Energy Audit & Management (EX-703 (B)) - Unit 4 Short Notes

UNIT 4: ENERGY AUDIT & MANAGEMENT - EXAM-FOCUSED SHORT NOTES

1. ENERGY AUDIT FUNDAMENTALS & REGULATORY FRAMEWORK

Definition & Concept

An Energy Audit is a systematic procedure to evaluate energy consumption patterns, identify areas of energy wastage, and recommend measures for conservation and cost reduction. It establishes a baseline for energy performance.

Purpose & Objectives:

• Quantify energy use and costs.

• Identify energy conservation opportunities (ECOs).

• Improve energy efficiency and reduce greenhouse gas emissions.

• Ensure compliance with regulations (e.g., BEE).

• Enhance operational reliability and productivity.

Types of Energy Auditing (Key Comparison)

[!TIP] Exam Focus: Distinguish Preliminary (identifies what to fix) from Detailed (provides how to fix with engineering design). Past papers frequently ask for this distinction.

Energy Manager: Roles & Duties

• Roles: Develop & implement energy policy, coordinate audit teams, analyze data, prioritize ECOs, prepare reports, monitor savings, train staff.

• Institutional Setup Steps:

  1. Obtain top management commitment.

  2. Form an energy management team.

  3. Conduct energy audit (walk-through → detailed).

  4. Identify and evaluate ECOs (technical & economic).

  5. Implement selected ECOs.

  6. Monitor, verify, and maintain savings.

  7. Continuously review and improve.

Bureau of Energy Efficiency (BEE) Regulations

• Designated Consumers (DCs): Industries, commercial buildings, etc., above specified energy consumption thresholds (e.g., > 1 MW connected load or > 6,00,000 units/year).

• Manners & Intervals:

  • Preliminary Audit: Every 3 years.

  • Detailed Audit: Every 3 years (must be conducted by an accredited energy auditor).

  • Reports must be submitted to BEE's PAT (Perform, Achieve, Trade) portal.

• Mandate: DCs must appoint a Certified Energy Manager (CEM).

Barriers & Mitigation

2. ENVIRONMENTAL ASPECTS OF ENERGY

Environmental Impact of Energy Sources

Systematic Environmental Assessment (Methodology)

1. Screening: Identify potential significant impacts.

2. Scoping: Define boundaries (spatial, temporal) and key issues.

3. Baseline Study: Collect existing environmental data.

4. Impact Prediction & Evaluation: Use models to quantify/magnitude of impacts.

5. Mitigation Measures: Propose plans to avoid, reduce, or offset impacts.

6. Public Consultation: Involve stakeholders.

7. Environmental Management Plan (EMP): Outline monitoring and compliance.

8. Decision Making: Integrate findings into project approval.

3. ELECTRICAL SYSTEMS & POWER QUALITY

Power Factor (PF) Management

• Definition: PF = $$\displaystyle \frac{\text{Real Power (kW)}}{\text{Apparent Power (kVA)}} = \cos\phi $$. It measures effective power utilization.

• Significance: High PF (close to 1) reduces current for same kW, lowering losses ($$\displaystyle I^2R $$), improving voltage regulation, and avoiding penalties.

• Causes of Low PF: Inductive loads (motors, transformers, reactors) cause current to lag voltage.

• Advantages of High PF:

  • Reduced kVA demand → lower electricity bills (capacity charges).

  • Lower system losses → energy savings.

  • Improved voltage profile.

  • Increased system capacity.

• Disadvantages of Low PF:

  • Higher current → larger cables, transformers needed.

  • Increased losses and voltage drop.

  • Penalty charges from utilities.

• PF Improvement with Capacitors:

  • Capacitors supply leading current, canceling lagging current from inductive loads.

  • Required Capacitor kVAr Calculation:

$$ \text{Required kVAr} = kW \times (\tan\phi_1 - \tan\phi_2) $$

    where $$\displaystyle \phi_1 $$ = current PF angle, $$\displaystyle \phi_2 $$ = desired PF angle.

