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Natural ventilation verification against CIBSE Guide A 2015

The 8 m building of Guide A's Figure 4.14, worked through in Examples 4.1 to 4.3 for the wind pressure on its two facades in open country and in an urban setting, and for the stack pressure across openings 4 m apart, run through the same calculation the app uses and compared with the printed tables.

Result
3 of 3 checks pass
Cases
2 worked examples
Version / published
v1.0 · 2026-09-25
Engine fingerprint
2921349afd15

Why we publish this

Guide A is the reference this calculation cites for its driving pressures. Chapter 4 prints one worked example with its inputs, its pressure coefficients and its results tabulated, so the calculation can be checked against the method rather than against its own code. The calculation reports the pressure difference across the building, windward minus leeward, which is what drives the flow, so the print's two facade pressures are compared as their difference.

What is not compared, and why

  • The wind-speed correction in Example 4.1. The print first corrects the meteorological 4 m/s at 10 m to the building height and terrain with its equation 4.14 and Table 4.9 (3.87 m/s in open country, 2.35 m/s in an urban setting). The calculation takes the wind speed at the building as an input, so the corrected speeds are given to it and the correction itself is not compared.
  • BS EN 16798-7 and CIBSE AM10. The calculator also follows both, but the held copies print no worked example; those paths are checked in the regression suite against hand calculations.

How to read the tables

  • Expected is the value printed in the standard, or a hand calculation from printed values. The working is shown under each quantity.
  • Tolerance is exact for tabulated values and selected sizes, and ±2 % for calculated quantities such as the wind and stack pressure differences.
  • Every check re-runs automatically whenever the calculation code changes, and this page is regenerated from those results. The engine fingerprint above identifies the calculation code the results came from.

Sources

  • CIBSE Guide A 2015, Environmental design

Printed page numbers refer to the editions above.

Worked examples

NV-01

Guide A Example 4.1 — wind pressure on the facades of an 8 m building, open country and urban

Inputs

  • Building 8 m high, wind normal to facade 1, outside air at 0 °C
  • Wind speed at building height 3.87 m/s (open country) and 2.35 m/s (urban), the print's corrected speeds
  • Pressure coefficients from Table 4.A1.1: facade 1 +0.7 and facade 2 −0.2 (open country); +0.2 and −0.25 (urban)
Checks for case NV-01
QuantityExpectedSourceMEPCalcΔToleranceResult
Wind pressure difference, windward to leeward, open country
Table 4.12: facade 1 6.6 Pa, facade 2 −1.9 Pa; difference 8.5 Pa
8.5Pa
CIBSE Guide A 2015, Environmental design
Chapter 4, Example 4.1 and Table 4.12 (held copy pp.360 and 364)
8.406Pa1.11 %±2 %Pass
Wind pressure difference, windward to leeward, urban
Table 4.12: facade 1 0.7 Pa, facade 2 −0.87 Pa; difference 1.57 Pa
1.57Pa
CIBSE Guide A 2015, Environmental design
Chapter 4, Example 4.1 and Table 4.12 (held copy pp.360 and 364)
1.55Pa1.27 %±2 %Pass

NV-02

Guide A Example 4.2 — stack pressure across openings 4 m apart, 20 °C inside and 0 °C outside

Inputs

  • Openings 3 and 4 are 4 m above openings 1 and 2; inside 20 °C, outside 0 °C
Checks for case NV-02
QuantityExpectedSourceMEPCalcΔToleranceResult
Stack pressure difference across the 4 m between openings
Table 4.13: −3.5 Pa at the upper openings relative to the lower (equation 4.17)
3.5Pa
CIBSE Guide A 2015, Environmental design
Chapter 4, Example 4.2 and Table 4.13 (held copy pp.361 and 364)
3.452Pa1.37 %±2 %Pass