CEM cheat sheet

Policy hierarchy: statutes set mandates, regulations implement them, executive orders and incentive programs steer voluntary action; a CEM should trace each requirement to its legal driver before designing a compliance plan.

Common policy instruments: mandatory codes, cap-and-trade, carbon taxes, renewable portfolio standards (RPS), feed-in tariffs, tax credits, grants, and white certificates (energy efficiency obligations).

RPS/clean energy standards obligate load-serving entities to procure a percentage of generation from qualifying renewables; renewable energy credits (RECs) are the tradable compliance currency.

Greenhouse gas accounting scopes: Scope 1 = direct fuel combustion and process emissions; Scope 2 = purchased electricity/steam; Scope 3 = value-chain emissions including business travel and purchased goods.

Benchmarking and disclosure mandates (e.g., building performance standards) typically require annual ENERGY STAR Portfolio Manager reporting and set escalating performance targets for large buildings.

ISO 50001 provides a Plan-Do-Check-Act energy management system framework; certification requires an energy policy, energy review, baseline, EnPIs, objectives, and internal audit.

Sustainability targets often follow science-based pathways (e.g., 1.5 C-aligned Scope 1+2 reduction) with interim milestones; verify boundary, base year, and market- vs location-based method.

Demand-side policy tools include appliance and equipment efficiency standards, utility energy efficiency portfolios, and building energy codes with stretch or reach tiers.

ASHRAE 90.1 applies to commercial buildings; IECC applies to residential and commercial; local jurisdiction adoption determines which edition and amendments govern a project.

90.1 compliance paths: prescriptive (envelope, lighting, HVAC tables), trade-off (building envelope trade-off option), and performance (whole-building energy cost budget).

Lighting power density (LPD) limits are expressed in W/ft2 by space type; interior LPD plus allowances for decorative, display, and exterior lighting determine compliance.

Economizer requirements are triggered by climate zone and cooling capacity; air-cooled units above the threshold must include economizer capability with high-limit shutoff.

Ventilation rates come from ASHRAE 62.1 (breathing zone outdoor airflow = Rp x occupants + Ra x floor area, adjusted by zone air distribution effectiveness).

NFPA 70 (NEC) governs electrical installation; NFPA 70E governs electrical workplace safety including arc flash boundaries and PPE categories.

ASHRAE 105 defines methods for expressing and comparing building energy performance, including site, source, and cost-based metrics.

Commissioning requirements: fundamental commissioning is mandatory in 90.1 for systems above thresholds; enhanced commissioning adds an independent Cx agent and ongoing commissioning.

Electric bill components: customer charge, demand charge ($/kW based on billing demand), energy charge ($/kWh), power factor penalty, and riders or adjustments.

Billing demand is typically the maximum 15- or 30-minute integrated kW in the billing period; ratchets may set billing demand as a percentage of the prior 11- or 12-month peak.

Time-of-use rates price energy by period (on-peak, mid-peak, off-peak); shifting load off-peak reduces energy cost but may not reduce demand charges.

Real-time pricing (RTP) and day-ahead hourly pricing expose customers to wholesale volatility; hedging, block purchases, or fixed-price contracts manage that risk.

Power factor: kW = kVA x PF; utilities often penalize PF below ~0.90-0.95; capacitor correction kVAR = kW x (tan(acos PF1) - tan(acos PF2)).

Natural gas tariffs include commodity, transportation, distribution, and demand charges; transportation customers may buy commodity from a marketer and pay the LDC for delivery.

Load factor = average load / peak load = (kWh in period) / (peak kW x hours in period); low load factors indicate demand-charge reduction opportunity.

Supply options include utility default service, competitive retail supply, direct access, community choice aggregation, and on-site generation or PPAs.

ASHRAE Level 1 = walk-through with utility bill analysis and low-cost recommendations; Level 2 = energy survey and analysis with end-use breakdown and cost estimates; Level 3 = detailed capital-intensive analysis with simulation and savings verification.

