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CEM: Energy Audits and Instrumentation

CEM · Work through your exam, one topic at a time.

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Energy Audits and Instrumentation

This domain tests audit levels, field measurement, data quality, and measurement and verification planning. CEM-style questions ask you to select an instrument, interpret a trend, or match an audit deliverable to the ASHRAE level.

Audit levels

  • Level 1 is a preliminary walk-through with utility-bill analysis, a rough end-use breakdown, and low-cost or no-cost opportunities.
  • Level 2 is an energy survey and analysis with a detailed end-use breakdown, a calibrated baseline, and savings and costs for specific measures.
  • Level 3 is a detailed analysis for capital-intensive projects, often using dynamic simulation, with a rigorous M&V plan.

Instrumentation

  • Power loggers record true RMS kW, kVA, kVAR, power factor, and demand over intervals; clamp-on CTs introduce ratio and accuracy issues.
  • Ultrasonic flow meters measure flow from outside the pipe; they need pipe material, diameter, and wall thickness.
  • Combustion analyzers measure O2, CO, CO2, and stack temperature to estimate excess air and combustion efficiency.
  • Infrared cameras find thermal bridging, missing insulation, and overheating electrical connections.
  • Anemometers, light meters, psychrometers, and occupancy loggers support spot and long-term measurements.

M&V options

IPMVP Option A isolates the retrofit and measures key parameters; Option B isolates it and measures all parameters; Option C uses the whole facility; Option D uses a calibrated simulation. Baseline adjustments are required when weather, occupancy, or production changes.

Worked example

A week of 15-minute demand data shows an average of 400 kW and a peak of 800 kW. Load factor = average ÷ peak = 400 ÷ 800 = 0.50, or 50%. Energy over the 168-hour week = 400 × 168 = 67,200 kWh. At $0.10/kWh, that week costs $6,720. The reasoning: load factor uses average demand over the same period as the peak and helps identify whether peaks or baseload drive the bill. A 50% load factor suggests both baseload and peak-management opportunities.

Traps that cost marks

  • Using a spot reading to estimate annual energy in a highly variable process.
  • Ignoring CT ratio, phase, or power factor when interpreting a portable meter.
  • Comparing a logged interval to a utility billing period without checking dates and time intervals.
  • Selecting Option C when only one measure is being verified and no whole-facility baseline exists.
  • Failing to calibrate sensors or document measurement boundaries.