MODELING OF ABSORPTION HEAT PUMPS: SOLAR APPLICATIONS EMPLOYING CHEMICAL STORAGE AND STEADY-STATE MODELING WITH A COMPARISON TO EXPERIMENTS

This work develops simulation models for absorption heat pumps (AHPs) with the goal of enabling a more analytical approach to their study and design. A continuous, liquid absorbent AHP with chemical storage is modeled using mass and energy balances and assuming mass transfer equilibrium. This model is used with the TRNSYS program to simulate the performance of an AHP in a residential solar-driven heating and cooling system. For the three U.S. climates investigated, an AHP using the NaSCN-NH(,3) chemical system provides significant non-purchased energy to the load. Compared to a conventional solar system, the heating performance of the AHP system is better at low collector areas but the cooling performance is slightly lower. The performance is generally improved by increasing the storage mass or thermal capacitance of the system. The two alternate control strategies studied were of little advantage.; The steady-state and cyclic testing of a prototype gas-fired ammonia-water AHP in an environmental chamber is described; measurements include temperatures, pressures, absorbent concentrations, flow rates and heat flows. The coefficient of performance and heating capacity depend most strongly on ambient temperature; varying the load water temperature and flow rate has lesser effects. The performance of the unit is sensitive to refrigerant charge, with the optimum charge varying with ambient temperature. This AHP shows a significant performance degradation in cyclic operation.; A modular, steady-state simulation program for absorption heat pumps is developed and validated with experimental data. The model utilizes an analysis of the refrigerant and absorbent inventory to set the system pressures. Property relations are supplied as separate subroutines. The rectifier, condenser, evaporator, and refrigerant heat exchanger are modeled with a general N-stream heat exchanger component employing a finite difference formulation. The analyzer is treated as a series of equilibrium stages. An analysis of simultaneous heat and mass transfer is applied to each row of the falling-film absorber. The agreement between experiments and simulations is generally good, although several needed refinements to the model are identified. A factorial design is carried out to investigate the performance sensitivity to design parameters.