Aqueous Lithium Bromide TES and R-123 Chiller in Series

Abstract

This paper presents an analysis of a cold thermal energy storage (TES) system operating in series with an R-123 chiller. A lithium bromide/water (LiBr/H2O) solution is used both as a refrigerant and as a cold thermal storage material. The refrigerant, liquid water, is extracted from the LiBr/H2O strong solution during the off-peak period. The liquid water and LiBr/H2O weak solution, a byproduct of the refrigerant recovery process, are used during the on-peak period to cool the building. Building waste heat is pumped by the R-123 compressor to a higher temperature during the off-peak period and is used in the generator to recover the thermal storage by reprocessing the stored solution to a higher lithium bromide concentration. The storage volumetric efficiency and system COP are determined and compared to storage systems based on water/ice and liquid water. The storage volumetric efficiency is greater than a water/ice system and far exceeds the value for a liquid water system. The proposed system, which uses an external heat pump as a source of generator heat, is also compared to another LiBr/H2O system that uses a self-contained internal heat pump (the compressor operates independently from the chiller and uses the liberated water refrigerant as its working fluid). The system presented here outperforms both the water/ice system and the internal heat pump LiBr/H2O system but is unable to match the liquid water system COP. However, it has other well-defined advantages over the liquid water system and appears to be a competitive alternative to conventional TES systems.