Convection Current Flow Rates

We have all seen those little diagrams of curved pointed lines that indicate convection currents in a grain bin.  How in the winter the air flows up through the middle and down the sides, and then in the summer where it flows down the center of the bin and up along the warm side walls.  We can also get convection currents right through the bin with air flowing through the fan, vents, and center opening.  But just how fast is the air moving with convection currents? Let’s see.

First of all, the only reason we get convection currents is because of the air being at two different temperatures.  Air is heavier if it is colder.  A column of cold air has more weight than a column of warm air, and consequently will push down with a pressure equal to the difference in weight.

According to , the weight of air is:

ºC         ºF         lbs/ft^3

10        50          7.786

21.1     70          7.492

32.2      90         7.219

If the outside air and the grain are the same temp, the air in the bin and air outside will have the same weight and there will be no pressure difference and therefore no convection current through the bin.   But let’s say that the grain is at room temperature of 21.1ºC , 70ºF, and the outside air is at 10º C.  That is quite a difference in temperature and also a difference in weight, 7.786 – 7.492 = 0.294 pounds per cubic feet.  But the grain in the bin is 20 feet high, so 20 x 0.294 = 5.88.  A column of air, 20 feet tall,  inside the bin weighs 5.88 lbs more than a corresponding 20 foot column of air outside. But 60% of this column is occupied by grain, and only 40% is air; so this column of air is only 2.35 lbs heavier.  But that is the pressure exerted over one square foot, psi or pounds per square inch is a more common unit of measure for pressure. 2.35/144 = .016 psi  This isn’t very much pressure, when you think of our car tires have 30 psi.   Another common pressure unit is inches of water.  How many inches of water would this pressure support? One psi would support a column of water 27.68 inches.  0.016 psi is equivalent to 0.452 “H20.

To determine the flow, one must have some appreciation for the grain resistance. From our past trials we saw that 3000 CFM required a pressure that would support 6 inches of water. Now if we said that pressure and flow were in a linear relationship, (it is not –it is closer to a squared),  the convection current would be about one thirteenth or 226 CFM.  This is a reasonable flow.  The bin we had was about 200 sq feet. so a flow of 226 CFM would be a vertical speed of 1 ft per second or about 1 kmph; but then again one must remember that this is only for a very significant temperature spread; as the temperature of the grain and the outside temperature become less, so too would there be a reduction in the convection current.

Avoid Condensation During Cool Down

Hi Ron it Jamie @ Victoor Seed Farm Inc. We had talked last fall about grain drying. I had a question for you. We are having a wet fall so far in AB. Relative Humidity Very High but if air temp around 8’C at night and grain @ 24’C will I put much moisture into Bin as I want to Just Cool Grain Down. We only have Temp Cables in Bin not moisture & Temp Cables. Grain from 13% Moisture with 2000 Bus of a 10,000 Bus Bin Testing 16%

On Sep 7, 2016, at 2:18 PM, Ron Palmer <> wrote:
> Jamie, this is exactly what my grain drying calculator was made for.  You can find it at  you just punch in the moisture content, 16, and the grain temp, 24, and the outside air temp of 8 and it comes back and tells you the outside relative humidity, below which, drying will occur.  If you scroll down to hard spring wheat it will give you 214.4%.  This means that as long as you have an outside relative humidity of less than 214 you will be drying your grain.  So, let’s say the RH is 85% outside;  85 is much less than 214, so yes you will be drying, and because there is such a huge difference, you will be drying a lot.  However you have another problem–a big problem.  The moisture coming off your grain will condense when it hits the cold roof walls and roof, and the moisture that you just got out of your grain is going to be raining back down onto your wheat.  You should have cooled and dried your grain as soon as you put it in the bin, before it got so cold.  But what to do now?  Turn your fan on when it is warmer so that condensation will not occur.       I used the calculator and plugged in 20 for an outside temp, and it came back with a threshold RH of 97.4   In fact any number below 100 and you won’t get condensation on the inside of your bin.  So, let’s say you turn your fan on when it is 20 and RH is 70.  Will you be drying? Yes quite a bit.  Will you get condensation? No   The temp of the grain will come down fairly quickly, in just a few hours of running your fan the grain temp will maybe go to 22, and then we can use a lower outside temp. and still be below the 100.   And sure enough these numbers give a calculated threshold RH of 97.5
> So, here is what you do.  Wait for a slightly warmer day of 19 to 20 degrees.  Turn your fan on and as the temperature of the day goes down, the temp of the grain will also go down.  I am thinking that you should be able to chase the grain temp down fast enough so that you won’t be getting condensation.  But you can use the calculator to make sure you are not in a situation where the threshold RH is larger than 100.    I have loaded the grain drying calculator onto my Iphone and use it like an app.
> Another thing,  we found that cooling your grain down by 15 C will typically remove 1% moisture.  You cooling the grain from 24 to say 9 C should get your moisture close to 15%

