Hybrid &Electrical Vehicles (EX-703 (A)) - Unit 4 Short Notes

UNIT 4: Energy Audit and Management

I. Fundamentals of Energy Management & Auditing

Energy Management: Definition & Objectives

• Definition: The proactive, organized, and systematic coordination of procurement, conversion, distribution, and use of energy to meet the requirements of an organization while minimizing energy costs and environmental impact.

• Objectives:

  • Reduce energy costs and waste.

  • Conserve energy resources.

  • Minimize environmental impact (GHG emissions).

  • Enhance energy security and reliability.

  • Comply with regulations and standards.

• Importance: Directly impacts operational costs, sustainability goals, and regulatory compliance.

Energy Audit: Definition & Purpose

• Definition: A systematic procedure to quantify energy consumption, identify areas of energy waste, and recommend measures for improving energy efficiency.

• Purpose: To establish a baseline, identify savings potential, prioritize actions, and justify investments in energy conservation.

Types of Energy Audits

Role & Responsibilities of an Energy Manager

• Duties: Develop energy policy, plan & implement audit programs, monitor consumption, prepare reports, promote awareness, and ensure compliance.

• Managerial Functions: Planning (set targets), Organizing (assign tasks), Directing (guide staff), Coordinating (sync activities), Controlling (track performance vs. plan).

Audit Process in an Institutional/Organizational Setting

1. Planning & Organizing: Secure management commitment, form audit team, define scope.

2. Data Collection: Gather historical energy data (bills), process flow diagrams, equipment lists.

3. Walk-through Survey: Identify major energy-consuming areas and obvious inefficiencies.

4. Detailed Measurement & Monitoring: Use instruments to quantify energy use (kWh, therm, steam) for key equipment/systems.

5. Analysis & Calculations: Compare against benchmarks, calculate savings potential for each measure.

6. Report Preparation: Present findings, recommendations, economic analysis (payback, NPV), and action plan.

7. Implementation & Follow-up: Prioritize and implement measures, monitor savings, and report results.

[!TIP] Common Pitfall: Skipping the baseline data collection step leads to unverifiable savings claims.

General Principles of Energy Management

• Systematic Approach: Treat the facility as an integrated energy system.

• Measurement & Verification (M&V): Quantify savings before and after implementation.

• Life Cycle Costing (LCC): Evaluate investments based on total cost over life, not just initial cost.

• Continuous Improvement: Regular audits and monitoring.

• Management Commitment: Top-down support is essential for success.

II. Electrical Systems Energy Efficiency

A. Power Factor (PF) Management

Significance & Benefits

• PF = Real Power (kW) / Apparent Power (kVA).

• Benefits of High PF (near 1.0):

  • Reduced current in conductors → smaller cable sizes, reduced I²R losses.

  • Lower kVA demand → reduced electricity bills (lower demand charges).

  • Improved voltage regulation.

  • Increased system capacity.

• Disadvantages of Low PF (lagging): Higher current, increased losses, penalty charges from utilities, reduced equipment life.

Capacitor Banks for PF Correction

• Working Principle: Capacitors supply leading reactive power (kVAr) to neutralize the lagging reactive power drawn by inductive loads (motors, transformers).

• Best Locations (Energy Conservation Perspective):

  1. Individual Motor Terminals (Load Correction): Most effective. Reduces current in entire upstream circuit.

  2. Distribution Boards/Sub-Busbars (Group Correction): For a group of similar loads.

  3. Main Incoming Feeder (Central Correction): Least effective, as reactive power circulates through the entire system.

• Key Formula:

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

Where $$\displaystyle \phi_1 $$ = initial PF angle, $$\displaystyle \phi_2 $$ = target PF angle.

Power System Aspects: HT vs. LT

• HT (High Tension): > 1 kV (e.g., 11kV, 33kV). Used for bulk power transmission/distribution. Lower current for same power → lower losses.

• LT (Low Tension): ≤ 1 kV (e.g., 415V, 230V). Used for final distribution to consumers. Higher current → higher losses if conductors are undersized.

• Reasons for Low PF in Systems: Over-sized motors operating at low load, lightly loaded transformers, use of induction furnaces/welding sets, poor maintenance.

