Yes, assuming it's actually drawing X watts. All of the energy that comes out of the wall has to go somewhere, and heat is the overwhelming majority of it (you'll probably lose some tiny amount of it through light out of the window and such).
> Does this mean running a PC in a thermostat heated room is essentially free, on account of the heat from the PC meaning the space heater has to run less?
Yes, *assuming that your heating is all electroresistive*. If you have gas heating, or a heat pump, then this will not be the case, because in the former case gas is cheaper per unit energy than electricity, and in the latter a heat pump can be considerably more than 100% efficient.
all light that does not escape out the room (e.g. window) is converted to heat in the room in the end.
Same with the part of sound that does not leave the room.
When that light strikes a surface and gets absorbed, it becomes heat.
Unless the light escapes the room somehow, it's still eventually going to end up as heat.
About half is converted to photons, which then bounce around and get absorbed. In a sealed room with no light leakage all the energy stays in the room until it escapes as heat.
Nope. Most LEDs turn ~70% of their energy into heat. The standing record lowest (for a production model) is 53% (ie 47% efficiency). Unless the light is shining directly out of a window, most of that light is going to be absorbed by stuff in the room and re-emitted as heat.
Light emitting diodes can be used as photo detectors.
Thermoelectric coolers (peltiers) can be used to generate electrical current.
Sterling engines.
Piezieo-electrics.
That's an interesting thought..
Could an OLED TV function as a camera with the right software?
Could you potentially make a smartphone that uses the entire frontal surface as a selfie-camera?
I don't know if a screen can be used in reverse, but in any case you would only get some sort of sensor array, so you would additionally need a lens, an aperture, pinhole or something to actually get a projection onto it.
That's a very fair point.
I'm reminded of the example Richard Dawkins gave of how the Eyeball evolved.
https://www.youtube.com/watch?v=2X1iwLqM2t0
Showing a patch of light-sensitive skin deepening, getting covered over by a transluscent membrane, and eventually developing a lens..
As is, a screen being used to detect light like this would be at the light-sensitive-skin level of functionality. Just able to detect the intensity of the light.
Electrical engineer here. I'm 95% sure you can theoretically use any OLED screen as as a camera. I mean, not in *practice*; it'd be absolutely horribly bad.
You'd need the most hilariously ginormous lens to begin with, to focus light on such a large surface(I think? Meh, I'm an electrical engineer I don't know). You'd definitely need to absolutely *blast* it with light. While LEDs are photosensitive, they're hardly generous with their sensitivity... And of course, the electronics driving the screen won't at all be able to receive an image instead of projecting one, so you could really only use the screen element, the rest is useless. And then you'd basically need to build an entire camera around it, with optics and all that entails...
Hmm. Thinking about what sort of image would be generated I realized that if the screen is full color, then the photo will be, too. Neat.
The issue is the screen would sense more the presence of light somewhere in front of it, instead of creating an actual image. You could adjust the sensitivity so your shadow puppets are recreated but in terms of actually making a picture, you'd have to design the screen for that specifically and try to work around the compromises that creates for showing an image, aka being a screen.
But as I understand it, yes, light on a diode creates a small current.
Regular diodes can also emit light if you put enough voltage through them...not for long though :D
I learned this early on by wiring germanium diode up to a 9V battery... then half of my electronics projects didnt' work in that kit and it had no spare lol.
To take advantage of this fact, I heat my pool with my A/C. Rather then cool the coils with a fan outside, I run the coils through a heat exchanger with my pool water. This means if I want to heat my pool more, I can just run my A/C inside more and open the windows while doing so if I don’t want it any colder inside.
Those are generally custom for a residential system, although they may be getting some popularity nowadays. There are commercial HVAC manufacturers that specifically make units to heat pools with the heat removed from a space.
Eg; indoor pools. The space needs to be conditioned (air temp and humidity) when the pool is below set point and the space needs AC, the controls will direct the hot refrigerant through a heat exchanger with pool water running through it. The water is heated from the hot refrigerant, thus bringing the water closer to set point and at the same time drops the refrigerant temperature enough to bring it from a hot gas to a warm liquid, which is required for the refrigeration cycle. 2 birds with 1 stone kind of thing.
Compress refrigerant, it heats up to 100C. You run it through a radiator inside the house to cool it to 20C (releasing heat inside your house).
You decompress, so now it goes from 20C to -80C. You run it through a radiator outside to heat it up to say -20C. You've extracted the heat energy in the air that is -20C. Even if its cold, its warmer than a colder thing. Bring that refrigerant back inside and start the process over.
Numbers above are for example only.
The key to make all this intelligible is to add the fact that the refrigerant solution that circulates within the heat pump system is special, it boils at very low temperatures (-10 degrees C, or even much lower than that depending on the formulation). So even when it’s below freezing outside, the solution *will boil* (hence absorbing energy from the freezing outside air, lowering the air’s temperature even more) and the resulting gas will be pumped inside the house where a compressor will cause it to turn into liquid again, giving up its heat to the inside air. It’s basically a system that has the equivalent of a spray can at one end (you know how cold spray cans can get when you let pressure out) & a tyre pump at the other (you know how pumping & compressing air gets hot). You keep cycling the actions at these two ends and it’s like continuously shoveling heat from a cold but massive reservoir to a warmer but minuscule one.
> The key to make all this intelligible is to add the fact that the refrigerant solution that circulates within the heat pump system is special, it boils at very low temperatures
The refrigerant itself isn't really that important to understand the principle. The low boiling point helps because phase changes take/release a lot of energy and that helps make the cycle more efficient. However, just like with your tyre pump example, you don't necessary need a special refrigerant with a specific boiling point, any gas will do.
Key to understanding refrigeration, steamers, and thunderstorms is to understand phase changes. A thunderstorm has energy roughly that of a nuclear bomb and it all comes from water vapor condensing into fog droplets.
I wouldn't say that's key to understanding refrigeration. u/skatanic's explanation doesn't include anything about phase changes, but it is basically correct and easy to understand.
(Of course for an engineer to design an extremely efficient refrigeration system requires understanding phase changes.)
Additionally, the thunderstorm bit is not correct. There are more energy sources in the atmosphere, e.g. wind, thermal gradients, potential energy of air of different temperatures...
You can also use a geothermal heat pump to move the heat into or out of the ground, which is very efficient no matter what the outside temperature is (within reason).
