Operational improvements to increase the efficiency of an absorption heat pump connected to a multi-effect distillation unit

• Experimental evaluation of a DEAHP performance connected to a MED unit.
• Identification of operational problems in a LiBr double effect heat pump.
• Results show increase in the COP, more stable behavior and faster start-up stage.

The performance of a double-effect LiBr–H2O absorption heat pump connected to a solar multi-effect desalination plant has been analyzed experimentally. A detailed study of the main operation problems has been carried out in a first experimental campaign with the aim of identifying new control strategies to improve the behavior of the system at stationary nominal conditions, as well as to increase its thermal efficiency. An improved control strategy is proposed to deal with the identified problems and has been validated in a second experimental campaign. Results of these experiments have shown an improvement of the heat pump performance when the refrigerant flows continuously between the low-temperature generator and the condenser. By avoiding intermittent water flow, it is easier to keep LiBr solution levels in both generators constant, gas consumption is lower, it takes less time to reach steady state and a higher average coefficient of performance is reached.