Measurement hierarchy: spot measurements, short-term monitoring (portable loggers over days-weeks), and long-term metering; use short-term data with load-shape assumptions to extrapolate annual use.

Power measurement: single-phase P = V x I x PF; three-phase P = sqrt(3) x V_LL x I x PF; verify with a power analyzer or clamp-on meter on the correct range.

Current transformers (CTs) and potential transformers (PTs) scale meter readings; a split-core CT must match the meter's input ratio to avoid factor-of-N errors.

Temperature: thermocouples (wide range, low accuracy), RTDs (stable, accurate), infrared thermometers (surface only, emissivity-dependent); calibrate against a known reference.

Airflow: pitot tube velocity pressure v = 4005 x sqrt(VP in in. w.c.) ft/min; hood balometers measure grille flow directly; tracer gas measures infiltration.

Combustion analysis: measure O2, CO, stack temperature, and ambient; compute excess air, CO2, and stack loss; high CO signals incomplete combustion and unsafe conditions.

Data quality: record instrument accuracy, calibration date, sampling interval, and measurement boundary; flag estimated values so savings calculations can be traced.

Simple payback = installed cost / annual savings; ignores time value and measure life, so use it only as a screening metric.

Life-cycle cost (LCC) discounts all future costs to present value; choose the alternative with the lowest LCC among options meeting the same functional requirement.

Net present value = sum of discounted cash flows minus initial cost; NPV > 0 means the project beats the discount rate; IRR is the rate where NPV = 0.

Levelized cost of energy (LCOE) = total lifecycle cost / total lifecycle energy produced; used to compare supply options with different capital and fuel profiles.

Savings verification follows IPMVP options: A (retrofit isolation, key parameters measured), B (retrofit isolation, all parameters measured), C (whole facility metering), D (calibrated simulation).

Energy use intensity (EUI) = annual site energy / floor area (kBtu/ft2 or kWh/m2); normalize for weather using heating/cooling degree days or regression.

Utility bill accounting: reconcile meter reads to invoices, separate supply and delivery charges, and track rate schedule changes; a 12-month baseline with weather normalization is standard.

Marginal vs average cost matters: energy efficiency savings are valued at the marginal rate (including demand and time-of-use effects), not the blended average $/kWh.

Three-phase relationships: P = sqrt(3) x V_LL x I x PF; S (kVA) = sqrt(P^2 + Q^2); Q (kVAR) = sqrt(3) x V x I x sin(theta).

Motor load estimation without a meter: use slip method (load = (synch speed - measured speed)/(synch speed - rated speed) x rated HP) or input power from nameplate efficiency.

Motor efficiency: NEMA Premium or IE3/IE4 classes; energy savings from VFDs follow affinity laws: flow proportional to speed, power proportional to speed cubed for centrifugal loads.

Harmonics: nonlinear loads (VFDs, LEDs, IT equipment) inject 5th, 7th, 11th... order currents; total harmonic distortion (THD) above IEEE 519 limits requires filters or reactors.

Transformer losses: no-load (core) loss is constant; load loss varies with the square of load; loading below ~30% or above ~75% warrants review for right-sizing.

Power factor correction capacitors must be sized to avoid leading PF at light load and to avoid resonance with harmonic filters; detuned reactors protect against 5th/7th harmonic amplification.

Motor starting: across-the-line draws 6-8x full-load current; soft starters, star-delta, autotransformer, and VFDs reduce starting current and demand spikes.

Demand control: peak shaving by load shedding, sequencing, or storage reduces billing demand; verify that demand intervals (15 vs 30 min) match the control strategy.

Efficacy (lm/W) compares sources: LED 100-180, fluorescent 60-100, metal halide 60-90, incandescent 10-17; always compare delivered lumens, not lamp lumens.

Lumen method: average maintained illuminance = (lamps x lumens per lamp x CU x LLF) / area; CU depends on room cavity ratio and reflectances.

Lighting power density (LPD) compliance uses W/ft2 by space type; controls credits and daylighting credits can offset LPD in 90.1 and IECC.