FAQ: Why has it taken so long to discover these new grain drying techniques.

I was doing some reading from a comprehensive text on grain drying: “Drying and Storage of Grains and Oilseeds” by Brooker.  It occurred to me that there were some preconceived notions about grain drying that have held in abeyance some of findings that I have published in my blog.  Sometimes researchers must make assumptions to fill in for gaps in the unknown.  But that doesn’t mean that the assumptions should be challenged when more information comes to light.  I believe that is what is happening here, now that we have hourly data of what is happening for grain drying on farm sized bins in a typical prairie environment. I think it would be interesting to discuss the status quo assumptions.

  1. For the ambient drying conditions, the mean or average temperature is used. But there is a large difference in the high and low temperatures during the day.  Our data was collected hourly and a compilation of many years of experimental data has led to the discovery of the diurnal drying cycle, that drying takes place at night and quite commonly wetting occurs during the day.
  2. In the literature,  there is mention of the outside air (at the mean temp) comes into equilibrium with the grain.  And the implication is that this equilibrium comes about instantly.  It implies that the grain becomes the same temperature as the air.  But what actually happens is that the air becomes the temperature as the grain.  Grain is a thousand times more dense than air, and holds way more heat.  Sure after many many air exchanges the grain will start to move to the temperature of the ambient air.  But the ambient air is not at a constant temperature (assumed again to be the mean), it is changing all the time, hour by hour. As such the ambient air and grain are never in equilibrium.
  3. Farmers and researchers both know that the top of the bin is the last to dry.  Some of the literature even talk about a drying front or drying zone moving upwards.  Our data showed that the bottom grain tended to be a few degrees warmer than the top.  This indeed would cause the bottom to dry more.  But what is causing the increased heat at the bottom.  I believe it is compression.  When a gas, like air, is compressed it immediately heats up and as the air works its way to the top it decompresses and subsequently cools.  It is quite typical for a fan to produce a pressure of 5 or 6 inches of water, and if one works through the math for this pressure increase with the equation, PV=nRT, one will see that indeed the temperature will increase with the compression.  This is important to understand because the way to mitigate this top/bottom drying difference is to use smaller fans with less pressure.  I have seen recommendations that would suggest the opposite.  This problem can be solved by using bigger fans with more air flow, which can only be achieved by having more pressure, more compression.
  4. It is suggested that aeration fans can be used for drying with a higher airflow of 1 CFM/bu  or it can be used for cooling at a lower air flow of  0.1 CFM/bu.   Our data shows that drying can also occur at lower air flows and that drying and cooling are synonymous.   Our data shows that cooling the grain with an aeration fan will dry it.  Heating the grain typically wets it.  Pyschrometric equations provide the rationale for this occurrence.
  5. The latent heat to dry the grain must come from external sources or from the ambient air.  The inherent heat in the grain itself does not seem to be considered.
  6. There is no scientific reasoning to determine what the air flow rate should be.  I have seen recommendations like: “Get to know from experience”  or the popular belief is 1 CFM/bu for drying,  0.1 for cooling.  But I have not found any basis in science to back this.
  7. No control strategy.  It is assumed that the fans will run continuously, 24/7, and the number of drying hours are based on the mean temperature.  It turns out that there are periods of time with wetting.
  8. The way to prevent spoilage is to get your grain dry, and to do it as quickly as possible.  Indeed having your grain dry is an important factor in preventing spoilage but having your grain cool or cold is even more important.  We can get the grain cooled quickly, but it might take days or weeks to get it dry.  We have been kind of brain washed into thinking that the only thing that is important is to get your grain dry.   What is of utmost importance is to get your grain into a safe condition, one with the least spoilage.  We have to change our mindset into thinking:  “How can I get my grain into a safe condition, with the least spoilage, as quickly as possible?”  We can take our time at drying, what’s the hurry?
  9. A humidistat can be used to determine when there are drying conditions.  I read yesterday that one researcher felt that setting the humidistat at 55% was the threshold humidity.  What’s wrong with this?  First a humidistat measures relative humidity not humidity.  And relative humidity and absolute humidity are not the same.  If you give me the temperature and the relative humidity, I can calculate the absolute humidity, but by just giving the relative humidity it means nothing.  It seems to me that the implication is that one should be using the mean temperature again.   I am not sure — but I will say this, using just a humidistat will not be a good control strategy for your fan.  I know this from experience.  In the 1970s we had a grain dryer that we tried to use a humidistat for control — it did not work at all.  And logically now, I can see why.  We now know that if the air in the bin has more water in it (absolute humidity is high) than the ambient outside air; we will have drying.  Let’s say the air inside the bin is 20ºC @ 70% RH, using the absolute humidity table –> 12 gr/m^3 .  Now let’s assume the humidistat is reading an RH of 55%, will there be drying?  Yes if the outside air temp is 10ºC @ 55%  gives an absolute humidity of 5 grams, which is less than the absolute humidity of the air inside, 12 gr so we will have drying.  For every cubic meter of air flowing through the bin there will be 7 grams of water removed.  However let’s see what happens if it is not 10ºC, but rather much warmer at 25º C.  Then the absolute humidity for air 25ºC @ 55% RH is 13 gr.  At this temperature, for every cubic meter of air that flows through the bin we will be adding 1 gr of water.  We will be wetting the grain down.  In conclusion, we see that relative humidity means nothing, unless it is qualified with a temperature.
  10. You have to have heat to dry and drying can only take place on hot days. And yes there is some truth that it does take energy or heat to evaporate the water from the grain.  But the heat does not necessarily have to come from the air. There is a significant amount of heat in the grain itself especially if the grain is at a higher temperature.  The trick is to use as much of that inherent latent heat in the grain for drying.

