Electricity and efficiency measures

What studies report for electricity

Electricity runs the saw line, debarker, chippers, conveyors, hydraulics, compressed air and dust extraction. Reported specific values are hard to compare because the reference unit (logs, green, dried or planed lumber) and the system boundary differ.

MBF is a thousand board feet. The conversion to m3 differs between documents (1.623, 1.59 and about 2.36 m3 per MBF appear) and the portal could not reconcile them. With 1.623 m3 per MBF, 100 / 1.623 = 61.6 kWh/m3 for the West Virginia average. With 2.36, the California figure becomes 194 / 2.36 = 82 kWh/m3. Take away only the order of magnitude: roughly 50-85 kWh/m3 in North America and 53-67 kWh/m3 in the Norwegian data. The wide survey range (31 to 588 kWh/MBF, a factor of nearly 19) warns against single benchmarks.

A US softwood inventory (2012 survey, Pacific Northwest) breaks electricity down by process: log yard 2.1 kWh per m3 of log, sawmill 26.4 per m3 of rough green lumber, kilns 11.5 per m3 of rough dry lumber, planer 14.3 per m3 of planed lumber. The rows have different reference units, so they must not be added.

Measures with documented results

The evidence is mixed; much comes from trade guides, so source and year are given.

• Variable speed drives on fans and pumps. The fan affinity laws, quoted in an Oregon guide (2024), say a fan at 80% of flow uses 51% of full power and at 50% flow about 13%. Typical simple paybacks: kiln fans 2-6 years, dust collection fans as short as 2 years. Fan electricity is 5-10% of kiln energy but up to 20% of its energy cost (Canada, 2011).
• Compressed air. In Austrian audits (2009 thesis, small unrepresentative sample) pneumatic systems had the largest electrical saving potential, about 28%. The Oregon guide says each 2 psi pressure reduction saves about 1%. A US project at a Weyerhaeuser sawmill (2000) saved about 1.3 million kWh a year for 55,000 USD with a one-year payback.
• Energy management. The Norwegian programme (policy, review, team, targets, weekly review) went with a fall from 66.8 to 53.1 kWh/m3, about 20%, worth roughly 90 thousand euros a year; awareness alone gave 2-5% in the first year. Energy is only about 5% of mill costs, which weakens the incentive.
• Heat side: kiln sealing and insulation, vent heat recovery, steam traps (payback under a year in the guide), excess-air optimisation.

Payback figures are typical estimates, not guarantees.

Worked examples

Fan. A kiln fan draws 40 kW at full flow. At 50% flow it uses 13%: 40 x 0.13 = 5.2 kW, saving 40 - 5.2 = 34.8 kW. Over 4,000 hours, 34.8 x 4,000 = 139,200 kWh (a physical upper-bound illustration: a real fan rarely runs at 50% all year).

Compressed air. A compressor system uses 500,000 kWh a year. Lowering the pressure by 6 psi saves about 6 / 2 = 3 steps of 1%, so 500,000 x 0.03 = 15,000 kWh (the 1% per 2 psi rule is approximate).

Programme. The Norwegian drop: (66.8 - 53.1) / 66.8 = 20.5%.

Checklist: electricity quick wins

• Measure the compressor on a stopped weekend; the running load is leak load.
• Interlock auxiliaries with the saw line so they stop when it stops.
• Fit variable speed drives where flow is regulated by dampers.
• Fix leaks, set pressure no higher than needed.
• Name a person, set a target, review weekly.

Key points

• Electricity values in the sources span roughly 50-85 kWh/m3, but the units and boundaries differ; MBF-to-m3 factors are inconsistent across documents.
• Process rows with different reference units must not be added.
• Fan affinity: 80% flow uses 51% of power, 50% flow about 13%; compressed air: about 1% saving per 2 psi.
• A Norwegian energy management programme was associated with about a 20% fall in specific electricity.
• Treat paybacks as indications from specific sources, not guarantees.