HVAC Formulas:-
CFM = ______BTU/Hr / ( 1.08 x Temperature Difference)
TON OF REFRIGERATION -The amount of heat required to melt a ton (2000 lbs.) of ice at 32°F 288,000 BTU/24 hr.,12,000 BTU/hr.
APPROXIMATELY 2 inches in Hg. (mercury) = 1 psi
WORK =Force (energy exerted) X Distance
ONE HORSEPOWER = 33,000 ft.-lb. of work in 1 minute
ONE HORSEPOWER = 746 Watts
CONVERTING KW to BTU: 1 KW = 3413 BTU’s
CONVERTING BTU to KW :3413 BTU’s = 1 KW
COULOMB = 6.24 X 1018 (1 Coulomb = 1 Amp)
OHM'S LAW = E=IxR
I =E / R
R =E / I Where: E = voltage (emf)
I = Amperage (current)
R = Resistance (load)
WATTS (POWER) = volts x amps or P = E x I
P(in KW) = (E x I) / 1000
U FACTOR = Reciprocal of R factor
1 / R = U
ONE FARAD CAPACITY =1 amp. stored under 1 volt of pressure
MFD (microfarad) = 1 MFD = 1 Farad / 1,000,000
LRA (Locked rotor amps) = LRA = FLA x 5 (NOTE: This is a commonly used rule-of-thumb, not a direct conversion)
RPM of motor = (60Hz x 120) / (No. of Poles)
1800 RPM Motor – slippage makes it about 1750
3600 RPM Motor – slippage makes it about 345
DRY AIR =78.0% Nitrogen
21.0% Oxygen
1.0% Other Gases
WET AIR = Same as dry air plus water vapor
SPECIFIC DENSITY = 1 / Specific Volume
SPECIFIC DENSITY OF AIR = 1 / 13.33 = .075 lbs./cu.ft.
STANDARD AIR = 24 Specific Heat (BTU’s needed to raise 1 lb. 1 degree)
SENSIBLE HEAT FORMULA (Furnaces): BTU/hr. – Specific Heat X Specific Density X 60 min./hr.
= X CFM X DT .24 X .075 X 60 X CFM X DT
= 1.08 X CFM X DT
ENTHALPHY = h = Sensible heat + Latent heat
TOTAL HEAT FORMULA (for cooling, humidifying or dehumidifying)
BTU/hr. = Specific Density X 60 min./hr. X CFM X Dh = 0.75 x 60 x CFM x Dh
= 4.5 x CFM x Dh
Where Dh = Change in Enthalpy
RELATIVE HUMIDITY = Moisture present / Moisture air can hold
SPECIFIC HUMIDITY = Grains of moisture per dry air 7000 GRAINS in 1 lb. of water
DEW POINT = When wet bulb equals dry bulb
TOTAL PRESSURE (Ductwork) = Static Pressure + Velocity Pressure
CFM = Area (sq. ft.) X Velocity (ft. min.)
HOW TO CALCULATE AREA
Rectangular Duct A=L x W
Round Duct A = (Pi)r² ...or...(Pi)D²/4
RETURN AIR GRILLES – Net free area = about 75%
3 PHASE VOLTAGE UNBALANCE = (100 x maximum deg. from average volts) / Average Volt
NET OIL PRESSURE = Gross Oil Pressure – Suction Pressure
NOTE: The suction pressure must be measured at the crankcase, not the service valve
COMPRESSION RATIO = Discharge Pressure Absolute / Suction Pressure Absolute
HEAT PUMP AUXILIARY HEAT – Sized at 100% of the load
ARI HEAT PUMP RATING POINTS = 47°F and 17°F
NON-BLEND REFRIGERANTS: Constant Pressure = Constant Temperature during Saturated Condition in an evaporator or condenser.
