Ben Whittle’s Uber Computer Update – Cooling and Airflow

Ben realised that as the Uber Computer is designed to be used in a bedroom where there is lots of dust, it is very important that all of the air intakes are filtered to prevent dust entering the compartments where the components will be. All of the components being visible through the top of the desk would not only be bad for looks, but having to clean it regularly would be a nightmare, as the only way into the compartments once the desk is built will be to remove the glass.

The high performance components will generate a lot of heat so good airflow through the main compartment is vital. Unfortunately the addition of filters restricts the airflow and may even require the use of a slightly different fan design to the standard fans just used to generate airflow. To help combat this Ben will be using 4 120mm fans mounted at the front of the desk which will suck air in through a single front mounted 480mm filter. The air will then be channelled to flow over the motherboard and other components and then through the vents in the expansion slots.

It really helps that most high end graphics cards generally intake from the air inside the chassis and exhaust through a vent in the expansion slot bracket as seen below:

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The graphics cards will be getting fresh air drawn from the front of the desk and the cooling design of the cards means that it will complement the airflow design quite nicely. The only other expansion card Ben plans to install will be the NVMe based storage, these are rarely fan cooled but they usually do come with a fairly chunky heatsink. He has vented blanking plates to install in the empty slots which will provide more than enough airflow around this card to provide adequate cooling.

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So the idea of the front intake fans is to generate airflow, but will a standard fan do the trick when mounted with a filter attached generating resistance? or will this require the use of a static pressure design? Only one way to find out…

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After testing both fans with the filter mounted Ben was very surprised by how much of a difference the static pressure design makes when it comes to forcing air through a filter or radiator. The fan designed to generate airflow clearly projects the air further than the static pressure model as you would expect. When the filter is mounted to the standard fan you can barely feel any air on the other side of the filter, with the static pressure model airflow is only slightly reduced on the other side of the filter. Static pressure fans it is then!

Thermal Management

Traditionally computer fans always had 3 pins in the connector, a ground, supply and tach signal for monitoring speed. Some motherboards were able to control the speed of the fans but only by varying the voltage/current available on that particular fan header until the fan reached the desired rotation speed. More modern fans receive a constant voltage and the rotation speed is determined via an on-board speed controller using pulse width modulation sent down a 4th wire.

As all of Ben’s intake fans are facing the same direction he sees having to set an RPM/temperature curve for each one individually as an unnecessary inconvenience. As the speed control signal is only one way and the rotation speed is still sent back down a separate wire his hope is that he will be able to link the PWM wire of all 4 fans together and control them all together, while still being able to monitor the speeds of each fan individually by connecting the tach wire to the relevant pin on the motherboards other fan headers.

The success of this is highly dependent on how the motherboard behaves if it realizes that individual PWM signals are making no difference to the fans rotation speed. At this stage the board may assume the fans connected are standard 3-pin fans and revert to the old way of controlling them and adjust the output voltage and current. If this happens he will have to supply 12v directly from the power supply in order for the fans to all receive a consistent current. Ben may have to give up on the idea of monitoring individual fan speeds altogether if it causes undesired results in the management software. This wouldn’t be a particularly big issue anyway, if a fan did fail there are four in a row and all of the temperatures are still monitored so there is no risk of failure due to overheating.

Ben says he will almost certainly be using an Asus motherboard in this system and he has found the options for fan control and thermal management on these boards to be plentiful to say the least. Ben’s current system allows him to set a RPM/temperature curve for each individual fan based on a fan and sensor combination of your choice, a very versatile system which allows you to have a virtually silent system under light load and a well cooled system under heavy load. The system works flawlessly in a standard build but to figure out how well it will behave in this more bespoke applications he will have to experiment a little.

Stay tuned for more Uber Computer updates.

 

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