Kiln Charge Water Weight, Energy, and Vent Load

Wood moisture content is on an OVEN-DRY basis -- water weight over the oven-dry wood weight, not over total weight -- and applying it to a green weight is wrong by exactly the moisture content. A 40,000 lb charge of green red oak at 85% is 21,622 lb of wood and 18,378 lb of water, so 46% of what came in the door is water. Taking it to 8% removes 16,649 lb, 1,995 gallons, over four tons out of a 20 ton charge. THE WRONG WAY, and the reason this exists: 40,000 times 77 points over 100 gives 30,800 lb, which is 14,151 lb too high -- an overstatement of 85%, the initial moisture content itself, because green weight is oven-dry weight times one plus that fraction. ONCE THE WATER TONNAGE IS KNOWN EVERYTHING FOLLOWS. At 2,000 BTU per pound of water -- well above the latent heat, because a conventional kiln also heats the wood, heats the kiln, and loses heat out the vents -- the charge needs 33.3 million BTU. Spread over a 28 day oak schedule the vent load is 24.8 lb of water an hour, which is what sizes the venting and, in a dehumidification kiln, the compressor. THE SCHEDULE CHECK IS THE THIRD USE. 77 points over 28 days is an average of 2.75 points per day, in the right range for 4/4 red oak. And by the time the charge reaches 30% moisture content, 71% of the water is already gone while barely half the schedule has run, with 4,757 lb still in the wood -- which is why a charge with twice the water takes far more than twice as long. A mass and energy calculation. It does not produce or validate a drying schedule: schedules are species, thickness, and grade specific, are published by the Forest Products Laboratory and by kiln manufacturers, and running wood faster than its schedule allows causes checking, honeycomb, collapse, and casehardening that no energy calculation predicts. The energy-per-pound figure is a broad range depending on kiln type, insulation, venting practice, and heat recovery; a dehumidification kiln's energy is electrical and follows different arithmetic. It does not address air drying, sticker spacing and airflow, equalizing and conditioning, stress relief, or the moisture content measurement itself, which is done with kiln samples and a meter. The applicable drying schedule, the kiln manufacturer, and the mill's own kiln samples govern.

oven-dry weight = green weight / (1 + moisture content / 100); water to remove = oven-dry weight x the moisture-content points removed / 100, at 8.3454 lb per US gallon; energy = that mass x an entered BTU per pound of water; vent load = the water divided by the schedule hours.

The oven-dry-basis moisture relation by name, with the Forest Products Laboratory dry-kiln schedules named as what governs the drying itself. The applicable drying schedule, the kiln manufacturer, and the mill's own kiln samples govern.

Mass and energy arithmetic on the charge weight and moisture contents the user enters; no published schedule or manufacturer table is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: green_weight_lb, mc_initial_pct, mc_final_pct, btu_per_lb_water, schedule_days, intermediate_mc_pct, oven_dry_lb, water_lb, water_gal, energy_mmbtu, wrong_way_lb, wrong_way_excess_lb, wrong_way_excess_pct, vent_lb_per_hr

• Moisture content is oven-dry basis so it can exceed 100%, and green weight times the percentage is wrongwood science convention
• Energy is well above latent heat roughly 1,500 to 2,500 BTU per pound of water for a conventional kilnkiln manufacturer data
• The measurement is kiln samples moisture content is measured with samples and a meter, not calculatedFPL dry-kiln practice