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Author Topic: (Updated w/ pics) Watercooled Rack of Servers - 50% completed  (Read 9831 times)
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Gerald Davis


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April 26, 2012, 04:31:02 AM
 #21

Let's say you preheat your water. You got 6kw of constant heat coming. Your water boiler doesn't heat the water constantly but just when it's temperature drops below a certain limit(when you use water). What happens to your excess heat? You don't plan on leaving your tap water running do you? Tongue

I guess it needs some kind of fancy temperature controlled bypass valve.

gpu loop ----> water 2 water heat exchanger ----> radiator ---> back to gpu loop

whatever heat isn't dumped into cold line of hot water heater is dumped into radiator.  Dumping the energy into hot water heater isn't necessary for cooling, I sized the radiator to handle 6 KW of heat even in 100F ambient temps.  However it is "free" energy.  Given the choice between heating the outside air or heating my hot water (and saving $300 per year)  will take the later. Smiley
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Gerald Davis


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April 26, 2012, 04:39:54 AM
 #22

In a closed up, that wont work well at all.

A simple solution is to have a by pass valve.

I would even use manual by pass valve : use both radiator and exchanger during the day, and only use radiator over night.

Why wouldn't it work well?  I have already tested it. 

Cold side has 60F flowing @ 2 gpm.  Hot side has 140F water flowing @ 10 gpm.  More than enough Delta T.

Remember this is a hot water PRE-heater  The cold side has cold inlet water.  The hotside transfers heat to the water BEFORE it goes into hot water heater tank.  IF water isn't flowing there is no heat transfer.

Not sure what by pass valve and only using radiator over night would accomplish.

 
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April 26, 2012, 04:50:41 AM
 #23

I have a high pressure pump on my LC rig, and I found that when a tiny leak appeared, I lost the card. I shifted the pump to after the cards, thus creating a negative pressure where the cards were. Now if a leak were to occur, I'd simply be suckin in air, rather than forcing out coolant.

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Gerald Davis


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April 26, 2012, 04:56:34 AM
 #24

I have a high pressure pump on my LC rig, and I found that when a tiny leak appeared, I lost the card. I shifted the pump to after the cards, thus creating a negative pressure where the cards were. Now if a leak were to occur, I'd simply be suckin in air, rather than forcing out coolant.

That may be a good idea.  Cetrifugal pumps tend to have poor suction so if a small leak did develop the flow would drop way down once enough air is sucked into the system and that would trip the flow sensor shutting everything down.  I might need to think about moving the pump.
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April 26, 2012, 04:59:10 AM
 #25

I have a high pressure pump on my LC rig, and I found that when a tiny leak appeared, I lost the card. I shifted the pump to after the cards, thus creating a negative pressure where the cards were. Now if a leak were to occur, I'd simply be suckin in air, rather than forcing out coolant.

That may be a good idea.  Cetrifugal pumps tend to have poor suction so if a small leak did develop the flow would drop way down once enough air is sucked into the system and that would trip the flow sensor shutting everything down.  I might need to think about moving the pump.

A shutdown sure beats a fried card.

Need and water blocks for 5870's?

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April 26, 2012, 05:00:44 AM
 #26

P.s. Snag some pix of the innards.

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Gerald Davis


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April 26, 2012, 05:14:25 AM
 #27

I have a high pressure pump on my LC rig, and I found that when a tiny leak appeared, I lost the card. I shifted the pump to after the cards, thus creating a negative pressure where the cards were. Now if a leak were to occur, I'd simply be suckin in air, rather than forcing out coolant.

In a close loop, there is no such thing negative or positive pressure. Its a sealed volume.


Once you have a leak it isn't a closed loop. Smiley
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Gerald Davis


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April 26, 2012, 05:15:29 AM
 #28

P.s. Snag some pix of the innards.

Will do.  Don't one to pull the existing rigs out of the rack but I will be building/converting rig #4 this weekend.  Will snap some shots.
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April 26, 2012, 05:18:10 AM
 #29

In a closed up, that wont work well at all.

A simple solution is to have a by pass valve.

I would even use manual by pass valve : use both radiator and exchanger during the day, and only use radiator over night.

Why wouldn't it work well?  I have already tested it. 

Cold side has 60F flowing @ 2 gpm.  Hot side has 140F water flowing @ 10 gpm.  More than enough Delta T.

Remember this is a hot water PRE-heater  The cold side has cold inlet water.  The hotside transfers heat to the water BEFORE it goes into hot water heater tank.  IF water isn't flowing there is no heat transfer.

Not sure what by pass valve and only using radiator over night would accomplish.

 

The by pass valve was to decrease the water volume. As your preheater line stands still, it hold excess heat that would transfer back to your watercooling loop having your radiator works harder.

During the day, not much of the problem. Obviously the best solution is to have a controlled by pass vale to bring the most efficiency.


I get what you are saying now but remember heat only flows from hotter side to cooler side.

The cold water line will never be hotter than the hot loop (loop carrying GPU waste heat).  At worst it will be the same temp (Delta T = 0) and there will be no heat flow. 

So water is flowing on cold water inlet to hot water heater heat will be transfered from hot loop to cold water raising its temp (and saving me energy).  When hot water is shut off, the water in line will reach equilibrium with hot loop and heat transfer stops.
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April 26, 2012, 12:40:50 PM
 #30

I have a strong feel to drop that radiator into a lake during summer  Grin

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Gerald Davis


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April 26, 2012, 02:52:16 PM
 #31

I completely understand what you're saying. I assumed the hot loop would actually get colder than the preheater side at night (thus cooling more volume = more energy). Are you planning to have the radiator outside?

