The LWF Blog
Fire Safety Engineering for Design – Pressure differential systems – Part 202
September 23, 2024 10:38 amLWF’s Fire Safety Engineering blog series is written for Architects, building designers and others in the construction industry to highlight and promote discussion on all topics around fire engineering. In part 201, LWF began to look at pressure differential systems, particularly depressurisation systems. In part 202, we look at the temperature of extraction fans and the use of the HVAC system.
In the ‘Handbook of Smoke Control Engineering’ by John H. Klote, James A. Milke and Paul G. Turnbull, a calculation is given for how to calculate exhaust fan temperature based on gas temperatures calculated using zone models or hand calculations:
where Tfan is the temperature of the gases in the exhaust fan (°C),Pj is the density of gases in space j (kg · m–3), Vj is the volumetric flow rate of exhaust from space j (m3 · s–1), Tj is the temperature of gases in space j (°C) and n is the number of spaces.
Alternatively, instead of calculating the exhaust fan temperature, the extraction fan procured to operate in the depressurisation zone may be a model capable of handling smoke at a temperature of 1000 °C for unsprinklered buildings, 300 °C for buildings with sprinkler protection.
HVAC System
A HVAC System is an acronym short for ‘Heating, Ventilation and Air Conditioning’ System. Such systems may be possible to use for smoke control, depending upon the type of system, the type of depressurisation system and the arrangement of the HVAC zones.
The use of the HVAC system in this manner is subject to local codes of practice and regulations, in addition to the system being appropriately coordinated to ensure it is capable of fulfilling the dual purpose of smoke control and day to day function.
Further information can be found in the Handbook of Smoke Control Engineering, as mentioned above.
Computer Modelling
Computer software is often used to undertake the necessary calculations for more complex smoke control designs. Many different software packages are suitable for purpose. CONTAM is a free downloadable software produced by NIST (US) and is a multizone indoor air quality and ventilation analysis program that is extensively used and may be suitable for purpose.
In part 203 of LWF’s series on fire engineering we will discuss the use of pressurisation systems. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.
Lawrence Webster Forrest has been working with their clients since 1986 to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact the LWF office on 0800 410 1130.
While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.