Hello,
I am running a L200M in a 20' shipping container structure. Most of my loads are air dried 8/4 slabs that read 25-35% core MC according to the 4 moisture probes.
I usually start these runs with a DB-WB of 110-95 to get the wood up to temp, and then after a few days go to 120-90 before sterilizing at the end. The compressor basically does not kick on ever during these runs. I do not have a steam system or anything, and my WET BULB (corrected!!) usually hangs around the mid to upper 80s initially then quickly falls to 72-75 for the majority of the run. I've looked at the EMC charts in the Nyle manual and 120-75 is too dry and I'm worried I'm overdrying the exterior of the wood. I have not dumped water in the kiln or anything like that as I have a colleague with a nyle L200 who advised me against it.
My question is... is this normal for air dried loads to not really need the compressor to remove humidity, and is it normal for the WB to go that low without any sort of humidification system?? I understand I'm not near the max BF capacity for the L200 with my current set up but i figured there would still be a need to dehumidify the chamber.
Compressor will not come on until the DB is at 80° or more. Anytime your DB is less than 80°, you unit is not running.
The requirements for the compressor to run on a L200:
1) Dry bulb over 80°F
2) Wet bulb actual temperature must 2°F over the wet bulb setpoint.
3) When the wet bulb actual equals the wet bulb setpoint the compressor will shutdown.
When drying slabs the slabs first have to heat up and the moisture has to move from the core to the surface, when this happens the wet bulb temperature will rise.
The dry bulb is well over 80 for the 6-8 weeks that I am running the kiln. My chamber is pretty well insulated so it only takes half a day or so to warm up the chamber air and contents.
The wet bulb temperature stays well below the recommended set point for the entirety of the kiln run. I have had loads where the compressor never turns on. I wanted to understand if this is normal for kiln loads of air dried wood under 30% MC at the core.
If this is not normal i want to start trouble shooting my unit, whether my chamber is too leaky or my probe sensors are not reading accurately.
You are not removing any moisture from the chamber when the compressor is not running.
This year I have had a lot of calls from people drying slabs and getting the moisture out. I would start by getting a pin type moisture meter and seeing what the moisture in the wood is doing. If it is drying without the compressor coming on then you may want to look for leaks, also you should be running the electric heat a lot more.
Something is wrong, certainly in a general sense.
With any load of wood, more so in a short, under capacity, load, once the compressor kicks on, assuming a well insulated kiln even in cold weather, the heat from the compressor will walk the temps up as the wood is being dried and will require venting.
The strips should be used to maintain heat any time the compressor is not running. Don't let the dB temps drop. The strips should only very rarely need to kick on to maintain temps. the kiln should hold for 24 hours or so, at least long enough for the Wb to come up to setpoint.
The compressor will kick off once the WB set point is reached, so if the WB continues to drop while the DB stays high or maintains, then you are loosing too much moist air either from the vents keeping the temps down or a leaking chamber. In a closed system, with no moisture removal, no compressor, no venting, no leaking, the Wb will virtually equal the Db in a day or so if the wood moisture content is about 20%, and even in the high teens..
30% moisture is actually pretty wet, so lots of moisture will be coming out of the drain line, about 5 gallons per day per 1,000 bdft per inch of thickness, and the WB should be chasing the DB closely unless moisture is being removed either by the compressor which isn't running or by the vents if the system is reaching DB set point, which it's not, or the chamber is leaking.
When you say your Db is 75, do you actually mean the Wb is 75?
So you are actually at 120 db and 75 Wb?
If yes, having a 45 degree depression is not good and way too dry unless the wood has stalled or you are in the latest end stages of finishing a load, say 9% or so. However the depression should be between 10 and 20 degrees as a general rule of thumb.
I'd need more info. What kind of wood is it? How many bdft in the load? How many baffle fans (hp) are running? What kind of vents auto or manual, and what is your outside temperature?
Your compressor may have tripped. Has your DB temp exceeded 132° at anytime with the compressor turned on?
I caught a mistake in my original post that i think confused those who replied. I did indeed mean the wet bulb hangs around 80 then settles around 75 or so. I will go back and edit the original post to correct that error!
I am able to maintain the kiln dry bulb at 110-120 (depending on set point) with the electric heating strips.
And now to reply to YH:
I am drying 8/4 walnut mainly that reads 25-30% on the 200M read out, and it is confirmed with pin style Lignomat versatec.
With slabs i am able to get about 2000-2500 bdft in a load easily, sometimes I am drying closer to 3000 if I am able to tetris them in and pack it a little closer to the walls than i probably should.
I have 4 fans bought from Nyle's store. The vents are automatic as that is included in the L200M currently. The louvres for the vent intake and exhaust are quite "leaky".
