Hot tub miners

[paraipan]

Well yeah, but isn't that what I said initially?

Yeah maybe I misunderstood but you can't rely on JUST a hot tub was my point.  What happens when the hot tub is at 50C and the GPUs are at 50C?  With nowhere for the heat to go the temp in both loops will rise and rise faster in the GPU loop until you hit GPU killing temps.

Having a water-air radiator after the hot tub gives you control over the GPU temps outside of what the temp of the hot tub is.

The tub looses heat over it's surface and body if not insulated. There are formulas to calculate the temperatures the system will reach equilibrium with a given input energy (GPU temps) and natural dissipation surface of the tubs. Don't forget to take into consideration overall loses in the pipes and heat exchanger too.

The answer is NO, you won't be put in the situation of needing a water-aid radiator, imo

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[DeathAndTaxes]

My thoughts exactly I think we were saying the same thing in different ways.

I may not go that elaborate for my setup but putting heat exchanger on cold input of hot water heater seems a no brainer.  That is the closest thing to "free energy" you can get.  

[Gomeler]

I don't see why it wouldn't work, although it would almost certainly raise the temperature of your GPU water loop. Either that or you'd need a huge heat exchanger to move much heat with only a few degrees deltaT.

No you just need a water-air heat exchanger to provide supplemental cooling downstream of the hot tub heat exchanger.


GPUs ---> Pump ----> Hot tub heat exchanger ---> Water/Air heat exchanger ---> back to GPUs

Would you though? If it takes x amount of watts for a hot tub to maintain temperature of y with it losing heat to evaporation/convection then so long as you input x or less watts then your water temperature won't exceed the original design. Issues would arise when you add more than x amount of watts to the water in the hot tub. Then the temperature would rise until the increased delta t between the water and ambient air caused an equilibrium to be reached through evaporation/convection. This isn't an issue for a heatsink but it is an issue for a heatsink that humans would like to enjoy sitting in. In that case then it would make sense to run a water/air HX before the hot tub so that you add less than x watts and then supplement to reach x watts.

No that would be bad.  Heat exchangers work better with a higher Delta T.  Cooling the water before getting to the hot tub would make it useless for transferring heat into the hot tub.  If temp is less than hot tub heat would actually flow to the GPU loop.  If the temps are close you would get minimal heat transfer.  Also you have little control over how "cool" you get the water.  Lastly the temps leaving the heat exchanger will be close to the hot tub temp.  So your "cold" input temp for GPUs will be 60C-70C.  You are cooling the GPUs with water higher than the temps you want them operating at.

Pretty simple to solve the "humans don't like it that hot problem".  The first is that the hot tub will never get hotter than the GPUs.  If you use something like cgminer to throttle GPUs based on temps then water in loop will never be hotter than the temps humans like.  If you want max GPU temps then you need a bypass valve.  If hot tub is < desired temp then water flows through heat exchanger.  If it is >= desired temp valve closes and water flows around the heat exchanger.

GPU (60C) ----->  hot water heat exchanger (drops temps to ~ hot tub temp say 55C)  ---->  air heat exchanger (50C) ----> water returning to GPUs (50C)

GPUs then heat water back up to 60C and the cycle starts over.

I suppose I should have used real temperature examples instead of abstract values. In my case I meant if the GPUs and hot tub started at 25C and you were adding more watts than the hot tub could dissipate that the water temperature would climb until an equillibrium was reached. So, if at some point your equilibrium is achieved at 87 Celsius, you could dump an unknown amount of watts before the water hits the hot tub so that your hot tub achieves a comfortable temperature. This way you don't throttle your farm(I mean we're here to make BTC, not heat a hot tub, right?) and you keep the humans happy. Hell, you could use a PID controller on the air/water HX to control the fans such that the outlet temperature of the water before it hits the hot tub is at the temperature you want the hot tub.

It would also appear that hot tubs run at around 60 Celsius. So, if your GPU inlet is 60 Celsius then you are looking at GPU temps around 75 Celsius which isn't half bad. You can't dramatically lower the inlet temperature unless you also dramatically lower the flow-rate as otherwise you won't have the time to heat up the water going through the blocks such that your outlet temperature is higher than your hot tub temperature.


