Drying Cold Corn

I got an interesting email from Tom in Ohio, wandering how he could dry his cold tough corn. It went something like this:

Hello Ron Palmer, hoping you can offer suggestion. South West Ohio U.S.A. 5000 bu. bin with 5 hp fan, 2500 bu of corn harvested Feb with air temp 20 f. and mc of 20.5. a cooking thermometer was inserted from top of corn today that read 50 f, probably colder farther down. Spring temps are fluctuating into 70’s f. with off and on rain in the 10 day forecast. Your trials involved grain that was much warmer than this corn, should it be warmed up with daytime air before starting the night time drying and to run or not during nights with rain??   Thanks you for any help/strategy to dry down corn. 

And my reply:

Tom:   You have some pretty tough corn at 20.5 % MC; however, the good news is that it is not heating at 50 deg. F.   So, the  question is: how are we going to get some of that moisture out.   And you are right in thinking that we need to get some heat into the corn, so that it has some energy to push the moisture out.  Actually most of the energy is used to change the water in the grain from liquid state to a gas state.   We have found that it takes about a 15 deg C (27 deg F) reduction in  temperature to evaporate the water to get a one point reduction in moisture content.  For example, let’s say that we have corn at 70 deg F @ 20% MC, and we run the aeration fan to get the corn down in temperature of 43 deg F  (70 – 27).  We should have reduced the MC by one point, 19%.   But how do we get energy into the corn??   Yes you can use the outside temp of the air to heat the corn; but, as you heat the grain this way, there is a good chance that you will be wetting the corn down.  So, yes use the heat of the day to get your your corn warmer, and then use the cool night air to cool it down and for every 27 deg F that you drag the corn down, you should be able to take the grain down one point.  We want to get this cycle going of getting energy into the corn during the day, and then cooling it at night to remove the water.   My first reaction would be for you to run the fan continuously; heat the corn during the day, and cool it down at night.  If you can get a 27 deg swing you could take out as much as a point a day.  However when the corn get closer to being dry, you might find that you are adding as much water during the day when you are heating the grain as you take out at night.   How will you know?   I suggest you use my Grain Drying Calculator. You can find it at  planetcalc/4959/ and it will tell you when the conditions are OK for drying.  I ported this website calculator to my cell phone, and I can use it anywhere.  Unfortunately the temperature entries are in Celsius, and I know you like F, so you have to convert.  To convert F to C, subtract 32, and then divide by 1.8.  So 32 F is 0 C.  70 F is 21 C,   50 F is 10 C.   I entered the following into my calculator.
Grain Moisture Content %     20.5  
Grain Temperature C    10         (this is 50 deg F, — this is what you told me the temperature of your corn was)Air Temperature     C     20        (this would be 70 F, the daytime high)
Now push calculate and scroll down to shelled corn, and you will see that you get a threshold relative humidity of 48.4%.  In other words if the relative humidity of the air outside is below this you will be drying.   I doubt this is the case for you, when you said there were showers around.  It is probably more like 70 or 80%, in which case you will be wetting you corn down.
OK let’s run the fan when it is 10 C or 50 F outside — what does the calculator give us — it says the threshold relative humidity is 93%.  So even though the air temp outside is the same as your corn temp; as long as the RH outside is less than 93%, you will be doing some decent drying.  Not bad. 

If we run the fan when the outside temp is just above the corn temp. say 15 C (59 F), and we run that through the calculator we get a threshold RH of 66.6%.  You might get this on a dryer day — but certainly if it is not raining.So, roughly speaking, it looks like we can run the fan without wetting down too much provided the temperature of the air does not exceed the temperature of the corn by more than 5 C or about 9 deg F.    But if you want to be more precise, use the calculator.    As the corn gets drier, you will find that the temperature difference will get less and less, and it will be more difficult to get some heat into the corn.I hope this helps//Ron


Open Bottom Plenum

Last year we measured the pressure drop across the perforated pipe in the bin when the aeration fan was one. We typically saw a one inch (of water) drop across this perforated pipe, (used a manometer). My thoughts were that an open bottom pipe or plenum would preclude this drop. I sketched out what such a thing could be and I ended up with design that had an open bottom pipe leading to a Christmas Tree looking rocket in the middle of the bin. louvers placed on the outside at 45 degrees provided direct grain exposure to the air from the fan.

