Design And Practical Validation Of A Hybrid Absorption/Compression Chiller Driven By Low-Grade Heat

For all applications of sorption chillers or heat pumps strict limits have to be met, arising from the physical properties of the working fluids. A minimum temperature of the driving heat source has to be provided and the temperature lift of the cycle is limited. As a consequence, the chiller has to be oversized for application in solar cooling or tri-generation systems in order to adapt for low-grade driving heat. Due to the limited temperature lift of the working pair water as refrigerant and lithium bromide as sorbens the use of dry cooling towers is not feasible and in heat pumps systems only moderate heating supply temperatures can be provided.When a mechanical compressor is integrated in the internal cycle of a sorption chiller, flexibility is obtained for a more compact and cost-efficient design and for adaptation to challenging operating conditions.Design and first experimental results of a hybrid absorption/compression cycle are presented. An electrically driven high-speed turbo compressor is directly integrated in the sorption process of a single-stage water/LiBr cycle providing a variable share of the required pressure rise between evaporator and condenser. The system shall be operable in pure sorption mode and in hybrid absorption/compression mode, offering a boost of cooling capacity or increased flexibility for operation with low-grade driving heat or increased temperature of heat rejection.