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Author Topic: DH Kiln setup  (Read 376 times)

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Offline JoshNZ

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DH Kiln setup
« on: November 24, 2021, 06:25:19 PM »
I've just got myself an Ebac DH+heater unit and a 20ft NOR/insulated container.

I'm just going about how to setup the air flow side of things, I wondered if anybody has tried an inflatable baffle to displace the unused air mass above a timber stack? I had this idea that I would mount the DH and row of fans on one side at the top, which can push air along the roof line to then move down the front of the timber stack and pass through it. I know this would require a canvas baffle or something similarly to prevent air simply moving over/around the stack back to the fans but I wondered if having an inflatable canvas that would occupy that entire dead space above the timber stack would be sensible? Having it inflatable would make it adjustable to the size of the timber stack I'm drying (and seal against it by air pressure inside) and also would remove that air mass from what the DH/heater has to work on, giving more control.

Any thoughts, or easier ways to do this?

Offline longtime lurker

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Re: DH Kiln setup
« Reply #1 on: November 25, 2021, 04:34:49 AM »
Air is pretty simple stuff at the kiln operation level... it always takes the easiest path. So you need a good baffle system that forces air through the stack so it can't just recirculate around the fan.
You also need plenty space in the plenum ( high pressure side of the kiln charge so that it cycles through the bottom of the stack not just the top. Air must flow to the bottom corners to get even drying.
And you need airspace on the low pressure side so the air can mix freely to keep the humidity level  consistent.

My first home built DH chamber was a disaster, always had a wet spot down low on one side of the charge. I eventually fixed it with more fans. Most chamber designs suck... we like to build rectangles and wonder why we can't get even airflow so we compensate with more and bigger fan decks. Air however likes curves and for all the high tech kilns out there none I've seen are in a chamber designed for laminar flow or even basic aerodynamic principles. Yet one more thing on my one day imma gonna build it list.
The quickest way to make a million dollars with a sawmill is to start with two million.

Offline JoshNZ

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Re: DH Kiln setup
« Reply #2 on: November 26, 2021, 04:03:03 AM »
I could probably add contour to the corners of the container. Unfortunately they don't make round shipping containers, not easily obtainable anyway hah.

I did a small sketch with some dimensions for a guy to give me a quote off, of a PVC baffle. Should give you an idea of what I'm trying to do below. Acheives most of what is mentioned above

 

So my understanding is you need to block that path above the timber back to the fans and force the air to travel through the timber but I also thought, by having that baffle air tight and inflateable it is perfectly adjustable to how high the timber stack ends up being, and also removes that air mass from the DH system (i.e. the air inside baffle isn't subject to kiln RH so doesn't delay effect of DH or lag effect after DH has shut off)

I'd even made a round corner there before you mentioned it look xD

Offline btulloh

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Re: DH Kiln setup
« Reply #3 on: November 26, 2021, 12:04:19 PM »
I n a plenum itís more about air pressure and not really about distribution of air flow.  The fans raise the pressure in the plenum and the discharge side has the lower pressure.  If all the bypass routes are eliminated the fans will tend to raise the air pressure uniformly no matter how they are aimed. When choosing fans, itís important to take into account the effect of static pressure on air volume produced by the fan. Some fan designs will have severely reduced volume when static pressure is increased.  This is significant in kiln fans.
HM126


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