Controls: occupancy/vacancy sensors, daylight dimming, time scheduling, and demand response; automatic shutoff is required in most commercial spaces.

Color metrics: CRI (Ra) for fidelity, CCT (2700-6500K) for appearance; TM-30 Rf/Rg gives a more complete color rendition picture for LED specification.

LED retrofit economics: verify driver compatibility, dimming protocol (0-10V, DALI, phase-cut), flicker, and thermal derating; lumen depreciation and driver life drive maintenance savings.

Exterior lighting: cutoff classifications (full cutoff, cutoff, semi-cutoff) control light trespass and skyglow; BUG rating summarizes backlight, uplight, and glare.

Lighting energy = watts x operating hours / 1000 (kWh); savings from controls require an hours-of-operation profile, not just wattage reduction.

Cooling load components: conduction through envelope, solar gain through glazing, internal gains (people, lights, equipment), and ventilation/infiltration latent and sensible loads.

Psychrometrics: sensible heat Qs = 1.08 x CFM x delta-T (Btu/h); latent heat Ql = 0.68 x CFM x delta-W (grains); total = 4.5 x CFM x delta-h.

Chiller efficiency: kW/ton = 12 / COP; IPLV/NPLV weight part-load performance; a 0.6 kW/ton chiller is roughly 5.9 COP.

Boiler and furnace efficiency: combustion efficiency from stack loss; AFUE for furnaces/boilers, thermal efficiency for hydronic; condensing units recover latent heat below dew point.

Economizer and free cooling: air-side economizer uses outdoor air when enthalpy or dry-bulb is favorable; water-side economizer uses cooling tower directly.

Envelope metrics: U-factor (Btu/h-ft2-F) is conductance; R-value is resistance; SHGC controls solar heat gain; air leakage measured in cfm50 or ACH50 by blower door.

VAV systems: minimum airflow settings, reheat coil sizing, static pressure reset, and supply air temperature reset are the highest-yield tuning measures.

Refrigerant management: GWP and ODP drive refrigerant selection; leak detection, recovery, and charge verification are required under EPA Section 608 rules.

BAS architecture: field devices (sensors, actuators) -> DDC controllers -> supervisory network -> operator workstation; protocols include BACnet, Modbus, LonWorks, and KNX.

Control loop tuning: proportional band, integral time, and derivative time; too much integral causes oscillation, too little causes offset; tune at design load and part load.

Schedules and optimal start: occupancy schedules with optimum start/stop reduce runtime; verify schedule overrides and holiday calendars during retrocommissioning.

Fault detection and diagnostics (FDD) identifies simultaneous heating and cooling, stuck valves, sensor drift, and schedule overruns; automated FDD is a core analytics function.

Energy information systems and M&V dashboards trend interval data (15-min) against a baseline; regression models (change-point) normalize for weather and occupancy.

AI/ML applications: load forecasting, model predictive control (MPC), anomaly detection, and automated setpoint optimization; require clean historical data and validation against measured savings.

Cybersecurity for OT: network segmentation, least-privilege accounts, firmware patching, and monitoring; BACnet/IP networks should not be exposed to the internet.

Sequence of operations is the control specification: document setpoints, staging, reset schedules, and safeties; most savings come from correcting sequences, not adding hardware.

Battery metrics: usable capacity (kWh) = nameplate x depth of discharge; round-trip efficiency typically 85-95% for lithium-ion; state of charge (SOC) and state of health (SOH) track condition.

Power vs energy: C-rate = power (kW) / capacity (kWh); a 2-hour system at 1C delivers its full capacity in 2 hours; duration drives the application.

Value streams: demand charge reduction, time-of-use arbitrage, demand response, frequency regulation, backup resilience, and renewable self-consumption.

Sizing rule: energy capacity must cover the discharge duration at the required power plus efficiency losses; verify inverter and interconnection limits.

Lithium-ion (NMC/LFP) dominates new stationary storage; LFP offers longer cycle life and better thermal stability; flow batteries suit long-duration applications.

Safety and code: NFPA 855 governs installation separation, fire suppression, and ventilation; UL 9540 covers the system, UL 9540A tests thermal runaway propagation.

