What to do when wet bulb reading is too low to kick on compressor?

[TBrown99]

We're finally starting to use our L-53 after setbacks the past two years. Our chamber is constructed quite well to standards and at the correct overall size.

On our second test load of poplar, we're using 120 dry bulb & 90 wet bulb drying schedule for 500 bf of Group 2 poplar (mostly 2x4s and 1.5x varied widths with some live edge slabs). Half of the load dried down to 6-8% within a week, starting at 30 average moisture. The first two days we threw off 40+ lbs of water each day. But the other half is still high 15-20%. We reloaded the remaining unfinished 250 bf and are trying to complete drying.

Our measured wet bulb doesn't rise above 81-82 so the condenser doesn't kick on as we don't reach 90 (which signals I believe a dryer room vs. 80 level). We use a Govee temperature and relative humidity device and it shows the chamber at 19-20% RH. This seems low.

What should we do? Should we simply set down the wet bulb to force the compressor to start working? Will this take the chamber too low for humidity and produce drying damage?

Thank you,
Toby

[K-Guy]

No, don't lower the wet bulb, the wood has to release more moisture to bring the temperature up. If it stays there for several days, the wood has locked up and isn't releasing moisture. To treat that you must be below 25% moisture, turn your compressor off, set your dry bulb to 140° and leave for a couple days till you see the moisture moving out of the core.

[doc henderson]

is the temp (dry bulb) 120°?

[TBrown99]

Yes, we were at 120F for a couple of days with wet bulb at around 80-82. We initially had flow with WB set below 80 but I reset to 90 because that's what the schedule calls for and b/c I'm concerned about low humidity damage. Anyway. I took Stan's advice, so we'll see in a couple of days. Already at 131 degrees. The RH devise is showing a further fall in RH from 18 to 17.5. WB is at 85.6, DB 131.3.

[doc henderson]

the higher the temp goes with the same amount or water in the air, the lower the RH humidity goes.  If you dropped the temp to 80, the RH would go up and you could pump more water out of the air, but you need to move water out of the wood, so the increase in temp will "boil" or motivate the contained water to the air so it can then be pumped out. 

[blackhawk]

Are you monitoring the actual EMC of the lumber?  At 120F and 20% RH, your kiln is just below a 4% EMC condition.  That is fine if the kiln condition is at 4%, but I don't let the actual lumber get below 5% EMC.  I monitor my lumber in the kiln real time with Lignomat probes.  If your driest lumber is getting close to 5%, you need to remove it or start adding water to the kiln. 

[TBrown99]

To update, we are continuing to "boil" this lumber charge although the kiln isn't quite at 140 yet, as the image below shows. A second image below shows the L-53 bulb readings. (Dry is at 137.1)

To answer Blackhawk's question: No, I'm not monitoring EMC. I don't have probes yet this seems like a good thing to have and I'm trying to not open the kiln door as it takes a long time to build up temperature.
I did just calculate EMC of the room and it's very low 2.x.

I did remove lumber that was dried to about 6-10% and I wrote MC range for each remaining piece.

I'll probably let the heat remain high until this evening and then begin cooling and turn compressor on. However, I expect the wet bulb will quickly go below 90 and I'll be back to where I was...

Does a fall under 90 wet bulb at a given temperature (say 120 dry bulb) represents an INCREASE in humidity level? If so, why doesn't this represent a good time to extract this moisture? Why would I wait until web bulb increases (space becomes dryer) to run the compressor?   

I'd like to emphasize that the first half of this load dried very well and we were very happy with the results (a first for us!).



 



 

[blackhawk]

You need to download the humidity graph from the Drying Hardwood Lumber manual here:  https://www.fs.usda.gov/research/treesearch/5710

If your dry bulb is at 120 and your wet bulb is set to 90, as the wet bulb drops the humidity is getting lower.  The difference between the DB and WB is called your wet bulb depression.  This is on the graph that I linked.  Your kiln EMC is extremely low right now.  I would turn off the heat now.  Monitor your Govee and if your Kiln EMC condition stays below 5% you need to throw some water in there on the floor to be safe. 

What I've seen on my L53 is that if you keep the kiln at 5% EMC the lumber will keep drying even though my compressor never comes on.  The moisture is coming out of the wood.  I see this as I monitor my EMC probes in the lumber.  I assume that even though the compressor is not cutting on and removing the water, the moisture is escaping through the small leaks in the vents and door. 

[TBrown99]

Okay, I will check this drying manual. Thanks.

To update, I let 140 F. run until this morning (maxing out at 138.5 F) and then reset to 120 F. quickly venting excess heat and settling presently at d121.4 and w85.6.
Relative Humidity by Govee reading is very low at 7.5%.

