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kiln question

Started by xlogger, December 24, 2013, 06:04:33 PM

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xlogger

I'm hoping to start on building a solar kiln by the spring. I have a customer that wants me to build it so it will get hot enough to kill off insects especially powder beetles. Will a solar kiln do that alone or could I add a heat source to help. I have an OWB close to where I will build the kiln and an extra port so I could run a line to it and  put a heat exchanger in the kiln. Would this work if needed?
Timberking 2000, Turbo slabber Mill, 584 Case, Bobcat 773, solar kiln, Nyle L-53 DH kiln

GeneWengert-WoodDoc

Except on a rare day, the solar kiln will not get hot enough to raise the entire wood temperature, shell and core, to 133 F.  An external heater is ok except a solar kiln has such large heat losses, that it will be very energy consuming.  So, the best idea is to have a separate hot box for sanitizing.

Note that once sanitize, the lumber can get infected with PPB after drying.  So, you and your customer and shipper must keep the wood away from any infected lumber.  A complaint a year after drying will come back to you and so be prepared with data and pictures of how you handle the wood so you can prove it was not you that caused an infection after drying.

Ok?
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

xlogger

Timberking 2000, Turbo slabber Mill, 584 Case, Bobcat 773, solar kiln, Nyle L-53 DH kiln

xlogger

Another Question Doc. How long does the lumber need to be in a kiln to rid PPB's and does it need to be 133° or higher all the time? I was thinking about building a solar kiln next year but this customer wants me to kiln this beams for him and I would have to build a kiln that would hold 16 ft beams that come out of old whse building. Not sure would it worth it, what is the normal charge? He's a good customer that I do work for and this would give me more work for him. As far as the OWB goes I have plenty of wood to supply it, it would just be the idea of how often I would have to put wood in it. If you don't think this would work at all, what would you suggest I look at? Thanks, Ricky
Timberking 2000, Turbo slabber Mill, 584 Case, Bobcat 773, solar kiln, Nyle L-53 DH kiln

bedway

Im confused (which is more often than not) ;D, but i thought a solar kiln would get the temperature over 133 degrees.

ancjr

Same as cooking a roast.  You set the oven @ 200f, the meat won't get to 160f temp at the core for MANY hours.  Turn off the heat before then, and it'll never get there.  Solar kilns have a short (relatively speaking) heating cycle limited to daylight hours and an even shorter peak heating period.  Hence, it'll dry the wood, but not kill all possible bugs.

pineywoods

Quote from: bedway on December 28, 2013, 09:16:27 AM
Im confused (which is more often than not) ;D, but i thought a solar kiln would get the temperature over 133 degrees.

There is ample room for confusion. Ours routinely top 180 degrees. The confusion factor is, they won't stay that hot over a 24 hr period. When the sun goes down, the heat source goes away. How much the interior will cool down is highly variable. Outside temp, insulation effectiveness, size and variety of the stack, whether the fans are running, and probably other factors. The cool down will definetly extend the drying time, but there is an upside to that. It allows the wood to stabilize resulting in fewer defects. I think most of the confusion results from trying to make a solar kiln operate like a conventional heated kiln. Don't work that way. Solar is a different beast.
1995 Wood Mizer LT 40, Liquid cooled kawasaki,homebuilt hydraulics. Homebuilt solar dry kiln.  Woodmaster 718 planner, Kubota M4700 with homemade forks and winch, stihl  028, 029, Ms390
100k bd ft club.Charter member of The Grumpy old Men

Sawdust Lover

xlogger, I had the same questions before building my Va Tech kiln. My temps never got over 130 on the hottest day here in the Blue Ridge mtns. I tested a reclaimed white oak log that was 6" x 10"x 6' that was in the kiln at 125 deg for 6 hrs. We took it out that evening just as the temp inside the kiln started to drop and the inside temp of the beam was 80 deg. My solar kiln works well but will never sterilize a beam and I don't think it would sterilize 5/4 lumber either. I have bought a Nyle kiln to do this.

GeneWengert-WoodDoc

To heat lumber to 133 F through and through, if the kiln is 160 F for about 20-24 hours, you can do it.  As mentioned, the transfer of heat from the air to the wood and then within the wood requires hotter temperatures than 133 F or even 140 F.  Also remember that the fans must be running to get the hot air into the lumber pile.  I do believe that many times, a small hot box heated with gas or even electric will be more reasonable.  Solar kilns will not get hot enough for a long enough time, even on a sunny day.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

xlogger

I would like to build a solar kiln but maybe I should build a good insulted  box and put in a heat exchanger from the outdoor wood boiler to it if you think that would be good enough? Has anyone here build one with using an 0wb for your heat supply? If so any suggestions? Thanks for any input on this.
Also if you had a customer that wanted use the kiln long enough to rid his boards from PPB what would you charge, saying he had a full load? Maybe a stack saying 16' long and 4-5 feet high.  Ricky
Timberking 2000, Turbo slabber Mill, 584 Case, Bobcat 773, solar kiln, Nyle L-53 DH kiln

scsmith42

(thinking out loud....)

It seems to me that the biggest heat loss from a solar kiln is through the collector.  For sterilization purposes, I wonder if you could cover the collector with some type of insulating blanket and add an auxilliary heat source inside the kiln chamber?

Gene, I'm recalling from one of my drying manuals (forget which one) that in order to sterilize lumber there are several different options, including getting the core of the lumber to 133F or higher for 30 minutes, or in lieu of 133F for 30 min there is a gradual scale that includes having the core of the lumber at 120F or higher for 60 hours, or something like that?
Peterson 10" WPF with 65' of track
Smith - Gallagher dedicated slabber
Tom's 3638D Baker band mill
and a mix of log handling heavy equipment.

