UNIT 3: ENERGY DATA COLLECTION, MEASUREMENT, & ANALYSIS TECHNIQUES
3.1. Pre-Audit Planning & Data Collection Strategy
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3.1.1. Audit Scope & Level of Detail:
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Preliminary Audit (Walk-through): Quick visual inspection, review of utility bills, identification of major problem areas and low-cost savings opportunities. Minimal measurement.
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Detailed Audit: Comprehensive data collection, in-situ measurements, system-level analysis, quantification of savings for all viable Energy Conservation Measures (ECMs). Requires significant time and instrumentation.
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3.1.2. Document Review:
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Utility Data: Analyze 12-24 months of electricity, gas, oil, water bills. Identify trends, peak demand, seasonal variations.
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Building Documentation: Obtain architectural plans, mechanical/electrical drawings, equipment schedules, and Operations & Maintenance (O&M) manuals.
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3.1.3. Systematic Data Collection Plan:
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Develop a walk-through survey checklist covering all energy-using systems.
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Create an equipment inventory template (type, capacity, age, condition, operating hours).
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Define operating schedules for different systems and occupancy types.
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3.1.4. Safety & Access:
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Obtain site permission and define safety protocols (lockout/tagout, confined space entry, PPE).
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Coordinate with facility staff for equipment access and safe measurement points.
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[!TIP] Exam Focus: Be able to differentiate between Preliminary and Detailed audit objectives and required effort. Always start with bill analysis before site visit.
3.2. Instrumentation & Measurement Tools for Energy Systems
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3.2.1. Electrical Measurements:
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Clamp-on Power Meters: Measure real power (kW), apparent power (kVA), power factor (PF), and harmonics without breaking the circuit. Essential for motor and panel audits.
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Data Loggers: Record voltage, current, power, and power quality parameters over time (e.g., 24-48 hrs) to capture operational cycles and demand profiles.
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Power Quality Analyzers: Diagnose issues like voltage sags/swells, harmonics distortion, transients.
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Motor Analyzers: Measure motor efficiency, RPM, slip, and winding condition.
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3.2.2. Thermal & HVAC Measurements:
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Infrared Thermography:
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Principle: Detects infrared radiation emitted by surfaces, creating a thermal image.
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Key Parameter: Emissivity must be set correctly for accurate temperature readings. Low-emissivity surfaces (e.g., shiny metal) require special treatment (tape, paint).
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Applications: Building envelope leaks (air, insulation), electrical faults (overheated connections), HVAC component failures ( coils, ducts).
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Temperature Measurement: Thermocouples (wide range, durable), RTDs (high accuracy, stable), Infrared Thermometers (non-contact spot readings).
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Airflow Measurement:
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Anemometers: Hot-wire (low velocity, high accuracy), vane (higher velocity).
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Flow Hoods: Directly measure supply/return air volume (CFM) from diffusers/grilles.
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Pitot Tubes: Measure duct velocity via pressure differential; requires traverse for accurate average velocity.
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Tracer Gas Decay: Quantifies building air leakage rate (used with blower door).
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Pressure Measurement: Manometers (digital or U-tube) measure static pressure in ducts, across filters/coils, and for fan performance.
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3.2.3. Fuel & Combustion Measurements:
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Combustion Analyzers: Inserted into flue to measure flue gas temperature, O₂, CO, CO₂. Used to calculate stack loss and combustion efficiency.
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Fuel Flow Meters: Positive displacement, turbine, or ultrasonic meters for oil/gas consumption measurement.
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3.2.4. Lighting & Plug Load Measurements:
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Light Meters (Illuminance): Measure foot-candles (fc) or lux at work plane. Used for compliance with lighting standards (e.g., IESNA).
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Plug Load Data Loggers: Measure energy use of individual equipment or circuits over time.
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[!TIP] Common Pitfall: Incorrect emissivity setting on IR camera leads to false temperature readings. Always verify with a known-emissivity reference tape.
3.3. Measurement Procedures for Key Systems
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3.3.1. Building Envelope:
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U-value (in-situ): Measured via heat flux method (sensors on interior/exterior surfaces) or temperature gradient method (multiple interior/exterior thermocouples over time). Complex, rarely done in standard audit.
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Air Leakage Testing (Blower Door Test):
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Install a calibrated fan in an exterior door.
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Depressurize (or pressurize) the building to a standard pressure (typically 50 Pa).
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Measure CFM₅₀ (cubic feet per minute of airflow at 50 Pa).
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Calculate Air Changes per Hour at 50 Pa (ACH₅₀):
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$$ACH_{50} = \frac{CFM_{50} \times 60}{Building\ Volume\ (ft^3)}$$
5. Use **tracer gas decay** with blower door to find **natural infiltration rate (ACH_nat)**.
* **Thermal Bridging:** Identified via IR thermography (cold spots on interior walls in winter) or detailed point-by-point temperature measurements.
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3.3.2. HVAC Systems:
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System/Component Efficiency:
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Chiller: Measure entering/leaving chilled water temperatures (ΔT) and flow rate to get cooling capacity (tons). Measure kW input. Efficiency = kW/ton.
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Boiler: Measure flue gas temperature, O₂/CO₂, fuel flow. Efficiency from combustion analyzer or input/output method.
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Cooling Tower: Measure entering/leaving water temperatures, flow rate, fan power. Range = ΔT, Approach = LWT - Wet-bulb.