Degradation: capacity fades with cycle count, temperature, and depth of discharge; warranty terms specify throughput (MWh) and end-of-life capacity percentage.

Controls integration: storage dispatch follows site load, tariff periods, and PV forecast; grid-tied systems need anti-islanding and interconnection agreement approval.

Steam system losses: stack loss (dry flue gas + latent moisture), blowdown, radiation, and steam leaks/traps; stack loss typically dominates and rises with excess air and stack temperature.

Combustion efficiency from flue gas: measure O2 or CO2 and stack temperature; optimum excess air for natural gas is roughly 5-10% O2 (about 10-15% excess air) depending on burner.

Blowdown: surface blowdown controls dissolved solids; blowdown rate % = (feedwater TDS / (maximum allowable boiler water TDS - feedwater TDS)) x 100.

Steam traps: failed-open traps waste steam; failed-closed traps cause water hammer and carryover; ultrasonic and infrared surveys are standard diagnostic methods.

Condensate return: returning hot condensate saves energy and makeup water; each 10 F rise in feedwater temperature reduces fuel use by roughly 1%.

Boiler efficiency metrics: combustion efficiency (flue loss method), thermal efficiency (output/input), and annual fuel utilization efficiency (AFUE) for small packaged units.

Steam distribution: pressure reduction, insulation of headers and valves, and trap maintenance are the highest-yield measures; flash steam recovery captures blowdown energy.

Boiler plant tuning: oxygen trim, stack temperature monitoring, and burner maintenance; a 1% reduction in excess O2 above optimum can save roughly 0.5-1% fuel.

Solar PV: capacity factor = actual kWh / (nameplate kW x 8760); typical fixed-tilt commercial PV in the US yields 13-18% capacity factor depending on location.

PV performance: P = irradiance (kW/m2) x area x efficiency x temperature derate; module temperature above 25 C reduces output by roughly 0.3-0.5%/C.

Net metering and interconnection: compensation rules (retail rate, avoided cost, or export tariffs) determine project economics; interconnection studies govern grid-tied approval.

Combined heat and power (CHP): overall efficiency = (electric + useful thermal) / fuel input; topping cycles produce power first, bottoming cycles use waste heat.

Wind: power in the wind proportional to rotor swept area x velocity cubed; capacity factor 25-45% for good onshore sites; cut-in, rated, and cut-out speeds define the curve.

Incentives: federal investment tax credit (ITC) or production tax credit (PTC), state rebates, and renewable energy credits; tax basis and depreciation (MACRS) affect payback.

Solar thermal and geothermal: solar hot water displaced fuel depends on load profile and storage; ground-source heat pumps use stable ground temperature for high COP.

Grid integration: inverter standards (IEEE 1547) govern voltage/frequency ride-through and anti-islanding; storage plus PV improves dispatchability.

Industrial system assessment order: motors and drives, compressed air, pumps and fans, process heating, steam, and refrigeration; compressed air is often the most expensive utility per unit of work.

Compressed air: leaks typically waste 20-30% of output; leak rate estimate via unloaded runtime or ultrasonic detection; 1 hp of compressed air can cost several times 1 hp of electricity.

Pumps and fans follow affinity laws: flow proportional to speed, head proportional to speed squared, power proportional to speed cubed; VFDs save most on variable-torque loads.

Pump/fan system curves: operating point is where the system curve meets the pump curve; throttling moves along the curve, speed control shifts the curve and saves energy.

Process heating: efficiency = heat delivered to load / fuel or electric input; losses include wall, opening, cooling water, and exhaust; recuperation and insulation are primary measures.

Refrigeration: COP = cooling delivered / work input; condenser cleanliness, floating head pressure, and suction pressure optimization are high-yield measures.

Industrial benchmarking: use specific energy consumption (SEC) in kWh or Btu per unit of product, normalized for production volume and product mix.

Demand response and load management: industrial loads can shed or shift process steps, chillers, or compressed air; verify production constraints before committing capacity.