Professional Certificate in Chilled Water System Design

A: A feels uncomfortable but it lines up with how chillers actually behave at high ambient. You’re trading efficiency, not capacity, and the unit can still meet load if the selection curve shows margin. B sounds principled, yet N+1 is about capacity at design conditions, not frozen approaches under upset operation. C borrows a comfort-cooling trick; in a data centre that supply temperature change hits rack delta-T and airflow balance fast. D assumes the tower has spare fan and wet-bulb headroom at 35C, which is rarely true when you’re already on the knee of the curve.

A: A works with the physics: flow first, temperature second. By backing off flow you let coils exchange heat properly again. B is a classic reflex, but it deepens the collapse by increasing flow demand and risking low evaporator LWT. C looks logical if you’re thinking starved coils, yet it drives even more low delta-T flow. D protects the chiller, not the system, and often pushes the evaporator toward tube velocity limits with no load benefit.

A: A stops you from flashing tubes or tripping on flow the first time you enable the machine. B is necessary, but a healthy motor won’t survive no flow. C feels thorough, yet valve stroking doesn’t guarantee system hydraulics. D matters in cold climates, though it won’t save an evaporator that never saw design flow.

A: A ties ambient sensitivity and head pressure together cleanly. B would show across all ambients, not only at 35C. C pushes lift from the cold side and usually drags evaporator performance with it, which you’re not seeing. D explains nuisance trips, but the pressure trend matching ambient rise points to real heat rejection limits.