A. Hemidi*, J. M. Seynhaeve, Y. Bartosiewicz

Universite catholique de Louvain UCL, Ecole Polytechnique de Louvain, Mechanical Engineering

Department, TERM Division,

Place du Levant 2, B-1348, Louvain-la-Neuve, Belgium.

* Email: amel. hemidi@uclouvain. be, Tel: +32 10 47 22 01, Fax: +32 10 45 26 92

Abstract

The PROFESSI project aims at optimizing an Ejector Air-Conditioning System (EACS). This paper presents a detailed rating modeling of this system. This model can predict the EACS performances when this system is submitted to climatic conditions changes. The effect of a subcooler integration is studied as well. It was concluded that the subcooler must be bypassed when the external temperature goes beyond a critical temperature. Before this threshold, the subcooler improves the COP and cooling capacity. Moreover, a solution is proposed in order to keep the operation of the system even at off-design condition through the use of a regulator heat- exchanger. An exergetic analysis allowed valorising the use of low grade energy for the EACS by comparing performances with a conventional vapor compression system.

Keywords: ejector air conditioning system, sizing, rating, exergy analysis.

1. Introduction

High electricity consumption and use of fluids with high Global Warming and Ozone Depletion Potentials are imputed to the air-conditioning, based on vapor compression systems. For energy saving and environmental protection issues, the solar ejector air-conditioning system (EACS) is mainly investigated in the research field to overcome these drawbacks. An EACS is composed of six main devices (fig. 1): the generator, the evaporator, the condenser, the pump, the throttling valve and the ejector. The generator is fed with the solar energy. The primary flow at high pressure Pg (generator) entrains the secondary flow at low pressure Pe (evaporator) within the ejector. Both

streams are mixed and compressed downstream out of the ejector to a backpressure Pc imposed by the condenser. The primary flow rate returns to the generator with the pump and the secondary expands through the throttling valve and goes back to the evaporator, where the cooling effect is achieved. In the foreseen bench, fraction a of mw is extracted from the generator to perform a

superheat. This system could be integrated into a combined domestic hot water/heating system, to use the extra power supplied by the solar collectors during summer. Several researchers carried out a rating study of the EACS, to determine performances according to given external and saturated temperatures [1,2]. An exergy analysis of the EACS was carried out by [3] to establish a distribution of losses due to the irreversibilities in the cycle.

A sizing program was developed to design the overall EACS and to choice the most appropriate refrigerant [4]. This paper is focused on the rating model, which consists in evaluating and predicting the performances of the chosen cycle under different climatic conditions. All the thermodynamic conditions at the refrigerant side are computed thanks to a detailed mathematical procedure for the heat exchangers and the ejector. Those sizing and rating program modules are

written in FORTRAN and coupled with the REFPROP/NIST routines. An exergetic analysis is proposed to compare performances of the EACS with a conventional vapor compression system in order to valorise the use of low grade energy. For this study, the refrigerant is the propane.