What are Drying Conditions? Grain Drying 101?

What are the outside air conditions necessary for the drying of grain?   It really is the ultimate question for grain drying.

To determine the threshold relative humidity for drying, we need to know a few more things: the moisture content of the grain, the temperature of the grain, and the temperature of the outside air.  With these we can determine the threshold relative humidity; if the relative humidity is greater than this, we will not get drying in fact we will get wetting and if the relative humidity is below this we will get drying.   The more it is below this threshold, the more it will dry.

But before we get into this, we need to understand the basics of grain drying.  Air  carries the water from the grain.  If the air entering the grain bin acquires more water as it flows through the grain, drying will occur.  If the air being expelled from the bin has more water in it than the air entering the bin through the fan — there will be drying.

The amount of water that is in the air is called the absolute humidity and typically has the units of grams per cubic meter.   A cubic meter of air, one meter by one meter by one meter, will be carrying a certain amount of water, W, and it can be precisely determined from its temperature, T,  and its relative humidity, RH, using the following pyschrometric equation:

W = WS x RH/100

Ws = 0.000289  T3 + 0.010873  T2 + 0.311043 T + 4.617135

Where W (grams/m3) is the amount water in one cubic meter of air, Ws (grams/m3) is the maximum amount of water that saturated air can hold at a specific temperature (T), expressed in 0C, and relative humidity (RH)  %.

To avoid the math, a graph can be used:

Water in the Air
Water in the Air  can be determined by finding the temperature of the air on the horizontal axis and then going up to the relative humidity. The absolute humidity is horizontally to the left.  For example, if the air is 25º C with a 50% relative humidity, it will be carrying 12 grams of water per cubic meter.

