Increase in power bill with 7870 CFX?

[BigChickenJim]

Dumb question here. Don't laugh.

I recently popped a second Gigabyte HD 7870 2GB into my rig for Crossfire. I have never used a multi-GPU configuration before. I knew that the extra card would result in more power draw and higher heat, but my PSU (CX 750) is more than capable of handling it and my case cooling (all air) is superb if I do say so myself.

Then a buddy of mine burst my bubble and told me that my power bill could go up by as much as $20 a month. That seems awfully steep and I'm inclined to blow him off, but I thought I'd run it by the experts here first.

Is a $20 increase really possible just by adding a second GPU?

For reference, I play around 2 hours a day in graphically demanding games (BF3, Total War, etc.). The computer is shut down when I'm not using it.

Thanks in advance for the help.

 

[TheUnk]

2 hours a day? No. That buddy is wrong.

 

[Silenus]

Um....No. Unless you were mining 24/7.

But lets do some quick math. Let say for those 2 hours a day you are really slamming the card. Now, even 250 watts is unrealistically high for the power it would use....but let's just say it is an extra 250 watts. That's .25 kWh x 2 hours a day = .5 kWh per day.

What are your electricity rates? Let's say they are $0.15 per KWH. That is $0.075 per day, or $2.25 for a 30 day month. So....no worries.

 

[ViRGE]

You'd have to tell us how much you're paying per KWh. But given the fact that the TDP on the 7870 is ~ 200W, even if it runs at full tilt for those two hours, you're only looking at (.2 * 30 * 2 =) 12KWh of additional power consumption for that 7870. Around here that would be less than $2 of electricity.

 

[BigChickenJim]

Ah. I guess my friend is, as I suspected, a moron. Of course, I'm not much better for *almost* believing him.

Truth be told I don't know my electricity rates due almost entirely to apathy. I just swallow the bills like a big, dumb pelican. Oh well. I'd happily pay $20 a month for my beloved hobby, but I'm glad I won't have to.

Thanks for the help, gents!

 

[Lonyo]

My housemate complained about my computers because our power bill went up compared to the same time last year.
Then he looked at the bill and saw we were using less electricity, they just jacked up the rates.
Always a good idea to check the bill, although where we are there is only one provider and no real tariff choices. Not paying attention to bills is a bad idea

 

[BigChickenJim]

My housemate complained about my computers because our power bill went up compared to the same time last year.
Then he looked at the bill and saw we were using less electricity, they just jacked up the rates.
Always a good idea to check the bill, although where we are there is only one provider and no real tariff choices. Not paying attention to bills is a bad idea

Welcome to the life of the over-worked but well-paid. Too busy to care, not quite broke enough to adapt. You're right, I should definitely pay more attention to the bill. But I won't.

Modern western citizens live under energy monopolies in nearly every geographic area. It's wrong and completely contrary to most free-market principles, but that's a discussion for another place. In reality, the choices available to you should you find your bill to be too high are generally turn the lights off, cut the power, or swallow the bill. The first two options aren't acceptable, so I open wide...

 

[iiiankiii]

Based on power consumption of a 7870 (150w or so), at 2 hours a day for 30 days, you will consume around 9kwh of additional power. At $0.15 kwh, that's roughly $1.35 more a month. lol Not anywhere near $20 a month.

 

[imaheadcase]

My fridge uses more power and I only have leftover pizza in it.

 

[TheUnk]

My fridge uses more power and I only have leftover pizza in it.

You say that as if a full fridge would use more power, when in fact it will use less.

 

[Larnz]

You say that as if a full fridge would use more power, when in fact it will use less.

I'll bite, how would a full fridge use less power? I would assume it effectivly would be the same? I am genuinely curious now .

 

[Stuka87]

A full fridge is less efficient, as there is more mass inside that requires cooling. Cooling empty air requires less energy than trying to cool a mass of objects that absorb the cool air around them.

 

[KingFatty]

Stuka87 I think you would be correct only during the very initial cooling of the warm fridge and warm contents. So yes, if you have a room temperature fridge full of room temperature food, it will take more energy to get all of that down to cooled temps, compared to a room temp fridge full of warm temp air.

But in practicality, a fridge is not cooling from initial warm conditions. Instead, the fridge is trying to maintain the contents at a cool temp. That's why a full fridge uses less power, because there is less air inside. The air is what gets swirled around and exchanged when you open the door.

In an empty fridge after cooling the air inside, a lot of the cool air would escape when you open the door (ever feel the cool wafting air on your feet?) and warm air would rush in. Then the fridge has to turn on and cool all that new warm air.

But in a full fridge, there is practically very little air to escape. so all the cool food/water/milk keeps that coolness inside the fridge, and very little cool air escapes and very little warm air comes inside. You close the door and the fridge just has to run a little bit.

Imagine a fridge full of milk jugs so no air can fit. You open the door, and the milk jugs barely even change temp. You close the door, and the fridge looks at the temp inside and doesn't even turn on because the milk stayed nice and cold. You'd have to leave the door open for a long time to warm up that milk. But, imagine if you filled the fridge with warm jugs of water. It would take forever for the fridge to cool them all down initially. But I don't buy warm jugs of water for my fridge, so that would never happen.

 

[blastingcap]

Welcome to the life of the over-worked but well-paid. Too busy to care, not quite broke enough to adapt. You're right, I should definitely pay more attention to the bill. But I won't.

