Simulation of an ammonia-water heat pump water heater with combustion products-driven evaporator

Abstract

The objective of this work is to simulate a single effect (SE) ammonia-water heat pump for domestic water heating, with innovative aspects for cycle simulation and eventual practical implementation. The following practical difficulties are addressed in the simulation: 1. seasonal temperature variations change the operating conditions of the distillation column, calling for insightful design to maintain a suitable refrigerant concentration in all seasons, and particularly in winter; 2. The evaporator activated by outdoor air suffers from immoderate heat transfer requirements, and these demands are considerably reduced if the activation is done by products of combustion; 3. Pumps have head requirements that can be assuaged by judicious selection and inlet solution subcooling. The variables that need to be controlled if the same column is to be used all year round are specified. As configured with the innovations mentioned, the cycle simulation yields a coefficient of performance within the expected range for a single effect, but it harbors the promise of a much smaller evaporator, of small overall height, and of a distillation column capable of operating effectively all year round with the same feed point.