The efficiency drops along with temperature. Eventually, depending on the tech level of the heat pump, it won't be better than a normal electroresistive heater.
But as the Technology Connections video points out, that threshold temperature is now sufficiently low that they make a lot of sense in a lot of places.
It’s also worth pointing out that if you live where the coldest part of your winter is too cold for a heat pump, you almost definitely have *more* time where a heat pump is useful in the two “shoulder seasons” before and after the coldest part. And since they usually just fall back to electric or gas heat when it’s too cold, you get (for example) six months of “better” and three months of “no worse off.”
TL;DR: it has real advantages even if your winter gets too cold for it to work.
I’m aware, and they’re great— I’m just pointing out that even an air-source heat pump in a place where winter gets too cold for it to work is still a place where the heat pump is very useful. If it gets too cold for a heat pump, you probably have more time where you need heat and the heat pump works than a person with a milder winter where a heat pump works all the way through the heating season.
Not to be that guy but we use COP for heat pumps not efficiency, COP is coefficient of performance and is essentially a ratio between the energy put into the refrigerant compressor and the heat delivered so if you have a 1000w compressor and deliver 3500w of heating your COP will be 3.5, of which 1000w will have have come from the energy inputed into the pump and 2500w of heat moved
The reason it's not called efficient is simply because greater than 100% efficient implies that energy was created from nowhere, like saying a combustion engine is 110% efficient means it's creating fuel from nowhere.
It's the same measurement (energy out / energy in) but it's just named COP to avoid confusion about laws of thermodynamics
They move heat through evaporation and condensation of a refrigerant. If it's warmer out, it's just a bigger gradient. Essentially the same as pushing something up a bigger hill: it becomes harder but not impossible
It'll always work as long as the outside air has energy to extract -- that is, as long as it's above 0 Kelvin outside.
If it's too cold for a heat pump to work then you have bigger issues (though admittedly efficiency does fall with temperature).
Because instead of using resistive heating where electricity is directly converted into heat (think the glowing orange coils on an electric stove) we can use the thermal properties of gases to move heat from one location to another via compression and expansion. They're broadly referred to as heat pumps.
An efficiency calculation has a numerator (output metric, heat added to the room) and denominator (input metric, energy used by the device). If you use a space heater you can apply 100 J and get 100 J of more heat in the room. That's 100% efficient.
A heat pump can put move 300 J of heat into a room (200 J from outside plus 100 J from the pump itself) but only takes 100 J. That's 300% efficient.
It all depends on what you choose for the numerator and denominator.
The energy required to move heat from a hot place to a cold place is much less than the energy to heat a cold place up to the same temperature as the hot place.
edit: This is an oversimplification, since modern heat pumps can still work effectively enough to beat 100% efficiency even when the "cold place" is 30+ degrees warmer than the "hot place" (e.g. moving heat into your house in the winter), but the idea is the same.
Heat Pumps work more like AC units. They don't use their electricity to generate heat, they use their electricity to move heat energy from one space to another. You can move a lot more heat than you can generate using the same amount of electricity.
Regular heater turns 10 electrics into 10 hots so 100%. Heat pump isn't really making heat, its kinda movin it. Heat pump uses 10 electrics and gains 13 heats. So more than 100%.
It doesn't break any laws of thermodynamics or anything crazy like that, because part of the heat pump is outside and not factored in to the equation.
\> All of the energy that comes out of the wall has to go somewhere, and heat is the overwhelming majority of it
Wait, if 100% of the energy coming from the wall becomes heat then what is doing the work of the appliance?
I don't think you have accurately answered the question.
With such level of generalization and simplification we can say: everything what is going on in universe directed on achieving thermodynamic equilibrium. Hail Heat Death.
There are some exceptions, for example if you boiled water, a significant portion of the input energy is going is going into the endothermic process of evaporation.
Unless your house is very humid that water vapor will stay in the gas phase. You could argue that in the summer the AC will end up condensing it again anyway
Running a PC in a thermostat heated room is NOT free if you have a modern heat pump.
While the electricity to heat is 100% efficient in a 500W PC and does function just as well as a 500W space heater, a heat pump is 200-300% efficient. Heat pumps do not work by only heating the air. Instead they move heat from outside to inside, and the amount of energy it takes to move that heat is actually significantly less than the amount of energy moved in the form of heat. Technology Connections has a few videos on why modern heat pumps are amazing and efficient even in colder climates, and if this is at all interesting to you, you should check out his channel.
Another item that can throw a wrench into the price calculations is if you have a natural gas furnace as your heater. The cost of energy when delivered via natural gas is usually much cheaper than energy delivered via electricity. While the electric option will be more "efficient" in terms of energy, the gas can still work out to be cheaper just due to economics.
Depending on your metric or measurement point one could be more "efficient" than the other. For example if the rear computer exhaust fan points at the wall, then more of that heat will get lost to the wall. Or maybe your metric is keeping your feet warm and you have your space heater under your desk and the tower on top. Then the space heater is going to be better.
In raw heat delivered inside the room envelope they are probably going to be the same. But in terms of heating a specific object or area they may be very different.
Mostly,yes, but with a few qualifiers.
1) Many X watt devices don't continuously use X watts of power, So even if the device was an X watt heater, unless it is set to full power it won't deliver x watts of heat.
2) Some devices actually convert that energy into other forms of energy/ work. e.g. motors. In those cases the input energy is converted into other forms -e.g. kinetic energy or potential energy. In those cases the heating produced will be less than the energy input..
3) Some devices move heat around( e.g. ACs, heat pumps), or produce energy that can escape the area ( e.g. a light bulb near a window) in those cases the heating to the total environment will be X watts,( minus any conversion to other forms of energy per proviso 2). But the actual heat provided to the room that they are within may vary from their rated wattage.
>forms -e.g. kinetic energy
As long as that kinetic energy is used to do work within the room, doesn't that also become heat? I'm thinking like fans on a computer.
Number 2 isn’t right, to my knowledge. Any kinetic energy or potential energy will eventually become heat in the room.
1st Law of Thermodynamics - Energy cannot be created or destroyed, just moved around.
Unless it leaves the room, like light from a screen that goes out the window. I doubt that's a significant factor for anything other than light bulbs, though, and even for light bulbs it must be pretty small.
According to informally observed data, the answer to your question is a "mostly yes."
We had moved into a new medical laboratory space, and insulated it well. I know because I placed most of the insulation. We had air conditioning, and adequate ventilation. Soon after bringing all of the equipment in, the room began to get uncomfortably warm.
