How much of the power drawn by a chip turns into heat?

Question

If I have a circuit with a computing chip drawing 1W, how much of that gets turned into heat?

EDIT: I mean turned into heat 1. straight away (not in 1000 years) and 2. within the vicinity of the device, typically in the same room

My understanding is that obviously the vast majority of the power is dissipated as heat, but I could not find a good source with some numbers. "99.99%" or "all of it, eventually" is often given but sadly without a proper source or irrefutable argument.

Context: I am investigating a domestic heater recycling heat from computing. Some company sells a 1000W device and they claim it is equivalent to any 1000W heater in terms of heating. But intuitively one might think that to produce 1000W of heat it must consume a lot more energy than a standard heater, since it's also doing computations...

Answer 1

If it drives no loads, all of it. 100 %.

If it drives loads, then subtract out the power to the loads.

The loads themselves may turn that power directly into heat as well, or into something that will eventually turn into heat.

since it's also doing computations

If you ignore quantum theory for a moment, then, from an energy analysis stand-point, all that doing computations does is generate heat.

Answer 2

Probably the only practical devices that draw meaningfully more energy than they release as heat are LEDs, and that is only if the light escapes the surroundings.

For example, a lamp with a high efficiency diode might convert only 60% of the energy it receives to heat with 40% becoming light. But unless that light is pointed out a window it still gets absorbed in the room and warms the room.

Answer 3

I am investigating a domestic heater recycling heat from computing.

Your PC is already such a heater. There's no need to "recycle" that heat. It's already there. It comes out the exhaust fan(s) on the case.

Some company sells a 1000W device and they claim it is equivalent to any 1000W heater in terms of heating.

Links, please.

All those expensive CPUs and GPUs are doing is converting 100% of power they consume into heat, and incidentally computing something on the side. Those computations "lock in" such minuscule amounts of heat that we have no way of measuring it. There's no need to "add" any heaters.

A PC is a heater!

But intuitively one might think that to produce 1000W of heat it must consume a lot more energy than a standard heater, since it's also doing computations...

That intuition is unnatural :)

When you got a data center, every single watt of energy* pouring into the networking and computing equipment is coming out as heat via the air conditioning system. That aspect of thermal design of data centers is perhaps the most straightforward. If you can supply 1MW into the data center, you better be able to remove 1MW of heat, or else the inside will thermally run away (well, until the GPU and CPU clock governors start slowing things down to prevent a meltdown).

*In practice, there is a little bit of optical energy leaving the data center via the fiber optics. The heat lost that way is usually offset almost perfectly by the heat dumped into the data center from the power of all the light coming from fiber optic transmitters elsewhere. For any full-duplex link with fibers in good condition, the transmit powers on both ends of the link will be the same, and the optical power absorbed by the receivers is the same as well.

Answer 4

Most power consumed by computer turns into heat. All computations and other chip and electronics activities being converted to heat. You may think this is 'waste', but all useful work that PC doing is possible only by consuming electrical energy and converting it to heat.

Exception1. Internal cooling fans work that some energy transform to air flow. Even that air flows if it is circulation inside the room also apparently converts to heat.

Exception2. Screen is emitting light. This light if its inside the room also mostly converts to heat.

Exception3. Some very small part of energy is conserved to charges and stored in Hard Drives/Capacitors/Other Energy storage devices. If Power turned odd OFF over undefined long time this stored energy also will be converted to heat.

Answer 5

Converting electricity to heat is an extremely easy process. All that is necessary is to provide a path for current to flow in such a manner that (1) the amount of current will not overload the source, and (2) the device's equilibrium temperature where it dissipates as much heat as its generates is low enough that the device doesn't self-destruct.

Suppose one has three boxes, one of which contains a 15 watt heater, one of which contains a 15 watt incandescent bulb, and one of which contains a 15 watt LED bulb, and feeds 15 watts of power to each bulb. In the first box, the heater will impart 15 joules of heat energy to the surrounding air each second. In the second box, the incandescent bulb might impart 7.5 watts of heat energy to the surrounding air, release 7 watts of infrared radiation, and 0.5 watt of visible radiation (light). The 7.5 watts of released radiation would then get converted to heat when it strikes the inside of the box. In the last box, the bulb might impart 5 watts of heat to the surrounding air and release 10 watts of visible radiation (light), which would then get converted to heat when it strikes the inside of the box.

In all cases, 15 watts of electrical energy would get converted to 15 watts of heat inside the box. The lights would first convert the energy into some other form that could serve some other useful purpose before it gets converted into heat, while the heater ignore the opportunity to do something useful with the energy in addition to producing heat.

The biggest caveat with using a "1000 watt" computer as a 1000-watt heater is that purpose-designed heaters are designed on the assumption that if they are below a certain temperature, they should convert 1000 watts electrical energy to heat without regard for whether everything useful they do besides produce heat (e.g. lighting up a temperature display) could be done with less than 1,000 watts. Computers, by contrast, are designed on the assumption that if they could serve all of their useful purposes besides producing heat while consuming less than the nameplate amount of energy, they should do so.