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Economizer Verification: Verify dampers modulate correctly based on outdoor air temperature/humidity. Measure mixed air temperature to confirm free cooling operation.
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Pump/Fan Affinity Laws: Measure flow (velocity×area), pressure (static pressure), and power (kW) at different speeds/damper positions to verify performance against theoretical curves:
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$$Q \propto N,\ H \propto N^2,\ P \propto N^3$$
(Where Q=flow, H=head/pressure, P=power, N=speed)
* **Temperature Differentials:** Measure ΔT across evaporator/condenser coils, heat exchangers to assess fouling or underperformance.
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3.3.3. Process & Industrial Systems:
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Motor Loads: Use clamp-on meter to measure actual kW under load. Compare to nameplate HP (1 HP ≈ 0.746 kW). Loaded efficiency is often lower than nameplate efficiency.
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Pump/Fan System Curves: Measure head (pressure) vs. flow at operating point. Compare to design curve to identify over-sizing or throttling losses.
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Compressed Air Audit:
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Leak Quantification: Use ultrasonic leak detector or measure compressor load with system off (pressure drop rate).
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Pressure Drop: Measure across filters, dryers, regulators to identify unnecessary restrictions.
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3.3.4. Lighting Systems:
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Measure illuminance (fc/lux) at task height on a grid.
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Count fixtures, note lamp type (T12, T8, LED), ballast type (magnetic, electronic).
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Verify occupancy sensor coverage and time-delay settings.
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3.4. Data Management & Analysis Fundamentals
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3.4.1. Data Organization:
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Maintain equipment schedules (inventory with measured data).
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Keep measurement logs (date, time, location, instrument, reading, operator).
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Use photographic documentation with notes for all findings.
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3.4.2. Energy Use Analysis:
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Consumption Calculation: $$\displaystyle Energy\ (kWh) = Power\ (kW) \times Operating\ Hours $$
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Degree-Day Normalization:
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Heating Degree Days (HDD): $$\displaystyle HDD = \sum (65°F - T_{avg}) $$ for days when $$\displaystyle T_{avg} < 65°F $$.
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Cooling Degree Days (CDD): $$\displaystyle CDD = \sum (T_{avg} - 65°F) $$ for days when $$\displaystyle T_{avg} > 65°F $$.
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Used to normalize energy use for weather variations between years or to a standard climate.
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Simple Regression Analysis: Plot monthly energy use (kWh) vs. driving variable (HDD, CDD, production units). The regression equation ($$\displaystyle y = mx + b $$) helps separate base load (y-intercept, b) from weather-dependent load (slope, m).
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Load Identification: From utility data analysis:
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Base Load: Constant, 24/7 consumption (refrigeration, servers).
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Weather-Dependent Load: Varies with HDD/CDD (HVAC).
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Schedule-Dependent Load: Varies with occupancy/operation hours (lighting, office equipment).
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3.4.3. Benchmarking:
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Compare measured Energy Use Intensity (EUI): $$\displaystyle EUI = \frac{Annual\ Energy\ Use\ (kWh\ or\ Btu)}{Floor\ Area\ (ft^2\ or\ m^2)} $$
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Compare against:
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Codes: ASHRAE 90.1, IECC.
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Standards: ENERGY STAR® Target Finder.
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Similar Buildings: Peer group comparison.
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3.4.4. Savings Quantification:
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Use measured baseline (as-found condition) to model proposed ECM.
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Simple Savings Formula: $$\displaystyle Annual\ Savings = (Baseline\ Use - Proposed\ Use) \times Operating\ Hours $$
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Example: Replacing a motor. Baseline kW (measured) vs. Proposed kW (new efficient motor). Savings = ΔkW × annual run hours.
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3.5. Quality Assurance, Uncertainty, & Reporting of Findings
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3.5.1. Instrument Accuracy & Calibration:
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Understand manufacturer's stated accuracy (e.g., ±1% of reading + 10 counts).
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Ensure instruments have valid calibration certificates.
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Measurement Uncertainty: Combined uncertainty from instrument accuracy, operator technique, and environmental conditions. Report significant figures accordingly.
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3.5.2. Data Consistency & Repeatability:
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Take multiple measurements at the same location and average.
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Document all measurement conditions (e.g., "outside air temp 85°F, humidity 60%").
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Ensure consistent units and conversion factors.
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3.5.3. Synthesizing Findings:
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Translate raw data into clear statements: "AHU-1 supply fan motor draws 15.2 kW under full load, 18% above nameplate kW (12.9 kW), indicating possible over-sizing or belt slip."
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Link measurements directly to ECM recommendations.
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3.5.4. Documentation for Each Data Point:
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What was measured (parameter: kW, °F, CFM).
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Where (specific location: "Main electrical room, Panel MDP, Phase A").
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How (instrument model, serial number).
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When (date, time).
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Conditions (system mode, outdoor weather).
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3.5.5. "As-Found" Condition Summary:
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Create a structured table or list summarizing all major deficiencies with supporting data and images.
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Example: "Boiler #2 combustion efficiency measured at 78% (flue temp 450°F, O₂ 3%). Target >85%. [Image: IR of boiler jacket showing heat loss]."
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[!TIP] Exam Strategy: Always state the baseline clearly before calculating savings. Report uncertainty when presenting precise measurements (e.g., "flow = 1200 ± 60 CFM").