4.1 Energy & Power Units (kWh, kW, Therms, MMBtu, Joules) and Conversion Calculations

AEE Certified Energy Manager CEM

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1 Chapter 1: Energy and Sustainability Policies, Codes, and Standards

1.1 Federal and State Energy Policies, Decarbonization Targets, and ESG Reporting 1.2 Building Energy Codes: ASHRAE Standard 90.1, IECC, and Compliance Paths 1.3 Energy Management Systems: ISO 50001, ENERGY STAR Benchmarking, and Portfolio Manager

2 Chapter 2: Energy Rates, Tariffs, and Supply Options

2.1 Utility Rate Structures: Volumetric vs. Demand Charges, Time-of-Use (TOU), and Real-Time Pricing 2.2 Demand Charges, Ratchets, Peak Shaving, and Power Factor Penalties 2.3 Energy Procurement, Deregulated Markets, Supply Contracts, and Green Tariffs 2.4 Demand-Side Management, Load Curtailment, and Transportation Energy Efficiency

3 Chapter 3: Energy Audits and Instrumentation

3.1 Energy Audit Methodologies: ASHRAE Level I, II, and III Audit Scopes 3.2 Audit Instrumentation, Data Loggers, Metering Accuracy, and Safety (PPE) 3.3 Baseline Energy Data, Utility Bill Disaggregation, and ECM Identification 3.4 Energy Modeling, Simulation, Digital Tools, and Performance Indicators

4 Chapter 4: Energy Accounting and Economics

4.1 Energy & Power Units (kWh, kW, Therms, MMBtu, Joules) and Conversion Calculations 4.2 Financial Metrics: Simple Payback Period, Return on Investment (ROI), and LCCA 4.3 Time Value of Money: Net Present Value (NPV), Internal Rate of Return (IRR), and Escalation 4.4 Advanced Financial Evaluation: Annual Worth, SIR, Depreciation, and Interest Formulas

5 Chapter 5: Electrical Power Systems and Motors

5.1 Electrical Fundamentals: Single/Three-Phase Power, Apparent/Real/Reactive Power, and Power Factor 5.2 Electric Motors: Efficiency Classes, Loading Calculations, NEMA Premium, and Losses 5.3 Variable Frequency Drives (VFDs), Affinity Laws, and Electrical Harmonics

6 Chapter 6: Lighting Systems

6.1 Lighting Fundamentals: Photometric Quantities (Lumens, Lux, Foot-Candles, CRI, CCT) and Efficacy 6.2 Lighting Technologies & Retrofits: LED Systems, Fluorescent/HID Replacement, and LPD 6.3 Lighting Controls: Occupancy/Vacancy Sensors, Daylight Harvesting, Dimming, and Task Tuning

7 Chapter 7: HVAC Systems and Building Envelope

7.1 HVAC Fundamentals & Psychrometrics: Dry-Bulb, Wet-Bulb, Dew Point, Relative Humidity, and Enthalpy 7.2 Cooling and Heating Equipment: Chillers (COP, kW/ton, EER, SEER), Heat Pumps, and Boilers 7.3 Air and Water Distribution: AHUs, VAV vs. CAV, Pumping Systems, Fans, and Economizers 7.4 Building Envelope: Heat Transfer (U-factor, R-value, SHGC), Infiltration, and Thermal Insulation 7.5 Building Envelope Calculations: Degree-Days, Solar Heat Gain, and Passive Design 7.6 Refrigerants, Cooling Towers, and Specialized HVAC Technologies (Absorption, VRF, Chilled Beams)

8 Chapter 8: Building Automation, Controls, and Artificial Intelligence Systems

8.1 Building Automation Systems (BAS) Architecture, BACnet, Modbus, and DDC Loops 8.2 Energy Control Strategies: Temperature/Pressure Resets, Night Setback, and Deadbands 8.3 Fault Detection & Diagnostics (FDD), Energy Analytics, and AI Optimization 8.4 IoT, Cloud-Based BAS, Expert Systems, and Cyber-Security

9 Chapter 9: Energy Storage Systems

9.1 Battery Energy Storage Systems (BESS): Technologies, Capacity, Efficiency, and Safety 9.2 Thermal Energy Storage (TES): Chilled Water, Ice Storage, and Phase Change Materials 9.3 Storage Dispatch Strategies, Tariff Integration, Peak Shaving, and Microgrid Integration

