A Constant Humidity Controller (CHC) is a specialist piece of crop drying equipment that automatically controls the temperature or humidity of air blown through stored grain. Rather than a burner that’s simply on or off, a CHC modulates the flame in real time — ensuring the air is always at the correct conditions for drying. The result is faster drying, lower fuel costs, and better grain quality.
How does a Constant Humidity Controller work?
The CHC works by measuring the humidity and temperature of the incoming air, then calculating how much heat needs to be added to reach the ideal drying conditions. On a warm, dry day, little or no heat may be needed. On a cold, damp day, more is required. The controller automatically adjusts the gas burner output to match, so the grain is always dried at the optimum rate — whatever the weather
Why is controlling humidity so important in grain drying?
Overdrying grain is a more serious problem than many farmers realise. For every 1% of moisture lost beyond the target, 1% of saleable weight is lost with it — directly reducing your yield and your returns. Physically, overdried grain becomes brittle and prone to cracking, which opens the door to insect damage, mould, and poor seed germination. For milling wheat, the consequences go further: excessive heat damages the gluten structure, reducing the protein quality and making the grain less suitable — or even unsuitable — for bread making. On top of the quality losses, running a gas burner or drying fan longer and harder than necessary is simply wasteful. The fuel costs of over-drying grain can be significant, particularly across a full harvest season, making precise humidity control not just a quality issue but an economic one.
If the air blown through grain is too humid, it will not dry the crop effectively and may even add moisture. If the air is too dry, it can over-dry the grain, causing it to crack and lose weight — both of which reduce its market value. By maintaining a constant target humidity in the drying air, a CHC ensures drying happens at the right pace without wasting fuel or damaging the crop.
The history of the Harvest Installations CHC
The Constant Humidity Controller was first developed in 1979 and was the founding product of Harvest Installations. It was an award-winning innovation at the time and has been refined and improved over the following four decades. Today, thousands of CHC units are in operation across the UK and internationally, covering all combinable crops and onions. The product is available in a range of sizes from 200,000 to 4,000,000 BTU/hr, making it suitable for small farm stores through to large commercial grain operations.
What are the benefits of using a CHC over a fixed-temperature dryer?
A fixed-temperature drying system applies a set amount of heat regardless of conditions, which means it is often inefficient — burning more gas than needed on dry days, or under-performing on damp days. A CHC adapts continuously, so fuel is only used when and to the degree it is needed. Over a harvest season this can represent a significant saving in gas costs. It also protects grain quality by avoiding the over-drying that a fixed-temperature system can cause when ambient conditions change.
Is a Constant Humidity Controller right for my farm?
A CHC is suitable for any farm that dries grain or other combinable crops in a floor-based store. It works with both new builds and existing stores, and can be integrated with our Maxi-Stirrer and Store Controller systems for a high temperature drying system. If you are unsure whether a CHC is the right solution for your setup, our team at Harvest Installations is happy to advise. We have been matching farmers with the right drying equipment since 1979.