A table could also be used and again a temperature of 25 ºC with a relative humidity of 50% will have air carrying 12 grams of water.  Sat Table



There is also a calculator online that can calculate the absolute humidity:

So, there are a number of ways to determine the absolute humidity of the air. If one knows the temperature and relative humidity of the air; the absolute humidity can be found by doing the math with the equation, or by using the graph or the table, or by going online and using the on-line calculator.

Now drying will occur if the absolute humidity of the outside air entering the bin through the fan, is less than the absolute humidity of the air being expelled from the bin.  For example, let’s say that the air outside entering the bin is 15°C @ 55% RH. The absolute humidity of the outside air is:  12.7 gr.  X  0.55 =  7 gr/m3.  The air being expelled is 25°C @ 45% RH with an absolute humidity: 23.7 gr x 0.45 = 10.67 gr/m3.  So for every cubic meter of air that flows through the bin of grain there is 10.67 – 7 = 3.67 grams of water being removed. Drying is occurring.

It should be noted that even though the relative humidity (RH) of the air entering, 55%, is greater than the RH of the air being expelled, 45%; the absolute humidity of the expelled air is higher than the outside air.  Relative humidity, by itself, means nothing; but if one knows both the RH and the temperature, then RH is very useful and can be used to easily calculate the absolute humidity.

If one knows the air flow through the bin, one can calculate the amount of drying.  In the above example 3.67 grams of water was removed for every cubic meter of air that flowed through the bin.  If the airflow was 3000 cubic feet per minute, CFM, then:

  • Are we drying? Yes 10.67 – 7 = 3.67 gr/m3
  • How much? 3000 CFM = 180,000 ft3/hr.

180000/35.41 x 3.67 = 18.6 kg/hr.  water  is removed every hour

The problem is that the air temperature and relative humidity continuously change during the day.  The temperature during the day can be more than 10 ºC higher than at night.

The above technique was used to measure the amount of grain drying done on an hourly basis with farm sized grain bins.  19 experimental drying trials were done with the fan running continuously, and the drying data was compiled to determine the amount of drying that was done in terms of the time of day.  A diurnal drying cycle was determined:

Diurnal Cycle

It can be seen that the greatest degree of drying occurred at night at about 2:00 AM, wetting occurred during the day, 14:00 or 2:00 PM and the transition from drying to wetting occurred at about 9:00 AM.

If drying occurs at night, and wetting during the day; wouldn’t it make sense to run the fans when we typically have the best drying conditions?  This was the basis for the recommendation that the fans should not be run continuously but rather only at night — the yard light rule:

On at night, you are bright; on  during the day, you will pay!

Finding the absolute humidity of the air inside the bin  involves the use of the temperature and relative humidity, but the bin is probably not equipped with relative humidity sensors. The relative humidity can be determined indirectly by  the use of EMC (Equilibrium Moisture Content) equations  —  a topic for another blog.

Notes to self about ideas for Future Blogs

  1.  Grain Drying 101    Drying Conditions if the absolute humidity of the air inside the bin is greater than the absolute humidity of the outside air.  Explain what absolute humidity is:  amount of water in one cubic meter, explain how it is different from relative humidity,  and that absolute humidity is calculated from the saturation curve and pro rated with the relative humidity.  Diurnal cycle and the night drying and the yardlight rule.
  2. Motor/Generator Set to make a portable system.  Especially good for remote sites that have no power.  Make use of the wasted heat from the motor.
  3. Plenum design, show how we waste energy (pressure) in going across the screen.  Better to use the electricity with a heater in front of a small fan. The pipe or plenum should be open on the bottom for the least resistance in getting the air into the grain.
  4. Time Constant Tau.  The time constant is the amount of time required for the outside air absolute humidity to get to 60% of the distance of the difference. A CFM/bu of 0.35 would be about 3 time contants and get us to over 90% of the way there.  This blog would show that 0.35 CFM/bu is kind of the sweet spot for using as much of the grains energy as possible, while still drying in a relatively short time.
  5. The argument for small fans:  less capital cost, less power infrastructure required, more uniform drying, use more of the inherent grains heat to dry, more efficient  — the downside is that it is a bit slower — but what is the hurry? How slow can you go.  The ideal fan size. CFM/bu
  6. More on condensation, and how to use the grain drying calculator to detect conditions for condensation.
  7. More specifics on how to use the grain calculator.
  8. Something for everybody, from the simplest strategy (yard light rule)  to the most advanced (absolute humidity) and the pros and cons of each. Depending on what you have.
  9. Long term storage, use whatever fan strategy until the end of January, in which you will get the grain frozen and cold as possible, and from January til the end of July keep the bin as sealed as possible.
  10. Roof vents don’t do much, and can actually result in condensation on the top layer of grain in the spring when the grain is cold and it is swiped by warm moist air circulating through the vents.
  11. Vertical in grain tubes.
  12. top dries first, compression causes heat
  13. safe days
  14. comparison of control strategies, continuous, nite, temp differential, absolute humidity.
  15. Flow from natural convection
  16. Energy in the grain to dry
  17. Grain Resistance
  18. Motor HP as we drop the flow in half, top down drying, HP 5 to 1
  19. First 24 Hours is critical
Ron Palmer
Ron Palmer

