Transfer Pump Sizing

UAE DOMESTIC WATER · MEP CALCULATION SHEET

Transfer Pump Sizing

Underground-to-overhead domestic water transfer pumps — demand, storage, head loss, power and NPSH, checked against UAE utility guidance and international hydraulic practice.

Project

Pump Tag

Units

SI · m, m³/h, bar

Date

Design Flow35.00 m³/h

TDH38.68 m

Motor7.50 kW

VelocityOK

NPSHOK

Demand & Storage

Daily demand, suggested transfer-pump flow and tank capacities.

Population served Residents / staff / beds served by this transfer system.

Design demand allowance

L/p/day

Litres / person / day. Typical Gulf design figures: apartment 200, villa 300, hotel 350–450, office 70–100 — confirm with project's authority-approved design brief.

Underground tank

Hours of average demand. DEWA minimum: 24 h.

Overhead tank

Hours of average demand held at roof level.

Target pump run time

h/day

Hours/day the transfer pump actually runs to move the full daily demand — sets the required pump flow rate.

DAILY DEMAND

70.00m³/day

70,000 L/day

AVERAGE FLOW

2.92m³/h

SUGGESTED PUMP FLOW

35.00m³/h

9.72 L/s · 583 L/min · 154 US gpm

UNDERGROUND TANK ≥

70.0m³

OVERHEAD TANK ≥

17.5m³

DEWA guidance: customer-side storage should cover at least 24 hours of average demand; where site levels require it, booster/transfer pumping is expected in the design (DEWA Guidelines for New Development Projects).

Hydraulics — Head & Velocity

Friction loss (Hazen–Williams), total dynamic head and pipe velocity check.

Design flow rate

m³/h

m³/h — carried through to Power (C) and NPSH (D) below.

Pipe material

Nominal size

Internal diameter

mm — from pipe class/schedule.

Discharge length

m, straight run.

Fittings allowance

% added as equivalent length.

Static lift

m, pump ℓ to tank overflow.

Required residual pressure at outlet

bar

bar — 0 for open discharge into an overhead tank.

Velocity limit to check against

VELOCITY

1.12m/s

OK vs

internal plumbing — general upper limit (ASHRAE / UPC practice)

FRICTION LOSS (H-W)

0.61m

VELOCITY HEAD

0.064m

TOTAL DYNAMIC HEAD

38.68m

Hazen–Williams (SI): h_f = 10.67 · L · Q^1.852 / (C^1.852 · D^4.87). DEWA velocity limits apply to its own network mains; internal plumbing commonly runs 1.5–2.4 m/s per ASHRAE/UPC practice.

Pump Power & Motor

Hydraulic and brake power, motor rating, duty/standby configuration.

Pump efficiency

% at duty point.

Motor efficiency

% — for electrical input only.

Design margin on shaft power

% headroom before rounding to standard motor frame.

Installation arrangement

HYDRAULIC POWER

3.69kW

SHAFT (BRAKE) POWER

5.68kW

7.61 HP

RECOMMENDED MOTOR

7.50kW

10.06 HP nameplate

ELECTRICAL INPUT (APPROX.)

6.31kW

Arrangement: Provide 2 pumps × 7.50 kW (1 duty + 1 standby); each pump is sized for the full design flow and head above.

NPSH Check

Available NPSH against a margin guideline informed by ANSI/HI 9.6.1.

Water temperature

°C

°C — use tank/ambient temperature.

Atmospheric pressure

kPa

kPa, sea level = 101.325.

Suction condition

Flooded suction Suction lift

Suction static head

m — tank level above (flooded) or below (lift) pump centreline.

Suction pipe length

Suction diameter

Pump NPSH required (NPSHr)

from manufacturer's published curve at the duty point.

VAPOUR PRESSURE

0.574m

SUCTION FRICTION LOSS

0.039m

NPSH AVAILABLE

11.22m

MARGIN OVER NPSHr

8.22m

PASS — comfortable margin

Guideline: NPSHa should exceed NPSHr by at least 1.3× NPSHr, or NPSHr + 0.6 m, whichever is larger — a conservative simplification of the margin concept in ANSI/HI 9.6.1. Suction friction assumes the pipe material selected in Section B plus a 20% fittings allowance. Always verify against the certified pump curve.

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Standards & References

Basis of calculation for each section above.

STORAGE

Demand & storage (Section A)

Daily demand = population × design allowance (L/person/day). DEWA guidance: customer-side storage should cover at least 24 hours of average demand, and where site levels require it, booster/transfer pumping is expected in the design (DEWA Guidelines for New Development Projects).

VELOCITY

Pipe velocity limits (Section B)

Internal plumbing commonly runs 1.5–2.4 m/s per ASHRAE / UPC practice. DEWA-aligned utility mains are typically checked to lower limits: transmission lines around 1.5 m/s and distribution mains around 1.0 m/s. Select the limit appropriate to where this pipe run sits.

HYDRAULICS

Hazen–Williams friction loss (Section B)

h_f = 10.67 · L · Q^1.852 / (C^1.852 · D^4.87), SI units (L, D in m; Q in m³/s). Typical C-factors: uPVC/HDPE 150, Copper 140, Ductile iron (cement-lined) 130, Concrete 120, Galvanised steel 100. Fittings allowance is added to straight length as equivalent length.

POWER

Pump & motor sizing (Section C)

Hydraulic power = ρgQH. Shaft power = hydraulic power ÷ pump efficiency. Electrical input = shaft power ÷ motor efficiency. Recommended motor is the next standard IEC frame size above shaft power plus a design margin, common Gulf consulting practice for continuous-duty domestic transfer sets. Two-pump duty+standby (2×100%) or duty+assist (2×50%) arrangements are typical for critical domestic water service in the UAE; each duty pump in a standby pair is still sized for the full flow and head shown above.

NPSH

NPSH margin (Section D)

NPSHa = atmospheric head ± suction static head − vapour pressure head − suction friction loss (sign of static head depends on flooded/lift condition). Guideline: NPSHa should exceed NPSHr by at least 1.3× NPSHr, or NPSHr + 0.6 m, whichever is larger — a conservative simplification of the margin concept in ANSI/HI 9.6.1.

DISCLAIMER

Preliminary sizing aid only

DEWA, Dubai Municipality, Trakhees and other UAE authority circulars are amended periodically. Confirm current figures with the authority having jurisdiction and have the final pump selection verified by a licensed mechanical/pump engineer before procurement or tender.