AEE Certified Energy Manager (CEM) cheat sheet

ASHRAE 90.1 applies to commercial and high-rise residential buildings; ASHRAE 90.2 applies to low-rise residential buildings.

The IECC is a model energy code; it becomes enforceable only after adoption by the authority having jurisdiction, including local amendments.

ASHRAE 62.1 sets minimum ventilation and indoor air quality requirements for commercial buildings; ASHRAE 62.2 covers residential buildings.

ASHRAE 55 defines acceptable thermal comfort conditions using operative temperature, humidity, air speed, and clothing/metabolic factors.

ASHRAE 100 provides energy efficiency requirements for existing commercial buildings, including O&M and retrofit guidance.

NFPA 70 is the National Electrical Code; NFPA 70E addresses electrical workplace safety; NFPA 70B addresses electrical equipment maintenance.

ISO 50001 specifies requirements for an energy management system; ISO 50002 covers energy audits; ISO 50006 addresses energy performance indicators and baselines.

ASHRAE audit levels: Level 1 walk-through, Level 2 energy survey and analysis, Level 3 detailed capital-intensive analysis.

Model codes are not automatically law: verify the locally adopted edition and amendments before applying a requirement.

S² = P² + Q² for apparent (kVA), real (kW), and reactive (kVAR) power; power factor PF = P/S = kW/kVA.

Balanced three-phase real power: P(kW) = √3 × V_LL × I × PF / 1000.

Motor input power: kW = √3 × V × I × PF / 1000; motor efficiency η = shaft output / electrical input.

Motor load factor ≈ measured input kW divided by rated input kW at operating voltage; part-load efficiency falls sharply below about 50% load.

Centrifugal fan or pump affinity laws: flow ∝ speed, head ∝ speed², power ∝ speed³, assuming constant system and density.

Voltage unbalance derates three-phase motors; NEMA derating factor depends on percent voltage unbalance, and current unbalance can exceed voltage unbalance.

Power factor correction capacitor kVAR = kW × (tan θ1 − tan θ2), where θ1 and θ2 are the initial and target power-factor angles.

Transformer losses consist of no-load core loss plus load-dependent I²R copper loss; efficiency peaks when copper loss equals core loss.

IEEE 519 limits harmonic current and voltage distortion at the point of common coupling; THD is a common screening metric.

Commissioning verifies systems meet the owner's project requirements (OPR) through documented design review, functional performance tests, and issue resolution.

Retrocommissioning applies the Cx process to existing buildings; monitoring-based commissioning uses trend data and analytics to persist savings.

ASHRAE Guideline 0 describes the commissioning process; ASHRAE Guideline 1.1 addresses HVAC&R commissioning.

Preventive maintenance is time- or usage-based; predictive maintenance uses vibration, thermography, oil analysis, or performance trends to schedule work.

Dirty filters, fouled coils, incorrect refrigerant charge, and simultaneous heating/cooling each degrade efficiency and are common commissioning findings.

An economizer functional test verifies damper travel, actuator linkage, changeover logic, and minimum outdoor-air position.

A CMMS tracks work orders, equipment histories, and maintenance costs; trended run hours and alarms support condition-based decisions.

Commissioning authority independence from design and construction reduces conflict of interest in verification.

Level 1 audit: walk-through survey and rough savings estimate; Level 2: energy survey with end-use breakdown and economic screening; Level 3: detailed analysis of capital-intensive measures.

Energy use index EUI = annual energy consumption / conditioned floor area; common units are kBtu/ft²·yr or kWh/m²·yr.

Heating and cooling degree days use a base temperature, commonly 65°F, to weather-normalize energy use.

Regression baseline: energy = intercept + slope × driver (e.g., HDD or CDD); R² indicates how much variation the model explains.

True-RMS meters are required for distorted or nonlinear loads; averaging meters can misread variable-frequency-drive and electronic loads.

Instrument accuracy stated as percent of reading is not interchangeable with percent of full scale; verify calibration and range before use.

Spot measurements capture one moment; continuous data logging captures duty cycles, schedules, and variability needed for savings estimates.

IPMVP options: A retrofit isolation with key parameters, B retrofit isolation with all parameters, C whole facility, D calibrated simulation.

CHP total efficiency = (useful electric output + recovered useful thermal output) / fuel energy input; well-matched systems can reach 60–80%.

CHP prime movers include reciprocating engines, gas turbines, microturbines, steam turbines, and fuel cells; electric efficiency and heat grade differ by type.

CHP sizing rule: match the prime mover to the base thermal or electric load that persists for many hours; oversized units cycle and lose efficiency.

Useful heat recovery sources include exhaust gas, jacket water, lube oil, and turbine exhaust; recoverable temperature limits the usable heat.

Annual PV energy ≈ array kW_DC × peak sun hours × performance ratio; performance ratio includes inverter, wiring, soiling, and temperature losses.