Open Bottom Rocket with Louvers, is 63″ tall by 27 ” across the bottom. It would be placed in the center of the bin with an 18″ delivery pipe. 6″ pipe radials would extend laterally on the other three sides. It provides 24 square feet of direct grain exposure. In comparison a ten percent perforated 18″ pipe has only 10 square feet.
The center tree structure provides more air in the middle to accommodate the peak of grain that occurs at the top of the bin, and would result in a more even distribution of airflow.
Because there is no pressure drop across the bottom, there would be an increase in flow and the lower compression would yield a lower temperature with less discrepancy to top/bottom drying. Overall the drying would be more effective and efficient.

The 18 ” and 6″ pipes could also be open bottom to provide more direct exposure. Being open bottom would preclude any fine buildup which plugs holes and also is a wonderful breeding ground for pathogens.

Open bottom pipes, would add more exposure for a total of 35 sq feet. If the material used for the louvers are 10% perforated, this will increase the exposure to 43 sq. feet. Remember that a 10% perforated pipe (18″) provides only 10.3 sq. feet. With this much more exposure, 4 X, it is obvious that this would be a better air delivery system.

Green Seeds & Long Term Storage

have been following your work the last few years and it is good stuff.  I do have a few questions though on how best to use the info based on a normal year and secondly advice for this year.  I farm close to Drumheller, AB and normally we get enough heat to harvest a dry crop.  This year not quite as nice, though it may turn warm yet.

Question 1.

How best to use natural air drying in a normal year for me.

In a normal harvest here, the crop gets preharvest roundup and the immature plants get desicated and are dry to ambient conditions when my combine arrives 2 weeks later.  It sounds like farmers might lose the ability to use preharvest roundup in the future.  Previous to preharvest roundup my crops would come in with varying moisture levels due to immature seeds.  The grain will average dry.  I have aeration in most of my bins, but they are all spread out in various fields and right now I use a generator to cool the grain overnight after storage and then again a night 2 weeks later when it is cooler and once more in December when it is cold.  Fuel for the generator is expensive and I would like to keep my costs down.

So my question is how the immature kernels affect natural air drying?  Looks like the grain will lose 1.5% moisture by the time it is cooled to final storage temperature.  So with immature kernels, I assume that it is safe to store when averaging dry if the fan runs somewhat to make sure the moisture equalizes in the bin.  Because some of the kernels are high moisture, should the bin sit for 24 hours before turning the fan on the first time to allow for moisture migration from the tougher kernels to the surrounding dryer kernels?  No, turn your fan on immediately, even while it is being filled — get the grain cooled as soon as possible to prevent spoilage, especially if it is tough and has green seeds in it.

Also, if by final storage the moisture is going to drop by say 1.5%, does that mean I could bin grain that is 1.5% average higher than dry even with uncure/immature kernels in it and the bin will average dry after final storage and the grain condition will keep for 6-8 months until sold?  I would say yes, it will keep without spoilage provided it is kept cold — really cold, below freezing.

I am just trying to come up with a workable system in case preharvest glyphosate is removed as a harvest tool.  I really dont want to go back to swathing as a way to kill the plants.  I would certainly get the jump on harvest by starting when the crop is a couple of points above dry, and then use your aeration to get it cold and dry. Aeration is way cheaper than swathing!

Question 2.

How to deal with grain that might get harvested tough this fall.

I have read most of your articles and it sounds like if the grain is 20 degrees C or more and only 2% above dry that it will dry during the cooling process by running the fans at night.  Once the core grain temperature drops close to freezing the amount of drying that occurs is minimal.  So assume grain will still be too tough to sell after cooling it (and hopefully drying it 1-2% in cooling).  I see 2 options and perhaps you can expand on these please or inject some ideas that I have not thought of short of getting a grain dryer.

