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Author Topic: Hot tub miners  (Read 5375 times)
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Mike Caldwell
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March 19, 2012, 08:53:59 PM
 #1

I had a random while reading about the development of ASICs and weighing the pros and cons of ASIC mining. It occurred to me that there are gigawatts of energy being consumed for heating hot tubs (of the outdoor style) and which, in most places, are heated year-round.

This last year I was mining.  Around the summer, I stopped mining because I believed it wasn't worth my time given the energy costs.  But about the same time, I decided to have my outdoor hot tub repaired (it came with the house when we moved in and I thought I'd finally give it a go).  I am guessing that the hot tub burns almost as much power keeping itself warm as my miners burned mining bitcoins because my power bill hasn't come down all that much.  (I had eight 5970's and four 5870's and calculated my usage to be 4kW).

I don't know how much money I spend on heating my hot tub, but I know it's a lot.

It occurred to me that if I could dump my mining heat into the hot tub, I would basically be getting free mining.

The only thing that stopped me was the hassle and opportunity cost of such a project.

That said, if there was such thing as a ready-made miner that I could strap on to my hot tub to dump the heat in there, it would be almost as good as free mining.

As I started this post, I mentioned ASIC mining.  ASIC mining is also relatively free.  But it is also, comparatively, "rocket science" compared to dumping heat into a hot tub.  It's expensive, and is vaporware at the moment.

If we are all clapping because "rocket scientists" are (hopefully) about to bring us free mining via ASICs, what about the thought of "joe the plumbers" bringing us free mining from Home Depot just by using some copper pipes to dump the mining heat somewhere where the heat is desired anyway?  If I felt that someone could deliver me and/or install a miner that heats my hot tub, and didn't look stupid-ass and wasn't loud, I would have no hesitation giving them a chunk of the proceeds of the power bill I was going to pay anyway.

And certainly I'm not the only person with a hot tub.



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March 19, 2012, 09:08:04 PM
 #2

I had a random while reading about the development of ASICs and weighing the pros and cons of ASIC mining. It occurred to me that there are gigawatts of energy being consumed for heating hot tubs (of the outdoor style) and which, in most places, are heated year-round.

This last year I was mining.  Around the summer, I stopped mining because I believed it wasn't worth my time given the energy costs.  But about the same time, I decided to have my outdoor hot tub repaired (it came with the house when we moved in and I thought I'd finally give it a go).  I am guessing that the hot tub burns almost as much power keeping itself warm as my miners burned mining bitcoins because my power bill hasn't come down all that much.  (I had eight 5970's and four 5870's and calculated my usage to be 4kW).

I don't know how much money I spend on heating my hot tub, but I know it's a lot.

It occurred to me that if I could dump my mining heat into the hot tub, I would basically be getting free mining.

The only thing that stopped me was the hassle and opportunity cost of such a project.

That said, if there was such thing as a ready-made miner that I could strap on to my hot tub to dump the heat in there, it would be almost as good as free mining.

As I started this post, I mentioned ASIC mining.  ASIC mining is also relatively free.  But it is also, comparatively, "rocket science" compared to dumping heat into a hot tub.  It's expensive, and is vaporware at the moment.

If we are all clapping because "rocket scientists" are (hopefully) about to bring us free mining via ASICs, what about the thought of "joe the plumbers" bringing us free mining from Home Depot just by using some copper pipes to dump the mining heat somewhere where the heat is desired anyway?  If I felt that someone could deliver me and/or install a miner that heats my hot tub, and didn't look stupid-ass and wasn't loud, I would have no hesitation giving them a chunk of the proceeds of the power bill I was going to pay anyway.

And certainly I'm not the only person with a hot tub.


I'm not a miner but I've given this a lot of thought. (Even before bitcoin, actually. My refridgerator is right next to my stove, exhausting excess heat while I'm paying for more electricity to heat the elements just an arm's reach away.)

Sadly, I don't have a solution for you.