Wind power in the rotor sweep is P = 0.5 × air density × swept area × wind speed³; the Betz limit is 59.3% of that power.

IEEE 1547 governs interconnection of distributed energy resources with the electric utility grid.

Net metering credits exported generation against imports; a power purchase agreement sets contracted energy price and term.

Sensible heat (IP): Q_s(Btu/h) ≈ 1.08 × CFM × ΔT(°F).

Latent heat (IP): Q_l(Btu/h) ≈ 0.68 × CFM × ΔW(grains/lb); total heat ≈ 4.5 × CFM × Δh(Btu/lb).

Cooling efficiency conversions: EER = 12 / (kW/ton); COP = EER / 3.412; COP ≈ 3.517 / (kW/ton).

Chiller plant efficiency improves with higher chilled-water supply temperature, lower condenser-water temperature, and higher chilled-water ΔT.

Air-side economizer uses outdoor air for free cooling when outdoor air enthalpy or dry-bulb is below return air; verify changeover and damper leakage.

VAV systems save fan energy with static-pressure reset and supply-air-temperature reset; excessive minimum airflow can waste reheat energy.

Boiler combustion efficiency = (input − stack losses) / input; stack temperature and excess air are key indicators.

Refrigerant charge diagnosis uses superheat and subcooling; low charge can reduce capacity and efficiency.

Energy recovery ventilator effectiveness = (actual heat transfer) / (maximum possible heat transfer) between airstreams.

DDC controllers use PID loops; proportional band, integral time, and derivative time must be tuned to the controlled process.

Scheduling with optimal start/stop reduces run time while meeting occupancy; override limits prevent indefinite after-hours operation.

BACnet, Modbus, and LonWorks are common BAS protocols; BACnet is an open ASHRAE/ANSI standard for interoperable building data.

Trend logs and alarms are the primary BAS diagnostic data for detecting simultaneous heating/cooling, stuck dampers, and schedule drift.

Demand-controlled ventilation uses CO2 or occupancy sensors to reset outdoor-air intake and reduce ventilation load.

A sequence of operations defines setpoints, interlocks, staging, and reset logic; commissioning verifies it matches design intent.

Point mapping and as-built documentation are needed to avoid control gaps when integrating third-party equipment.

Reset schedules for supply air temperature, static pressure, and chilled water temperature reduce energy while maintaining comfort.

TES shifts cooling or heating production to off-peak hours, reducing peak demand charges and allowing smaller chillers or boilers.

Sensible chilled-water storage capacity Q = m × c_p × ΔT; water's c_p is about 1 Btu/lb·°F.

Ice storage uses latent heat of fusion of about 144 Btu/lb, giving much higher volumetric storage density than chilled water.

Full storage meets the entire peak load from storage; partial storage runs chillers and storage together to reduce first cost.

TES charging and discharging must be controlled with tank temperature, state of charge, and chiller staging to avoid standby losses.

Phase-change materials store energy at a nearly constant temperature and can fit space-constrained retrofits.

TES economics depend on time-of-use rate spread, demand charges, and the number of charge/discharge cycles per year.

Luminous efficacy = lumens / watts; LEDs commonly exceed 100 lm/W, while incandescent lamps are about 10–17 lm/W.

Lighting power density LPD = installed lighting watts / floor area; energy codes set maximum LPD by space type.

Lumen method: number of luminaires = (target illuminance × area) / (lumens per luminaire × coefficient of utilization × maintenance factor).

Lighting controls include occupancy sensing, daylight dimming, scheduling, and task tuning; each reduces hours or power.

CRI describes color rendering (0–100), and CCT describes light appearance in kelvin; neither alone measures energy efficiency.

Ballast factor scales lamp output and input power; a lower ballast factor reduces both light output and wattage.

LED retrofits can reduce wattage and maintenance; verify luminaire efficacy, glare control, dimming compatibility, and code compliance.

Daylighting photosensor control must be commissioned with setpoints and deadbands to avoid nuisance switching or dimming.

ESPC: an energy service company implements efficiency measures and guarantees energy or cost savings that repay project costs over the term.

IPMVP savings = baseline energy − reporting-period energy ± adjustments for weather, occupancy, and other agreed variables.

Measurement boundary defines which meters, systems, and fuels are included; double counting must be avoided across measures.

Option A uses key-parameter measurement with some stipulated values; Option B measures all parameters affecting the retrofit's energy use.

Option C uses whole-building utility data and is suited to projects with many interactive measures; Option D uses calibrated simulation.

M&V plans specify baseline, measurement boundary, methods, frequency, uncertainty, and reporting responsibilities.

Shared-savings and guaranteed-savings contracts allocate risk differently; contract terms define baseline adjustments and savings verification.

Routine and non-routine adjustments separate weather or occupancy changes from true measure performance.