Silo Aeration is a process of forcing air through grain to reduce its temperature. It is a very useful storage management tool which can preserve grain from deterioration, especially where the moisture content of the grain is above its safe level.
Aeration can be used as effectively in sealed stores as in unsealed ones – sealed stores merely requiring the provision of an air-exhaust ventilator which can be sealed whenever fumigation is to be carried out.
Reducing grain temperatures by aeration offers numerous benefits:
- It reduces the rate of insect population growth
- It reduces the rate of microbial (or mould) development
- It preserves germination viability and it prolongs the effectiveness of insecticide chemicals where these are used.
Aeration – how it works
When a silo is full of grain there is a surprising amount of space taken up by air gaps between the grains. For example, if you store 100 tonnes of barley it will require a silo volume of about 130 m³. Of that volume around 80 m³ is taken up by grain. The remaining 50 m³ is air space between the individual grains.
We are interested in this air surrounding the grain when it comes to aeration cooling or drying.
With no movement of air in the silo, this entrapped air around the grain slowly (over a few days) comes into equilibrium (balance) with the grain temperature and moisture. For example, if we filled the silo with freshly harvested wheat at 14% mc and with a typical grain temperature at harvest of around 30°C, the relative humidity of the air surround the grain in the silo would move to approximately 73% relative humidity (RH) and grain temperature may rise towards approximately 35°C due to grain respiration activity. These dangerous grain storage conditions would remain unless we introduce outside (ambient) air that has a lower temperature and preferably a lower RH than the equilibrium that has been reached.
Well managed cooling aeration typically reduces grain temperature to the safe level of 20°C and below within days. However, reducing grain moisture to safe long-term storage levels generally takes one to four weeks utilizing much larger air flow rates to reliably achieve the desired result.