Numerical Problem Pattern (PF Improvement & Penalty):

1. Calculate initial kVA demand: $$\displaystyle \text{kVA}_1 = \frac{\text{kW}}{\text{PF}_1} $$.

2. Find kW from given data (if not directly given, use $$\displaystyle \text{kW} = \text{kVA}_1 \times \text{PF}_1 $$).

3. Calculate required kVAr for target PF.

4. New kVA demand: $$\displaystyle \text{kVA}_2 = \sqrt{(\text{kW})^2 + (\text{kVAr}_{\text{new}})^2} $$.

5. Penalty: If improved PF < utility's minimum, penalty = (Minimum PF - Actual PF) × Penalty Rate × 100 (for % dip).

B. Harmonics in Power Systems

Effects & Problems

• Increased Heating: In motors, transformers, and cables (due to harmonic currents).

• Misfiring in Drives: Problems in AC/DC drives and UPS systems.

• Neutral Conductor Overloading: In 3-phase 4-wire systems (triplen harmonics add in neutral).

• Capacitor Failure: Resonance with system inductance, leading to overcurrent.

• Relay & Metering Errors: Maloperation of protective relays and inaccurate energy meter readings.

• Telephone Interference.

Sources & Evaluation

• Sources (Non-linear Loads): Rectifiers (AC/DC drives), UPS/inverters, arc furnaces, welding machines, fluorescent lamps with electronic ballasts, switched-mode power supplies (computers).

• Evaluation Procedure:

  1. Identify major non-linear loads.

  2. Measure harmonic current spectrum using a Power Quality Analyzer.

  3. Calculate Total Harmonic Distortion (THD) for current (THDi) and voltage (THDv):

$$ \text{THD}_i (\%) = \frac{\sqrt{\sum_{h=2}^{40} I_h^2}}{I_1} \times 100 $$

    (Where $$\displaystyle I_h $$ is RMS current at harmonic order *h*, $$\displaystyle I_1 $$ is fundamental current).

4.  Compare with standards (e.g., IEEE 519).

C. Energy Efficient Motors (EEMs)

Construction & Features (vs. Standard Motors)

• Higher Grade Core Material: Thinner, higher silicon steel laminations → reduced core losses.

• Increased Copper: More copper in stator windings → lower winding resistance → lower I²R losses.

• Optimized Aerodynamic Design: Reduced fan losses.

• Improved Bearing Design: Reduced friction losses.

• Tighter Manufacturing Tolerances.

Advantages

• Higher efficiency (typically 2-5% points higher) at full and part load.

• Lower operating temperature → longer insulation life.

• Reduced energy costs over life.

• Often better power factor.

Performance Assessment & Part Load

• Motor Loading from Input Parameters:

  1. Input Power (kW) = √3 × V × I × PF (for 3-phase).

  2. Loading (%) = (Input kW / Full Load kW rating) × 100.

• Efficiency at Part Load: EEMs maintain higher efficiency at part load compared to standard motors, which drop off more steeply.

D. Lighting Systems

LED Lighting: Technology & Advantages

• Technology: Light Emitting Diode. Semiconductor device that emits light when current flows.

• Advantages over Conventional (Fluorescent/Metal Halide):

  • High Efficacy: 100-150+ lumens/Watt vs. 60-100 for fluorescent.

  • Long Life: 50,000-100,000 hours.

  • Instant On/Off: No warm-up time.

  • Directional Light: Reduces losses.

  • No Mercury Content.

  • Dimmable.

Scope for Energy Conservation

• Technology Upgrade: Replace incandescent, fluorescent, HID lamps with LEDs.

• Optimizing Illumination Levels: Use only required lux (see table below).

• Lighting Controls: Occupancy sensors, daylight harvesting, timers.

• Regular Maintenance: Cleaning fixtures, replacing failed lamps promptly.

Design Parameters: Recommended Illuminance (Lux) Levels

E. Transformer Losses & Minimization

• Core (Iron) Losses: Hysteresis & Eddy current losses in core. Constant (occur even at no-load).

  • Minimization: Use high-grade, thin, grain-oriented silicon steel cores.

• Copper (Winding) Losses: I²R losses in windings. Variable (proportional to load²).

  • Minimization: Use larger cross-section copper conductors, improve cooling.

• Stray Losses: Due to leakage flux causing eddy currents in structural parts.

• Dielectric Losses: In insulation material (oil/paper).

• Minimization Strategies: Select right-sized transformer (avoid light loading), use amorphous core transformers (very low core loss), ensure proper maintenance (oil quality), operate near rated capacity (for distribution transformers).

