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.

Duty Cycle of Absolute Humidity Controller

I took a look at the duty cycle (on time/total time) for the different bins:

Delage Bins Start End Percent Duty Cycle (on time/total time)

Bin 14 Aug 11 to Aug 21 73.6%
Bin 15 Aug 11  to Aug 21 64.8%

Bin 17 Aug 30 to Sep 6   94%
Bin 19 Aug 22 to Sep 6   95.6%

The IHARF bins were on almost constantly. And what is really strange is that the absolute humidity in the bin would increase, even when it was blasted with air that had a lower absolute humidity. I can’t explain it? Maybe it has to do with sensor placement in the bin? Were we really sensing or getting a true sample of the the exhaust air? Or perhaps we just had really good drying conditions for the period of time that we did the run? I would think that the Delage bins would be closer to the norm as far as duty cycle goes.

Grain Drying Calculator Update

I have added soybeans and yellow peas to my grain drying calculator at planetcalc.com/4959/   This calculator gives the relative humidity, below which, drying will occur.  It only requires the temperature and moisture % of the grain, as well as the outside temperature and by using EMC equations it calculates the absolute moisture in the air, entering and leaving the bin.  It can be easily loaded onto an Iphone.

Supplemental Heat — Cycling Works the Best

I was just talking to a farmer, who farms west of North Battleford.  He had the same difficulties this fall with harvest and had plenty of tough grain to deal with.  He purchased a diesel heater, that put the equivalent of 75,000 btu/hr. into a 5000 bushel bin with a 3 HP aeration fan.   He conducted a little experiment — when did he get the best drying?  When the supplemental heat was left on continuously, or when it was cycled  heating the grain up and cooling it down.  He told me that clearly the cycling resulted in much better drying, and he was curious as to why.   I have received this same question from others.  Here is what I think is happening.

It comes down to vapour pressure.  The air has a vapour pressure that is trying to push water into the grain.  The two factors that effect vapour pressure for air are the amount of water in the air and the temperature.  The dominant factor for the vapour pressure for air is definitely temperature — the higher the temperature the more the pressure.  The grain also exerts a vapour pressure and again the dominant factor is temperature.  So, if the grain is warmer than the surrounding air, the grain most likely will have a greater vapour pressure and water will be pushed out of the grain and into the air.  The opposite will occur when the surrounding air is at a higher temperature than the grain — it is most likely that the air will have a higher pressure and water will move from the air into the grain.  Wetting will occur.

When supplemental heat is applied continuously, the grain becomes more or less the same temperature as the air.  As such the vapour pressures of each are more or less the same, and little drying occurs.  On the other hand if the grain is warmed, and then cooled with cool or even cold air with very little vapour pressure; there will be lots of water being pushed out of the grain and into the air. Lot’s of drying.   Back to our old adage “Cooling is drying” and our data indicates our rule of thumb:   “For every 15 C that the grain is cooled, 1% moisture will be removed.

Here is what our farmer did to get good results with cycling.  He had temperature sensors on a cable spaced 4 feet apart.

He would run the heat (75,000 btu/hr) into his bin until he got the first 3 or 4 sensors on the bottom of the bin to 25 C. This may take a day or two.  He would then cool the grain, using cold night air (5 C), and get the grain down to maybe 10 C.   Each cycle removed about 1% moisture.   After a couple of cycles, he moved the entire contents of the bin to another bin.  He called it tipping?  And if the grain was still not dry he would go through another cycle.  He always ended up with grain being brought to as low a temperature as possible.

And this brings me to another note, as I think of it.  I was at a conference in which Sarah Foster gave a presentation on germination rates, etc.  She was from a seed lab in Winnipeg.  I asked her if you could ever get seeds too cold,  No, definitely not was her reply.  However can you get grain cold enough to kill off the fusarium?  Yes was her reply, but she wasn’t sure at exactly what temperature.  She is looking into it.

Back to my farmer;   he is so pleased with the drying technique that he has come up with that he now plans to start harvest when his grain is a couple of points higher than dry.  He said he might be able to get a two day jump on things. And later in the fall, he will be able to start earlier in the morning.  Yes, he might be paying a bit for supplemental heat (diesel fuel) but that is offset by getting his grain safely into the bin.  And now that he knows how to get his grain dry in a matter of days, he can still sell his crop in short order.



Supplemental Heat: Act V Using the Grain Drying Calculator, A Balancing Act

I have blogged about the grain drying calculator, http://planetcalc.com/4959/

I explained how to use it without supplemental heat, but not how to use it when supplemental heat is used.  The short answer is that you use it in the same fashion.  You still enter the moisture content of the grain, the temperature of the grain, and the ambient outside temperature of the air (before it is heated). The resulting RHthres will indicate whether or not drying will occur.

