Modelling and experimental analysis of a GAX NH3–H2O gas-driven absorption heat pump

• An ammonia–water gas-driven GAX absorption heat pump is tested in a laboratory.
• A mathematical model of the cycle is calibrated against experimental data.
• Drawbacks affecting performance at conditions other than design are explained.
• Efficiency enhancements at partial loads by varying solution flow are predicted.

The experimental analysis of a gas-driven NH3–H2O heat pump whose cycle approaches the GAX concept is carried out. Full load operation is investigated by varying hot water temperatures and partial load operation is investigated by decreasing gas input down to 50% of the full load value. Numerical simulations bolster measurements accuracy and provide insight on the variation of cycle COP and Gas Utilization Efficiency (GUE), based on gross calorific value. A nearly constant GUE of about 1.5 is found for hot water temperatures lower than 50 °C. The GUE steadily decreases above 50 °C, reaching about 1.33 at 60 °C. The COP varies more smoothly, from 1.73 at 45 °C to 1.60 at 60 °C. The GUE and COP reduction at 50% of the nominal gas input is 6.8% and 6.4%, respectively. Simulations suggest that performances at partial loads can improve if active control of solution mass flow rate is implemented.