Option A.  Dry in Spring

Cool the tough grain at night and if the moisture is low enough for safe storage, it could be dried in the spring.  Just not sure what proper procedure would be in the spring and what the economic numbers would look like.  Outside air would be warm, so if supplemental heat is added I assume the condensation at the roof thing would  not be an issue.  I assume that the grain mass would have to be warmed up with supplemental heat, but perhaps it could be warmed up during the day, then shut fan off, resume heating the following day and once the grain temp is warm enough you start cooling at night and removing moisture.  Just not sure how warming up a mass of tough grain slowly would work as spoilage might be an issue.  Your work showing you add moisture during the day and removing moisture at night is going to come into play here, but not sure how the grain can get warmed up with ambient air and not add moisture to the grain during warm up.   If you get your grain as cold as possible by running your fan in late December for one cold night, we might get the grain down to -20 C.  Even if it is tough, it will not be spoiling.  Now seal the bin up the best you can, for two reasons: 1. We want to keep the grain as cold as possible, for as long as possible, and 2. We don’t want warm spring breezes, containing lots of water, from hitting your cold grain and condensation forming.  During the winter the grain will warm about 1 C per week with the bin kind of acting like a solar collector, and heat coming in through the walls and roof.   Monitor the temperature of the grain, and when it naturally gets to 15 to 20 C, start pulling it back down as cold as you can.  This will probably be in August or Sept.  and continue with the practice of getting the grain as cold as possible.  Let’s say we pull it down again from 20 to 0 — we will have taken another point out and it should be close to dry by now, but even if it isn’t, keep the grain temp as low as possible; seal the bin up at Xmas and repeat yearly.  Your grain should end up dry, and more importantly with no spoilage and no expensive supplemental heat.

Option B.

Add supplemental heat to the natural air drying fans.  I see your work in the blogs about condensation at the roof being a problem.   Is it possible that you are missing the effect that heating may have on the roof panels themselves?  If enough heat is passing through the grain, could it be heating the roof panels and changing the condensation point to allow more humid air to escape the bin and condensate outside.  Would higher airflow rates, higher plenum temperatures, much fuller or shallower grain depths make the condensation different?  I am thinking there is a strategy here that is being overlooked, much like people were overlooking the effect grain temperature was having on running the aeration fans at night to dry grain (which you proved).  Type of aeration system (full floor, pit, rocket, round tube, inverted v) probably all work different. Biggest downfall that I see is severely overdry grain in the bottom of the bin by adding enough heat and airflow to keep condensation at the roof minimized.  Not sure if the whole bin could be over dried and then mixed with untouched tough grain and be mixed together, moved to a different aeration bin and run the fan a little to equalize?  Your blog showing the 50,000 btu heater and removing 0.3% moisture every night is good, but too slow for what I need to do.  I would require a huge power service to run that many fans, which I do not have, so trying to explore other options.    I would only use supplemental heat if you were in a hurry to sell your grain as dry.   As my blog says: heat the grain during the day, and cool it at night.  and you don’t have to worry about over heating the grain, it takes 12 hours to heat 5000 bushels, see

Supplemental Heat: Act III How Long to Heat Grain 5 C

 

Supplemental Heat on Tough Canola

 Colin:
    I will try to answer your questions, but I will qualify my reply with some uncertainty because we did very little work with supplemental heat.  My reply will be embedded in your original email below, (blue):

