7 ms·
Definition of efficiency (from Google): the ratio of the useful work performed by a machine or in a process to the total energy expended or heat taken in. Heat
by drran 6y ago
Definition of efficiency (from Google): the ratio of the useful work performed by a machine or in a process to the total energy expended or heat taken in.
Heat pumps are >100% efficient.
Usually, we cannot convert all input energy into useful work, so efficiency is always <100%, because of energy losses, which are producing waste heat. However, in case of heater, heat is the "useful work", so electrical heaters have "impossible" 100% efficiency, while heat pumps have even more "impossible" >100% efficiency.
- seniorsassycat 6y agoA heat pump in a −273 °C space will convert electricity to heat at a 1:1 ratio. If you count the heat taken from the space around the condenser, which you should based on Google's definition, heat pumps are only 100% efficient. Calling heat pumps >100% efficient is like calling my solar water heater >100% efficient. True if you only count the electrical input, and not other sources of energy.
- CobrastanJorji 6y agoYou will be pleased to know that the majority of heat pumps are installed in homes whose exteriors stay above 0 kelvin year round. Also, in what I assume is an efficiency feature, most heat pumps do not allow operation in a zero Kelvin environment. Also, to nit pick: Kelvins are not degrees and do not use a ° sign.
- Nition 6y agoDamn, I've been looking for a zero Kelvin heat pump that works in a vacuum to heat my spherical cows.
- omgwtfbyobbq 6y agoMaybe you wouldn't need to heat them so much if they weren't frictionless.
- mey 6y agoGotta watch out for that Maxwell brand heat pump.
- drran 6y agoAre you trying to liquify vacuum? It's challenging. Try to use a heat pump based on the Casemir effect, fluctuating virtual particles violate the energy conservation of the system for short periods.
- LeifCarrotson 6y agoAnd, as a bonus efficiency feature, most heat pumps are installed with the condenser external to the home! Yes, if you draw an imaginary box around the home and the outdoor/underground condenser, they're exactly 100% efficient, but if you only consider the inside of the home and ignore that the condenser is taking in heat energy from the outside, they're more than 100% efficient.
- seniorsassycat 6y agoThe power station and natural gas plants are outside my house too, so my restive floor heaters and furnace are >100% efficient.
- minitoar 6y agoJust draw an imaginary line around my pocket book then. I pay for the energy I'm getting from the power station. Beyond capex, I don't pay for the energy I'm getting from the heat exchanger.
- _carbyau_ 6y agoAnecdotally, I have come across hotel bar fridges running in entirely enclosed cupboards. Even the power cord exited the box with a rubber seal. Nice attention to detail in physical craftmanship though!
- seniorsassycat 6y agodid not realize kelvin is not a degree. I fixed my comment.
- LocalH 6y agoGood thing they wrote −273 °C and not "0 °K".
- stopping 6y agoThis is incorrect. We measure the "efficiency" of a heat pump by the amount of heat moved into a space divided by the work energy provided to the pump (electricity in this case). This is called the "coefficient of performance". Typical heat pumps have a CoP of 3 or more. Meaning, you can spend 100W of electricity to pump 300W of heat into your home. A purely resistive heater only has a CoP of 1.
- OJFord 6y ago> or heat taken in.
- drran 6y agoAmbient heat is not a "heat taken in", because you don't need to supply it. Usually, heat is taken out from the system and dissipate as ambient heat, so a heat pump can use the same heat again and again, without exhausting of ambient heat.
- OJFord 6y agoOf course you need to supply it, you wouldn't use one in Antarctica . (I'm no refrigerant expert, but I assume there's nothing that would work well enough to be worthwhile.) The only reason I can think of for 'or heat taken in' in that definition is exactly to stop people claiming >100% efficiency for heat pumps, which is a corollary for perpetual motion, and equal nonsense. > so a heat pump can use the same heat again and again, without exhausting of ambient heat. That's just not true, they are heat interfaces, thermal energy is transferred from outside to a refigerant, to inside (or inside water, or whatever). If this were true, they would have a closed tank of hot air as well as a closed refigerant loop (as the vast majority do) so it would always be oprrating optimally in any environment, never running out of hot air. The clue's in the name - pump! - they just move heat about, you wouldn't claim pumping water is >100% efficient because you're creating water out of nothing and you'll never run out of water in the infinitely massive lake you're pumping from, would you? Put a box over it. Look at what goes into the box and what comes out, on all sides. Efficiency = Outs / Ins. It's a yield. A ratio of how much of what you put in you get back out in the form you want.
- drran 6y agoEnglish is not my native language. Did I use the word "ambient" properly?
- OJFord 6y agoAssuming I understood your argument correctly, yes. :) (ambient foo = the foo all around; usually used w.r.t. temperature, e.g. food cooling to ambient temperature in the room) The air outside that is the input to your heat pump is already there, already at whatever temperature, that's your argument right? So, yes, it is, but my point is that you can't ignore it as an input just because you don't have to order (and pay for) some air to supply. In calculating efficiency, you have to put an imaginary box around the heat pump, and look at what's going in, and what (that is the desired useful thing) is coming out. If inputs don't cost you anything, that means you might not care about lower efficiency, but it doesn't mean that the efficiency isn't lower.
- piracy1 6y agoI consider personal enrichment as a sort of useful work as it stands to replace my own 'useful work'
- coldtea 6y agoPerhaps parent meant useful with the caveat that "it also wont fuck up the climate, and assist in huge destruction and killing millions in the process of making me rich". Which is so selfish of him. Why should the safety of billions matter over me becoming rich? /s
- piracy1 6y agonet useful minus externalities. Sure
- fomine3 6y agoTotally agreed but I wonder is it applied to extremely cold situation. Possibly outside unit produce heat but not all heat supplied to room.