Leaving computers on 24/7 - effect?

[Mise]

In my house we obey the laws of thermodynamics

To respond to you and PrinceScamp, all the energy has to go somewhere, and it ends up as heat. For there to be an inefficiency, the energy would have to leave your house by another form - as I said, the most likely issue is sound.

Or work done in moving something from point A to point B, such as a fan.

That's power, not efficiency. And since we're discussing cost (either monetary, or cost to the environment), why does the speed matter?

Surely it matters in figuring out whether leaving a computer on all night is a "good idea" or not? If it doesn't actually help in heating your room, then what's the point in mentioning heating at all? And if it actually is wasteful enough to be good at heating your room, it's probably a good idea to turn it off if you're not using it, for heating or otherwise.

The lightbulb efficiency is how much is coverted to *light* as opposed to immediately being transmitted as heat. But it all ends up as heat eventually.

How does visible light end up as heat? Air doesn't absorb visible light at all, and our bodies reflect most of it.

An electric fan is also 100% efficient at coverting energy to heat, ultimately. The energy used by the computer's fans still ultimately ends up as heat.

How?? If I move an object from point A to point B, most of that energy is simply used up in moving the object. Hardly any of it will be released as heat (mostly from my body, but a tiny amount in friction too). Fans move air from point A to point B.

Granted, though, I may have overestimated how much energy a computer fan uses. PrinceScamp's computer has 5, so that makes 15w -- not much compared to the rest of the machine, but not insignificant either.

And my gas powered radiators radiators have no fans to "pump it around the room", but they still work (the answer is the heat moves by convection).

My radiators are freaking huge compared to a computer. The thing takes up half my bedroom wall. PrinceScamp said it earlier -- they have a large surface area so they heat the room up quicker. Either you spend energy on a fan to pump air around the room, or you spend energy heating a larger surface area. Fans bring the air to the heating element, whereas radiators bring the heating element to the air.

The reason a computer would be poor at heating a room in most cases is not because they're inefficient, but it's because they don't use that much energy compared to the kind of energy you use when heating a home. As Genocidicbunny points out, the energy used by most computers isn't that much more than a (non-energy saving) lightbulb.

For a comparison, my small electric heater uses 3000W - 10 times as much as a typical desktop computer. And even that won't heat my whole house very well. (And before you say it, no, gas wouldn't make any different - a 3000W gas heater would have exactly the same effect, the difference being that the cost of the gas would be cheaper, because there's an inefficiency in making the electricity in the first place).

By arguing that computers aren't very good heaters, you're just arguing the point that the cost difference between gas and electricity isn't so much after all. You can't have it both ways and claim that computers waste lots of energy, but also aren't very good heaters.

Yes, exactly - as I said, they're either far too wasteful to be left on when you're not using it, or it's completely useless to leave it on, in which case saving $10 is a pretty compelling reason to turn it off if you're not using it.

 

[Genocidicbunny]

Yes, exactly - as I said, they're either far too wasteful to be left on when you're not using it, or it's completely useless to leave it on, in which case saving $10 is a pretty compelling reason to turn it off if you're not using it.

I dont think anyone ever said anything about using your computer as your sole source of heat. Its more so as an addition to the heater you normally use. In that case, it's not nearly as wasteful.

Additionally, not all of us have gas. In that case, leaving your computer on just redirects where the electricity is used. Either way, the same amount would be used and you would still pay the same electrical bill.

And as said, computers and radiators, would create the same amount of heat. Those mechanical fans? That energy eventually becomes heat too. Assuming a properly insulated room, the only difference between a computer and a radiator is how long it takes them to heat up the room. The time it takes has no bearing on efficiency of electricity -> heat conversion.

Mise, have you taken Physics or Chemistry? If you have, you gotta know that energy cannot be created or destroyed.

How does visible light end up as heat? Air doesn't absorb visible light at all, and our bodies reflect most of it.

The walls of your room absorb and re-emit the light at infrared wavelengths. Infrared light is 'heat'

How?? If I move an object from point A to point B, most of that energy is simply used up in moving the object. Hardly any of it will be released as heat (mostly from my body, but a tiny amount in friction too). Fans move air from point A to point B.

Because energy cannot be destroyed. Eventually the energy put into the fan will become heat.

My radiators are freaking huge compared to a computer. The thing takes up half my bedroom wall. PrinceScamp said it earlier -- they have a large surface area so they heat the room up quicker. Either you spend energy on a fan to pump air around the room, or you spend energy heating a larger surface area. Fans bring the air to the heating element, whereas radiators bring the heating element to the air.

Again, the energy will eventually end up as heat.

 

[aimeeandbeatles]

You know, the cheapest way to get heat is to grab a blanket.

My room is the coldest in the house. I keep it cold because an overheating computer isn't pretty. So that removes any benefit of using computer to heat up my room. However the blue light on the front is so bright I don't need to turn on a lamp.

What is that wobbly air you sometimes see coming off the road on a hot day? Is that the infrared light?


