on the back of the box for my seasonic super tornado, there is a big section about how the psu will conserve your electricity bill. in fact 2/3 of the thing is taken up by this bragging.. "improves energy utilization to cut your bill in half". there is a diagram with an arrow labelled "Apparent Power (utility bill)" at a phase offset to "AC input (working power)" and the reactive power is indicated. there is also a table which claims the PSU will give you savings of $186 and $485 off your electricity bill compared to a generic passive PFC and non PFC psu, respectively, per year. they are claiming it will pay for itself in less than a year! i am worried about this claim..
apparent power is the product of rms voltage and rms current, meaning the voltage and current are sort-of-averaged before the product is taken. apparent power is measured in Volt Amps (VA) and not Watts (props to seasonic for getting this right in their diagram), and there is a good reason for this - a watt is a measure of power (energy consumption/supply) but an electrical device can have a nonzero 'apparent power' without actually consuming any energy. e.g. capacitors and inductors, these are conservative devices. imagine driving a cap with an AC source, the circuit can't dissipitate energy so any charge just sloshes around in there and energy is conserved - you need some resistance to remove energy.
capacitance and inductance is the wattless component of a load. by saying their power supply has a power factor of 0.99, all seasonic are really saying is that the device basically appears (to the outlet) to be a big resistor.
now here's the thing, your electricity meter should measure the true power drawn by a load (by integrating the instantaneous product of voltage and current). in australia, this is required by law.
my question is, to anyone living in the US, do your electricity meters measure apparent power? it should NOT measure the apparent power, because then you are being charged for energy which you are not using. it would surprise me if this was not a requirement in your country. but then again it would also surprise me if seasonic were making an erroneous claim on the back of their box - this would clearly be misleading and false advertising, because if you have a good power meter the 0.99 PF won't save you a cent. i suppose i'm in for a surprise no matter what! (unless there is some reason i've missed, for these not to be mutually exclusive)
POWER FACTOR: about your US power bill...
Moderators: NeilBlanchard, Ralf Hutter, sthayashi, Lawrence Lee, Devonavar
My yank electric meter looks like this:
Reads KILOWATTHOURS
After a little Googling, it seems that in the USA, industrial users are often charged for low power factor, but residential customers are not. However, after just a little research I became convinced that using a PFC PSU in your PC is the right thing to do; both in terms of social responsibility and environmental responsibility. Utilities must build capacity to supply both real power and reactive power, yet reactive power does no useful work. This extra capacity to handle reactive power demands is wasteful and can cause unnecessary pollution.
Residential customers, however, will not save any money directly related to PFC PC PSU's. High efficiency will help but unless reactive power is measured and billed PFC will not.
This article, entitled Reactive Power - The Myth! is good reading for those who want to understand the issue thoroughly.
Reads KILOWATTHOURS
After a little Googling, it seems that in the USA, industrial users are often charged for low power factor, but residential customers are not. However, after just a little research I became convinced that using a PFC PSU in your PC is the right thing to do; both in terms of social responsibility and environmental responsibility. Utilities must build capacity to supply both real power and reactive power, yet reactive power does no useful work. This extra capacity to handle reactive power demands is wasteful and can cause unnecessary pollution.
Residential customers, however, will not save any money directly related to PFC PC PSU's. High efficiency will help but unless reactive power is measured and billed PFC will not.
This article, entitled Reactive Power - The Myth! is good reading for those who want to understand the issue thoroughly.