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E. HVAC EQUATIONS (METRIC UNITS)

E. HVAC EQUATIONS (METRIC UNITS)

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CHAPTER 14

METRIC UNITS
Table 14-28 FAN EQUATIONS
I/s = Litres per second

m3/s = Cubic metres per second
rad/s= Radians per second
P = Static or Total Pressure (Pa)
kW = Kilowatts
d = Density (kg/m3)

Table 14-29 PUMP EQUATIONS

I/s = Litres per second

m3/s = Cubic metres per second
rad/s = Radians per second
D = Impeller diameter
H = Head (kPa)
BP = Brake horsepower

14.59

DUCT

DESIGN

TABLES

AND

CHARTS

METRIC UNITS
Table 14-30 HYDRONIC EQUATIONS
Q = Heat flow (kilowatts)
At = Temperature difference (°C)
m3/s (used for large volumes) = Cubic metres per second
= Litres per second

l/s

m3/s)2
c) AP =(

AP = Pressure diff. (Pa or kPa)
)

=

(/,)s

Cv = Valve constant (dimensionless)
WP = Water power (kW) or (W)
m3/s = Cubic metres per second

I/s = Litres per second
Sp. Gr. = Specific gravity (use 1.0 for water)
BP = Brake power (kW)
E, = Efficiency of Pump
H = Head (Pa) or (m)
NPSHA = Net positive suction head available
Pa = Atm. press. (Pa)
(Std. Atm. press. = 101,325 Pa)
Ps = Pressure at pump centerline (Pa)
V2

2g

Velocity head at point Ps (m)

Pvp = Absolute vapor pressure (Pa)
g = Gravity acceleration (9.807 m/s2)
h = Head loss (m)
f = Friction factor (dimensionless)
L = Length of pipe (m)
D = Internal diameter (m)
V = Velocity (m/s)

14.60

CHAPTER 14

Table 14-31 ELECTRIC EQUATIONS

kW = Kilowatts

I= Amps (A)
E = Volts (V)
P.F. = Power factor

R = ohms ( )
P. = watts (W)

*Nameplate ratings

Table 14-32 AIR DENSITY CORRECTION FACTORS (Metric Units)

DUCT

F

DESIGN

TABLES

AND

CHARTS

METRIC UNITS
AND EQUIVALENTS

Table 14-33 METRIC UNITS (Basic & Derived) (13)

Unit

Symbol

Quantity

Equivalent or
Relationship

ampere

A

Electric current

Same as U. S.

candela

cd

Luminous intensity

1 cd/m2 = 0.292 ft lamberts

Temperature

°F = 1.8 C + 32o

oCCelsius

coulomb

C

Electric charge

Same as U.S.

farad

F

Electric capacitance

Same as U.S.

henry

H

Electric inductance

Same as U.S.

hertz

Hz

Frequency

Same as cycles per second

joule

J

Energy, work, heat

1 J = 0.7376 ft-lb
= 0.000948 Btu

kelvin
oF

K

Thermodynamic
temperature

°K = °C + 273.15o
+ 459.67

1.8
kilogram

kg

Mass

1 kg = 2.2046 lb

litre

I

Liquid volume

1 1= 1.056qt = 0.264 gal

lumens

Im

Luminous flux

1lm/m2 = 0.0929 ft candles

lux

Ix

Illuminance

1 Ix = 0.0929 ft candles

metre

m

Length

1 m= 3.281 ft

mole

mol

Amount of substance

-

newton

N

Force

1 N = kg m/s2 = 0.2248 lb (force)

Electrical resistance

Same as U.S.

Pressure, stress

1 Pa = N/m2 = 0.000145 psi

ohm
pascal

Pa

radian

rad

Plane angle

= 0.004022 in. w.g.
1 rad = 57.29°

second

s

Time

Same as U.S.

siemens

S

Electric conductance

steradian

sr

Solid angle

volt

V

Electric potential

Same as U. S.

watt

W

Power, heat flow

1 W = J/s = 3.4122 Btu/hr
1 W = 0.000284 tons of refrig.

14.62

.oC

CHAPTER 14

Table 14-34 METRIC EQUIVALENTS (13)

Quantity

Symbol

Unit

U.S. Relationship

acceleration

m/s2

metres per second squared

1 m/s2 = 3.281 ft/sec2

angular velocity

rad/s

radians per second

1 rad/sec = 9.549 rpm

area

m2

square metre

1 m2 = 10.76 sq ft

atmospheric pressure

-

101.325 kPa

29.92 in Hg = 14.696 psi

density

kg/m3

kilograms per cubic metre

1 kg/m3 = 0.0624 lb/cu ft

density, air

-

1.2 kg/m3

density, water

_

0.075 lb/cu ft

1000 kg/m3

62.4 lb/cu ft

duct friction loss

Pa/m

pascals per metre

1 Pa/m = 0.1224 in.w.g./100'

enthalpy

kJ/kg

kilojoule per kilogram

1 kJ/kg = 0.4299 Btu/lb dry air

9.8067 m/s2

32.2 ft/sec2

gravity
heat flow

W

watt

1 W = 3.412 Btu/hr

length (normal)

m

metre

1 m = 3.281 ft = 39.37 in.

linear velocity

m/s

metres per second

1 m/s = 196.9 fpm

mass flow rate

kg/s

kilograms per second

1 kg/s

moment of inertia

kg.m2

kilograms x square metre

1 kg. ·m2 = 23.73 lb ·sq ft

power

W

watt

1 W = 0.00134 hp'

pressure

kPa
Pa

kilopascal (1000 pascals)
pascal

1 kPa = 0.296 in Hg = 0.145 psi
1 Pa = 0.004015 in.w.g.

specific heat-air (Cp)

1000 J/kg. oC

1000 J/kg C = 1 kJ/kg
= 0.2388 Btu/lb °F

specific heat-air (Cv)

717 J/kg. oC

0.17 Btu/lb°F

specific heat-water

4190 J/kg · °C

1.0 Btu/lb° F

cubic metres per kilogram

1 m3/kg = 16.019 cu ft/lb

watt millimetre per
square metre °C

1 W ·mm/m2 ·°C
= 0.0069 Btu ·in/ft2 ·hr ·°F

cubic metres per second
litres per second
1m3/s = 1000 I/s
1 ml = litres/1000

1 m3/s = 2118.88 cfm (air).
1 I/s = 2.12 cfm (air)
1 m3/s = 15,850 gpm (water)
1 ml/s = 1.05 gph (water)

specific volume

m3/kg

thermal conductivity W · mm/m2 ·°C
volume flow rate

m3/s
I/s

7936.6 lb/hr

14.63