frost Heave In Cold Storage Facilities

By Matt Gurreri

One of the biggest dangers to your cold storage space could be right under the feet – frost heave. In this post we address what frost heave is, how it occurs, and just why electrical heating cables supply the most reliable methods to prevent it.

Frost heave occurs once the temperature of saturated sub-grade soil below the concrete floors of a cold storage space dips below 32°F causing pockets of moisture within the soil to freeze. At fault here’s cold air penetrating the storage area’s concrete floor and at night floor’s protective insulation. Heated air in soil moves toward the cooler, lower pressure air in the storage room before two are balanced. After the sub-grade soil freezes it forms ice lenses that push upward with enormous pressure, “heaving” the concrete above, lifting columns, and distorting the building’s foundation resulting close in doors that don’t. Frost heaving could cause cryogenic tanks to collapse and leak LNG furthermore, which may be hazardous to the surroundings. If left unchecked, severe frost heave can lead to a whole building being demolished and condemned.

Exemplory case of frost heave damage

Frost heave moves slow. Initially you might only see small bulges and cracks in the concrete. Or you might spot the floor grade becoming uneven, resulting in disrupted pallets, tilted racks, and problems maneuvering forklifts. The room’s corners can happen to be sinking also. Without repair, this can continue before structural integrity of the building is severely compromised. Repairs can be extremely expensive. The frozen soil should be re-compacted and remediated. New concrete floors need to be re-poured. While being repaired, the available room is shutdown to permit the ice to thaw and the ground to settle. This can take weeks in some instances and disrupts productivity obviously. Racks are emptied of inventory and removed.

To avert soil under the slab from freezing, underfloor heating systems are installed. The quantity of heat required would depend on the slab surface temperature, just how much insulation has been installed, the thermal properties of the soil, and the quantity of moisture within it. Top quality, moisture-impermeable insulation ideal for below-grade application could be installed to reduce the quantity of heat required, although its cost prohibits used in large areas usually. The quantity of heat necessary could be decreased with poly vapor barriers further, slip-sheet, and non-frost-susceptible back-fill. Generally, one inch of insulation is the same as about two feet of soil thermally.

Soil Heating Methods

Each soil heating method has its benefits and drawbacks. The proper system for the facility will be dependant on design and installation, life cycle costs, and maintenance requirements. Is really a brief summary of every method below.

Natural Ventilation: This technique depends upon air flowing freely through ductwork within the concrete below the insulation. The benefit of natural ventilation is that it’s an easy task to install and requires without any maintenance. And undoubtedly, you can find no energy costs. On the downside, it really is vunerable to frost, requires regular inspections to guarantee the ductwork is clear, also it should be installed above walk out. Designing these operational systems could be tricky due to complex thermodynamic calculations.

Forced Ventilation: This technique uses heated air forced through ductwork within the cold space by way of a fan. This heated air is collected from exhaust air from the process or engine room sometimes. On the plus side, forced ventilation provides control on the temperature of the new air being circulated. The duct sizes could be smaller than in natural ventilation, aswell. However, it could be expensive to set up, is at the mercy of blocked or damaged ductwork, and should be inspected regularly. Condensation is commonplace within the ductwork that could turn to ice resulting in plugged up system and pipes failure.

Pumped Fluid: Here, heated pumped fluid is sent by way of a piping network beneath the slab in order that its heat is released to avoid soil freezing. Fluids are usually heated to 65°F with popular fluid being Glycol approximately. Benefits of pumped fluid systems are reliable operation, the price efficiency of using waste heat from the refrigeration system, and the capability to operate the operational system year-round no real matter what the weather. Disadvantages of pump fluid systems are the difficulty of locating leaks and repairing them. Piping material deteriorates as time passes to causes leaks, which presents an environmental issue with Glycol and costly repairs.

Another Option: Electrical Heating Cables

Possibly the most suitable choice for preventing frost heave may be the installing self-regulating electrical heating cables within conduit embedded in the substructure. Self-regulated cables adjust their heat output with temperature fluctuations for safer automatically, better operations.

In a self-regulated cable, the electrical energy wires are co-extruded right into a heating element comprising a polymer-based material with carbon particles. This gives a resistance path, a circuit across the amount of the heating cable hence. Resistance and then the precise output of the heating cable vary dependant on the outside temperature, because of microscopic expansion and contraction of the polymer. Power output is reduced because the temperature increases. Conversely, at lower temperatures, the charged power is increased. No thermostat is necessary as the cables automatically vary their heat output predicated on changes in the encompassing temperature. Self-regulated cables deliver maximum freeze protection and temperature maintenance plus could be cut to any length on-site efficiently. Energy-saving digital temperature controllers could be put into give users regulation over single heater segments with remote alarm contacts and GFCI protection.

In comparison with air or glycol systems, self-regulated cables provide superior control and monitoring, with less maintenance, if they are protecting cold rooms, freezers, ice arenas, or any refrigerated commercial application virtually. Conduit allows cables to be replaced with newer cables if the need plus

Another that we now have no environmental issues as you can find with glycol. Due to its solubility in lack and water of adsorption and partitioning to soils, propylene glycol has high mobility in soil and the potential to leach into groundwater. The rate of biodegradation is slower in lower ambient soil temperatures found underneath cold storage spaces.

Cross-section exemplory case of a power heating cable system installation (Supplied by Emerson)

Design Considerations For Electrical Heating Cables

Establishing the right design, procurement, and installing self-regulating electrical heating cables ensures a long-term heat tracing solution for the cold space for storage. Design considerations would are the size of the facility’s surface, the thickness of the concrete, insulation and substrate, the available room temperature, and if the installation is above or below grade.

The layout of the conduit – which may be either non-metallic or metallic – is really a major design factor. Conduit could be installed in a “looping” pattern in order that NEMA 4 junction boxes could be conveniently situated along one wall. Or if the area long too, the contractor can run straight conduit beneath the floor that locates junction boxes on walls opposite one another. Normally, these junction boxes are installed 1’ to 2’ above the concrete surface. Additionally, be careful compared to that the layout and amount of bends ought to be arranged to ensure that the pulling force isn’t be excessive. Per the National Electrical Code, Article 348-10, “There shall not become more than the exact carbon copy of four quarter bends (360 degrees total) between pull points, e.g., conduit boxes and bodies.”).

Heating cables ought to be tested at the very least of 3 x:
1. While on the reel still,
2. After connecting end and power terminations, and
3. Upon completion of the concrete pour.

Installing electrical heating cables under the floor of cold storage spaces maintains above freezing soil temperatures, preventing ice accumulating in the bottom below and the costly damages of frost heave. Weighed against traditional method of protection, electrical heating cables are simpler to design, install and keep maintaining, environmentally safe, and energy conserving.

Gurreri is product marketing manager
for EasyHeat, Emerson Automation Solutions . He holds a International and Mechanical Engineering degree from Marquette University in Chicago, and a an MBA from Northwestern University’s Kellogg School of Management. Guerreri has over ten years of experience in operations and power engineering with Emerson, Eaton, and RM Energy.