Message Thread:
Dehumidification air speed
8/6/16
Website: http://australiancuttingboards.com.au
I have just finished building a simple DH kiln The size is 2.400mm High By 2.400mm wide. 3.600 long. I have loaded a stack of 35mm camphor laurel into it. With 25mm stickers The stack is 1200 wide. and a length of 3.600mm ans 1.800mm in height. I have 6 x 250 mm bathroom exhaust fans. I am concerned regarding the output of the fans. On the intake side the reading is 1250 feet per minute per fan. So the overall adding all fans together is 7500 feet per minute. This is cycling through the stack. I am not detecting much movement of air on the out side of the flow. I am not sure if I have built up enough pressure to evenly push air through the whole stack. I am concerned about getting mould problems so I havent fired the kiln up yet. All help appreciated
View higher quality, full size image (1840 X 3264)
8/6/16 #3: Dehumidification air speed ...
Website: http://www.tsmfarms.com
Your square corners (walls meeting ceiling) are part of the problem. The air hits flat into them then misses all the circulation up. Next...is there a air space down the back wall for the air to flow down and through the stacks?? Do you have a set of plans or is this guess work?? Drying is a tricky process BUT you can learn it. My concern at this time would be mould due to it sitting in the kiln and NO air movement.
I ask these questions because after seeing your website it's obvious you've been buying your "KD" wood somewhere else and haven't ever ran a kiln by your setup and comments. 7500 cfms is quite a bit BUT I don't know what is needed for your setup BUT you should be feeling air movement. Is that a Dehumidifier or just a heater in pics??? I see several lines or wires...is this part of the drying setup or other???
I own a small self built kiln also BUT I done alot of research prior to building.
Your stating KD wood is this also sterilized or just dried to a certain MC?? Yes it can be done either way and should be both.
Keep us posted.....Oh Yeah....BEAUTIFUL boards your building!!!!
8/7/16 #4: Dehumidification air speed ...
Website: http://www.australiancuttingboards.com.au
Thank you for the reply, the kiln was loaded 2 days ago. I have the same amount of space on the other side of the stack, the wires are fed into the stack and attached with screws so I can get a correct reading without having to open the kiln. I basically followed a design i found online (http://dnr.wi.gov/topic/forestmanagement/documents/pub/FR-396.pdf) We sell a lot of boards a year and because of demand for camphor laurel bread boards I could not find a good supply of kiln dried timber. I have researched the subject a lot before considering building my own kiln. I am using an air conditioner with a hose connected to the outside for collecting and measuring the amount of moisture that is removed on a daily basis in conjunction with a heater to get the temp up to 60c. I also have a humistat installed for relative humidity and also temp control. I found a kiln drying schedule and intend to follow it. I lit a candle and held where the stickers are and there is a slight change in the movement of the flame, which tells me that there is some movement of air at the bottom of the stack.I took the image displayed after connecting one of the 2 large doors. I have uploaded another image of when I eas painting the internal. The walls are ceiling and doors are insulated with r4 grade insulation. My aim is the reach mc of about 15 to 18. regards Stuart
8/7/16 #5: Dehumidification air speed ...
You are confusing FPM and CFM. FPM is the velocity of the air and when average air velocity FPM over an area is multiplied by the area, you have CFM. I am sure the area that has 1250 FPM is much less than a square foot so you have much, much less air flow than you calculate. A typical toilet exhaust fan is usually 75-100 CFM. But don't worry about it. See how it dries after this load. The volume of air has more to do with the amount of water the dehumidifier takes out and you have a small one. It will be slow but might work out.
8/7/16 #6: Dehumidification air speed ...
Website: http://australiancuttingboards.com.au
Thank you Don for the response, I looked up the specifications on the fans and the air movement is 294 CFM per fan. So by multiplying 294 x 6 =1765 CFM. I started the drying process 12 hours ago the temp was 60°F (16°c) and now it is up to 82°F (28°C). The amount of moisture in my bucket is 2.9 gallons (11 litres.). The drying schedule says for camphor 140°F (60°C). I am aiming for 104°F (40°C) to start then slowly work my way up to 170°F (76.5°C) dry bulb for 20% to 15% MC. The wood is measuring above 50% MC at the moment. All comments are appreciated. regards Stuart
8/7/16 #7: Dehumidification air speed ...
