Abbreviations, Symbols, and Units
| A | area | m2 |
| A | (unit) | amperes |
| B | magnetic field intensity | weber/m2 |
| Bcm | nonflow availability | J |
| Bcv | flow availability | J |
| Btu | (unit) | British thermal unit |
| bbl | (unit) | oil barrel |
| C | capacitance | F |
| C | contrast | dimensionless |
| C | thermal conductance | W/K |
| Cap | rated capacity | ton |
| Ccf | (unit) | 100 ft3 |
| CDD | (unit) | cooling degree days |
| CF | coincidence factor | dimensionless |
| CFM | (unit) | cubic ft/min |
| CL | connected load | W |
| COP | coefficient of performance | dimensionless |
| CRF | capital recovery factor | dimensionless |
| CRI | color rendering index | dimensionless |
| CUSUM | cumulative sum (chart) | acronym |
| Ct | current transformer ratio | dimensionless |
| cal | (unit) | calorie |
| cd | (unit) | candela |
| cm | (unit) | centimeter |
| cp | specific heat | J/kg·K |
| D | diameter | m |
| D | demand (electrical) | kW |
| D | distance | miles |
| De | equivalent diameter | m |
| Dlux | (unit) | 10 lx |
| E | energy, work, heat | J or kWh |
| E | specific energy | J/kg |
| EER | energy efficiency ratio | Btu/Wh |
| Ef | emission factor | g CO2/gallon |
| EFLH | equivalent full load hours | h |
| EMO | energy management opportunity | acronym |
| EUPF | energy use performance factor | varies |
| eo | electricity price escalation | dimensionless |
| F | force | N |
| F | (unit) | farad |
| f | friction factor | dimensionless |
| fc | (unit) | foot-candle |
| ft | (unit) | foot |
| f | frequency | Hz |
| G | 1 billion—109 | giga |
| g | acceleration of gravity | m/s2 |
| g | (unit) | gram |
| H | (unit) | henry |
| H | pump head | m |
| H | enthalpy | J |
| H | annual operating hours | h |
| HDD | (unit) | heating degree days |
| HSPF | heating seasonal performance factor | Btu/Wh |
| HUOD | hours use of demand | h |
| HVAC | heating, ventilating, and air conditioning | acronym |
| Hz | (unit) | hertz |
| h | specific enthalpy | J/kg |
| h | (unit) | hour |
| ha | hectare | 104 m2 |
| hc | convective heat transfer coefficient | W/m2·K |
| hp | (unit) | horsepower |
| I | illumination (illuminance) | lm/m2 |
| i | interest rate | dimensionless |
| IE | interactive effects factor | dimensionless |
| IPMVP® | International Performance Measurement and Verification Protocol | acronym |
| IRR | internal rate of return | dimensionless |
| ITC | investment tax credit | dimensionless |
| i | electrical current | A |
| in | (unit) | inch |
| J | (unit) | joule |
| j | √−1 | dimensionless |
| K | (unit) | kelvin |
| Kh | meter constant | kWh/revolution |
| kh | material constant | dimensionless |
| k | thermal conductivity | W/m·K |
| k | one thousand—103 | kilo |
| L or l | length, thickness | m |
| L | inductance | H |
| l | (unit) | liter |
| L | luminance | cd/m2 |
| L | project life | yr |
| LI | luminous intensity | cd |
| LF | load factor | dimensionless |
| l | load fraction | % |
| lb | (unit) | pound |
| lm | (unit) | lumen |
| lx | (unit) | lux |
| M | 1,000,000—106 | mega |
| M | molar mass ratio | dimensionless |
| MBtu | (unit) | 106 Btu |
| M&V | measurement and verification | acronym |
 |
mass flow rate | kg/s |
| m | mass | kg |
| m | (unit) | meter |
| min | (unit) | minute |
| mo | (unit) | month |
| mpg | (unit) | miles/gallon |
| mt | (unit) | metric ton |
| N | motor speed | Hz or RPM |
| N | (unit) | newton |
| N or n | number (quantity) of something | dimensionless |
| NPV | net present value | $ |
| Om | maintenance and operating costs | $/yr |
| P | pressure | N/m2 or Pa |
| P | present investment | $ |
| Pa | (unit) | pascal |
| Pt | potential transformer ratio | dimensionless |
| PW | present worth | $ |
| PWF | present worth factor | dimensionless |
| ΔP | pressure drop or differential | N/m2 |
| p | period of time | s or h |
| pf | power factor | dimensionless |
| pp | pumping power | W |
| Q | heat transfer | J |
 |
rate of heat transfer | W |
| Q | power | W |
| quad | (unit) | 1015 Btu |
| R | resistance | ohms |
| R | thermal resistance | K/W |
| R | universal gas constant | 8316.6 J/kg·K |
| ROI | return on investment | dimensionless |
| RPM | (unit) | revolutions per minute |
| r | radius | m |
| S | apparent power | kVA |
| S | entropy | J/K |
| s | (unit) | second |
| Sv | salvage value | $ |
| SEER | seasonal energy efficiency ratio | Btu/Wh |
| T | temperature | °C, K, °F, or °R |
| T | torque | N·m |
| T or t | time | s |
| tr | tax rate | dimensionless |
| U | overall heat transfer coefficient | W/m2·K |
| U | internal energy | J |
| V | volume | m3 |
| VARs | (unit) | volt-ampere-reactive |
| VAR | reactive component of power | VARs |
| v | velocity | m/s |
| v or V | voltage | V |
| V | (unit) | volt |
 |
volumetric flow rate | m3/s |
| W | (unit) | W |
| W | work done | J |
 |
rate of work, power | W |
| w | weight fraction | % |
| X | reactance | ohms |
| x | excess air fraction | % |
| yr | (unit) | year |
| Z | impedance | ohms |
| z | elevation | m |
| Greek letters | ||
| Δ | incremental change | dimensionless |
 |
effectiveness | dimensionless |
|
emissivity | dimensionless |
| η | efficiency | dimensionless |
| θ | phase angle | degrees |
| μ | specific internal energy | J/kg |
| μo | potential energy | J/mol |
| ρ | density | kg/m3 |
| ρ | line resistivity | ohms/m |
| σ | Stefan–Boltzmann constant | 5.67×10−8 W/m2·K4 |
| Φ | phase | dimensionless |
| ΦL | luminous flux | lumen |
| ω | angular velocity | radiant/second |
| Ω | (unit) | ohms |
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