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Author Topic: RH issues?  (Read 1902 times)

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Offline SoftWood

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RH issues?
« on: October 05, 2018, 02:15:12 AM »
I知 hoping for some help or insight on a few issues I知 having. First time trying to dry my own. 
It痴 a freshly setup dehumidifier kiln with an ld3000 & twin 16 axial fans. The equipment I bought used, I know the Ebac doesn稚 get much love on here but it has been a working unit for the past 8 years. 
Room dimensions are 14遅11遅7 & I致e just stickered up 500 bf into a stack in the center of the room with the fans blowing directly on the end of the stack. It痴 mostly 1 western red cedar with some 2 on the bottom of the stack. MC was between 25 & 35, bit of a mixed bag. 
 Today is day 3 of running, my main question is about RH in the kiln. 
That first day/night the RH inside was up around %91-93 & there was water puddling on the floor, I got a little worried & with no room vent, I left the door open for day 2 to get rid of all that humidity. I live on the west coast so outside RH is around %60 right now but it did work. Kiln temp was set for 68f that first day & 5 degrees hotter each day now. 

2nd day I increased the dehumidifier run time to 90 which is 54 minutes out of an hour & left the door open a foot or so & that helped keep the RH in the kiln around 60, when I close the door now it rises into high 70痴.

Sorry if this is drawn out.  I guess my main questions are: with no room vent, should I be leaving the door open for the first few days to help get rid of that initial moisture dump? Or is it normal & should I just let the dehumidifier take it out on its own, however long that takes?

I知 a little nervous about going either way with it, I don稚 want to leave it too wet in the kiln for too long but I also don稚 want to bring the RH down too far right away. & as I知 increasing the heat I知 also concerned about being hot & humid inside there. 

I致e read that I知 going to need the RH to be down to %35 at the end of the cycle to have the MC around %8. But something I can稚 find much info on is any kind of schedule related to RH. 

Offline Don P

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Re: RH issues?
« Reply #1 on: October 05, 2018, 06:20:14 AM »
Welcome Softwood. Umm don't be bashing Ebac, I've got one ;D
It sounds like your unit is draining on da floor. You need to check the drain tube, make sure it is not plugged or kinked and drain it outside the kiln. The kiln warmth is helping to release the moisture from the wood. As the moist air passes over the cool coils it condenses on them and then drips to the pan at the base of the unit. You then need to drain that liquid water out of the kiln chamber through a tube.

Since I'm not telling on myself I'll tell a story. My little Ebac is over at a friends shop. It wasn't drying and when he opened up the floor was wet and the rh was very high. The tube was pinched, the drain pan was overflowing and the moist air was just going round and round in there. It sounds like you might have the same thing going on.

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Re: RH issues?
« Reply #2 on: October 05, 2018, 06:52:37 AM »
Dont worry guys, Ive had the same with a Nyle.

Actually still got thr same issue with the one Nyle... theres a constant drip of condensation from the pipe between compressor and condenser. I could probably rig a drain but no biggie given the species I dry.
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Re: RH issues?
« Reply #3 on: October 05, 2018, 07:46:39 AM »
If there is standing water then for some reason the DH unit is being overloaded or otherwise unable to get rid of the moisture that it has condensed.  

Some troubleshooting is in order. 

Either the refrigeration unit is operating properly, condensing the water vapor as a liquid into its catch basin, but is physically unable to get it outside.  If so, you will see standing water in the catch basin, overflowing.  As people have said, open it up and look for blocked drain lines, which are very common, a leak between the catch basin and the drain line (typically a 50 cent fitting), or other signs of leaking that may require a little caulk.  All the water that comes off the coils should successfully exit the unit and outside.

The other option is that the refirdgeration unit simply cannot remove the moisture being generated and is being overloaded.  Assuming there is not too much wood in the kiln then reach inside and look at the compressor and coils.  The compressor line should be frosty cold, much like the air conditioner line in your vehicle, and the coil should be cool to the touch, with moisture visibly condensing on the fins and dropping into the catch pan while you watch.  If not, then check the compressor, and make sure it痴 operating correctly.    
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Offline GeneWengert-WoodDoc

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Re: RH issues?
« Reply #4 on: October 05, 2018, 10:43:57 AM »
If there is liquid water, then the DH unit is not removing the water, as several postings suggested. With this high humidity, the DH should be removing the maximum amount of water, which should be around 4 pints per hour. If you are not close to that value, and the drain is working, then your compressor is not working. It could be low on gas, but it is likely that the air temperature is too low. For example, many compressors require 80 or 85 F before they work. Cooler than that results in freezing coils and no dehumidification until the ice melts.

