Energy Audit Lab (EX-705) - Unit 4 Short Notes

UNIT 4: ADVANCED AUDIT TECHNIQUES & SPECIALIZED SYSTEMS

4.0 Introduction & Scope of Unit 4

• Transition: Moves beyond walk-through audits to comprehensive/detailed audits requiring quantitative measurement and system-level analysis.

• Focus: Specialized energy end-uses (HVAC, process equipment, compressed air) and advanced diagnostic tools.

• Safety: Paramount when interacting with live electrical panels, pressurized systems, and high-temperature surfaces. Must follow lockout/tagout (LOTO) and PPE protocols.

4.1 Advanced Diagnostic Tools & Instrumentation

4.1.1 Thermal Imaging (Infrared Thermography)

• Principle: All objects emit IR radiation proportional to surface temperature. Camera detects this radiation to create a thermal map (thermogram).

• Key Applications:

  • Building Envelope: Air leakage (cold spots in winter, hot spots in summer), insulation voids (thermal bridging), moisture intrusion.

  • Electrical Systems: Loose/overloaded connections (hot spots), imbalanced phases, failing components.

  • Steam/Process: Trapped steam, insulation failure, valve/heat exchanger malfunction.

• Interpretation: Look for abnormal hot spots, cold spots, and irregular thermal patterns vs. expected norm.

• Critical Limitations: Emissivity (must be set correctly), reflected ambient temperature, distance to target, weather conditions.

  [!TIP] Exam Focus: Always state emissivity setting and environmental conditions when reporting thermographic findings. A shiny surface (low emissivity) can mask a true high temperature.

4.1.2 Combustion Analysis & Flue Gas Monitoring

• Instrument: Combustion analyzer measures O₂, CO, CO₂, stack temperature (T_stack), and sometimes flue gas velocity.

• Primary Calculation: Combustion Efficiency (η_comb)

  For natural gas (simplified):

$$ \eta_{comb} = 100\% - \left( \frac{L_{sensible} + L_{latent}}{Input} \right) \times 100\% $$

Where losses are calculated from **stack temperature**, **excess air** (from O₂/CO₂), and **flue gas composition**.

• Diagnosis: High O₂ = excessive excess air (loss). High CO = incomplete combustion (safety & efficiency issue). High T_stack = heat loss.

4.1.3 Data Loggers & Continuous Monitoring

• Purpose: Capture temporal variations in energy use and environmental conditions.

• Types: Power (kW, kWh), temperature (T), humidity (RH), pressure (P), flow (CFM, GPM).

• Deployment Strategy:

  1. Select Points: Based on audit objectives (e.g., main electrical panel, AHU discharge, production line).

  2. Duration: Minimum 1-2 weeks to capture weekly cycle; longer for seasonal systems.

  3. Sampling Rate: 15-min or 1-hour intervals typical for energy analysis.

• Analysis: Time-series plots are the first step to identify patterns, schedules, and anomalies.

4.1.4 Advanced Power Quality Analysis

• Parameters Measured:

  • Harmonics: Distorted waveforms (current & voltage). Cause: non-linear loads (VFDs, computers). Effect: heating in conductors/transformers, nuisance tripping.

  • Voltage Sags/Swells: Short-duration voltage deviations.

  • Transients: Very short-duration spikes.

  • Power Factor (PF): Ratio of real power (kW) to apparent power (kVA). Low PF increases current and losses.

• Correlation: Poor PQ can cause equipment malfunction, premature failure, and increased energy losses.

4.2 Detailed Audit of Core Building Systems

4.2.1 HVAC System Deep Dive

• Chiller/Compressor Performance:

  • Coefficient of Performance (COP): COP = Cooling Output (kW) / Power Input (kW)

  • kW/ton: (Power Input kW) / (Cooling Capacity in tons). Lower is better.

• Cooling Tower: Range = T_hot - T_cold; Approach = T_cold - Wet-bulb. Lower approach = better efficiency.