I am planning on using a frost fighter heater to add some heat to aid in drying down canola in hopes that I can pick away at harvest until weather gets better. I have a pretty good handling and monitoring system. 7500 bushel hopper bins each with 7hp fans, temp/moisture cables and remote fan control that can be operated via the Intragrain website or mobile. My first question is how tough would be safe to start taking canola off? I was hoping to start at around a MC of 14 but Mother Nature doesn’t want to let it get down to that. Last sample I ran was MC of 15.6. It has 0 greens and combines well so I’d hate to wait for worse conditions. At this point I am just hoping to get canola down to 12 with heat and air if possible. This seems to be the threshold that the elevators will start to take it. I also have a few thousand bushels off at 8-8.5 so could blend a little if needed.
         If I were you I would take your canola off at 15; but cool it down immediately — as cold as possible. Let’s say your canola came in at 15 C and you cooled it down to 0. You will be doing two things, first and most importantly you will be making it safe.  It will not be spoiling at 0.  The next day assuming it is a reasonably nice day, apply the supplemental heat to the bin, using the day time temperature plus the heater we might be throwing air at it that is 20 C.  I would heat the grain all day.  The bottom will warm first but the heat will gradually get to the top.  It probably would take all day.  If you don’t get the heat right to the top, it is not the end of the world; but you must realize that you will only be drying the bottom when we cool it down. If your heater is big enough, the heat might get to the top; shut the heat and fan off and turn it on again at night to cool it down.  OK so let’s say that we got the temp of the grain to 15 C.  Then cool it down the following night to say 0, and we should have taken about 1 point out. Follow this same strategy 3, 4  or 5 days and nights and you should have at least the bottom dry. As the bottom becomes dry, remove it, and continue the process with the much thinner layer in the bin.  Do this heat during the day/ dry at night thing until that too is dry.
My second question is should I run the fans without heat to cool the grain down to outside temperatures?  Yes, I like your idea of only filling the bins to half, and then immediately cooling down to say 0 C. Once cold, it can sit there for a week or a month, waiting for its turn for a dose of supplemental heat   When I took the last sample the outside temp was 5 degrees and the grain was 13.8 oddly enough. I have read your blog and plan on doing cycles of heating grain up and then cooling it off. I have lots of space to move stuff around if needed so my plan is to run the heater to pairs of bins and fill half to 2/3rds full. Raise the temps of those 2 bins and then move to the next 2 while cooling the first 2 off. I could keep going in that rotation for awhile if needed. Perfect!
I would also be able to shift those bins to a number of other empty bins. Thirdly, when doing the cycling what temperature should a guy aim for on the top end. As warm as you can get it by applying heat for one day. Depending on the size of your heater, I doubt that you will be able to raise the heat at the top by more than 10 to 15 degrees.  I did some calculations on one of my blogs, I would have to check.  With a modest heater of 50,000 Btu/hr. I think you should be able to raise the temp of 4000 bu by 15 degrees  —  I would have to check — I would have to know your heater size, daytime temperature etc. It’s all about the specific heat of the canola.
Seeing as every 15 degrees is equal to 1% moisture should I aim for a grain temp of 15 and cool to 0 each time?  Yes
Judging by the weather for next 2 weeks it seems like that could be very doable. What calculations would I use to figure out how long this might take for each cycle?  Each cycle should be over a day.  Heat it up during the day, using the daytime heat,and then cool at night.  Always cool it immediately.  Do not leave the warm grain for any length of time.
Just so I can avoid combining too much too fast. Also, does the 15 degrees = 1% rule apply below 0? Would getting grain to -15 be the same as knocking off 1%? No it would not.  There are two things that would mitigate that rule of thumb 15C/%.   If the canola was dry, say 9% — if you cooled it 15C, you won’t get to 8%, you would only see slight drying.  And if it is cold; say you cooled the Canola from 0 to -15, my guess would be that you might take out a half a point?   The rule assumes the grain is tough, and the temperature is around room temp, 20C.
I appreciate the work you’ve done on this. We farm in area where dryers are rare and we’ve never experienced this kind of delay. Even in 2016 we were done combine the 3rd week of September.

—

Thanks,
Colin Cameron
Kenita Farms LTD

What I Would Do If I were Farming

I am not a farmer, but I grew up on the farm and have been involved in farming my whole life.  In doing so I have learned a lot about grain aeration from doing research and analyzing data, as well as from my past farm experience.

What I would do:

1. I would have all my bins equipped with open bottom plenums and quick attach — ready for small aeration fans.

2.  I would use small fans.  Since the flow only goes up with the cubed root of the power (HP). In going from 7 HP to 1 HP,  even though this is a drastic cut in power, the flow is not even halved. The capital cost is about a half.

POWER        FLOW                 PRESSURE      COST(Flaman)

10 HP            2,150 CFM              3.1             $ 2300

7 HP              1,91                         2.6             $ 2100

5 HP             1,700                        2.2              $ 1700

3 HP              1.44                        1.732           $ 1300

2 HP              1,200                       1.4              $ 1100 ??

1 HP             1,000                       1.0              $ 900    ??

OPI temp cable is $400, while a moisture cable is $1000.

3. Since I have aeration, I would use it and start my harvest when the grain is tough (2 points above dry). So if wheat dry is 14.5 %,, then I would start combining when the MC is 16.5%.   Getting an early start to harvest by a couple of days reducing the risk of having my grain exposed to the elements.  Also I could start combining earlier in the morning and go later into the evening if I am willing to harvest tough grain.

4.  We know that the bottom of the bin dries first, so I would put the tougher grain on the bottom, and the drier grain closer to the top.  Starting the harvest day with tough grain,– put it on the bottom, even if it meant moving to a new bin.

