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Comment by xenocyon | Hacker News Reader

1. At an individual/hobbyist level this is a fine thing to do, if one is already a cryptocurrency enthusiast.

2. At a social/planning level it is important to remember that opportunity costs matter, and this should not be recommended as public policy. One kWh of electricity could either be used for mining bitcoin (creating at most one kWh of indoor heat), or it could be used for running a heat pump[*], yielding multiple kWh of indoor heat due to the magic of heat pumps and their >100% "efficiency"[**].

[*] Yes, I realize the OP is already using a heat pump, but assisting it with preheat is inherently less efficient than plowing the same energy into running the heat pump itself.

[**] Yes, heat pumps aren't >100% efficient per a physics textbook, but what most people care about is that you can use them to get >1 joule of indoor heat from 1 joule of energy input, which feels magical when compared to electric heaters, gas furnaces etc.

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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.

A 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.

You 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.

Damn, I've been looking for a zero Kelvin heat pump that works in a vacuum to heat my spherical cows.

Maybe you wouldn't need to heat them so much if they weren't frictionless.

Gotta watch out for that Maxwell brand heat pump.

Are 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.

And, 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.

The power station and natural gas plants are outside my house too, so my restive floor heaters and furnace are >100% efficient.

Just 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.

Anecdotally, 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!

did not realize kelvin is not a degree. I fixed my comment.

Good thing they wrote −273 °C and not "0 °K".

Pretty sure they edited it.

I was under the impression that HN indicated when a comment was edited. Maybe not and I got mixed up with elsewhere.

Edit: Apparently I'm completely wrong. Carry on and I'll eat my downvotes with aplomb.

This 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.

> or heat taken in.

Ambient 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.

Of 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.

English is not my native language. Did I use the word "ambient" properly?

Assuming 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.

1) If we put a very small box around the heat pump, then we will see that temperature in the box increases at constant rate, because of energy loses at the pump. I.e., it will work as a resistive heater, by converting 100% of input electricity into heat, which is the goal. Eventually, the heat pump will stop, because the goal is reached, thus we will have 0 input energy and 0 useful work.

2) To keep the pump running and keep temperature at steady level, we will need to leak heat at constant rate to the second box. Thus, the pump will work at "impossible" 100% of efficiency again: it will convert all input electricity into heat.

If we leak heat at high rate, then the pump will not be able to keep up, but it will still work at 100% efficiency.

If we redirect some leaked heat from the second box back to the pump as input, so it will pump it back into the box, then it will work at 100% of efficiency + additional heat pumped from the second box. Moreover, temperature in the second box will continue to increase at constant rate, so it will reach equilibrium at some point of time again.

3) For the pump to work indefinitely at steady rate, we need something to dump energy into, with infinite capacity. Also, we can use a fraction of this infinite capacity as infinite input into the system, thus the pump will work at 100% + additional heat.

IMHO, first two systems are worthless, because they doomed to reach equilibrium and stop at 0/0.

I consider personal enrichment as a sort of useful work as it stands to replace my own 'useful work'

Perhaps 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

net useful minus externalities. Sure

Totally agreed but I wonder is it applied to extremely cold situation. Possibly outside unit produce heat but not all heat supplied to room.

OP is in Austria where it often gets below freezing.

Air/air heat pumps and ventilation heat exchangers tend to freeze up when it gets too cold. So heat pumps often need to run in reverse (to melt the ice on the condenser) and heat exchangers need to pre-heat air with resistive heating to prevent ice build up.

If he can pre-heat the air with a crypto miner that would be better than either of the above.

Consumer-grade heat pumps do not approach the theoretical thermodynamic efficiency limit especially when the outside temperature is significantly below freezing temperature as that complicates design. Plus they do not last forever and it takes a lot of energy to make them. So a hybrid design with an electrical pre-heater for really cold weather can be the least consuming in the total balance of energy. But then one can just as well mine crypto currencies in the preheater just as the article described.

Looks like even OP with their fancy own home didn't actually install a heat pump the way which will make it more than 100% efficient, what about the large horde of people who rent and can't do a thing about how their house is heated? It's trivial to find out if your heating system is actually efficient and if it's not why shouldnt you run crypto mining?

I am renting a house and can't do a thing about how my house is heated. How do I find out if my heating system is efficient?

> didn't actually install a heat pump the way which will make it more than 100% efficient

Or, more likely, they installed a heat pump of a suitable capacity for 80+% of the expected conditions, with a pragmatic "old school" pre-heater to make up when conditions are out near the end of the bell curve.

> why shouldn't you run crypto mining?

I think the key takeaway here is that any time you're using resistive electrical heating for air, crypto mining is a suitable alternative to just making resistive nichrome wire glow red. Whether the cost of 1000W worth of GPU cards compared to the cost of a cheap 1000W fan/column heater makes sense for you is a different question. Whether the payout in whatever crypto you're mining ever comes close to breakeven on the cost of the mining rig and it's depreciation as it becomes more and more out of date is another question. If, like the article's author, you can build an effectively zero cost mining rig from parts on hand, then it's almost certainly worthwhile (modulo what you value your time building/configuring/maintaining it...)

(And there's the deeper ethical question of whether participating in a Proof Of Work cryptocurrency at all is just outrageously leveraging your personal heating requirements into a planet burning speculative ponzi scheme "asset" trashfire...)

An alternative to using heat pumps is to use gas heating. Gas heating lets you achieve >100% "efficiency" relative to electric heating because you don't have to pay the price of converting the gas into electricity.

There is another non-trivial advantage of natural gas. Energy losses from sending it over pipes are smaller that electricity losses in transmission lines, https://www.eng-tips.com/viewthread.cfm?qid=76881

This section of this book:

https://www.withouthotair.com/c21/page_150.shtml

Has some calculations that show that using gas to generate electricity (in a modern gas fired power station) which you then use to run heat pumps for heating - is overall more efficient than just using the gas for heat given real world numbers. (It does go on to show the limitations of how much ground-source heat pumping you can do without freezing the ground - his ballpark numbers suggest maybe only 25% of the heating requirements for a typical British suburb could be met with just ground-sourced heat pumps before you'd freeze the available ground...)

(That whole chapter starting back on page 140, and the whole book - are well worth reading in my opinion.)

People sure talk a lot about heat pumps, but from what I read, they're best suited to around 10 C, which in my climate is a brief interval between the seasons changing and hardly requires heat at all. It may be two or three times as efficient, in a sense, but if it's not usable all winter, it can't save much energy, can it?

I think that applies to air source heat pumps, but if you have another medium that might be better.

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