Still around.
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March 19, 2012, 09:13:50 PM
 #3

This could potentially work. I run a water loop for my 5970s and the water temperature is around 40-45 Celsius. A quick Google search puts hot tub temperatures in the 38-40 Celsius range. So, with a simple PID controller you could use GPUs for the bulk heating requirement for a hot tub and have a smaller heating element attached to the PID controller to maintain the water temp at the comfort range you want. The ideal solution would be a water/water heat exchanger so that your waterblocks aren't exposed to whatever chemicals/bacteria reside in your hot tub.

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March 19, 2012, 09:16:43 PM
 #4

Watercooling is your only viable option.

You just need a water to water heat exchanger.  You will still need a water to air heat exchanger (radiator) "downstream" to remove the rest of the heat.  You need somewhere to dump "excess" BTUs.  Your hot tub can only take so many BTUs so the system can't rely on ONLY the hot tub as a heat sink.

One issue is that due to thermodynamics your hot tub will never be hotter than the coolant loop.  If you want your GPU running at 60C that means 130F to 140F hot tub.  If you are ok w/ 70C GPU you are looking at 140F-150F hot tub.

The issue is it isn't going to be (with current technology) cheap or maintenance free.  Water cooling will transfer essentially all the heat produced by the miners.  If you needed the heat anyways (to heat your hot tub, preheat your hot water heater, or warm your home) that energy cost is essentially free.  

That is the thought behind my watercooled server rack in the hardware section.  I don't have a hot tub but I intend to put a water-water heat exchanger on the cold water inlet of the hot water heater.  This should preheat the cold water entering the hot water heater from 60F to ~120F+ saving energy the hot water heater needs to expend.
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March 19, 2012, 09:19:28 PM
 #5

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.
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Gerald Davis


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March 19, 2012, 09:21:14 PM
 #6

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
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March 19, 2012, 09:22:06 PM
 #7

It would be smarter and more practical to just plug your watercooling loop into the main hot water system of your house. Then you'd at least get use out of it at all times (rather than only when you use the hot tub) and your hot water is typically around 50C which is good for computer use. Hot tubs tend to be a bit hotter depending on personal preference.

I'm not sure it is worth the plumbing effort but it would be fun to play around with. I prefer to just keep it simple and mine for waste heat in the winter. In the summer, I will shut down all mining.
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March 19, 2012, 09:28:08 PM
 #8

It would be smarter and more practical to just plug your watercooling loop into the main hot water system of your house. Then you'd at least get use out of it at all times (rather than only when you use the hot tub) and your hot water is typically around 50C which is good for computer use. Hot tubs tend to be a bit hotter depending on personal preference.

I'm not sure it is worth the plumbing effort but it would be fun to play around with. I prefer to just keep it simple and mine for waste heat in the winter. In the summer, I will shut down all mining.
The typical household water pressure is 70-100psi, way to much for available gpu water coolers.
You may be able to come up with a custom solution, milling the water blocks yourself, but that's what I call risky.

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Gerald Davis


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March 19, 2012, 09:29:27 PM
 #9

It would be smarter and more practical to just plug your watercooling loop into the main hot water system of your house. Then you'd at least get use out of it at all times (rather than only when you use the hot tub) and your hot water is typically around 50C which is good for computer use. Hot tubs tend to be a bit hotter depending on personal preference.

I'm not sure it is worth the plumbing effort but it would be fun to play around with. I prefer to just keep it simple and mine for waste heat in the winter. In the summer, I will shut down all mining.
The typical household water pressure is 70-100psi, way to much for available gpu water coolers.
You may be able to come up with a custom solution, milling the water blocks yourself, but that's what I call risky.

One word.  HEAT EXCHANGER.  Ok I lied it is two words.

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March 19, 2012, 09:31:39 PM
 #10

It would be smarter and more practical to just plug your watercooling loop into the main hot water system of your house. Then you'd at least get use out of it at all times (rather than only when you use the hot tub) and your hot water is typically around 50C which is good for computer use. Hot tubs tend to be a bit hotter depending on personal preference.