Website: http://www.tsmfarms.com
Stuart, I'm a little concerned on your drying schedule. I do a completely different schedule DUE to I totally AD to below 20% (safety zone with most woods, most say very difficult to damage wood in kiln at or below this) and probably near 12-14% MC AD prior going in kiln BUT I have time to do this.
You stated your going in @ 50% MC and shooting for 140* for camphor. I'm not familiar with this wood BUT normally this sounds a little hot for that MC in most of my hardwoods. I noticed your goal is 15-18% which in our /USA is usually AD and 6-10% is KD goal due to our climate averages indoors. Please double check your final goal and this my be appropriate for your region.
Gene usually has some great guidelines with dying, maybe he can chime in.
8/7/16 #8: Dehumidification air speed ...
Website: http://www.tsmfarms.com
Oooops I'm sorry. That should've said "....great tips on drying..." Sorry I just reread.
8/8/16 #10: Dehumidification air speed ...
Website: http://australiancuttingboards.com.au
Tim I am following
Dry Kiln Schedules for Commercial Woods
Temperate and Tropical
Cinnamomum spp. (cinnamon wood, camphor wood)Table 94 T10-D2.
I performed temp test in the kiln this morning and have found there is a 4°c difference from the top to the bottom of the pile, so i have ordered higher velocity fans which create 1125 cfm which will give me 6075 cfm which is about five times more I am hoping this will create enough pressure within the plenum for an more even flow of air Regards Stuart
8/8/16 #11: Dehumidification air speed ...
If this is a residential dehumidifier, it probably will not be able to run much above 110F and the temperature will kill the fan motors. Keep your temperature below 100F unless you have a dehumidifier that was designed to operate at higher temperatures and still dehumidify, let alone live.
8/8/16 #12: Dehumidification air speed ...
Website: http://www.tsmfarms.com
Thanks Don, I had forgotten about the temp safety switches in residential products to prevent fires.
Stuart the multi level temp checking is very handy for this reason. Also if you'll add a 45* angle in the one top corner opposite of the fans will direct that air down with less resistance and you'll be surprised how much flow and temp change that will make. IF you have access to sheetmetal you can curve that corner for even better results.
8/9/16 #13: Dehumidification air speed ...
Website: http://australiancuttingboards.com.au
I appreciate all the advice, I am going to open up the kiln and add a 45° angle when the 6 new fans arrive. I have read that people have successfully used old window air conditioners, so I purchased one in great condition for $100 off a guy who repairs them. regards Stuart
8/9/16 #14: Dehumidification air speed ...
Website: http://www.tsmfarms.com
IF your using a window air conditioning for the DHing (I've not heard of a kiln using this style, I use a home DH which are designed just for removing moisture, they also put off heat in this type enviroment) then what are you using for your heat source??? Here in the USA most of our residential products have heat safety disconnects/relays that shut down their operations above (I think) 110* room temp. ....so that would make heating without correct parts almost impossible to sterilize.My DH would shut down also if I don't keep below it. I let my unit create it's own heat so I'm usually in 90* range...then I boost at the end with other heat source to 135* for sterilizing the hardwoods I have.
8/9/16 #16: Dehumidification air speed ...
I already have a heat source in the kiln, the airconditioner gives out more heat than cold plus the heat coming off the fans. The unit I have been using is a dehumidifier plus air conditioner. I will run at about 100°F then sterilize with the heat source. Air conditioners run the same as a dehumidifier. Which I proved with the unit im using. I did notice the relay kicking in about every 10 minutes. I have been extracting about one litre an hour so far. regards Stuart
8/9/16 #17: Dehumidification air speed ...
