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Dryer Exhaust

Dryer Exhaust

(OP)
6 dryers, 6"dia vents at 500 cfm, run on gas at 75 mbh each, commercial 30lbs capacity Speedqueen

high rise bldg laundry

10 ton dedicated rtu serves the room Currently balanced to 3200 cfm.
This unit can only do 800cfm oa (per model number)

Dryer vents tied to two headers (set of 3 dryers each). First grille on header is return air from room It is balanced to 1600 cfm.
A backdraft damper is used to reduce the air to 1100, 600 and then 100 cfm through the grille as each dryer comes on.

2 return grilles back to rtu,
2 headers combine to inlet of an exhaust fan at 3200 cfm

The RTU should be able to bring in 3200 CFM of oa, in order for the system to work when all dryers are running.

There is no transfer duct to the room from adjacent spaces. The room door from elev lobby is open so some air can flow in. Other side of elevator lobby is swimming pool. No offices, or apartments to transfer air from.

1. Should the RTU be replaced with 3200 cfm OA unit? That will be costly.
2. All return will have to be exhausted to the outdoors if all 6 dryers are running. In this case the RTU will only be able to heat the air to 60 degf in winter and have a coil discharge of 70F and not 55F in summer. OA at 95/78 and 10 for summer/winter

Can the system work without increasing the OA?

Worst case: Can the air only be heated in winter and not cooled in summer fully to save energy? Let the room temp go to 85 or 90 in summer.








RE: Dryer Exhaust

1. 6" dia. appears too small for 500 cfm. That will have a dp of 1.6" w.g./100' for galvanized steel.
2. Bring in outside air directly to the dryers. It will greatly simplify the controls. That way, the RTU is not bothered. Trying to link the dryers to the RTU is way too complex.

RE: Dryer Exhaust

Rmusa,
One setup for a dryer room in a high rise hotel, is to set the dryers in a row, then build a wall boxing them in with the fronts of the dryers protruding slightly through the wall, leave sufficient room behind for access for maintenance personnel, cut a hole through an outside wall , or bring in an outside air duct feeding the dryers directly inside the boxed in area.
Take your vent ducts to a centrifugal lint filter to clean the residual entrained lint out of the exhaust air before discharging the air. The factory lint filters on a speed queen industrial dryer only get about 85% of the lint. If you do have to run horizontally with the exhaust duct put cleanout doors every 10 feet.
B.E.

You are judged not by what you know, but by what you can do.

RE: Dryer Exhaust

(OP)
Attached speedqueen data shows 6" dryer vent will discharge 500 cfm, for 30lb tumbler dryer. (trashcanman)
I have seen the partition wall flush with the front of dryer at one installation. Can this wall be in the middle of the dryers with only half of the dryer inside the wall box? In case there is a coin/card box installed on top?

7 dryers will be in a row with a common header duct on top. The 6" vents will tie into the header. The header will be tied to inlet of fan
mounted on roof above. The make-up air will be ducted into the box from the roof/sidewall with motorized dampers. The dampers will open and any one of the dryers on will start the exhaust fan. If only two dryers are running at 1000 cfm and fan is exhausting at 3500 cfm, will it lower the dryer's or the whole systems performance? Don't want added cost of a VFD.

If the make up air is supplied into the boxed in area behind the dryers where does the makeup air enter the dryer?
Is it from the bottom or from the back? The front of dryer does not look like has an opening. Is it preferred to heat this makeup air or raw air works? Will raw air make the room cold in winter?

RE: Dryer Exhaust

The inlet for the dryer should be in the back or side depending on the model. Again depending on the model the outlet air will be on the back , it is rarely on the top. Do not heat or cool the makeup air the raw air will make the room cold in winter and hot in summer but only behind the wall.
You can set the dryers forward out of the wall , as long as you do not obstruct the intake vent, It is unusual to have the coin box on the top , they are most often in the front wall of the dryer. at 5'-3" high a short person will have to stretch up to get money into the machine.
Again beware of lint in the header , put cleanout doors in.
B.E.

You are judged not by what you know, but by what you can do.

RE: Dryer Exhaust

Download or get the installation manual from Speed Queen or get it from their rep. It will provide locations for all connections. It will also provide required clearances.
BTW, air inlet is in the back.
If you're not going to use VFD to accommodate diversity, use a motorized damper to control the static pressure in the exhaust air duct.

Just curious, why take exhaust to the roof? If the room has an exterior wall (recommended), take the dryer exhaust to a vent cap and ditch the fan (it isn't needed if the run is short enough). Shouldn't be hard to locate make-up air louver 10 feet from vent cap, and provide with backdraft damper.

Then RTU need only be sized for occupant and sensible loads. Depending on type of system in rest of building, you may be able to ditch the RTU as well and provide conditioned air from another unit.

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