*   **New kVA Demand after Correction:**

$$ \text{New kVA} = \frac{kW}{\text{New PF}} $$

• Best Location for Capacitors: At the load terminals (near inductive load). This minimizes distribution losses by reducing current throughout the upstream circuit.

• HT vs. LT Lines:

  • HT (High Tension): > 1000V (typically 11kV, 33kV). Used for transmission/distribution. Lower current for same power → lower losses.

  • LT (Low Tension): ≤ 1000V (415V/230V). Used for final distribution to consumers. Higher current → higher losses over distance.

Harmonics in Power Systems

• Major Problems:

  • Additional Heating: In motors, transformers, cables ($$\displaystyle I_{rms}^2R $$ losses).

  • Resonance: With system capacitance, causing voltage amplification and overvoltages.

  • Malfunction: Sensitive electronic equipment (computers, PLCs) can fail or operate erratically.

  • Neutral Overloading: In 3-phase 4-wire systems, triplen harmonics (3rd, 9th...) add in neutral.

  • Torque Pulsations: In motors, causing vibration and mechanical stress.

• Sources (Non-linear Loads): UPS systems, VFDs (Variable Frequency Drives), computers, rectifiers, arc furnaces, fluorescent lamps with magnetic ballasts.

• Generation Mechanism: Non-linear loads draw current in non-sinusoidal pulses, distorting the pure sinusoidal voltage waveform (Fourier series decomposition).

• Evaluation: Total Harmonic Distortion (THD) is the key metric.

$$ \text{THD} = \frac{\sqrt{\sum_{n=2}^{\infty} I_n^2}}{I_1} \times 100\% $$

(for current THD, $$\displaystyle I_1 $$ is fundamental component). IEEE 519 standard provides recommended limits.

Energy-Efficient Motors

• Constructional Differences:

  • Core: Thinner, higher-grade silicon steel laminations → lower core losses.

  • Windings: More copper (larger cross-section) → lower $$\displaystyle I^2R $$ losses.

  • Air Gap: Optimized (slightly larger) to reduce stray losses.

  • Bearings: High-quality, low-friction bearings.

• Advantages: Higher efficiency (2-5% points), lower operating temperature, longer life, better performance at part-load.

• Motor Loading Calculation (from input data):

  1. Input Power (kW) = $$\displaystyle \sqrt{3} \times V \times I \times PF \times 10^{-3} $$

  2. Full Load Input (kW) = $$\displaystyle \frac{\text{Rated kW}}{\text{Full Load Efficiency}} $$

  3. Loading % = $$\displaystyle \frac{\text{Input Power}}{\text{Full Load Input}} \times 100 $$

Transformer Losses & Efficiency

• Losses:

  • Core (Iron) Losses: Constant, occur whenever energized (hysteresis, eddy currents). Minimized by using CRGO (Cold Rolled Grain Oriented) steel.

  • Copper (Load) Losses: Vary with square of load current ($$\displaystyle I^2R $$). Minimized by using larger conductor cross-section.

• Efficiency: $$\displaystyle \eta = \frac{\text{Output Power}}{\text{Output Power} + \text{Total Losses}} $$.

• Loss Minimization: Optimal design (core/copper loss balance), use of amorphous metal cores (for distribution transformers), proper cooling, and avoiding overloading.

4. THERMAL SYSTEMS & BOILERS

Boiler Efficiency & Performance

• Direct Method (Input-Output):

$$ \eta_{\text{direct}} = \frac{\text{Steam Generation} \times (h_{\text{steam}} - h_{\text{feedwater}})}{\text{Fuel Consumption} \times \text{GCV}} \times 100\% $$

(Simple, measures actual performance).

• Indirect Method (Losses):

$$ \eta_{\text{indirect}} = 100 - (\text{Loss due to flue gas} + \text{Loss due to moisture} + \text{Loss due to unburnt fuel} + ...) $$

(Identifies individual losses for improvement).

• GCV vs. NCV Basis:

  • GCV (Gross Calorific Value): Includes latent heat of vaporization in fuel moisture.

  • NCV (Net Calorific Value): Excludes latent heat (more practical for boilers as flue gas vapor is not condensed).

