Hybrid cooling and heating absorption heat pump cycle with thermal energy storage

This study presents a hybrid cooling/heating absorption heat pump with thermal energy storage. This system consists of low- and high-pressure absorber/evaporator pairs, using H2O/LiBr as the working fluid, and it is driven by low-temperature heat source of 80 °C to supply cooling and heating effects simultaneously. Using solution and refrigerant reservoirs, the system can store thermal energy in the form of chemical potential owing to the concentration glide. Applying the building cooling/heating temperature conditions, the operating concentration range of the system is constrained to 0.49–0.59 LiBr mass fraction. In this range, a system performance analysis is conducted through simulation modeling. The maximum total COP of the hybrid heat pump cycle reaches 0.80, which is same as the maximum COP of the single-effect absorption chiller with the same operating conditions. In storage mode, the maximum total COP is reduced to 0.30 due to the lack of internal heat recovery, while a maximum energy storage density (ESD) of 402.4 kJ/kg is achieved. In particular, the performance of the storage mode is dominantly affected by the solution circulation ratio, indicating the design criteria for the proposed system.