AAHX Passive-Split Loop Thermosyphon Heat Exchanger System

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The precool and reheat coils are not one continuous flat slab with a center divider.  In fact, the two coil sections may be separated by many feet and/or oriented at an angle to each other.

AAHX Pumped Split Loop Configurations

AAHX Pumped Split Loop Configurations

In a SLT AAHX, the ½” diameter coil tubes are rotated 90°, such that the coil tubes are vertical.  Each row of vertical tubes is brazed into a top and bottom manifold.  The top manifold is a vapor tube that will transfer the evaporated vapor from the precool coil to the reheat coil.  The bottom manifold is a liquid tube that will return condensed liquid from the reheat coil to the precool coil.  The reheat coil is placed slightly above the precool coil such that liquid can be returned by gravity. As the liquid boils in the precool coil, the vapor generated naturally rises and travels toward the reheat coil to condense and complete the loop.

Passive-Split Heat Exchangers offer a high degree of installation flexibility since the heat exchanger coils do not have to be side-by-side or in series with the incoming/return airflow.  Since the system is passive there are no pumps required. Performance is comparable to a pumped glycol loop system. Systems can be engineered >100 feet apart.

Split-Passive Sytems can be used in lab applications where the Exiting Energy Recovery Coil can be coated to receive common return airflow that collects the building’s air from multiple fume hoods with potential airborne corrosives.

Valve control located between air streams

AAHX Passive SLT with Summer / Winter operation & frost control



  • An integrated 0-10Vdc proportional ball valve may be placed in the vapor line to modulate the amount of heat transferred.
  • This control method is simple and cost-effective by placing a refrigerant grade, actuated ball valve in the vapor line between the precool and reheat coils.  Closing the valves stops the flow of vapor, essentially shutting down the SLT. Valves can be added to all or just some of the coil circuits to shut down various proportions of the unit for more complete control.
  • Integrated Filter racks

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