  • Conversion: $$\displaystyle \eta_{\text{NCV}} = \eta_{\text{GCV}} \times \frac{\text{GCV}}{\text{NCV}} $$ (since output is same, input energy basis changes).

  • Approximate NCV = GCV - (0.09 × %H + 0.0245 × %M) (kcal/kg).

• Part-Load Efficiency: Boiler efficiency typically decreases at part-load due to higher radiation/convection losses relative to output. Selection Logic: For a given total steam requirement, operate boilers at or near full load for highest overall efficiency.

• Part-Load Strategy Calculation (Example from Past Paper):

  • Given: 2 identical boilers (15 TPH, 82% eff @ 100% load). Part-load eff: 78% @ 75% load, 66% @ 45% load.

  • Requirement: 20 TPH.

  • Option A: Both at 10 TPH (66.7% load → use 75% eff data? Interpolate or use nearest). Option B: One at 15 TPH (82%), other at 5 TPH (33% → use 45% eff data?).

  • Calculate Fuel Consumption for each option:

    Fuel (Option) = $$\displaystyle \frac{\text{Steam Output}}{\text{Efficiency}} $$

  • % Savings: $$\displaystyle \frac{\text{Fuel}_{\text{higher}} - \text{Fuel}_{\text{lower}}}{\text{Fuel}_{\text{higher}}} \times 100\% $$

  • Conclusion: Usually, Option B (one full, one part) saves more fuel as it keeps one boiler at high efficiency.

Combustion & Furnace Optimization

• Furnace Classification: By heat source (combustion, electrical, solar), by material (metallurgical, ceramic), by operation (batch, continuous).

• Minimum Excess Air: Excess air beyond stoichiometric requirement carries heat away in flue gas. Advantages of minimum excess air:

  • Reduces flue gas losses (major boiler loss).

  • Reduces fan power consumption.

  • Lowers NOx formation (at high temps).

• Achieving Optimal Excess Air: Use flue gas analyzer to measure O₂ or CO in flue gas. Target O₂ levels: ~2-4% for boilers, ~1-3% for furnaces. Adjust air dampers accordingly.

• Low-Pressure Steam Efficiency: At lower pressure, steam has higher enthalpy of evaporation (more latent heat per kg). For heating applications (where only latent heat is used), low-pressure steam delivers more useful heat per unit mass, improving system efficiency despite lower temperature.

Steam System Management

• Distribution: Steam mains, risers, drips, traps. Insulation of all distribution lines is mandatory.

• Steam Traps:

  • Working: Automatic valve that discharges condensate, air, and non-condensables while retaining live steam.

  • Types: Mechanical (float & thermostatic), thermostatic (bimetallic, bellows), thermodynamic (disc).

  • Performance Assessment Methods:

    1. Visual/Audio Inspection: (for thermodynamic traps - "click" sound).

    2. Temperature Measurement: Downstream of trap should be near saturation temp if working.

    3. Ultrasonic Testing: Detects flow noise.

    4. Infrared Thermography: Hot trap = failed open; cold trap = failed closed.

• Condensate Recovery:

  • Process: Collect condensate from traps, filter, pump back to boiler feedwater system.

  • Benefits: Saves boiler feedwater (and treatment cost), recovers heat (enthalpy), reduces water discharge.

• Flash Steam Utilization: High-pressure condensate, when throttled to low pressure, generates flash steam (latent heat). This low-pressure flash steam can be used for low-temperature heating (e.g., tank heating, space heating) before condensate is recovered.

Thermal Insulation

• Economic Thickness of Insulation (ETI): The insulation thickness that minimizes the sum of annualized capital cost (of insulation) and annual heat loss cost. Thicker insulation reduces loss but costs more.

• Factors Influencing ETI:

  • Fuel cost (higher → favors thicker insulation).

  • Insulation material cost & thermal conductivity (λ).

  • Surface temperature & ambient conditions.

  • Interest/discount rate.

  • Expected life of insulation.

