Drying Energy Requirement & Heat the Crop, Budget the Fuel
Dries paddy
Drying to a safe moisture costs heat to evaporate water — enter the wet mass, the start and target moisture and the dryer efficiency to get the water removed, dried weight and energy in MJ and kWh.
Set the drying batch
Next: budget 81.5 kWh (294 MJ) of input heat to pull 90.9 kg of water out, leaving 909 kg of dried product — size the burner or fan-heater accordingly.
Uses water's latent heat of vaporisation (~2.26 MJ/kg) divided by dryer efficiency. Real dryers also lose heat to the air, walls and exhaust, so add a margin.
Drying energy — key facts
- Dried weight
- dry matter ÷ (1 − target moisture)
- Water removed
- wet mass − dried weight
- Energy
- water × 2.26 MJ ÷ efficiency
- Latent heat
- ≈ 2.26 MJ per kg water
- 1 kWh
- = 3.6 MJ
- Dryer efficiency
- ≈ 50–70% typical
- Safe cereal moisture
- ≈ 12–14%
- Privacy
- Runs in your browser; nothing uploaded
Drying is mostly the cost of boiling off water
A wet crop will not store — it moulds, heats and is eaten — so it must be dried to a safe moisture. Almost all of the energy that takes goes into evaporating water, and water is expensive to evaporate: about 2.26 MJ for every kilogram. Because a dryer wastes heat up the stack and through its walls, the real fuel energy is the ideal evaporation energy divided by the dryer's efficiency. Knowing both the water to remove and the energy to remove it is how you size a dryer and budget fuel.
This tool gives the water removed, the dried weight and the heat energy in MJ and kWh from the wet mass, the start and target moisture and the dryer efficiency. Use it to size a dryer, convert energy into diesel, LPG or firewood, and compare sun drying against mechanical drying. Pair it with the Grain Drying Cost and Safe Storage Moisture tools to plan the whole harvest.
Size the dryer
Match the heat supply to the water you must remove.
Budget the fuel
Turn megajoules into litres of diesel or kg of LPG.
Compare methods
Weigh sun drying against a mechanical dryer.
Hit safe moisture
Know the dried weight that stores without spoiling.
Frequently Asked Questions
How is the drying energy calculated?+
First the tool finds the dry matter — wet mass × (1 − initial moisture). It then finds the dried weight that holds the same dry matter at the target moisture, and the difference is the water removed. The heat energy is the water removed times the latent heat of evaporation (about 2.26 MJ per kg) divided by the dryer efficiency, so a less efficient dryer needs proportionally more energy.
Why divide by the dryer efficiency?+
Only part of the heat a dryer produces actually evaporates water — the rest is lost up the stack, through walls and in heating the grain itself. Dividing the ideal evaporation energy by the efficiency (as a fraction) inflates it to the real fuel-side energy you must supply. A 60% efficient dryer needs about two-thirds more energy than the ideal minimum.
How much water does drying actually remove?+
Less than people expect, because moisture is measured against the whole weight, not the dry matter. Drying a tonne of paddy from 22% to 13% moisture removes about 103 kg of water and leaves roughly 897 kg of grain. The tool reports both the water removed and the dried weight so you can plan tonnage and energy together.
What latent heat does the tool use?+
It uses about 2.26 MJ per kilogram of water — the latent heat of vaporisation of water near 100°C. In real grain drying the figure is a little higher because the last moisture is held more tightly in the kernel, but 2.26 MJ/kg is the standard planning value and keeps the estimate on the conservative-to-realistic side for typical drying temperatures.
What dryer efficiency should I assume?+
Continuous-flow and mixed-flow grain dryers commonly run at 50–70% thermal efficiency, while simple batch and bin dryers can be lower. Sun drying has no fuel cost but is weather-bound. If you do not know your dryer's efficiency, start around 60% and refine it from your measured fuel use against the water you actually removed.
How do I turn the energy into fuel?+
Divide the energy by the fuel's heating value: diesel holds about 38 MJ per litre, LPG about 46 MJ/kg and firewood roughly 15 MJ/kg (air-dried). So a job needing 250 MJ uses about 6.6 litres of diesel before burner losses. The kWh figure the tool also reports is handy for electric or heat-pump dryers.
Why dry grain at all?+
Grain stored above its safe moisture moulds, heats, loses germination and gets eaten by insects, so a wet crop can be ruined within weeks. Drying to the safe moisture for the crop — about 12–14% for cereals — lets it store for months. The energy this tool reports is the price of that safety, which is why efficient drying matters.
Are the figures exact?+
They are realistic planning figures from a clean latent-heat balance. Real energy use shifts with ambient humidity, airflow, grain type and how tightly the last moisture is bound, so treat the result as a working estimate. Use it to size a dryer, budget fuel and compare options, then calibrate against your measured fuel use.