Cleanroom PCW (process cooling water) is a secondary loop for process-tool heat exchangers, not ordinary chilled water. It needs clean piping, stable water quality, steady pressure, precise temperature control, and no corrosion, scale or leaks. Isolate the primary loop with a plate heat exchanger. Use 304 or 316L stainless, TIG-welded with argon purge. Connect tools after hydrotest, flush and passivation.
The costliest problems usually do not show up on the pump-room display. They start inside the pipe. If the weld root oxidizes and turns black, the oxide scale keeps flaking during operation and plugs the tool heat exchanger. If the tool hookup is made before flushing is accepted, particles go straight into the precision cooling passages. Rework almost always costs more than getting the argon purge, slope, hydrotest and flush right the first time.
This article explains the PCW construction hold points that should be written into the briefing and the handover, from the standpoint of NUNXIN (暖心自控) work on cleanroom temperature, humidity and controls. It does not cite third-party site cases. Pipe slope and hydrostatic testing are checked against published national standards. Tool-side temperature-stability requirements follow the design documents and the tool specification; unpublished figures are not presented as NUNXIN product guarantees.
How is PCW different from ordinary chilled water, and why isolate the two loops?
PCW is the secondary loop that serves process tools. The primary side is often chilled water or cooling water. The two sides should be isolated by a plate heat exchanger, each with its own valves and strainers, so the loops cannot cross-contaminate. When the drawings are developed, prefer reverse-return piping to reduce flow fighting and hydraulic imbalance. Secondary piping in the clean area should reserve valves, blowdown ports and sample ports, and the vent and drain points should be explicit. Supply and return flow a