Input power? ENERGY in input, and POWER is outputted.
You pay for kW-hr of electricity (ENERGY), yet the electric fire is rated in kW (POWER) A boiler uses 50,000 BTUs of ENERGY and outputs BTU/hr (POWER) The boiler may output 25,000 BTU/hr, hence making it 50% efficient.
Don't confuse energy and power.
He didn't (perhaps the confusion is elsewhere?), that's why he used the word "power" when he meant power and not "energy"! You can look at input energy or power and output energy or power.
Power is energy expended per unit time. On the input side of an electrical appliance, the power is V*I (for dc, to a first approximation for ac). On the output side it is (for a motor) how much physical work is being done per unit time. Once you have run the appliance for a while you can say what the input energy consumed was (V*I*seconds or, in your example V*I*hours/1000) and how much energy was used doing the physical work (the rest being lost in heat, noise etc).
That's exactly what you have done.
Energy is the arithmetical product of power and time.
Both are input and output from a system.
It is quite correct to relate input power and output power.
It is not correct to calculate boiler efficiency on energy in vs. power out. Introducing deprecated units such as BTUs serves only to confuse further.
The correct definition of efficiency is in terms of power out vs. power in on an instantaneous basis or of energy out vs. energy in over a period of time, perhaps under varying operating conditions.. This of course, does not account for weightings in methods like SEDBUK, but that's another story.
The important point is that the same units must be used for both the input and output aspects.
.andy
To email, substitute .nospam with .gl
No, energy is inputted, but the amount of energy inputted in a given period of time represents the power input.
Once again, confusion reigns supreme on planet IMM.
Performance
If you want to go backwards, yes.
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, 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).
So he was confused then, as he meant something different.
Excellent.
So, perhaps a 1000W diy tool rated for 3 hours continuous use should be sold as a 10.8MJ tool, whereas a 1000W industrial tool rated for 10 hours continuous use would be sold as a 36MJ tool?
That'd help (confuse).
-- Richard Sampson
email me at richard at olifant d-ot co do-t uk
You need to read my post on this.
What is actualy stored in the drill battery? Scotch Mist?
Mo more helpful or confusing than it already is.
limitations,
I see noth> > Input power? ENERGY in input, and POWER is outputted.
which implies to any normal reader that you meant if you are talking about input, you use energy, and if you are talking about output, you use power, which is nonsense and implies confusion in your head. Electrical appliances are rated in kW of input power - the opposite of what you said. The output power in total, will, of course, be the same. The proportion of the output power that does something useful (in a drill for example) is a different (lower) value.
Or higher, if it's an over-unity device. I have no doubt that IMM has several of those in his well insulated house, and probably uses one to run his electromagnetic water descaler.
See "used the word "power" when he meant power and not "energy"!"
Quite clear.
manufacturers
What the hell are you talking about?
The first mention of the word Energy was when you introduced it into the thread, and it was not at all clear what you were objecting to.
Perhaps you would oblige and post the exact paragraph or phrase that you consider to be incorrect because nobody else reading this thread can work out what you're on about.
-- Richard Sampson
email me at richard at olifant d-ot co do-t uk
limitations,
It's a completely meaningless figure to quote and only has relevance if you know the duration that a tool is used.
And if you quote energy input for a tool when it is used over a standardised measure of time, e.g. 1 hour, then you are quoting power. so we're right back to where we started.
We have an electrical power tool. The manufacturers have a legal obligation to quote the input power. This is useful because it means you know what you can plug it into (ie "do I have to unroll my cable reel or not?")
What we want to know as a (potential) user of the tool is how much it can actually convert into usable power rather than heat in the windings, from the bearing friction, etc.
So, output power would be rather useful figure to quote.
However, manufacturers are not obliged to quote output power, and only a handful of non-diy brands do this.
Even if they were obliged to quote this, it is highly unlikely that they would give it any more prominence than in small print because it will always be less than the input power, and the higher the headline figure the better.
Now, what irrelevancies are you going to introduce now, I wonder?
-- Richard Sampson
email me at richard at olifant d-ot co do-t uk
Yes I know, but he was jumbling them together in the same description and that is not correct.
The point is that the comparison must be power out vs. power in or energy out vs. energy in whether or not there is an electrical to mechanical conversion.
Energy in and power out is not a meaningful relationship.
.andy
To email, substitute .nospam with .gl
You're flannelling.........
.andy
To email, substitute .nospam with .gl
A "product" arithmetically means multiplication. This is what you learn after you can cope with addition and subtraction.
BTUs and BTU/hr are deprecated units.
Well cut and pasted, except for the deprecated units of HP, BTUs and Therms which should be abolished.
However your original statement was
"ENERGY in input, and POWER is outputted."
and that is incorrect.
.andy
To email, substitute .nospam with .gl
Energy.
However, it's use in the drill is over a period of time and so the instantaneous input to the drill motor is power and not energy as is the output.
One does not measure drills in terms of energy output but power output.
Do remember that you are conversing with people with science and engineering degrees here.....
.andy
To email, substitute .nospam with .gl
The joule in the crown?
.andy
To email, substitute .nospam with .gl
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