10 Chapter 10: Boiler and Steam Systems

10.1 Boiler Fundamentals & Efficiency: Combustion Efficiency, Excess Air, and Stack Losses 10.2 Steam Distribution & Traps: Steam Trap Types, Failure Modes, Testing, and Insulation 10.3 Condensate Recovery, Boiler Blowdown Control, and Waste Heat Recovery

11 Chapter 11: Distributed Generation and Renewable Energy Systems

11.1 Solar Photovoltaic (PV) and Wind Energy Systems: Design, Inverters, and Capacity Factor 11.2 Combined Heat and Power (CHP) / Cogeneration: Thermal Efficiency and System Sizing 11.3 Grid Interconnection, Net Metering, Islanding, and Microgrid Resilience 11.4 Biomass, Geothermal, Hydropower, Solar Thermal, and Waste-to-Energy Systems

12 Chapter 12: Industrial Systems

12.1 Compressed Air Systems: Efficiency, Pressure Drop, Leak Management, and Receiver Storage 12.2 Industrial Process Heating, Cooling Towers, and Industrial Refrigeration 12.3 Production-Normalized Energy Metrics, Pumping System Optimization, and Process Integration

13 Chapter 13: Operations, Maintenance, and Commissioning

13.1 Preventive, Predictive, and Reliability-Centered Maintenance Strategies 13.2 Building Commissioning: Existing Building Commissioning (EBCx) & Retro-Commissioning (RCx) 13.3 Savings Persistence, Continuous Commissioning, Sensor Calibration, and Alarms 13.4 Quantifying O&M Losses: Compressed Air Leaks, Steam Traps, Boiler Scale, and Group Relamping 13.5 CMMS, Water Treatment, and Human Behavior in Energy Management

14 Chapter 14: Energy Savings Performance Contracting and Measurement & Verification

14.1 Energy Savings Performance Contracting (ESPC), ESCO Roles, and Financing Models 14.2 Measurement and Verification (M&V): IPMVP Options A, B, C, and D 14.3 Baselines, Weather Normalization, Non-Routine Adjustments, and M&V Reporting

4.1 Energy & Power Units (kWh, kW, Therms, MMBtu, Joules) and Conversion Calculations

Key Takeaways Explain This Topic AI

Power is the rate of energy consumption (e.g., kW, Btu/hr), while Energy is the total amount consumed over time (e.g., kWh, Therms, MMBtu).

A critical foundational skill for the CEM exam is converting between energy units using exact conversion factors, such as 1 kWh = 3,412 Btu and 1 Therm = 100,000 Btu.

Establishing an accurate energy baseline requires a thorough understanding of utility bills, rate structures, and proper unit accounting to ensure that savings calculations are valid.

When evaluating thermal vs. electrical systems, standardizing units into a common denominator (often MMBtu or kWh) is essential for accurate economic comparison.

Last updated: July 2026

Energy & Power Units and Conversion Calculations

Quick Answer: The CEM exam demands absolute precision in distinguishing between Energy (quantity) and Power (rate) and requires you to convert between various units fluidly. For example, knowing that 1 kWh = 3,412 Btu, 1 Therm = 100,000 Btu, 1 MMBtu = 1,000,000 Btu, 1 HP = 0.746 kW, and 1 Ton of cooling = 12,000 Btu/hr is non-negotiable for passing the exam.

Energy accounting forms the bedrock of any energy management program. Before you can calculate the financial return of an energy conservation measure (ECM), you must accurately quantify the energy savings. This requires a rigorous understanding of energy and power units, the ability to perform complex unit conversions, and the skill to establish a valid baseline against which savings can be measured.

The Fundamental Distinction: Energy vs. Power

One of the most common pitfalls for CEM candidates is confusing energy and power.

Power is the rate at which energy is generated, transmitted, or consumed. It is an instantaneous measurement. Think of power as the speed of a car (miles per hour) or the flow rate of water in a pipe (gallons per minute). Common units of power include:

Kilowatts (kW) or Megawatts (MW)
British Thermal Units per hour (Btu/hr)
Horsepower (HP)
Tons of Refrigeration (Tons)

Energy , on the other hand, is the total quantity of work performed or fuel consumed over a specific period. It is the product of power and time. Returning to the analogy, if power is the speed, energy is the total distance traveled. If power is the flow rate, energy is the total volume of water collected in a bucket. Common units of energy include:

Kilowatt-hours (kWh) or Megawatt-hours (MWh)
British Thermal Units (Btu) or Million Btu (MMBtu)
Therms
Joules (J) or Kilojoules (kJ)

When utility companies bill commercial and industrial customers, they typically charge for both. Energy charges (measured in kWh or Therms) bill for the total volume consumed during the billing cycle. Demand charges (measured in kW) bill for the highest peak rate of consumption (usually averaged over a 15- or 30-minute interval) during that same period.