I thought they created energy with nuclear?

 

[Genocidicbunny]

No, that 'wobbly air' you see is air heated by the surface of the road. On a hot day, the road can go well above 100F. The air that comes in contact with the gas becomes heated. Above it, you have cooler air. Hot and cold air refract light differently, so when the two mix, you have light from a single source going in multiple directions.

Infrared light on the other hand is not visible to the naked eye. http://en.wikipedia.org/wiki/Electromagnetic_spectrum for more information about light and its spectrum.

I thought they created energy with nuclear?

I dont quite get what you mean. If you mean nuclear reactors, then it doesnt really matter. Electricity is electricity. The source doesnt matter. It is still just a flow of electrons.

 

[Maniacal]

Hydroelectric dams provide almost all of the electricity here, though wood and natural gas are often used for heating (they are a heck of a lot cheaper too, although not as cheap as they used to be).

Anyways, my original question/position was how fast would a human body heat up the room compared to the heat generated by your computer. Not using the computer as a heater (although this discussion has been interesting).

 

[Genocidicbunny]

Well, for the sake of argument, lets use Zelig's number of 100W for the heat output of a human. Now, lets take my computer for the other half of this example. It outputs 300W of heat on idle. Already, the computer is 3 times as fast, due to producing more heat per hour, three times more specifically.

A human doesnt have too much airflow. Breathing does get a good amount of heat out, but my computer moves quite a bit more air than that. 5 intake fans and 2 exhaust results in a significant amount of airflow. Even if a human body has more surface area dissipating heat, in this case, the computer can heat a room 2-3x faster. Were they dealing with the same amount of heat put out, the human body would likely win, due to the surface area alone.

 

[Mise]

Assuming a properly insulated room, the only difference between a computer and a radiator is how long it takes them to heat up the room. The time it takes has no bearing on efficiency of electricity -> heat conversion.

Of course it does, because efficiency isn't just electricity -> heat conversion, it's useful energy out / energy in. "Useful" in this context means energy that doesn't just linger around in your computer case, or ejected into the corner of the room. It means energy used in actually getting warm air around the room. Yeah, that work done by the fan on the air will eventually become heat. But that's not why electric heaters have fans on them. I mean, in my opinion anyway, it's really disingenuous to say that the fan's work in moving air from A to B will eventually raise temps in the room, because that's really not the point! The point isn't to impart KE to the air in order to raise its temperature, the point is to move air around the room to facilitate conduction. I mean, the fact that you can say that everything is 100% efficient at converting to heat -- doesn't that tell you something's a bit... off... about the way you're looking at this?

 

[Genocidicbunny]

Of course it does, because efficiency isn't just electricity -> heat conversion, it's useful energy out / energy in. "Useful" in this context means energy that doesn't just linger around in your computer case, or ejected into the corner of the room. It means energy used in actually getting warm air around the room. Yeah, that work done by the fan on the air will eventually become heat. But that's not why electric heaters have fans on them. I mean, in my opinion anyway, it's really disingenuous to say that the fan's work in moving air from A to B will eventually raise temps in the room, because that's really not the point! The point isn't to impart KE to the air in order to raise its temperature, the point is to move air around the room to facilitate conduction. I mean, the fact that you can say that everything is 100% efficient at converting to heat -- doesn't that tell you something's a bit... off... about the way you're looking at this?

Maybe in whatever world you're in, but in this one, we obey the laws of thermodynamics and conservation of energy. Also, yes efficiency has different meanings. Whatever meaning you're thinking of, it is not the one you'd use when talking about conversion of energy. In this case, efficiency is your ratio of input to output, which is 1.

No, the fact that I can say that everything is in the end 100% efficient at converting to heat means I've taken a chemistry or physics course somewhere along the way and learned a tad bit about how energy works.

 

[GrandAdmiral]

Because energy cannot be destroyed. Eventually the energy put into the fan will become heat.
......
Again, the energy will eventually end up as heat.

But the heat conversion doesn't necessarily have to happen inside of the room. That is why airflow and emmition does mater. A device that converts energy to heat as efficiently as another might heat a room less efficiently because of the way it distributes the heat.

 

[Genocidicbunny]

But the heat conversion doesn't necessarily have to happen inside of the room. That is why airflow and emmition does mater. A device that converts energy to heat as efficiently as another might heat a room less efficiently because of the way it distributes the heat.

Correct, but Mise's question at that time was

How?? If I move an object from point A to point B, most of that energy is simply used up in moving the object. Hardly any of it will be released as heat (mostly from my body, but a tiny amount in friction too). Fans move air from point A to point B.

This topic is getting old. A computer can function as a viable addition to your heating if you use electricity as your primary heating source, since the energy conversion is as effective. If you don't mind a slightly longer wait, then its as good as having a small electric heater. If you are using gas as your primary heating source, then the computer will be less efficient. On the other hand, if your only heating source is your own body, a more powerful computer will be more effective.

