I get inspired by a lot of things. Sometimes I’m inspired by idiotic and impractical things just because I find them fascinating and I want to apply the logic in more reasonable scenarios. After watching the Linus Tech Tips series Whole Room Water Cooling Project I started thinking about impractical ways to water cool my own system while keeping it as quiet as possible. For some reason I decided on using a fish tank to act as both a reservoir and passive radiator, relying on convection and evaporation to provide a powerful one-two punch of cooling.
Instead of jumping into the deep end I started with a very simple setup, opting to cool only the CPU since I wasn’t sure exactly how effective the tank would cool the water. The loop starts in the tank, flows through a water-feature pump submerged in the tank, though a soft tube to the water block, then back into the tank. The dimensions of the tank where a huge unknown since the volume determined how long the water would take to heat up and the surface area would determine it’s cooling characteristics. After a lot of research and goofing around in Excel I came up with this chart to determine how long it would take to heat a given volume of water with various heat loads (that is, how many components I added to the cooling loop and if they’re at idle or full load).
The processor I was using at the time, an AMD Phenom II X4 965, had a maximum heat output of 140 watts. Given that, we can use a range of tank sizes to determine how long it would take to heat the water. For example, it would take 6.6 hours to raise 10 gallons of water 30 degrees Fahrenheit, or from a normal room temperature to around 100 degrees, my target maximum water temperature. Given that a 100% workload across all four CPU cores for over 6 hours is not a reasonable workload I figured this was a good size, providing cooling under a worst-case scenario.
What the chart above doesn’t take into account is cooling; it only addresses heating the water. This system has essentially three sources of cooling: radiation through the sides of the container, surface radiation, and evaporation. Based on testing I did the tank was able to radiate 48-70 watts, depending on temperature, through the glass sides when the top was sealed. According to this chart a 30 degree Fahrenheit difference between water temperature and ambient temperature produces 130 watts of cooling per square foot. However, the tank I’m using has a surface area of 1.2 square feet, producing a total heat loss of 156 watts. That puts our total at 204~226 watts of cooling meaning the water should never actually reach 30 degrees above ambient. So far everything looks good, but how does it work in practice?
To test the real cooling performance of this system I ran Prime95 for five hours then let it idle overnight (I didn’t take measurements while I was asleep so there are no data points). We can see the average difference between CPU temperature and water temperature is 9.2 degrees Celsius which has more to do with the water block’s performance than anything. More importantly, the peak CPU temperature came in at 38 degrees Celsius. To put that in perspective, on the all-in-one water cooling solution that was previously on this same CPU I was seeing temperatures in the high 50s under gaming load which is much less stressful than Prime95 and on standard air cooling you might see high 60s, low 70s, or even higher if you’re overclocking. Compared to that, 38 degrees is absolutely frigid.
At this point we know it works both on paper and in practice, but what is it like to live with? Let’s start with the bad parts.
It isn’t silent. Seems insane for a passive system but it really isn’t that simple. It’s quiet, sure, but only sometimes. The pump is cheap and meant to be used outdoors. The pump itself vibrates, meaning I can’t use its suction cup feet to mount to to the walls of floor of the tank as pictured above because it transfers that vibration straight to the glass and into the room. My solution has been to position it so that it sort of floats in the water, not contacting anything but the water. It still makes sound but you really only hear it when the rest of the system is off. Speaking of which, there are still other system components that generate noise. The biggest offender was my dual GTX 560 Ti SLi setup which, under load, sounded like four jet engines in a screaming match. When those were idle the case fans are the source of noise. Not much, but when the rest of the system is so quiet little noises become moderate noises. Basically by removing the one fan cooling my CPU I did little if anything to quiet the rest of my system down at all.
With evaporation being responsible for half my system cooling a lot of water evaporates. It takes a long time but the occasional trips to the drug store for more distilled water are a bit inconvenient. Summer time makes the system operate at a higher overall temperature, too, which increases the evaporation that much more.
It’s not all that pretty. I had bought the blue glass rocks to spice up the tank and had some plans to make it look nicer but I just never bothered. It takes up a huge amount of space and cleaning it between refills isn’t fun.
It’s not all bad, though, the cooling performance is insane and it cost half of what a typical water cooling loop would. In all this system should cost around $130 USD which is about the price of a radiator and reservoir alone.
If your goal is silent computing this isn’t the way to go. High quality air cooling can do much better with little to no maintenance. Traditional water cooling loops can achieve similar performance with quieter results assuming you’ve invested in high quality fans. That said, if your goal is to build a cheap water cooling loop that works well then I can’t think of a better solution.