I've read that another issue with home units is the high acids in the water coming from some species of wood. Rusts them out in no time.
8/10/16 #18: Dehumidification air speed ...
Website: http://australiancuttingboards.com.au
I have the window Air conditioner up and running in the kiln, my output has doubled to 2.1 litres an hour. at rh 64 and temp 36°C. Do these figures look ok? regards Stuart.
On the issue of the air conditioner rusting out I do have access to others for replacement. Regards Stuart
8/11/16 #19: Dehumidification air speed ...
Website: http://australiancuttingboards.com.au
Thank you for all your help Tennessee Tim, I upgraded the fans and did what you suggested and install a 45 degree baffler which has helped enormously, the breeze is actually going to the floor,which will help the bottom of the stack catch up to the rest. Then I may need to turn the fans down a touch so that it is even through the whole stack. Regards Stuart
View higher quality, full size image (3264 X 1840)
View higher quality, full size image (3264 X 1840)
8/11/16 #20: Dehumidification air speed ...
The temperature limit on heat pumps (which is the name for air conditioners, refrigerator compressors, dehumidifies, etc.) is not for fire control, but reflects that performance of the gas used in the compressor and its lubrication. Most cannot run above 115 F about.
The original posting says that the lumber pile is 8 feet long and the stickers are 1" thick (1/12 foot) and there are about 30 layers. So, this means that the air space is 1/12 x 8 x 30 or 20 square feet. So, then take the cfm and divide by 20 to get the velocity. So, 1200 cfm means 60 feet per minute. For white wood drying and pine, we need over 600 rpm velocity. For most hardwoods, 300 fpm.
We also need a good sized space between the wall and the edge of the lumber pile. I suggest at least four feet. Plus as mentioned, using a curved baffle in the top corners will help flow.
Do you reverse air flow?
It is fundamental that the volume of air going into a load is identical to the air coming out. So, if you have 300 fpm air velocity going in (which is extremely hard to measure accurately without spending thousands of dollars), you must have the same average coming out (which is easy to measure). If air flow out is low, so is the incoming.
Note the the original posting says that width is 2,400 mm. (In the US, we use a comma and not a decimal.), but it looks closer to three or four feet...1000mm. So it would seem that this load is about 900 to 1000 BF and so it will be about 28 pints or 3-1/2 gallons of water per 1% MC loss. So, your one liter per hour is about 7 gallons per day or 2% MC loss, which is fairly low for this species, and most species.
8/11/16 #21: Dehumidification air speed ...
I think I have it wrong...the chamber is 8' wide, but the lumber stack is 4' wide and 6' high. The air flow data is still correct.
Now with 6 fans, if there were perfect air flow, we would have 360 fpm which is fine for many wet hardwoods. However, with the fans blowing directly onto a flat wall, you will not achieve the rated vales.
The plenum space is just two feet (and the photo shows that some places it is even less) which means that air flow at any fan speed will be variable with a pile this high.
8/11/16 #22: Dehumidification air speed ...
Website: http://australiancuttingboards.com.au
Thank you for responding, I have upgraded the fans which are rated at 1125 cfm for each fan, I have six fans which take the air flow to 6750 cfm. I installed some black plastic sheet on the rear wall to help with air flow and have some metal sheet coming to attache at 45° angle to help air flow. My output of moisture is now up to 12 gallons a day since I changed the air conditioner. At present I am not reversing air flow. Is there a auto switch that will reverse the fans? regards Stuart
8/11/16 #23: Dehumidification air speed ...
Website: http://www.nyle.com
One thing you might try if you have trouble getting even air flow from bottom to top is putting in shelf brackets and putting some narrow (100-150 mm) horizontally and them moving them up and down to deflect air into the pile. One customer who was an aircraft engineer by trade, did this and got it really well balanced. It is pretty difficult to reverse single phase fans and with such a narrow load, you would not see any significant improvement and it would make balancing the load trickier.
8/13/16 #24: Dehumidification air speed ...
