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 Example: A 150 lb. man climbs a flight of stairs 100 ft. high Work = 150 lb. X 100 ft. Work = 15,000 ft.-lb. ONE HORSEPOWER = 33,000 ft.-lb. of work in 1 minute ONE HORSEPOWER =
746 Watts CONVERTING KW to BTU: 1 KW = 3413 BTU s Example: A 20 KW heater (20 KW X 3413 BTU/KW = 68,260 BTU s) CONVERTING BTU to KW 3413 BTU s = 1 KW Example: A 100,000 BTU/hr. oil or gas furnace (100,000 / 3413 = 29.3 KW) COULOMB = 6.24 X 1018 (1 Coulomb = 1 Amp) OHM'S LAW = E = I x R 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 Example: If R = 19: U = 1 / 19 =.05 (BTU s transferred / 1 Sq.Ft. / 1ºF / 1 Hour) VA (how the secondary of a transformer is rated) = volts X amps Example: 24V x.41a = 10 VA
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) TEV (shown in equilibrium) 46.7# (Bulb Pressure) = 9.7# (Spring Pressure) + 37# (Evaporator Pressure) Where: Bulb Pressure = opening force Spring and Evaporator Pressures = closing forces RPM of motor = (60Hz x 120) / (No. of Poles) 1800 RPM Motor slippage makes it about 1750 3600 RPM Motor slippage makes it about 3450
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 Volts
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 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 NATURAL GAS COMBUSTION: Excess Air = 50% 15 ft.3 of air to burn 1 ft.3 of methane produces: 16 ft.3 of flue gases: 1 ft.3 of oxygen 12 ft.3 of nitrogen 1 ft.3 of carbon dioxide 2 ft.3 of water vapor Another 15 ft.3 of air is added at the draft hood GAS PIPING (Sizing CF/hr.) = Input BTU s Heating Value Example: 80,000 Input BTU s 1000 (Heating Value per CF of Natural Gas) = 80 CF/hr.
Example: 80,000 Input BTU s 2550 (Heating Value per CF of Propane) = 31 CF/hr. FLAMMABILITY LIMITS Propane Butane Natural Gas 2.4-9.5 1.9-8.5 4-14 COMBUSTION AIR NEEDED (PC=Perfect Combustion) (RC=Real Combustion) Propane 23.5 ft.3 (PC) 36 ft.3 (RC) Natural Gas 10 ft.3 (PC) 15 ft.3 (RC)
ULTIMATE CO2 13.7% 11.8% 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 OIL BURNER STACK TEMPERATURE (Net) = Highest Stack Temperature minus Room Temperature Example: 520 Stack Temp. 70 Room Temp. = Net Stack Temperature of 450 KELVIN TO CELSIUS: C = K 273
CELSIUS TO KELVIN: K = C + 273 ABSOLUTE TEMPERATURE MEASURED IN KELVINS SINE = side opposite COSINE = side adjacent Sin = hypotenuse Cos = hypotenuse TANGENT = side opposite / side adjacent PERIMETER OF SQUARE: P = 4s Where: P = Perimeter and s = side PERIMETER OF RECTANGLE: P = 2l + 2w P Perimeter l = length
w = width PERIMETER OF SQUARE P = a + b + c + d (P = Perimeter) a = 1st side b = 2nd side c = 3rd side d= 4 th 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 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) PYTHAGOREAN THEOREM: c2 = a2 + b2 Where: c = hypotenuse a & b = sides Capacity of Schedule 80 steel pipe in foot per length in US gallons: 1 =.0374 1-1/4 =.0666 1-1/2 =.0918 2 =.1535 2-1/2 =.22 3 =.344 4 =.5970 5 =.947 Example 2-1/2" pipe =.22 x 10 feet = 2.2 gallons capacity Infrared Thermometer Adjustment Values: Material/Emissivity Aluminum Bright/0.09
Anodized/0.55 Oxidized/0.2 to 0.3 Brass Bright/0.03 Oxidized/0.61 Chromium Polished/0.08 Copper Bright/0.05 Oxidized/0.78 Iron and Steel Polished/0.55 Oxidized/0.85 Nickel Polished/0.05 Oxidized/0.95 Zinc Bright/0.23 Oxidized/0.23 Brick Building/0.45 Paints White/0.9 Black/0.86 Oil Paints (all)/0.92
Roofing Paper /0.91 Rubber /0.94 Silica /0.42 to 0.62 Water /0.92 Weights and Specific Heats of Substances Material/Weight (Ib./ft³)/Specific Heat (Btu/lb) Gases Air (normal temp)/0.075/0.24 Metals Aluminum/166.5/0.214 Copper/552/0.094 Iron/480/0.118 Lead/710/0.030 Mercury/847/0.033 Steel/492/0.117 Zinc/446/0.096 Liquids Alcohol/49.6/0.60 Glycerin/83.6/0.576 Oil/57.5/0.400 Water/62.4/1.000
Others Concrete/147/0.19 Cork/15/0.48 Glass/164/0.199 Ice/57.5/0.504 Masonry/112/0.200 Paper/58/0.324 Rubber/59/0.48 Sand/100/0.195 Stone/138-200/0.20 Tar/75/0.35 Wood, Oak/48/0.57 Wood, Pine/38/0.47 Linear Measurement Equivalents (U.S. Conventional - SI Metric) 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 o 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/lb Btu/hr= 0.2931W