Modern western citizens live under energy monopolies in nearly every geographic area. It's wrong and completely contrary to most free-market principles, but that's a discussion for another place. In reality, the choices available to you should you find your bill to be too high are generally turn the lights off, cut the power, or swallow the bill. The first two options aren't acceptable, so I open wide...

People have this religious fervor when they talk about the free market, but perfectly free markets do not exist. Two words: natural monopoly. Too expensive to have tons of wires running to your house from 1003125 companies. Don't like it? Get solar panels. http://en.wikipedia.org/wiki/Natural_monopoly

A full fridge is less efficient, as there is more mass inside that requires cooling. Cooling empty air requires less energy than trying to cool a mass of objects that absorb the cool air around them.

Wrong. KingF already explained this but let me put it this way, if your freezer were 100% full of ice and no room for ANY air, if you open the freezer door and then close it, almost nothing changed and you would use almost no power. But if it were an empty freezer, the cold air would gush out and warm air would rush in as you closed the door. Your freezer would have to work to cool down the resulting not-so-cold air.

 

[BigChickenJim]

Blastingcap, I wouldn't classify my comment as an exhibition of "religious fervor." Yours, on the other hand...

I'm an educated man and I am familiar with the idea of natural monopoly. I'm also familiar with the concept of using the correct forums for political debate. I'd happily talk economic philosophy in another context, but this isn't the place.

 

[Arkaign]

Great point BlastingCap, without derailing this too much, have you seen 'The Smartest Guys in the Room'? It's a really interesting expose not just of Enron, but of energy as a whole.

Go for it OP!!

 

[Ben90]

Stuka87 I think you would be correct only during the very initial cooling of the warm fridge and warm contents. So yes, if you have a room temperature fridge full of room temperature food, it will take more energy to get all of that down to cooled temps, compared to a room temp fridge full of warm temp air.

But in practicality, a fridge is not cooling from initial warm conditions. Instead, the fridge is trying to maintain the contents at a cool temp. That's why a full fridge uses less power, because there is less air inside. The air is what gets swirled around and exchanged when you open the door.

In an empty fridge after cooling the air inside, a lot of the cool air would escape when you open the door (ever feel the cool wafting air on your feet?) and warm air would rush in. Then the fridge has to turn on and cool all that new warm air.

But in a full fridge, there is practically very little air to escape. so all the cool food/water/milk keeps that coolness inside the fridge, and very little cool air escapes and very little warm air comes inside. You close the door and the fridge just has to run a little bit.

Imagine a fridge full of milk jugs so no air can fit. You open the door, and the milk jugs barely even change temp. You close the door, and the fridge looks at the temp inside and doesn't even turn on because the milk stayed nice and cold. You'd have to leave the door open for a long time to warm up that milk. But, imagine if you filled the fridge with warm jugs of water. It would take forever for the fridge to cool them all down initially. But I don't buy warm jugs of water for my fridge, so that would never happen.

Theoretically, a full refrigerator will use less electricity than an empty one even though the amount of heat that radiates in is the same in both scenarios.

An empty refrigerator goes through heat/cold cycles faster which means the compressor needs to run shorter cycles more often. A full will need to do longer cycles less often. Since there is some overhead getting the evaporator to operating temperature, the longer cycles wins out in efficiency.

Realistically though, I wasted more electricity typing that then the difference between the two scenarios running for the rest of my life.

 

[spat55]

You say that as if a full fridge would use more power, when in fact it will use less.

Full fridge is better as it has more in it to insulate it, if you have a empty fridge all it has is cool air which has to be constantly cooled. Don't have much evidence but I have always thought this, so you might want to get some newspapers in there.

 

[Eureka]

Today I learned about refridgerator physics.


Also for the OP, I wouldn't worry about computer power in the least. Even running it all day, 24/7, 100% load, you should barely breach $30/month in power.

 

[Chiropteran]

This thread is great, I hope everyone keeps it in mind. As shown, even a 200W difference from a video card equates to about $2/month.

Now think about all those silly comments about bulldozer's power consumption. Even the most demanding modern games don't load more than 3 cores. Thus, while bulldozer may peak at 90W higher than Intel, when gaming and only using 3-4 cores at most the actual power usage difference is closer to 40-50W. Given the calculations above, that is about $.50 per month, or $6 per year.

 

[BallaTheFeared]

This thread is great

Yes it is, I had no idea when I clicked on it I'd be treated to such an entertaining discussion on the (in)efficiency of refrigerator cooling.

 

[KingFatty]

It's just weird that fridge is spelled with a letter "d" but refrigerator is not?

Another issue to consider on power savings of crossfire, is doesn't the AMD driver shut down the 2nd card when you are not gaming? So in windows or other uses, the power consumption would be unchanged from one card?

 

[B-Riz]

It's just weird that fridge is spelled with a letter "d" but refrigerator is not?

Another issue to consider on power savings of crossfire, is doesn't the AMD driver shut down the 2nd card when you are not gaming? So in windows or other uses, the power consumption would be unchanged from one card?

Blame Frigidaire for it all.

http://en.wikipedia.org/wiki/Frigidaire

 

[bryanW1995]

I am now smarter for having read this Anandtech thread.

Thank you, gents. It's been too long since I've been here...