Pretty interesting discussion. Would be fun to run a stirling engine from your waste heat to power the fans that provide cooling in a more traditional watercooled setup.

[rjk]

There's already someone here that heats his bathroom floors with his watercooled GPUs - sorry I've forgotten the nick. But there are pics on the forum somewhere.

EDIT: It's sturle, and here is the link: https://bitcointalk.org/index.php?topic=3707.msg53879#msg53879

[paraipan]

My thoughts exactly I think we were saying the same thing in different ways.

I may not go that elaborate for my setup but putting heat exchanger on cold input of hot water heater seems a no brainer.  That is the closest thing to "free energy" you can get.  

a miner's wet dream... free energy or heating, whichever comes first

You could have a adjustable pump on the GPU side to increase or decrease the flow in case the cooling rate isn't sufficient, and make sure it's a big tub and have more than one heat exchanger, the rest is getting paid to enjoy such hot tub with family and friends


didn't saw that post rjk thanks, my fav line...

The best thing about my water cooling and floor heating is that my wife keeps nagging me to buy a second 5970 to make the floor warmer

i should look into it more, yeah

[TheLittleDuke]

Or radiant floor heat!

[MrTeal]

A 60C hot tub? Remind me never to visit your house. That's the temperature you use for Sous-vide.

[rjk]

Does anyone have any actual numbers on heat loss of such a tub? How much can I expect one to dissipate?

[Global BTC]

How about using a heat pump between the GPU cooler loop and the pool heating loop? It will add to the power draw, but the GPU:s will get cooler and the pool a lot warmer.

An outdoor hot tub can dissipate very large amounts of heat if it's not covered. I'm pretty sure it's more than 1kW. Most of the dissipation is done by the water when it vaporizes.

[MrTeal]

How about using a heat pump between the GPU cooler loop and the pool heating loop? It will add to the power draw, but the GPU:s will get cooler and the pool a lot warmer.

An outdoor hot tub can dissipate very large amounts of heat if it's not covered. I'm pretty sure it's more than 1kW. Most of the dissipation is done by the water when it vaporizes.

Really though, if your aim is to save money your first order of business should be to insulate your hot tub and buy a proper spa cover. I don't have exact figures, but a good covered spa doesn't take much power to keep warm as long as outdoor temperatures are reasonable. If you like to run your hot tub in the winter it's a different story of course, everything looses heat at -40.

[paraipan]

Does anyone have any actual numbers on heat loss of such a tub? How much can I expect one to dissipate?

You have too much unknown variables to be able successfully calculate all that, like primary and secondary circuit water volume and ambient exposure (insulation missing), inefficient heat exchangers and all that. Building it with a decent size tub, exchangers and GPU's, with the ability to add or remove some of them from the circuit easily, should give better results to reach some conclusions.

A rough estimate is that you would lose more than half of the energy you put in, so with 1kw rigs should give aprox 400-500w heat, and this value goes down with more energy we put in, better for the miner in this case.

[vapourminer]

hot tubs are around 40c (104 F). at least mine is.

as for heating your hot water with mining energy, a (very expensive, heh) roundabout way is have a geothermal HVAC system installed. in the summer when its in AC mode, excess indoor heat is used to heat your hot water tanks via its heat pump (so it can actually get it to 160 F if there enough warm air in the house). excess heat after the hot water tanks reach their temp is dumped into the ground. so, more or less free hot water in the summer

only practical for small scale mining setups (free gigs maybe?) but if youre gonna go geothermal (we are) its a nice bonus.

I know, not exactly what you guys are talking about... but..  figured Id toss it out. maybe someone here can devise a dedicated small scale home brew version. a heat pump seems to be one good way to regulating temps and moving the heat to where you want it. lotta sharp minds here, some one may think of something.

