Internal Heat Exchange A/C System

Denso Corporation has developed a unique double-pipe internal heat exchanger for Automotive air conditioning systems.  The new system increases cooling performance by 12%, reduces annual fuel consumption by an estimated 1% and reduces compressor pulley ratios for low engine speed under load. The system was first introduced in 2006 in the Middle and Near East on the Toyota Prado and Lexus GX470.

The double-pipe internal heat exchanger integrates two pipes, which are separated in a Conventional refrigeration cycle, into one pipe with inner and outer tubes.  In the refrigeration cycle, the low-temperature gaseous (vapor) flows in the inner tube, and exchanges heat with the high-temperature liquid refrigerant flowing in the gap between the inner and outer tubes.


In the double tube design, the inner tube wall has spiral grooves that face the outer tube enhancing heat exchange.  This allows the internal heat exchanger to achieve a higher cooling performance within a shorter pipe length of only 40 centimeters (16 inches).

This design and performance will be even more important to have when refrigerant R134A is replaced with the new 1234yf refrigerant.

Other advantages are: 

  1. uses less space.
  2. easily bent without crushing the internal Spiral design.
  3. superior over current and competitor designs at low engine speeds typically seen in diesel engines.
  4. lightweight for reduced vehicle mass.