The Fractal Design Celsius S24 & S36 AIO Coolers Review

Testing Results, Low Fan Speed

Before dissecting our low fan speed results, we should begin by noting that the design of the Celsius AIO coolers suggests that the fans will be powered by the cooler itself, from the hub on the radiator. With the whole assembly powered by a single cable, applying any fan speed control to the cooler will also affect the liquid pump as well. This particular pump does not react properly to a reduced voltage input, essentially requiring PWM control. Using a PWM voltage regulator, we reduced the speed of both kits down to their minimum operating point, which brought the speed of the fans down to 550-560 RPM.

The thermal performance of the Celsius kits with their fans and pumps driven down to minimum speed produced some very interesting results. Individually, the Celsius S24 displayed comparatively good thermal performance in conjunction with exceptionally low noise levels. The average thermal resistance of 0.1154 °C/W is mediocre when compared to that of other similarly sized coolers, but the sound pressure reading of 32.1 dB(A) is the lowest that we have recorded up to this date. Other recently released products could possibly rival the acoustics performance of the Celsius S24 if both the fans and the pump were driven via PWM controllers, but the Celsius series offers the convenience of concurrently driving everything via a single PWM signal/cable.

However, the reduction of the pump’s speed alongside with the fans does not work as well for the larger version of the Celsius. The Celsius S36 not only did not perform significantly better than the S24 during this test, but it actually performed worse, especially at low load levels. Our assumption is that the small ceramic pump is not powerful enough to have its speed reduced that much and still be able to cope with the resistance of such a large radiator, meaning that the liquid flow was lowered to the point that outweighed the benefit of the greater heat exchange area. Regardless of equipment, measuring the flow without interfering with the factory configuration was all but impossible, so we cannot currently put our theory to the test. Nonetheless, irrespectively of the correct answer, the fact is that the Celsius S24 performs better than the large S36 with the speed of the pump and fans down to their minimum setting.