For kiln schedules and how to covert them to DH, see

https://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr57.pdf



Note that 500 bf of green aestern red cedar or pine
will need about 500 pints of water removed or about 2 pints per hour average for an 8-10 day schedule.

Note thar moisture meters do not measure the moisture above 28% MC accurately. Could be 50% MC.

It is common practice to have the fans blow air on the edge of the pile and not the end.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline SoftWood

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Re: RH issues?
« Reply #5 on: October 05, 2018, 12:43:32 PM »
Thank you everyone for the replies & suggestions!  
I wasn稚 thinking equipment failure. I値l take a look today at the drip pan for leaks.  But it seems to be water everywhere, the concrete starts off light grey & an hour later it痴 dark grey, another hour & there is super tiny water droplets forming over the whole surface & then they keep forming & join to make up bigger pockets of water. 
I know the compressor is fairly new on the Ebac as well, he said it was & it痴 still shiny compared to the rest. 

The coils are freezing up for a few minutes each cycle then defrosting & running through the drain to outside. 
I知 going to stick a bucket under the drain today & see how much it catches.
 
I値l move my fans to the edge of the stack instead of blowing on the end, thank you for the tip!

Im bumping my temp up to 95 today & finally 104 the next day so I should see right away if that is part of my problem, too low of temps. 




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Re: RH issues?
« Reply #6 on: October 05, 2018, 02:21:05 PM »
If the coils are freezing up then the compressor etc must be working. That makes it sound like the temperature is too low. Once the coils freeze the unit essentially has to shut down while they defrost. With a slightly higher temp you won't get the ice forming, just a steady trickle of condensation dripping out of the condenser.
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Offline YellowHammer

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Re: RH issues?
« Reply #7 on: October 05, 2018, 02:34:39 PM »
Although it痴 counterintuitive, coils freezing up is one of the classic signs of low Freon.  I知 not familiar with the Ebac unit, but with a Nyle, the coils should never freeze.  They should be cool but not that cold.   
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Offline SoftWood

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Re: RH issues?
« Reply #8 on: October 05, 2018, 09:07:58 PM »
The manual says it痴 normal for them to freeze & need to defrost for 6 minutes, or something along those lines.  
Does it make sense that the lumber is actually losing MC in such a wet, high RH environment?  Checked it with my moisture meter & one piece that started out at 25 is down to 11, but the RH is around 72% in the kiln today. 

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Re: RH issues?
« Reply #9 on: October 05, 2018, 11:09:55 PM »
If you search for an EMC table on the web, it will give values that the wood will try to drop to, based on the actual RH and Temp at that time.  
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Re: RH issues?
« Reply #10 on: October 06, 2018, 02:58:45 AM »
Temp of 95F and 70% humidity and wood should settle out to around 12% MC.  So the numbers aren't crazy. 
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Offline Don P

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Re: RH issues?
« Reply #11 on: October 06, 2018, 09:50:20 AM »
There was one comment there that has me wondering. If it is an uninsulated slab in ground contact and this is just starting, is the slab simply below dew point?

Offline SoftWood

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Re: RH issues?
« Reply #12 on: October 06, 2018, 09:14:09 PM »
Beautiful!  Thank you for the EMC chart suggestion.
Just need to figure out a schedule or timeframe to go by, as to how long to run the dehumidifier for how many days I知 looking to dry it in.
Added some cheap floor fans to try & get more air movement but the standing water is definitely getting to be less, RH is down to 70.  It is an uninsulated slab though.

Offline GeneWengert-WoodDoc

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Re: RH issues?
« Reply #13 on: October 08, 2018, 02:07:17 PM »
You can insulate an existing slab easily yourself by digging a narrow, vertical trench about 24" deep and 3"wide around the outside edge of the slab and then stick in 2" thick, 24" wide styrofoam insulated panel all the way around and backfill.  You need to have the panels vertical and tight against the slab痴 edge.  This is called perimeter insulation.  If there is a concrete vertical part of the walls sticking above the ground, the insulation should also cover the wall above ground.  Concrete is not a good insulator.  Dry soil under the slab is a good insulator.

