Performance of heat pump water heater (HPWH) with and without liquid-separation: Detailed experimental comparisons

Heat pump water heater (HPWH) is recognized a very interesting technology due to its ability of energy saving and has gained extensive promotions and applications. In this paper, a heat transfer enhancement approach, i.e. liquid-separation condensation, is implemented to the wrapped-around microchannel condenser coil in the HPWH. The feasibility of liquid-separation is attempted to verify since the water heating-up of HPWH is a dynamic process. Serials of experiments are conducted based on the standard procedure and time-divided testing to reveal the system performance and behaviors of condenser coil and water tank. The results indicate that compared to the conventional HPWH (CHPWH), the liquid-separation HPWH (LHPWH) has a higher efficiency of 4.88% that is mainly contributed by its lower power consumption of 4.31% and lower condensing pressure. Regarding the condenser coil, the liquid-separation microchannel coil (LMC) has lower pressure drop and less severe flow misdistribution than the convention coil (CMC). Moreover, less stratification and higher overall heat transfer coefficients are also found for the LMC. FLIR confirms that there exists the liquid-separation in the headers of LMC. It is expected to obtain higher performance if the path arrangements of LMC are optimized.