[FreeSpaceFreak]

If I switch on my laptop and it draws, let's say 100 W of power continuously, does that mean it produces 100 W of heat? Or are there also energy flows that do not eventually end up as waste heat?

' cuz if it does, you know, I could have an old pc running the seti@home or any of the other @home projects, make a contribution to science, and still have the equivalent of a 100 W heater in my room.

[Klaustrophobia]

pretty much.  a tiny bit of the energy is expended in other ways, such as moving parts (fans, drives) or lighting LEDS up, but it's close enough to assume you've got a 100 W heater.  however, it wouldn't be very economical to use it as such.  your normal heating system is WAY more efficient. 

[jr2]

In other words, a 100W heater will produce much more BTUs (actual heat output) than a 100W computer.

However, considering that most small electric heaters are something like 700-1000W on low, and 1200-1600W on high, if a 100-250W computer is producing enough heat to keep you comfortable, go for it.  (Although, consider that the 700-1600W heater will only use that many Watts whilst heating; if it has a thermostat, it will turn off once the temperature has risen to your set level... so, you'd have to figure the average electrical consumption.  Heh, have fun.  )

[FreeSpaceFreak]

pretty much.  a tiny bit of the energy is expended in other ways, such as moving parts (fans, drives) or lighting LEDS up, but it's close enough to assume you've got a 100 W heater.

Well the airflow from the fan is subject to viscous dissipation, which in the end produces heat. Same way for the screen: the emitted photons eventually are absorbed somewhere, heating up the absorbing surface. So they're still heating the room. The energy from the spinning drives needs to go somewhere as well; be it warming up of the brakes (do they have those?), drag in the bearings or something else, it probably ends up as heat.

however, it wouldn't be very economical to use it as such.  your normal heating system is WAY more efficient.

What makes a heating system efficient? Normally, you try to minimize waste heat, as that's the main source of energy loss; but I'd argue waste heat is not really a problem in a heater. So how would a normal heating system be more efficient than a computer, in converting the same amount of electrical power into warmth?

[Klaustrophobia]

What makes a heating system efficient? Normally, you try to minimize waste heat, as that's the main source of energy loss; but I'd argue waste heat is not really a problem in a heater. So how would a normal heating system be more efficient than a computer, in converting the same amount of electrical power into warmth?

if you have electric heat, it's a heat pump, which is a heat engine in reverse.  the output is the sum of the energy input plus the amount of heat it sucks from the outside, meaning a net efficiency greater than 1.  if you have gas heat, it's not more efficient thermodynamics wise, but it's typically far cheaper per BTU, and heats much more quickly.

[Sciguy]

if you have electric heat, it's a heat pump, which is a heat engine in reverse.  the output is the sum of the energy input plus the amount of heat it sucks from the outside, meaning a net efficiency greater than 1.  if you have gas heat, it's not more efficient thermodynamics wise, but it's typically far cheaper per BTU, and heats much more quickly.

It is actually impossible to get an efficiency greater than 1 (blame the universe, I am just the messenger).  Electricity is generally more efficient than gas by virtue of the fact that more of the energy actually goes into producing heat.  Gas burns, some energy is lost due to creating the light from the fire, a properly designed electric heater will not have this.  Additionally Gas heaters are dependent on the amount of gas actually being burned which may or may not be all the available gas depending on local conditions (humidity, etc.).

If I switch on my laptop and it draws, let's say 100 W of power continuously, does that mean it produces 100 W of heat? Or are there also energy flows that do not eventually end up as waste heat?

' cuz if it does, you know, I could have an old pc running the seti@home or any of the other @home projects, make a contribution to science, and still have the equivalent of a 100 W heater in my room.

There are most definitely other energy flows.  Powering all of the various systems requires energy.  The big draw is of course the processor (and GPU if you have one) but things like HDDs, fans, lights, the Motherboard itself all contribute.  I would hope that all of these parts are combined at least 50% efficient, meaning that you really only have an ~50 watt heater.

[Nuke]

The energy from the spinning drives needs to go somewhere as well; be it warming up of the brakes (do they have those?), drag in the bearings or something else, it probably ends up as heat.

they dont need breaks, they use stepper motors. stepper motors have a number of poles, and you usually cycle through them to turn the motor, if you stop cycling, the motor stops turning. this kind of motor is used where you need to accurate control the angle of the shaft its attached to. you do however have to dissipate the magnetic field energy stored in the coils when they are turned off. a charged inductor with no place for the charge to go gets rid of the energy by upping the voltage until it can arc somewhere, and this is not good for the electronics (though this kinda effect is used in boost converters to take a lower voltage and turn it into a higher one). you usually use a reverse biased diode across the terminals of the coil to allow it to discharge the energy. since diodes have a small voltage drop, waste heat is produced. this is called a flyback diode since it loops the current flow backwards until the magnetic field completely collapses.

[Klaustrophobia]

if you have electric heat, it's a heat pump, which is a heat engine in reverse.  the output is the sum of the energy input plus the amount of heat it sucks from the outside, meaning a net efficiency greater than 1.  if you have gas heat, it's not more efficient thermodynamics wise, but it's typically far cheaper per BTU, and heats much more quickly.

It is actually impossible to get an efficiency greater than 1 (blame the universe, I am just the messenger).  Electricity is generally more efficient than gas by virtue of the fact that more of the energy actually goes into producing heat.  Gas burns, some energy is lost due to creating the light from the fire, a properly designed electric heater will not have this.  Additionally Gas heaters are dependent on the amount of gas actually being burned which may or may not be all the available gas depending on local conditions (humidity, etc.).

