Air drying 4/4 Red Oak

[Cazzhrdwd]

Moisture has gotten down to 17% but has slowed dramatically, kiln is 127 degrees. I'm going to shut off the compressor and raise the temp up to 160 to try and get it moving again. I normally have to do this two times.

I talked to the manufacturer today, he thought I was having these issues because of wide boards. 60% of my loads are 10" and wider, with many being up to 18" wide
So I'd like to ask you guys some more advice. If the wide boards are indeed holding onto this moisture, would it be better on the next load to start off as usual with 90 degrees, and after 2-3 days start raising the temp up 1 degree per day, it would follow the schedule pretty closely anyway, it just wouldn't have the sudden change in temp with the typical schedule. The idea is keeping the core coming down at a continuous rate, thereby, not having any checking from the core being so different then the shell.

[Cazzhrdwd]

^
Any thoughts on this?

[WDH]

At 17%, I run the kiln wide open.  I set the dry bulb at 120° and the wet bulb at 75° and the compressor runs full out.  I have had good luck with this so far with no quality issues.  However, I have only put air dried red oak in the kiln so far, and it has all been around 15 - 17% moisture going in. 

[Cazzhrdwd]

That's where I'm at now WDH, one difference is my temp is at 128°. I couldn't get the final moister to move out at 120°. At 129° its coming down about 1% per day.

[YellowHammer]

That's where I'm at now WDH, one difference is my temp is at 128°. I couldn't get the final moister to move out at 120°. At 129° its coming down about 1% per day.

I've never took a hard look inside my L200M, but does yours have a high pressure refrigerant safety cutout switch?  My other kiln, an L53, used to switch off the compressor at 130°F.  The switch had to be reset manually which is a total pain.

[Cazzhrdwd]

That's where I'm at now WDH, one difference is my temp is at 128°. I couldn't get the final moister to move out at 120°. At 129° its coming down about 1% per day.

I've never took a hard look inside, but does the L200M have a high pressure refrigerant safety cutout switch?  My other kiln used to switch off the compressor at 130°F.  The switch had to be reset manually which is a total pain.

Yes it does, it pops at 133°. I'm running just under it. I leave the side panel off on the unit so the switch is easy to reset, but I haven't had to do it yet.

[Denny]

Conventional kiln guy here. At 17% I'd be at 140-110 @ 38% RH and the ol' T4-D2 RO schedule calls for an even more aggressive 140-90 @ 14% RH.  When I go under 15% MC I'm up to 160-115 @ 25% RH.  Do you guys ever get up to these temps ?  I read where Gene says dehumid kilns usually only go to 150.

"would it be better on the next load to start off as usual with 90 degrees, and after 2-3 days start raising the temp up 1 degree per day"
Whats the initial moisture content at ?  I start my green RO charges either at 100-98 @ 93% RH or 100-97 @ 89% RH. My green RO charges are sometimes in the mid to high 90's initial MC.  I stay above 87% RH until im under 50% MC.
My kilns are controlled with MRC5000 controllers with Partlow loop controllers, all setup by Dennis at PC Specialties and I always use set point ramping for my RO charges. I set my dry bulb temp to raise 1 degree per hour and only do 10 degrees per move. It puts a nice steady draw on the lumber IMO.
Another thought... keep in mind that my experience is with conventional kilns, but by asking if 90 degrees is a good starting temp is not looking at the bigger picture which includes relative humidity. I guess some guys use EMC, but I'm a RH guy. Ninety degrees at 50% RH is not a good idea for starting a green RO charge, while 90 degrees at 90% RH is good.  I dunno, maybe you DE-humidification guys dont use RH like a conventional kiln is operated, I'm still learning about de-humi kilns.

[Cazzhrdwd]

Conventional kiln guy here. At 17% I'd be at 140-110 @ 38% RH and the ol' T4-D2 RO schedule calls for an even more aggressive 140-90 @ 14% RH.  When I go under 15% MC I'm up to 160-115 @ 25% RH.  Do you guys ever get up to these temps ?  I read where Gene says dehumid kilns usually only go to 150.