I have realized that I have a big problem with fan air distorting (decreasing) the wet bulb readings. I have a 4-fan bank with a hinged baffle hanging below (800 cfm each). I also have two 800 cfm and one 500 cfm independent fans trained on about 10' of baseboard radiation (hydro from wood boiler) fin sections -- back side of the load near bulbs -- as supplementary heat source. I noticed that after cool down this morning when I turned the fan bank back on, web bulb decreased rapidly. (This was without even the influence of the other 3 fans.)

Should I try to totally isolate the dry and wet bulb lines? I was thinking of screwing a small box to my wall, mount bulbs inside and hanging light fabric over the front. What type of material or design would work well here? I need to cut the draft while allowing some air flow. Is this an essential modification?

[doc henderson]

Have you been able to check the MC of the wood?  I think you do not want the wet bulb in direct breeze from the fan but should be in a representative environment (air) of the rest of the kiln.  The dry bulb will not matter as there is no moisture to evaporate.  the wet bulb should have evaporative cooling depending on how dry the surrounding air is.  that is how it works and the dryer the air, the wider the depression when compared to the dry bulb.  I would think putting it (wet bulb) in the path of fan air would facilitate evaporation and further lower the wet bulb temp distorting the depression and giving a false drier reading.  Sounds like the gradient is high based on the schedule.  Maybe time to add some water to the kiln so the surface to core gradient is not so large, or at least let the wood catch up.  Disclaimer, I do not have a kiln, but love thinking through these issues.  I do have a science background.  good luck.

[doc henderson]

you also dumped some moisture suspended in the warm air.  so it may be even dryer in the kiln.  Look at your graph.  If you just turned down the heat without running the DH or vent, the RH would have come back up to where it was at the prev. temp or higher.  If you had an empty kiln with a certain amount of water in the air, the relative humidity will go up and down opposite the temp reliably.  It seems dry, but if you cooled the air temp, you could reach 100% RH inside the kiln with the current water in the kiln.  The air can hold more water the warmer it gets and the is what the relative humidity is.  how much water is in the air compared to the max. the air could hold at that temp.  I am just thinking outload and sorry if you already know all this.

[blackhawk]

The wet bulb needs to be somewhat out of the air flow.  Stan at Nyle suggested that I shield mine and that is what I did.  It definitely helped but I could never get it perfect.  That is why I use the Govee to help me know exactly what is happening in the kiln.  See my last post in this thread to see what I did to shield my wet bulb:  https://forestryforum.com/board/index.php?topic=121782.0

[doc henderson]

TB remember you could put this wood in a heated airconditioned shop, and it will dry fine.  It will take longer.  also, a solar kiln has nighttime temps of near ambient outside temp, with a high humidity and that relaxes the stress in the wood, but also takes longer and has/requires less control.   you want to get this wood moving, but do not want to produce stress and surface defects.  you can be more aggressive as the MC decreases.  What is the current MC of the load?  to get back to a schedule you can turn down the heat or add water back to the kiln, or let it go and see how it goes.  air movement across the surface also becomes less important/effective as the wood dries.

[TBrown99]

Just checked the charge... I had thrown in 3 pieces of boxwood elder (very soft maple sample with full red streaks), and I was impressed to see 6 readings at 6.2 with a high of 6.5. (Started at 20 and 25-27.) The poplar wasn't that amazingly low but 16 samples showed 8.1 with 10.6 as the high. So, I'm pretty surprised.

This round helped me understand that our chamber can go to 140 F while I was thinking the limit was 130 from previous tests. Just have to wait a while. Though I can't say I was entirely comfortable going to bed with those temps (which is probably irrational fear on my part) but the chamber is attached to our 30x50 shop (with a 25' loose housing extension in the back... which is filling up with some fine lumber) containing a non-trivial amt of tools & machines.

I will provide details of the outcome soon.

[TBrown99]

Indeed, I had some amazing drying with some hard maple boards standing up in the main shop area, which has a Modine hydronic heater circulating a bit of air, but also 3 DYI air cleaner fans help to move air as well. Presently, RH is 30%. Our kiln is housed in our shop side shed within a slightly larger chamber which I also aim to use for pre-drying.

From what I understand, 120 F conditions is in the very gentle range and I don't have to worry about case hardening. Though other defects must be a concern...

Adding water has come up twice now so I'll research this.

TB remember you could put this wood in a heated airconditioned shop, and it will dry fine.  It will take longer.  also, a solar kiln has nighttime temps of near ambient outside temp, with a high humidity and that relaxes the stress in the wood, but also takes longer and has/requires less control.   you want to get this wood moving, but do not want to produce stress and surface defects.  you can be more aggressive as the MC decreases.  What is the current MC of the load?  to get back to a schedule you can turn sown the heat or add water back to the kiln, or let it go and see how it goes.  air movement across the surface also becomes less important/effective as the wood dries.

