A localized area in an insulated structure where higher thermal conductivity materials create a pathway for accelerated heat transfer, bypassing surrounding insulation and causing concentrated thermal losses. In refrigerated vehicles, thermal bridges at structural joints, fasteners, door frames, and floor supports can account for 15-35% of total heat infiltration—yet standard loadbox construction treats thermal bridging as an acceptable compromise rather than an engineering problem requiring solution.
How Thermal Bridges Work
Heat always seeks the path of least resistance. In an insulated loadbox:
- Foam insulation panels resist heat transfer (high R-value)
- Metal structural members conduct heat readily (low R-value)
- Wherever metal spans from exterior to interior, heat bypasses insulation
- Concentrated heat flow occurs at these “bridge” points
The result: cold spots on interior surfaces where thermal bridges penetrate, increased refrigeration load to compensate for bypassed insulation, and potential condensation/ice formation at bridge locations.
Common Thermal Bridge Locations in Refrigerated Vehicles
| Location | Cause | Impact |
|---|---|---|
| Floor frame | Metal chassis rails under loadbox | 20-40% of floor heat gain |
| Door seals | Metal frame surrounding insulation | Major infiltration pathway |
| Wall joints | Panel connection hardware | Linear heat bypass |
| Roof mounts | TRU mounting brackets | Concentrated heat entry |
| Tie-down points | Load securing hardware | Penetrating connections |
Quantifying Thermal Bridge Impact
Research on refrigerated vehicle construction demonstrates:
- Thermal bridges can increase total heat load 15-35% beyond calculated insulation values
- Floor thermal bridges are particularly severe due to urban heat island pavement radiation
- Door frame bridges worsen with age as seals deteriorate
- Poorly constructed bodies show thermal bridges visible on infrared imaging
South African Thermal Bridge Concerns
South African operating conditions amplify thermal bridge problems:
Summer Pavement Heat
- Pavement surfaces reach 55-65°C in direct sun
- Floor thermal bridges conduct this extreme heat directly into cargo space
- Standard chassis-mounted loadbox designs maximize this exposure
- Urban heat island compounds radiant heat loading
High Temperature Differentials
- Ambient 40°C, cargo -18°C = 58K differential
- Every thermal bridge pathway works harder under extreme differential
- European-designed bodies optimized for 32°C ambient underperform
Construction Quality Variation
- Local loadbox builders prioritize cost over thermal performance
- Thermal bridge mitigation adds construction expense
- Competitive pressure drives toward minimum viable insulation
Thermal Bridge Mitigation
Professional refrigerated body construction addresses thermal bridges through:
- Thermal break materials at structural connections
- Continuous insulation layers covering all surfaces
- Minimized fastener penetrations through insulation
- Isolated floor construction above chassis rails
- High-quality door seals with thermal breaks in frames
These measures add 10-20% to construction cost but reduce operating costs and improve temperature performance throughout vehicle service life.
Detection Methods
Thermal bridges can be identified through:
- Infrared thermal imaging revealing temperature patterns
- Ice formation at specific interior locations
- Condensation patterns indicating cold spots
- Temperature mapping showing localized warm areas
Related Terms: Insulation R-Value, Thermal Load, Urban Heat Island Effect