Freezer Slab Underfloor Heat and Frost Heave

The mechanism is slow: a freezer pulls heat out of the ground continuously, the frost line advances downward over months and years, and when soil moisture in that zone freezes it expands. The resulting heave is not uniform, so the slab cracks, and by the time it is visible the ice lens is well established. Underfloor heat holds a thin layer of soil above 32 degF so the front never starts. Two sizing facts follow. The load is small -- typically well under a watt per square foot -- because the insulation above it is doing the real work, so the answer is a modest system that must run reliably rather than a large one. And the design is fail-conscious: an electric grid cast into the slab cannot be repaired without demolishing the freezer, which is why glycol tubing in a sand bed with accessible headers, or a ventilated air system, is preferred on large boxes. The energy is continuous and it adds up, so the annual figure is reported next to the capacity -- and the alternative it should be compared against is a slab replacement, which is not a maintenance item. A steady-state screen using an ENTERED assembly U-factor: it does not model transient frost penetration, soil moisture, or groundwater, size the insulation, or design the header and manifold layout. The geotechnical report, the insulation design, and the refrigeration engineer of record govern.

Q = U x A x (target soil temperature - room temperature); watts = Q / 3.412141633; tube length = Q / the entered output per foot; on-centre spacing = area / tube length, in inches; annual energy = watts x hours.

The steady-state below-slab heat loss as freezer floor practice writes it, with the frost-heave mechanism as ASHRAE Refrigeration describes it: soil moisture freezing beneath a low-temperature room expands and heaves the slab, so the soil is held above 32 degF. The assembly U-factor and the tube output are ENTERED. It does not model transient frost penetration, soil moisture or groundwater, and it does not size the insulation.

One steady-state conduction relation and one exact unit conversion.

Estimate. AHJ and licensed professional govern.

Field names used by the API: floor_area_ft2, room_temp_f, target_soil_temp_f, u_factor, tube_output_btuh_per_ft, energy_rate_per_kwh, hours_per_year, td_f, heat_loss_btuh, watts, watts_per_ft2, tube_length_ft, spacing_in, annual_kwh, annual_cost

• Steady state transient frost penetration and soil moisture are not modelledthe geotechnical report
• The assembly U-factor is entered it depends on the insulation, the slab and the sub-basethe insulation design
• It does not lay out the grid header and manifold design and serviceability are the real decisionthe refrigeration engineer of record