I do, its the only way I can get the last bit of moisture out. 140° will not do it, at least not as fast as I'd like.

"would it be better on the next load to start off as usual with 90 degrees, and after 2-3 days start raising the temp up 1 degree per day"
Whats the initial moisture content at ?  I start my green RO charges either at 100-98 @ 93% RH or 100-97 @ 89% RH. My green RO charges are sometimes in the mid to high 90's initial MC.  I stay above 87% RH until im under 50% MC.

My loads start with an initial of around 50-55
Your schedule is close to what mine says.

My kilns are controlled with MRC5000 controllers with Partlow loop controllers, all setup by Dennis at PC Specialties and I always use set point ramping for my RO charges. I set my dry bulb temp to raise 1 degree per hour and only do 10 degrees per move. It puts a nice steady draw on the lumber IMO.
Another thought... keep in mind that my experience is with conventional kilns, but by asking if 90 degrees is a good starting temp is not looking at the bigger picture which includes relative humidity. I guess some guys use EMC, but I'm a RH guy. Ninety degrees at 50% RH is not a good idea for starting a green RO charge, while 90 degrees at 90% RH is good.  I dunno, maybe you DE-humidification guys dont use RH like a conventional kiln is operated, I'm still learning about de-humi kilns.

I start my green oak at 90-87 or I can do it at 100-97. I would like to raise it 1° per day, because I think I can keep the water coming out in a more uniform way, provided everything stays under control, I can always slow down. The schedule I'm using works great at first but then slows to a crawl. I've noticed when I've kept the temp moving up, it seems to keep water moving better.

Gene would you comment on this?

[Den Socling]

I wouldn't run any kiln without setpoint ramping. Free water steadily comes down and the amount of energy needed (heat) steadily needs increased. Not daily or weekly steps. Hourly increases.

[Cazzhrdwd]

I wouldn't run any kiln without setpoint ramping. Free water steadily comes down and the amount of energy needed (heat) steadily needs increased. Not daily or weekly steps. Hourly increases.

My kiln does not have a controller for that. The schedule calls for the temp to go up by 10. Starts at 90°-100°-110° and finally 120°

I'm not sure I understand what you're saying.

[WDH]

I dunno, maybe you DE-humidification guys dont use RH like a conventional kiln is operated, I'm still learning about de-humi kilns.

I am a very little dehumidification kiln guy and I use RH just like you do to set the set points.  Just cannot go over 130 degrees or the compressor will shut down. 

[GeneWengert-WoodDoc]

A two,degree depression is too high and the lumber will not dry very fast at all and will get really moldy.  However, you indicate good drying rates, so I suspect you likely have a one or maybe more error in temperature measurement.  For this reason, when drying at high MCs we rely on the drying rate to fine tune the settings.  So, 4/4 red oak should and can safely average 2.5% daily MC loss with no pieces over 3.8% MC loss.

The maximum temperature is 110 F, but certainly 100 or 105 F is a bit more conservative and is a good choice.

I am teaching an advanced drying class Nov 11-12 in Johnson City, TN that you would find very helpful.  It is sponsored by the Ohio Valley Dry Kiln Assn, Appalachian DKA! And SE Dry Kiln Club and more.  More info will be in the training link at this site.

[Den Socling]

Hi Gene,
That rate of 2.5% per day for 4/4 Red Oak is interesting. I've dried 4/4 Red Oak at a rate of 2.5% per HOUR with excellent results. I just checked my records. I first did that way back in March of 2004. You would think that vacuum kilns would be all over the place by now.
Den

[GeneWengert-WoodDoc]

The lack of vacuum kilns is often because the company has a boiler and fuel. Also, they do not understand drying costs and do not have capital.

[Denny]

Dam thats crazy... one would naturally think that the RO would blow apart with 2.5% hourly losses. How the heck does a vacuum kiln safely achieve these big losses ?  How can RO psychically survive that much water loss in a vacuum kiln but blows apart in other kiln types ?  whats the science behind it ??