Website: http://australiancuttingboards.com.au
Thank you for responding, Iam getting plenty on movement through the stack with the new fans.the kiln is running at 61% RH. and at 118° F. I am using a domestic window air conditioner 240 rated at 2400 watt . The unit is removing 20 gallons per day. The kiln is very well insulated will R4 insulation. I want to dry the timber as fast as I can without effecting the air conditioner. One thought I have is diverting the cold back onto the compressor to try and minimize the heat, I don't want to control with a thermostat as this would shut down the unit for too long. Any thought on this subject would be greatly appreciated. Regards Stuart
8/22/16 #25: Dehumidification air speed ...
Website: http://australiancuttingboards.com.au
Hi there, I am concerned with my drying schedule. At the moment The Kiln is running at 148°F (61°C). RH is 38%. In the last 10 hours I have pulled out 6.34 gallons (24 liters). I am concerned about my MC still over 50% I think it is bordering on this. My MC Instrument reader only goes to 50%. In the last 16 days I have pulled out 187 gallons (700 liters) of moisture. The stack is approximately 1820 board Feet in the kiln at present. I am running 2 modified wall air conditioners. I changed the cooling direction back onto the Air Conditioner compressor to help with cooling. The six booster fans are running at approx 180°F (80°C). My main concern is I am too low on the humidity. All help appreciated. Regards Stuart
8/23/16 #26: Dehumidification air speed ...
Website: http://www.nyle.com
It sounds as though you didn't know the initial moisture content so that makes it hard to know where you are. You have to bear in mind that all of the water leaving the lumber does not come out the drain. The heat generated by the fans has to vented or leaked away and that can carry a good amount of water. Did you calculate how much more water has to come out to meet your final MC? It seems as though your meter reading of 50% is probably not correct. Can you do a weight sample test?
8/23/16 #27: Dehumidification air speed ...
At 1800 BF of a dense wood, you can expect about 6 gallons will equal 1. % MC. Double that for softwoods.
So, you have lost about 30% MC. If this lumber was fresh from the sawmill, then you high temperature and low humidity are not what we would run for most hardwoods, but might be used for pine.
What schedule are you using? A time based schedule is questionable for softwoods in a DH unit. Most time schedules are for large heating and venting systems.
8/23/16 #28: Dehumidification air speed ...
I assume you are using pins to get the MC. Did you drive the pins halfway into the lumber from the face? If so, you have the core, not the average MC. Also be aware that above 30% MC, the readings from a moisture meter are not valid. So, 50% MC could be 32% MC.
8/23/16 #29: Dehumidification air speed ...
If the core is 32% and the shell is 6% MC, then you could have an average of 20% MC.
But maybe your wires are not good, so disconnect one wire from the probe in the kiln and see if you still read over 50%. There could be a short in the wires due to insulation failure in the wires.
8/23/16 #31: Dehumidification air speed ...
Thank you for responding.The camphor laurel was reasonably fresh from the mill. I have used 25mm screws on 35mm timber. Because It is the first load I have 8 separate testing points with wires running to the outside for testing. I cant actually access the screws as I screwed them into the center of the stack for a better indication of the moisture content. The kiln is not vented as I am working on getting a good indication of moisture loss which means the fans are not vented. I have been thinking about venting to bring down the temp which will unfortunately bring in humidity from the outside. Should I vent? All help is appreciated. regards Stuart
8/23/16 #33: Dehumidification air speed ...
Website: http://australiancuttingboards.com.au
I forgot to mention that I am following
Dry Kiln Schedules for Commercial Woods
Temperate and Tropical
Cinnamomum spp. (cinnamon wood, camphor wood)Table 94 T10-D2. regards Stuart
8/23/16 #34: Dehumidification air speed ...
Website: http://nyle.com
Nice website.
Normally we recommend screws go 1/3 the thickness and some screws are coated and some are not. Some go across the grain and some with the grain. They all have a correction factor for species and temperature. If you don't have correction factors, you can get them from whoever made the meter.
8/23/16 #35: Dehumidification air speed ...