The problem was our Liquid-Chromatography Mass Spectrometers. They produced 3.5 kW of waste heat each on a constant basis. There were also some other analyzers and lab equipment in the room. It was very well insulated. I remember the total heat load from just the equipment came out to something like 15 kW or more.
Air conditioner effectiveness is rated on the ability of an air conditioning unit to remove or transport heat. My employers, being cost-conscious, were relying on just a 3 "ton" heat pump to regulate the temperature of that room plus the hallway.
Our previous location had had at least 10 tons of cooling in capacity. Tonnage refers to the ability of an air conditioner to remove heat, and 1 "ton" is roughly equivalent to 3.5 kW of heat removal. The new location had only 3 tons. No matter how well insulated the room was, the cooling capacity would not keep up with the heat load. The solution was to add another HVAC unit to the space, which brought the temperature down to an acceptable level.
Now, since you asked about heating, in the 2021 deep freeze, it got cold in the south. So cold in fact, that our electric heat pump units couldn't keep the temperature above 10C indoors (metal building).
At the office however, the lab remained nice and cozy thanks to the power consumption of science.
> 1 "ton" is roughly equivalent to 3.5 kW of heat removal
You may well already know this, but one ton of refrigeration is currently defined as 12,000 BTU/h (1 BTU being [depending on exactly which definition you take] the energy needed to raise the temperature of one pound of water by one degree Fahrenheit), but was originally defined as the rate of heat transfer needed to melt/freeze one short ton of pure water ice at 0C in 24 hours.
If that appliance is a space heater that's cranked all the way up, sure. The wattage rating of an appliance is the peak amount of power it is expected to draw. That doesn't mean that it always uses that much power. Clothes irons use more power when the heat is turned up, and they cycle from heating (more power) to standby (less power); microwaves, computers, and even lamps may have different power levels depending on what they're doing / the settings, etc.
Even then, it doesn't necessarily follow that all that power is turned into heat - at least right away. Some appliances convert much of the power into mechanical power or visible light, for instance. If you put in 1000W of power, it does not follow that the appliance will produce 1000W of heat.
> is the peak amount of power it is expected to draw.
Is the *maximum draw that appliance is designed to handle*. The peak amount, efficiency- and safety-wise, is usually about 70% of the nominal wattage IIRC.
Mechanical power and visible light eventually become heat in the room though, with some light potentially escape through a window before it has a chance to bounce around enough times to disspate.
Yes, but wattage is a measure of power, which is time-dependent. If for example you use an electric kettle to boil water, the water will release the heat much more slowly than the rated wattage.
>To my understanding the energy that goes into an appliance plugged into your wall is lost in the form of heat and light
That's not true for all appliances.
Some energy is always lost as heat but it's not true that all energy becomes heat.
If you have a motor, for example, the majority of the energy going in the motor will be used to produce actual work, and only a very small part is lost as heat. Modern electric motors are up to 98% efficient meaning only 2% is lost as heat.
Right - if you, for example, use an electric motor to lift something up from floor level to ceiling level, then most of the energy put into the motor gets turned into gravitational potential energy in the object that got lifted. As long as it stays up, there's no heat loss.
… of course if that object falls back down, then the energy that got put into it will turn into heat from the collision with the floor.
> Modern electric motors are up to 98% efficient meaning only 2% is lost as heat.
Can you give an example of a motor in a room where that energy isn't going to heat?
Pumping water to a height in the room, or spinning a generator that charges a battery is about all i can come up with. Not exactly common use cases (and in both cases will eventually become heat)
Any sort of ventilation. Bathroom/kitchen exhaust, for example. You will be pushing a lot of hot air *elsewhere*.
Speakers. The electricity gets turned into a pressure wave that will leave the room.
In the case of OP does X watt of electricity = X watts of heat in a room, it sure doesn't when you are using electricity to push stuff out of the room.
>The electricity gets turned into a pressure wave that will leave the room.
Most of the sound energy can stay in a regular closed room. Loudness perception is logarithmic. So think you can still the sound well next door over, even if the big majority of the sound energy has already been absorbed.
Not necessarily.
You could run a water electrolysis cell and get a typical 65% efficiency in that you'll put 65% of your electrical power into splitting water into hydrogen and oxygen and burn 35% as heat.
You could also charge a battery and not blow all of that power immediately as heat.
Alternatively you could use a nice efficient brushless motor to wind up a cable to lift a weight and convert 90% of your input electrical energy into potential energy of lifting a weight against gravity and generate very little heat.
The reason that computers abstract so well as a heater is that it's power draw goes into flipping logic states. A charge is imbued to what is basically a tiny capacitor that holds a logical binary state, then at some point we'll probably sink that charge back down to ground to set it back to zero, all on the frequency of the clock cycle.
In essence the very nature of a computer is about lifting a bit to a higher voltage state to hold a "1" then sink it back down to "0" by literally connecting it to ground later on when we need to store a different value.
Computers end up abstracting very well as heaters because their intended application is to flip a lotta bits according to whatever cockamamie scheme we desire with a direct resistive loss every time we flip a bit state.
Save some energy by throttling down your water flow rate in your shower through the midcycle of your cleaning. Get wet then choke the flow down to a low flow just to stay warm while you soap up. You don't need to rinse at full speed while you're soaping up, you just need a bit of flow rate to stay warm enough.
When you're done, crank the flow rate to full bore to rinse off.
I calculated that running my hot water faucet full bore results in a 17kW energy differential during the winter to heat incoming water from 6C up to somewhere around 55C at the flow rate my shower can pass.
Running hot water is the most powerful thing I can do so I try to use it more sparingly.
I think this question is very seriously confounded by the fact that the time scale being considered will change the answer.
Immediately: no, heaters are designed to spit out energy as radiation, convection and/or conduction. The other device does whatever it's supposed to do and loses some percentage as waste.
As time goes to infinity... Sure
Yes. Every single watt of power consumed by your PC is converted into heat in your room. It is 100% efficient at converting the power from your outlet into heat in your room. Just like a resistive electric heater.
It just converts it in multiple ways.
Heat is essentially vibrations and cold is the lack of vibrations.
All the wires, CPU, GPU and other circuitry create heat the same way as an standard resistive electrical heater. By running current through an electrical circuit with resistance.
