Guide for Interface Developers — EnergyPlus 9.4

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Standard EnergyPlus Units[LINK]

EnergyPlus expects information in a single unit system (SI). This requires interface developers to convert user inputs from those preferred by architects and engineers into the standard metric units of EnergyPlus. EnergyPlus will not perform any units conversions and will not have any unit conversion routines.

ASCII with no spaces is used for abbreviations. Note that exponents appear without any indication of exponentiation: i.e., kg/m3 not kg/m^3 or kg/m**3. Also note the use of dashes. We have W/m2-K not W/m2*K or W/(m2*K).

At the end we note the “problem” variables – the inputs that have non-standard units. Inputs using these units will have to be changed and the code checked to see how the quantities are used internally.

Standard EnergyPlus Units
Quantity unit abbreviation
angular degrees degree deg
Length meter m
Area square meter m2
Volume cubic meter m3
Time seconds s
Frequency Hertz Hz
Temperature Celsius C
absolute temperature Kelvin K
temperature difference Kelvin delK
speed meters per second m/s
energy (or work) Joules J
power Watts W
mass kilograms kg
force Newton N
mass flow kilograms per second kg/s
volume flow cubic meters per second m3/s
pressure Pascals Pa
pressure difference Pascals delPa
specific enthalpy Joules per kilogram J/kg
density kilograms per cubic meter kg/m3
heat flux watts per square meter W/m2
specific heat ———————————————————————— J/kg-K
conductivity ———————————————————————— W/m-K
diffusivity ———————————————————————— m2/s
heat transfer coefficient ———————————————————————— W/m2-K
R-value ———————————————————————— m2-K/W
heating or cooling capacity Watts W
electric potential volts V
electric current Amperes A
illuminace lux lx
luminous flux lumen lm
luminous intensity candelas cd
luminance candelas per square meter cd/m2
vapor diffusivity m2/s
viscosity ———————————————————————— kg/m-s
porosity ———————————————————————— m3/m3
thermal gradient coeff for moisture capacity ———————————————————————— kg/kg-K
isothermal moisture capacity ———————————————————————— m3/kg