Yeah the radiator will be outside but my goal is to maximize the amount of energy "harvested" for heating water so the loop is

GPU (heat source)   ---> water2water exchanger (preheater) -----> radiator (outside) ----> coolant back to GPUs.

Quote
Btw, if you're doing this, are you gonna build the exchanger? I figure it would be similar with the exchanger using in a TEC chilled watercooling rig (pressure loss is huge tho)

I will be using flat plate heat exchanger.
You can reduce pressure loss by using more plates.

http://www.brazetek.com/brazed-plate-heat-exchangers

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April 26, 2012, 04:42:12 PM
 #32

these plate heat exchangers sound like a good plan in theory. A couple of questions rises though. Are they capable of handling the water pressure in your cold water line and do they have enough flow? ...okay you said you could put a few in but still. You only run hot water like 0.1% of a day, double or triple that if you got a wife. So during that time you could save money. My point being that you would actually have to ditch that water boiler all together and build a custom water boiler that constantly circulates the boiler water through your heat exchanger to have any kind of hope to save money. Your water boiler is still going to keep that water heated during that 99.9% of the day Wink

House heating during winter times would yield a lot better ROI IMHO.

Oh and another thing I thought about. What is the temp that your pump can take(if you are considering moving it to the other side)? What will it do to its life span? I'd say the water coming from your 24 GPU rig will be burning hot. Your tubes will melt Wink

If you think my comments have benefitted you it would be nice to hear thanks Smiley

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Gerald Davis


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April 26, 2012, 05:20:58 PM
 #33

For high efficiency water heater standing losses are less than 20%.  So if you use x BTUs of energy per day/week/month/year 0.8x is heating up cold water and only 0.2x (or less) is keeping that water hot.

I use about ~$300 per year in hot water so lets assume that is ~$240 toward heating up water, and $60 towards keeping it hot.  Heat exchanger should be able to preheat 60F water to >120F for "free" using the waste heat of the GPU loop.

Sure having a custom built hot water heater with an internal water to water heat exchanger and bypass valve and backup heat source would provide even better efficiency but it also would cost a LOT more, and provide only a marginal increase in savings.

So:
spending $80 on heat exchanger (+ parts &  labor) = recovery 80%-90% of energy costs
vs
spending $1500 on new custom hot water heater (+ parts & a lot more labor = recovery 90% - 100% of energy cost.

Simply put using heat exchanger as a pre-heater is "good enough" and provides a much higher ROI%.  Another way to look at it is every BTU of energy dumped into the cold water line is a BTU the hot water heater doesn't need to expend.  "Free" BTUs vs paid BTUs.


Regarding pressure & flow.  Flat plate exchangers they can handle much greater pressure than home water systems.  They are often used in industrial cooling applications.  Those brazetek models have burst rating of 400 psi.  They make them in all sizes able to handle 10gpm up to 100gpm+ at various pressure losses. 
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April 26, 2012, 05:30:34 PM
 #34

Hi,
I have a similar setup, with 12 cards (9 5970 and 4 5870) working flowlessly for about 1 year.  The diferrence is that I ran them in series. I'm using a Koolance heat exchanger connected to the cold water line. Will soon add 5 more cards.

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Gerald Davis


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April 26, 2012, 05:37:07 PM
 #35

Hi,
I have a similar setup, with 12 cards (9 5970 and 4 5870) working flowlesly for about 1 year.  The diferrence is that I ran them in series. I'm using a Koolance heat exchanger connected to the cold water line. Will soon add 5 more cards.


Awesome.  First I have heard of anyone else doing this.
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April 26, 2012, 05:42:15 PM
 #36

Yeah, the heat was driving me insane last summer.

Hi,
I have a similar setup, with 12 cards (9 5970 and 4 5870) working flowlesly for about 1 year.  The diferrence is that I ran them in series. I'm using a Koolance heat exchanger connected to the cold water line. Will soon add 5 more cards.


Awesome.  First I have heard of anyone else doing this.

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April 26, 2012, 06:00:51 PM
 #37

Connecting the loops in series would allow higher temps to be dumped into the heat exchager right? The higher delta T the better. But it also means that your rigs run hotter or at least some of them do. Which might create more energy consumption due to the worse switching efficiency of higher temps on GPU.

If you think my comments have benefitted you it would be nice to hear thanks Smiley

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April 26, 2012, 06:12:39 PM
 #38

Yes, you right. First card is at 20C last at 40C. To lower the temperatures I can increase the cold water debit, but I want to keep the noise down.

Connecting the loops in series would allow higher temps to be dumped into the heat exchager right? The higher delta T the better. But it also means that your rigs run hotter or at least some of them do. Which might create more energy consumption due to the worse switching efficiency of higher temps on GPU.

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April 26, 2012, 06:22:31 PM
 #39

I have a high pressure pump on my LC rig, and I found that when a tiny leak appeared, I lost the card. I shifted the pump to after the cards, thus creating a negative pressure where the cards were. Now if a leak were to occur, I'd simply be suckin in air, rather than forcing out coolant.

In a close loop, there is no such thing negative or positive pressure. Its a sealed volume.


Once you have a leak it isn't a closed loop. Smiley

Besides, restrict the water flow in your closed loop (such as running it through a water block compared to 1 inch hose), and you can bet your ass you'll have negative and positive pressure on either side of the restriction.

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April 27, 2012, 01:37:47 AM
 #40

AH, yours is a sealed system? MY system has the overflow tank, thus there is a positive and negative pressure. Thus if air enters from the suction, it's released in the overflow tank.

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