Best way to chill your loop with another liquid?

[flogge]

My house has ground-source heat and a hot water pre-heater built into the refrigeration unit. This system will dump heat from the AC system into a water loop from my hot-water heater, thus during the summer cooling season, I get some free hot water. Eventually I want to install a tankless on-demand water heater and use the current 40 gallon tank heater as a pre-heated storage tank.

This is where the CPU water cooling comes in. The copper lines running from the water heater to the heat pump unit pass directly under my office in the crawl space. I would like to cut into the cold side of that loop and cool my computer water loop with the cold water from the bottom of the pre-heat storage tank. This loop has a ~10W AC pump which is controlled by the heat pump, but I can cut into the wiring and control it myself as well as letting the heat pump turn it on.

I will have high-pressure(50-75 psi) water which I can control the flow of that should maintain temps of 50-90 Fahrenheit depending on the season, hot water use, etc. I have 2 options so far for transferring heat from the WC loop to the high-pressure water.

Option 1: Fish tank as a reservoir. high-pressure water runs through a car AC evaporator or condenser which is submerged in the fish tank. This has the benefit of simplicity and serves as my reservoir, but is bulky and prone to water evaporation and contamination.

Option 2: coiled annular tube heat exchanger. These are used in many of the heat pumps to transfer heat between 2 fluids. Basically its a copper tube inside a larger copper tube which is then sealed and coiled so that the 2 fluids are on either side of the inner copper tube wall but cannot mix. The keeps the system smaller. Most likely the exchanger will be the only thing outside the PC case.

http://sentry-equip.com/Products/dual-tube-coil-heat-exchanger.htm

Other options are welcome or observations about the ones I have here. I think during winter I can probably get some nice overclocks by pulling 50F water from the ground pipes, but the main goal here is to harvest the heat from my PC to get free hot water.

 

[vjcsmoke]

Interesting project... I'd go for the smaller solution. Besides fish tanks can get nasty if the water isn't cleaned regular. Do you really want to deal with that?

 

[entropist]

so, if you want to dive off a bit... set up a tec cooling plate between your wc loop and a circulated loop off your potable hot water tank. then you can pump some serious heat. Also, you can run whatever you like to kill algae in one loop and keep the other safe to drink...

 

[Archmage]

I like the Tube-in-Tube idea better.

Koolance has some plate fluid-to-fluid heat-exchangers: http://www.koolance.com/water-cooling/default.php?cPath=54_119

There are some bigger plate heat exchangers available if you look around.

I know I wouldn't feel so bad about using the power for sub-ambient cooling and multiple video cards if I recycled the heat. That's always nice to see.

 

[flogge]

The koolance plate Xchangers look pretty good, but I wonder if nooks and crannys inside would have any stagnation effects on the potable water. The tubular heat exchanger should be just like additional copper tubing. I'm not looking to dump huge amounts of heat in the water. My current usage is 900-1800 kwH/month depending on heat/cooling requirements, so if I dump 500W of heat into the water heater continuously, that would amount to 1/3 of my lowest month's usage for the whole house.

 

[flogge]

1/2" tubing 12 feet long would have a surface area of 1.57 sq feet with copper material. I think the larger koolance unit has about 2 sq feet of plate surface that is stainless steel. It is rated to move 4 kw at a 20C Delta. If I need to move 500W I should be able to maintain a Delta below 15C even if I cycle the pump off and on on the potable water side and try to get 1-2kW heat transfer while the pump is running. That should keep a good number of cores running in F@H or Boinc.

 

[Romir]

I used one of these brazed plate heat exchangers for my dedicated ground loop before deciding to directly connect into it. The turbulence created inside the plate HX make them more efficient than an surface area analysis would suggest. I wouldn't worry about stagnation, but if you have hard water, sediments can build up within these over time.

It seemed to work very well at load with the 5970 pulling at least 500w from the wall at 1.3v. At idle, my PC loop was also within 1c of the ground loop.

 

[flogge]

Good point on the turbulence. That might make a difference in the heat transfer. After crunching some numbers and looking at the amount of energy it takes to offset heat loss in a water heater, I'm going to have to put a radiator on the system as well, but I will use a thermostat to control the fans. I'm not going to get very low temps for the PC and still be able to harvest much heat for the water heater.

My order will be res-pump-CPUs/GPUS-liquid exchanger-radiator-res. 3 thermostats will be necessary to operate everything. Thermostat 1 will be on the inlet of the liquid exchanger on the PC loop, set at 40-45C. It will control the potable water pump. Thermostat 2 will be on the inlet to the liquid exchanger on teh potable water loop. It will be set to cut power to the pump if the incoming potable water exceeds a certain temp, maybe 35 C. This way my potable pump won't run forever with a low Delta C. This also avoids the possibility of the potable loop adding heat to the PC loop. The 3rd thermostat will be located at the radiator inlet and will turn on the fans if the loop exceeds 45-50C. I will get adjustable thermostats so I can modify my temp settings for different situations. During winter I might be able to do some nice OC runs with 15-20C water.