[TBrown99]

Did you find most of this guide to be useful? I'm probably going to order a print copy from my local printer from the PDF. Thank you!

You need to download the humidity graph from the Drying Hardwood Lumber manual here:  https://www.fs.usda.gov/research/treesearch/5710

[doc henderson]

sounds like you are moving forward.  some will end with some conditioning.  More info will be great and we all can learn.  thanks.  Doc.

[blackhawk]

Did you find most of this guide to be useful? I'm probably going to order a print copy from my local printer from the PDF. Thank you!

Yes, I read it front to back.  It is really the go to document for drying.  The schedules in the Nyle manual are fine but they are conservative.

[TBrown99]

We checked 50% of the charge with multiple probe readings and found some sub-6% with highest reading at 9.0 with the average around 7.0 to 8.0. There was some "knobby warping" by knots, sorry I don't know the technical term. Our goal is to avoid having to apply high heat (140) and to resolve the problem of WB being to low. More troubleshooting will be required. I think it's time we make a short video of our install and solicit critical feedback.

[jimF]

The wetbulb needs to be in the full airflow to record the actual wetbulb temperature.
By venting to get rid of the "excess" heat you are ridding the kiln of any moisture that came out of the wood further stalling the wetbulb reading. 120 and 140 is considered low temperatures and would not cause any damage to the wood. Although casehardening can and does occur even at these temperatures.
By increasing the temperature to 140, you are providing more energy that is needed to cause evaporation. With out heat you don't provide the potential for the water to evaporate.

[doc henderson]

to get the humidity up, might have been better to let the temp come down without venting, so the water remains in the kiln.  Kiln drying is controlling the temp and RH (wet bulb depression), so to prevent the potential degrade you follow a schedule.  Maybe other could let us know what they do to condition wood at the end.  I think some will add water.  This would reverse the drying direction adding moisture back to the wood from the outside in.  Trying to balance the core and shell.  Is the range of MC between differing species or thicknesses of wood?

[jimF]

The last step in the drying process, conditioning, is not to balance the MC between the core and shell but to increase the compression stresses during moisture gain so that the stresses are reduced ridding the lumber of casehardening.  You see, when wood is under high enough stresses and the moisture content is changed the stresses are reduced.
As a added benefit, the moisture gradient is also reduced.
There is usually a step before conditioning, called equaliztion, that is to reduce the majority of the moisture gradient within and between the boards.

[K-Guy]

You need enough airflow to get an accurate reading but if you have too much, it prematurely dries the wick out.

[Larry]

My wick was drying out because of too much airflow.  I used a piece of foam insulation and moved it around a bit to find the perfect place.  It's off to the side a few inches from the wet bulb so it doesn't block the airflow, just slows it down a little.

[jimF]

The reason the wick dries out quickly is not because the airflow is too high.  It is because the water supply is not sufficient. By controlling the airflow you may be recording the readings you want but not the accurate reading. The accurate wetbulb readings is a measure of the potential evaporation rate which needs full airflow to measure. In commercial settings the wetbulb is placed in the incoming air plenum; meaning fulll airfflow and full heat before it enters the stack = most evaporation at the given settings.

[Larry]

How do you get a sufficient water supply?

[jimF]

Do you have a water line going into the well for the wick? Does it have a float valve to allow flow as the level drops?

[doc henderson]

Jim, airflow can facilitate evaporation so too much air seems would give a false reading as well.  you would need a representative sample of air moving past the wick.  water moves in a gradient, and more evaporation drops the temp and dryer air causes more evaporation.  When you add a time such as cfm then the amount of water that can evaporate into the local environment never comes to any equilibrium, and more water is evaporated as the flow increases.

[K-Guy]

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Re: What to do when wet bulb reading is too low to kick on compressor?
« Reply #25 on: Yesterday at 09:45:30 PM »
QuoteAdd Multi Quote
How do you get a sufficient water supply?

How do you get a sufficient water supply?

Larger kilns have tray and use a sock or sleeve type wick. The tray has a float valve connected to a water line to keep them full.

[jimF]

Wetbulb temperature is a measure energy transfer by evaporation, or a measure of the potential to evaporate water - a partial potential to evaporate water. To get an accurate measure full airflow is needed at the temperature of the entering air.

A side note: the condition of the wick needs to be clean and not coated with salt or lime build up from hardwater being used, nor a bacterial film build up. These contaminations can alter the the temperature and make it appear to dry out.