III. Thermal Systems Energy Efficiency

A. Boiler Systems

Efficiency Assessment

• Direct Method (Input-Output):

$$ \eta_{\text{boiler}} (\%) = \frac{\text{Steam Output (Enthalpy)}}{\text{Fuel Input (GCV)}} \times 100 $$

Simple, measures overall performance.

• Indirect Method (Loss Method):

$$ \eta = 100 - (\text{L1} + \text{L2} + ... + \text{L6}) $$

Where L1 = Loss due to dry flue gas, L2 = Loss due to moisture in fuel, L3 = Loss due to moisture in air, L4 = Loss due to unburnt carbon, L5 = Loss due to unburnt hydrocarbons/CO, L6 = Loss due to radiation/convection.

More detailed, identifies loss sources.

GCV vs. NCV Basis

• GCV (Higher Heating Value): Includes latent heat of vaporization of water in fuel/exhaust.

• NCV (Lower Heating Value): Excludes latent heat (water vapor leaves as vapor).

• Conversion:

$$ \text{NCV} = \text{GCV} - 9 \times \text{H}_2\% \times \text{GCV} $$

(Approx. 9% of hydrogen content's latent heat).

> [!TIP] Boiler efficiency on NCV basis will be **higher** than on GCV basis for the same performance.

Operational Optimization & Part Load

• Part Load Efficiency: Boiler efficiency typically decreases at part load due to higher radiation/convection losses and poorer combustion control.

• Multiple Boilers Load Sharing: Aim to operate boilers at or near their maximum efficiency point (usually 70-100% load). Avoid running one boiler at very low load while another is off.

• Calculation Problem: Compare total fuel consumption for different load-sharing strategies (e.g., 2 boilers at 10 TPH each vs. 1 at 15 TPH + 1 at 5 TPH) using their part-load efficiency curves.

Combustion & Insulation

• Minimum Excess Air: Essential for complete combustion but excess air carries heat away in flue gases. Optimal excess air minimizes total losses (unburnt fuel loss vs. flue gas loss).

• Achieving Optimal Excess Air: Use oxygen trim control in combustion system, regularly tune burners, monitor O₂/CO in flue gas.

• Economic Thickness of Insulation: Thickness where annual cost of heat loss = annual cost of insulation. Beyond this, additional insulation cost outweighs saved fuel cost. Determined by calculating cumulative cost over insulation life.

B. Steam Systems

Steam Traps

• Working: Automatic device that discharges condensate, air, and non-condensable gases while preventing the passage of steam.

• Common Types:

  • Thermodynamic: Uses kinetic energy of steam/condensate.

  • Float & Thermostatic: Uses float for condensate, thermostatic element for air.

  • Inverted Bucket: Uses inverted bucket as float.

• Performance Assessment:

  • Visual/Audio: Listen for continuous discharge (failure), feel for temperature difference.

  • Temperature Measurement: Upstream vs. downstream temperature.

  • Ultrasonic Testing: Detects sound frequency of steam/condensate.

  • Thermography: Identifies failed traps (cold downstream).

Distribution & Recovery

• Distribution Losses: Radiation from uninsulated pipes, leaks at joints/valves, pressure drops, condensate not returned.

• Condensate Recovery:

  • Process: Collect hot condensate from steam traps and equipment, return to boiler feedwater system.

  • Benefits: Saves fuel (preheats feedwater), saves water, reduces boiler blowdown (lower TDS), reduces water treatment costs.

• Flash Steam Utilization:

  • Principle: When high-pressure condensate is throttled to a lower pressure, a portion flashes into steam (flash steam).

  • Example: Condensate from a 10 bar process (saturation temp ~180°C) is discharged to a 2 bar condensate receiver. The enthalpy drop generates flash steam at 2 bar (~120°C), which can be used for low-pressure process heating.

C. Thermic Fluid Heating

• Working Principle: Uses a heat transfer oil (thermic fluid) circulated in a closed loop. Oil is heated in a furnace/coil (like a boiler) and pumped to heat exchangers in processes, then returns to heater.

• Advantages over Steam:

  • No Pressure: Operates at low pressure (even at >300°C) → no boiler regulations, no explosion risk.

  • Precise Temperature Control: Easier to control at high temperatures.

  • No Water Treatment: No scaling, corrosion, or blowdown losses.

  • Rapid Start-up.

  • Applications: Chemical, pharmaceutical, textile, food processing where high, precise temperatures are needed without high pressure.

D. Furnaces

• Concept: Enclosed structure for applying heat to materials (metals, ceramics).

