A dryer’s running cost is dominated by one thing: the energy needed to turn liquid water in the product into vapor and carry it away. Once you estimate that water load, you can compare technologies — hot-air, heat-pump, freeze — on a like-for-like basis. Start from the dryer category and the specific model you are weighing, such as an industrial hot-air dryer or an air-to-air energy-saving dryer.
The core equation
The latent heat of vaporization of water is about 2260 kJ/kg, or roughly 0.628 kWh per kg of water removed. A first estimate of the heating energy per hour is:
E ≈ m_water × 0.628 (kWh/h, latent) + sensible heat to raise product to drying temperature
The sensible-heat term is usually small next to the latent term, so the water-removal rate is the number that matters most.
Step-by-step
- Find the water to remove per hour. From the feed rate and moisture content before and after drying. Dry solids are conserved, so compute solids first, then the water leaving as vapor.
- Multiply by 0.628 kWh/kg for the latent load.
- Add sensible heat to lift the product from ambient to drying temperature (specific heat of the wet product × mass × ΔT). Often 5–15% of the latent term.
- Divide by system efficiency / COP. An electric resistance heater is near 100% efficient at the element but loses heat to the surroundings; a heat-pump dryer uses a coefficient of performance (COP) of roughly 3–4, so the electrical input is roughly one-third to one-quarter of the thermal duty.
Worked example
Drying 100 kg/h of product from 80% moisture to 10% moisture: dry solids = 20 kg/h; final total mass = 20 / 0.90 = 22.2 kg/h; water remaining = 2.2 kg/h; water removed ≈ 77.8 kg/h. Latent energy ≈ 77.8 × 0.628 ≈ 48.9 kWh/h. A resistance heater supplying that duty draws close to 49 kWh of electricity per hour (before losses); a heat-pump dryer at COP 3.5 draws roughly 14 kWh/h for the same water removal. The gap is the operating saving that justifies a heat-pump or air-to-air design on continuous duty.
Other levers that change the bill
Insulation quality, heat recovery from exhaust, humidity control (don’t over-ventilate), loading density and matching capacity to real throughput all shift the effective efficiency. Oversizing a dryer does not dry faster — it just heats more empty air. Size from the capacity method first, then compare energy per kg of water removed, not just the nameplate power.
Frequently asked questions
What is the single biggest energy factor in drying? The mass of water you must evaporate per hour. Roughly 0.628 kWh of heat is needed per kg of water removed, so cutting the water load (or raising input solids) cuts the bill more than any heater tweak.
Why do heat-pump dryers cost less to run? A heat pump moves heat with a COP of roughly 3–4, so the electrical input is a fraction of the thermal duty. On continuous duty that difference compounds into a large operating saving versus straight electric resistance heating.
Does a bigger dryer dry faster? Not necessarily. Past the point your throughput needs, extra capacity mostly heats more air. Match the dryer to real kg/h of water removal, then improve insulation and heat recovery.
Get a configuration that fits your line
These comparisons are starting points. Send us your product, target hourly throughput and package type, and we will point you to the right machine and a matching auxiliary layout. Request a quote or browse the full range under each product category.