5. Start the fans immediately, even while filling the bins.   First day is critical.

6. Have a double temperature sensor (thermistor) hung in the center of the bin, half way down.  I would use two thermistors because of redundancy and validation. The cable coming through the top hole and down the side of the bin would be available to check the temperature of the grain with a handheld device and it could also be used to plug into a controller on the fan.

7. The controller on the fan would be attached to the cable in #6 and also be able to measure the temperature of the outside air. The fan would turn on if:  the outside air temperature < grain temperature.   AND if the outside air had a relative humidity <  adjustable RH (85% – 65%) So we need an adjustable RH sensor like the ones on humidifiers for residential furnaces.

8.  To determine where to set the RH in #7, I would use the grain calculator.  Set the grain temp, in the calculator, to what I measured the grain temp from the thermistors, the outside air temp also would be set to the grain temp; and the moisture content to my best guess as to what the moisture content is.   When we first load the grain into the bin, we probably would know the MC, and then for every 15 C that we lower the grain temp, take a point off this initial MC.   After all this is entered, push calculate and get the RH thres, looking through the list for the grain type in the bin.  Set the RH on the controller to the RHthres. For example:  let’s say we have barley that was loaded into the bin at 16% moisture (MC) and 30 C.  The outside temp is 22 C and outside RH is 73%.  So in the calculator we enter 16 for the MC,  30 for Grain Temp, and 30 for the outside air Temp.  Push Calculate,  the RHthres for Barley comes up as 75.9%.  So we set the RH on the controller to 76%.  Will the fan turn on?  Yes, the outside air < grain temp (22<30 )  AND the outisde RH is less than the setting (73% < 85%).     We come back the next day and we find that the barley has cooled to 20 C so we should take two thirds of a point off 15% -> 15.4%. Each day we check: First day     second day  third day   fourth day   fifth day

Moisture Content         16%               15.4%           15%             14.9%          14.9%

Grain Temp & Air T      30                   20                   15               13                 12.9

RH set to RHthres         75.9                 70.7               67.2             66                 66

Why do we set the Air Temp in the Calculator to the Grain Temp?  Because that is the worst case RH, and it sets the Absolute Humidity.  If this is graphed on the Psychrometric Chart we see that as the temperature gets colder, the same RH produces a smaller Absolute Humidity Value.  Or even drier air is required to turn the fan on.    Lowering the setting on the RH knob will also lower the duty cycle of the fan, as it should because we are starting to cherry pick and have the fan on only when there are good drying conditions.   If we are in a little more of a hurry to dry our grain, then we should leave the RH setting higher.  This would be at the risk of having the fan run when there are slight wetting conditions when the grain temp and air temp are almost the same.  But it will not miss as much of the drying conditions.

9, Supplemental Heat:  See the other blogs on supplemental heat.  This is only required if the MC is more than 2 points above dry.   There is no way around it, it will cost money to dry the grain — but I do think it can be done for about 10 cents per bushel per point dried.  I have worked out a number of examples in previous blogs.   In general we want to heat the grain during the day, using the naturally higher temperatures of the day, and then cool at night using the cooler dry night air.   Use the rule of thumb.  For every 15 C cooled is a point removed MC.

10. For a bin that is a bit stubborn in getting dry.  I would tip the bin by taking out a few hundred bushels from the bottom to invert the cone at the top.

11.  Seal the bin in January after we have cooled the grain down as cold as possible.  Get the mindset.  The colder the better.  The colder the safer.

You might ask why I would go with the differential temp controller as opposed to the absolute humidity controller.  Yes, the absolute humidity controller is theoretically the best, and controls the fan such that it catches all the times we have drying conditions.  The differential controller misses some slight drying times because we are not willing to sit there and do the calculations every hour, so we set the RH to the worst case.  However when one considers the cost, simplicity and reliability I think it is the better choice.  The overall system is inexpensive and you don’t really need the expensive internet monitoring, or computing. The controller on the fan is very simple, inexpensive and reliable. The absolute humidity controller requires a calculation of the absolute humidity, which is fairly complicated.  As well we must rely on relative humidity sensors that I have found to be expensive, not that accurate and not that reliable. I have had many RH sensors go bad on me.  Any foreign material that gets on the film — they are toast.  So the absolute humidity controller is fine for the perfectionist who demands the optimum (the researcher); but a farmer is looking for the best answer in getting the job done with a balance of effectiveness, cost, and reliability.

If one goes out and manually checks to make sure the temperature of the bin is low i.e. that the system is working, then we know that our grain is safe, not spoiling and really that’s the most important thing.

