Radiator Fan Orientation and Shroud Testing
Welcome to my fan/shroud testing. Over time I've heard
and seen a few experiements around fan orientation and shrouds, some
that were conflicting with others and before I spend too much time
testing more radiators, I figured it was time to put my own questions
to test and see what I can find out about things like fans pushing vs
pulling and shroud depth optimization.
First and formost since most users usually run just one set of fans and
you can place them on either side of the radiator, there is always the
question of which side? Do you install the fan on the side and
"Push" air through the radiator, or do you put it on the back side and
"Pull" air through like a vacuum? Users with experience with fans
and dust buildup quickly realise that the hub in the center of the fan
leaves a dead spot where very little air flows. You'll also
notice that this dead spot is worse when a fan is pushing air vs.
pulling air. Then there are shrouds, many people have reported
worthwhile improvements to installing shrouds on the radiator, but I'm
not sure there has been any clarity as to where the shrouds help or
what depth is optimal.
Before running these tests, I had always thought running fans in pull,
and adding a shroud is best. Better yet would be two fans in pull.
I based all of this on having witnessed the flow through the
radiator being much more distributed in pull (Less hub effect) as well
as the thought that removing the fan heat from getting into the
radiator is also good benefit to pull. I had also heard from
various forum sources that the best shroud depth would be several times
the diameter of the hub to help straighten out the air flow. Well now
that I had a radiator test bench setup, I figured it was time to put
some of these ideas to some testing.
Before I go too far, I'd like to thanks the following sponsors for making this test possible with sample products to use.
Radiator = XSPC RS120
A special thanks to Paul from XSPC for providing me with an
RS120 single radiator. The RS120 is an excellent radiator
specifically designed for low speed fans (21mm thickness with approximately a 13.0 FPI fin density). I particularly wanted
to do this tesing on a single radiator because it enables me to utilize
more fans and shrouds to test with, and I would expect to see similar
performance gains on other radiators as well.
Shrouds = The Feser Company (TFC) Shrouds
A special thanks to Martin from The Feser Company (TFC) for their new
universal shround. I'm really excited about this shroud because
for the first time we have a universal and stackable shroud that looks
great and fits on any 120mm fan radiator, these are very impressive and
sharp looking shrouds.
I utilized the same testing methodology as I do for my other radiator testing, you can refer to those details here under "Testing Specifications"
The only thing I did differently is change the fans from my
normal "Pull" to various push or pull or push/pull with different
shroud depths. The heat load was kept constant using a 120V 3amp
variac and dialing in one of my 300 watt water heaters to the desired amount of wattage. Fan RPM
was held constant in all tests rather than voltage as I used my
crystalfontz PWM controller which does a nice job at holding RPM very
constant and easily controlled by a slider.
So in the ead I did the same logging of temperatures for extended
periods of time to average out constant recordings typically over a
30minute period after at least a 30 minute warm up time frame (90minutes for the first warm up).
Then these tests were individually plotted to ensure stability in
the delta temperature and averaged and summarized.
A typical test run for one data point. Ambient temperature varies, but temperatures are continuously logged and averaged.
Test Results 38mm Single Fan, 2000RPM
Above is a look at the results
from a direct delta vs shroud depth. Very suprising to me, my
standard method of using the fans in pull is not the best. In
addition the common thought that the deeper the shroud, the better is also not
true, both push and pull benefitted the most from a single depth 30mm
shroud and push with one shroud yielded the best temperatures which was
about 1.9C better than a fan in pull as I had typically been using.
It's very apparent to me, the hub dead spot affect is only one
performance variable. The closer proximity of the fan blades is
also creating turbulence and additional efficiency closer to the
radiator, and there is also likely some benefit in push due to air's
ability to compress and increased density (improved thermal properties)
that's playing some role in these results.
Now to take these results and compare relative to the worst case (Pull No Shroud) to get some percentages:
We gained over a single fan pull as shown above, nearly 18.5% using push with one TFC shroud vs pull no shroud.
Or for pull, almost 16% using the shroud in pull vs. pull without shroud...very nice!!
It also appears the shroud depth of 30mm is nearly optimal in both push
and pull, this was obviously designed at this depth for good reason.
Conclusion for Single 38mm Fan - 2000 RPM
The obvious winner here is to use
a fan in a push condition if no shroud is used, which provides about a
9% gain, and better yet, a fan in push with one TFC shroud which is
approximately 30mm in depth. The fan in push with TFC shroud is
producing nearly a 19% gain over a fan in pull, that's a significant
gain! I would highly recommend the use of shrouds where you have
room to fit them. It's a very simple modification that results in
substantial radiator performance gains while reducing fan noise.
