Dynamic simulations of an absorption system with different working pairs at chiller and heat pump application

Abstract

This work describes the dynamic simulation of a direct air-cooled single effect solar-driven absorption system and demonstrates the numerical results of the absorption system with different working pairs. The working pairs used in the chiller mode are LiBr-H2O and Carrol-H2O (Carrol contains LiBr and EG -Ethylene glycol- with a mass ratio at 4.5:1), while in the heat pump mode, EG is introduced in the evaporator to avoid freezing problem which limits the operation condition. The numerical modelling was implemented on a modular object-oriented simulation platform (NEST platform tool), which allows the linking between different components, considered as objects, which can be either an empirical-based model or a more detailed CFD calculation if necessary. Specifically, flat plate collectors coupled with a storage tank is introduced assisting the heat source for the absorption system, and all the components are implemented based on mass, momentum, and energy balances. The goal of this work is to compare the general performance like COP and working capacity between LiBr-H2O and Carrol-H2O in chiller mode and the performance of working pair Carrol-H2O at heat pump mode in dynamic operation. Finally, various simulations at each case are performed with meteorologic data of Barcelona and Madrid in summer and winter, and the heat source consists of 30 m2 solar collectors and an auxiliary heater. The solar collectors used in the system are high efficiency flat solar collectors. The fraction of solar energy in heat source varies depends on the total radiation in the area, which could reach 0.65 on a sunny day or attributes less than 0.1 on a cloudy day.