Case study: supply ventilation for an office floor

Published on 16 October 2026 by Raul Rodríguez

A 6,000 m³/h supply network for an office floor, from the first version to the report. These are the steps an engineer would take, with the figures the app gives. You can repeat it: it is the example that opens in Vortia 3D.

1. The starting point

The fan supplies 6,000 m³/h through a Ø500 galvanised sheet steel main duct that runs across the floor. Four circular ceiling diffusers hang from tee spigots and a branch takes air to a meeting room with a grille.

Air at 20 °C and sea level, airtightness class B, non-residential use (offices). Terminals with 30–40 Pa pressure drop at their nominal airflow, from the catalogue.

2. First calculation: the air does not go where it should

Diffuser 4, at the end of a straight Ø400 run, takes 40 % too much; the meeting room gets 27 % too little. The app also warns of 8.5 m/s in the main duct, above the 8 m/s recommended for offices because of noise. The fan needs 92 Pa.

3. Sizing by airflow

“Size the network” by maximum velocity: 7 m/s in the main and 4 m/s in the branches, the defaults for non-residential use. The app shows the changes before applying them:

• Fan outlet from Ø500 to Ø560.
• Diffuser spigots from Ø250 to Ø315 and the room branch from Ø315 to Ø400.
• Two new reducers on the main: to Ø450 after the room and to Ø280 before Diffuser 4.

Result: maximum velocity of 7.1 m/s, the fan goes from 92 to 76 Pa (−17 %) and the airflow split ends up between −7 % and +5 %. Better, but the room is still short.

4. Balancing the dampers

To fine-tune you need something to adjust: a butterfly damper on each diffuser spigot and another on the final run. “Balance dampers” closes them just enough:

The room damper stays open: it is the index branch and the one that sets the pressure. The maximum error is 0.4 %. The price of balancing: the fan goes from 76 to 81 Pa.

5. Noise: what the hydraulic calculation does not see

Without catalogue data, the app estimates the fan sound power from its airflow and pressure. With that estimate, the noise reaching the rooms through the ducts exceeds the 40 dB(A) limit of the Spanish noise regulation (RD 1367/2007) for offices by 13–16 dB. In an office network without a silencer this is normal, which is why it is worth seeing before installation.

Every noise warning comes with its fix. With “Add silencer”, the app tries generic silencers from 0.6 to 2 m, with and without a pod, and keeps the one that brings every room within its limit with the lowest pressure drop:

• Circular silencer with a central pod (bullet), 2.0 m long, 50 mm absorbent, Ø750 mm casing, just after the first straight run.
• Attenuation: 14 dB at 250 Hz, 25 at 500 Hz, 26 at 1,000 and 2,000 Hz and 24 at 4,000 Hz.
• Pressure drop: 25 Pa at 6.8 m/s.

These are generic values (Sabine’s formula for lined ducts) for selection and space planning. The model installed must provide at least that attenuation by octave band: if you have its catalogue, switch the component to “Manufacturer’s data” and the app uses its ΔP and attenuation.

6. The fan and its duty point

With the curve of a Ø560 axial fan (a generic example curve, not a commercial model), the app crosses the fan curve with the system curve, recalculated at several airflows with the dampers in position and the silencer:

• Design point: 6,015 m³/h (6,000 plus 15 of leakage) at 107 Pa total pressure.
• Without a drive, at 50 Hz: 6,802 m³/h, 13 % too much, at 136 Pa and 0.52 kW.
• With a drive at 44.2 Hz: the design airflow with 0.36 kW, 31 % less power.
• Specific fan power: 193 W/(m³/s), category SFP 0 (EN 16798-3).

7. The report

The PDF report contains design data, terminals, duty point, checks, pressure profile, noise, component details, materials (silencer included) and regulations. Verdict: it meets the calculation criteria, 8 of 8 checks passed.

Summary

Download the example report11-page PDF with the “EXAMPLE” watermark