 

 

 

What RH is low enough to Dry?

I have been asked this question again and again and the first thing I say is that the temperature is more important than the Relative Humidity (RH).  So first, only turn the fan on if:       OutSide Air Temp  <  Grain Temp.

However, doesn’t the RH of the outside air and the Moisture Content (MC) of the grain also come into play?  Absolutely.   And the way we can answer this question is to use the calculator   planetcalc.com/4959/     Make the grain temp and air temp the same and try at  10 C       20 C      30 C   and calculate corresponding RHt

Flax    9% MC                        61.6%    66.2      70.4

Flax   10% MC                       68.1         72.1      75.6

Flax   11%                               73.2        76.7        80

Flax    12%                              77.4         80.4        83

Wheat 16                                 73.5        75.6

Wheat 15                                  68.3        70.6

Wheat 14                                   62.4        65

Yellow Peas 16                            73.5      75.6

Yellow Peas 15                            69          71.3

Yellow Peas 14                            63.8         66.4

Conclusion:   If one is to build a controller that is controlled by temp, that is:

Fan On IF:      Outside Air Temp  <  Grain Temp      on must also consider RH,

AND    Outside Air RH <    80%    to start when grain temp and MC high

<   70% when grain  cooled and MC close to dry

We almost need to have the RH on a variable knob, so that on the first day when we first start the fan after filling the bin, the grain is warm and maybe a little on the tough side, we put the RH knob to 80%.  After a day or so, the grain will have been cooled down, and therefore drier, so we might put the knob at 75%.  And then, maybe after a week or so we turn the knob down to 70%.  Following this practice should keep the grain cold and only have the fan on when we have drying conditions.   This would make for a simple reliable controller that would keep the grain safe and dry.

Recommendations for Grain Aeration

I have 11 recommendations for aeration.  These are conclusions that I have reached after considering all that I have learned in the past years from the data collected and analyzed, farmer discussions,  and practical considerations.

  1. All steel grain storage bins should be equipped with aeration storage bins.  To prevent spoilage, the grain must be cooled, even if it is dry.  The stored grain is very valuable, and cooling the grain is a very cost effective means of ensuring its safety and protecting its quality.  Even if the bin is not near grid power, a gen-set could be used to power the aeration fan for a couple of days to cool the grain.
  2. Smaller fans could be used.  We don’t really need the 10 or even 5 HP fans. One, two and at most 3 HP fans will do.  There are many advantages to do this.
    • Reducing the fan size from say 5 hp to 1 hp, does not reduce the airflow by the same ratio. The airflow might be halved.  If our main concern is to cool the grain, then the cooling might take twice as long — instead of taking one night to cool, it takes two. So what. But the power we use is only 2/5. We save power.
    • The infrastructure of installing large power sites is reduced tremendously.
    • Lower capital costs.  A one hp fan is obviously much less than a 5 HP.
    • A smaller fan is more portable.  One fan can be shared with many bins.
    • A smaller fan creates less pressure, which in turn causes less difference in top to bottom temperature, (from compression) and less difference in top to bottom moisture content.
  3. Open bottom screen.  I have observed a loss of 1 inch of water, or more going across the screen.  What a waste.  An open bottom screen would essentially reduce this loss in pressure to zero.
  4. Fan on first day and night until 9 the next morning.  We observed time and time again that we got as much as a 1 % reduction in Moisture Content in the first 24 hours.  This was even more evident when the grain came off the field hot. The fan should be turned on even as the bin is being filled.  We want to get the grain cooled down immediately.  Stop the spoilage as soon as possible.
  5. If no sensors and no knowledge of anything, not even the MC or temp of the grain, then use the YardLight Rule to turn the fan on. “On at night, you are bright; on during the day, you will pay”
  6. If we know just a little bit — let’s say the Grain Temperature and the Grain Moisture Content; then one can use the Calculator to determine if drying will occur:   www.planetcalc.com/4959/
  7. Many farmers have a temperature string in their grain, and they don’t know anything else.   The moisture content of the grain is unknown.  We do know the temperature of the air outside and its relative humidity.   We should then turn the fan on if:    Air Temp Outside < Grain Temp   AND   the RH outside < 80%  Better yet this simple algorithm should be realized with electronics that does this comparison continuously and controls the fan automatically.  This control algorithm is slightly less effective than the Absolute Humidity Controller BUT it is simpler, less costly,(requires no math or computer), and is more reliable. A simple thermistor in the bin will provide the temperature, and the temp and RH can easily be measured right at the fan. The electronics consists of a comparator and an actuator.   This would be my choice for an automatic controller, even though the optimum controller is theoretically the Absolute Controller.   The Absolute Humidity Controller requires the Grain Temp and RH as well as the Outside Air Temp and RH. The RH of the grain can be measured with a sensor, but it is not that accurate, and can easily be damaged with dirty air AND these sensors are much more expensive than the temperature sensor.  The other way of obtaining the RH of the grain is through EMC equations, but then one must know the grain type, the temp of the grain, and the MC of the grain.  This requires a computer.  More money, more complication, and therefore less reliable.
  8. Cool grain til January, then seal the bin until July.  Let the grain warm up naturally through the walls of the bin.  And then if you are going to store the grain for another year.  Unseal the bin and apply the fans using #7 until January. This will keep the grain as cold as possible, with the least spoilage.
  9. To obtain the temperature of the grain, two thermistors should be placed in the center of the bin, just a little higher than half way up.  Why two thermistors?  For reliability and validation.  If the two thermistors are reading the same value, then you can be assured that you have a reliable temperature value.
  10. The bottom always dries first, so one could remove a couple of hundred bushels from the bottom after a week or so.   Especially if the grain went in with a MC that was more than 2 points higher than dry.   In taking out the dry grain at the bottom, it would invert the cone at the top, and lower the overall depth as well as providing some mechanical movement, all to enhance the drying.
  11. Supplemental Heat might be need for MC more than 2.5 points above dry.   Use the natural bounce of the day by pumping energy into the grain during the day, and then by cooling and drying at night.  Also consider using #10 with this.

