Airflow & Fans

U-flow rationale · pressure budget · CFD

Why U-flow (not cross-flow or overhead)

Topology	Airflow	Passes	SMER	Verdict
U-flow (selected)	10,653 m³/h	8	4.03	Best lowest airflow per kg water, simplest ducts
Cross-flow with side plenums	~26,000 m³/h	2	~1.8	Poor evaporator churns sensible heat; coil duty ~190 kW
Overhead down-flow	~30,000 m³/h	1	~1.7	Poor high fan duty, vertical moisture gradient

Pressure budget

Element	ΔP (Pa)	Notes
Trolley stack (8 passes × 40 Pa)	320	Each pass through one trolley depth at 2.8 m/s face velocity
Distribution plenum + U-turn	30	Door-end turning plenum
Evaporator + condenser coils	60	Fin-and-tube, 4-row each
Total required	410	—
Fan configured static	450	Margin for filter loading

S5 — Air circuit schematic, pressure staircase along the air path, full spec table.

CFD simulation (qualitative)

The 2D lattice-Boltzmann slice below shows the velocity field and relative pressure in a plane through the supply channel. The fan-wall jet is clearly visible, the U-turn at the door end, and the suction at the return. Dead zones are minimal.

Velocity magnitude — fan jet, channel flow, U-turn recirculation.

Relative pressure — high (red) at supply, low (blue) at suction.

Fan schedule

Item	Spec	Qty
Recirculation fans	Centrifugal backward-curved, 5,400 m³/h @ 450 Pa each, 1.2 kW motor (IE3)	2 (one per channel)
Location	Fan wall at heat-pump partition, one supply + one return opening per channel	—
Drives	Direct-drive, VFD-controlled for multi-stage velocity trim	2 VFDs