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Energy Recovery Heat Pipes

Energy recovery heat pipes from Heat Pipe Technology (HPT) provide economical and reliable recovery of both heating and cooling.  This means that the payback time of your investment is minimal.  HPT heat pipes are economical because of their low initial cost and minimum maintenance requirement.  The only maintenance required is periodic cleaning similar to any air conditioning coil.  HPT heat pipes are reliable because they are passive with no moving parts (except for optional dampers).

For several years, energy recovery heat pipes have been constructed using relatively large diameter tubes.  This is because they have been single tubes that must handle vapor flowing in one direction and liquid flowing in the opposite direction simultaneously.  Also, to be able to transfer heat in one direction during the heating season, and the opposite direction during the cooling season, they have normally been equipped with a tilting mechanism. HPT utilizes a loop circuit that allows for equal heating and cooling recovery (see HRM-H™) or optimization for either the more prominent heat or cooling recovery while still allowing for appreciable recovery the rest of the time (see HRM-Z™)

Because of HPT's unique circuit design, heating and cooling recovery can normally be accomplished without a tilt mechanism or any other seasonal changeover procedure.  To make use of this unique bi-directional energy transfer feature, the air streams should be arranged side-by-side as in A and B, or with one directional energy transfer featuring over-and-under as C.

  1. Side-by-side horizontal air streams with heat pipes in a vertical plane (HRM-H™)
  2. Side-by-side horizontal air streams with heat pipes in a vertical plane optimized for heat or cool recovery (HRM-Z™)
  3. Over-and-under horizontal air streams with heat pipes in a vertical plane (HRM-O™)

Two way heat transfer
Two way heat transfer
One way heat transfer


Comfort Energy Recovery

HPT energy recovery heat pipes can be used for comfort-to-comfort applications or for process applications. Comfort-to-comfort applications include heat only recovery for cooler climates, cooling only recovery for warm climates, or more often, both heating and cooling recovery.  HPT heat pipes are used for heat/cooling recovery all the way from cold northern climates with harsh winters to the heat of the tropics.

For heat recovery during the heating season, the leaving temperature of the exhaust air stream may be lowered to near freezing or below freezing.  Such conditions normally result in the formation of frost on the exhaust side of the heat pipe with partial or complete blockage of the air stream.  To remedy this situation, HPT offers an optional bypass damper on the supply side of the heat pipe.  With the bypass damper opened, air is bypassed around the supply side of the heat pipe so that the leaving temperature of the exhaust air stream is kept warm enough (36°F or higher) to prevent frost formation.  For economizer operation, a bypass damper on the supply side may also be needed.

Process Energy Recovery

For process applications, heat/cooling recovery can also take place in either direction.  Process applications frequently involve air temperatures elevated above normal room conditions.  The heat pipes can be made to withstand temperatures up to 200°F.  For air streams with corrosive components, the heat pipes can be provided with a protective coating resistant to a wide variety of acids and alkalis.  Heat pipes can also be fabricated with both fins and tubes made of copper.


See illustration on previous page showing two different energy recovery heat pipe orientations.  A normal installation will have the two air streams arranged such that they are flowing in opposite directions through the heat pipe.  This is called counter-flow.  Counter-flow operation provides the maximum heat transfer.  If necessary, due to design considerations, the air streams may need to flow in the same direction through the heat pipe.  This is called parallel flow.  Parallel flow can still provide valuable energy savings, but at a reduced rate

Drain Pans

Drain pans are required to capture moisture condensation or for coil cleaning purposes in both supply and exhaust sides of the heat pipes.  Intermediate drain pans may also be required when heat pipes are installed in stackable sections. Drain pans are not provided by HPT.

Energy Recovery Heat Pipe Sizes

Heat Pipe Technology offers energy recovery heat pipes in sizes customized for the particular application.  Options for these Heat Pipes include all the options for the standard size heat pipes.  Heat pipes can have up to 8 rows of tubes, 10, 12, 14 FPI aluminum or 10, 12 FPI copper fins, and can be up to 200 inches long.