A mobile air-cooled absorption chiller of triple-effect

Earlier investigations carried out to determine the available heat from engine exhaust gases of Madrid city buses permitted us to obtain about 15 kWh as result. This heat, supplied to the generator of a mobile air-cooled lithium bromide single-effect absorption chiller (COP=0.6) generated a cooling power of 7 kw, which is not enough to get the comfort conditions in a city bus. Furthermore, the size and weight of the prototype manufactured were larger than those of the mechanical vapor compression system of the same cooling power used until now. In this paper we present an air-cooled triple-effect system, in which the refrigerant absorption has been separated from the heat transfer. Its components are described and the process variables calculated obtaining: maximum boiling temperatures of about 275 degrees C, solution concentrations between 60% and 70%, absolute pressures between 0.10 bar and 12 bar, available heat of about 12 kWh, COP=1.5-1.7. and a cooling capacity between 15 kW and 20 kW. The separation ct the absorption process into two phases has the advantage of a lower absorption temperature than in those with a simultaneous process of mass and heat transfer. On the other hand, the solution concentration in the absorber is also lower, which increases the COP, and lowers the size and weight. The designed system has a power/volume and power/weight ratios on the same order as those of air-cooled mechanical vapor compression systems of the same cooling power.