When you started your kiln at 65 F, if the slab was much cooler, it would indeed condense water in the cool spots.  This can be an issue in the winter, but in the summer, the slab and soil would usually be 80 F and not an issue.  As it condenses water, it will drop the RH unless more water is coming out of the wood than is being condensed.  As vapor condenses, it also releases heat and warms the slab.

As mentioned, frozen coils are almost always an indication of low Freon gas.  If the compressor continues to run, the unit can overheat and shorten compressor life dramatically.  Plus, the ice blocks the air flow.  Expensive compressors will have sensors that prevent this.  Also, some units have a "sight glass" in the line that will show bubbles if the gas is low.  A technician can check the gas pressure easily, but they actually let a little gas escape, so in some cases a better approach is to turn on the unit and measure the temperature difference between incoming air to the cold coils and the cool air temperature as it leaves the cold coils.  We would expect at least 30 F cooling.  Auto parts supply sell a/c gas, but unless you know exactly what gas you have, and the auto parts has the identical gas, do not do-it-yourself.  Since this is a new unit for you, a technician "house call" seems prudent.
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Re: RH issues?
« Reply #14 on: October 08, 2018, 03:39:16 PM »

As I said, I致e never broken into an Ebac unit.  However, I have worked on my Nyle refrideration system once or twice.   ::)

https://diy.stackexchange.com/questions/48450/why-do-the-evaporator-and-suction-lines-freeze-when-there-is-low-refrigerant

This is a picture of a properly charged Nyle, notice the frost line on the copper pipe goes right to the edge of the bulkhead.  However, on the other side, there is enough heat being absorbed to insure their is no frost on the same line, or the fins, just on the other side.  This insures maximum condensation without freeze up for a continuous removal of water.  It痴 interesting that others who have EBAC units see coil freeze up then thawing, also.  This is unusual to me as generally the only time a unit can call for an intentional defrost cycle is to reverse the valve and actually apply heat to the coil.  This is not uncommin in homeowner heat pump units as during a heating cycle the reverser valve will switch and actually provide air conditioning to a house for a certain period of time during the hour long heat cycle, the ones I致e seen are 45 minutes of heat then 15 minutes of air conditioning, even in the winter, to heat the coils and melt ice.  However, the coils should never fully ice, and even in a heat pump it indicates a low Freon charge.  I壇 call Ebac and get a reading on this, if nothing else it痴 costing electricity, as while the coils are frozen, no water can condense.   



  
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Offline SoftWood

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Re: RH issues?
« Reply #15 on: October 13, 2018, 07:33:53 PM »
Ok, things seem to going in the right direction for me now.
But is it normal to have some lumber drying faster than others?  Same thickness. 
I know some was wetter than others when I was stacking it & testing the MC. I just figured the drier stuff would absorb some of the moisture from the wet stuff to even out everything in the room. Then all the lumber would be finished at the same time, instead of pulling a few pieces out today, few more in 2-3 days, few more next week.

Offline GeneWengert-WoodDoc

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Re: RH issues?
« Reply #16 on: October 13, 2018, 11:04:46 PM »
Lumber drying rates depend on the incoming MC, small thickness variation, heartwood vs. sapwood, flatsawn vs. quartersawn, and wide vs. narrow.  By far, incoming MC is a big factor and it does not moderate much as drying proceeds until right near the end.

Another big factor is that moisture meters do not read accurately above 30% average MC. So, some readings are way off and then daily losses are not accurate.
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Re: RH issues?
« Reply #17 on: October 14, 2018, 12:57:43 AM »
Yes, it痴 normal to have different species same thickness dry at much different rates.  Some species give up their moisture readily, some hold on to it and even lock up occasionally.  It痴 just one of the problems with mixed loads.

