Dell Z620

[Antionette Eastin]

Customliquid cooling solutions can be difficult to specify, expensive, and refined proprietary workstation designs such as the HP z-series are resistent to subversion. This is logical as overclocking and changing the cooling could affect reliability and longevity as well as potentially make the system noisy and use more energy. Certainly, be especially careful of any upgrades of a system under warranty.

But, a dual 92mm fan version would cover the top PCIe slot cover. I could see that a single-fan radiator would work, but I could not find a closed loop liquid cooler with a single 92mm fan. These are all 120mm = too wide.

This is feasible as it would effecively extract from the entire rear panel openings in addition to the two 92mm case fans. Fabrication from 1/16" plexi should not be terribly difficult. The mounting panel is not shown in this model, which uses the same holes as the case mounting.

Notice that the z420 cooler has a special small diameter fan - it's just visible to the upper right, below the radiator. This directs downward air flow to the chipset- which is the same location on the very similar z420 and z620 boards. A nice little enhancement.

So, the cooler does project though the shroud downward side. There is a cubistic black plastic guard that protects the 2nd CPU riser visible to the lower left of the radiator, but there is plenty of clearance.

I was concerned that the air intake side vertical support for the shroud might somewhat impede the air flow into the fan, but the CPU temperatures with all eight cores at 4.1GHz at idle were very encouraging:

After some experimentation, using intel Extreme Tuning Utility, which had been very successful in April in the z420, I settled on running all cores of the E5-1680 v2 at 4.3GHz with the goal of having a Passmark Single Thread Mark of 2300:

This shows that during the Passmark test results posted above- by the way, the very long version, that the maximum Package temperature rose to a maximum of 63C and the maximum individual core temerature was 58C. This is quite comfortable for the E5-1680 v2, which is rated to 85C. A similar rendering run on z420_2 all cores at 4.1GHz using the standard fan /heatsink would see a Package maximum of 74-78C with individual core maximums at 65-71C- uncomfortable for the E5-1660 v2 rated to 72C.

These clock speeds and temoerature results are not in the league of our Forum friend Brian1965's z620 whose Tower of Cooling is so very-well, -cool, but in my variegated uses: 3D modeling, (architecture and industrial design), graphic design, simulation, and CPU rendering I think it's going to have very good performance and reliability. This z620 in effect replaces two systems: the z420_2 and z620_1 which has 2X Xeon E5-2690 8C@ 2.9/3.8GHz for CPU rendering. However, I discovered that the CPU rendering I use- VRay, is not epsecially good at running on two processors- the z420 E5-1660 v2 six core could be faster.

This is also a request that HP consider a liquid cooling option for all the Xeon E5 z-series. As the high core count + simultaneously high single-thread (= high clock speeds) performance race is on, there are some hot E5's in our future.

For anyone with the Z620 the fact that you verified that the Z420 liquid cooler fits without any modifications will no doubt be very helpful. This is a very good and clean no-fuss solution. The small fan cooling the VRM is definietly a welcome addition, since the Z420 / Z620 boards have no heatsinks on these components and when overclocking they get very hot.

The only potential thing that I would be concerned about is liquid evaporation over time as is the case in all AIO type units - but should that occur there are probably some methods of refilling / bleeding the unit and in any case at that price you could equally well just get another unit.

As for the push pull, for the second fan, I am thinking the easiest thing to do would be to just get a second HP CPU fan, or use the one from your air cooler and rig it up to the CPU PWM connector, where the first fan is located. At the ghetto level you could cut the connector of the second fan, strip the wires from under the cable insulation and insert these into the cpu plug connector of the first fan - attaching the connector to the motherboard would keep the cables in place. Obviously for the second fan you would just use the GND, 12V and PWM cables, the Tach signal would come from the first fan and since they are the same this would ensure proper PWM operation.

My idea of adding a second fan has been along the lines you mentioned, to make a splitter/ adapter for the 5-pin pump / fan motherboard connection out of the connector of the original fan /heatsink and mount the original CPU fan on a fabriated sheet metal, U-shaped bracket. The bracket makes a kind of clip under and over the radiator and has mounting holes for a CPU or case fan. The problems with this scheme is in making the brackets accurately enough in a metal gauge heavy enough for theaded mounting points. plus it needs to work on a correct spring tension- I can't drill into the radiator and don't want to solder to it. This kind of fabrication is difficult to achieve at home. I am also concerned at the power limits of the motherboard connector and whether splitting a PWM connection voltage will affect that control. I tried raising the cooler speed with the BIOS Thermal setting, but the liquid cooler went into RPM hunting- noisily speeding and slowing. This is the problem with modifications, each change upsets a hidden layer of design parameters.

I am still interested in that improving the thermal effieciency as the cooling is the limitation on clock speed. Our friend Brian1965 had spectacular results of a stable 4.7GHz - the highest clock speed of any HP z-series I've read, but required a cooling tower taller than the z620, drawn in Solidworks, and fabricated with a 2000W laser. Fantastic work, and the cooling capacity allowed a flirtation with 4.8GHz.

With my project, using the z420 liquid cooIer did allow a usable 4.5GHz but when running large test VRay renderings it was pushing a sustained 80C on several cores. Eventually, the 4.5GHz proved unstable when running multiple 3D CAD and photo editing programs simulataneously. Running at 80C+ is not impossible for the E5-1680 v2 which is rated to 85C , but I'm a believer in testing the limits and taking a step back - 4.3GHz is enough, epecially with a CPU that cost more than $1,700 new. Anyway, in a number of applications, the E5-1680 v2 runs at it's standard all-core speed of 3.4Ghz. The all-core speed limitation is the reason that the z420 E5-1660 v2 could run smaller renderings faster as it's all-core clock speed is 3.9GHz. the all-core speed is the reason that I considered moving the z420 E5-1660 v2 into the z620 as I ran it for a good while at 4.2 GHz on the standard fan/heatsink. With the liquid cooler, it may be possible to run it 4.4 or 4.5GHz and have a single thread rating over 2400.

Again, thank you for you interest in the project. This would not have happened at all if you hadn't mentioned in April the application of the Extreme Tuning Utility to some Xeon E5-1600 v2 series CPU's on proprietray systems.

For the fan bracket I think you are right that it will be difficult to devise a solution at home which will ensure a good fit (tight enough that it doesn't fall off, but not too tight so as not to cause vibrations) and which looks presentable / OEM like. The fan bracket idea, perhaps also adapting an exisitng one and bending / shaping it into place seems like a good one though.

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