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Is It Worth Investing In a High-Efficiency Power Supply?
MrSeb writes "If you've gone shopping for a power supply any time over the last few years, you've probably noticed the explosive proliferation of various 80 Plus ratings. As initially conceived, an 80 Plus certification was a way for PSU manufacturers to validate that their power supply units were at least 80% efficient at 25%, 50%, 75%, and 100% of full load. In the pre-80 Plus days, PSU prices normally clustered around a given wattage output. The advent of the various 80 Plus levels has created a second variable that can have a significant impact on unit price. This leads us to three important questions: How much power can you save by moving to a higher-efficiency supply, what's the premium of doing so, and how long does it take to make back your initial investment?"
Scenario 1: an always-on computer running near-idle for four years.
Idle power draw, 85% efficient PSU: 66 watts
Idle power draw, 80% efficient PSU: 70 watts
Delta: 4 watts
Total power difference over the four-year life of the computer: 140 kilowatt-hours.
At 5.5 cents per kilowatt-hour (cheapest power in the US), building with a more-efficient power supply makes sense if it costs no more than $7.70 beyond what the less-efficient power supply does.
Scenario 2: an always-on computer running Folding@Home for four years using both CPU and GPU.
Power draw, 90% efficient PSU: 215 watts
Power draw, 80% efficient PSU: 245 watts
Delta: 30 watts
Total power difference over the four-year life of the computer: 1.05 megawatt-hours.
At 36 cents per kilowatt-hour (most expensive power in the US), building with a more-efficient power supply makes sense if it costs no more than $378 beyond what a less-efficient power supply does.
The second scenario represents someone running F@H on a modern high-end computer in Hawaii -- not exactly "unrealistic".
"They redundantly repeated themselves over and over again incessantly without end ad infinitum" -- ibid.
That was true in the past when the PSU wasn't a particularly valued component and the industry standard method of rating their power output was 'think of a number, any number. Now write that number on the side.'
It's *less* true these days if you're buying from one of the decent brands. The numbers they write on their spec sheets actually bear some kind of resemblance to reality, these days: you can actually accurately spec up your expected draw against the capabilities of a PSU and expect it to more or less work out. It's worth leaving a bit of safety room, but you don't really need 2X.
While GP is woefully incorrect and you're right to call him out on it, your explanation isn't right either. Heat pumps can in fact pump against a gradient, and are mostly used to pump heat from a cold to a hot place. Air-source heat pumps (ie. coupled to the outside air rather than a geothermal reservoir) are used in parts of the US to heat houses in the winter and cool them in the summer. They're also what makes a refrigerator work. A fridge pulls heat from a cold place (inside the fridge) to a warmer place (outside the fridge). The resulting decrease in entropy needs to be balanced by an equal of greater increase in entropy, which is accomplished by converting electricity to heat. Or, to avoid the thermodynamic jargon, you're pumping against a gradient, so you need to spend energy to do so. The heat produced at the back of your fridge is the sum of the heat that was pulled out of the interior of the fridge + the heat-equivalent of the electricity the fridge consumed. This is also what an A/C does. Now, if we turn the A/C inside-out, so that it pumps heat from outside to inside, then you have the kind of heat pump we use to heat our homes in the winter. The sum of the heat that was pulled from outside and the heat-equivalent of the electricity the device consumes is larger than the heat-equivalent of the electricity alone, thus the pump brings more heat into your home than a resistor using the same amount of electricity. GP suggested to generate electricity from this heat gradient, but the flaw in his thinking is that the heat pump as well as any electricity generation device he can come up with are bound by the Carnot efficiency, so you can never get more electricity out than you put in.
You're thinking of hardwaresecrets.com - they do the type of PS reviews only an EE truly appreciates! :)