Performance of a mechanically-driven loop heat pipe heat recovery system

Abstract

A mechanically-driven loop heat pipe heat recovery system by booster and refrigerant pump was proposed to match the all-year fresh air load varying greatly with ambient temperature in an energy recovery ventilation unit and enhance its energy-saving potentials. The system prototype was developed and the experimental setup established in which the booster and pump can operate together or separately. Namely, the prototype could be running in pump-driven loop heat pipe (PLHP) mode, booster-driven loop heat pipe (BLHP) mode or booster combining with pump-driven loop heat pipe (CLHP) mode. The heat transfer characteristics of the prototype running in these three modes under winter and summer conditions were studied, respectively. The results showed that the temperature effectiveness of CLHP was greater than that of PLHP or BLHP under all-year conditions. When outdoor temperature is −15 °C, the temperature effectiveness of CLHP is 78.0% and 52.5% higher than that of PLHP and BLHP, respectively, and the heating EER of CLHP is 29.6% higher than that of BLHP. When outdoor temperature is 40 °C, the CLHP has 19.5% higher of temperature effectiveness and 21.7% higher of cooling EER comparing with the BLHP, respectively. In winter, BLHP performs better when outdoor temperature is greater than 7.5 °C while CLHP performs better when outdoor temperature is lower than 7.5 °C. And BLHP has better performance when outdoor temperature is lower than 35 °C in summer while CLHP performs better when outdoor temperature is higher than 35 °C. The composite system can switch its operating mode according to the fresh air load, which can improve effectively the year-round performance of the system to recover heat in building ventilation.