Alternative Heating Systems: Thermic Fluid

• Working: Heat transfer oil (thermic fluid) is heated in a furnace/coil (no phase change) and circulated to heat exchangers for process heating. Operates at high temperatures (up to 350°C) at low pressures.

• Comparison with Steam:

  | Aspect | Steam System | Thermic Fluid System | | :--- | :--- | :--- | | Pressure | High pressure required for high temp. | Low pressure, even at high temp. | | Risk | Explosion hazard, scaling/corrosion. | Fire risk if leaks, no scaling. | | Temperature | Limited by pressure (e.g., 10 bar ≈ 180°C). | High temperatures possible (350°C+). | | Applications | General heating, humidification. | High-temperature, precise control processes (chemical, textile, food). |

5. MECHANICAL SYSTEMS: PUMPS, FANS & DRIVES

Pumping Systems

• Affinity Laws (Centrifugal Pumps/Fans):

  1. Flow (Q) ∝ Speed (N)

  2. Head (H) ∝ $$\displaystyle N^2 $$

  3. Power (P) ∝ $$\displaystyle N^3 $$

  • Implication: Small reduction in speed drastically reduces power consumption.

• Factors Affecting Performance: System curve (static head + friction head), pump curve, fluid properties, wear (impeller, wear ring).

• Energy Conservation Opportunities:

  • Impeller Trimming: Reduce impeller diameter → reduces flow, head, power (use affinity laws).

  • Variable Speed Drives (VSDs): Adjust speed to match system demand (most efficient).

  • Parallel Operation: Used to increase flow capacity. Significance: Allows operation of fewer pumps at higher load (better efficiency) and redundancy. Avoid running all pumps at part-load.

  • Reduce system resistance (larger pipes, remove throttling valves).

  • Repair/restore worn components.

Fan Systems

• Design & Selection: Based on required airflow (CFM) and static pressure (inches WC). Consider efficiency, noise, material.

• Performance Evaluation: Compare operating point (from system curve) with fan curve. Check for over-sizing.

• Conservation Measures: Similar to pumps: VSDs, impeller trimming, inlet/outlet dampers (less efficient than VSD), reduce system resistance, fix leaks, parallel operation optimization.

• Comparison with Pumps: Affinity laws apply identically. Fan power is proportional to $$\displaystyle N^3 $$ and cube of impeller diameter.

6. LIGHTING SYSTEMS

Lighting Fundamentals

• Illumination (Lux): Luminous flux (lumens) per unit area. 1 Lux = 1 lumen/m². Measured by Lux Meter.

• Key Metrics: Luminous efficacy (lumens/Watt), Lumen maintenance (% output at end of life), Color Rendering Index (CRI).

Energy Conservation in Lighting

• Major Opportunities:

  1. Lamp Replacement: Replace inefficient lamps (e.g., T12 fluorescent, halogen) with LEDs or T5 fluorescents.

  2. Ballast Optimization: Replace magnetic ballasts with electronic ballasts (lower losses, no flicker).

  3. Controls: Occupancy sensors, daylight harvesting sensors, timers, dimmers.

  4. Daylight Harvesting: Use photosensors to dim/turn off lights near windows.

  5. Cleaning & Maintenance: Regular cleaning of luminaires.

  6. Task Lighting: Provide light only where needed.

• LED Advantages:

  • Very high efficacy (100-150+ lm/W vs. 60-100 for fluorescent).

  • Long life (50,000+ hours).

  • Instant on, no UV/IR, dimmable, robust.

• Savings Calculation (Lamp Replacement):

  • Annual Energy Savings (kWh) = (No. of Lamps) × (W_old - W_new) × (Operating Hours) / 1000

  • Annual Cost Savings (Rs) = Energy Savings × Electricity Rate (Rs/kWh)

  • Simple Payback Period (Years) = $$\displaystyle \frac{\text{Additional Cost of New Lamp}}{\text{Annual Cost Savings}} $$

  • Example (from Dec 2024): Replace 500W → 350W, 350W → 150W, 125W → 60W for 4500 hrs @ Rs. 5.5/unit.

    • Calculate savings for each type separately, sum them.

    • Payback = Total investment / Total annual savings.