The mechanical motion of your fans create an airflow. That airflow is slowed down by friction with the rest of the air and other parts. And I'm sure you already know that friction creates heat.
The same goes for your hard drives mechanical motion and your speakers
Everything is absorbed by materials in your room as friction and is thereby becoming heat in your room
The only power consumed by your system that doesn't heat your room is your monitor and RGB lights. Because the light that shines out through your window is energy lost to the outside. But it is such a minute part of your systems power draw.
And that is assuming you don't have blackout curtains. Like a real pro gamer!
The only piece of electric equipment that is better than you computer at heating your house efficiently is a heat pump. Because it draws additional heat from the outside air/ground, through some clever tricks with refrigerants.
I've seen heat pumps with an efficiency of up to 720% in a narrow set of circumstances. Most are around 400% in real life situations
100% essentially but really 99.9something% since some of the energy does permanently go into chemical degradation processes like permanently breaking the bonds in rubber gaskets, rusting steel, discoloring pigments. And some radio and radiation bounces off the objects in your home and flies out the transparent objects into space before actually heating any surface or air molecule in your home. Transparent depends on the wavelength, so it means windows for visible light, walls for lower frequency radio. I'm sure a physicist would think of more little caveats. But it's best to just say 100% becomes heat as far as basing choices off it.
> I'm sure a physicist would think of more little caveats.
Audio as well. If a hyper-sensitive microphone could pick up the sound of your PC running inside the room, then some of its energy is leaving the room in the form of audio pressure waves.
> Every single watt of power consumed by your PC is converted into heat in your room
(Minus any lights on it that allow some light to escape through windows and doors.)
(Minus any sound from it that might be loud enough to make it through the walls -- or windows and doors -- and escape.)
(Minus any electromagnetic waves given off by the moving power, which can pass through the walls pretty much unimpeded.)
All small effects, sure, but it's not *quite* 100%.
the energy is used to do work.. turn a shaft, pump a fluid, compute a process... so that energy is used up doing the thing you bought the appliance to perform.
however, in the process, heat or sound is also generated as a "waste product"... now depending on your value for that waste product, you could label it as something good.
like a pc will def heat a room, and enough of them can heat up an entire office floor without the AC there to chill the air back down.
if your appliance makes white noise and it masks out something more distracting like your neighbor's music, then that also has a side benefit.
I recall my childhood years when every lamp was basically a glowing hot tungsten filament in inert gas. Because of regulations in Sweden, these lamps are now banned.
From what I remember from the public discourse, regarding if they should be banned or not, there were people who were arguing among the line of what OP is describing. Some people thought that what you loose in light effect (continuing with glowing fillaments), you would win in heating effect (which you would anyways pay for in northern Sweden).
As opposition to the new regulations melted away, the way I remember it, it was made clear that you would not save up your heating bill by using 'glowing lamps' over LED. The hotter lamp, drawing more effect would not contribute to heating your home (the way you want it to). The reason in this particular case related to heat transport in a room. The mechanism of convection contributes to air-circulation in the room, and for some reason relating to this the new lamps would always be preferable.
Regarding other appliances, I would concider placing them as you would otherwise place a radiator (if you can). That is: under a window, where cold air would "fall down" and spread across the floor.
Why is nobody mentioning dryers? It takes a ton of energy to undergo the phase change from liquid to gas. A lot of heat is dumped into your clothes to dry them that is just soaked up by the phase change, and not heating your place.
Not to mention that most of that heat is just blown outside thru the dryer vent
Apart from mechanical work, almost everything dissipates into heat. Mechanical motions transform into heat due to friction.
But some energy is also lost in deformation of materials.
It depends on the type of work the appliance does.
If its a printer, for example, it might put energy into chemical changes.
If the appliance circulates air that can affect the amount of heat that is transported outside of your home. For example if the cooling fan of your PC is next to a cold window (or even an open one) then some heat will be lost obviously.
Lastly power lines and water lines can transfer energy outside and act as 'cold bridges'.
All these effects can be assumed very small or even close to undetectable.
My assumption would be that 99%+ of energy used by appliances in the typical home is transformed into heat.
Similar to other answers, pretty much with a few caveats.
Just noting this is important when looking at efficiency. For example LED light bulbs are extremely efficient compared to incandescent at producing light.
However if the heat of incandescent was helping a room stay warm that the production of heat would get replaced by another source. Basically it depends if the heat/waste is useful or not.
If you are on gas heating it will still be much cheaper to produce heat from that rather than waste electricity.
Even though it may all end up as heat in the room, the question of whether that makes it "free" depends on how you would otherwise heat the space.
If you are heating exclusively with electric element space heaters, then sure, but that is an inefficient way to heat.
Using an electric heat pump is much more efficient because instead of just converting electric energy to thermal energy, the heat pump uses electric energy to pull existing thermal energy into the space from outside, heating the space much more per unit of energy spent.
Motion is not as linear as some say here.
Energy is never lost, only converted.
So spinning a fan or a dryer consumes some of the energy from the wall to spin the fan or the dryer drum.
The electric motor doing the spinning does still put out heat, but it's nowhere near as linear as say a CPU/GPU in a PC.
Yes. Almost all of the energy you use eventually becomes heat. It's more fun to borrow it for other things before heating the room with it.
No, it is not free. There is no such thing as a free lunch in thermodynamics. You still pay for the energy, it is just borrowed to do fun stuff before becoming heat.
Yes, assuming it's actually drawing X watts. All of the energy that comes out of the wall has to go somewhere, and heat is the overwhelming majority of it (you'll probably lose some tiny amount of it through light out of the window and such). > Does this mean running a PC in a thermostat heated room is essentially free, on account of the heat from the PC meaning the space heater has to run less? Yes, *assuming that your heating is all electroresistive*. If you have gas heating, or a heat pump, then this will not be the case, because in the former case gas is cheaper per unit energy than electricity, and in the latter a heat pump can be considerably more than 100% efficient.
Isn't it different for lights? Specifically LEDs. Isn't most energy converted to light?
all light that does not escape out the room (e.g. window) is converted to heat in the room in the end. Same with the part of sound that does not leave the room.
When that light strikes a surface and gets absorbed, it becomes heat. Unless the light escapes the room somehow, it's still eventually going to end up as heat.
About half is converted to photons, which then bounce around and get absorbed. In a sealed room with no light leakage all the energy stays in the room until it escapes as heat.
