Cool Walls

On the wall now near desks are plates with power and ethernet (and phone until VoIP takes over.) I’ve been wondering if we shouldn’t add another jack — air, and plumb our walls with pipes to move air for cooling electronic devices.

This idea started by reading about a guy who attached a plastic vent hose from the output of his PC fan to a hole he cut in his wall. This directs much of the heat and some of the noise into the wall and up to the attic.

I started wondering, shouldn’t we deliberately plumb our houses to cool our devices? And even more, our office buildings? And can we put the blowers at the other end of the pipes, to move the noise away from our devices? How much would we save on air conditioning?

Read on…

Aside from the vent described above, which would lead outside in the summer and cut AC costs, the choice seems to be suck or blow, or perhaps both.

At first, suck seems the obvious choice, since on hot days, we would suck the hot air away from the devices and save the cost of air conditioning to take the heat out the hard way. Back of envelope numbers suggest this doesn’t pay for itself in AC savings except perhaps in server rooms, but the silent PC aspect may make it worth it.

Sucking — in a system similar to central vacuum cleaners — requires internal pipes that are solid enough to not collapse under the negative pressure, and appropriate valves on the wall jacks to keep a good seal. Today most PC and power supply fans blow out, which is similar to what the sucking pipe would do. A sucking system will suck in debris and dust and must deal with that. When it’s hot, sucked air would be vented outside. When it’s cold, it would be recirculated (or vented through a heat exchanger.)

Blowing, on the other hand, can be done with a cheaper pipe and possibly simpler valves. However, a blown air feed can also be directed to multiple places in the PC, so you could have some of the pressure blow on the CPU heat sink, graphics chips and drives. I am not sure if suction could do this as well, meaning you would still require fans on the very hot devices but not the system fans. (With enough air-flow you could probably have fanless heatsinks.) In addition, a blow system could simply be the output of the main air conditioner, as a means for it to do some of its job. Imagine the PC being the source of cool air in the room! You would get much better component life, fewer failed hard drives, etc.

One answer might be to do both, since it’s not that much more work to plumb a double pipe over a single one. However, there are limits in how large a hole we can cut in studs when running the pipes through them. Airflow through the small holes will be faster and may make noise. Of course once we can get to the ducts and plenums of a forced-air furnace we have lots of room. In retrofits, we might even run the PC cooling pipes through the furnace ducts. Doing both gives you all the benefits, and in addition you can even seal the device with soundproofing, allowing for ultra-quiet devices.

No reason not to apply this cooling system to more than PCs. Any device that gets hot enough to need a fan — including home theatre devices and HTPCs, video projectors and even the fridge, stoves and dishwasher. Why should the dryer be the only device with a vent?

Now, when it comes to electronics, we probably can’t get rid of the system fan, but that’s OK because they are pretty cheap. We need it in case the master system goes off or fails, which it will sometimes do, if only for maintenance. Or we could have devices that can shut down quickly if the airflow stops or they get too hot, if that’s acceptable.

Water cooling could also be considered, since that’s quiet and uses much smaller pipes. But of course if it breaks, it’s a lot nastier. However, we tolerate much higher pressure water pipes in our walls already.

For more redundancy we could also consider just having the fans in the walls rather than having a central fan. This is more distributed and fault-tolerant and could allow much shorter plumbing, but loses out on central economies (such as a single valve that directs the air outside or inside based on the temperature.)

Numbers: You need about 33w of AC to cool 100w of heat, at 11 EER. So an always-on PC putting out 100W requires about 27 kwh per year if the AC is on 100 days for 8 hours. So that’s only about $3/year of saving per PC, which is nice to have but doesn’t pay for the ducting. However, it may still be worth it for the silent devices.

blow vs. suck

An aspect of suction is that it's non-directional - a suction will pull equally from all directions, so it doesn't have particularly good 'reverse fan' properties.

Blowing cold air sounds much more useful than suctioning hot air.

Blowing hot air might also be useful. It would be nice to have a heated blanket which put warm air directly underneath. Much cheaper than heating the whole house, without many of the problems of electric blankets.

Yes, as I point out you can

Yes, as I point out you can cool the CPU and drives directly with blown air. However, today most PCs are cooled by a fan in the power supply that blows air out of the PC, effectively the same as a hose connected to that outlet sucking air from it. This is not enough cooling, thus the need for an extra fan on the CPU and GPU, something blowing could fix.

Home Server Closet

I have a large home server closet in the basement. It has two vertical racks, one about half-full with computers, the other about half full of video cable, ethernet cable, and telephone cable patch panels. There is a large 220v UPS, and the transformers for the solar panels on our roof.

The room is so warm that we have to have three fans, 1 pulling air in from outside, 2 exhausting air into the basement. We probably have the driest and warmest basement in our neighborhood, and none of the mold problems of our neighbors.

If I was to design the house over again, I'd figure out some way to incorporate a way to use this heat for the whole house.

BTW, related to your piping into walls, Maire wishes in our remodel that we'd gone with an in-wall vacuum hose system.

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