Short Answer for Grain Aeration

I get asked this straight forward question about grain drying all the time.
My cousin Mark recently emailed me:
I was reading an article about grain drying with aeration that you worked on.
 You mentioned that it is best to run fans at night.
We have some peas that are dry but with some green kochia and other weeds.
We will have the same with some wheat that we will combine soon as the Kochia will get swathed but I suspect it will not dry down much as we will combine in probably 5 – 7 days.
What is the recommended drying – cooling times and what concerns should I have with Humidity and Temperature?
I replied:
I don’t have a really short answer to question, but even if you didn’t know anything else, this would be a good rule to follow — even if your grain is dry.
1.  As soon as your bin is full (even before it is full) turn the fan on and run it until 9:00 AM the next morning.  The exception to this rule would be if it is raining or very high humidity.
2. Thereafter, run the fan every night until your grain is cooled down and dry.  This might be for a few nights, or it might be for several weeks if you have tough grain.  The cold clear nights will be the most effective for drying.  Again if it is raining, don’t run the fans.
OK that’s the simplest; if you want to be more precise about drying conditions, you would only want to run the fan when there are conditions for drying and that is when the absolute humidity of the air outside is less than the absolute humidity of the air in the bin.  Absolute humidity is the actual amount of water in the air.  It is not the same as relative humidity; but relative humidity can be used to calculate the absolute humidity.  And they are kind of ugly equations that are tough to do even with a calculator.  So, I made an internet calculator that does the calculations for you. It can be found at   You can load it onto your cell phone and use it like an app.  You simply enter the moisture content of your grain, the temperature of your grain, and the temperature of the outside air.  It calculates, what I call, the threshold relative humidity.  If the relative humidity of the outside air is less than this you will have drying conditions and the fan should be turned on.  If the outside air’s relative humidity is greater than this, you will not have drying conditions and obviously you should keep the fan turned off.  If you really want to get up to speed on grain drying, read my blog at   It explains everything, even why you get condensation in a bin and why the bottom always dries first etc.

Another rule of thumb that mostly works (98% accurate):  You will have drying conditions when the outside air is at a lower temperature than the grain temperature and the relative humidity of the air < 85%   This is not as accurate as the calculator because it does not take into account the moisture content of the grain; however it does not require any calculations or calculators

I hope this helps, let me know if you have any other questions

Thanks a bunch Ron.
As long as the relative humidity outside is less than 85 in the evening – I will run the fans and turn them off in the morning
Last night Environment Canada showed the Humidity at 90% so I should not run them at that point

Grain Drying Questions from Quebec

Here is a question I got from Quebec:

“Mr. Palmer, Last fall we discussed a lot about grain ventilation. I remember how you where generous on this subject. I want to share with you what we do. This year we will do other observations. The producer where we will make observations will get a 4 noodles cable with Stormax. (20’ x 20’ silo). However, control will be executed by water balance at least for the stop time. Re-start will be done manually or by timer followed automatic running. I will try to share you these informations including stormax data if possible. Do you think this approach is good ? Do you have suggestions ?