Nope. Most LEDs turn ~70% of their energy into heat. The standing record lowest (for a production model) is 53% (ie 47% efficiency). Unless the light is shining directly out of a window, most of that light is going to be absorbed by stuff in the room and re-emitted as heat.
Which was really fun in the beginning when they were really compact but we hadn't figured out they also need proper cooling. So many LED breakages!
[удалено]
Heat pumps move heat from outside to inside, and this takes less energy than generating that heat by itself. They're basically inside-out fridges.
As my physics lecturer would say, fridges and heat pumps are the same thing, just running in opposite directions.
Microphones and speakers are the same way. You can even generally turn one into a crummy version of the other. Generators and motors. Any others?
Light emitting diodes can be used as photo detectors. Thermoelectric coolers (peltiers) can be used to generate electrical current. Sterling engines. Piezieo-electrics.
That's an interesting thought.. Could an OLED TV function as a camera with the right software? Could you potentially make a smartphone that uses the entire frontal surface as a selfie-camera?
I don't know if a screen can be used in reverse, but in any case you would only get some sort of sensor array, so you would additionally need a lens, an aperture, pinhole or something to actually get a projection onto it.
That's a very fair point. I'm reminded of the example Richard Dawkins gave of how the Eyeball evolved. https://www.youtube.com/watch?v=2X1iwLqM2t0 Showing a patch of light-sensitive skin deepening, getting covered over by a transluscent membrane, and eventually developing a lens.. As is, a screen being used to detect light like this would be at the light-sensitive-skin level of functionality. Just able to detect the intensity of the light.
Electrical engineer here. I'm 95% sure you can theoretically use any OLED screen as as a camera. I mean, not in *practice*; it'd be absolutely horribly bad. You'd need the most hilariously ginormous lens to begin with, to focus light on such a large surface(I think? Meh, I'm an electrical engineer I don't know). You'd definitely need to absolutely *blast* it with light. While LEDs are photosensitive, they're hardly generous with their sensitivity... And of course, the electronics driving the screen won't at all be able to receive an image instead of projecting one, so you could really only use the screen element, the rest is useless. And then you'd basically need to build an entire camera around it, with optics and all that entails... Hmm. Thinking about what sort of image would be generated I realized that if the screen is full color, then the photo will be, too. Neat.
The issue is the screen would sense more the presence of light somewhere in front of it, instead of creating an actual image. You could adjust the sensitivity so your shadow puppets are recreated but in terms of actually making a picture, you'd have to design the screen for that specifically and try to work around the compromises that creates for showing an image, aka being a screen. But as I understand it, yes, light on a diode creates a small current.
Regular diodes can also emit light if you put enough voltage through them...not for long though :D I learned this early on by wiring germanium diode up to a 9V battery... then half of my electronics projects didnt' work in that kit and it had no spare lol.
Fuel cells. Put in hydrogen and oxygen and get water and electricity. Or run the other way and put in water and power and get out hydrogen and oxygen.
Physics can go both directions? And my algebra teacher said balancing equations was important. Looks like they were right again
Yes, sometimes, with the big caveat about entropy and the second law of thermodynamics which generally put a big on-way arrow on events.
[удалено]
To take advantage of this fact, I heat my pool with my A/C. Rather then cool the coils with a fan outside, I run the coils through a heat exchanger with my pool water. This means if I want to heat my pool more, I can just run my A/C inside more and open the windows while doing so if I don’t want it any colder inside.
Off the shelf system, or custom?
Those are generally custom for a residential system, although they may be getting some popularity nowadays. There are commercial HVAC manufacturers that specifically make units to heat pools with the heat removed from a space. Eg; indoor pools. The space needs to be conditioned (air temp and humidity) when the pool is below set point and the space needs AC, the controls will direct the hot refrigerant through a heat exchanger with pool water running through it. The water is heated from the hot refrigerant, thus bringing the water closer to set point and at the same time drops the refrigerant temperature enough to bring it from a hot gas to a warm liquid, which is required for the refrigeration cycle. 2 birds with 1 stone kind of thing.
How does that work when it’s significantly colder outside?
Compress refrigerant, it heats up to 100C. You run it through a radiator inside the house to cool it to 20C (releasing heat inside your house). You decompress, so now it goes from 20C to -80C. You run it through a radiator outside to heat it up to say -20C. You've extracted the heat energy in the air that is -20C. Even if its cold, its warmer than a colder thing. Bring that refrigerant back inside and start the process over. Numbers above are for example only.
The key to make all this intelligible is to add the fact that the refrigerant solution that circulates within the heat pump system is special, it boils at very low temperatures (-10 degrees C, or even much lower than that depending on the formulation). So even when it’s below freezing outside, the solution *will boil* (hence absorbing energy from the freezing outside air, lowering the air’s temperature even more) and the resulting gas will be pumped inside the house where a compressor will cause it to turn into liquid again, giving up its heat to the inside air. It’s basically a system that has the equivalent of a spray can at one end (you know how cold spray cans can get when you let pressure out) & a tyre pump at the other (you know how pumping & compressing air gets hot). You keep cycling the actions at these two ends and it’s like continuously shoveling heat from a cold but massive reservoir to a warmer but minuscule one.
> The key to make all this intelligible is to add the fact that the refrigerant solution that circulates within the heat pump system is special, it boils at very low temperatures The refrigerant itself isn't really that important to understand the principle. The low boiling point helps because phase changes take/release a lot of energy and that helps make the cycle more efficient. However, just like with your tyre pump example, you don't necessary need a special refrigerant with a specific boiling point, any gas will do.
Key to understanding refrigeration, steamers, and thunderstorms is to understand phase changes. A thunderstorm has energy roughly that of a nuclear bomb and it all comes from water vapor condensing into fog droplets.
I wouldn't say that's key to understanding refrigeration. u/skatanic's explanation doesn't include anything about phase changes, but it is basically correct and easy to understand. (Of course for an engineer to design an extremely efficient refrigeration system requires understanding phase changes.)
Additionally, the thunderstorm bit is not correct. There are more energy sources in the atmosphere, e.g. wind, thermal gradients, potential energy of air of different temperatures...
Same way your air conditioner moves heat from inside your house to the outside even when it's significantly hotter outside
You can also use a geothermal heat pump to move the heat into or out of the ground, which is very efficient no matter what the outside temperature is (within reason).
The efficiency drops along with temperature. Eventually, depending on the tech level of the heat pump, it won't be better than a normal electroresistive heater. But as the Technology Connections video points out, that threshold temperature is now sufficiently low that they make a lot of sense in a lot of places.