[doc henderson]

yes, wet bulb depression and it seems it could be enhanced (increased depression) with increased air flow.  There is an energy required for a phase change (evaporation) from liquid to vapor, and that drops the temp of the wet bulb in the wick.  It is supposed to be from gradient from saturated to dryer air, not wind speed.  The dryer the air, the more evaporation and drop in temp from dry bulb to wet bulb.  Is there a limit to the airflow that results in an accurate reading?

[jimF]

As you said "There is an energy required for a phase change (evaporation) from liquid to vapor". Energy is supplied by the air and there by transferred to the wood/water system. If the airflow is insufficient there is insufficient amount of energy to evaporate the full potential of water, thereby not accurately indicating the wetbulb temperature. If I remember correctly, about 200 ft/min is the minimum limit of airflow to provide equilibrium heat transfer to the wood/water and evaporation of the water to the air.

[TBrown99]

Whoa! A SECOND page here. I still haven't fully processed the first one though I'm working on it. (I have a full copy of "Drying Hardwood Lumber" by USDA in my hands as I write!).

I've noticed that the three good thermometers which I have in the kiln all -- and on average -- suggest that the L-53 dry bulb figure is 1.5-2 degrees warmer.   
 
I made a short video showing our L-53 setup with narration ( you might have to activate the sound ),

Shared album - Tobias C. Brown - Google Photos

The video doesn't show the drain & bucket just by the L-53 control box.

The main fix list includes redoing the front door, installing floor over uninsulated concrete, and putting the one radiant section down into the main area. I may also have to make a quick access door in order to get the main door right.

Thanks!

[doc henderson]

Nice job on the kiln!

[GBar]

TBrown99,
You may consider your Govee to be giving you false RH readings.  As Blackhawk said, the cited numbers would be below 4% EMC (e.g. 18RH and 120 Degrees = 3.6 EMC). it is not likely.  As others have alluded to: How does it compare to your other source - the Nyle DB/WB readings?

There are some handy calculators online to provide exact calculations and better than interpolating charts.
For RH Calc from DB/WB: Dew Point And Relative Humidity Calculator
For EMC from Temp/Humidity (my favorite): Wood Equilibrium Moisture Content Table And Calculator
CSG cites formula derivation from US Forest Products Laboratory.

I have three temp sources in my kiln to compare and all are within one degree: Penn/Johnson Controller, Fireboard BBQ thermometer with 6 100K Thermistor probes, and AC Infinity Swiss made Temp/RH sensor that is super accurate.  For moisture: the AC Infinity sensor and the Lignomat EMC sensor.  They match in EMC reasonably.

You may consider another source of RH to compare with Nyle DB/WB.  The AC Infinity App records temp and RH, can view readouts, graphs, change settings on phone, download CSV file to PC, and more. WiFi allow monitor of kiln RH and Temp anywhere there is internet to your phone.  I can monitor kiln and change settings anywhere in the country while away from kiln.  I would attach a screen shot, but the Gallery is off line.

[K-Guy]

Nice Job
I have a couple of suggestions for you. Call me at 800-777-6953 ext. 6 to discuss them.
Stan

[TBrown99]

Hi Stan,

I will be in touch. I'm still catching up with things.

Toby

[TBrown99]

Stan gave me some excellent guidance today which I'll act on:

• Move fan truss out to 3 feet (It's at 2'-4"). This will improve air flow.
  
  • Stop using the individual accessory fans. The 4 fan bank is quite enough!
• Move fin tubes at least 6" off back wall
  
  • This will allow them to heat much better as they will have much more airflow.
• Move exhaust fan
  
  • Bad air flow with current install.
    
    • Install fan inside room and go directly out wall.
    • Use 14" vent duct
  • Stop exhausting moist or smelly air into shop.
  • Also recommended making intake vent straight too.
    
    • However, it seems the exhaust has been working very well... even with the intake blocked, so we may not change this. It takes about 2 minutes to reduce temp. I blocked it to avoid cold air exposure.
• Trim back the plywood stack top pieces
  
  • Extending these to the back wall restricts air flow
• Spray paint fin tube cooper with Rust-Oleum
  
  • Something that is not merely paint

Other longer term changes:
Thermostat for radiant tied into control box.

• In some cases it's better to avoid activating exhaust vent, other times desirable. So, control radiant fins with thermostat...

Add more insulation but not too much. If it's heating up okay, don't put more. That inner room could get very hot in the summer and be harder to cool.

[TBrown99]

I completed modifications to our chamber including:
--Move fan bank out 8-9" (stronger air flow)
--Move radiant fins out 4-5" off wall vs against wall (so air passes through better)
--Improve sealing around door and other spots
--Added a 2nd 7' radiant section so 2.5 total now.
--Because we use the fan bank model, we cut back our top plywood covers (no longer going to the back wall) to allow better air flow. This was a KEY change and greatly improved flow through the stack.
I didn't redirect the exhaust line yet as the current "curvy" line seems void excess heat rapidly.