The producer is supposed to fill it with 2-3 crops (first : rye…temporary storage, second : Oats…temporary storage, third : soya). In the litterature I did not find EMC equation for rye. Is it similar to wheat ? Do you think Opi systems have it ?”

I gave the following reply:

Good to hear from you. I will try to answer your questions. I am not sure what a 4 noodle cable is, I am assuming it is one with 4 senors, that is 4 sensor temp and 4 senors for relative humidity. I am assuming that you are doing a water balance to stop by calculating the absolute humidity of the discharge air and comparing it to the absolute humidity of the inlet air. And you only stop the fan if the absolute humidity of the inlet air is greater than the absolute humidity of the discharge air? Great. To turn the fan on we can’t use the discharge air, but we do want to know what the absolute humidity of the air in the silo is? There are two ways to do this. 1. this is the best way and it can be done if you have a temp and RH sensor in the core of your grain or crop. Use the T and RH as you did before to determine the absolute humidity. 2. If you don’t have the RH sensor in the body of grain, and only the temp of the grain, you can use EMC equations. By plugging in the moisture content and temp of your grain, you can determine the RH to which it will find equilibrium. Use this RH and T to determine the absolute humidity. If this absolute humidity is greater than the absolute humidity of the outside air, then you have a drying condition and the fan should be turned on. You can use the calculator that I made to do this for you. Just plug in the temp and moisture content of your grain, and the outside temp, and the calculator gives you an RH thrreshold, if the outside RH is below this then you will be drying, anything above this, and it will be wetting. Actually the only thing I am doing with the calculator is the math for the EMC equations. And no I don’t know the EMC equation for rye, but with a little digging I am sure I could find it. I think it would be OK to use wheat — it would be close.
My calculator can be found at Grain Drying Calculator

Grain Drying all comes down to something pretty simple. If the outside air has an absolute humidity less than the absolute humidity of the air inside your bin or silo, then you have a drying condition. The only thing you need to calculate the absolute humidity is the temperature and the relative humidity. When the fan is on, the relative humidity is read at the point of discharge and when the fan is off you get the relative humidity by reading an RH sensor directly in the body of grain, or if you don’t have this RH sensor then you must resort to using an EMC equation (or my calculator) to determine the RH.


Still thank you Mr Palmer, Yes it is supposed to be an Opi Cable with 4 points reading of T, RH and EMC. When you talk about a T&RH sensor in the grain, what position do you suggest : at the top, at the surface or in the grain and if so how deep ?

The sensor in the grain, the RH & T sensor, should represent as much as possible the entire grain bulk. We know that the bottom has more variation than the top. So I am thinking in the center of the bin or silo, about two thirds to three quarters the way up. You don’t want it too high because shrinkage may lower the grain and leave the sensor exposed to the air, which can be greatly influenced by the open discharge port. We also considered averaging several sensors to get an average T and RH, but one can get into trouble really quickly because the pyschrometric equations to calculate absolute humidity are non-linear, so I think using just a single sensor might be better.
Also the fan must be off for some time to use this sensor, as one must wait for the air in the grain to ‘equalize’ with the grain. I am thinking at least a half an hour or maybe an hour..
Ron Palmer


Integris of Opi Systems has the capability to start and stop automatically the ventilator by comparison of grain EMC with air intake. To stop ventilator, how this decision is good considering air is not equalized with the grain. To be correct and to take the good decision, ventilator should it be off for a while and then make the calculation after 0,5-1 h ? Do you think so ? Another explanation : Would they correct the reading, considering it is not in a stabilized situation ?

I also ask myself if the decision to stop or to start is depending of one, a combination or the average of all sensors in the bin.

I hope all these questions are not bothering you. Your informations are very usefull to understand.

EMC is equilibrium moisture content, notice the word equilibrium! You must wait some time for equilibrium to occur. Our data shows that you can not correctly do an EMC while the fan is running. You get the wrong value.  The correct way to control the fan is with the absolute humidity, and if you have RH sensors, there is no need to even do an EMC.


Where are we going with Mechanized Farming?