• Classifications:

  • By Heat Source: Oil/gas fired, electric, coal fired.

  • By Operation: Batch, continuous.

  • By Atmosphere: Air, controlled atmosphere (inert, reducing).

  • By Temperature: Low (<700°C), medium (700-1200°C), high (>1200°C).

• Role in Steel Industry: Used for reheating slabs/billets before rolling, heat treatment (annealing, hardening), forging.

• Energy Conservation Opportunities:

  • Optimal Combustion: Correct air-fuel ratio, high flame temperature.

  • Preheating Combustion Air/Fuel: Recuperators/regenerators.

  • Insulation: High-quality, low-thermal-conductivity linings.

  • Minimizing Heat Loss: Sealing openings, using proper door designs.

  • Recovering Waste Heat: From flue gases for feedwater/combustion air heating.

  • Process Integration: Optimizing furnace scheduling and loading.

IV. Fluid Systems Energy Efficiency

A. Pumps

Factors Affecting Performance & Efficiency

• System Curve: Static head + friction head (∝ flow²).

• Pump Curve: Head vs. Flow for a given speed/impeller.

• Best Efficiency Point (BEP): Point on pump curve with highest efficiency. Operating far from BEP causes:

  • Increased recirculation, cavitation, vibration.

  • Reduced bearing/seal life.

  • Lower efficiency.

• Affinity Laws (for centrifugal pumps):

$$ Q \propto N, \quad H \propto N^2, \quad P \propto N^3 $$

(Where Q=flow, H=head, N=speed, P=power).

Significance of Parallel Operation

• Used to increase flow capacity or provide redundancy.

• System Head remains same, total flow is sum of individual flows.

• Key: Pumps in parallel should have similar head-capacity curves. Mismatched pumps can lead to one pump "backing" the other (flowing backwards), wasting energy.

Energy Conservation Opportunities

• Right-Sizing: Select pump for required system head & flow at BEP.

• Variable Speed Drives (VSD/VFD): Match pump output to system demand by reducing speed (major savings as $$\displaystyle P \propto N^3 $$).

• Impeller Trimming: Reduce impeller diameter if flow is permanently lower than design.

• Reduce System Resistance: Use larger pipes, fewer fittings, open valves fully.

• Regular Maintenance: Clean impellers, check wear rings, align couplings.

B. Fans

Fan Design & Selection Criteria

• Types: Axial, Centrifugal (forward-curved, backward-curved, radial).

• Selection Based On:

  • Required Airflow (CFM/m³/s).

  • Required Static Pressure (inches w.g./Pa).

  • Gas Properties (density, temperature, presence of dust).

  • Efficiency: Backward-curved fans are generally most efficient.

  • Noise Level.

Performance Evaluation

• Fan Laws (Similar to Pumps):

$$ Q \propto N, \quad SP \propto N^2, \quad P \propto N^3 $$

• Efficiency Calculation:

$$ \eta_{\text{fan}} = \frac{\text{Air Power Output}}{\text{Shaft Power Input}} = \frac{Q \times SP}{\text{Brake HP} \times 6356} $$

(For Q in CFM, SP in inches w.g., BHP in HP).

• Measurement: Use Anemometer (velocity), Manometer (pressure), Power Meter.

Efficient System Operation

• Avoid Throttling: Do not use dampers to reduce flow; use VFD instead.

• Clean Fans & Ducts: Dust buildup increases resistance.

• Seal Leaks: In ductwork.

• Operate at High Efficiency Point: On the fan curve, usually near peak efficiency.

• Use Variable Air Volume (VAV) Systems with VFDs where demand varies.

V. Economic Analysis for Energy Projects

A. Life Cycle Costing (LCC)

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

• Process:

  1. Identify all costs (capital, O&M, energy, disposal).

  2. Convert all costs to Present Worth (PW) using discount rate.

  3. Sum all present worths → LCC.

• Significance: Compares alternatives with different initial costs and operating costs. Favors higher initial cost, lower operating cost options (like EEMs).

• Effect on Investment: Justifies spending more upfront for long-term savings.

B. Payback Period

• Simple Payback Period (SPP):

$$ \text{SPP (years)} = \frac{\text{Initial Investment}}{\text{Annual Net Savings}} $$

• Significance: Simple, intuitive measure of risk/recovery time.

• Risk Analysis: Shorter payback = lower risk (investment recovered quickly). Considers uncertainty of future savings/inflation? No.

• Merits: Easy to calculate, understand.

