Month: February 2018

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.