The effect of improper refrigerant charging on the performance of a residential heat pump with fixed expansion devices (capillary tube and short tube orifice)

Abstract

An experimental study concerned with the off-design refrigerant charging of a heat pump in cooling mode is presented. A series of experiments was conducted to characterize the effects of refrigerant charge, type of expansion device (capillary tube and short tube orifice), and outdoor temperature (82OF to 100°F) on the system performance (capacity, EER, SEER, etc.) of a heat pump. A three-ton residential air conditioner unit was charged with R-22 refrigerant in 5% increments from -20% to +20% of full charge to cover the full range of charging conditions. The investigation of off-design charging indicated that the system performance variables of the unit with the capillary tube were more sensitive to off-design charging than the system with the short tube orifice. The results of experimentation showed that the short tube orifice system performance variables showed a small variation with the refrigerant charge but a strong dependence on the outdoor temperature.