This paper aims to design, construct, and test the CLOHP/CV air-preheater for reduced relative humidity in drying systems for recovering the waste heat from the drying cycle. The CLOHP/CV heat-exchanger consisted of 3.58 m long copper tubes, with an internal diameter of 0.002 m. The evaporator and condenser sections were 0.19 m long, the adiabatic sections were 0.08 m long, the hot-air velocities were 0.5, 0.75 and 1 m/s with the hot-air temperatures being 50, 60 and 70 degrees C, and the relative humidity was 100%. The working fluid was R134a with the filling ratio of 50%. It can be concluded that, with an increase in the hot-air temperature from 50 to 70 degrees C, the heat-transfer rate slightly increases. The velocity increases from 0.5, 0.75 to 1 m/s and the heat-transfer rate slightly decreases. The velocity increases from 0.5, 0.75 to 1 m/s and the effectiveness slightly decreases. The hot-air temperature increases from 50 to 70 degrees C and the effectiveness slightly increases. The relative humidity reduced to the range 54-72% from 89% to 100%. The CLOHP/CV air-preheater can reduce the relative humidity and achieve energy thrift. (c) 2006 Elsevier Ltd. All rights reserved.