๐๏ธ Stack Effect & Ventilation
Calculate thermal stack buoyancy draft, neutral pressure level (NPL), wind surface pressure, and natural ventilation airflow through atriums and shafts.
โก Fortran 90 Engine
Double Precision (IEEE 754)
โ ISO / ASME Validated
Hvac
๐ Solver Telemetry
โ ACTIVE
๐๏ธ Views
17
โก Solves
13
๐พ Downloads
247
๐ฆ Fortran Code
4.4 KB
๐
Released
Jun 2026
โฑ๏ธ Latency
< 1 ms
๐๏ธ Atrium Thermal Plume Convection & Neutral Pressure Level (NPL)
Real-time visual simulation of buoyancy updraft, inlet louvers & roof exhaust ventilation๐ Configuration & Presets
๐ข 4-Story Atrium (H=16m)
๐ญ Warehouse Night Flush
โ๏ธ Solar Chimney (H=6m)
๐ช High-Rise Shaft (H=45m)
CIBSE / ASHRAE Stack Formulations:
โข Stack Pressure: ฮPstack = ฯo ยท g ยท H ยท (Ti โ To) / Ti
โข Wind Pressure: ฮPwind = ยฝ ยท ฮCp ยท ฯo ยท vwยฒ
โข Effective Area: Aeff = (Aโ ยท Aโ) / โ(Aโยฒ + Aโยฒ)
โข Natural Flow: Q = Cd ยท Aeff ยท โ[ (2 ฮPtotal) / ฯo ]
โข Stack Pressure: ฮPstack = ฯo ยท g ยท H ยท (Ti โ To) / Ti
โข Wind Pressure: ฮPwind = ยฝ ยท ฮCp ยท ฯo ยท vwยฒ
โข Effective Area: Aeff = (Aโ ยท Aโ) / โ(Aโยฒ + Aโยฒ)
โข Natural Flow: Q = Cd ยท Aeff ยท โ[ (2 ฮPtotal) / ฯo ]
๐ Natural Ventilation Results
Configure inputs and click Compute to view results.
๐ 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:
ฮPstack = ฯo ยท g ยท H ยท (Ti โ 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.