I have been drying since July so exterior temps have varied between 85-90 F down to 20 deg (Michigan weather!). The kiln insulation seems fit for the job since I was able to easily reach 150 for sterilization at the low end of the exterior temp spectrum. I have pressed the reset button for the compressor but honestly the compressor doesn't even try to turn on due to the low WB reading.
So I take it I should check the chamber for gross leaks and go from there.
Most walnut stalls at about 15%, so at 30% water should be coming out readily at 120°F.
Yes, the Nyle vents leak quite a bit, I put duct tape over the inlet side of mine, especially in cold weather.
The L2000 M probes are reasonably accurate, more so as the moistures gets lower.
The other issues is that you may not be getting enough airflow through the stacks.
Have you cycled a normal load of wood through it, such as poplar or cherry? Walnut can be cranky.
The compressor won't cycle until it hits your WB setpoint. With 8/4 walnut, under 20%, the kiln should be set at 120/98.
4/4 walnut can tolerate 8% moisture loss per day, 8/4 can tolerate 4% per day. So your wood isn't in danger, no matter what the conditions, as long as you are not removing moisture that fast.
You should be seeing a steady 1% to 3% per day, however.
The most important thing to do is put a 5 gallon bucket under the condensate line, outside the kiln. That lets you see how much the compressor is remover, vs moisture loss though other means.
I would check for leaks, but you may have stalled walnut.
Put another species in, preferably 4/4 red oak, poplar, etc to get a feel for how it's supposed to work.
When I commission a new kiln, or make changes, I like to pour 5 to 10 gallons of water in the floor, with the kiln empty. Set the controller for 120/75 for continuous operation. A 5 gallon bucket under the condensate line will help determine how much water is coming out, and if I put 10 gallons in, I should get 10 gallons, out. But I won't. The rest is being vented so now I will have a ratio of gallons lost through the vents and leaks vs removed by the compressor.
The easiest way to see if you have leaks is to go to your nearest big rig repair shop. They should have big smoke bombs just for the purpose of checking to see if their cargo trailers are leak free. Set one of these inside the kiln and see where the smoke comes out,
So i started with low hanging fruit... I taped up the intake vent to block any lost air flow through that. I inspected the rest of my unit and cant see where a ton of air would be escaping. It's a standard (non-reefer) container and it's been spray foamed with 3" layer on all the walls. Most of the floor is sprayed as well minus strips where my track system lay (i wanted to save every bit of height for my lumber stack).
When i shut the container door I can hear the louvres on the exhaust blow open, and this always led me to think my chamber was decently tight. However I am still getting low WB temps even with the intake vent blocked.
After taping up the vent last night, i loaded the kiln with a half load of 8/4 walnut thats at 55-60% MC (WET!!) and set for DB-WB of 90-88, and the DB-WB this afternoon was 90-82 and steady there! Electric heater was clicking on periodically to keep the kiln warm. I forced the compressor on by setting a low WB and i went inside and felt the evap coils... they were cold and already saw liquid condensing and dripping off them into the drain trough. Seems like the unit is in fine shape as it's only had 3 loads run through it.
Other than leakage maybe through the exh vent, floor or door... i can only think my wet bulb probe is not reading correctly or somehow is in a local cold spot in the kiln. I set it up according to the manual's directions (4' off the ground, 4' from the kiln unit).
Sounds like the kiln machine is operating correctly. There is a 6 minute delay from command on to actually powering the compressor.
Which side are the vents located? The exhaust vent should be on the kiln machine side (low pressure) and the intake vent should be on the baffle fan exit side (high pressure). The louvers are passive, and will open slightly when mounted to the wrong side. Mounted correctly, they will be forced closed until the auto vent blower turns on. The Nyle instructions are backward. Mounted incorrectly, the passive louvers will always be open slightly and leaking lots of air.
Tape up both vents, no compressor, raise the temp to 100F, see what happens after a day or so. Then there should be no air or moisture leaving the kiln at all. Basically, a closed box. The WB and DB should match almost match when (if) the air becomes saturated.
Did you foam and seal where your wires and plumbing come into the kiln chamber?
To test you probes, remove the wet sock off the WB probe and it should exactly match the DB probe reading. They are exactly the same probes, and are interchangeable.
Then place the wet sock over the DB probe and it will become the WB. How does it compare?
Don't place the WB probe near a fan, and especially not near the output of the kiln machine. Its needs to be far away in a representative airflow. If its anywhere near the kiln machine itself, it will be reading the dry air coming out and giving a very false reading.
I'm curious about your foam, is it closed cell?
A small leak in a kiln is really a big leak because one side of the fan baffle is under vacuum, the other side is pressurized. So a small hole is really a big funnel.
