Exhaust Duct for Laundry Dryers

2 choices:

1. If you are joining them, an exhaust fan must have more cfm then the total of all the dryers. This will create a negative pressure and prevent any backups,and aid in cooling.

2. When the ducts are joined, the total cross sectional area must be >= to the sum of the areas of the ducts before they are joined. Do not join two 4 inch ducts into one 4 inch duct it will create a back pressure if you are just blowing from the dryers. The individual exhausts will also require reed valves that close when the dryer is not in use.

i.e .5² feet X 4 outlets = 2² feet minimum for the combined duct.

Regardless of what is done, regular cleaning will be required.

Thanks. But can the combined duct size be reduced since a fan is put in place? or does that rule apply to when not considering the usage of a fan?

Yes, the combined duct size can be reduced if the exhaust fan is at the end, and sucking the air out. If you are using just one duct size, the suction pressure will be highest at the exhaust fan, and every time you split the line in two, the suction pressure will be cut in half. You are saving in duct size, but adding in the cost of buying and operating a fan.

The rule of >= size is only for blowing into the ducts when there is no exhaust fan.

well space is always a big issue on a ship.....good to know the possible alternatives when the need arises.

thanks alot！

Ship??

Well that can open other possibilities!

find some dry compressed air source which can be bled into the dryers instead of inlet air. e.g. engine room air. the damp clothes will then dry at room temperature as the water in the clothes evaporates into the expanding air stream. the positive pressure in the dryers will ensure the duct air does not re-enter and should allow a much smaller duct size as well.

Check valve where each one of the exhausts tie in to the main exhaust line to check the back flow from the other dryers or from the laundry room vent fan. A larger main exhaust line.

The reed valves should work as Techno said. However if you have powered dryers, a sure method to prevent back flow is to install motorized dampers, each interlocked to open when its respective dryer turns on and close (spring close) when it goes off.

This would cost a little more and require wiring of power to the actuators. A good idea would be to use the dryer's power and a step down transformer to low voltage (24 vac). Then you could use low voltage actuators and possibly plenum cable if the ship's specs allow it. If the specs do not allow for running plenum cable, you will have to run your cables in conduit, low voltage or not. If you are required to use conduit and your dryers are powered by 120 vac, you might as well use 120 vac actuators and save the cost and wiring labor of the transformers. It's just always good to use low voltage (24 vac) for safety reasons whenever possible.