I was not able to get into the stack to sample for moisture content so I chose a point which had a high reading near the edge about 2 feet in. I performed the microwave test the timber weighed 13.6 grams and dried to 9.6 grams. the moisture content is approx 42.6%. In 1800 BF how do I calculate amount of water needed to be removed to get down to 15% MC? regards Stuart
8/23/16 #36: Dehumidification air speed ...
Do you have any guidelines for the weight of 1000 BF? If not, go to the right side of the screen and click on "timber and lumber calculators." You can get the weight at a given MC. so, let us assume you did this and the weight at 48% MC (average MC, not the wettest and not the core) is 3600 pounds. You divide 3600 by 1.48 and thIs gives you the estimated oven dry weight of 2432 pounds for 1000 BF. Divide by 100 to get the weight of 1% MC of 24.3 pounds. Divide by 8 pounds per gallon to get three gallons per 1% MC. Because you have 1800 BF, multiply by 1.8.
Now not every piece is 48% MC, and the weight is an estimate, so the answer is merely an approximation. Some pieces will be much drier at the end and others wetter. This is why there is an equalization step.
Finally, because you want to dry from 48% to 15% MC, multiply the answer by 33 to get the total water. Of course, you have other water losses, as Don mentioned.
8/24/16 #37: Dehumidification air speed ...
Do you have any guidelines for the weight of 1000 BF? If not, go to the right side of the screen and click on "timber and lumber calculators." You can get the weight at a given MC. so, let us assume you did this and the weight at 48% MC (average MC, not the wettest and not the core) is 3600 pounds. You divide 3600 by 1.48 and thIs gives you the estimated oven dry weight of 2432 pounds for 1000 BF. Divide by 100 to get the weight of 1% MC of 24.3 pounds. Divide by 8 pounds per gallon to get three gallons per 1% MC. Because you have 1800 BF, multiply by 1.8.
Now not every piece is 48% MC, and the weight is an estimate, so the answer is merely an approximation. Some pieces will be much drier at the end and others wetter. This is why there is an equalization step.
Finally, because you want to dry from 48% to 15% MC, multiply the answer by 33 to get the total water. Of course, you have other water losses, as Don mentioned.
8/24/16 #39: Dehumidification air speed ...
Unfortunately camphor Laurel is not in the list regards Stuart
8/24/16 #40: Dehumidification air speed ...
Where is the best position to vent some of the heat from my dh kiln. It is way too hot at 143°F(62°C). The drying schedule wants 80° RH at this temp. Or is there another alternative I can use. I feel like I am chasing my tail with this issue. regards Stuart
8/24/16 #41: Dehumidification air speed ...
Use the weight data for hackberry wood, as it is comparable to camphor laurel.
8/25/16 #42: Dehumidification air speed ...
Website: http://australiancuttingboards.com.au
Thank you for the help. regards Stuart
9/9/16 #43: Dehumidification air speed ...
Website: http://australiancuttingboards.com.au
Hi there my first charge is about to come out it was interesting how it dried it was showing 30% more on the moisture meter and I turned it off oa few days ago the reach the rh and Mc for my area which is 12%mc, the timber has dried basically to the same MC all the way through. I have been air drying the next charge which is sitting at about 20%mc at the moment, will be interesting to sea how much timger was damaged in the charge.So thak you to all who gave me there help, I want to attach my probes within the kiln again (screw with wires then the leads to the outside of the kiln for testing MC) on this charge I would like to fix to the edge of the slab instead of the centre of the slab. It will be easier for me to attach to the side of the stack. If I go into the center of the side will i still get a good reading? regards Stuart
5/10/21 #44: Dehumidification air speed ...
Website: https://www.seacoastair.com/fl-heating/air-conditi...
If this is a residential dehumidifier, it probably will not be able to run much above 110F and the temperature will kill the fan motors. Keep your temperature below 100F unless you have a dehumidifier that was designed to operate at higher temperatures and still dehumidify, let alone live.
|