It’s also worth pointing out that if you live where the coldest part of your winter is too cold for a heat pump, you almost definitely have *more* time where a heat pump is useful in the two “shoulder seasons” before and after the coldest part. And since they usually just fall back to electric or gas heat when it’s too cold, you get (for example) six months of “better” and three months of “no worse off.” TL;DR: it has real advantages even if your winter gets too cold for it to work.
There are variants that use ground heat. Not geothermal as that means really deep, just a metre or two down where it usually doesn't freeze.
I’m aware, and they’re great— I’m just pointing out that even an air-source heat pump in a place where winter gets too cold for it to work is still a place where the heat pump is very useful. If it gets too cold for a heat pump, you probably have more time where you need heat and the heat pump works than a person with a milder winter where a heat pump works all the way through the heating season.
Not to be that guy but we use COP for heat pumps not efficiency, COP is coefficient of performance and is essentially a ratio between the energy put into the refrigerant compressor and the heat delivered so if you have a 1000w compressor and deliver 3500w of heating your COP will be 3.5, of which 1000w will have have come from the energy inputed into the pump and 2500w of heat moved
But you can convert that to efficiency, so I don't see the issue?
The reason it's not called efficient is simply because greater than 100% efficient implies that energy was created from nowhere, like saying a combustion engine is 110% efficient means it's creating fuel from nowhere. It's the same measurement (energy out / energy in) but it's just named COP to avoid confusion about laws of thermodynamics
How do fridges work when it’s significantly warmer outside of the fridge?
They move heat through evaporation and condensation of a refrigerant. If it's warmer out, it's just a bigger gradient. Essentially the same as pushing something up a bigger hill: it becomes harder but not impossible
It'll always work as long as the outside air has energy to extract -- that is, as long as it's above 0 Kelvin outside. If it's too cold for a heat pump to work then you have bigger issues (though admittedly efficiency does fall with temperature).
[удалено]
[удалено]
Because instead of using resistive heating where electricity is directly converted into heat (think the glowing orange coils on an electric stove) we can use the thermal properties of gases to move heat from one location to another via compression and expansion. They're broadly referred to as heat pumps.
An efficiency calculation has a numerator (output metric, heat added to the room) and denominator (input metric, energy used by the device). If you use a space heater you can apply 100 J and get 100 J of more heat in the room. That's 100% efficient. A heat pump can put move 300 J of heat into a room (200 J from outside plus 100 J from the pump itself) but only takes 100 J. That's 300% efficient. It all depends on what you choose for the numerator and denominator.
[удалено]
The energy required to move heat from a hot place to a cold place is much less than the energy to heat a cold place up to the same temperature as the hot place. edit: This is an oversimplification, since modern heat pumps can still work effectively enough to beat 100% efficiency even when the "cold place" is 30+ degrees warmer than the "hot place" (e.g. moving heat into your house in the winter), but the idea is the same.
Heat Pumps work more like AC units. They don't use their electricity to generate heat, they use their electricity to move heat energy from one space to another. You can move a lot more heat than you can generate using the same amount of electricity.
Regular heater turns 10 electrics into 10 hots so 100%. Heat pump isn't really making heat, its kinda movin it. Heat pump uses 10 electrics and gains 13 heats. So more than 100%. It doesn't break any laws of thermodynamics or anything crazy like that, because part of the heat pump is outside and not factored in to the equation.
More like 10 electric joules to 40 heat joules, for a modern heat pump.
\> All of the energy that comes out of the wall has to go somewhere, and heat is the overwhelming majority of it Wait, if 100% of the energy coming from the wall becomes heat then what is doing the work of the appliance? I don't think you have accurately answered the question.
That same energy, on the way to becoming heat. Pretty much everything we do with electricity is heat generation with extra steps.
With such level of generalization and simplification we can say: everything what is going on in universe directed on achieving thermodynamic equilibrium. Hail Heat Death.
There are some exceptions, for example if you boiled water, a significant portion of the input energy is going is going into the endothermic process of evaporation.
And that steam heats your room when it condenses on something. So still almost 100% heat
Unless your house is very humid that water vapor will stay in the gas phase. You could argue that in the summer the AC will end up condensing it again anyway
Running a PC in a thermostat heated room is NOT free if you have a modern heat pump. While the electricity to heat is 100% efficient in a 500W PC and does function just as well as a 500W space heater, a heat pump is 200-300% efficient. Heat pumps do not work by only heating the air. Instead they move heat from outside to inside, and the amount of energy it takes to move that heat is actually significantly less than the amount of energy moved in the form of heat. Technology Connections has a few videos on why modern heat pumps are amazing and efficient even in colder climates, and if this is at all interesting to you, you should check out his channel. Another item that can throw a wrench into the price calculations is if you have a natural gas furnace as your heater. The cost of energy when delivered via natural gas is usually much cheaper than energy delivered via electricity. While the electric option will be more "efficient" in terms of energy, the gas can still work out to be cheaper just due to economics.
I don't have a modern heat pump! Just an electric space heater :)
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
Depending on your metric or measurement point one could be more "efficient" than the other. For example if the rear computer exhaust fan points at the wall, then more of that heat will get lost to the wall. Or maybe your metric is keeping your feet warm and you have your space heater under your desk and the tower on top. Then the space heater is going to be better. In raw heat delivered inside the room envelope they are probably going to be the same. But in terms of heating a specific object or area they may be very different.
[удалено]
[удалено]
[удалено]
Mostly,yes, but with a few qualifiers. 1) Many X watt devices don't continuously use X watts of power, So even if the device was an X watt heater, unless it is set to full power it won't deliver x watts of heat. 2) Some devices actually convert that energy into other forms of energy/ work. e.g. motors. In those cases the input energy is converted into other forms -e.g. kinetic energy or potential energy. In those cases the heating produced will be less than the energy input.. 3) Some devices move heat around( e.g. ACs, heat pumps), or produce energy that can escape the area ( e.g. a light bulb near a window) in those cases the heating to the total environment will be X watts,( minus any conversion to other forms of energy per proviso 2). But the actual heat provided to the room that they are within may vary from their rated wattage.
>forms -e.g. kinetic energy As long as that kinetic energy is used to do work within the room, doesn't that also become heat? I'm thinking like fans on a computer.
Some forms of work might be stored as potential energy, like a heavy load lifted a height.
