CEM flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Scope 2 emissions

Indirect greenhouse gas emissions from purchased electricity, steam, heat, or cooling. Reported using location-based (grid average) or market-based (contractual instruments such as RECs) methods.

Renewable portfolio standard

A policy requiring load-serving entities to supply a minimum percentage of electricity from qualifying renewable sources, typically verified through tradable renewable energy credits.

ASHRAE 90.1

The commercial building energy standard covering envelope, lighting, HVAC, and service water. Jurisdictions adopt specific editions; compliance can be prescriptive, trade-off, or performance based.

Lighting power density

Allowable installed lighting watts per square foot by space type under energy codes. Interior LPD plus allowances for decorative, display, and exterior lighting determine compliance.

Billing demand

The kW value used to compute the demand charge, usually the highest 15- or 30-minute interval in the billing period, sometimes subject to a ratchet based on prior peaks.

Load factor

Average load divided by peak load over a period: kWh / (peak kW x hours). A low load factor signals demand-charge reduction potential.

Power factor correction

Adding capacitors to reduce reactive power. Required kVAR = kW x (tan(acos PF1) - tan(acos PF2)); avoid leading power factor at light load and harmonic resonance.

ASHRAE Level 2 audit

An energy survey and analysis that breaks down end-use consumption, evaluates measures with cost and savings estimates, and supports capital planning.

Pitot tube airflow

Velocity in ft/min equals 4005 times the square root of velocity pressure in inches of water column. Used with duct area to compute volumetric flow.

Combustion excess air

Air supplied beyond stoichiometric requirement. Measured via flue O2 or CO2; too little risks CO and smoke, too much wastes fuel up the stack.

Simple payback

Installed cost divided by annual savings, expressed in years. A screening metric that ignores time value of money and measure life.

IPMVP Option C

Whole-facility metering approach to savings verification. Compares utility bills before and after a retrofit, normalized for weather and other variables.

Energy use intensity

Annual site energy divided by floor area, expressed in kBtu/ft2 or kWh/m2. Used to benchmark buildings and track performance over time.

Affinity laws

For centrifugal fans and pumps: flow varies with speed, head with speed squared, and power with speed cubed. Basis for VFD energy savings.

NEMA Premium motor

An efficiency class for general-purpose induction motors. Replacing standard-efficiency motors with premium units reduces losses, especially at part load.

Motor slip method

Estimates motor load from measured speed: load fraction = (synchronous speed - measured speed) / (synchronous speed - rated speed) times rated horsepower.

Lumen method

Average maintained illuminance equals lamps times lumens per lamp times coefficient of utilization times light loss factor, divided by room area.

LED efficacy

Delivered lumens per watt. LED systems typically reach 100-180 lm/W versus 60-100 for fluorescent and 10-17 for incandescent lamps.

Color rendering index

A 0-100 scale describing how faithfully a source renders colors versus a reference. TM-30 Rf and Rg provide a more complete LED specification.

Economizer

A control strategy using cool outdoor air or a water-side heat exchanger to provide free cooling when conditions are favorable, reducing mechanical refrigeration.

Sensible heat equation

Qs (Btu/h) = 1.08 x CFM x temperature difference in Fahrenheit. Latent heat uses 0.68 x CFM x humidity ratio difference in grains.

U-factor and R-value

U-factor is assembly conductance in Btu/h-ft2-F; R-value is thermal resistance, the reciprocal of U. Lower U and higher R mean better envelope performance.

BACnet

A building automation communication protocol for sensors, controllers, and workstations. Supports interoperability across vendors; should be segmented from public networks.

Fault detection and diagnostics

Automated analytics that identify operational faults such as simultaneous heating and cooling, stuck dampers, sensor drift, and schedule overruns from trend data.

Model predictive control

A control method that optimizes setpoints over a future horizon using a building model, weather and occupancy forecasts, and equipment constraints.

NFPA 855

The standard for stationary energy storage system installation, covering separation distances, fire suppression, ventilation, and hazard mitigation requirements.

Battery C-rate

Charge or discharge power divided by capacity. A 1C rate discharges a full battery in one hour; a 0.5C rate takes two hours.

Blowdown rate

Percentage of feedwater drained to control boiler dissolved solids: feedwater TDS divided by (maximum boiler water TDS minus feedwater TDS) times 100.

Steam trap survey

Inspection using ultrasonic and infrared tools to find traps failed open (steam loss) or failed closed (water hammer, carryover). A core steam-system measure.

PV capacity factor

Actual annual generation divided by nameplate capacity times 8760 hours. Typical fixed-tilt commercial PV reaches roughly 13-18% depending on location.

CHP overall efficiency

Useful electric output plus useful thermal output divided by fuel input. Topping and bottoming cycles capture waste heat that would otherwise be rejected.

Specific energy consumption

Industrial energy use per unit of product, such as kWh per ton. Normalizing for production volume and product mix enables benchmarking across plants.

Compressed air leak cost

Leaks often waste 20-30% of compressor output. Estimate leak rate from compressor unloaded runtime; ultrasonic surveys locate and prioritize repairs.