Energetic evaluation of thermal energy storage options for high efficiency solar cooling systems.

Thermal energy storage (TES) plays an important role in ensuring continuous heat supply to solar powered thermal systems such as solar cooling plants. Various sensible and latent heat storage material options are available when designing a solar cooling system. Latent heat materials are known to have higher energy density resulting in lower storage volume. However, it is unclear if there are any energy benefits due to these materials while used in a typical solar cooling application. In this paper we investigate the system performance of different storage materials while delivering cooling to a typical commercial building in Australia. This system uses high efficiency triple effect absorption chiller as the cooling delivery system. Heat requirement for this chiller is provided through parabolic trough collectors delivering heat over 200 °C. A suitable approach for storage system design that enables direct comparison of sensible and latent heat storage benefits is described in this paper. In order to simulate the latent heat storage system, a new numerical model has been developed, validated with experimental data and implemented in the simulation environment as an external library. Commercially available liquid sensible storage materials have been compared against latent heat materials with a phase change temperatures suitable for triple effect chiller operation. A parametric analysis of the system design parameters such as the collector area, storage volume has been carried out. Results from annual simulations have been presented for fixed cooling load and variable cooling load scenarios. Latent heat storage systems functioned with high storage efficiency compared to sensible heat storage systems, a reflection of low heat losses due to reduced storage sizes. It is seen that the collectors have higher yield while functioning with a sensible heat storage medium. As a result, for the chosen configuration, the sensible heat storage materials provided higher annual performance than the latent heat material choices. [ABSTRACT FROM AUTHOR]