I'm not sure it is worth the plumbing effort but it would be fun to play around with. I prefer to just keep it simple and mine for waste heat in the winter. In the summer, I will shut down all mining.
The typical household water pressure is 70-100psi, way to much for available gpu water coolers.
You may be able to come up with a custom solution, milling the water blocks yourself, but that's what I call risky.

One word.  HEAT EXCHANGER.  Ok I lied it is two words.


Exactly what I was thinking, though I'd have to think a while as to where exactly I would tie it in.
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March 19, 2012, 09:33:09 PM
 #11

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.

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March 19, 2012, 09:38:07 PM
 #12

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


You could get the GPU input water back down close to ambient using a water/air heat exchanger after the hot tub, but in order to dump heat into the hot tub you'd need the water out of the GPU to be hotter than the water in the hot tub loop. If you keep your hot tub at 40C and his existing water temperature is around 40-45C, he would need a pretty big heat exchanger to dump any meaningful amount of heat into the tub with only a couple degrees deltaT.
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Gerald Davis


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March 19, 2012, 09:41:14 PM
 #13

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.
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Gerald Davis


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March 19, 2012, 09:42:25 PM
 #14

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


You could get the GPU input water back down close to ambient using a water/air heat exchanger after the hot tub, but in order to dump heat into the hot tub you'd need the water out of the GPU to be hotter than the water in the hot tub loop. If you keep your hot tub at 40C and his existing water temperature is around 40-45C, he would need a pretty big heat exchanger to dump any meaningful amount of heat into the tub with only a couple degrees deltaT.

Then run your GPUs a little hotter.  60C is nothing for a GPU.  60C vs 40C is more than enough Delta T.
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March 19, 2012, 09:44:01 PM
 #15

Well yeah, but isn't that what I said initially? Smiley
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March 19, 2012, 09:49:42 PM
 #16

Incidentally, I was looking at replacing my drain stack in my basement with a double output waste water heat exchanger to help recover some of the cost of heating water. I don't have a water setup, but it would be pretty trivial to implement a water loop into a system like that.
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March 19, 2012, 09:49:58 PM
 #17

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.

A heat exchanger indeed but not necessarily too big if you place the coil on the bottom of it link, casascius is on to something here.

Maybe we could use existent solar heat exchangers for hot tubs and and have it all installed in no time. The overall temperature would keep a constant level given the water surface with the ambient is far greater than a fan cooled radiator and you would have the water heated for free.

I suppose you already know that GPU water circuit can't be bothered with anything else than distilled water so a heat exchanger is the key part in doing all this.

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March 19, 2012, 09:54:24 PM
 #18

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

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.
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March 19, 2012, 10:02:32 PM
 #19

This opens the door for other things heat related as well.  I use my miners for heaters in the house.  Have not turned the furnace on in months and struggle to keep the house under 72 lol

I buy and sell GPUs, most 5850s and 7970s. 
jimzolorenzo@gmail.com  -- Make an offer.
http://myworld.ebay.com/i_buy_5850s  -- current inventory
I have a couple bare bone mining rigs for sale as well.

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March 19, 2012, 10:02:38 PM
 #20

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

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.

Yeah, I didn't mean that the hot tub would be only heat sink, just that the idea of heating the hot tub with excess GPU heat is sound. Even outside of other cooling for the GPUs, you'd probably need additional bypasses and controls to give you adjustment over the hot tub temperature.

Depending on where your GPUs are, you might even want to look into something like this.


GPUs --> Big Pump --> Hot tub heat exchanger --> Hot water tank cold input heat exchanger --> Cold water to shower heat exchanger --> Water/Air heat exchanger ---> back to GPUs

Run water/air exchanger fans on a temperature sensor so they turn off when not needed, and your GPU input temperature could very well be below ambient when you're taking a shower. Wink
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