A STUDY OF FROST HEAVE PREVENTION SYSTEMS
Thermalinc's Electric Heat Cable System vs. Hydronic (Glycol) Systems
Design, Failure Points & Monitoring
Frost heave prevention systems protect refrigerated slabs — freezer floors, cold storage warehouses, and similar structures — from ground freezing beneath the slab. Left unprotected, moisture in the subgrade forms ice lenses that expand the soil upward, cracking and buckling the structural slab above. Two mainstream approaches exist to keep the soil above freezing indefinitely: hydronic (glycol) systems, which circulate warmed fluid through buried piping, and Thermalinc's electric heat cable system, which runs self-regulating heating cable through buried conduit. This sheet compares the two approaches component-by-component, details the failure points inherent to each, and outlines the monitoring and protection architecture used on Thermalinc's electric system described below.
System Components — Side by Side
| System Component | Hydronic (Glycol) System | Thermalinc's Electric Heat Cable System |
|---|---|---|
| Heat delivery medium | Glycol/water solution circulated through buried HDPE piping loops | Self-regulating heat cable pulled into buried 3/4″ or 1″ conduit |
| Heat source | Electric or waste-heat glycol heater, boiler, or refrigeration heat-reclaim package | Direct electric resistance in the cable itself |
| Fluid handling | Circulator pump, expansion tank, air separator, fill/purge valves, glycol concentration maintenance | None required — no fluid in the system |
| Distribution / zoning | Balancing manifold with flow meters/balancing valves per loop | PLC-controlled circuits switched by solid-state relays (SSR) |
| Protection devices | Pressure relief, low-flow interlock on heater, freeze protection for mechanical room equipment | Main disconnect, dedicated breaker per circuit, GFI (ground-fault) protection per circuit |
| Monitoring | Soil temperature sensors; optional flow/pump status | Soil/floor temperature sensors with low-temp alarm and event-duration history; per-circuit end-of-line (EOL) voltage sensing for SSR fault detection in both directions; fault logging |
| Operator interface / annunciation | Typically limited to building management system (BMS) integration, if present | Color interactive display, 98 dB audible horn, and a red stack light that remains illuminated after the horn is silenced for as long as the fault persists |
| Mechanical room footprint | Pump, heater, expansion tank, air separator, manifold, fill station | PLC panel, breakers/GFI, SSR bank — no fluid components |
Hydronic (Glycol) System — Failure Points
A hydronic system introduces a closed fluid loop with mechanical, hydraulic, and chemical elements — each an additional point where the system can degrade or fail, in addition to the electrical components common to any heated system.
| Failure Point | What Can Go Wrong | Consequence |
|---|---|---|
| Glycol leak (buried loop) | Pinhole leak, fitting failure, or fusion joint defect in buried HDPE piping | Glycol lost to soil (environmental/reporting concern), gradual pressure/flow loss, slow-developing cold spot that may not be noticed for a long time — buried leaks are difficult and costly to locate and repair |
| Circulator pump failure | Bearing wear, seal failure, electrical/motor fault, impeller wear from glycol | Loss of flow to entire manifold — all loops lose heat delivery simultaneously unless a standby pump is installed |
| Air lock / inadequate air separation | Trapped air not purged during fill, or air separator undersized/fouled | Localized flow reduction or pump cavitation/noise; heater hot-spot risk if air reaches the element |
| Loss of flow at heater | Pump failure, closed valve, clogged strainer, or flow-switch fault not caught | Heater element can overheat or scorch fluid without adequate flow across it — safety and reliability risk |
| Manifold balancing valve drift | Valve setting changes over time (vibration, service work, unqualified adjustment) | One or more loops under- or over-flowed; far end of an under-flowed loop is a potential cold spot |
| Expansion tank failure | Bladder rupture, loss of pre-charge, waterlogged tank | Loss of system pressure control; can cause relief valve discharge, pump cavitation, or air ingress |
| Glycol degradation over time | Concentration drift, additive depletion, oxidation from air contamination | Reduced freeze protection margin, increased corrosion risk to pump/heater/piping — requires periodic testing (refractometer) and fluid maintenance |
| Corrosion | Improper inhibitor package for wetted metals (aluminum, brass, cast iron, steel) | Internal component degradation, leaks, and reduced heat transfer over the life of the system |
