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humidity in solar kiln?

Started by xlogger, September 06, 2015, 07:52:52 AM

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xlogger

What is the normal humidity % you try to maintain in a solar kiln? My kiln showed 66% after a rainy day this week and I ran my DH that night and it was still at 66% in the morning. Only took out around a quart of water, maybe I need another DH?
Timberking 2000, Turbo slabber Mill, 584 Case, Bobcat 773, solar kiln, Nyle L-53 DH kiln

Tree Dan

My kiln has never been that high its at 35% at this time of day 121F in the kiln.
All my wood has been air dried ,maybe that's why ???
I think Humidity depends on a lot of things.. :snowball:
Wood Mizer LT40HD, Kubota KX71, New Holland LS150, Case TR270
6400 John Deere/with loader,General 20" planer, Stihl 880, Stihl 361, Dolmar 460, Husqvarna 50  and a few shovels,
60" and 30" Log Rite cant hooks, 2 home built Tree Spades, Homemade log splitter

GeneWengert-WoodDoc

Humidity depends on -
Green or dry lumber?
Vents open or closed?
Check prone species or not?
Sunny or not?

Generally at the end of drying, 35% RH average is good.  It will be higher at night and lower during the day.  Without DH, run fans only during daylight.  Otherwise you will stop at about 12% MC which is 65% RH average.

Of course, with wetter wood, 100% RH at night is good to relieve stresses and then we might have 60% or higher average RH depending on species, MC, etc.

For 1000 BF of lumber like oak,  each 1% MC loss is about 32 pints.  So, your 1 quart is not much moisture loss for possibly a lot of electricity.  Sounds like compressor is not working well, assuming it is running 100%.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

xlogger

The 66% was as high as I've seen it, after a rainy day. Usually in the 40's. I have a closed kiln like Pineywood's and have some maple around 12% and some red oak that I'm not sure now, probably higher around high teens. I pm pineywoods and he said a quart might be in line with what I have. He suggested on a second dh but for now I can only run one due a voltage drop in a long line, that I hope to correct that in the next few weeks. I might go ahead and get a replacement dh just to make sure if the other is good.
Gene, you where correct on what you said awhile back, After building the first kiln plan on room for the second one.
Timberking 2000, Turbo slabber Mill, 584 Case, Bobcat 773, solar kiln, Nyle L-53 DH kiln

GeneWengert-WoodDoc

Thanks.  Glad to know I was able to give some advice that helped you.

So, if your kiln holds 1000 BF and you get one quart, that is about 0.1% MC loss from the DH unit.  Not a big impact compared to the amount of water evaporated from the solar heating.  Maybe a different compressor will get more water and be worthwhile?  Or maybe the MC is so low that there is not much water coming out of the wood at the low temperature.

I wonder how many hours it was running, as a unit that draws 8 amps that ran 10 hours would use about $1 of electricity (8 amps x 120 v x 10 hrs x $0.15 / kWh).  Seems pretty expensive, even if the compressor itself was free.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Tree Dan

If your kiln is the closed type of kiln...why not put some vents in it and vent some of that wet air out during the day.
Then you still have the option of running the DH at night when the fans shut down.
If I could get enough power from the sun I would have my fans off the hydro as well, and run them from a solar sourse.
8 amps at 120 Volts Is the same as just under 10 - 100 watt light bulbs running all at the same time.
My 2nd load of hardwood is about to come out of the kiln now, and Im surprized on how fast this kiln is drying the wood.
On a good hot day like today I like to close the vents and get the temps way up there, then I will open them full near the end of the afternoon to blast out the moisture, then I close them for the night.
This has been working for me.
Wood Mizer LT40HD, Kubota KX71, New Holland LS150, Case TR270
6400 John Deere/with loader,General 20" planer, Stihl 880, Stihl 361, Dolmar 460, Husqvarna 50  and a few shovels,
60" and 30" Log Rite cant hooks, 2 home built Tree Spades, Homemade log splitter

xlogger

I've notice in the last two nights that my DH is freezing up at bottom of the fins and getting very little water. I think I'll order a new one from amazon today. Wonder what makes them freeze up?
Timberking 2000, Turbo slabber Mill, 584 Case, Bobcat 773, solar kiln, Nyle L-53 DH kiln

Tree Dan

Quote from: xlogger on September 08, 2015, 06:28:16 AM
I've notice in the last two nights that my DH is freezing up at bottom of the fins and getting very little water. I think I'll order a new one from amazon today. Wonder what makes them freeze up?
It could maybe be the fan, filter or needs a good cleaning.
There could be components not right up to working condition as well.
I too would just get a new one for your closed style kiln
Cheers
Wood Mizer LT40HD, Kubota KX71, New Holland LS150, Case TR270
6400 John Deere/with loader,General 20" planer, Stihl 880, Stihl 361, Dolmar 460, Husqvarna 50  and a few shovels,
60" and 30" Log Rite cant hooks, 2 home built Tree Spades, Homemade log splitter

YellowHammer

Quote from: xlogger on September 08, 2015, 06:28:16 AM
I've notice in the last two nights that my DH is freezing up at bottom of the fins and getting very little water. I think I'll order a new one from amazon today. Wonder what makes them freeze up?

