Energy Audits
Core concepts
Know the three audit levels defined by ASHRAE: Level 1 (walk-through) identifies low-cost opportunities and rough costs; Level 2 (energy survey and analysis) provides detailed energy-use breakdown, financial analysis, and a prioritized list of measures; Level 3 (detailed analysis) adds rigorous engineering modeling, often for major capital projects. Candidates should understand data collection: utility bill analysis (12+ months), interval data, nameplate and run-hour inventories, spot measurements, and benchmarking against peers.
Traps to watch
Questions often blur the boundary between Level 2 and Level 3 - Level 3 requires detailed simulation or sub-metering, not just more walk-through time. Another trap is treating nameplate data as actual load; apply load factors and diversity. Watch for confusion between end-use disaggregation and benchmarking - benchmarking compares to peers, disaggregation explains your own consumption. Also beware audit recommendations that ignore interactive effects (e.g., lighting savings that increase heating load).
Worked example
A motor nameplate reads 50 hp (37.3 kW) but runs at 60% average load for 4,000 hours per year. Annual energy = 37.3 kW × 0.60 × 4,000 h ≈ 89,500 kWh. At $0.10/kWh that is about $8,950 per year. Compare this to a measured value before recommending replacement.
Deliverables and quality
A credible audit report states scope, methods, assumptions, baseline, measure descriptions, savings calculations, costs, and uncertainty. Document measurement instruments and calibration. Note that savings estimates carry uncertainty bands; state them.