Wednesday, May 6, 2015

House fan for vertical windows: DIY Version with 120mm fans!

I had a problem.  I solved a problem.  In extreme overkill form, as is right and proper.

The problem was that my office ran too hot in the summer.  It's on the southwest corner of the house, and has both a good southern exposure and a good western exposure.  Also, it's on the second floor.  And, finally, the house is poorly insulated.

Prevailing winds get me a bit of ventilation, but the direction of the wind will force the hot air from the office into the rest of the upstairs, and generally make the rest of the upstairs hot and miserable to be in.  This is not a good solution.

The last few summers, this led to the office being more or less uninhabitable in the afternoons.  Several times a year, I have to shut down computers because they've tripped thermal alarm setpoints and are beeping loudly about the heat.  I've lived with this, but this year, the ferrets are in the office, and they don't deal with high heat.  So, I set about finding a new solution.

The solution was to find a way to exhaust hot air from the office, against the prevailing winds (yes, I know, this is terrible, but... it was either that or move the office, so, I'm just fighting nature).

So I fought nature.  And, so far, am winning.

A common suggestion people had was to use box fans.  I've tried this, and it simply doesn't work well.  They have nearly no static pressure, and flail wildly at the air instead of moving it when they have to fight a little bit of wind.  There's also the problem of sealing up the space above them - it's hard to do this well.  The end result is a lot of noise, and very little useful airflow.

After some bouncing of ideas around the Ars forums, someone suggested using computer fans.  A little bit of research later, and this looked like a good idea to me!

Picking fans took some time.  I knew I wanted Deltas, as they make amazing fans, and I don't want to worry about this thing failing on me or requiring rebuilding.  My first thought was to go with the high RPM fans with stators - something like the Delta FFB1212EH-F00 or the Delta FFB1212EHE-F00.  Unfortunately, they're unreasonably loud - close to 60db (and a stack of them will be even louder).

I ended up going with 6x Delta AFC1212D-PWM fans.  They don't have stators, but are rated 113CFM at 46db, are ball bearing Deltas (which means they should last roughly the rest of my life), and don't draw too much current.

To fit my windows, I used some aluminum L angle stock.  The fans are 25mm thick, so I found some 80/20 Inc 25 Series 25mm x 25mm x 3mm Mill Finish Aluminum Angle Stock and ordered it.  The length of this is 1220mm, so I can fit almost exactly 10 fans on it.  I used 6 for my initial build.

I mounted the fans with 3M automotive double sided tape.  It's expensive, but it's a very high quality double sided foam tape, and it helps to damp the vibrations from the fans before they can use the window as a speaker.

The wiring comes out of the fans and into some wiring loom.  I used a blend of crimp butt joiners and side connectors to do the wiring, though I'd do it with exclusively butt joiners next time to make it cleaner.

 I'd also run the wiring out through the side of the bracket with grommets to clean up the lines slightly more.

Power is supplied with a commodity 10A 12v PSU from eBay.  I tried a 5A PSU, and despite drawing less than 5A, two different 5A supplies failed on me (either overheated badly or overheated and tripped a thermal breaker internally).  So... buyer beware, eBay PSUs from China won't run rated power.  Surprising roughly nobody.

The end result is an awesome set of blowers that fits in my window and exhausts somewhere around 600CFM - I have to fight the office door to close it when the fans are on, and it does a great job of drawing air through the house.

Downsides: It did cost about $200. :/

Build Parts List

1x 3M 5952 VHB Double-Sided Foam Tape - 1⁄2" x 36 yds @ $75 (I only used a fraction of it)
Assorted wiring, wire loom, connectors I had laying around: $10-ish

July 2015 Update

The fans have been working great!  Even with 95F Seattle heat (which is very unusual), the house is remaining habitable upstairs.  It's not as cool as one might like it, but it's not nearly as bad as previous years - server chassis heat alarms aren't going off, for one.

One addition since the original deployment is a standard lamp timer.  Turning the fans on automatically in the afternoon and off in the morning has been a huge improvement - I don't have to think about it anymore, and I don't inadvertently suck in hot 10AM air.

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