Thermosiphon heat recovery uses natural convection to circulate a heat transfer fluid between coils without mechanical pumps, recovering 35-55% of sensible heat energy. Warm exhaust air heats liquid in the lower coil, which becomes less dense and rises naturally to the upper coil where it releases heat to cool supply air, then descends to repeat the cycle. This passive approach requires only gravity-driven circulation.
Technical Details
Thermosiphon systems use water or glycol solutions in closed loops with vertical rise of 1-3 meters between coils. Coils typically contain aluminum or copper construction with 4-6 tube rows. Natural circulation rates range from 0.1-0.5 gallons per minute depending on temperature differential and piping configuration. The system generates circulation pressure of 50-200 Pa through buoyancy forces. Operating effectiveness depends on maintaining proper coil positioning and adequate vertical separation.
Applications and Practical Significance
Thermosiphon systems are ideal for applications where pump reliability is critical or energy consumption must be minimized, such as remote buildings or emergency facilities. They cost 20-30% less than pumped runaround systems. However, circulation effectiveness requires precise vertical coil arrangement and performs best with temperature differentials exceeding 10°C, limiting application in moderate climates.