🏛️ Stack Effect & Ventilation

Calculate thermal stack buoyancy draft, neutral pressure level (NPL), wind surface pressure, and natural ventilation airflow through atriums and shafts.

⚡ Fortran 90 Engine Double Precision (IEEE 754) ✓ ISO / ASME Validated

📊 Solver Telemetry ● ACTIVE

👁️ Consultations 17

⚡ Calculs faits 13

💾 Téléchargements 140 📦 Code Fortran 4.4 KB

📅 Mise en service Jun 2026

⏱️ Latence < 1 ms

🏛️ Atrium Thermal Plume Convection & Neutral Pressure Level (NPL)

Real-time visual simulation of buoyancy updraft, inlet louvers & roof exhaust ventilation

📝 Configuration & Presets

🏢 4-Story Atrium (H=16m) 🏭 Warehouse Night Flush ☀️ Solar Chimney (H=6m) 🚪 High-Rise Shaft (H=45m)

📐 Geometry & Louver Opening Areas

Stack / Atrium Height H [m]:

Building Volume V [m³]: Used for Air Changes per Hour (ACH)

Lower Inlet Open Area A₁ [m²]:

Upper Outlet Open Area A₂ [m²]:

🌡️ Temperatures & Wind Pressure

Indoor Air Temperature T_i [°C]:

Outdoor Ambient Temperature T_o [°C]:

Wind Velocity at Roof Level [m/s]:

Wind Pressure Coeff ΔC_p: Typical: 0.60 (sheltered) to 0.90 (exposed)

CIBSE / ASHRAE Stack Formulations:
• Stack Pressure: ΔP_stack = ρ_o · g · H · (T_i − T_o) / T_i
• Wind Pressure: ΔP_wind = ½ · ΔC_p · ρ_o · v_w²
• Effective Area: A_eff = (A₁ · A₂) / √(A₁² + A₂²)
• Natural Flow: Q = C_d · A_eff · √[ (2 ΔP_total) / ρ_o ]

📊 Natural Ventilation Results

📊 Output Summary
💾 Fortran Source

Natural Ventilation Airflow Rate

Q = 20,617 m³/h (12,134 CFM)

Air Change Rate: 4.30 ACH (Building Volume = 4,800 m³)

NPL = 8.9 m

Thermal Stack Head (ΔP_stack) 6.49 Pa ΔT = 10.0 °C (Buoyancy)

Wind Driving Head (ΔP_wind) 3.87 Pa 3.0 m/s (ΔC_p = 0.7)

Total Driving Pressure 7.56 Pa Combined Vector Head

Effective Opening Area (A_eff) 2.63 m² Inlet 3.5m² / Outlet 4m²

📈 Ventilation Flow Rate (m³/h) vs Stack Height H

📉 Ventilation Flow Rate vs Temperature Difference (ΔT)

=================================================================
 THERMOFLUIDCALC — NATURAL VENTILATION & STACK EFFECT REPORT
=================================================================
Case Title                 : 4-Story Commercial Building Center Atrium Natural Ventilation
Stack / Atrium Height (H)  : 16.00 m
Inlet / Outlet Open Areas  : 3.50 m2 (Inlet) / 4.00 m2 (Outlet)
Effective Opening Area     : 2.63 m2
Indoor / Outdoor Air Temp  : 24.0 °C (In) / 14.0 °C (Out) -> ΔT = 10.0 °C
Roof Wind Speed & Coeff    : 3.00 m/s (ΔCp = 0.70)
-----------------------------------------------------------------
Thermal Stack Buoyancy Head: 6.49 Pa
Wind Surface Driving Head  : 3.87 Pa
Combined Total Driving Head: 7.56 Pa
Neutral Pressure Level NPL : 8.93 m above base (55.8 % height)
NATURAL VENTILATION FLOW   : 20,616.5 m3/h (12,134 CFM)
Air Change Rate (ACH)      : 4.30 h-1 (Building V = 4800 m3)
=================================================================

📘 Calculation Methodology & CIBSE Standards

Thermal Buoyancy & Stack Effect

Warm indoor air is less dense than cold outdoor air, creating an upward hydrostatic pressure gradient driving warm air out upper roof openings:

                    ΔPstack = ρo · g · H · (Ti − To) / Ti
                

Neutral Pressure Level (NPL)

The NPL is the elevation where indoor and outdoor pressures are equal. Below the NPL, air infiltrates inwards; above the NPL, air exhausts outwards.

Key Engineering Assumptions

Standard discharge coefficient $C_d = 0.62$ across louver openings.
Combined stack and wind driving heads summed in quadrature per BS 5925.
Uniform vertical temperature distribution inside the stack envelope.

ThermoFluidCalc Engineering Report