• Air-Side Economizer: Verify controls free-cooling when outdoor air enthalpy < return air enthalpy.

• Duct Leakage: Measured with duct blaster (pressurizes duct system). Reported as CFM @ X Pa or % of design flow.

• Pump/Fan Affinity Laws: (Q1/Q2) = (N1/N2), (P1/P2) = (N1/N2)², (HP1/HP2) = (N1/N2)³. Critical for VFD savings estimation.

4.2.2 Lighting System Advanced Analysis

• Photometric Survey: Measure foot-candles (fc) at workplane. Calculate Uniformity Ratio = Min fc / Avg fc. Target > 0.7 for offices.

• Lighting Power Density (LPD): Total Connected Lighting Power (W) / Total Lighted Area (ft² or m²). Compare to ASHRAE 90.1/IECC code limits.

• Control Verification: Test occupancy sensors (time delay, sensitivity), daylight harvesting (dimming response, setpoint).

4.2.3 Building Envelope Detailed Investigation

• Blower Door Test:

  • Procedure: Pressurize/depressurize building to 50 Pa, measure airflow (CFM50).

  • Key Metric: Air Changes per Hour at 50 Pa (ACH50):

$$ ACH50 = \frac{CFM50 \times 60}{Building\ Volume\ (ft³)} $$

*   **Interpretation:** Lower ACH50 = tighter envelope. Typical: Existing homes ~5-10 ACH50, New codes ~3-5 ACH50.

• Leak Path Identification: Use smoke pencil at suspected leaks during blower door test. Thermography shows cold air infiltration in winter.

• Window Performance: Estimate U-value (winter) and SHGC (summer) from NFRC label or visual inspection. Assess shading devices.

4.3 Industrial & Process Energy Audit Focus

4.3.1 Process Heating Systems

• Furnace Heat Balance: Input Energy = Useful Heat to Load + Stack Losses + Radiation/Convection Losses + Other Losses.

• Insulation Surface Loss: Q_loss = U * A * (T_surface - T_ambient). U = overall heat transfer coefficient.

• Optimization: Reduce excess air (measure O₂), repair insulation, recover waste heat (e.g., from flue gas).

4.3.2 Process Cooling & Refrigeration

• Refrigeration Cycle Performance:

  • Superheat: T_suction_line - Saturation T at suction pressure. Indicates refrigerant charge.

  • Subcooling: Saturation T at condenser pressure - T_liquid_line. Indicates full condenser.

  • Target values specified by manufacturer.

• Evaporator/Condenser: Check for fouling (high approach temperatures), proper air/water flow.

4.3.3 Compressed Air System Audit

• System Mapping: Create a one-line diagram of compressors, dryers, receivers, distribution.

• Key Metric: Specific Power (kW/100 CFM):

$$ Specific\ Power = \frac{Total\ Compressor\ Input\ Power\ (kW)}{Total\ Free\ Air\ Delivery\ (CFM)} \times 100 $$

*   **Benchmark:** Well-maintained system ~20-25 kW/100 CFM. Leaky/poorly controlled >30.

• Leak Survey: Use ultrasonic detector or flow meter to quantify leaks (CFM). Leaks can be 20-30% of total production.

• Air Flow Measurement: In-line flow meters, or calculate from pressure drop across orifice/venturi.

4.3.4 Motor & Drive Systems

• Motor Efficiency: Compare nameplate efficiency to measured load (using clamp-on kW meter or motor analyzer). Motors are most efficient at 75-100% load.

• VFD Audit:

  • Savings Estimation: Use Affinity Laws for centrifugal loads (fans, pumps). Power ∝ Speed³.

  • Check for: Harmonics (use power quality analyzer), proper cooling, application suitability (not for constant torque at low speed).

• Belt Drives: Inspect for tension (too loose = slip), alignment (misalignment = bearing wear, energy loss). Consider synchronous belts for higher efficiency.

4.4 Energy Data Analysis & Benchmarking

4.4.1 Creating Detailed Energy Baselines

• Normalized Baseline Model: Energy Use = f(Independent Variables).