Additionally, any device which markets itself as a "1000 watt" heater would be expected to be able to dissipate 1000 watts of heat continuously without overheating. By contrast, a "1000 watt" computer would merely guarantee that it wouldn't consume more than 1,000 watts, and not necessarily guarantee that it would be able to continuously dissipate 1,000 watts without overheating. A properly designed computer should be designed so that if it starts to overheat, it will reduce its power consumption sufficiently to prevent damage, but such power reduction would limit the computer's usefulness as a heater.

Answer 6

There is no other exit.

There is no mysterious place the heat goes. There is no quantum heatsink that depends on faster-than-light signaling to wick away CPU heat and deposit in the core of the star Vega. (There's an episode of Star Trek The Orville: the civilization that attacks the Federation for smoking them out of their homeworld by thoughtless use of quantum heatsinks lol).

It is compulsory for all the wattage your computer uses to turn into same wattage of heat. The non-heat electrical energy sent down Ethernet cables or fiber-optic is so negligible as compared to AC mains input, that calling it "rounding error" overstates it.

Unless it's PoE, in which case yeah, that is passed through.

The Cadet baseboard mining heater

Many electric heaters come in baseboard form. About 12” tall, 4” deep and multiples of 2 feet long. They are 250 watts per foot. Standardized sizes exist, so they easily swap.

So, meet the Cadet baseboard miner. Instead of very boring resistive heaters, it's a stack of heatsinks stuffed with ASICs. Costs exactly the same as the old baseboard to run, and gives the same heat, but Bitcoins show up in your account :)

It really is like that.

PC wattage simply converts to heat at 3.41 BTUs per watt-hour.

Building a PC, you know you're already obliged to deal with heat removal. Well, where you send it is where it goes... simple as that. Example: Linus Tech Tips tried a few times to water cool PCs and ship their heat to radiators outside. Because otherwise with too many PCs in a room, you need supplemental A/C.

The economics of a Cadet baseboard miner would not work, however... it would only compute on a % duty cycle during heating season, not enough to pay for the cost of the ASICs. Also, normal thermostats do a hard power cut to the unit, and that would be result in abandoned work; so you'd hardwire the heater and use the W signal from a common "gas furnace" 'stat (Honeywell, Nest) to tell it to do an orderly shutdown.

Answer 7

One company sells a 1000W device and they claim it is equivalent to any 1000W heater in terms of heating. But intuitively one might think that to produce 1000W of heat it must consume a lot more energy than a standard heater, since it's also doing computations...

The fallacy here is thinking "computing power" as if it's a form of energy, in analogues to mechanical power or energy. In this line of reasoning, a computer would be a machine that converts the "electric power" from the mains into "computing power" and "heating power", and its heating efficiency must be lower than 100%.

But it's incorrect. While information usually requires energy to process or maintain, but at the end of the day, information in itself is a mathematical abstraction, it is not a physical form of energy or power. Ignoring electromagnetic radiation, a computer is a machine that converts 100% of electric power input into 100% of the waste heat, and this is just the price you pay for information processing, an inevitable side-effect. For the same amount of computation, you pay more or less depending on your computer's model and generation.

End of the story. There is "conservation of energy and mass", but there's no "conservation of energy and information" (when I was young, I made exactly the same mistake).

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Well, there actually is to an extent. According to the idea of reversible computing, a computer generates waste heat only because the computation is not logically and physically reversible. In other words, the waste heat is produced by the information "lost" during computing (and some even argue there's a connection between thermodynamic entropy and information entropy). If one can build a logic circuit that somehow can preserve all the intermediate results, then there's a possibility to make the circuit physically reversible as well. After computation, the circuit can partially recycle the energy used. One possible implementation is adiabatic circuits, which incorporates inductors and capacitors as part of the logic circuit to reduce loss. They are compatible with the current CMOS semiconductor manufacturing process, but the energy recovery is limited.

Some science fiction stories imagine that the computer of the future can take a single "drop" of energy, reusing it repeatedly, allowing a much more powerful supercomputer. But at the current stage, it's still highly speculative.

Answer 8

A bit more than 100%. When the computer is off, its dynamic memory cells can take more states than when it is on when it just can occupy the states corresponding to 0 and 1. So when it is on, the states it can be in are reduced and the loss of entropy is given off as heat. When you switch it off again, it stops coercing states and reassumes full states.

Of course, this "state warming" at switching-off time is more than compensated for by the remaining operating heat dissipating.

Other than this paradoxic-seeming artifact of digital computing (which would not be the same for analog or quantum computers), every bit of energy put in will be given off as heat. The only exception are temporary energy storages like capacitors, rechargeable batteries, the momentum of rotating disks and similar items.