| Freeze exposure of mechanical equipment | Pump, heater, manifold, or exposed header piping located in or near an unconditioned space | The freeze-protection equipment itself becomes vulnerable to freezing if not properly located or protected |
| Header run heat loss | Un-modeled or underestimated heat loss between mechanical room and slab loop field | Glycol arrives at the manifold below design temperature, undermining the loop delta-T the whole system was sized around |
| Single point of failure at manifold/pump | One pump and one heater typically serve the entire loop field unless redundancy is designed in | A single component failure can take the entire frost-heave protection system offline at once |
| Loss of incoming power | Utility outage or upstream electrical fault | Pump and heater both stop — a limitation shared with the electric system, which also cannot operate without power |
Thermalinc's Electric Heat Cable System — Failure Points
An electric system removes the fluid loop entirely — no pump, no glycol, no expansion tank, no air separator, no manifold balancing. The remaining failure points are electrical in nature and, as detailed below, are directly monitored and self-diagnosing by design.
| Failure Point | What Can Go Wrong | Consequence | Correction |
|---|---|---|---|
| Cable damage in conduit | Physical damage during installation or from ground movement | Detected as a failed-open condition (no far-end voltage on a call for heat) the same way an SSR failure is detected | Easily replaced cable — simply pull the old cable out of the conduit and pull in new, readily available cable. No trenching or slab work |
| SSR failed shorted (conducting) | Solid-state relay fails in the "on" state | Circuit stays energized even when the PLC is not calling for heat — detected immediately by far-end voltage present with no call for heat, alarmed for replacement | Replace the failed SSR at the panel; the fault is isolated to that one circuit, so no field work or cable access is needed |
| SSR failed open / cable or splice fault | SSR fails open, cable is damaged, or a splice/connection degrades | No voltage at the far end while the PLC is calling for heat — detected immediately and alarmed as a loss-of-heat condition on that circuit | Swap the SSR first, since it's the simplest check; if voltage still doesn't reach the far end, the fault is in the cable or a splice and is repaired or the cable segment is replaced through conduit |
| Ground fault on a circuit | Insulation damage or moisture ingress at a cable or connection point | Circuit-specific GFI protection trips that circuit — isolates the fault to a single zone rather than the whole system, and is independently monitored | Locate and repair the insulation break or moisture entry point, then reset the GFI for that circuit; the rest of the system stays online the entire time |
| Overcurrent on a circuit | Cable or connection fault drawing excess current | Dedicated breaker per circuit trips and isolates only the affected zone | Inspect and correct the cause of the excess current draw, then reset the breaker for that circuit only |
| Loss of incoming power | Utility outage or upstream electrical fault, ahead of the main disconnect | With no incoming power, the PLC, alarms, and display all lose power along with the heat cable circuits — there is no local alarm during the outage itself. This is a limitation shared with the hydronic system, whose pump and heater also stop without power | Restore utility power or correct the upstream electrical fault; both system types resume normal operation automatically once power is back, no reconfiguration needed |
| Floor/soil temperature trending toward freezing | Any upstream cause (SSR, cable, breaker) or an undersized zone, while the system has power | Independently monitored floor temperature sensor with low-temperature alarm — a direct check that doesn’t depend on the electrical circuit’s own self-reporting being correct. Like the rest of the system, the sensor itself needs power to report | Use the fault log and per-circuit voltage sensing to identify which upstream circuit or component is actually responsible, then apply the specific correction above for that fault |
Protection & Monitoring Architecture (Electric System)
Every circuit in this electric system is protected and independently monitored across multiple layers, from the main disconnect down to direct floor temperature sensing, with all faults logged and clearly annunciated to an operator — giving electrical-fault detection, physical confirmation that the protected area is staying above the freeze-risk threshold, and a permanent record of any event.
