We improved temperature stability and resilience in chilled water systems by optimising buffer vessel geometry, inlet and outlet design and control for data centres. A computational fluid dynamics model of the tank resolved stratification, short-circuiting risk and recharge efficiency across transients representative of load steps and chiller cycling. Nozzle orientation, diffuser elements and internal baffles were varied to quantify their impact on mixing and effective volume. Key performance indicators included temperature uniformity at supply and return, head loss and time to recover after a disturbance. Mesh and solver checks ensured robust trends, and parametric sweeps produced response maps that translate directly into engineering choices. Layouts were identified that stabilise supply temperatures and limit mixing during recharge without undue pressure drop, supporting reliable operation at low approach temperatures. The outcome was an implementation ready set of design changes and a reusable model to inform commissioning and future capacity increases in data-centre deployments.