AHU / FCU Sizing

Enter an air handler or fan-coil unit's cooling capacity to get the chilled-water coil flow and pipe size, the supply airflow, and the round / spiral supply duct diameter — the duct we fabricate in-house. Related: chiller plant pipe sizing.

Cooling capacity (per unit)

Number of identical units

Chilled water ΔT (°C) Typical 5–6 °C across the coil.

Supply air ΔT (°C) Room minus off-coil supply temperature (typ. 9–12 °C).

Sensible heat ratio (SHR) Sensible ÷ total cooling; ~0.75–0.9 for comfort cooling.

Supply duct velocity (m/s) Typical 5–8 m/s for commercial supply ducts.

Advanced limits (water pipe)

Max velocity (m/s)

Max friction (Pa/m)

Hazen-Williams C

Unit capacity

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Chilled water flow

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Supply airflow

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Item	Quantity	Size	Velocity

Method: coil flow = capacity ÷ (4.187 × ΔT_water); supply airflow = (capacity × SHR) ÷ (1.2 × 1.005 × ΔT_air); round duct Ø from airflow at the target velocity (rounded to 25 mm). Pipe to ASHRAE / SNI limits (Hazen-Williams). Indicative only — confirm against the selected unit's catalogue data. We fabricate the matching square & spiral duct in-house — get a quote.

We Make the Duct, Too

Square and spiral ducting fabricated in our 4,500 m² Jakarta workshop — sized, made and installed to match your AHUs and FCUs.