 

[Mise]

I don't think I ever questioned your intelligence, education or planet of origin here, so I'm not sure why the hostility towards me... What Grand Admiral was saying was exactly what I was getting at.

A computer can function as a viable addition to your heating if you use electricity as your primary heating source, since the energy conversion is as effective.

"Since"? That's exactly what's wrong with your analysis!! That the energy used by a computer eventually ends up as heat has precious little to do with how effective it is at heating a room! As you keep on saying, every electrical device is 100% efficient at converting electricity to heat eventually -- so by your own logic, every electrical device should be a viable addition to heating. You might as well say that calling your friends on your mobile phone or listening to an iPod is a viable addition to heating. But nobody would say that. Ask yourself why.

A lightbulb is a useless heater, because the heat output by it just lingers around the ceiling -- it's not useful work out. Similar thing with a computer.

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EDIT: Maybe an example would help.... 1 sec... k done.

Imagine three types of heater. Heater A has a small heating element consuming 1kw of electricity (Ah), and a fan consuming another 1kw of electricity (Af). Heater B also has a small heating element consuming 1kw of electricity (Bh), but instead of a fan, it has a second small heating element, consuming 1kw of energy (Bh'). Heater C, instead, has two 1kw fans (Cf and Cf') and no heating element.

I think we can all agree (and if not there is absolutely no point continuing) that heater A is more effective at heating a room than heater B, because of improved airflow. That is, heater A produces more useful work than heater B. The difference between A and B is the presence of the fan; clearly, fan Af's useful work is not in heating (via imparting KE to particles), but in moving air around and facilitating conduction. Similarly, Heater C will no doubt be the worst performer of all, since, even though the 1kw will eventually end up as heat, it will not actually do a great deal to raise the temperature of the room. In this case, the only useful work done by Cf and Cf' is to impart KE to the air and raise temps eventually. In each case, you have the same components at the same rating, but doing different amounts of useful work. You're trying to claim that all three heaters will be just as effective -- but that's clearly not true.

 

[Genocidicbunny]

Okay, lets talk about efficiency of heat dissipation then. A modern computer has as much surface area as your average heater panel. It has higher airflow over those surfaces than a regular panel heater as well, due to the effect of the case and heatsink fans. For the vast majority of the heat output by a computer (CPU, GPU and PSU) there is relatively high airflow over their cooling surfaces.

Lets then take an electric heater of the same capacity. You have a large surface area spread through a larger space, which allows you more heat capacity in the air itself. This means that the heat put out by the heater gets transferred to the air faster than just the heatsinks in a computer. When you consider the increased airflow over the computer heatsinks though, the two are pretty close.

So in this case, with an equivalent electric heater, a computer with one or two case fans and a decently sized heatsink will heat a room as quickly.

You might as well say that calling your friends on your mobile phone or listening to an iPod is a viable addition to heating. But nobody would say that. Ask yourself why.

I don't have to ask myself why. I would never call either of the two viable additions, because compared to the total energy output you need to heat a room, a small electrical device such as an ipod or mobile phone has a negligible heat output. They put out maybe a couple watts of heat at most, several hundred milliwatts on average. When compared to 300W that the heater or computer puts out, they don't make up even close to a percent.

 

[Mise]

My living room used to have 3x 100w lightbulbs... You gonna argue that a computer is about as effective as a lightbulb at heating a room? Cos I'd agree....

 

[Genocidicbunny]

No, I will not. Your lightbulbs have a tiny amount of surface area. Ever look at a computer heatsink though? I'd argue mine, on the CPU and GPU is about square meter combined.

 

[Mise]

Inside the case... Case fans aren't built to move heat around the room, they're built to move heat from inside the case to outside the case. They don't care where it goes from there, so it just lingers around the case, in the same way that a lightbulb's heat lingers around the ceiling. Obviously it's better to linger around the case, where it can rise by convection to body-level (and is already fairly close to your body anyway), than the ceiling, where it is actually completely useless. But it's not much better. And it's certainly not "as effective" at heating a room as a heater of the same rating -- because that actually pushes heat around the room.

 

[Genocidicbunny]

Okay, you know what, Im done with you.

A computer can be a viable addition or in some cases replacement to regular electric heating. I've got an example of this to support my claim.

 

[Mise]

You're done with claiming that just because all energy output by electrical devices eventually result in heat, all electrical devices are "as effective" as heating with an equally rated electric heater? Good...

 

[Genocidicbunny]

Did I ever claim that? Seriously, did I? I dont think I ever said anything about all electrical devices. I spoke of computers specifically.

 

[Turner]

And now would be a good time to calm down a bit.....

 

[Mise]

Did I ever claim that? Seriously, did I? I dont think I ever said anything about all electrical devices. I spoke of computers specifically.

The reason you gave, i.e. that all energy output eventually ends up as heat, and all that stuff about obeying the laws of thermodynamics in your house, can be applied to any electrical device. If you're now saying your reasoning was wrong, then again, I'd agree with you...