Many dehumidifies don't like to run below 65F or so, however some will operate well below that.  I have one that will operate nearly down to 40F.  That's important because solar kilns really slow down in the winter with cold temps and a distinct lack of solar. So a dehumidifier that works at low temps is very useful. Also, I'd recommend one with an external drain.

Several things such as the fan going out causing loss of airflow can cause a DH to ice up, also check evaporator coils and fins to make sure everything is clean.

Partially frozen coils are a classic sign of low refrigerant pressures. The refrigerant is going from liquid phase to gas phase in the coil about where the frost forms.  So the system is operating at too low a pressure (compressor failing) or too low a refrigerant charge (pinhole leak).
YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

xlogger

It looks clean inside, but I order a new one this morning. Not riding around anymore looking for used ones that not working correct.
Timberking 2000, Turbo slabber Mill, 584 Case, Bobcat 773, solar kiln, Nyle L-53 DH kiln

GeneWengert-WoodDoc

YellowHammer is right on target, especially with his last paragraph.

A bit more...Understand that if the dew point of the air is under 32 F, this means that the cold coils must be under 32 F in order to condense water out of the air.  So, ice will form.  Also, if the cold coils are below 32 F at any dew point, ice will form.  So, there are two considerations...turn the compressor off when the coils are too cold and let them warm up and melt the ice and let the melted water run out, or provide some heated air to the coils to keep melting the ice.  So, most inexpensive compressors will only run well at 65 F or hotter.  The refrigerant, that also provides lubrication, often begins to perform poorly over 110 F in inexpensive units, leading to early failures.

Note that if the dew point is under 32 F in a kiln with air temperatures over 65 F, then the humidity in the kiln is very low.  This low humidity should cause a load of wet (above 8% MC) lumber to dry which would increase the humidity and dew point.  If the dew point remains low, then the wood must be quite dry or the fans are not working.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

xlogger

The unit I got coming today is a 50 pint size that should only be running from 41° to 96°. It has on off timer so on cold nights I hope to be able to have it cut off in evenings or later in nights that going to be below 41°. It also have a set for RH that I can set from 35% to 96%. Would or should I set it at the lowest? Gene I got a chart now that I figure the dew point so thanks on that. Also is there a DH that would work better in kilns? Where might I find it? Thanks
Timberking 2000, Turbo slabber Mill, 584 Case, Bobcat 773, solar kiln, Nyle L-53 DH kiln

Den Socling

That's what Nyle does. DH for kilns - even little ones.

xlogger

L200 is the smallest one I see, little pricey for a solar kiln.
Timberking 2000, Turbo slabber Mill, 584 Case, Bobcat 773, solar kiln, Nyle L-53 DH kiln

WDH

I have the L53.  It is smaller than the L200.  Up to 1000 BF of slow drying species like oak and 400 BF of fast drying species like pine. 
Woodmizer LT40HDD35, John Deere 2155, Kubota M5-111, Kubota L2501, Nyle L53 Dehumidification Kiln, and a passion for all things with leafs, twigs, and bark.  hamsleyhardwood.com

Glenn1

I have the same Nyle Kiln as WDH.  It's an L53 and you are welcome to come and see it.
Vacutherm IDry, Nyle 53 Kiln, New Holland Skid Steer, Kaufman Gooseneck Trailer, Whitney 32A Planer

GeneWengert-WoodDoc

Solar drying does indeed look cheaper, but consider that the cost of the kiln is about $1500 for 1000 BF.  In a good year, you might dry 5 loads of air dried lumber.  The kiln should last five years before you begin to have major maintenance.  So, that is $1500 for 25 loads or 25 MBF.  So that is about $60 per MBF.  If you only get four loads a year, then the cost is $75 per MBF.

We are talking about equipment only here, not energy. 

A DH kiln building and equipment would probably cost about $65,000 for a 20 MBF kiln that would dry 25 loads per year and last about 10 years without major maintenance, on the average.  So, that is 5 million BF dried in 10 years for $65,000 or $13 per MBF.  We could increase this by 10% for maintenance with some manufacturer's equipment.

Let's say that fan energy and loading time per MBF are equal, so the only other main difference would be energy costs.  The DH will use about $30 to $50 per MBF dried, depending on incoming MC and electric cost.  So, a DH would be $13 + $30 to $13 + $50.  Bottom line is that a solar kiln is not much, if any, cheaper than the DH kiln.