  • Common Variables: Production units, Degree-Days (HDD/CDD), Occupancy, Weather (Dry-bulb, Wet-bulb).

• Regression Analysis: Use statistical software (Excel, Minitab).

  • Simple Linear: Y = a + bX (e.g., kWh vs. HDD).

  • Multiple Linear: Y = a + b1X1 + b2X2 + ... (e.g., kWh vs. Production + CDD).

  • R² value indicates goodness of fit (>0.7 generally acceptable).

4.4.2 Benchmarking Against Standards & Peers

• ENERGY STAR Portfolio Manager: Calculates Energy Use Intensity (EUI) = Total Site Energy (kBtu or kWh) / Gross Floor Area (ft² or m²).

  • Source EUI includes transmission/distribution losses (more comprehensive).

  • Scores 1-100; Score ≥ 75 qualifies for ENERGY STAR certification.

• ASHRAE Levels: Level 1 (benchmarking), Level 2 (detailed audit), Level 3 (capital-intensive, sub-metered).

4.4.3 Identifying Anomalies & Savings Opportunities from Data

• Interval Data Analysis (e.g., 15-min kW):

  • 24/7 Loads: Non-zero minimum demand indicates base load waste (lights, equipment left on).

  • Scheduling Issues: Peak demand occurring outside production hours.

  • Demand Spikes: Identify large, short-duration loads.

  • Seasonal Shifts: Compare monthly profiles to identify HVAC-dominated vs. process-dominated usage.

4.5 Savings Calculation & Measure Evaluation

4.5.1 Engineering Calculations for ECMs

• Incorporate Part-Load Performance: Use performance curves (e.g., chiller COP vs. load %) instead of full-load values.

• Interactive Effects: Account for ** HVAC interactions** (e.g., lighting retrofit reduces cooling load).

  • Example: Cooling energy savings = Lighting kWh reduction * (1 / COP) * (Fraction of lighting heat that becomes cooling load).

4.5.2 Measurement & Verification (M&V) Concepts

• IPMVP (International Performance Measurement & Verification Protocol):

  • Option A: Retrofit Isolation, Key Parameter Measurement.

  • Option B: Retrofit Isolation, All Parameter Measurement.

  • Option C: Whole Facility.

  • Option D: Calibrated Simulation.

• Core Concepts: Define savings (Baseline - Post-retrofit), measurement boundary, and baseline period.

4.6 Advanced Reporting & Presentation of Findings

• Report Structure:

  1. Executive Summary (key findings, costs, savings, ROI).

  2. Facility Description & Audit Scope.

  3. Detailed Findings by System (with data, thermograms, calculations).

  4. Recommended ECMs (detailed savings calc, cost, payback).

  5. Implementation Plan (prioritized, phased).

  6. Technical Appendices (raw data, instrument specs, assumptions).

• Financial Analysis: Present Simple Payback, Net Present Value (NPV), Internal Rate of Return (IRR).

• Communication: Use graphs (time-series, bar charts), tables (ECM summary), and annotated images (thermograms, photos). Clearly state risks, assumptions, and uncertainty in savings estimates.

4.7 Unit 4 Lab Practicals & Case Studies (Synthesis)

• Practical 1: Blower Door & Thermography: Set up blower door, conduct test, calculate ACH50. Use IR camera to identify leakage paths during test.

• Practical 2: Compressed Air Audit: Map system, measure compressor power & flow, conduct ultrasonic leak survey, calculate specific power (kW/100 CFM), quantify leak load.

• Practical 3: Interval Data Analysis: Import 1-month 15-min kW data into spreadsheet. Create baseline model (e.g., vs. production or degree-days). Identify non-production hours with significant load, schedule deviations.

• Case Study: Integrates tools from 4.1-4.5 for a complex facility. Requires synthesizing thermography, combustion analysis, sub-metering, and system-specific calculations into a cohesive report with prioritized ECMs.