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.