• Demerits: Ignores time value of money, cash flows after payback, and profitability beyond payback.

C. Net Present Value (NPV)

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

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

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

• Decision Rule: Accept if NPV > 0 (project adds value).

• Advantages over SPP:

  • Considers time value of money.

  • Includes all cash flows over project life.

  • Measures absolute profitability.

• Numerical Example (from paper):

  • Investment = Rs. 2000, Life = 2 years, Savings = Rs. 22000/year, Discount rate = 15%.

  • PW of Year 1 savings = 22000 / (1.15) = 19130.43

  • PW of Year 2 savings = 22000 / (1.15)² = 16635.59

  • Total PW of savings = 35766.02

  • NPV = 35766.02 - 2000 = \boxed{Rs. 33766.02} (Strongly positive → accept).

D. Internal Rate of Return (IRR)

• Definition: Discount rate (r) that makes NPV = 0.

• Significance: Represents the true annual rate of return on the invested capital. Compare IRR to hurdle rate (minimum required return). Accept if IRR > hurdle rate.

• Calculation: Usually by trial-and-error or financial calculator/software.

E. Energy Service Company (ESCO)

• Basic Concept: A company that provides comprehensive energy services to clients, including energy audit, implementation of conservation measures, and financing.

• Business Model (Performance Contracting):

  1. ESCO conducts free audit, proposes measures.

  2. ESCO arranges 100% financing for the project.

  3. ESCO installs and maintains equipment.

  4. Client repays ESCO from the actual energy cost savings achieved.

  5. After payback, savings accrue to client.

• Role: Overcomes client's lack of capital, expertise, and risk aversion. Guarantees savings.

VI. Environmental Aspects of Energy

• Environmental Aspects of Energy Consumption:

  • Non-renewable (Coal, Oil, Gas): GHG emissions (CO₂, CH₄), air pollutants (SOₓ, NOₓ, PM), water use/pollution, land degradation, thermal pollution.

  • Renewable (Solar, Wind, Hydro, Biomass): Lower GHG, but have site-specific impacts: land use (solar/wind farms), bird/bat mortality (wind), water use/ecosystem disruption (large hydro), air pollution from biomass combustion.

• Elements of Systematic Environmental Assessment:

  • Life Cycle Assessment (LCA): Evaluates environmental impact from "cradle to grave" (raw material extraction → disposal).

  • Carbon Footprinting: Quantifies total GHG emissions (CO₂e).

  • Environmental Impact Assessment (EIA): For new projects.

  • Resource Efficiency Metrics: Energy/water/material intensity per unit output.

VII. Energy Audit Implementation & Case Studies

Instruments & Monitoring

Regulatory Framework (BEE - India)

• Manners & Intervals:

  • Designated Consumers (DCs): Large energy-intensive industries, commercial buildings, etc. Mandated to conduct periodic energy audits.

  • Frequency: Once every 3 years for most DCs. First audit within 1 year of notification as DC.

  • Auditor: Must be Certified Energy Auditor (CEA) accredited by BEE.

  • Report Submission: To BEE and designated state agency.

  • Follow-up: Implementation of recommendations is monitored.

Numerical Problem-Solving Summary

1. PF Improvement: Use $$\displaystyle \text{kVAr} = kW(\tan\phi_1 - \tan\phi_2) $$. Find new kVA. Calculate penalty based on % dip.

2. Boiler Efficiency (GCV to NCV): Use $$\displaystyle \text{NCV} = \text{GCV} - 9 \times H_2\% \times \text{GCV} $$. Efficiency on NCV = (Output / (Input × NCV/GCV)) × 100.

3. Multiple Boilers: For given steam load, calculate total fuel required for each operating strategy using their part-load efficiencies. Compare fuel consumption → % savings.

4. Lighting Retrofit:

   • Energy Savings = (No. of lamps × (Old Watt - New Watt) × Operating Hours) / 1000.

   • Cost Savings = Energy Savings × Tariff.

   • Simple Payback = (Total Lamp Cost) / (Annual Cost Savings).

5. Economic Methods: Apply formulas for NPV, IRR as shown above. Always discount future cash flows.

Final Exam Strategy: Focus on numerical problems from PF, Boiler Efficiency (GCV/NCV), Multiple Boilers, Lighting Retrofit, NPV. Be precise with definitions (Energy Audit types, ESCO, LCC). Draw labeled diagrams for Steam Traps, Furnaces, Thermic Fluid System when asked. Always state assumptions and show clear steps in calculations.