Tumbleweeds v Leaf Blower

turbulent v laminar

The worst nightmares are those we build around ourselves.

I received a request for an assessment, and one of the claimed issues was airway irritation. I went about most of the assessment, and then the client, to demonstrate the airway irritation, turned on the new air conditioning system, which had been off, waiting for me to experience it.

Within about one minute I began experiencing airway irritation, with two additional minutes of exposure I walked out to a back porch, and told the client that unless she turned the system off, I would not come back in.

She turned the system off, and once the dust settled, I proceeded to explain.

The home was old. It initially had no air conditioning system (it might have been built before there were such things). When asked to install this system, the contractor considered the viable options, and the available space, and suggested a high velocity system. This type of system uses pipes in lieu of ductwork, and is minimally invasive demolition-wise to open walls / floors to install the system.

The moniker “high velocity” reflects the type of air flow within the system, as well as outside of it.

Once the air stream enters the living space, it moves the air surrounding it in a turbulent way.

Remember those tumbleweeds that collect under the bed, or the sofa, or the fridge? Those tumbleweeds settled there due to laminar air flow, where with the effect of gravity, however slight, the tumbleweed would gradually drop closer to a surface where the air flow was reduced, and eventually settle, add to the others, and grow in size, until they’re big enough to acquire names.

More technically, turbulent air flow (or liquid flow for that matter) is such that the aggregate mass has a general main direction, but when looked at in close scrutiny there are individual air flows that form swirls and eddies, like in a river, where some of the fluid directions are entirely against the main flow direction.

Laminar air flow is such that the entire mass flows int he same direction, but the flow is “separated” into sheets, as it where, of different flow speeds. That is, those sheets closer to a surface are moving the slowest, while those near the center of the flow are moving the fastest. Laminar air flow allows dust to settle on horizontal surfaces.

What happens then, if you bring in a leaf blower and begin to wield it about? Those tumbleweeds that had acquired names, along with their many smaller cousins, become liberated and find another parking lot, one that is moist and sticky. Your nose and lungs.

So if you can imagine attaching a hose to your nose, and placing the other end of it on the floor, under that bed, or that sofa, or the fridge . . . I think you get the idea.

High velocity systems can only be tolerated when the dust accumulation is minuscule. Meaning vacuuming on a daily basis. Everywhere. Who does that level of cleaning?

So when your old house needs to have an air conditioning system installed, realize that unless you allow for sufficient demolition to install a proper system, you will not be able to tolerate a high velocity system, and it may very well not get used, unless you do the extensive cleaning first (in hot and humid conditions), and then settle down for cooling by turning it on. (In my way of thinking, this would be like staying in a sauna until I could tolerate it no more, then jumping into extremely cold water. I shudder to think of suffering thermal stress cracking.) Any area you did not clean thoroughly, will come back to remind you of itself.



Contribution from a friend, and elaboration by me:

All portable vacuums have a turbulent flow exhaust. So while you are vacuuming in front of you, the unit is stirring up stuff behind you for you to inhale. You might try to have the unit say, in the hall (cleaned previously), while you start vacuuming a room, and gradually bring the unit into the room, but it’s going to be impossible for you to control the unit, to keep its exhaust aimed “where there is no settled dust,” if there is such a place. I suggested a shop-vac outdoors, with additional hose to bring the suction where you need it. She suggested a central vac system. Nice idea, if its exhaust is directed outdoors through a dedicated pipe. If it’s not so equipped, then it’s very relevant where it exhausts. I saw one unit exhausting near an HVAC air handler. The unit’s ductwork not hermetically sealed, presented the problem that if you were vacuuming anywhere, the exhaust would provide very very fine dust, that would be picked up by the HVAC and made available airborne everywhere . . .