If I switch on my laptop and it draws, let's say 100 W of power continuously, does that mean it produces 100 W of heat? Or are there also energy flows that do not eventually end up as waste heat?

' cuz if it does, you know, I could have an old pc running the seti@home or any of the other @home projects, make a contribution to science, and still have the equivalent of a 100 W heater in my room.

There are most definitely other energy flows.  Powering all of the various systems requires energy.  The big draw is of course the processor (and GPU if you have one) but things like HDDs, fans, lights, the Motherboard itself all contribute.  I would hope that all of these parts are combined at least 50% efficient, meaning that you really only have an ~50 watt heater.

where efficiency is defined as desired output/required electrical input, yes heat pumps have efficiencies greater than one.  but since people are fond of stating the second law of thermodynamics as "efficiencies >1 are not possible" the efficiency of a device is sometimes renamed the coefficient of performance. 

yes, the computer 'uses' power.  it's not sucking up 100 watts just for giggles.  but it doesn't make energy disappear.  the electrical energy must do either of two things: perform physical work, or be converted to some other form of energy and released.  nearly all of the latter will be heat, with a little light thrown in.  and as people after me said, the work that gets done eventually ends up as heat also.  i should have known i was going to get called on that and not skipped over it. 

one final note back to the OP, i don't think seti@home counts as making a contribution to science. 

[z64555]

I honestly don't think 100W power consumed = 100W power converted into heat... no, no.

There's power going into the display, power going to spin up/position the HDD.

You could run a scientific test to see what's actually going on. 

[redsniper]

It all goes to heat eventually. See: the rest of this thread.

[pecenipicek]

one final note back to the OP, i don't think seti@home counts as making a contribution to science. 

hey, at least it isnt 100% useless as bitmining is.

besides, there's always folding@home.

[z64555]

It all goes to heat eventually. See: the rest of this thread.

Yes, but not all at the same time. 

[redsniper]

It all goes to heat eventually. See: the rest of this thread.

Yes, but not all at the same time. 

Yes, but all in the same room. Except for like... light from the monitor going out a window or something.

[FreeSpaceFreak]

It all goes to heat eventually. See: the rest of this thread.

Yes, but not all at the same time. 

Yes, but all in the same room. Except for like... light from the monitor going out a window or something.

Exactly, screen photons going out the window are the only thing I could think of that will not eventually warm up the room. There shouldn't normally be any power that goes down the grounding, right?

they dont need breaks, they use stepper motors. stepper motors have a number of poles, and you usually cycle through them to turn the motor, if you stop cycling, the motor stops turning. this kind of motor is used where you need to accurate control the angle of the shaft its attached to. you do however have to dissipate the magnetic field energy stored in the coils when they are turned off. a charged inductor with no place for the charge to go gets rid of the energy by upping the voltage until it can arc somewhere, and this is not good for the electronics (though this kinda effect is used in boost converters to take a lower voltage and turn it into a higher one). you usually use a reverse biased diode across the terminals of the coil to allow it to discharge the energy. since diodes have a small voltage drop, waste heat is produced. this is called a flyback diode since it loops the current flow backwards until the magnetic field completely collapses.

Hmm, so that's how it works... Makes more sense than motor+brakes indeed, given the precision required.

one final note back to the OP, i don't think seti@home counts as making a contribution to science. 

Heh, yeah, I'd probably go with the World Community Grid or Climateprediction.net. Even though the sci-fi nerd in me is screaming, the odds of getting an actual extraterrestrial signal here by radio are pretty small.

[jr2]

Do folding@home, help people out.  SETI... heck, even if we found a signal, so what?  It won't be going anywhere unless the civilization disappears, and by the time we get it, and they get our reply... well, we could both be gone by then.  Or at least have figured out sub-space / multi-dimensional portals / hyperspace / warp theory / what-have-you (if we don't figure this out, honestly, then it's a waiting game.  You can exchange signals, but the lag makes it have rather questionable benefits.  Currently, any signals we broadcast basically just say "we are intelligent, and we are here", right?)

[IronBeer]

Currently, any signals we broadcast basically just say "we are intelligent, and we are here", right?

Not exactly....

[NGTM-1R]

Not exactly....

If you can get here, it's massively not energy-efficient to come for anything besides maybe scientific curiosity.

[Sciguy]

where efficiency is defined as desired output/required electrical input, yes heat pumps have efficiencies greater than one.  but since people are fond of stating the second law of thermodynamics as "efficiencies >1 are not possible" the efficiency of a device is sometimes renamed the coefficient of performance. 

Thermodynamic efficiency is defined as Desired output/Total Energy Input in which case efficiencies of greater than one are impossible.  I study physics so that is the first place I go to when I hear efficiency...  The Coefficient of performance is actually an energy transfer efficiency and is fundamentally a different thing.  (Although the 2nd law still holds.  More heat is extracted from the cold reservoir than makes it to your desired location it just isn't relevant to the discussion of heat pumping efficiency.)

Resistive electric heaters are not heat pumps.  Those were what I was thinking of when I made my comments.  I was not aware of other types of electric heating that operate on the principles of heat pumping, My bad.

[Bobboau]

the total entropy of the system is going up, a heat pump makes the environment outside colder and the environment inside hotter, more heat is put into the building than electricity used. when measureing heat/electricity the efficiency is >1. if this doesn't sound right you are using the wrong definition of the word efficiency.

If you can get here, it's massively not energy-efficient to come for anything besides maybe scientific curiosity.

you are assuming the aliens don't have some sort of 'purity' religion.

[NGTM-1R]

you are assuming the aliens don't have some sort of 'purity' religion.

It seems a reasonable assumption considering they have nearly free energy. Their blasting hymns into the universe would drown out ever finding us.