Fan Curve on AIO

Steyn_ · November 22, 2018

Hello,

So I've recently setup my new system with an Corsair H150i to cool my cpu.

I've read somewhere that you should set up your fan curve for the water temperature, not the cpu temperature.

It sounds pretty logical, but is there any truth in this? And how much does it really matter?

I also would have no clue what temperatures to even aim for.

Any tips/insights would be very appreciated.

corrado33 · November 22, 2018

Water cooling likes to use the "delta T" stat. Delta T is simply the difference in temperature between the room temp and your water at the cool side of your rad.

For a CPU loop, people tend to shoot for less than 10 degrees C.

For a GPU loop, people tend to shoot for less than 15-20 degrees C.

So if the temperature in your room is 20C, you should set the fans at max speed when the water temp reaches 30C for a CPU loop.

That said, I don't water cool, and I just got this from reading stuff online and doing a lot of research. (Eventually decided against water cooling.)

Look at this graph.

Basically this plots how good certain coolers with certain fans work when you apply a certain load to it. So, say for example, you had the cooler described by the RED line. If your CPU was on that alone, it'd be around 100 W or up to 250 overclocked, your delta T would be between 2 degrees (for 100W) and ~5 C (for 250W).

So basically if you have your cpu and gpu in the loop, add their wattages, then find the curve for your cooler, and it'll tell you what sort of delta t to expect. Or, since those curves are hard to come by, simply run a stress test on your cpu and set the fans to max speed, then lower the speed and see how the temp changes. Eventually you'll find a noise to temp ratio you are comfortable with.

For Science! · November 22, 2018

1 hour ago, Steyn_ said:

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Yes, it makes sense to have your fans tied to the water temperature, in my opinion it is the only way to correctly set up a watercooling loop, especially if you have GPUs and CPUS in the same loop. The water is what transports the heat from the CPU to the radiator, and is thus reflective of the cooling potential of the loop.

For example, you may have an overclocked, non-delidded 7700K, and so the TIM is limiting the transfer, and so the CPU gets to 80 degrees under load. If you have a standard motherboard, this will ramp the fans to 100%, although the water is still cold and so there is no reason to. Only when the water starts to heat up, then you need to start ramping the fans. Controlling fan speed by the water temperature lets you take advantage of the large heat capacity of water to achieve much more gentle acoustic profiles than fans that go too fast too early.

Furthermore, the pumps such as the Asetek pump or DDC/D5 are rated to operated below 60 degrees, and so if the water temperature creeps to this point, you will be damaging the loop and so it is important to make sure there is something in place to directly control for this. There aren't many scenarios this may happen (CPU cold, but water hot) but its good practice to ensure there is a direct correlation between fan speed and water temperature.