Sawdust Lover

Quote from: xlogger on December 29, 2013, 05:57:10 AM
I would like to build a solar kiln but maybe I should build a good insulted  box and put in a heat exchanger from the outdoor wood boiler to it if you think that would be good enough? Has anyone here build one with using an 0wb for your heat supply? If so any suggestions? Thanks for any input on this.
Also if you had a customer that wanted use the kiln long enough to rid his boards from PPB what would you charge, saying he had a full load? Maybe a stack saying 16' long and 4-5 feet high.  Ricky
I have paid .50 a bf to dry my lumber. So if you had a stack like that which is around 1500 bf + or - you could maybe get $750.00. I think most people get more like .30 a bf which is what I will charge. I would not buy a kiln to dry lumber for other people because it would stay empty half the year. And I also won't dry other peoples lumber until I have dried my own for a while to make sure I know what I'm doing.

xlogger

That's about how many bd ft I was thinking and he did mention $.30 a bd ft. I was just not sure on the price. I know what you are saying about practicing on my lumber first. All this guy wants is to kill the PPB, some of this beams are near 80-100 years. Of course some are maybe just 40 yo also. But they should be dry. Ricky
Timberking 2000, Turbo slabber Mill, 584 Case, Bobcat 773, solar kiln, Nyle L-53 DH kiln

GeneWengert-WoodDoc

I do not believe that 120 F will provide sterilization of the wood.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

scsmith42

Gene, I found the chart that I was recalling, and the temperature was slightly higher than the 120F that I mentioned earlier. 

It's in Chapter 7, Kiln Schedules, AH188 of the USDA Dry Kiln Operators Manual.  The chart is table 7-31, Schedule for killing Lyctus (powder post) beetles and their eggs.

The table lists several different temps and dry bulb temps and wet bulb depressions; the lowest is 125F with a wet bulb depression of 15, 61% RH, EMC of 9.7.  Per the table, 4/4 lumber needs 46 hours, 8/4 48 hours, and 12/4 50 hours.

The table also states that 140 dry bulb with 7 wet bulb depression only requires 3 - 7 hours (4/4 to 12/4).

My interpretation of that table was that in my DH kiln if I completed the load at 125F (instead of the 120F in the Nyle manual) for at least two days, then this was also serving to sterilize the load w/o needing to take it up to 140 overnight.

I typically go to 140 anyway, but am curious if you agree with the table or if the knowledge changed since the early 70's when this manual was produced.  Thanks much.

Scott
Peterson 10" WPF with 65' of track
Smith - Gallagher dedicated slabber
Tom's 3638D Baker band mill
and a mix of log handling heavy equipment.

GeneWengert-WoodDoc

This data was from a study in Europe in the 1940s and has been thought to be incorrect for some time.  Although it shows up in the DKOM, the USDA people concerned about insects in wood established other protocal more recently.  You will note that such a chart is not given in DRYING EASTERN HARDWOODS (1976) or DRYING HARDWOOD LUMBER (2002), both USDA publications.  It is not clear to me that when the DKOM was revised that the people doing the revision did not use publications and info from their own laboratory.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

scsmith42

Gene, thanks for the additional insight; I will definitely remember this.

Peterson 10" WPF with 65' of track
Smith - Gallagher dedicated slabber
Tom's 3638D Baker band mill
and a mix of log handling heavy equipment.

MattJ

What are the thoughts on this publication http://www.fpl.fs.fed.us/documnts/fplrp/fpl_rp626.pdf  ?  They state you need to hit 133F for 30min and the heating charts suggest that from 160F you can hit 133 internally pretty quickly.  I'm thinking a well built, perhaps overbuilt solar kiln in the southern US during the warm months might have a fighting chance of hitting this.

Matt

scsmith42

Matt, I think that the problem would be heat loss through the collector.  My solar kiln has hit 135 during the summer, but I can't imagine it hitting 160. 

It would probably require some type of very special insulated glass for the panels.
Peterson 10" WPF with 65' of track
Smith - Gallagher dedicated slabber
Tom's 3638D Baker band mill
and a mix of log handling heavy equipment.

AnthonyW

From a materials use efficiency point of view, using the channel between the collector and the glazing panels for airflow is an obvious choice.

To reduce loss through the glazing could one:
1) Seal the the glazing and the collector panels to the sides of the kiln to make it air tight to minimize losses
2) For the airflow channel add 1x3s and plywood below the collectors and heat the air from the bottom of the collector rather than the top. Presuming of course metal collector material is used so the heat can transfer from the top to the bottom.

Thoughts?
'97 Wood-Mizer LT25 All Manual with 15HP Kohler

GeneWengert-WoodDoc

The referenced publication uses steam heated air at over 90% RH at 160 F on soaking wet wood in one case.   The time with dry wood would be much longer.  We cannot achieve 160 F air temperature in a solar kiln with wet wood and also have the air going through the load of lumber.  The drying wood will use the heat to evaporate water and not to merely heat the wood.

Also, when heating wet wood, the velocity of the air greatly affects heat transfer rates, yet this is not mentioned.  Most solar kilns would not have the air flow they used in their work.  Also, they seem to ignore that when steam is injected to achieve the high RH, there is also condensation of this steam on the cold wood which releases the heat of evaporation and gives much faster heat transfer.  In a solar kiln, we do not have steam input.  In fact, depending on the steam pressure, the heating times will vary.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

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