So you have decided to put aeration on your silos but are confused about what is needed.
Before you make a selection, it is important to identify what you really want to do:
1. Maintain the grain in its current condition while allowing a gentle airflow to even out any major differences
2. Cool the grain to a temperature that eliminates live insect
3. Dry the grain to a standard acceptable for bulk storage
The answer will have a major impact on the selection process since recommended airflows vary greatly between the 3 different processes.
Once you have made your selection, now comes the question as to how you are going to power the fans? In many cases, power supply to farms is very limited. Many farms only have dual phase supply which restricts the size of the fans available to 2.2 kW
The result may be that even though you really would like to cool your grain, the available fans are way too small to have an impact. A solution would be to install a 3 phase generator (hire or buy) and now you have much more choice as to what size fan you can select.
Consider these recommendations:
Maintenance air: 0.5 to 1 l/s/t (litres per second per tonne)
Cooling air: 3 to 4 l/s/t
Drying air: 15 to 20 l/s/t
As the airflow requirements are affected by the tonnage, it means that with less grain in your silo you can get away with a smaller fan.
This explains why some silo manufacturers provide aeration systems capable of cooling and drying, but add to that, that the drying only works when the silo is half full.
And even then, your system may be struggling when the design was based on wheat and you are trying to dry canola.
When selecting a fan, it is important to ensure that the fan is capable of pushing the air through your column of grain. The taller the column the harder the fans needs to work. In addition, the smaller the gaps between the grain types, the harder it is again.
So if you are considering storing canola, or even worse chia, then don’t make the mistake to size the fan on storing wheat.
The fan size
So now have all the information to select a fan, but does this mean that the smallest suitable fan is the right decision?
Consider this: you want to cool your grain and there are a number of really cool days coming up. So you think, that will do it for me only to realise that the capacity to move the cooling front though the silo is just enough to cool halve the amount of grain.
Cooling front, what is that? The front is the area between the improved grain and the grain that still needs improving
When grain is being cooled, or dried for that matter, the grain condition improves from the air inlet upwards and not like some people think across the entire content of the bin. As the first section is being cooled, heat transfer is no longer needed in the bottom part so that the cool air can start cooling the next section up. And the higher the airflow, the quicker this front moves up.
This means that with a slightly larger fan, you might be able to get all that cold air and cool your grain much quicker.
When to aerate
It makes sense that when drying grain, you want low humidity air and when cooling you want low temperature air. But what if the cool air is high in humidity, would you still use it?
In fact the correct selection of the right air is not a simple exercise and this is when controllers come in. And just like with the selection of the fans, there are many options.
Some controller are really not much more than a time clock while others do monitor the ambient air condition and make aeration decisions based on the temperature and humidity of the inlet air. This however still doesn’t solve the question if the stored grain really needs that air i.e. is the grain already cool enough and running the fan(s) longer is only costing you energy.
The best solution is to know what is happening inside the silo and control your fans based on the capacity of the inlet air to improve the condition of the grain.
There is only one such a controller and that is the Aeration Manager from Aeration Control Australia. So if you are really serious about aeration, give us a call at 1300 IND AUTO