Modeling of an ammonia-water absorption heat pump water heater for residential applications

An investigation of a direct gas-fired single-effect ammonia-water absorption heat pump water heater for residential applications is presented. Combustion of natural gas provides heat to the desorber where refrigerant is generated. The absorber and condenser are hydronically coupled in parallel to a hot water storage tank, while the evaporator is hydronically coupled to an ambient air heat exchanger that extracts ambient heat. A thermodynamic model is developed and the system configuration is optimized to provide a baseline heating capacity of 2.79 kW at a coefficient of performance of 1.74. A detailed parametric study over a range of water and ambient temperatures is used to understand the variation in system performance as the water is heated from 14.5 to a minimum of 57.0 degrees C. The performance of the heat pump coupled to a 227-liter storage tank is also modeled for three different scenarios, a cold start response to a 76-liter draw, and response to stand-by losses. The absorption heat pump water heater is found to achieve coefficients of performance better than those of commercially available gas fired heaters and electric heat pump units. (C) 2017 Elsevier Ltd and IIR. All rights reserved.