Thermal–economic design optimization of an instant cooling water dispenser with a vapor compression refrigeration system

Water dispensers (WDs) are widely used in residential and commercial applications. Conventional reservoir-type water dispensers (RC-WDs) consume high standby energy and pose a risk of bacterial growth, whereas instant cooling WDs (IC-WDs) with a vapor compression refrigeration (VCR) reduce energy use and enhance hygiene by eliminating the reservoir. However, the transient thermal performance and economic feasibility of IC-WDs are rarely optimized simultaneously, particularly with the stringent geometric constraints in cooling modules. In this study, the thermal and economic performance of an IC-WD with a VCR system was optimized using a transient simulation model developed in Dymola and validated through steady-state and dynamic experiments. The baseline system is defined as a representative heat exchanger, having an evaporator height fraction ( HF eva ) of 19.3 % with an evaporator outer diameter ( OD eva ) of 6.5 mm and a water-coil outer diameter ( OD watercoil ) of 6.4 mm. The effects of evaporator and water-coil geometric parameters were investigated under on-mode operation without and with water discharge. The results showed that an optimized system having HF eva of 43.4 % with OD eva of 6.5 mm, and OD watercoil of 6.4 mm achieved the best trade-off between thermal performance and flow resistance. Compared with the baseline system ( HF eva of 19.3 %), the optimized IC-WD improved the on-mode performance by 8.8 % and reduced the daily and annual energy consumptions by 7.1 % and 10.3 %, respectively, under the Energy Star standard conditions. Over a 7.2-year product lifetime, the lifecycle cost decreased by 5.7 % without increasing the initial cost. These findings demonstrate that the geometric optimization of IC-WDs can significantly enhance their instantaneous cooling performance and cost-effectiveness. • An instant cooling-water dispenser (IC-WD) with a vapor compression is analyzed. • Evaporator and water coil of the IC-WD are optimized using a simulation model. • Optimized IC-WD achieves an 8.8 % increase in on-mode performance. • Annual energy consumption of optimized IC-WD decreases by 10.3 %. • Lifecycle cost of optimized IC-WD decreases by 5.7 % compared with the baseline.