How does temperature affect pressure in a closed cold water distribution system, and what practical implication does this have?

• A. Pressure is largely independent of temperature; temperature changes mainly affect water density slightly, so design focuses on friction and static head.
• B. Temperature directly increases pressure; must oversize pumps in hot weather.
• C. Temperature reduces pressure linearly; needs constant cooling.
• D. Temperature has no effect on any property; ignore.

Answer: (A)

In a closed cold-water distribution network, the pressure you see is mainly determined by the elevation difference (static head) and the resistance to flow inside the piping (friction losses). Temperature does push water to expand a little and it can slightly change density and viscosity, but these effects are small in a fixed-volume loop. The result is that the overall pressure doesn’t swing a lot with typical temperature changes. Practically, this means you design and operate the system by focusing on delivering the required pressure through proper head and minimizing friction losses, rather than relying on temperature effects to set or limit pressure. Pump sizing and control are driven by flow demands and head losses, not by hot-weather pressure changes.