I will still need to add "not too much" insulation on the exterior wall (to reduce some heat loss but not set conditions for overheating in summer months). I have 13 R now (but with a heated surrounding chamber, not exposed to outdoors directly) and will add 6-10 R layer. I'm considering putting a poly fabric barrier too. Also more sealing is needed around door as moisture is still showing from current load.

I installed our third "test" charge yesterday consisting of about 600 bf of the following:

All 9/4.

85% basswood, 20.3% with 19 readings, 30% high. Many readings below 20%.
10% white pine, 23% with 12 readings, 33.9%.
5% poplar, 24.3% with 6 readings, 27.4%.

Set to 120/90 schedule.

The kiln room heated up much faster with the additional radiant though I continue to use 2 - 800CFM accessory individual fans trained directly on the radiant vs. 4 before...).

Once temperature was reached, water started flowing as expected. However, over night flow stopped. I expect that wet bulb decreased below 90. Temp sensors indicate that exhaust came on 3-4 times.

I'm starting to expect that the Nyle dry bulb thermometer reports 3-4 degrees below actual temperature. I have TWO quality heat sensors just by the Nyle thermometer and this is what they show. So, I tried increasing dry bulb setting to 122-124 and flow resumed (wet bulb rising above 90 and holding).  I'll call Stan on this if I don't hear back here.

Steady as she goes!

[TBrown99]

I just did a short test as flow stopped. This occurred while WB was holding above 90 (compressor on) temp at 120.5 by Nyle thermometer. Aux fans trained on radiant were off. Nyle temp set to 122 (so l53 holding at the low range before kicking heat back on). I tweaked temp up to 123 and turned on the two aux fans. Within 30 minutes, temps rise 2-3 degrees and good flow from drain line resumes. Not much change in WB.

At this hotter level, Govee sensor shows 119.7 while 2nd sensor SensorPush shows 120.5.

How often is the Nyle thermometer off? Anyway. It appears that my system only works when DB is adjusted up a few degrees. This may explain original issue with WB not exceeding 90...   

[doc henderson]

good info.  did you mean dry bulb tweaked temp tweaked to 123 and by flow I assume you mean water coming out from the DH unit?  thanks.

"Anyway. It appears that my system only works when WB is adjusted up a few degrees"

"I tweaked temp up to 123 and turned on the two aux fans. Within 30 minutes, temps rise 2-3 degrees and good flow resumes. Not much change in WB"

[TBrown99]

Thanks Doc. You're right on with those two errors. FIXED in the original!

WB-->DB
Flow resumed... from the drain line.

I'm going to need to call Stan as I'm struggling to make this work. (I have DB temp 120 and WB above 90 but flow from L53 is inconsistent. Drips sometimes, doesn't other times. I can tweak up the temp and it picks up but the compressor isn't supposed to operate above 120.) I'm thinking I shouldn't need to micro manage like this.

  

[doc henderson]

good idea to call stan.  not sure why it would produce more at a higher temp as that lower the relative humidity.  have you tried dropping the wet bulb setting telling the compressor to come on at an even lower RH, or wider gap in DB/WB, or in other words a larger WB depression.

although raising the DB, or lowering the WB creates a larger overall depression that correlates with a goal of a lesser RH.

I may be getting myself confused.    can you set the WB lower and see if you make more water.  are you saying that no water was flowing, despite the compressor running?

[TBrown99]

Stan said before that I should not simply set down the WB level and, indeed, I tried this and it would reliably begin the bucket filling drops of water   I expect it's problematic because you want to maintain a base level of humidity to avoid quality degrade issues (splitting? not sure exactly).

Instead, he recommended turning off compressor and leaving at 140 for a couple of days, forcing out humidity. Then back to 120 and hopefully higher WB.

My best idea now is that the Nyle thermometer is reading 2-4 degrees too low. I've read that Govee is accurate .5 deg. Not sure. But my other sensor also reads lower than Nyle. I have a third coming to test more.

I turned off my aux. fans used to generate heat and cut the water flow from my boiler (base board radiants) to 50% figuring I'd see how the system responds. It's been an hour so far and while the Nyle heater was on, it has stopped early 119.3... with WB close to target 89.6. I was hoping the rise to 122 would bring the compressor back on. But again, the heater cut on me. Not sure why. Back out to the barn! I'll open the radiant boiler water flow to full to maybe get a bit more heat out. (I'm not going to turn the aux fans on except for sterilization and initial heat up...)

I don't recall the dehumidification indicator coming on in the past but it is coming on. Maybe it also has, just seems new.