Thank the stars for this forum... what a great place to learn about the different drying techniques and kilns.

[Cazzhrdwd]

Dam thats crazy... one would naturally think that the RO would blow apart with 2.5% hourly losses. How the heck does a vacuum kiln safely achieve these big losses ?  How can RO psychically survive that much water loss in a vacuum kiln but blows apart in other kiln types ?  whats the science behind it ??

Thank the stars for this forum... what a great place to learn about the different drying techniques and kilns.

My understanding is the vacuum lowers the boiling point of water to 105° which allows it to safely leave without hurting the wood.

[Cazzhrdwd]

Dam thats crazy... one would naturally think that the RO would blow apart with 2.5% hourly losses. How the heck does a vacuum kiln safely achieve these big losses ?  How can RO psychically survive that much water loss in a vacuum kiln but blows apart in other kiln types ?  whats the science behind it ??

Thank the stars for this forum... what a great place to learn about the different drying techniques and kilns.

My understanding is the vacuum lowers the boiling point of water to 105° which allows it to safely leave without hurting the wood.

[Denny]

"My understanding is the vacuum lowers the boiling point of water to 105° which allows it to safely leave without hurting the wood."

Now thats pretty neat. Thanks for the reply.

[Den Socling]

The temperature of the wood is set by the chamber pressure (vacuum). At the pressure we run, the water boils around 100'F so the wood does not get warmer than 100 until the amount of free water is significantly reduced. In a conventional kiln you dry with a humidity gradient. You are slowly skimming water off the surface. With vacuum kilns and a porous species like Red Oak, you can boil water from inside the wood.
Gene, we have lots of kilns that are heated with wood waste boilers. I believe you hit the nail on the head when you say they don't understand drying cost. I followed up on a company one time and they were reporting yields in excess of 100%. I asked how that could be. Their yield of 100% allowed a certain percentage of degrade. They had just learned to live with wasted wood!

[Cazzhrdwd]

The initial cost of a vacuum kiln is most likely what kills the deal for folks. For thick lumber 8/4 and above, I can't imagine drying with anything else. A friend of mine made his own and from what he showed me in pictures and dry time, they're incredible with thick lumber. I'm stuck in a groove of putting green lumber on sticks then in the kiln for a time. If I had a vacuum kiln I'd get worn out filling the kiln every three days with new lumber.

[Cazzhrdwd]

When I checked into them if I can remember, a small 1000 BDF kiln was in the range of 50,000? Den I'm sure will set me straight on that, but when you figure the time it takes to dry and very little degrade, they're well worth the money.

[Den Socling]

We build a 1250 bf kiln and I hate it. It's too expensive at $95,000. It's for universities and such. We just shipped the first a new model called a VK16. It can dry 16' lumber or two 8's end to end. It holds about 3200 bf of 8/4 and cost $117,000. Consider that you can dry most 8/4 in a week or less, fresh off the saw with Zero degrade, and you can do the math. If you have a market for 12/4 or 16/4, it can do it.

[Magicman]

Dam thats crazy...Thank the stars for this forum... what a great place to learn about the different drying techniques and kilns.

Just a reminder that "DanG" is the official FF cuss word.   

[Cazzhrdwd]

We build a 1250 bf kiln and I hate it. It's too expensive at $95,000. It's for universities and such. We just shipped the first a new model called a VK16. It can dry 16' lumber or two 8's end to end. It holds about 3200 bf of 8/4 and cost $117,000. Consider that you can dry most 8/4 in a week or less, fresh off the saw with Zero degrade, and you can do the math. If you have a market for 12/4 or 16/4, it can do it.

Its still worth it if you have the market. No other efficient way for a small operation to do it. Even if I was doing 4/4 with it, I'd have it paid for the first year.

[Den Socling]

It's a lot of money but the bottom line does work. We are now building a kiln for Louisville Slugger. It's easier for the big companies to make the investment. But considering the payoff, I'm surprised more smaller companies don't make the investment. They could grow big in a hurry.