Building the Laboratory – Air Flow & PVC Ducts

My young mother plants have been thriving. They are a lush green color and though they were off to a slow start now make notable growth every day. However, I do find their stems to be weaker than they should be at this age. I blame this on poor air flow.

Plants reputedly grow their stems and branches stronger in reaction to wind, which makes perfect sense. The room I keep the laboratory in has no windows and thus virtually no air flow. To correct this I bought a small $7 blower fan from the thrift shop. It has three speed settings (I only plan to use the highest for now) and it even oscillates, so I got a nifty synchronous motor out of the base. I’m quite upset with myself for not taking a picture before disassembling it, but that’s a burden I’ll have to bear.

I would rather have a central fan blower that uses ducts to push a breeze to all the plants than to have individual fans for each bucket. A central fan means less wires, less power supplies, less things in my way and fewer moving parts. After talking it over with my buddy I narrowed it down to two designs.

To house the blower I epoxied its motor to the inside of a 4x4x2 PVC 45 Wye. I cut end caps out of PVC stock for the 4 inch openings of the Wye. One end cap is solid, and the other has a hole for blower intake. The 2″ opening of the Wye is the exhaust and feeds to the rest of the system.

Bill of Materials

-1/4″ PVC Stock
-4x4x2 PVC 45 Wye
-2x2x1.5 PVC Tee
-2″ PVC Street Elbow
-2×1.5 PVC Reducer
-(2) 1.5 PVC Wide Elbows
-(2) 1.5 Test Caps/Plugs
-18′ of 1.5″ PVC Pipe
-3′ of 2″ PVC Pipe

This first attempt uses 2″ PVC Pipe for the riser which bridges the shelves and reduces to 1-1/2″ PVC Pipe at the fittings which runs above the garden buckets. At first I put slits in to the 1-1/2″ pipe, but the breeze was too weak, so I drilled larger holes in to these slits. The breeze was so effective that the stems of my basil doubled in girth over the course of two days.

….

As it turns out, the 1-1/2″ diameter PVC is too wide and gets in the way of my grow light panels. So, I rebuilt the system reducing to 3/4″ pipe and lowered the vents closer to the system.

I would write a bill of materials for this version, but I do not recommend replicating it. Though the blower still makes a decent breeze it is significantly weaker than before. I’m certain this is because the reduction out of the Wye is far too abrupt to generate a strong air flow. I will rebuild this system again soon and keep you updated. The reduction in PVC needs to occur smoothly and over the run of the whole system.