Units of measure:

Any time we deal with the subject of energy, power, pressure or heat, various definitions are required to make meaningful calculations and comparisons. This section explains the meaning of the 'SI' or metric units, and compares them to the imperial or US units.

Every attempt has been made to ensure accuracy on these figures. In all your calculations, be sure the result makes sense, and that you are not getting a result that seems out of proportion to the input numbers. In dealing with energy transfer, be sure to factor in losses due to in-efficiencies. This is very important when comparing costs from the BTU's produced from burning fossil fuels to KWh / BTU's achieved from electrical heat sources.

Definitions

Ampere

-Unit of electrical current, a quantity of electron flow equal to 6 * 1018 electrons / second. Analogous to water volume or quantity flowing in a pipe.

Volt	-Unit of potential difference or electromotive force. Analogous to water pressure in a pipe. In a house, normal wall voltage is 117 volts. Stoves and dryers use 240 volts.

Watt	-Unit of power, the product of amps times volts. The rate of work done in a set unit of time. Equal to the energy spent by one amp flowing through one ohm for one second.

Ohm	-The measure of electrical resistance equal to that resistance which dissipates energy at the rate of one watt from a current of one ampere.

Joules - kilowatts - BTU's

1 Joule 1 Joule 1 Joule 1 GJ 1 BTU 1 kW 1 kWh 1 kWh

1 watt flowing for one second 1 Newton / metre 0.000948 BTU 948,000 BTU 1054.6 Joule 3412 BTU / hr 3412 BTU 3.6 Mega Joule

Definition of a BTU
Energy required to heat one pound of water by 1 degree F.
10 BTU = 10 pounds (1 imperial gallon ) heated by 1 degree F.


Energy

1 Watt hour 1 kWh 1 Therm

3.413 BTU 3413 BTU 100000 BTU

Power and Heat flow

1 kW 1 kW 1 Ton 1 HP 1 hp

0.948 BTU/sec = 3413 BTU/hr 1.3415 HP = 738 ft lb/sec = 44,268 ft lb/min 12000 BTU/hr 0.764 kW = 2546 BTU/hr 0.7455 kW = 550 ft lb/sec = 33000 ft lb/min

Volumes and conversions.

litre cubic ft us gallon imp gallon cubic foot cubic meter

= US gal * 0.26442 = litres * 28.313 = litre * 3.785 = litre * 4.5459 = US gallons * 7.49 = 1000 litres

Length

meters feet km miles

= feet * 0.3048 = meters * 3.281 = miles * 1.609 = km * 0.621

Pressure
1 PSI = 6894.76 Newtons / sq. m = 6894.76 Pascal
Absolute Pressure = psia = Gauge pressure (psig) + 14.7


Chemical content of fuels
1 ft^3 of natural gas = 1020 BTU (chemical energy constant)
1 gallon (US) # 2 fuel oil = 140,000 BTU
1 gallon (US) propane = 91,200 BTU


Calorie (c)
Heat required to raise 1 gm. water by 1 degree C.
Kilocalorie (C) = 1000 calories. C = food calorie

0 1

E-Mail

Add Favorite

Print It

Free Sign Up - Start Making Money on Flixya »

Comments