TFC Shroud = 10-16% More Performance & Less Fan Noise!!
Push/Pull Update Single 38mm Fan - 2000 RPM
I have also finshed a little
more testing with push/pull configurations with two fans. While I
don't think very many people actually run fans on both sides, it's
certainly an easy enough option. In the end, the push/pull
configurations was as expected better than either push or pull with a
single fan. In this scenario you gain the benefit of more fan
pressure and result in an increased amount of flow rate. I even
purposely adjusted the RPM of the fans to match 2000 again even though
running push/pull will have a tendency to increse the fans RPM slightly
at the same voltage. In addition I tested with shrouds again as
well and found the single 30mm thickness to be ideal once again.
You don't see quite the shroud gains as the single fan scenarios,
but still a worthwhile improvement considering you also get lower
noise. I found many folks have a hard time understand curve
charts, so this time I broke it down into a basic bar chart with mini
schematics of the fan setup to help clarify. Somewhat
suprisingly, you nearly get 2 fan performance with a single fan plus
Push/Push and Pull/Pull Update Single 38mm Fan - 2000 RPM
I had this whacky idea that
maybe running two fans on top of each other on either side would be
another viable option, so I tested that. Push/Push came out at 9.1C,
which is barely any better than just one fan in push. Pull/Pull came
out at 8.9C which a little better, but still not worthwhile.
Bottom line, if you want to run two fans, run one on either side of
the radiator in a push/pull configuration.
Push vs Pull vs Push/Shroud vs Pull/Shroud 25mm Fan - 1350 RPM
Now that we had the
stronger and larger hub 38mm testing done, it was time to do a few
quick tests to see if the trends continue with with slow speed fans.
In order to keep water deltas down a bit, I turned the heat down
arbitrarily to 150 watts total and proceeded and complete 4 more tests.
Note these tests were run at a reduced heat load of 150 watts.
Push vs Pull has now changed places, but shrouds still continue to
provide a good benefit, predominantly on the pull side similar to the
larger gain in pull with the 38mm testing.
didn't complete the full series of tests, this was enough for me to see
there is some emerging trends going on. The push vs. pull
question appears to really depend on the fan power. I believe the
gains in the 38mm showing more benefit in push is due to pressure and
turbulence. At these stronger speeds, the added pressure
compressing the air along with higher turbulence across the radiator in
push is providing the best benefit. This appears to change
however for the lower speed fan where pull actually does better.
I believe at this slower speed pressure and air flow is so slow
that it's simply not turbulent enough to show gain in push and the
radiator performs better with the more evenly distributed air flow over
the radiator that's provided in a pull condition.
TFC Shrouds and shrouds in general -
Always provide a good performance benefit and reduce noise at the same time. Highly recommended in all
radiator setups particularly for higher speed fans unless the space does not make them an option. You
can see as much as 10-16% gains on higher speed 38mm fans and 6%
gains with slow speed fans. Generally the higher the fan
speed and the larger the fan hub, the more gain you will see with
shrouds. Optimal depth appears to be somewhere around 30mm +-,
this is likely to depend on hub diameter and RPM to some extent.
Push Vs Pull
- This depends on fan speed/power. The high speed fans at 2000RPM
with a 38mm fan thickness provided the best performance in a push
condition. The slow speed fans with 1350RPM with a 25mm fan
thickness provided the best performance in a pull condition. I
would estimate that performance line is likely to cross in the
1500-1700RPM range where they are equal. So.... slow speed =
pull, high speed = push, medium speed = it doesn't really matter.
2 fans Push/Pull vs others
- It was very clear that when using two fans per radiator section, that
the radiator intself acts as a flow spreader and provided great benefit
to straightening out the air for the second fan in a push/pull
configuration. Just like doubling up with a pump, there is a
pressure benefit to doubling up on fans and this translates to about a
20-30% performance gain. The added fan pressure simply means and
added gain in air flow and corresponding performance. None of the
experimental pull/pull or push/push configurations provided any
noteworthy benefit as it seams the air is simply too disturbed from the
first fan to allow the second to perform properly when air is moving.
I would always recommend a push/pull configuration for two fans
and add a shroud to both sides if space allows.
I hope this was useful
information, again I'd like to thank my sponsors below. With out
their contribution in parts, this test couldn't happen...thanks!