My sensors are showing falling humidity level so despite the lack of flow into my bucket, I expect it's not all wasted time. The humidity is getting out somewhere.

I'm starting to ramble. Getting tired! 

 

[TBrown99]

The big point here is that if I could turn up the heat 2 degrees, this would likely put me in 90 compressor area (sitting at 119.6/89.9 now... just sitting there...) But the compressor isn't supposed to be on above 120. My theory is that the thermometer isn't accurate, as suggested by two good quality sensors (Govee and Sensor Plus).

I will soon have a third sensor as I purchased a Inkbird WiFi ITC-308 to control my auxiliary heat fans (which blow directly on the radiants)... Stan had mentioned that I should add thermostats in my boiler water lines but this may be an easy alternative... thermostat tied to the fans automating switching on / off according to set points.

(Instead of just sitting there, I'm temped to set temp to 121 and WB to 89.)

[doc henderson]

Ok so the compressor is doing its job.  that was the only reason to suggest lowering WB was to make sure the compressor was not only on but doing its job.

I agree you do not want to create a schedule that dries wood too fast and degrades it.  you can turn off the compressor and turn up the heat to boil off water and when you reduce the temp the RH will go up and a higher WB setting will now turn on the compressor and put out water.

these are relativily soft woods, and wet.  so water should pour out. 

[doc henderson]

I think as long as you follow the MC loss each day and not overdo it you should be fine.  this is how we all learn.  thanks for letting me follow along!

I do not know when the compressor shuts itself off and if it relies on the unit temp to do that.  You could also do as stan suggested for a few days then drop the temp and sort of move water in a pumping fashion.  I do not know if any of these woods tend to stall, like walnut.  

[TBrown99]

Not wanting to see an empty bucket tomorrow morning (15 lbs of water first 24 hrs), I set WB down to 88.

Again, my only thought is that the dry bulb thermometer isn't taking correct readings. If it were adjusted just two degrees lower and matched the lower readings of my two other sensors (placed just by the Nyle one) the system would be working as expected. I need to know the odds of a mis-calibrated Nyle thermo.

I'm surprised that the Nyle heater struggles to maintain 120 even though I have two 7' radiant sections in the room. But those aren't so good at generating heat without air flow, so maybe it makes sense. The problem is that if I turn the aux fans on them, it gets too hot and the exhaust fan cycles. (I'm not totally clear why getting rid of the moisture that way isn't desirable.)

[doc henderson]

I do not think it is bad, but it may be why the compressor does not come on and or not much water comes out via the DH.  the thermostat that you plan to attach to control the heat may help not overheat.  It could be bad if you are way off schedule for a hard to dry wood like oak if it goes too fast.  I think it would be interesting to try what Stan suggested.  turn off the compressor, and heat to 140 like a sterilization cycle then turn off the heat and turn the compressor back on.  I think YH does something similar with walnut that has stalled.  can the directed fans be wired to come on only when heat is called for (by the radiant heat)?

[doc henderson]

a solar kiln gets rid of moisture that way and defeats the purpose of the DH to some degree, but it is fast.  if you are paying for the heat, then it is wasteful to overheat.  Do you have a current MC for the wood?  Stan is the man to ask about the temp probe calibration and or replacement.

[TBrown99]

Okay, I spoke with Stan. 

The big message is that below 25% moisture, you can't damage the lumber by more aggressive drying. So, instead of the "raise temp to 140" approach, it will be good to adjust WB lower and heat higher (but be mindful that the compressor may cut near 130 which would require manual switch reset). 

So, here's goes... 

Will catch up further later on...

[doc henderson]

Nice.  keep us in the loop!  thanks.

[TBrown99]

I pinned moisture levels two days ago after seeing no drip flow after tweaking the DB higher to 125 & WB down to 80 per Stan's advice.

The single 1" board was dry (below 8) but the 9/4 were still often in high teens. (So, after 4 days...) I was expecting to see lower numbers. (Everything else is 9/4)

After 24 hours, no sign of moisture. Therefore, I reset to "boil it out" for half a day reaching 138 degrees for several hours. (Last time Stan advised 2 full days.). I let the temp come down expecting to see moisture once compressor came on. Nothing.

Moisture levels on my Govee sensors are getting quite low 11.4% now at 120 db.

So, I was at a loss as to what to try next. I decided to just let it go at 120/80 for several more days. Full air flow.

What's happening then is the exhaust fan is kicking on in 12-20 minute heating cycles from the L53 box controls. So, moisture is exiting. But this isn't how I was expecting this to work. And I'm not sure if that's a bad scenario.

Perhaps I should have done a 48 hr "boil it" try. But I don't sleep as well at night when the room is maxing out temperature, though it's probably in irrational concern.