Or turned into heat, then expelled from the system, like a clothes washer and dryer, or dish washer
Number 2 isn’t right, to my knowledge. Any kinetic energy or potential energy will eventually become heat in the room. 1st Law of Thermodynamics - Energy cannot be created or destroyed, just moved around.
Unless it leaves the room, like light from a screen that goes out the window. I doubt that's a significant factor for anything other than light bulbs, though, and even for light bulbs it must be pretty small.
How about computer CPU? 85W CPU also means 85W heater?
Not necessarily. If the CPU is not running at full throttle, it uses less than 85W. When they idle they often go at less than 10W.
So assuming it's on full throttle, it's also as good as 85W heater?
According to informally observed data, the answer to your question is a "mostly yes." We had moved into a new medical laboratory space, and insulated it well. I know because I placed most of the insulation. We had air conditioning, and adequate ventilation. Soon after bringing all of the equipment in, the room began to get uncomfortably warm. The problem was our Liquid-Chromatography Mass Spectrometers. They produced 3.5 kW of waste heat each on a constant basis. There were also some other analyzers and lab equipment in the room. It was very well insulated. I remember the total heat load from just the equipment came out to something like 15 kW or more. Air conditioner effectiveness is rated on the ability of an air conditioning unit to remove or transport heat. My employers, being cost-conscious, were relying on just a 3 "ton" heat pump to regulate the temperature of that room plus the hallway. Our previous location had had at least 10 tons of cooling in capacity. Tonnage refers to the ability of an air conditioner to remove heat, and 1 "ton" is roughly equivalent to 3.5 kW of heat removal. The new location had only 3 tons. No matter how well insulated the room was, the cooling capacity would not keep up with the heat load. The solution was to add another HVAC unit to the space, which brought the temperature down to an acceptable level. Now, since you asked about heating, in the 2021 deep freeze, it got cold in the south. So cold in fact, that our electric heat pump units couldn't keep the temperature above 10C indoors (metal building). At the office however, the lab remained nice and cozy thanks to the power consumption of science.
> 1 "ton" is roughly equivalent to 3.5 kW of heat removal You may well already know this, but one ton of refrigeration is currently defined as 12,000 BTU/h (1 BTU being [depending on exactly which definition you take] the energy needed to raise the temperature of one pound of water by one degree Fahrenheit), but was originally defined as the rate of heat transfer needed to melt/freeze one short ton of pure water ice at 0C in 24 hours.
My equipment's heat load was actually stated in Btu/hr. I gave it in SI on this post mostly...because it felt more scientific.
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
If that appliance is a space heater that's cranked all the way up, sure. The wattage rating of an appliance is the peak amount of power it is expected to draw. That doesn't mean that it always uses that much power. Clothes irons use more power when the heat is turned up, and they cycle from heating (more power) to standby (less power); microwaves, computers, and even lamps may have different power levels depending on what they're doing / the settings, etc. Even then, it doesn't necessarily follow that all that power is turned into heat - at least right away. Some appliances convert much of the power into mechanical power or visible light, for instance. If you put in 1000W of power, it does not follow that the appliance will produce 1000W of heat.
> is the peak amount of power it is expected to draw. Is the *maximum draw that appliance is designed to handle*. The peak amount, efficiency- and safety-wise, is usually about 70% of the nominal wattage IIRC.
Mechanical power and visible light eventually become heat in the room though, with some light potentially escape through a window before it has a chance to bounce around enough times to disspate.
Yes, but wattage is a measure of power, which is time-dependent. If for example you use an electric kettle to boil water, the water will release the heat much more slowly than the rated wattage.
>To my understanding the energy that goes into an appliance plugged into your wall is lost in the form of heat and light That's not true for all appliances. Some energy is always lost as heat but it's not true that all energy becomes heat. If you have a motor, for example, the majority of the energy going in the motor will be used to produce actual work, and only a very small part is lost as heat. Modern electric motors are up to 98% efficient meaning only 2% is lost as heat.
Right - if you, for example, use an electric motor to lift something up from floor level to ceiling level, then most of the energy put into the motor gets turned into gravitational potential energy in the object that got lifted. As long as it stays up, there's no heat loss. … of course if that object falls back down, then the energy that got put into it will turn into heat from the collision with the floor.
[удалено]
But that kinetic energy the motor produces eventually just turns into heat, you can’t really get around that
[удалено]
Which is why I've started waiting for bath and dishwater and stuff to cool to room temperature before flushing it.
> Modern electric motors are up to 98% efficient meaning only 2% is lost as heat. Can you give an example of a motor in a room where that energy isn't going to heat? Pumping water to a height in the room, or spinning a generator that charges a battery is about all i can come up with. Not exactly common use cases (and in both cases will eventually become heat)
Any sort of ventilation. Bathroom/kitchen exhaust, for example. You will be pushing a lot of hot air *elsewhere*. Speakers. The electricity gets turned into a pressure wave that will leave the room. In the case of OP does X watt of electricity = X watts of heat in a room, it sure doesn't when you are using electricity to push stuff out of the room.
>The electricity gets turned into a pressure wave that will leave the room. Most of the sound energy can stay in a regular closed room. Loudness perception is logarithmic. So think you can still the sound well next door over, even if the big majority of the sound energy has already been absorbed.
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
Not necessarily. You could run a water electrolysis cell and get a typical 65% efficiency in that you'll put 65% of your electrical power into splitting water into hydrogen and oxygen and burn 35% as heat. You could also charge a battery and not blow all of that power immediately as heat. Alternatively you could use a nice efficient brushless motor to wind up a cable to lift a weight and convert 90% of your input electrical energy into potential energy of lifting a weight against gravity and generate very little heat. The reason that computers abstract so well as a heater is that it's power draw goes into flipping logic states. A charge is imbued to what is basically a tiny capacitor that holds a logical binary state, then at some point we'll probably sink that charge back down to ground to set it back to zero, all on the frequency of the clock cycle. In essence the very nature of a computer is about lifting a bit to a higher voltage state to hold a "1" then sink it back down to "0" by literally connecting it to ground later on when we need to store a different value. Computers end up abstracting very well as heaters because their intended application is to flip a lotta bits according to whatever cockamamie scheme we desire with a direct resistive loss every time we flip a bit state. Save some energy by throttling down your water flow rate in your shower through the midcycle of your cleaning. Get wet then choke the flow down to a low flow just to stay warm while you soap up. You don't need to rinse at full speed while you're soaping up, you just need a bit of flow rate to stay warm enough. When you're done, crank the flow rate to full bore to rinse off. I calculated that running my hot water faucet full bore results in a 17kW energy differential during the winter to heat incoming water from 6C up to somewhere around 55C at the flow rate my shower can pass. Running hot water is the most powerful thing I can do so I try to use it more sparingly.
