Thresholds in computing: Part 7 – ITX cooling

(Part 7 in a series of posts on small-form-factor computing)

Previously on Thresholds in computing, we crossed the 120W threshold and shrunk the PSU to picoPSU-size, leaving CPU cooling to be the main factor in determining case size.

More than a year ago, I bought a Realan E-Q6 ITX case, walking my talk and trying to see what it is like, shoehorning a high-end quad-core setup into such a tiny case. I’d tried this earlier, in a previous post on PSU efficiency, but I don’t have the power meter I used to make those measurements any more, and my setup has changed a bit since then. I didn’t actually use a picoPSU, but the 120W LR1005 PSU bundled with the case is about equivalent.

Another thing to note: I am not a hardware reviewer, and don’t make it a point to keep static setups that I can use to assess the performance of various coolers that I come across. All I’m using is lm_sensors reporting and a power meter acquired off eBay.

Temperatures #

My initial setup was an i7-3770K cooled by a cheap PCCooler S85 (ultra low profile coolers are really hard to come by). These coolers are generically known as 1U coolers (from the 1U rack unit form factor used in rack servers), and are ~28mm (1.1″) tall. That makes them no taller than the height of the ITX backplane (where the connection ports are).

Realan E-Q6, i7-3770K, PCCooler S85 – front view
Realan E-Q6, i7-3770K, PCCooler S85 – front view

Realan E-Q6, i7-3770K, PCCooler S85 – top view
Realan E-Q6, i7-3770K, PCCooler S85 – top view

The results aren’t surprising—more than 90°C at load, and 50°C idle. Even with high ambient temperatures of 30°C, that’s still a pretty hot setup. I tried lowering the long-duration TDP settings to 55W in BIOS (anything lower seemed to produce no effect), with some effect: it took longer for the desktop to hit 90°C, but it still managed to do so anyway.

There were other heat-related problems as well. The memory modules were situated right next to the heatsink, so when the CPU is under load it blows hot air directly onto them, which is never a good thing. The SSD was situated immediately to the right of the CPU as well, and quickly hit temperatures of 55°C during video encoding or gaming. Definitely not conducive for system longevity.

E-Q6 v2 #

Inspired by the Steam Machine beta kit, I went and got the same cooler used in that setup—a Zalman CNPS2X.

Zalman CNPS2X
Zalman CNPS2X CPU cooler

I made a custom shroud for airflow control as well.

Zalman CNPS2X, with shroud
Zalman CNPS2X, with shroud

The shroud isolates the memory modules (not visible above, but there is a piece of corrugated cardboard between the CPU and memory), so that they do not heat up as much. The extension to the right isolates the SSD, so that airflow from the heatsink does not come into direct contact with the SSD.

Intake air is further separated from warm exhaust (which exits mainly from the left and right side vents) by the top mounting plate. this mounting plate also holds the SSD.

Zalman CNPS2X, with mounting plate placed
Zalman CNPS2X, with mounting plate placed

I had earlier custom-modded the case to add an intake vent at the top; the case is originally fully covered at the top otherwise. The intake holes are still kind of small though; this could definitely use some improvement.

Realan E-Q6, covered
Realan E-Q6, covered

With these modifications, the system now idles at 47°C, and the SSD is running ~4°C cooler at idle as well. At load, the SSD peaks at 44°C, while the CPU now very slowly reaches 90°C and hovers around there. Definitely still far from ideal, but this is to be expected from a 77W desktop CPU, even with the TDP settings artificially lowered in BIOS.

Same performance, lower power #

Right now I would be happy to stay at i7-3770 levels of performance while watching TDP and power consumption drop with each processor generation—the additional 10–20% performance boost doesn’t make my desktop feel any faster, when most tasks I do are limited by storage and networking latency instead.

The 65W i7-4770R compares favourably to the 84W i7-4770K, dropping TDP more than 20% in exchange for a 5% hit in multithreaded performance. This still puts it ahead of the previous-generation i7-3770K though. Power consumption numbers are good as well. The Gigabyte Brix Pro, using that same processor, idles at 15W and peaks at 88W.

With lower-power CPUs, such as the T-model CPUs, such a tiny build is likely to be feasible. Unfortunately, performance comparisons between the i7-4770K and i7-4770T are almost impossible to find, so it’s hard to know how much of a performance hit we’ll take from that. But it’s exciting to think that with each generation we can get better performance with lower power consumption, in this same tiny case. All we need is a better way to handle case cooling now… we are largely constrained by mechanical factors here (cooling fans and heatsinks), and unfortunately these do not scale impressively with each generation.

On to Thresholds in computing: Part 8 – Thin-ITX vs Mini-ITX

See also

Thresholds in computing: Part 6 – How much power does a desktop need?