I still need to work on sealing the unit and adding insulation from 13 r to 30 r.

My basic feeling is that I just need to give it a bit more time. 4 days is probably too short.

Thanks

[doc henderson]

so, you have varying thickness of wood in the kiln.  is that what accounts for the range of MC.  are they all the same species?  If you drop the DB to 80 the RH will go up, and you might condense water, but that would serve to further lower the RH in the kiln when the temp goes back up.  can you check the wood with a pin less to see what it reads.  very frustrating and interesting problem.  

[doc henderson]

so, is the moisture content still decreasing each day?  what is your target.  I am sorry if you already said.  I am remembering parts of this thread with an oak thread.

[TBrown99]

No, I only had one test piece of 1" basswood in this charge. Everything else is 9/4, mostly basswood, some pine & poplar.

I took the poplar out because it could stand more air drying. (It was serving mainly to hold plywood top.)

I removed the top.

I'll check levels maybe tonight. RH by my Govee sensor continues to fall, 10.5 now.

My target is 7-8.

[doc henderson]

If it continues to drop at a decent rate, you may be losing enough moisture to keep going.

[TBrown99]

I shut off the aux heat last night and temp fell from 120 to 115 overnight. So, L53 can't maintain heat even after 4 days of warm up. So, I need to return to insulating and sealing leaks. This will have multiple benefits.

[Hamajama]

What moisture meter are you using? I ran into a very similar issue with this a few months back with a charge of 16% air dried 9/4 Magnolia. Called Stan, tried to boil the moisture out, seemingly nothing. The Delmhorst J2000 has a temperature setting to adjust the measurements outside of normal temps.

From the manual: 

The J-2000 defaults to a temperature of 70ºF. As wood temperature increases, its electrical resistance decreases and indicated moisture content rises. Lower wood temperatures result in lower indicated moisture content. A correction is necessary if the wood temperature is outside the range of 50ºF (10ºC) to 90ºF (32ºC). Set the temperature accordingly and the meter will make the correction.

It might be completely unrelated, but when I realized this and made my adjustments, I was getting much more accurate readings and the wood had already reached 6-7%.

[TBrown99]

Thanks for sharing this experience. 

I do adjust my Delhorst temp. And I've started using the longer pins given this is 9/4.

[TBrown99]

Are you monitoring the actual EMC of the lumber?  At 120F and 20% RH, your kiln is just below a 4% EMC condition.  That is fine if the kiln condition is at 4%, but I don't let the actual lumber get below 5% EMC.  I monitor my lumber in the kiln real time with Lignomat probes.  If your driest lumber is getting close to 5%, you need to remove it or start adding water to the kiln. 

What are the options with the Lingomat probes? Which product do you use?

I already own the Delhorst 2000 so perhaps there's a similar product in that line..

[blackhawk]

What are the options with the Lingomat probes? Which product do you use?

I already own the Delhorst 2000 so perhaps there's a similar product in that line..

I use the Lignomat K2-33M system:  K2-33M  You can buy the PK probes separately and they offer many different lengths.

The K2-33M comes with a Ligno K meter, which is a pin only meter.  If you don't have a pinless meter already, they have a VersaTec model that is both pin and pinless.  You would just need to call and ask if you could substitute in the VersaTec meter in the K2-33M package.

[TBrown99]

I'm documenting the following as I use this single thread for future feedback instead of starting new threads all the time.

As I mentioned, last night I turned off the flow of hot water to my kiln which feeds about 17' of radiant baseboard fin heaters, which I train independent fans on to increase release of heat. (BTW, short of fitting my boiler lines with t-stats, Stans advice, I rec'd an InkBird device to control the fans instead ITC-308 Wifi. Excited to test this...)

Temps held last night until 1:00 am. Perhaps the residual heat in the boiler lines finally faded out... but the drop from there was pretty steady so I'm not sure whether something else occurred. Anyway. The L53 was unable to maintain 120. Temp went from 118.4 to 114.7 at 10:46, so about 10 hours.

Does this represent rapid heat loss? Does it indicate that I have lots of insulating work to do? The chamber is inside a heated chamber, 80 degrees. The outdoor temp is now 50 F. The decline seems to finally be settling out at this level. 

[TBrown99]

I ended the basswood drying session. Everything looks to be 10-12% with long probes. 9/4. simply leaving it in for a few more days would help but this level will be fine for these pieces for now. There's no major unexpected checking / cracking. Looks good.

I did the heat treatment 130 degrees (higher actually) for 30 minutes (actually a lot longer).

