I wanted to ask about using the terms “aeration” and “natural air-drying.” I’m trying to avoid confusion – I found in a grain aeration spreadsheet by PAMI the following definition:Aeration = grain conditioning/cooling low airflow rate (0.1-0.2 cfm/bu) Natural air Drying = removing moisture from grain high airflow rate (1-2 cfm/bu)
Natural aeration or Natural Air Drying would be using the natural ambient air (no supplemental heat) to condition the grain. I think it is generally accepted that the fan is pumping air into a steel bin. Our research has shown that Cooling is Drying and whether you have an air flow of 1 CFM/bu or 0.1 CFM/bu, you will be cooling and drying the grain. I am not sure where the distinction between airflows for cooling and drying came about, but in fact they are related. Even at very low air flows, you will still be drying — albeit somewhat slower, but; there are advantages to drying slower. 1. Because the higher flows make for more pressure on the bottom of the bin, they also will create more of a difference in top to bottom of the bin drying. Slower flows have a more even distribution of top/bottom drying. 2. You will use more of the heat energy in the grain to push the water out of the grain. 3. You will use much less electrical energy with a smaller fan — even if it takes a bit longer. We found the sweet spot for flow to be about 0.4 CFM/bu. You get the advantages, as mentioned above, and you still get the grain dried in a reasonable time. But back to answering your question: Natural Air Drying and Natural Aeration are really the same thing.
Do you agree with these definitions? Natural air-drying seems to be both a somewhat general term for the two methods and also a specific term for the high airflow rate method – thus my confusion.
Also, would you have any figures on the costs to run a grain aeration fan? You said it would be pennies on the dollar – do you know where I can find more specific numbers?
Here is the math that you can use to calculate the cost. In Sask the cost of a KiloWatt Hour is about $ 0.13 1 HP requires 0.74 KW So to run a 1 HP fan for 1 hour cost 9.62 cents — lets round it off to 10 cents. A 5 HP fan would cost 50 cents per hour or 12 dollars a day. A 10 HP fan would cost $24/day. You can take it from there.
I was looking at your presentation and the diurnal drying cycle graph – it shows drying starting at 6:00 pm and wetting starting at 9:30 am (with best drying happening at 2 am). So, after that initial 24 hour drying period during/after harvest, are those the times farmers should be following for natural aeration?
After the initial 24 hours, the fan should only be run if the outside air temperature is less than the grain temperature. This will probably be at night. And as the temperature of the grain goes down, there will be warm nights that the fan should not be run at all.