Abstract
The report summarizes the findings of ASHRAE Research project 1173, by Purdue University to assess the impact of varying refrigerant charge on air conditioner (AC) system performance. This project tested six residential air conditioners with varying the system charge in a wide range, using TXV or fixed-orifice as the expansion device. In summary, the systems using fixed-orifices are much more sensitive to reduction of the system charge than using TXVs. The systems using fixed-orifices had noticeable performance degradations when reducing the system charge below 90% relative to the factory charge; the systems using TXVs experienced drastic performance penalties when decreasing the system charge below 80%. In the cases, the TXVs were all fully open and couldn’t control the target superheat degree. In order to limit the system charge for lower-GWP refrigerants, without degrading the system performance much, the AC systems are recommended to use TXV and compact heat exchangers, i.e. micro-channel heat exchangers.