[doc henderson]

well insulation only acts to slow movement of heat so you may need more.  If I understand, your kiln container is inside of a conditioned space, so that makes the temp gradient less (like being summer all year long).  I do not know if that temp drop over that time is normal or not.  the initial holding of temp is from residual heat in the radiant heat, but also the wood and kiln mass as well.  If you further insulate and seal things up, it may save on heat loss and increase your ability to finely tune your kiln and follow schedules.  leaks will bleed heat and moisture and make it hard to keep temps and humidity up.  Would you say it is minimally insulated now?

[TBrown99]

yes, the drying chamber is inside a larger yet small drying chamber which has heat too so it can get up to 90+ (I'll be drying 4' stickers in here). But no condenser this outer area. 

The manual says minimum r-30. I'm at r-13 (1-2" foamboard layer. So, I can add 13 more or 3 inches to bring me to 30. I expect that a good job here and more sealing would make a big difference in holding heat & humidity.

Given that Nyle sells supplemental heaters, I expect that maintaining 120 with the L53 isn't uncommon. Anyway. I'm guessing that some math on that heat loss rate would help evaluate but that's beyond my pay scale.

[blackhawk]

I think that you need more insulation.  My kiln is outside as a stand alone structure and I can hold 120F with just Nyle's built in heater element.  It will hold this way as long as outdoor temps are 35F or above.  I have R25 in my walls, R10 foam under the concrete, and R42 in my ceiling.

For heat treating, you need to be up to at least 140F.  The core of the lumber must reach 133F and be held there for a minimum of 30 minutes. Once I reach 140F, I hold there for 24 hours just to be safe.  I have a thick block of wood that I keep in the kiln with a temperature probe embedded in it so that I can monitor the temperature of the actual lumber.

[TBrown99]

Updates: 

I received the Lingo-Versa system with 3 pins and 1 EMC line. Very excited to get this setup / in use. 
My next charge will be 9/4 white pine.

My top priority now is to insulate / seal more. The key here will be to make my inserts between studs easy to remove for Summer operation (to avoid overheating issues). I'll use some poly sheet between fitted layers so I can easily pull out.

I've setup the InkBird ITC 308 to control auxiliary heat (basically a switch control for fans trained on radiant fins to accelerate heating). Very easy to deploy and use with a nice app interface to control remotely with. (I'll still need to control fluid flow via the hand valves. Perhaps I'll eventually get some controls there as well.) FYI, the InkBird ($35) temp probe tracks closely to the Nyle probe so I'm now suspecting the Govee (& Sensor Plus) sensors as tracking too low. I'm searching for a way to get a solid reading on the temperature... and then calibrate sensors from there.

Thanks    

[K-Guy]

@blackhawk 
You said:
The core of the lumber must reach 133F and be held there for a minimum of 30 minutes.

The USDA requirement is 133°F for 45 minutes at the core of each board.

[blackhawk]

@blackhawk
You said:
The core of the lumber must reach 133F and be held there for a minimum of 30 minutes.

The USDA requirement is 133°F for 45 minutes at the core of each board.

Stan - I was going by these two documents from the USDA.  Both of them call out 133F for 30 minutes at the core.  

https://www.fpl.fs.usda.gov/documnts/fplrp/fpl_rp626.pdf
https://www.fpl.fs.usda.gov/documnts/fplgtr/fplgtr282/chapter_20_fpl_gtr282.pdf

[K-Guy]

@blackhawk 
I stand corrected but would still the 45 minute time frame as a bit of overkill. 

Also, whenever you see them talking about ISPM-15, they are talking about international regulations for packaging(pallets, etc.) used in overseas shipping.

[TBrown99]

Okay, this kiln room is suddenly getting more real, as my neighbor manufactures these lamp posts, 50 at a time, via his bending process,

https://www.roomandboard.com/catalog/lighting/floor-lamps/streeter-wood-floor-lamp/

He normally let's them air dry for 2 weeks (1x2 walnut, oak), from 20% to dry, and has asked if I can dry these for him, he believes in 1 day.

I deployed my Ligno-Versa 3-probe, 1-emc but the switch box wasn't made properly so they are sending a replacement. (The dial was set to 9-12, not 1-4 and it turned roughly, not clicking into positions.) Regardless, the manual doesn't seem to explain the actual operation. I have more information from Grete here but still I need help understanding... I've appealed to her for further assistance, waiting to hear back, but I'll now contact Blackhawk above, as he has a similar system...

I'm dragging it on insulating. 

My intention is to mill some white pine 5/4 and do a 4th test load with probes. 

I've realized that I still should move my exhaust line as Stan suggested... While the fan works fine, reduces temp quickly when necessary, I'm guessing that with heat rising, it provides an escape for heat even though the fins work.  

 

[beenthere]

Toby
What country are you from? Would help if you would click on your profile and update some information. Helps to understand your posts. 
Thanks

[TBrown99]

Done!