[rjk]

So I drew this up for fun. Uses a 4-way ball valve, which you might be able to get an electrically controlled version of and make the heater automated. This drawing shows the use of an external radiator in case the tub is too hot.



Maybe someone knows of some way to make this same idea, but with some kind of continuously variable valve. That would be the best thing to do.

[vapourminer]

So I drew this up for fun. Uses a 4-way ball valve, which you might be able to get an electrically controlled version of and make the heater automated. This drawing shows the use of an external radiator in case the tub is too hot.

Maybe someone knows of some way to make this same idea, but with some kind of continuously variable valve. That would be the best thing to do.

couldnt you just run the water to air and water to spa loops in parallel (ie 2 loops). use stepper motors connected to valves to adjust flow to each, and some logic chips (with temp sensors in the spa) controlled via rs 232 port to control the steppers. computer program monitors the temps. water flow can be through one, the other or both loops, depending.

[casascius]

For me, the answer to deal with the problem of "what do I do when the hot tub is already hot enough?" needs no valves: it is a software solution to simply lower the hash rate when the extra heat is not needed.  Given that the original purpose is to mine with free power, there is no point in using more power than the hot tub needs for heat because that power is no longer free.

[rjk]

For me, the answer to deal with the problem of "what do I do when the hot tub is already hot enough?" needs no valves: it is a software solution to simply lower the hash rate when the extra heat is not needed.  Given that the original purpose is to mine with free power, there is no point in using more power than the hot tub needs for heat because that power is no longer free.

That makes it real simple then, just a couple pumps, a heat exchanger and a temp sensor with communications to your computer to control it.

[vapourminer]

For me, the answer to deal with the problem of "what do I do when the hot tub is already hot enough?" needs no valves: it is a software solution to simply lower the hash rate when the extra heat is not needed.  Given that the original purpose is to mine with free power, there is no point in using more power than the hot tub needs for heat because that power is no longer free.

what if you need to reduce the hash rate near zero? no fun it that.

outdoor temp in the 90's, with the sun beating down on it, spas can easily get near their 104 optimum temp with no extra heat input (dont forget using it increases its temp too as the spa's pump also heats it [friction] while its running, for scheduled filtration periods and in actual use). spas have an overheat cutout because of this.

[DeathAndTaxes]

For me, the answer to deal with the problem of "what do I do when the hot tub is already hot enough?" needs no valves: it is a software solution to simply lower the hash rate when the extra heat is not needed.  Given that the original purpose is to mine with free power, there is no point in using more power than the hot tub needs for heat because that power is no longer free.

That makes it real simple then, just a couple pumps, a heat exchanger and a temp sensor with communications to your computer to control it.

If you want to be cheap no need for temp sensor.  Just use temp sensor on the GPU and cgminer.  With sufficient flow on both sides of the heat exchanger the two loops will reach equilibrium within a few degrees of each other.  So if GPU are 50C then the hot tub may not be exactly 50C it might be 45C or 42C but it isn't going to be 80C or 20C.

[vapourminer]

If you want to be cheap no need for temp sensor.  Just use temp sensor on the GPU and cgminer.  With sufficient flow on both sides of the heat exchanger the two loops will reach equilibrium within a few degrees of each other.  So if GPU are 50C then the hot tub may not be exactly 50C it might be 45C or 42C but it isn't going to be 80C or 20C.

how long do you think you can dump a few kilowatts of heat into a 500 gallon insulated hottub (that already generates heat during its filter cycles even when its not in actual use with people)?

youre gonna throttle your farm down when the tubs at temp?

BTW hottubs are 104 F (40 C).

[MrTeal]

how long do you think you can dump a few kilowatts of heat into a 500 gallon insulated hottub (that already generates heat during its filter cycles even when its not in actual use with people)?

youre gonna throttle your farm down when the tubs at temp?

For me, the answer to deal with the problem of "what do I do when the hot tub is already hot enough?" needs no valves: it is a software solution to simply lower the hash rate when the extra heat is not needed.  Given that the original purpose is to mine with free power, there is no point in using more power than the hot tub needs for heat because that power is no longer free.