Ventilation air requirement Calculator

1. Definition

A ventilation air requirement calculator determines the minimum outdoor air needed for a room or building space to maintain indoor air quality, dilute contaminants, and meet ASHRAE/standard ventilation requirements. It can be based on air changes per hour (ACH) or per-person ventilation rates (L/s per person).

2. Background Theory

Ventilation requirements depend on:

a) ACH Method

Air changes per hour define how many times the total room volume is replaced with outside air.

Q=ACH×Volume

Where:

• Q = airflow (m³/h)

• Volume = L × W × H

b) Per-Person Method

Often used in offices, classrooms, commercial spaces:

Q=Occupants×(L/s per person)

Convert to m³/h:

1 L/s=3.6 m3/h

Both methods aim to maintain acceptable indoor air quality (IAQ), limiting CO₂ buildup, odors, and pollutants.

3. How the Calculator Works

1. User enters room dimensions and number of occupants.

2. User chooses either:
   ACH method → uses room volume × ACH
   Per-Person method → uses occupants × ventilation per person

3. The calculator computes:

   • Airflow (L/s)

   • Airflow (CFM)

   • Airflow (m³/h)

4. Results show the required fresh air supply.

While this calculator provides a quick estimate of ventilation air requirements, real HVAC systems involve complex airflow interactions, mixing effectiveness, stratification, diffuser performance, and pressure imbalances that simple ACH or per-person formulas cannot model. For engineers who need to understand real airflow distribution, ventilation efficiency, and indoor air quality patterns, tensorHVAC-Pro provides an intuitive HVAC-focused simulation platform—built for HVAC engineers, not CFD experts. It allows you to visualize airflow, temperature distribution, contaminant dilution, and ventilation performance throughout the entire space with engineering-level accuracy.