2024

Saari Jussi; Pitkäoja Antti; Uusitalo Antti; Lipiäinen Satu; Ritvanen Jouni

This study presents the optimization (capital cost minimization) of a low-pressure brazed plate pentane evaporator for a two-stage 5 MW th heat pump concept for district heat generation using an air collector heat source. Pentane was chosen as the work fluid through requirements for low environmental impact, and centrifugal compressor design constraints. The evaporator operates in a natural-circulation loop with a drum to separate the liquid and vapor phases before the superheater and compressor. The low saturation pressure of pentane at low temperatures and consequent sensitivity of saturated temperature to even very small pressure changes, a highly unusual temperature profile with minimum temperature difference at the middle of the plate is obtained. A Cuckoo Search variant augmented with a modified Hooke-Jeeves search for terminal convergence was used in the optimization. The optimized design consists of two large, 3.8×1.8 meter, evaporators in parallel, with over 300 plates each. Despite the large size, at an estimated 200 000 € cost, the sizing appears technically and economically feasible.