Pump selection and pipe sizing for a 480-bed student residence

Kestrel's Pretoria residence has 480 beds over six floors. Municipal water fills a 60 m³ ground-level sump. A single 5.5 kW pump lifts it to a 40 m³ roof tank, and gravity feeds the floors from there. Both the sump and the roof tank are standard because city supply is cut for hours at a time, and the Pune twin will face the same intermittent supply.

Three things go wrong. Between 06:30 and 08:00 the roof tank empties faster than the pump refills it, and the top two floors get a trickle. The pump has burnt out twice in 18 months, and the maintenance team suspects it runs far from its best efficiency point. The electricity bill for pumping is R4,100 a month, which the finance manager thinks is too high.

The facts you have: - the roof tank outlet is 22.5 m above the sump water level; - the rising main is 68 m of 50 mm HDPE with six bends and two valves; - the top-floor showers are only 3.2 m below the roof tank outlet and need at least 1.0 bar to work well; - residents use about 150 L per person per day, and 45% of that happens in the morning peak.

Your job is to: - calculate the demand and peak flow; - size the rising main and the distribution pipes; - draw the system curve and select a pump from a real manufacturer curve; - size a small booster set for floors 5 and 6; - work out the running cost in rand and rupees.

You need no site visit. Everything is done by hand calculation and a spreadsheet, with an optional network check in the free EPANET software.

Done looks like a pump that refills the tank in under 3 hours, works near its best efficiency point, gives top-floor pressure of at least 1.0 bar, and costs less to run than today.