Using Dryer as Exhaust Fan?
Using Dryer as Exhaust Fan?
(OP)
We are working on improving the ventilation to our factory. Our current dryer runs at a constant 45,000 cfm when it is running. I was looking at ducting this into our factory to act as 2 exhaust fans. Being a food grade plant, we maintain positive pressure of roughly .2" wg, to maintain this, we would be adding at the minimum 45,000 cfm of intake fans. My concerns on doing this is the exhaust fan is capable of 20" wg. To prevent this motor from sucking in our walls, I would be adding a pressure sensor to the factory to monitor the pressure. This would kick the dryer fan off if too much vacuum is sensed within the factory. To prevent the operators from running this fan in 'hand' mode, I would wire in a keyed switch to the MCC bucket. I would think I'd want to connect up the new intake fans to VFD's such that they ramp up with the dryer to maintain our pressure, also controlled by the pressure sensor. My other thought would be to wire each intake fan up to a different pressure sensor for redundancy sake.
Thoughts / Comments?
Thoughts / Comments?





RE: Using Dryer as Exhaust Fan?
RE: Using Dryer as Exhaust Fan?
My rational behind this is; the dryer is the main source of heat in the plant, so we don't need the additional ventilation to be running when the dryer isn't running. Which is why it would make sense to use it's exhaust fan in lieu of additional exhaust HVAC fans. I'm currently checking the noise level to make sure sound of the dryer air inlet isn't going to be deafening in our factory.
RE: Using Dryer as Exhaust Fan?
RE: Using Dryer as Exhaust Fan?
RE: Using Dryer as Exhaust Fan?
RE: Using Dryer as Exhaust Fan?
The dryer pulls air from outside, and rejects it back outside through an exhaust stack.
I'm not concerned about the CFM on the dryer, if anything, it should be higher due to the small amount of positive pressure within the factory.
Just trying to see if anyone has tried this before, or if I'm overlooking any other important details.
Overview of current layout
RE: Using Dryer as Exhaust Fan?
RE: Using Dryer as Exhaust Fan?
You have to install fans to make this work anyway.
So just install ventilation fans and have a ventilation system and a drier system. Separate.
Don't unnecessarily tie the two together. Too much to go wrong.
RE: Using Dryer as Exhaust Fan?
RE: Using Dryer as Exhaust Fan?
RE: Using Dryer as Exhaust Fan?
@mintjuliep - We already have the fans as shown on the CAD drawing, they are a long ways from being enough, which is why we are adding more. I understand the KISS principle, but at the same time, it seems like such a waste to have a 45,000 cfm exhaust fan constantly running that is pulling air in from outside, as well as multiple exhaust fans pulling out the same volume.
@bronyraur - That's exactly the rationale behind this. The airflow in this plant is horrid, the plant is packed with hot equipment. My hope is that with a big centrally located exhaust inlet, we would have a lot more flow covering the plant instead of just blowing around near the walls, with a small amount escaping through the penthouse (that's what we call the top extension bit).
I'm all for other ideas as well! Thanks guys!
RE: Using Dryer as Exhaust Fan?
The fan type may influence how you control it.
RE: Using Dryer as Exhaust Fan?
- why not enough?
RE: Using Dryer as Exhaust Fan?
Dryer exhaust fan curve FYI
@317069 - we have added several heat intensive processes, as well as an additional dryer. Due to these changes, the plant is now uncomfortably hot.
RE: Using Dryer as Exhaust Fan?
it is a good idea but the question is about the factory air being exhausted, does it have the same parameters od the outside air such as: temperature, humidity...etc. if it does not, would it effect drying process.
RE: Using Dryer as Exhaust Fan?
RE: Using Dryer as Exhaust Fan?
You mention adding several heat intensive processes. Where are these relative to your dryer? If they are not close to the dryer (lots of new ductowrk) or there is workspace between these new processes and the dryer, having ventilation air moving over these processes towards the dryer is not going to solve your worker comfort problem since you are now heating this ventilation air and your workers with your new processes. The work spaces between the new processes and dryer will likely be warmer than outside (not desirable for south Florida).
I think you would be better off leaving the dryer as is, adding the new supply fans as intended (probably do not need 45,000 cfm of new) and add exhaust fans or gravity vents in the roof above the new heat generating processes. Intent being to direct air heated by the new processes away from your workers and their work areas.
Not knowing exactly what you are producing or how interrelated the drying process is with the new process, keeping the dryer's ventilation separate from the rest of the building allows you take it out of service (planned or otherwise) without affecting your worker comfort.
For worker comfort, have you considered adding A/C to high traffic areas or inspection locations? It wouldn't have to be a big VAV system with central AHU trying to cool the entire plant, but just enough in places where your workers need to stand for more than a minute or two to provide a cool spot. Ductless mini-split systems in select areas with a local occupancy sensor would probably work and be a welcome relief to your workers.
RE: Using Dryer as Exhaust Fan?
dbill74 - whew, lot to reply to here;
This is a fairly old, heavily modified drying system, no warranty issues to worry about here. The new ducting would actually be shorter, as we could cut it down lower in the 'penthouse'.
I'm starting to lean more this direction for simplicity's sake. We're actually going to be adding over 100,000 cfm of new ventilation. The new dryer, is insulated with 2" of insulation, but is still expected to loose roughly 1/2 million btu/hr. With our new process, summer running is expected to increase, so we want to get this place nice and ventilated.
As far as area specific cooling, this is less of an option as a good portion of the process involves operators walking around monitoring various aspects of the process. This might come in handy in our packaging area where we do have employees staying in the same location for longer periods of time
Thank you all for the input!