Advanced absorption heat pumps for domestic heatings - New developments

A test rig for a controllable absorption heat pump (AHP) specified for domestic heatings with the working pair ammonia-water was fabricated and tested in stationary operation. The AHP is directly fired by means of an adjustable gas burner and has a maximum heat capacity of 20 kW. The throttles for the refrigerant and for the weak solution are servo valves. Additionally the AHP is equipped with storages in the refrigerant loop and the solution circuit. Thus it is possible to vary the circulating mass flows and the concentration of the weak and the strong solution in a wide range. Therefore the operation conditions of the AHP can be adjusted in respect to the requested heating capacity, the temperature of the heat source normally ambient air or ground heat - and the temperature of the heating water. The refrigerant vapor out of the generator is purified by partial condensation with the strong solution instead of water as coolant. This process is well described with a model, where the main resistance for the mass transfer is assumed to be in the vapor phase. In stationary operation COPs were obtained between 1.4 and 1.7 for temperatures of the heat source ambient air between -10 and 10 degrees C and heating water temperatures between 35 and 55 degrees C. Future work should focus on the realization of the so-called Generator-Absorber Heat Exchanger process, which promises a significant improvement of the COPs.