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 coefcient Dimensionless

C

d

Discharge coefcient Dimensionless

C

p

Pressure coefcient Dimensionless

C

v

Flow coefcient Dimensionless

c Specic heat J/kg °C

c Sound velocity in the air m/s

c

p

Specic heat at constant pressure J/kg °C

CLF Cooling load factor Dimensionless

CLTD Cooling load temperature difference °C

COP Coefcient 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 efciency 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 coefcient W/m

2

°C

h Specic 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 coefcient 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 coefcient W/m

2

°C

u Velocity m/s

V Volume m

3

V

Volume ow rate

m

3

/s

ν

Specic 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

Humidication efciency 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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