A transient computer simulation of an ammonia-water heat pump in cooling mode

A transient model of a single effect, ammonia-water absorption heat pump with spindown has been developed. This model can be used to simulate the performance of the system for a range of feedback controls, and for varying initial and ambient conditions. These results can then be used to make predictions of the trends of system responses for various set conditions. For this model, the house size and the mass of machine components must be specified, and a few simplifying assumptions were made. Matlab with Simulink (a software package with a Runge-Kutta routine) was used to run this simulation. The model itself consisted of eight nonlinear coupled differential equations. The predicted variables reached steady-state values similar to those predicted by a different steady-state model. A PD control loop improved the response time of the system but caused some overshoot. The model is capable of predicting the transient temperature response of the generator, condenser, absorber, evaporator, solution heat exchanger and the house being cooled. The profiles of solution mass stored in the generator and condenser, the mass flow rates and pressures can be determined. For the assumed cycle conditions, changing the values of the thermal masses in the components has only a minor effect on the coefficient of performance (COP). Also only a 1% reduction in COP occurred when using an on-off generator control system as opposed to having a constant generator heat input.