m Ransley said:
How do I compare Kwh costs to Ng. I pay 0.12 Kwh and 1$ per therm. Is
one therm equal to 100000 btu and 1 kwh hr equal to 450btu? Is my cost
for electricity nearly 300% that of Ng?.
A BTU is a measure of ENERGY. 1 lb of water raised 1F. No power there at
all. The POWER is energy by time hence BTU/hr for output.
You can have an electric motor turning a compressor. The compressors input
is power in.
To clarify for you:
POWER
The watt (W) is a unit of Power.
The kilowatt (kW) is simply 1,000 watts. A one-bar 1 kilowatt electric fire
or ten 100 watt light bulbs will consume one kilowatt.
BTU/hr is a unit of Power
ENERGY
Energy is Power x Time.
You pay for energy not power. What you have to pay for is the product of
power and time. This is obvious - the electric fire operating for three
hours is going to cost three times a much as for one hour. Therefore the
chargeable electricity 'unit' is the:
kilowatt-hour (kWh) Which is ENERGY.
This is by tradition in the world of electricity metering just called a
'unit'. What you are paying for is energy, rather than power.
kWh is energy
Wh is energy
BTU is energy.
BOILERS & CAR ENGINES
Although some people think of the watt (a unit of power) as an electrical
unit, it's not restricted to electricity. Boilers, whether powered by
natural gas, LPG or oil, and heat emitters (radiators) have power outputs
quoted in watts or kilowatts. So do car engines nowadays.
In days gone by in the UK, boilers etc. were rated in British thermal units
(BTU or formerly BThU) per hour (BThU/hr), which is POWER.
The BTU is a unit of ENERGY
The BTU is not power. Hence the division by time (BTU divided by hr
[BTU/hr]) to get power. People often speak of say, a "60,000 BTU boiler";
when what they really mean is 60,000 BTU/hr.
One kWh (energy) is equivalent to 3,412 BTU (energy) Note: One figure has a
time factor and one does not.
A 60,000 BTU/hr (power) boiler is rated at approx 17.6 kW (power). Note: The
time factor figures are reversed for power.
For the engine, horsepower was used, and:
One HP is 746W.
So a 75 kW engine is equivalent to near enough 100 HP.
GAS
Is charged in kWh (energy), just like electricity. There is a difference
though in that the electricity meter measures kWh directly, whereas the gas
meter records the volume of gas used in multiples of 100 cubic feet (or in
cubic metres on newer ones). The calculation to get from volume to energy
in kWh (energy) is shown on the gas bill.
The conversion factor is not constant since it involves the calorific value
of the fuel, which varies from region to region.
THERM
Again, in the past, and still in the USA, gas was charged for by yet another
energy unit, the Therm. One therm is simply 100,000 BTU (energy),
equivalent therefore to 29.31 kWh (energy).