Modeling and Transient Analysis of a Novel Adsorption Cycle Concept for Solar Cooling
Abstract
When solar cooling is employed to generate chilled water utilizing heat from non-tracking solar thermal collectors to drive the thermodynamic cycle, there commonly is a choice between single stage absorption or adsorption chillers. In most installations realized to date, absorption chillers have been chosen due to their superior coefficient of performance (COP) and lower investment costs (see e.g. Henning, 2007). This paper reports on a way to improve the COP of adsorption chillers to make them competetive with their absorption counterparts while avoiding some of the limitations of the latter. As has been pointed out by Cerkvenik et al. (2001), the cycling of inert mass and incomplete heat recovery between adsorbers are the key factors that lead to a lower COP of adsorption chillers compared to absorption ones. Therefore it is mainly the lack of an equivalent to the solution heat exchanger that limits the COP of the adsorption cycle. The idea of the cycle analyzed here is that instead of employing multiple adsorbers to improve heat recovery, the heat recoverable during adsorption could be stored at many temperature levels within a stratified thermal storage until needed for the next desorption half cycle. This cycle concept named “Stratisorp” was first presented by Schmidt et al. (2007), patent applications are pending (Munz et al., 2009). A thermodynamic analysis of the cycle for the case of a high temperature system with zeolite 13 X and thermal oil as heat transfer fluid has been presented by Schwamberger et al. (2011, 2011a).