Optimum dynamic operation of integrated absorption-compression refrigeration cycles and thermal energy storage systems for district cooling

Abstract

A holistic approach is presented for the systematic assessment of the steady-state and dynamic performance of integrated absorption-compression refrigeration configurations that exploit thermal energy storage (TES). Thirteen configurations are evaluated including a dual vapor compression cycle (VCR), stand-alone single and double absorption refrigeration cycles (ABR) with two different working fluids (conventional NH3/H2O and novel acetaldehyde/DMF mixture), and their combinations thereof (VCR-ABR in parallel or cascaded configurations). The evaluation criteria combine steady-state performance metrics such as capital and energy cost, coefficient of performance (COP) and cooling water utilization, with dynamic operation indicators such as demand satisfaction, cooling and total energy utilities during transients between different operating levels. The dynamic operation optimization variables are the energy input per hour and the share of cooling output heading to each end-user. For all combined configurations, the resulting VCR cost is significantly lower compared to the nominal case of a dual VCR. The cascaded VCR-ABR configurations exhibit 241% higher VCR COP values than the nominal case. The latter also presents an average of 8.79% higher cooling water utilization than all the alternatives. The employment of TES enables the satisfaction of higher cooling demand than the cycle’s nominal cooling capacity. ABR-equipped configurations satisfy the cooling demand 16.47% more effectively than the dual VCR. The latter is attributed to the ABR ability to operate in part load when at nominal efficiency, while presenting better dynamic cooling water use. The electricity requirements are reduced by 49% and 69% in the parallel and cascaded VCR-ABR configurations, compared to the nominal case.