Experimental investigation on vapor injection ASHP for electric rail vehicles in cold region

In this study, a vapor injection (VI) air-source heat pump (ASHP) for electric rail vehicles in cold region was developed and the heating performance at ambient temperature -5 degrees C and -20 degrees C was experimentally investigated. The effect of VI-branch electronic expansion valve (EEV2) opening on refrigerant flow distribution and heating performance of the system was analyzed. The mass flow rate of VI-branch increases with the increasing of EEV2 opening, and the main-branch mass flow rate also has increase about 9.1% at - 5 degrees C and 12.3% at -20 degrees C because of the small change of inlet density of main-branch electronic expansion valve (EEV1). The ratio coefficients between the mass flow rate ratio and the pressure ratio of the W-branch to the main-branch fitted from the experimental results are about 0.435 and the initial value is determined by the suction temperature and injection temperature. The maximum heating COP is 2.18 at the injection ratio of 0.18 under the condition of -5/15 degrees C and the maximum heating COP is 1.92 at the injection ratio of 0.29 under - 20/15 degrees C, with 12.6% and 19.3% improvement of heating capacity compared with non-injection cycle. As the superheat of VI-branch is in the range of 5-10 degrees C, the COP gets a maximum.