Critical Unit Conversions

The CEM exam will routinely present problems that mix units. A chiller's capacity might be given in Tons, its efficiency in kW/Ton, and its operating hours in hours/year. To determine the annual energy cost, you must navigate these units flawlessly.

Here are the non-negotiable conversion factors you must memorize:

Electricity Conversions
1 Kilowatt-hour (kWh) = 3,412 Btu
1 Kilowatt (kW) = 3,412 Btu/hr
1 Megawatt-hour (MWh) = 1,000 kWh = 3,412,000 Btu
1 Horsepower (HP) = 0.746 kW = 746 Watts
1 Horsepower (HP) = 2,545 Btu/hr
Thermal Conversions (Natural Gas, Steam, Chilled Water)
1 Therm = 100,000 Btu
1 MMBtu = 1,000,000 Btu = 10 Therms
1 Ton of Cooling (Refrigeration) = 12,000 Btu/hr
1 Ton-hour = 12,000 Btu
1 Boiler Horsepower (BHP) = 33,475 Btu/hr

1 Pound of Steam (typical latent heat) ≈ 1,000 Btu (varies slightly by pressure, but 1,000 is a standard rule of thumb for exams unless otherwise specified)

Metric/SI Conversions

While the US version of the CEM relies heavily on Imperial units (IP), you must also be familiar with SI units:

1 Joule (J) = 1 Watt-second (W·s)
1 kWh = 3.6 Megajoules (MJ) = 3,600 Kilojoules (kJ)
1 Btu = 1,055 Joules = 1.055 kJ
Normalizing Units for Comparison

To conduct energy accounting, you often need to sum up all the energy streams entering a facility. You cannot add kWh to Therms directly. You must convert everything to a common denominator. In the US, this common denominator is usually the MMBtu (Million Btu).

Worked Example: Total Facility Energy Calculation

Consider an industrial facility that consumes the following in a given year:

Electricity: 2,500,000 kWh
Natural Gas: 45,000 Therms
Diesel Fuel: 5,000 Gallons (assume 139,000 Btu/gallon)

What is the total annual energy consumption in MMBtu?

Step 1: Convert Electricity to MMBtu
Energy = 2,500,000 kWh
Conversion: 1 kWh = 3,412 Btu
Total Btu = 2,500,000 kWh × 3,412 Btu/kWh = 8,530,000,000 Btu
Total MMBtu = 8,530,000,000 / 1,000,000 = 8,530 MMBtu
Step 2: Convert Natural Gas to MMBtu
Energy = 45,000 Therms
Conversion: 1 Therm = 100,000 Btu
Total Btu = 45,000 Therms × 100,000 Btu/Therm = 4,500,000,000 Btu
Total MMBtu = 4,500,000,000 / 1,000,000 = 4,500 MMBtu
Step 3: Convert Diesel Fuel to MMBtu
Energy = 5,000 Gallons
Conversion: 1 Gallon = 139,000 Btu
Total Btu = 5,000 Gallons × 139,000 Btu/Gallon = 695,000,000 Btu
Total MMBtu = 695,000,000 / 1,000,000 = 695 MMBtu
Step 4: Sum the Totals
Total Facility Energy = 8,530 + 4,500 + 695 = 13,725 MMBtu

This normalized figure is critical for benchmarking the facility against others (e.g., calculating Energy Use Intensity or EUI in kBtu/sq ft) and for greenhouse gas (GHG) accounting.

Establishing the Energy Baseline

The baseline represents the energy performance of a facility before any energy conservation measures are implemented. It serves as the reference point for calculating savings.

When establishing a baseline, you must consider:

Data Period: Typically a minimum of 12 consecutive months to capture seasonal variations.

Independent Variables: Weather (Heating Degree Days / Cooling Degree Days), production volume, or occupancy rates that affect energy use.

Utility Rate Structures: Energy costs are rarely a flat rate. You must understand block rates, time-of-use (TOU) rates, demand ratchets, and power factor penalties.

When an ECM reduces electricity consumption (kWh), you calculate the savings using the marginal energy rate. When an ECM reduces peak power (kW), you calculate savings using the demand rate. If the reduction in kW occurs off-peak, it may yield zero demand savings depending on the utility tariff. Understanding these nuances—rooted in the difference between energy and power—is what separates a successful CEM candidate from the rest.