CFM calculations for 2017

The following are calculations for the CFM and CFM/bu. for the eight bins we had trials on for 2017. We measured the airflow into the fans in km/hr. so the first conversion is to get this into ft/min because we eventually want to get to cubic feet per minute.

kmph –> ft./min 1 kmph = 0.9113 ft/sec = 54.678 ft./min   H2O pressure

Bin 18 (3500 bu, Diam 23″) 11.2 km/hr x 54.678 = 612.4 ft/min x Area (pi r^2) 23/12/2 2.88sq ft = 1767 CFM /3500 0.50 CFM/bu          5.5″/7.4″

Bin 19 (3500 bu, Diam 23″) 11.2 km/hr x 54.678 = 612.4 ft/min x Area (pi r^2) 23/12/2 2.88sq ft = 1767 CFM /3500 0.50 CFM/bu          5.5″/7.4″

Bin 9 (2200 bu, Diam 15″) 30 km/hr x 54.678 = 1640 ft/min x Area (pi r^2) 15/12/2 1.22 sq ft = 2013 CFM /2000   1.0 CFM/bu                3.25″/5.0″

Bin 10 (2200 bu, Diam 15″) 30 km/hr x 54.678 = 1640 ft/min x Area (pi r^2) 15/12/2 1.22 sq ft = 2013 CFM /2000 1.0 CFM/bu              3.25″/5.0″

Bin 15 (10000 bu, Diam 15″) 70 km/hr x 54.678 = 3827 ft/min x Area (pi r^2) 15/12/2 1.22 sq ft = 4669 CFM /10000 0.466 CFM/bu  6″ (inside )

Bin 14 (5000 bu, Diam 15″) 85 km/hr x 54.678 = 4647 ft/min x Area (pi r^2) 15/12/2 1.22 sq ft = 5669 CFM /5000 1.13 CFM/bu                            5″

Bin 16 (3500 bu, Diam 16″) 18 km/hr x 54.678 = 984 ft/min x Area (pi r^2) 16/12/2 1.39 sq ft = 1373 CFM /3500 0.3925 CFM/bu                  5″/6″

Bin 16 (3500 bu, Diam 16″) 18 km/hr x 54.678 = 984 ft/min x Area (pi r^2) 16/12/2 1.39 sq ft = 1373 CFM /3500 0.3925 CFM/bu            4.8″/5.75″

The pressure is in inches of water ; the first number is outside the plenum and the number after the / is the inside of the plenum, so you can see the pressure drop across the perforated holes in the pipe.