One might conclude, that you will get the same answer for RHthres whether you are applying heat or not; and this is quite true — at first, but if heat is applied the temp of the grain will increase.  My Act III blog on Supplemental Heat indicated that it would take 12.3 hours to heat the grain 5 ºC with a 50,000 btu heater.  However I failed to mention the two implied assumptions: 1) that the grain body heated up uniformly and 2) the ambient outside temp remained the same.  Neither of these assumptions are true.

The grain will heat at the bottom of the bin first, and the so called “warming-front” will slowly work its way to the top.  If you have a cable with multiple temperature sensors, you will see this first hand.

The ambient air temperature also varies by 10-15 ºC.  The air going through the heater will get a boost in temperature, above the ambient, by maybe 20-30 ºC. So, let’s say the outside air temperature has a low of 5, and a high of 15; and the temperature rise through the heater is 30 C.  Let’s say we turn the heater on when it is cold outside, 5 C and so is the grain, 5 C.  After one hour, the bottom of the bin might increase to 10 C, while the top stays at 5.  After two hours the grain will be even warmer at the bottom, maybe 15, and as time goes on the bottom will get warmer and warmer with a wave of heat slowly creeping up the bin.  We have a string of temperature sensors, so we can actually watch this wave.  Eventually the top of the grain will also be getting warmer.

Now comes the tricky part, when should the heat be turned off in order to curtail condensation?  Remember we never want the top of the grain temperature to exceed the outside ambient temperature by more than 5 C.   Let’s say that we are approaching the highest temp of the day, 15.  Maybe the top of the grain is 10 C, and the bottom 30 C.  Everything is fine — no condensation — yet.  As the day cools off, to 5 C, the wave of heat will continue to heat the grain at the top, even if we turn the heat off. In a few hours the top of the grain may become 15 C and as we approach the low of the day, 5C — we will have conditions for condensation — the grain is 10 C higher than the ambient temp.

What would be ideal would be to apply heat such that the top layer of grain is always 5 ºC warmer than the outside air.  There are two difficulties with this. First there is a huge delay from the time we apply heat at the bottom until it reaches the top layer.  It would be hours, and it depends on so many things, such as air flow rate, heater size, bin size, etc. And to anticipate this delay is really difficult.  The other complicating factor is that the ambient temperature changes, and sure we can get a forecast of the temperature, it is not entirely accurate. And then to monitor and control this whole mess.

Let’s take on the heat wave delay problem.  The outside air goes up and down in temperature in a somewhat predictable fashion.  Somewhat of a sinusoid in shape, with the warmest part of the day taking place a couple of hours after noon, and the coldest part of the day a couple hours after midnight. Typically we see a difference in the high to low temperature of 10 – 15 ºC.   We ideally would like to apply supplemental heat such that the top layer of grain is always 5 to 6 degrees warmer than the outside temp.  The problem is there is a delay in applying the heat to the bottom of the bin to when it gets to the top.  What is this delay?  To determine the delay we could model the system, but this is a trickly onerous task — and there are so many variables.  The other way to find out what this delay is, would be to review the data of our runs, and see what it is.  I did just that, and I examined two trial runs, 9 10P and 09 09W.  Clearly the delay was close to 6 hours.  The flow was close to 1.2 CFM/bu and if we lowered the flow to 0.3 CFM/bu we would increase the delay accordingly to 24 hours.  The temperature of the top layer of grain will be synchronized with the daily cycle of temperature change of the outside air. We can use the rate of flow of air to adjust the delay and set it where we get a 24 hour delay.

Now the other problem, we want to add supplemental heat to keep the top layer of grain  5 to 6 ºC above ambient, we want a 5-6 ºC rise, throughout the whole day.  We would keep the fan running continuously, and the heater running continuously to provide a 5 C rise.  What size heater do we need for this?

In my earlier blog: “Big Heater for supplemental heat Example” I had a farmer with a 1.4 million btu/hr heater at 5,000 CFM. It produced a 30 C rise in temp.  Supposing we have a 3500 bushel bin, we would need 1000 CFM to get the synchronizing daily delay of 0.3 CFM/bu.   The rise we would get with a 50,000 btu furnace would be 50,000/1,400,000 x 5000/1000 x 30 = 5.35 ºC — Perfect.  A 50,000 btu furnace with 1000 CFM should do the job to give a 5 C rise with a 24 hour delay.  We might have to use some trial and error to fine tune this.