Exhaust duct layout refresher
Exhaust duct layout refresher
(OP)
Hi
I haven't worked on a lot of HVAC lately, and now have to work on a job that require a design of an exhaust system. Somebody proposed a system as shown in the attached diagram. The system has exhaust branch ducts, and are combined into a main, but each branch has an inline exhaust fan before the main. My first impression is that it is not going to work, but if we have either of the two condition, would it works?
1. interlock the two fans so that they always run together
2. have a damper after EF-1 and EF-2
Thanks so much!
I haven't worked on a lot of HVAC lately, and now have to work on a job that require a design of an exhaust system. Somebody proposed a system as shown in the attached diagram. The system has exhaust branch ducts, and are combined into a main, but each branch has an inline exhaust fan before the main. My first impression is that it is not going to work, but if we have either of the two condition, would it works?
1. interlock the two fans so that they always run together
2. have a damper after EF-1 and EF-2
Thanks so much!





RE: Exhaust duct layout refresher
Lot of things that could go wrong however.
RE: Exhaust duct layout refresher
The common discharge duct is the only real problem with the system as shown. If the fans are constant speed and always both on, it's not a huge problem with proper T&B, but if they modulate independently, you will likely have control problems.
RE: Exhaust duct layout refresher
Andy W.
RE: Exhaust duct layout refresher
Read about control of fans in parallel.
RE: Exhaust duct layout refresher
RE: Exhaust duct layout refresher
I don't seem to remember clearly whether they're doable or not. Or maybe doable but not a good engineering practice.
Is this kind of setup discussed in the ASHRAE handbook, or somewhere else?
RE: Exhaust duct layout refresher
This is done all the time for toilet exhaust in hotels. The individual fans discharge into a vertical exhaust riser. Each fan has a backdraft damper. The riser is sized as if all fans run at once.
snip
You know, what I notice unfailingly about exhaust fans in hotel/motel bathroom is how poorly they work.......
RE: Exhaust duct layout refresher
If the two zones in question are not required to work at the same time,this is the simplest arrangement you could use.
RE: Exhaust duct layout refresher