209
Appendix A: Nomenclature
Symbols, Terms, Units, and Subscripts
Symbol Description Unit
A Surface area m
2
A
c
Cross-sectional area of a duct m
2
ADPI Air distribution performance index Dimensionless
BF Bypass factor Dimensionless
C Unit thermal conductance W/(m
2
/°C)
C Loss coefcient Dimensionless
C
d
Discharge coefcient Dimensionless
C
p
Pressure coefcient Dimensionless
C
v
Flow coefcient Dimensionless
c Specic heat J/kg °C
c Sound velocity in the air m/s
c
p
Specic heat at constant pressure J/kg °C
CLF Cooling load factor Dimensionless
CLTD Cooling load temperature difference °C
COP Coefcient of performance Dimensionless
cfm Volume ow rate ft
3
/min
D Diameter m
DD Degree-days °C day
DR Daily range of temperature °C
EER Energy efciency ratio Dimensionless
f Friction factor Dimensionless
G Irradiation W/m
2
g Local acceleration due to gravity m/s
2
H Head m
H Enthalpy J
h Heat transfer coefcient W/m
2
°C
h Specic enthalpy J/kg
h
fg
Latent heat of vaporization or condensation J/kg
hp Horsepower hp
k Thermal conductivity Wm/m
2
°C
L Total length m
L
p
Sound pressure level dB
L
W
Sound power level dB
L
WA
A-weighted sound power level dB(A)
LH Latent heat W
LMTD Log mean temperature difference °C
Continued
210 Appendix A: Nomenclature
Symbols, Terms, Units, and Subscripts (Continued)
Symbol Description Unit
M Molecular weight kg/kmol
m Mass kg
m
Mass ow rate kg/s
NC Noise criteria Dimensionless
NTU Number of transfer units Dimensionless
Nu Nusselt number Dimensionless
P Circumference length m
P
E
Electrical motor input power W
p Static pressure Pa
p
d
Dynamic pressure Pa
p
i
Partial pressure of component i Pa
Pr Prandtl number Dimensionless
Q Total energy input J
Q
Heat transfer rate W
q Heat transfer per unit mass J/kg
R Gas constant J/(kg K)
r Thermal resistance m
2
°C/W
r Radius m
r
f
Fouling resistance m
2
°C/W
R
Universal gas constant = 8.314
J/mol.K
Re Reynolds number Dimensionless
rpm Revolutions per minute Dimensionless
SC Shading coefcient Dimensionless
SH Sensible heat W
SHF Sensible heat factor Dimensionless
T Temperature °C
T Absolute temperature K
TH Total heat W
U Internal energy J
U Overall heat transfer coefcient W/m
2
°C
u Velocity m/s
V Volume m
3
V
Volume ow rate
m
3
/s
ν
Specic volume m
3
/kg
W Work J
W
Power
W
ω
Moisture content, also known as humidity ratio
kg
υ
/kg
a
x Length m
y Length m
z Length m
Δp Pressure drop Pa
211Appendix A: Nomenclature
Symbols, Terms, Units, and Subscripts (Continued)
Symbol Description Unit
η
h
Humidication efciency Dimensionless
μ Dynamic viscosity kg/ms
ν
Kinematic viscosity m
2
/s
r Density kg/m
3
φ
Relative humidity %
Subscripts
a Air, dry air, added
adp Apparatus dew point
as Adiabatic saturation
atm Atmospheric
avg Average
b Branch
c Cool, coil, cold, condenser, cross section or minimum free
area, ceiling
cl Center line
cw Chilled water
cwr Chilled water return
cws Chilled water supply
D Diameter
d Design
db Dry bulb
dp Dew point
e Evaporator
f Friction, fouling
fg Phase change (liquid/vapor)
Floor
g Saturated vapor
h Hot
i At state i when i is a letter or number, component i in a gas
mixture
m Mixed
o Outdoor
p Constant pressure
r Rejected
R Room or recirculated
s Saturation, supply
t Total
ν
Water vapor, constant volume
νs
Saturated water vapor at a given dry-bulb temperature
w Water
wb Wet bulb
Continued
212 Appendix A: Nomenclature
Symbols, Terms, Units, and Subscripts (Continued)
Symbol Description Unit
Superscripts
* Properties of saturated air at a given wet-bulb temperature
Abbreviations
AC Air conditioning
AHU Air handling unit
ASHRAE American Society of Heating, Refrigerating, and Air-
Conditioning Engineers
BHP Brake horsepower
DX Direct expansion, dry expansion
FCU Fan coil unit
HVAC&R Heating, ventilating, air conditioning, and refrigeration
SI International System of Units

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