Overheating in common corridors in residential buildings has become an increasingly vexing problem, which can be addressed by using a two-shaft smoke control system for day-to-day ventilation. One of the major issues is how many floors we can ventilate concurrently while still achieving a reasonable air flow balance between floors.
We covered the topic in our recent webinar on Ventilation solutions for overheated corridors in apartment buildings and the Question and Answers session at the end threw up an interesting idea.
The issue: achieving a good air flow balance between floors
The difficulty in getting a good balance between floors is that the system is designed primarily to provide a relatively large air flow from one floor only and we are adapting it to provide a small air flow, at least an order of magnitude smaller, from multiple floors.
If we use the same corridor vent for smoke and day-to-day ventilation, the vent is massively oversized for the day-to-day air flow, and control is difficult (if not impossible) without compromising the air flow rate in smoke mode.
Possible solutions to improve air flow balance
1. Separate vents used for day-to-day ventilation. The balance can be improved by using separate, smaller vents specifically for day-to-day ventilation, on either the inlet or exhaust. If these have an adjustable open position then a reasonable balance can be achieved over a limited number of floors.
It’s therefore normal practice to limit the number of floors being ventilated concurrently, rotating between groups of floors over a set period. This is not necessarily ideal but it does work in practice.
2. Inlet fan at ground level and extract fan at roof level. An alternative, if two similar smoke shafts are available, is to have the inlet fan at ground level and the extract fan at roof level, analogous to a reverse return water system, to give a good inherent balance. However, this may not be practical, depending upon the building layout.
A new, interesting alternative: use constant volume boxes on the vents
The Q&A threw up third possible solution, which could be suitable when either the inlet or exhaust has separate corridor vents for day-to-day use:
Q. Can we use constant volume boxes on the vents to each floor to aid balance and commissioning?
A. This would only be practical where mechanical ventilation is provided and separate vents are used for day to day ventilation on one shaft as the difference in ventilation rates would make a dual purpose smoke and day to day vent impractical.
This solution could work well, as long as there is sufficient space for the box, in cases where we have such vents mounted above the corridor ceiling. We would still need the fire resistant vent behind the box, so the cost would increase.
Of course any solution that increases the ventilation rate will also increase fan speed and noise, so additional attenuation will be needed.
The design of dual purpose systems in residential blocks is constantly evolving. Could this be the next evolution?
Read our previous articles:
Or listen to the recording of our webinar complete with Q&A session:
Paul Compton is a Technical Director for Colt, experienced in smoke control, HVAC, solar shading and louvre systems.