Life Underwater: Thoughts on Liquid Cooling

One of the last things I did before coming to work for Corsair was a long, detailed article about my first venture into watercooling. Watercooling can be incredibly intimidating, but just like building a PC is for a neophyte, it can be easy to understand once you know the way the pieces fit together. Watercooling is also something near and dear to the hearts of those of us here at Corsair; our Hydro Series closed loop coolers are very popular, but our cases are also designed to effectively house custom loops.

What’s amusing is that in the process of learning about watercooling and even assembling your own loop, it’s very easy to forget about the cooling itself. We don’t really think about cooling capacity when we build a garden variety system using air coolers; we choose a cooler for the CPU, a case that has decent airflow, and then maybe we choose the variant of our video card or cards based on the custom cooler that it ships with. But key to all of this is that our cooling is all fundamentally separate; we’re sharing airflow, but that’s not something we think about a whole lot (though maybe we should).

A custom liquid cooling loop is a completely different animal. My personal loop runs in this sequence, which probably isn’t ideal, but is definitely the most practical:

• Chipset (Z87, power circuitry, and PLX switch)
• Intel Core i7-4770K ES @ 4.5GHz, 1.24V
• GeForce GTX 780 @ 1.15GHz core, 7GHz GDDR5
• Second GeForce GTX 780 @ 1.15GHz core, 7GHz GDDR5
• 360mm radiator with six SP120 Quiet Edition PWM fans in push-pull
• Pump and reservoir
• 240mm radiator with two SP120 Quiet Edition PWM fans
• …and back to the chipset

You could argue that it’s essentially aggregating heat and then dissipating it in batches, but remember that water has a tremendous heat capacity; it takes a lot of heat to raise coolant temperature significantly. It’s also very easy to grossly overestimate the amount of radiator cooling capacity you actually require, though a key benefit of watercooling is being able to take a specific amount of heat and spread it out across as much surface area as possible.

Now here’s what’s easy to forget and where it gets tricky: in an air cooled system, component temperatures are primarily governed by their individual cooling. In a watercooled system, however, you’re sharing cooling capacity between all of your components. That cooling capacity is also governed by how rapidly your loop dissipates heat, which is in turn governed by the airflow pouring through the radiators but also by the flow rate of your pump. This isn’t something you actively have to calculate (although many forum members certainly do), but it is something you’ll experience.

When stress testing my system early on, I found that I could get my CPU overclock to a certain range, and I could get my GPU overclocks to a certain range, but if I tested them simultaneously heat became a tremendous issue. This was due to fan speeds and flow rate being too low; once I adjusted the pump speed and tweaked the fans, things went a lot more smoothly.

I do think it’s important to note that custom liquid cooling loops are really only useful for cooling GPUs anymore, though. The CPU can be handled just fine by a closed loop cooler; a Hydro Series H110 is going to be hard to beat without switching to something much more exotic. But remember that a CPU has a much higher heat density than a high end graphics card and has TIM and a heatspreader to transfer heat through before it gets to the waterblock; a GPU will have lower heat density since high-end GPUs are often substantially larger than CPU dies are, and will be making direct contact with the waterblock. Heat transfer is fast and efficient off of a GPU into a loop. In my experience, a liquid cooling loop can actually slash GPU load temperatures in half or better. With all that said, if you’re going to watercool the graphics cards, there’s no real reason not to include the CPU in the loop.

Ultimately I find working with liquid cooling to be interesting because of the way it can radically change not just your approach to cooling your system, but your entire mode of thinking. Tightly unified cooling capacity is a game-changer, but being able to share that capacity can improve efficiency; alternatively, being able to offer a surfeit of cooling capacity can keep both thermals and noise down. The thermal control a custom loop can offer is tough to beat and a fascinating challenge for the curious enthusiast.