BTU (British Thermal Unit) Calculations
1 BTU=1 DEGREE FARENHEIT INCREASE IN ONE POUND OF WATER.
8.34 POUNDS IN ONE GALLON
BTU EXAMPLE:
Incoming water 50F outgoing water 120F 120  50 = DELTA T 70F
BTU's for 1 gallon of water is 70 (delta T) * 8.34 (pounds per gallon) = 583.8 BTU's
Flow Rate 2 Gallons per Minute
2 Gallons * 60 minutes = 120 Gallons per hour
120 Gallons * 583.8 BTU's per Gallon = 70,056 BTU's per Hour
Solar Constant (measured outside the earth's atmosphere by satellite) is about 1.3 kilowatts (1,366 watts) per square meter (kW/m²)
The maximum value is about 1 Kw (1,000 watts) per sq meter, measured at the earth's exposed surface, when the sun is directly overhead.
Solar Insolation Maximum sun energy (irradiance) reaching the surface of the earth over a given time period.
kWh (kiloWatt hour) to BTU examples:
1 kWh = 3,412 btu's (per square meter when the sun is directly overhead)
90,000 btu's x 0.00029307108 = 26.37 kWh
Correct Flow Rates for Evacuated Tube Collector
0.026 to 0.066 Gallons per Minute per Tube
0.1 to 0.25 Liters per Minute per Tube
Volume Equivalents
231 CUBIC INCHES PER GALLON
7.481 GALLONS PER CUBIC FOOT
1.02 GALLONS PER 100' OF ½" PIPE
2.29 GALLONS PER 100' OF ¾" PIPE
4.08 GALLONS PER 100' OF 1" PIPE
Energy Conversions
1 kWh (kilo watt hours) = 3412.1415 BTU's
1 BTU = 0.00029307108 kWh
Btu Content of Common Energy Units
 1 barrel (42 gallons) of crude oil = 5,800,000 Btu
 1 gallon of gasoline = 124,000 Btu (based on U.S. consumption, 2008)
 1 gallon of diesel fuel = 139,000 Btu
 1 gallon of heating oil = 139,000 Btu
 1 barrel of residual fuel oil = 6,287,000 Btu
 1 cubic foot of natural gas = 1,028 Btu (based on U.S. consumption, 2008)
 1 gallon of propane = 91,000 Btu
 1 short ton of coal = 19,988,000 Btu (based on U.S. consumption, 2008)
 1 kilowatthour of electricity = 3,412 Btu
Formulas
DELTA T = TEMPERATURE DIFFERENCE BETWEEN TWO VALUES (100F90F = 10F DELTA T)
C TO F CONVERSION (C*1.8) + 32 = F
F TO C CONVERSION (F  32.0) / 1.8 = C
LBS * 0.453592 = KILOGRAMS
KILOGRAMS * 2.204623 = POUNDS
GALLONS * 3.785412 = LITERS
LITERS * 0.264272 = GALLONS
QUARTS * 0.946353 = LITERS
LITERS * 1.056688 = QUARTS