| Protection / Monitoring Layer | Function |
|---|---|
| Main disconnect | A single point electrical connection for the system — one main switch that disconnects power, with lockout/tagout (LOTO), providing safe shutdown and lockout of the whole system for service |
| Dedicated circuit breaker — per circuit | Overcurrent protection isolated to a single zone; a fault on one circuit does not affect the others |
| GFI protection — per circuit | Ground-fault protection isolated to a single zone, independently monitored by the PLC |
| Far-end voltage sensing — per circuit | Confirms actual cable energization at the far end of the run, catching both an SSR failed shorted and an SSR failed open or cable/connection fault |
| Floor/soil temperature sensor — low alarm | Independent, ground-sensing confirmation that each zone is operating within the safe temperature threshold |
| Fault logging | Every fault is recorded with its precise location — building a permanent, reviewable fault history rather than relying on someone having witnessed the event |
| Troubleshooting guide — fault history | A brief troubleshooting guide is included within the fault history to help correct the problem |
| Low-temperature event timer/history | Records and timestamps the duration of any low-temperature condition, so a marginal or intermittent event is captured and documented, not just a hard alarm trip |
| Color interactive display | Local operator interface for real-time system status, circuit-by-circuit conditions, and review of fault and temperature history without needing a separate laptop or software |
| 98 dB audible horn | Sounds immediately on any fault condition to ensure the alarm is noticed in an active facility environment |
| Stack light — red, latching after horn silence | Silencing the horn does not clear the alarm — the red stack light remains illuminated for as long as the fault condition still exists, so a silenced horn can never be mistaken for a resolved fault |
| Digital output — BMS interlock | Separate digital output for interlocking with building maintenance systems |
| Peak setback — remote input | Remote input provides setback temperature operation during peak electrical hours |
| Sensor fault alarm | Alarm indication if any temperature sensor fails |
| PLC-based supervisory control | Centralizes all of the above into a single point of alarm annunciation, display, and historical/trend logging |
Summary: Why This Matters
Hydronic Systems
- More components — pump, heater, expansion tank, air separator, manifold, fill/purge system — means more individual points of potential failure
- A glycol leak in a buried loop is difficult to locate, costly to repair, and raises environmental/reporting considerations
- A single pump or heater failure can take the entire loop field offline unless standby equipment is designed in
- Requires ongoing fluid maintenance — concentration testing, corrosion inhibitor monitoring — for the life of the system
- The freeze-protection equipment itself (pump, heater, manifold) must be protected from freezing if located in or near an unconditioned space
- Primary advantage: can use waste heat from refrigeration equipment, which may lower operating cost on very large installations
Thermalinc's Electric Heat Cable System
- No fluid, no leak risk into the soil, no pump, no expansion tank, no glycol maintenance
- Circuit-level isolation — a fault on one zone (breaker trip, GFI trip, cable fault) does not affect the others
- Full-coverage, self-diagnosing fault detection: far-end voltage sensing catches both an SSR failed shorted and an SSR failed open or cable/connection fault
- Independent floor/soil temperature monitoring with low-temperature alarm provides ground-truth confirmation, regardless of what any single electrical component reports
- Main disconnect, per-circuit breakers, and per-circuit GFI protection give layered, zone-isolated protection consistent with standard electrical safety practice
- Built-in fault logging and low-temperature event history create a permanent, reviewable record
- Color interactive display, 98 dB horn, and a latching red stack light ensure faults are noticed immediately and cannot be forgotten once the horn is silenced
- Simpler mechanical room footprint — no fluid-handling equipment to install, commission, or service
Back to the overview.
This is one piece of the full freezer floor frost heave prevention system. Back to Freezer Floor Frost Heave Prevention →
This is one piece of the full freezer floor frost heave prevention system. Back to Freezer Floor Frost Heave Prevention →