BLENDS – Changing Temperature during Saturated Condition in an evaporator or condenser (See Glide)
28 INCHES OF WC = 1 psi
CALCULATING OIL NOZZLE SIZE (GPH):
BTU Input = Nozzle Size (GPH)
140,000 BTU’s
OR
BTU Output =140,000 X Efficiency of Furnace
FURNACE EFFICIENCY: % Efficiency = energy output / energy input
KELVIN TO CELSIUS: C = K – 273
CELSIUS TO KELVIN:
K = C + 273
ABSOLUTE TEMPERATURE MEASURED IN KELVINS
PERIMETER OF SQUARE:
P = 4s Where: P = Perimeter and s = side
PERIMETER OF RECTANGLE:
P = 2l + 2w P – Perimeter
l = length
PERIMETER OF SQUARE
P = a + b + c + d (P = Perimeter) a = 1st side
b = 2nd side
c = 3rd side
b= 4 side
PERIMETER OF CIRCLE:
C = (Pi)D = 2(Pi)r
Where: C = Circumference
(Pi) = 3.1416
D = Diameter
r = radius
AREA OF SQUARE: a = s² = s x s
A = Area
s = side
AREA OF RECTANGLE: A= l x w
Where:
A = Area
l = length
w = width
AREA OF TRIANGLE: A = 1/2bh
Where:
A = Area
b = base
h = height
AREA OF CIRCLE: A = (Pi)r² = (Pi) D²/4 Where:
A = Area
(Pi) = 3.1416
r = radius
D = Diameter
VOLUME OF RECTANGULAR SOLID:V = l x w x h
Where: V = Volume
l = length
w = width
h = height
VOLUME OF CYLINDRICAL SOLID: V = (Pi)r²h = (Pi) D²/4 x h
Where:
V = Volume
w = width
p = 3.1416
r = Radius
D = Diameter
h = height
CAPACITANCE IN SERIES: C = 1 / (C1 + C2)
CAPACITANCE IN PARALLEL: C = C1 + C2 + . . . . .
GAS LAWS:
Boyle’s Law: P1 V1 = P2 V2
Where:
P = Pressure (absolute)
V = Volume
Charles ’ Law: P1 / T1 = P2 / T2
Where:
P = Pressure (absolute)
T = Temperature (absolute)
General Gas Law: (P1 x V1) / T1 = (P2 x V2) / T2
Where:
P = Pressure (absolute)
V = Volume
T = Temperature (absolute)
Linear Measurement Equivalents (U.S. Conventional - SIMetric) 1 inch =2.54 cm
25.4 mm
25400 µm
1 foot =12"
0.304 m
30.48 cm
1 yard =3'
0.914 m
91.44 cm
1 micron =
0.0000394"
1 millimeter =
1000 µm
0.0394"
1 centimeter =10 mm
0.3937"
1 meter = 100 cm
39.37"
1 kilometer =1000m
0.62137 miles
Area Equivalents ( U.S. to Metric )
1 in²=0.0065m²
1 ft²=144 in²
0.093 m²
1 yd²=1296 in²=9 ft²=0.836 m²
Volume Equivalents ( U.S. and Metric )
1 in³=0.016 L=16.39 cm³
1 ft³=1728 in³=7.481 gal=28.317 L=0.0283 m³=28317 cm³
1 yd³=27 ft³=46656 in³
1 gal=0.1337 ft³=3.79 L=231 in³=3785 cm³
1 cm³=0.0610237 in³
1 L=61.03 in³
1000 cm³
0.2642 gal
Velocity Equivalents
1 mi/hr=
1.47 ft/sec
0.87 knot
1.61 km/hr
0.45m/sec
1 ft/sec=
0.68 mi/hr
60 ft/min
0.59 knot
1.1 km/hr
0.305 m/sec
1 m/sec=
3.28 ft/sec
2.24 mi/hr
1.94 knot
3.6 km/hr
1 km/hr=0.91 ft/sec
0.62 mi/hr
0.54 knot
0.28 m/sec
Heat Equivalents
1 Btu=252 calories
1054.4 J (Joules)
1 kcal (kilocalorie)= 1000 cal
4.1840 kJ
1 Btu/lb=0.5556 kcal/kg
2.3244 kJ/kg
1kcal/kg=1.8 Btu/l
Btu/hr=0.2931W.
THANK YOU !!!