For a non mixed, homogeneous load, it much undesired to have the same species, same thickness, same general MC, dry at different rates, causing wet spots in the stack, or dry zones.  This is generally an indication of uneven or insufficient air flow, although there is usually a slight variation until the entire load gets down to single digits.  Some species prefer a higher airflow, such as poplar, likes in the 650 feet per minute range, whereas oak seems to do best at 250 fpm.  Certainly, it痴 not optimal to pull pieces out one by one as they get done, much better to get the whole load finished at the same time, generally within a day or two at most.  Random drying of the same species, same thickness is generally a symptom of a bigger issue and once resolved, makes the stack drying rate much more uniform and synchronized.  
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Re: RH issues?
« Reply #18 on: October 14, 2018, 07:58:40 AM »
Some species prefer a higher airflow, such as poplar, likes in the 650 feet per minute range, whereas oak seems to do best at 250 fpm


This is an excellent observation and has given me food for thought. My Northland has one large fan that pulls through a grid that's attached to a "tunnel". (ie. it sits at the back of the kiln and pulls it down a tunnel that runs the entire side)

It's difficult, if not impossible to use baffling to control air volume/speed due to space restraints once the cart is in.

I wonder if a rheostat at the control panel would work to vary the fan. Might be a straight-forward solution. Thoughts?
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Re: RH issues?
« Reply #19 on: October 14, 2018, 08:22:04 AM »
A rheostat is probably not a good choice.  It depends on the type of motor of course, but generally it lowers the efficiency of the motor dramatically and wastes a lot of juice as heat.  A large enough rheostat is not cheap even if you can find one.  There are solid state controls available, but those motors really don't work efficiently being controlled that way.

Replacing the fan motor with a small 3ph motor and using a VFD to control the speed would work.  If the fan is a radial motor design, mounting could be a challenge.  If it's belt driven it wouldn't be that hard.   Fractional hp motors are pretty easy to come by and small VFD's are pretty cheap.

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Offline Don P

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Re: RH issues?
« Reply #20 on: October 14, 2018, 08:35:30 AM »
If it's belt drive a couple of step pulleys might do the trick.

Offline GeneWengert-WoodDoc

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Re: RH issues?
« Reply #21 on: October 14, 2018, 08:18:38 PM »
A variety of MCs as the wood dries is not unusual, as I stated already.  The risk is that we might over-dry the drier pieces (creating more warp, poorer machining, and poorer gluing) while waiting for the wettest to dry.  So, the best procedure is to put humidity in the kiln that prevents over drying but still allows the wetter pieces to dry.  For example, when drying wood that we want to have at 7.0% MC at the end, we might put in a humidity that prevents drying under 6.0% MC, which is 6.0% EMC.  Some might use 5.5% EMC.  In other words, never let the kiln conditions or the wood MC of the driest pieces go under 6.0% EMC.

If we do not do this, but instead use lower humidities or EMCs, then there is a process called equalization.  The kiln humidity is increased at the end of drying (using special rules on when to start and when to end).  However, cupping and poor machining caused by over-drying are not fully repaired in equalization.  Equalization can take 24 to 72 hours in order to get uniform MC, and the correct final MC.  Equalization is described in all drying texts.

In the first process described in the first paragraph above, the kiln is essentially equalizing for a long time, which does slow drying perhaps by a day, but this extra time is offset because no standard equalization is needed...24 to 72 hours is not needed.  Plus the lumber quality is higher.

Regarding air flow, when we get under 30% MC, air flow no longer controls drying speed...it is RH and temperature.
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Re: RH issues?
« Reply #22 on: October 15, 2018, 08:14:54 AM »

The graph that says it all, Drying Rate vs Air Velocity.  You can see how at say 40% MC, higher airflow, such as 600 fpm will dry wood about twice as fast as 200 fpm.  So assuming the wood can tolerate it, you can save a lot of time with with higher velocities.  

Conversely, for oak and other wood that requires a low drying rate, and isn't prone to sticker stain, a lower air velocity will inherently dry slower and provide a safety margin.  

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Re: RH issues?
« Reply #23 on: November 29, 2018, 10:05:07 PM »
May seem like a ridiculous idea once I hear from one of you guys but is there any reason not to pull my lumber out piece by piece as it reaches say %6 MC & then put it back in, all at the same time to heat back up & equalize to %8? 

