Variable Naming

The following lists of variable names and subscribs shall be used for the implementation of models of the BuildingSystems library. In both lists the conventions of the Modelica Standard Library (MSL) and the Modelica IBPSA Library (https://ibpsa.github.io/project1) are generally considered.

8.1 Variables

• Greek symbols are expressed with their written-out name: alpha, beta, gamma etc..

• Geometric variable names are described with their full names: length, with, diameter etc..

• Dimensionless variables are abbreviated with two letters (Pr, Re, Gr, Nu etc.).

• The dimension and size of a vector variable is declared with the variable name:

  Modelica.SIunits.Length posVec[3];
  

BuildingSystems	Modelica IBPSA Library	Meaning	SI unit	Modelica Type
A	A	Area	m2	Modelica.SIUnits.Area
abs	abs	Short-wave absorptance	1	BuildingSystems.Types.Absorptance
alpha		Convective heat transfer coeff.	W/(m2.K)	Modelica.SIUnits.SurfaceCoefficientOfHeatTransfer
angle		Angle in radiant	rad	Modelica.SIUnits.Angle
angleDeg		Angle in degree	deg	BuildingSystems.Types.Angle_deg
beta		Moisture transfer coefficient	kg/(m2.Pa.s)	BuildingSystems.Types.MoistureTransferCoefficient
c		Specific heat capacity	J/(kg.K)	Modelica.SIUnits.SpecificHeatCapacity
cp		Spec. heat capacity (const. p)	J/(kg.K)	Modelica.SIUnits.SpecificHeatCapacityAtConstantPressure
cv		Spec. heat capacity (const. V)	J/(kg.K)	Modelica.SIUnits.SpecificHeatCapacityAtConstantVolume
C	C	Heat capacity	J/K	Modelica.SIUnits.HeatCapacity
CLt		Liquid transport conductance	kg/(s.m)	BuildingSystems.Types.CoefficientOfLiquidTransport
CMd		Moisture diffusion conductance	kg/(s.Pa)	BuildingSystems.Types.CoefficientOfMoistureDiffusion
CTh		Thermal conductance	W/K	Modelica.SIUnits.ThermalConductance
diameter	diameter	Diameter	m	Modelica.SIUnits.Diameter
distance		Distance	m	Modelica.SIUnits.Length
dp	dp	Pressure difference	Pa	Modelica.SIUnits.PressureDifference
dx,dy,dz		Differential length in 3D space	m	Modelica.SIUnits.Length
epsilson		Long-wave emittance	1	Modelica.SIUnits.Emissivity
eta		Efficiency	1	Modelica.SIUnits.Efficiency
ViewFac		View factor	1	BuildingSystems.Types.ViewFactor
h	h	Specific enthalpy	J/kg	Modelica.SIUnits.SpecificEnthalpy
height		Height	m	Modelica.SIUnits.Length
I		Current	A	Modelica.SIUnits.Current
Irr		Solar irradiation	W/m2	Modelica.SIUnits.RadiantEnergyFluenceRate
k	k	Air path flow coefficient	m3/(s.Pa)	BuildingSystems.Types.FlowCoefficient
lambda		Heat conductivity	W/(m.K)	Modelica.SIUnits.ThermalConductivity
latitudeDeg		Latitude of the location	deg	BuildingSystems.Types.Angle_deg
length		Length	m	Modelica.SIUnits.Length
longitudeDeg		Longitude of the location	deg	BuildingSystems.Types.Angle_deg
n	n	Number of something (1,2,3,...)	1	Real
m	m	Air path flow exponent	1	Real
m	m	Mass	kg	Modelica.SIUnits.Mass
m_flow	m_flow	Mass flow rate	kg/s	Modelica.SIUnits.MassFlowRate
ny		Kinematic viscosity	m2/s	Modelica.SIUnits.KinematicViscosity
p	p	Pressure	Pa	Modelica.SIUnits.Pressure
P	P	Power	W	Modelica.SIUnits.Power
posX,posY,PosZ		Space coordinates (x,y,z dim.)	m	Modelica.SIUnits.Length
posVec[3]		position vector (x,y,z coord.)	m	Modelica.SIUnits.Length
phi	phi	Relative humidity	1	BuildingSystems.Types.RelativeHumidity
Pr	Pr	Prandtl number	1	Modelica.SIUnits.PrandtlNumber
Q	Q	Heat	J	Modelica.SIUnits.Heat
Q_flow	Q_flow	Heat flow rate	J/s	Modelica.SIUnits.HeatFlowRate
R		Electrical resistance	Ohm	Modelica.SIUnits.Resistance
rho	rho	Density	kg/m3	Modelica.SIUnits.Density
Re	Re	Reynolds number	1	Modelica.SIUnits.ReynoldsNumber
T	T	Thermodynamic temperature	K	Modelica.SIUnits.Temp_K
tau		Transmittance	1	Real
time	time	Time	s	Modelica.SIUnits.Time
thickness		Thickness	m	Modelica.SIUnits.Thickness
U	U	Internal energy	J	Modelica.SIUnits.Energy
U		Voltage	V	Modelica.SIUnits.Voltage
UVal		U-value	W/(m2.K)	Modelica.SIunits.CoefficientOfHeatTransfer
v	v	Velocity	m/s	Modelica.SIUnits.Velocity
vVec[3]		Velocity vector (x,y,z comp.)	m/s	Modelica.SIUnits.Velocity
vX, vY, vZ		Velocity magnitude (x,y,z dim.)	m/s	Modelica.SIUnits.Velocity
V	V	Volume	m3	Modelica.SIUnits.Volume
w		Water content	kg/m3	Modelica.SIUnits.MassConcentration
width		Width	m	Modelica.SIUnits.Length
x		Absolute humidity	kg/kg	Modelica.SIUnits.MassFraction
Xi	Xi	Mass fraction of substance i	kg/kg	Modelica.SIUnits.MassFraction

8.2 Subscripts of variable names

In general subscripts shall be combined with variable names by the use of the lowerCamelCase notation: e.g. vAir (velocity of the air).

BuildingsSystems	Modelica IBPSA Library	Meaning
Air		Air
Amb		Ambient
Azi		Azimuth
constant	constant	Constant value
Dec		Declination
Deg		Degree
Der		Derivation
Dir	Dir	Direct
Dif	Dif	Diffuse
flow	flow	Flow of energy or mass
Hor	Hor	Horizontal
Hr		Hour
Inc		Incident
Layers		Layers of a construction
Mean		Mean value
Nodes		Numerical nodes
nominal	nominal	Nominal value
Sat	Sat	Saturation
start	start	Start value
Til	Til	Tilted
Tot		Total
X, Y, Z		Subscripts of the 3D space
Ver		Vertical
Zen		Zenith

• There are some exceptions for
  • Flow variables: e.g. Q_flow, m_flow, ...
  • Start variables: e.g. T_start, p_start ...
  • Indices of ports: e.g. port_a, port_b, heatPort_x1, heatPort_x2, radiationPort_in, radiationPort_out ...
  • Nominal variables: e.g. T_nominal, m_flow_nominal ...
  • Constant variables: e.g. x_constant ...