7. FINANCIAL & ECONOMIC ANALYSIS

Life Cycle Costing (LCC)

• Definition: Total cost of owning and operating an asset over its entire life (initial cost + operating + maintenance + disposal - salvage).

• Process: Identify all cost components, assign them to time periods, convert to present value using discount rate, sum.

• Application in Energy Management: Compare alternatives (e.g., standard vs. efficient motor, insulation thickness). The option with lowest LCC is preferred, even if initial cost is higher.

• Effect: Shifts decision from lowest first cost to lowest total ownership cost.

Investment Appraisal Techniques

• Simple Payback Period (SPP):

  • Definition: Time required for cumulative annual savings to equal the initial investment.

  • Calculation: SPP = $$\displaystyle \frac{\text{Initial Investment}}{\text{Annual Net Savings}} $$

  • Significance: Simple, intuitive measure of risk (shorter payback = less risk).

  • Limitations: Ignores cash flows after payback, time value of money, profitability.

• Risk Analysis in Payback: Incorporate uncertainty in savings estimates (e.g., energy prices, usage). Use sensitivity analysis or probabilistic payback (Monte Carlo simulation) to assess likelihood of achieving target payback.

• Net Present Value (NPV):

  • Definition: Sum of all future cash flows (savings - costs) discounted to present value.

  • Formula:

$$ \text{NPV} = \sum_{t=1}^{n} \frac{\text{CF}_t}{(1+r)^t} - \text{Initial Investment} $$

    where $$\displaystyle \text{CF}_t $$ = net cash flow in year *t*, *r* = discount rate, *n* = life.

*   **Interpretation:**

    *   NPV > 0: Project adds value (accept).

    *   NPV = 0: Break-even.

    *   NPV < 0: Project destroys value (reject).

*   **Advantage over SPP:** Considers **time value of money** and **entire project life**.

*   **Calculation Example (Dec 2024):** Lamp cost Rs. 2000, annual savings Rs. 22000 for 2 years, r=15%.

    *   Year 1 PV = 22000 / (1.15) = 19130.43

    *   Year 2 PV = 22000 / (1.15)² = 16635.59

    *   Total PV of Savings = 35766.02

    *   NPV = 35766.02 - 2000 = **33766.02 Rs** (Positive, accept).

• Internal Rate of Return (IRR):

  • Definition: The discount rate (r) that makes NPV = 0. It is the annualized effective compounded return rate.

  • Significance: Measures profitability. Compare IRR to hurdle rate (minimum acceptable return). If IRR > hurdle rate, accept.

Energy Service Company (ESCO) Concept

• Basic Model: ESCO provides performance-based contracting. It designs, finances, implements, and guarantees energy savings from ECOs. Client pays ESCO from the actual savings.

• Functions: Energy audit, project design, financing, installation, monitoring & verification (M&V), maintenance.

• Performance Contracting: Legal agreement where ESCO guarantees a certain level of savings. Client uses savings to pay ESCO's fee and investment cost. No upfront cost for client.

• Role: Overcomes financial and technical barriers for clients, especially in public/industrial sectors.

8. INSTRUMENTATION & MONITORING

Key Instruments for Energy Audit

Working Principle: Power Analyzer

• Principle: Uses voltage and current transformers (or Hall effect sensors) to sample waveforms. Digital signal processing (DSP) computes:

  • Real Power (kW): Average of instantaneous voltage × current product.

  • Reactive Power (kVAr): $$\displaystyle \sqrt{kVA^2 - kW^2} $$.

  • Power Factor: kW / kVA.

  • Harmonics: FFT (Fast Fourier Transform) of waveforms to separate fundamental and harmonic components, then calculate THD.

• Use in Audit: Identifies low PF, harmonic distortion, unbalanced loads, and measures energy consumption (kWh) of individual equipment.

[!TIP] Exam Focus: Be prepared to list instruments and explain one (often Power Analyzer or Flue Gas Analyzer). Know key formulas for PF, motor loading, boiler efficiency, and lighting savings. Distinguish Preliminary vs. Detailed Audit and Define ESCO are almost certain questions.