I have been away for awhile as I was on holidays and then I got caught up in domestic chores.  I have been meaning to do some blogging for awhile now, but that task has been degraded to a lower priority.  I have been thinking about expanding my blogs to more than just grain drying, although I will continue with that as well.  I want to turn my attention to my old work of agricultural mechanization.  Here are some of things I am considering blogging.

  1.  I have been in agricultural innovation for most of my career, and I would like to put some ideas that could be used to “think outside the box”.  We get so used to doing things a certain way, that we don’t even consider new ways.  If I were teaching the growing of crops to students, I would give them a real project.  I would supply a bag of seeds, of which each student would select ten. At the end of say a hundred days, we would grade the students ability to grow the best plants by measuring the yield originating from those ten seeds.   Then looking at the ones with the best results — study exactly what was done in the growing process. Now it is just a matter of joining the dots in coming up with the machinery to do this on a much larger scale.
  2. Getting rid of herbicides:  If we grew plants in rows, or better yet grids in which the plants are equally spaced in the row, we could actually use the plants as guides or beacons and track and lock onto the position using simple video imaging.  Anything green that is not in this grid, would by default be considered a weed and be removed with the surgical guidance of a water knife.
  3. Small is more efficient.  I would go through all the reasons that small equipment, like maybe 8 feet wide, is much more efficient than the large wide equipment we have now.
  4. Direct injection spraying.  Why aren’t we going there??
  5. How mechanized do we want to get?  Are we building a house of cards.  Are we really helping the world by taking that very small farmer from subsistence.
  6. Do we really want the highest yield no matter what?  The cost?  The environment?

Condensation a problem in fall and spring.

In a previous blog, I explained how condensation could be a problem in the fall with warm grain and cold outside air.  The rough rule of thumb was that there was a potential for condensation on the roof if the grain was ten degrees warmer than the outside; but a more precise determination could be made with the grain drying calculator.  The recommendation was not to turn your fan on if the RH from the calculator was above 100%.

There is another time, in the spring that condensation could be a problem. When the grain is very cold and the outside air temp is much warmer and holding a fair amount of water. This air enters the bin through the fan entrance, the top or vents; and it hits the cold grain — it will cool past its dew point and condensation may well occur.  This will happen mostly on the poor old top layer, that may well have had water dumped on it from fall condensation, and it is the last layer in the bin to dry.  No wonder the crust always forms on the very most top layer.

To prevent condensation in the spring, the best thing to do would be to not let the warm air in.   The bin should be sealed.  The top lid closed tight, the fan covered and all vents covered.  Indeed, this is a time when vents will actually be the cause for grain damage.  Sealing the bin in mid winter, after the grain has been cooled to its lowest possible temperature, will also keep the grain as cold as possible for as long as possible.  Yes the grain will still warm up from conduction through the walls; but it will be a warming without adding water.  At the end of the summer, when the grain has warmed up and the nights again are getting cold, the bin can be opened up and the grain again cooled.  And this process could be done for years of very safe grain storage.

Energy to Lower MC by 1% for one bushel of wheat

With this blog, we would like to know what it might cost to use supplemental electrical energy to remove one percent moisture content, MC, from one bushel of wheat.


  1. All the energy goes into evaporation.
  2. wheat  60 lb/bu
  3. Cost of electrical energy  is 0.12/kW hr.
  4. Latent heat of evaporation,  energy to evaporate  2257 kJ/kg

One bushel is 60 lbs, so 1% MC would have a weight of  0.6 lbs or 0.2722 kg

2257/.2722 = 614.4 kJ to evaporate 1% MC from one bushel of wheat  and to put this into hours divide by 3600  =  0.17 kW hr.   and in terms of dollars,  0.17 x $ 0.12 = $ 0.02 to evaporate enough water out of a bushel of wheat to lower the MC by 1%.    That doesn’t sound like much but for 3500 bushels, it would cost $71.68, and to drop by 2% MC it would be $143.36.  It must also be remember that this is the ideal efficiency.  In the real world, we may have to double our cost again.

Could we use the free heat in the air to dry grain?  —  I think so; but it will take careful management and control of the aeration fans.