Annual cooling 
Overall annual efficiency of a cooling system 
N/A 


Annual heating 
Overall annual efficiency of a heating system 
N/A 


Battery energy ratio 
The ratio of accumulated nonactive energy divided by battery energy. 
N/A 


Boiler 
Efficiency of boiler equipment 
N/A 


Combined energy factor 
Combined Energy Factor (CEF) is the energy performance metric for clothes dryers; the higher the CEF the more efficient the clothes dryer. CEF is the quotient of the test load size, 8.45 lbs for standard dryers and 3 lbs for compact dryers, C, divided by the sum of the machine electric energy use during standby and operational cycles. The equation is shown here: CEF = C (lbs) / (Eon + Estandby). The units are pounds per kWh, the higher the value, the more efficient the clothes dryer is. 
n/a 
EPA 

Combustion 
The measure of how much energy is extracted from the fuel and is the ratio of heat transferred to the combustion air divided by the heat input of the fuel. (01) 
n/a 


Efficacy 
The amount of light (luminous flux) produced by a light source, usually measured in lumens, as a ratio of the amount of power consumed to produce it, usually measured in watts. 
n/a 


Efficiency 
A ratio of energy output to input. 
N/A 


Energy conversion 
The percentage of the energy to which the cell is exposed to (input resource) that is actually converted into effective energy (output resource) under standard testing conditions. For solar cells, this is calculated by dividing a cell's power output (in watts) at its maximum power point by the input light (in watts per square meter) and the surface area of the solar cell (in square meters). 
n/a 


Energy factor 
A factor is used to compare the relative efficiency of water heaters, dishwashers, clothes washers, and clothes dryers. Energy Factor (EF) is the quotient of the capacity equipment divided by the sum of the equipment electrical energy for mechanical operation or standby, and the water heating energy. The units are volume (or weight) per energy per cycle. For dishwashers, the EF is the reciprocal of the sum of energy per cycle, and expressed in cycles per kWh. The higher the EF value means a more efficient equipment. It is the ENERGY STAR energy performance metric. This factor may vary based on equipment features such as water heating boosters or truncated cycles. The federal EnergyGuide label on equipment shows the annual energy consumption and cost, which use the energy factor. The EF does not appear on the EnergyGuide label. Unlike annual energy use, the EF does not take into account the estimated annual energy use in standby mode. The energy factor for a dehumidifier is calculated by dividing the water removed from the air by the energy consumed, measured in liters per kilowatt hour (L/kWh). 
n/a 
EPA 

Energy recovery 
The net total energy (sensible plus latent, also called enthalpy) recovered by the supply airstream adjusted by electric consumption, case heat loss or heat gain, air leakage and air flow mass imbalance between the two airstreams, as a percent of the potential total energy that could be recovered plus associated fan energy. 
n/a 
NREL 

External quantum 
The external quantum efficiency of a solar cell is the percentage of photons that are converted to electric current when the cell is operated under short circuit conditions after the reflected and transmitted light has been lost. 
n/a 


Fill factor 
The fill factor is the ratio of the actual maximum attainable power to the product of the open circuit voltage and short circuit current. 
N/A 


Heat recovery 
Efficiency of sensible heat recovery in percentage. 
n/a 


Idle energy rate 
Idle energy rate represents the total idle energy consumed by the machine including all tank heaters) and controls, or while maintaining at a stabilized operating condition or temperature such as a thermostat(s) set point during the time period specified. Booster heater (internal or external) energy consumption should not be included. It's measured while equipment is enclosed. Also called standby energy rate. For cooking equipment, the purposes of the idle rate can be normalized based on the area of the (bottom) cooking surface. 
n/a 
EPA 

Off cycle heat loss coefficient 
The heat loss coefficient to ambient conditions. Btu/h·ft2·°F 
n/a 


Power usage effectiveness 
PUE is a measure of data center infrastructure efficiency, representing the amount of energy that is needed per unit delivered to IT equipment. It is computed as the total annual source energy divided by the annual IT source energy. 
N/A 
EPA 

Rated sensible heat ratio 
The fraction of total energy transfer between the evaporator coil and air that is associated with sensible capacity (change in air temperature) expressed as a dimensionless value. 
N/A 


Recirculation energy loss rate 
Rate of heat loss from the recirculation loop when operating. 
n/a 


Recovery 
The ratio of energy delivered to heat cold water compared to the energy consumed by the water heater, as determined following standardized DOE testing procedure. 
N/A 
DOE 

Reflectance 
Reflectance is the ratio of the energy reflected from the surface of the interface to the total incident energy. There is a reflection of light at the interface between the first layer of a solar cell and the incident medium, usually air, and there is also reflection at the interfaces between the individual layers within the solar cell. All these processes result in a total reflectance between the solar cell and air. This means that a part of the incident energy that can be converted into a usable energy by the solar cell is lost by reflection. 
N/A 
Solar Cells 

Thermal 
The efficiency of heat transfer between the combustion process and the heated steam, water, or air. (01) 
n/a 


Water factor 
Water Factor, WF, is the quotient of the total weighted percycle water consumption, Q, divided by the capacity of the clothes washer, C. The lower the value, the more water efficient the clothes washer is. The equation is: WF = Q/C. WF is the ENERGY STAR water performance metric that allows the comparison of clothes washer water consumption independent of clothes washer capacity. 
n/a 
ENERGY STAR 
