Capacity enhancement of air conditioning systems by direct integration of a latent heat storage unit

With increasing use of renewable energy sources, efficient and consistent use of these energies leads to the necessity of storage facilities. These systems allow for uncoupling of energy production and consumption. Besides battery storages linked to electrical heat pumps, thermal storages have huge potential to provide flexibility for heating and cooling purposes. In combination with air/air-based air-conditioning systems, in particular latent heat storages (LHS) offer several advantages. In this publication, the use of a LHS serving as a subcooler for the liquid refrigerant flow leaving the condenser of a vapor compression cycle is investigated. The concept aims at an increase of the peak cooling power of the refrigeration cycle by unloading the LHS. Theoretical and experimental investigations using a LHS containing paraffin as phase change material (PCM) are presented. The results of the calculation model underline the feasibility and predict an increase of the cycle's refrigeration capacity by about 30% during unloading of the LHS, resulting from a sub-cooling of the refrigerant by about 25 K. The storage concept and theoretical characterization of the thermal behavior of the LHS during loading and unloading are demonstrated and validated by laboratory experiments. With these findings, a practical proof for the implementation of direct heat exchange between refrigerant and phase change material is given, going beyond conceptual considerations presented in literature.