Key considerations for smoke shaft systems: 8. Dual purpose systems

Posted by Paul Compton on 02/09/14 11:30

Coltshaft-224636-editedIn the last article in our series about designing smoke shaft systems, we discuss dual purpose systems.

Why dual purpose?

  • Is your current project an apartment block?
  • Are your corridors landlocked?
  • Is the building well sealed and insulated? (of course it is)

And most importantly:

  • Do you have hot water pipes running above the corridor ceilings?

If you’ve answered yes to all four questions you need a dual purpose system.

The move to centralised heating and hot water systems has raised a new problem, overheating of common corridors. Something you never used to worry about has suddenly become a hot topic.
Fortunately the lobbies at least and, with extended corridor configurations, the whole corridor, have a ventilation system installed for smoke extract. Why not make use of it?

Day-to-day ventilation 

If you’ve been in an upper storey lobby with a smoke shaft system operating, your immediate reaction might be that this is much too noisy and draughty for day-to-day use. Bear with me.
For day-to-day usage, noise is definitely a problem. The problem is usually solved by either using a separate, small and quiet fan or by adding attenuators and inverter speed control to the smoke extract fan. Draught is not a problem. The reduced overall air flow rate and the ventilation of multiple floors together mean each corridor has a much lower flow rate than it would have in fire mode.

Getting the balance right

The difficulty when designing these systems is to get the control and balancing right. Solutions vary between the cheap and cheerful and the sophisticated, depending upon budget and performance objectives.
At the budget end, the system might open the normal smoke extract vents on say 3 floors at a time, extracting from those floors for a short period then cycling through until all floors have been ventilated. It’s a crude solution offering limited temperature control, but it keeps initial costs to a minimum.
A more sophisticated system might use separate, smaller dampers for air supply or extract, allowing balancing over more floors and providing constant ventilation to each floor when needed and better temperature control.
Of course any simple ventilation scheme is not going to be able to maintain corridor temperatures lower than a few degrees above external ambient.  


If simple ventilation is not enough, then cooling using a dual purpose system is now possible with the new Colt Coolshaft. It uses evaporative cooling technology to provide active pre-cooling of the incoming air and, if there is a fire, it is able to ventilate the common area effectively to allow the smoke to escape. With low running costs and the ability to cool corridors below external ambient, Coolshaft just might be the answer to your prayers.

If you wish to know more about evaporative cooling and CoolShaft for residential buildings, you can visit our product page, where you will also find the results of a recent CFD model we made of conditions in the corridor of a residential building with no ventilation, with natural ventilation, and with CoolShaft.


Learn more about designing a dual purpose shaft system in our recorded webinar, which is available here.

If you missed my previous articles in this series, you can find them here:

  1. The builder’s work shaft
  2. Natural or mechanical?
  3. On the roof
  4. What type of shaft vent?
  5. Noise
  6. Extended travel distance
  7. Power

Paul Compton Paul Compton is Technical Director for Colt, experienced in smoke control, HVAC, solar shading and louvre systems.

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Topics: Smoke ventilation, Smoke shafts, Smoke Shaft Series