So today I was working on a project where some design alterations where necessary. We are changing the AC in a shopping centre from individual units, to combined AHU's (Air handling Units). Basically what was happening was that each shop had its own small unit, which as we all know is vastly less efficient than a combined unit. In this instance, we are bringing a duct in from the plantroom, which is situated on the roof, and feeding multiple shops along the pedestrian mall via ducting. the fire consultant has declared that each shop is its own Fire Zone, thus when ducting goes between two shops, a fire damper is required. Now a fire damper is a mechanical device that will shut off at a signal from the fire panel, preventing the flow of smoke through the system. It also creates a barrier for flammable materials being transported through the duct. These are fairly costly pieces of equipment, and thus avoiding using them is advantageous. When a duct passes from the pedestrian mall into a shop, no fire damper is required, so the obvious solution is to have the main duct situated in the ceiling void of the pedestrian mall and to feed the shops from there.
In some instances this cannot happen, unless a complete redesign of the internal ducting is done, which would require removal of the ceiling, and much disturbance to the shop. As this centre is currently operating, and shut-down for the retail areas must be minimised, we have tried to keep the original ducting as much as possible, so sometimes it is necessary to come in through another shop.
A useful tip that I picked up in doing this redesign, was when I was working at the end of a stretch of duct, where a large duct feeds off the main duct, and a small duct continues on to feed a small shop. I was going to make a transformation after the large duct had fed off, and then make a bend into the shop. However I was advised that I should rather oversize the small duct and bring it to the end, and then take a shoe off that duct. this would cause a balance of pressure in the end of the duct, which would allow for the correct amount of air to travel down both the large duct and the smaller one.
