Her's a link to where I saw this

Here is a link that might be useful: Amish Inflator

That's kind of cool! I can see that working. I'm assembling a low tunnel now with 2 layers of film for overwintering here in USDA5 & maybe I'll cobble together something like that...thanks for the post randall.

Dan

It should be easy to incorporate a one-way flap valve to prevent deflation when there is little wind.

dcarch

Can anyone provide some extra information regarding the construction of a 2 layer greenhouse, for which this would be useful, please?

Thanks!

The two layers are just a double layer of poly. They are fastened as 'one layer' where you'd normally fasten them to the structure. It's just the bread of the sandwich. The air intake is through a tube mounted to a flange sandwiched between the layers and a hole in the interior film accommodating the apparatus.

I got a chuckle out of the Amish inflation device. Too cool. The only problem is that when it's cold and there is little wind, there is also little inflation. I can't pull the figure off the top of my head, but there is a value for the proper pressure of inflation. Any little bit helps, but if it's underinflated you aren't getting as much thermal insulation as you could be.

I agree with the little wind problem, and I'll give my doubled poly low-tunnel one of these anyway in the fall, as I'd have two layers anyway, if the parts are under, say, 7.50. My problem also will be that the sun can warm my air layer quite well and forcing cooler air in there may speed my convection currents/conduction a bit. Still an interesting idea using no power.

Dan

The one pictured is missing the funnel on it. Underinflation is probably not as likely as one thinks especially if you could put a check valve in the air flow. Check valves on electric inflators can cut run time from 24/7 down to as little as 2 hours a day if sealed tight. Cool air going in rather than warmed inside air reduces condensation. It really doesn't take a lot of air to keep decent inflation, I am loking forward to getting the cover on my greenhouse so I can try one of these, no power, what's not to like.

1. You don't need high pressure to inflat. A huge air structure (tennis court bubble tent) uses a few small fans to support.

2. "---The one pictured is missing the funnel on it.---"
Not really. With minor Vanturi effect in aerodynamics, adding a funnel gives you no benifits.

dcarch

The inflation fans are squirrel cage blowers, and very efficient. My eighty foot structure takes an airflow of 640 cubic feet per minute to maintain inflation. And it does with two tiny fans. It also depends on outside temperature how much pressure the fans have to exert to maintain adequate pillow. They work harder in cold weather, or actually more correctly put....they don't work harder, but there is a lot more back-pressure causing resistance against the motor. I think you are correct..... the funnel on the tube could be self-defeating in some circumstances.

I don't know about the funnel whether it helps or not, it said it was supposed to have one. I have been trying to figure an easy way to make the swivel so it moves easily,but is sealed well. Apparently these things work as somebody uses them.

"Posted by randallpink Zone 5 (My Page) ---
I don't know about the funnel whether it helps or not, it said it was supposed to have one. I have been trying to figure an easy way to make the swivel so it moves easily,but is sealed well. Apparently these things work as somebody uses them. "

I don't think the funnel will work based on the fluid dynamics law, and the Venturi effect of static regain and dynamic pressure. I know it is kind of against common sense.

I am not saying what shows in the picture doesn't work. I am curious how the little wane can overcome a great deal of turning friction without using ballbearings.

dcarch

FWIW, I assumed it had ball bearings in there already.

Dan

My thinking is why not just sandwich a few ping pong balls in between the layers?

Problem with any air movement near the layers is the convection/conduction heat lost.

dcarch

That's a good point, I'm concerned about injecting cold air in the gap rather than the warm from inside (altho as above, condensation will be the issue, but convective and conductive losses may be greater).

The design for my low tunnel is cattle panel and lath on the inside, which will be the spacer for the two layers. The top layer is on top of the mesh, so no sag. For mesh, pingpong balls would work, but for hoops, you have no way of holding them unless you adhere them to the film. hmm....

Dan

A good friend in Chattanooga built a twin wall, polyethylene greenhouse. He used the heated air from inside the greenhouse to blow between the two layers. The warm air made the air space between the two layers a better insulator. He grows some nightly fine orchids.

You should use outside air for inflation as the RH is generally lower than the air in the greenhouse. Condensation forms on the inside surface of the cold outer cover as the outside air temperature drops.
Cold air in the cavity will create a smaller temperature differential from the inside to outside which reduces heatloss.

I posted this on a physics forum and BY THEORY a funnel shouldn't help as pressure is pressure , but as it is not an absolute sealed system the airflow would be increased so should help.

"Posted by randallpink Zone 5 --------
I posted this on a physics forum and BY THEORY a funnel shouldn't help as pressure is pressure , but as it is not an absolute sealed system the airflow would be increased so should help."

In general, unless the system is designed using the Venturi static re-gain feature, you gain nothing in pressure or air flow no matter what size the funnel is.

It's almost like the pressure of water remain the same regardless of the size of the swimming pool.

dcarch

Any extra air not captured by the funnel and forced down into the tube will not go into the tube any faster or better or more efficiently, due to the fixed capacity of the tube. I suppose I can picture some turbulent flow created (e.g. vortices) that may negatively affect inflow, but I wouldn't place a wager on it.

Dan