Now, Den can come in with his vacuum kiln that has a $100,000 cost, but short drying time (lots of loads per year) make this attractive.  But, what really makes it attractive is that it can dry thick products that are extremely difficult to dry conventionally.

The point of all this is to consider the total cost over time, and not just the initial capital cost. 

I have seldom seen a non-profitable drying operation.  But, I have seen a fair number that had such poor cash flow and cash management that they could not make monthly payments to workers, electric company, and the bank so they had to be sold.  Stated another way, you can dry lumber every day, but you only make a profit when the dry lumber is sold.  You must have species that have big differences between green and KD prices, and have products that people want to buy.  A large inventory of dry lumber is not helpful.  (Attending advanced lumber drying classes is also a good idea- -expensive for travel and living costs, but well worth the cost because of the practical knowledge gained.)

I hope these thoughts help people in our industry make wiser decisions.  Perhaps a little preachy, but at my age, I either preach or reminisce.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

xlogger

Gene, I know what your are saying is correct. I see that more now that I built my solar kiln. I'm now planning on building my second kiln with my main heat source using my owb. But also I'm keeping in mind about in the future if I see I need one putting something like a Nyle in it. I guess my question on what is the best DH I should get was a home unit for my solar kiln. But I got a new one yesterday and put it in last night so I'll see what if any different it makes.
I see where others on here use there dh night and day. My new one said not to run it over 95° or near that. If I do that and I might it has a one year replacement, so we see what happens there. As far as cost goes running one I'm not putting in cheaper wood and not planning on doing so. So I hope my product covers the electric cost.
Glenn, I am going to get together with you and soon I hope, I'd like to go up to the wood store and maybe we can go together and get some ideas.
Timberking 2000, Turbo slabber Mill, 584 Case, Bobcat 773, solar kiln, Nyle L-53 DH kiln

GeneWengert-WoodDoc

Thanks.  If you have questions, let me know, as it is hard to summarize in a few words sometimes.

If you run the DH at night, its performance is enhanced by covering the collector with an insulated
blanket.

As soon as you run the DH more often than at night, you will find that covering the collector and running a DH in a totally closed and insulated box is quicker, more energy efficient than using solar.  Further, due to the price of electricity,  well insulated 2x6 walls are worth it.  In any case, with a DH, in a solar kiln, insulate the solar cover at night.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

flatrock58

I got an old dehumidifier from my parents house that was low on Freon and would freeze up some and not dehumidify any.  I put a  Bullet Piercing Valve in the low pressure line and added freon and it has been working fine for two months.  I am sure it will run low again some time but it was a cheap solution.  I need to start looking at yard sales to see if I can find any deals on used dehumidifiers.
2001 LT40 Super Kubota 42
6' extension
resaw attachment
CBN Sharpener
Cooks Dual Tooth Setter
Solar Kiln

xlogger

I got a new one from amazon two days ago and it fill up the tank the first night and cut itself off. I hook a drain on it. Should of got one weeks ago. Probably not get a used one again to waste my time.
Thanks for the info Gene. My next kiln will completely box in with some pex pipes running threw from OWB to supply some heat along with a DH. At least that's my plan.
I'll only plan on putting in wood that has air dried or in solar kiln down into the teens.
Timberking 2000, Turbo slabber Mill, 584 Case, Bobcat 773, solar kiln, Nyle L-53 DH kiln

GeneWengert-WoodDoc

Awesome indeed.

Once the kiln is warm enough to start the DH, if the kiln is insulated well, the heat from the compressor ( motor heat and heat from the hot coil) will keep the kiln warm all the time.  In fact, some kilns will overheat and have to use a fan powered vent to exhaunt the heat to keep the temperature at the maximum required level.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

WDH

With my kiln, more heat is an issue rather than not enough heat.  I am drying some 9/4 red oak and persimmon now, and the water removal is slow.  I have to be careful that the kiln does not over heat.  Running about a 30° dry bulb-wet bulb depression, wood at 15% moisture.  Hard to keep the dry bulb less than 120 degrees with out venting.  It is a ballet dance. 
Woodmizer LT40HDD35, John Deere 2155, Kubota M5-111, Kubota L2501, Nyle L53 Dehumidification Kiln, and a passion for all things with leafs, twigs, and bark.  hamsleyhardwood.com

GeneWengert-WoodDoc

For almost all species of lumber at 15% MC or lower, we can safely go to 160 F with an EMC of about 6.0%.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

WDH

At above 133°, the compressor on the Nyle L53 will trip out.  I cannot run the compressor at temps above that.  The 9/4 dries really slow.  I wish that I could get to 160°.  I can only get that high with the compressor off and the heater on to sterilize the load. 
Woodmizer LT40HDD35, John Deere 2155, Kubota M5-111, Kubota L2501, Nyle L53 Dehumidification Kiln, and a passion for all things with leafs, twigs, and bark.  hamsleyhardwood.com

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