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Re: RH issues?
« Reply #24 on: November 30, 2018, 09:19:12 PM »
What we do in most kilns is to keep the kiln at 6% EMC. This prevents any lumber from drying under 6% MC. Continue with this EMC until the wettest gets to 8% MC.  Ok?
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Re: RH issues?
« Reply #25 on: November 30, 2018, 11:08:53 PM »
The key is to set the EMC conditions at a minimum acceptable level so the wood can稚 get below that.  All the wood in the system will converge to but not go under that level, it won稚 just keep drying out more and more. It痴 an EMCSN (EMC Safety Net) and will keep from overdying the wood even if all the boards start at different levels.  
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Re: RH issues?
« Reply #26 on: December 05, 2018, 06:39:38 PM »
Thank you for the continual help Gene & YellowHammer! 
It痴 making sense what you池e saying & im aiming for that now but I am getting defeated.
I知 getting close, RH wise, to start checking lumber to see where I知 at & did so today & im pretty far off from what the ecm charts say I should be at. 
I have a hygrometer/temp gauge in the kiln that records the min & max.
My temp is constant between 102-104 & RH is down to 41-44 last night/today, it dropped a few percent each of the last couple days. I havnt bothered checking the wood since the first week because I figured I am so far off still, but when I probed the wood today, 3/4 of it is showing %6, as low as my meter goes. But by the charts I should only be in the mid 7痴.
Had planned to try & keep it around %35 RH in there until all lumber showed the same MC. 


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Re: RH issues?
« Reply #27 on: December 06, 2018, 05:56:48 AM »
How are you measuring MC...Equipment brand name?  If needle type, are they insulated and how deep?  Species or temperature corrections? 
Do you measure humidity with a wet-bulb and have good air flow on the bulb?
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Re: RH issues?
« Reply #28 on: December 06, 2018, 01:01:50 PM »
It痴 a Lignomat mini E/D meter with 3/16 pins, I don稚 think they are insulated.  I used a dry bulb, species is western red cedar. 

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Re: RH issues?
« Reply #29 on: December 06, 2018, 02:05:30 PM »
One of the most useful skills you can learn is how to oven dry wood to measure true moisture content. It sounds a little intimidating, but is very easy, and with an accurate food or better scale, will tell you exactly what your wood is at, if your meter is reading incorrectly, and will give you a gold standard approach to measurements.  Ironically, once you have a sample specimen in the kiln, it takes aout the same effort to put it on a scale and calculate the result as it does to hammer pins in.  Well... not quite as fast, ;D  but certainly more accurate. 

 
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Offline GeneWengert-WoodDoc

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Re: RH issues?
« Reply #30 on: December 06, 2018, 03:38:44 PM »
With this meter, you are getting mainly the surface MC.  The core is likely wetter, so the average MC of the piece is likely higher than 6% MC.

Even so, at 45% RH at room temperature, we would expect to see around 8% MC.  The temperature correction, using the temperature where the needles are driven, is about 1% MC for every 20 F hotter than room temperature.  Add when colder and subtract when hotter.  So, in your case, either the meter is wrong or your humidity is wrong.
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Re: RH issues?
« Reply #31 on: December 08, 2018, 03:27:53 PM »
The gf isn稚 convinced that it値l be fine to oven test the wood, but I知 working on her.

I did get the moisture meter somewhat sorted. Got some longer pins, 7/16, & now its showing a higher MC. 
May be a late question now but where is the proper place to probe the lumber?  Obviously getting a different number when I prove the end vs the face.  It痴 only 4/4 stuff but I hate sacrificing a board by probing

Offline btulloh

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Re: RH issues?
« Reply #32 on: December 08, 2018, 03:34:17 PM »
Pick up an older microwave that somebody is ditching or off craigslist.  In this case the gf is on firm ground.  I wouldn't do it in the house either, even with a dedicated mw.  You can, but .... interesting fumes come out of the sample.  It is really instructive and useful to try the oven dry method even if you don't use it all the time.  There are multiple threads on here about using the microwave oven.
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Re: RH issues?
« Reply #33 on: December 08, 2018, 03:57:25 PM »
Yup, the microwave ends up smelling of whatever wood you happened to be cooking. As well a boiling off the water vapour there seems to be some resins and other chemicals come out as well (same as any high temp kiln) Likely depends on the wood, but any species of cedar is going to leave something behind.

And then if you use too much power, and set fire to the wood, you have a whole other smokey mess to clean up.  :D
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