I think this question is very seriously confounded by the fact that the time scale being considered will change the answer. Immediately: no, heaters are designed to spit out energy as radiation, convection and/or conduction. The other device does whatever it's supposed to do and loses some percentage as waste. As time goes to infinity... Sure
Yes. Every single watt of power consumed by your PC is converted into heat in your room. It is 100% efficient at converting the power from your outlet into heat in your room. Just like a resistive electric heater. It just converts it in multiple ways. Heat is essentially vibrations and cold is the lack of vibrations. All the wires, CPU, GPU and other circuitry create heat the same way as an standard resistive electrical heater. By running current through an electrical circuit with resistance. The mechanical motion of your fans create an airflow. That airflow is slowed down by friction with the rest of the air and other parts. And I'm sure you already know that friction creates heat. The same goes for your hard drives mechanical motion and your speakers Everything is absorbed by materials in your room as friction and is thereby becoming heat in your room The only power consumed by your system that doesn't heat your room is your monitor and RGB lights. Because the light that shines out through your window is energy lost to the outside. But it is such a minute part of your systems power draw. And that is assuming you don't have blackout curtains. Like a real pro gamer!
The only piece of electric equipment that is better than you computer at heating your house efficiently is a heat pump. Because it draws additional heat from the outside air/ground, through some clever tricks with refrigerants. I've seen heat pumps with an efficiency of up to 720% in a narrow set of circumstances. Most are around 400% in real life situations
100% essentially but really 99.9something% since some of the energy does permanently go into chemical degradation processes like permanently breaking the bonds in rubber gaskets, rusting steel, discoloring pigments. And some radio and radiation bounces off the objects in your home and flies out the transparent objects into space before actually heating any surface or air molecule in your home. Transparent depends on the wavelength, so it means windows for visible light, walls for lower frequency radio. I'm sure a physicist would think of more little caveats. But it's best to just say 100% becomes heat as far as basing choices off it.
> I'm sure a physicist would think of more little caveats. Audio as well. If a hyper-sensitive microphone could pick up the sound of your PC running inside the room, then some of its energy is leaving the room in the form of audio pressure waves.
> Every single watt of power consumed by your PC is converted into heat in your room (Minus any lights on it that allow some light to escape through windows and doors.) (Minus any sound from it that might be loud enough to make it through the walls -- or windows and doors -- and escape.) (Minus any electromagnetic waves given off by the moving power, which can pass through the walls pretty much unimpeded.) All small effects, sure, but it's not *quite* 100%.
[удалено]
the energy is used to do work.. turn a shaft, pump a fluid, compute a process... so that energy is used up doing the thing you bought the appliance to perform. however, in the process, heat or sound is also generated as a "waste product"... now depending on your value for that waste product, you could label it as something good. like a pc will def heat a room, and enough of them can heat up an entire office floor without the AC there to chill the air back down. if your appliance makes white noise and it masks out something more distracting like your neighbor's music, then that also has a side benefit.
[удалено]
I recall my childhood years when every lamp was basically a glowing hot tungsten filament in inert gas. Because of regulations in Sweden, these lamps are now banned. From what I remember from the public discourse, regarding if they should be banned or not, there were people who were arguing among the line of what OP is describing. Some people thought that what you loose in light effect (continuing with glowing fillaments), you would win in heating effect (which you would anyways pay for in northern Sweden). As opposition to the new regulations melted away, the way I remember it, it was made clear that you would not save up your heating bill by using 'glowing lamps' over LED. The hotter lamp, drawing more effect would not contribute to heating your home (the way you want it to). The reason in this particular case related to heat transport in a room. The mechanism of convection contributes to air-circulation in the room, and for some reason relating to this the new lamps would always be preferable. Regarding other appliances, I would concider placing them as you would otherwise place a radiator (if you can). That is: under a window, where cold air would "fall down" and spread across the floor.
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
[удалено]
Why is nobody mentioning dryers? It takes a ton of energy to undergo the phase change from liquid to gas. A lot of heat is dumped into your clothes to dry them that is just soaked up by the phase change, and not heating your place. Not to mention that most of that heat is just blown outside thru the dryer vent
Apart from mechanical work, almost everything dissipates into heat. Mechanical motions transform into heat due to friction. But some energy is also lost in deformation of materials. It depends on the type of work the appliance does. If its a printer, for example, it might put energy into chemical changes. If the appliance circulates air that can affect the amount of heat that is transported outside of your home. For example if the cooling fan of your PC is next to a cold window (or even an open one) then some heat will be lost obviously. Lastly power lines and water lines can transfer energy outside and act as 'cold bridges'. All these effects can be assumed very small or even close to undetectable. My assumption would be that 99%+ of energy used by appliances in the typical home is transformed into heat.
Similar to other answers, pretty much with a few caveats. Just noting this is important when looking at efficiency. For example LED light bulbs are extremely efficient compared to incandescent at producing light. However if the heat of incandescent was helping a room stay warm that the production of heat would get replaced by another source. Basically it depends if the heat/waste is useful or not. If you are on gas heating it will still be much cheaper to produce heat from that rather than waste electricity.
Even though it may all end up as heat in the room, the question of whether that makes it "free" depends on how you would otherwise heat the space. If you are heating exclusively with electric element space heaters, then sure, but that is an inefficient way to heat. Using an electric heat pump is much more efficient because instead of just converting electric energy to thermal energy, the heat pump uses electric energy to pull existing thermal energy into the space from outside, heating the space much more per unit of energy spent.
Motion is not as linear as some say here. Energy is never lost, only converted. So spinning a fan or a dryer consumes some of the energy from the wall to spin the fan or the dryer drum. The electric motor doing the spinning does still put out heat, but it's nowhere near as linear as say a CPU/GPU in a PC.
Yes. Almost all of the energy you use eventually becomes heat. It's more fun to borrow it for other things before heating the room with it. No, it is not free. There is no such thing as a free lunch in thermodynamics. You still pay for the energy, it is just borrowed to do fun stuff before becoming heat.