A novel idea for returning dust collector air to shop from basement

[Thomas Wilson]

I have a conventional ducted heat pump system in my shop. It is in the basement. My dust collector will soon be moved to the basement as well. The basement is heated and cooled by the central system. I had a thought that maybe I could allow the HVAC’s return air to serve as the DC’s return. I need to add a downstairs return on the HVAC. One was not provided in the original HVAC installation. I could design it sufficiently large to return the DC air as well. So DC air would flow into the lower return and return upstairs going both backward through the upstairs return and forward through the air handler and duct system. Need to compute return flows and pressure drops for cases where HVAC is off and on. Math is fun.

My goal is to reduce the number of large holes in my floor. First holes are ugly. Second, it is hard to find any sort of grate that would allow a lot of air flow and be strong enough for tools to roll over it.

[Bill Dufour]

Look at storm drain grates used for roads.

[Thomas Wilson]

Look at storm drain grates used for roads.

Yes. Those would take the load, but as a cyclist, I am acutely aware that a wheel would fall into the slits.

I think I have come up with a workable plan. The space between the basement and shop floor is two layers , the shop floor and about 18” below that a framed ceiling to which we will attach 5/8” fire rated sheetrock. The dust collector will be in a closet in the basement with fire rated sheetrock on the exterior walls which forms the fire barrier for the closet. The ceiling of that closet can be open to the space between floors. That space can be thought of as a huge plenum for the dust collector return. I can cut holes in the shop floor in any convenient place to allow air to flow back to the shop. I will probably build a base cabinet or two with open bottoms to let air in and a louvered return air grate on the side. I could have as many as needed to get the pressure drop sufficiently low.

Some time ago, I offered the idea of ducting clean dc return air to the place an operator would be standing while generating dust to create a bubble of clean air around him/her. I could do that with this idea. What that bubble is called in gas dynamics is a jet. To create a jet that that extends high enough to be useful, i.e. head high, would require high air velocity at the opening which would not work with conventional high-volume-low-pressure dust collectors. It might work with Oneida’s Smartcell. This is the kind of stuff I dream about while standing in a cloud of sanding dust.

[Tom Bender]

In automotive paint booths this concept has been engineered to a high level. (It's important to purge the red paint mist before spraying white or you get a Mary Kay)

Current state of the art is a full ceiling diffuser with very even distribution, and a full floor exhaust grill. Anything less and the bad stuff gets entrained defeating the design.

[Alan Lightstone]

I have similar setup in my shop with the DC in a closet, but the raised access floor stops at the doorway. So there is an 18" by 36" opening from the DC closet to the space underneath the floor. Essentially a plenum. There are a few opening in the floor in the shop, which seem sufficient to provide a path for the return air to return to the shop.

Works quite well, and reduces noise as well. I could have made a more circuitous path to reduce noise even further, but it's pretty good as is.