Do you have any pictures?
I did notice that when I adjusted the WB temp low that it took a few minutes to hear the clunk of the relay for the compressor.
I have the vents installed correctly, intake side is on the fan exit side so the louvres are forced closed by air. I saw the incorrect directions in the Nyle manual and called Stan to discuss. He got me headed in the right direction.
I foamed and sealed the power cable penetration into the unit, but the sensor cable hole is not sealed well (just has some paper towel stuffed in there to block air flow). I will spray foam this and check both to make sure i'm not getting moist air coming out of either one.
I know the WB will reach DB temp when the sock dries out as this happened during one of my loads. Ironically that's the only time the compressor has kicked on during a load haha! I caught it quickly so it didn't damage the wood.
Right now my WB and DB are mounted about 4' high and 6" off the kiln wall on the machine side of the chamber. Ive seen on this forum Gene W saying airflow is good for the WB (600 fpm?), and i've also seen pictures where people shield it... My guess is that you want to measure the humidity of the air just as it exits the stacks and has picked up moisture, but I could be wrong in that. I also purchased a 4 pack of temp and humidistat probes and placed them in the kiln last night. The RH readings matched what the DB-WB probes were reporting, and I saw the air at the top of the kiln going through the fan was at or near the DB temp.
The foam is closed cell spray foam, professionally sprayed. Last night I inspected the chamber at around 95 deg F DB interior and 38 F exterior. I saw condensation dripping near the top edge of the door seal and then some more in the back corner. I'm guessing there is local cold zones where the moisture is condensing. There are strips of the floor near the rails that are not insulated, and i felt these areas with my hand and they didn't feel overly cold or moist. One thing I did notice is that I need to baffle the area between my 3x3 bunks on my cart. I'm getting a lot of air flow through that area. I don't have a air speed meter but I do feel decent air flow coming through the wood. I baffle the ends of the kiln and any gaps in the stack with rigid foam and HF moving blankets.
I need to empty the kiln in the next few days and try the water method to see how much moisture my kiln is trapping and allowing the compressor to remove. Once I empty it I will get some pictures.
Thanks YH!!!
Good news! ... and then another curious issue.
With the wire penetrations spray foamed from both sides and both intake and exhaust fans taped up and sealed, the WB increased as I suspect it should.
I set the kiln at 95-90 overnight. I had compressor off and vent off as the intake-exhaust ducts were blocked.
When i checked it this morning it was at 98-92, and I have never seen a depression that low, so it appears the air leaks were my problem. Looks like the fan motor heat rejection alone can heat the kiln in the 90s with the exterior temperature being unseasonably warm in MI, and the wood was releasing moisture into the kiln. My electric heater used to have to click on very often to keep the chamber warm, so this is good news for the power bill!
I encountered another concern though, when I turned on the compressor to dehumidify the chamber my kiln entered what I would call a "runaway state". With the compressor on, the Dry Bulb was climbing FAST and the WB was slowly climbing in connection to that. I was pulling water outta the drain but the increasing DB temp did not allow the WB to fall below the set point so the comp kept running and adding more and more heat to the kiln. The vent fan was not on since they ducts are taped so I had to crack the door and let the air escape that way and let the kiln cool down. The kiln was going increasing in DB by about 1 degree per minute while i was standing there observing the readout!!
I cut the tape off the vent ducts and turned the fan on, but the vent fan still did not remove enough air to lower the DB-WB due to the compressor heat. I was really surprised how much that compressor heated the chamber. I would suspect if i let this condition continue that the compressor would heat the chamber until it hit the safety shut off point! Has anyone else had this issue with the vent not being able to replace enough air to lower the DB when the comp is on?
I've had that happen, but the kiln safety is actually at about 134F (based on pressure) and its hard to get that high with both vents fully open and flowing.
Make sure that the intake and exhaust louvers are actually opening. They have a tendency to bind, and not open enough, even though the exhaust fan is functioning. Another trick is to crimp some fishing weights to the vertical bar that connects the louvers and when done correctly, they will open much more readily.
Make sure your exhaust vent fan has the correct voltage it's rated at. The particular fan used can come as either 110V or 220V and make sure its running the correct voltage.
The baffle fans put out a lot of heat, that's why asked earlier about how many and what hp your fans are. They will generate lots of heat, and I turn some of mine on and off both for circulation as wells heat.
YH,
Seems that the minute i take the tape off the vents the WB drops to -10 depression and holds there without any need for compressor. Putting my hand near the intake i can feel hot, humid air pouring out.
I'll need to figure out how to allow the vents to remain unblocked for function while not losing so much air.
Thanks for all your feedback!