Network Room Cooling - Part 2

Cooling a Network Room: Airflow, Air Conditioning and Noise

What changes once you have more than one rack.

Part 2 of two.

A single wall rack in a home or small office is a simple problem: ventilate it, keep it dry, keep it clean. Once there is more than one rack, the room itself becomes the cooling system, and a few new things start to matter.

The reasons have not changed. Heat dries out the capacitors inside every power supply, and lead-acid UPS batteries lose half their design life for every 8 °C above 25 °C. What changes is how you deal with it.

◆ Not every switch breathes the same way

This surprises people. Some switches pull air front to back, some back to front, and many compact or home-grade units pull side to side. Several enterprise models are even sold in two versions with deliberately opposite airflow, so the installer can match them to the room.

If you rack them without checking, one device’s hot exhaust becomes its neighbour’s fresh air intake — and you will never find that fault in the configuration. Read the airflow arrow on every device before deciding where it sits, then arrange the room so everything breathes the same way: cold side facing one direction, hot side the other. That is the idea behind hot and cold aisles in a data centre, and it scales down to two racks perfectly well.

Leave space while you are at it — in front, behind, above and below. An empty rack unit is not wasted money. A rack packed solid from top to bottom cannot move air between devices, however good the room is.

◆ Where the hot equipment goes

In a passively cooled rack with no forced airflow, heat stratifies: the air at the top is hottest, and anything below a hot device is warmed by it all day. So in that kind of rack, put the biggest heat producers high and keep heat-sensitive equipment low.

But do not turn that into an absolute rule, because two things override it:

•    Weight. A UPS with batteries can weigh 30 to 60 kg. It goes at the bottom, always — a top-heavy rack is a tipping hazard. Where the UPS is large and hot, house it separately rather than argue about which shelf.

•    Airflow direction. In a properly ventilated room where every device draws from the front and exhausts to the rear, which shelf a device sits on matters far less than which way it faces. Getting the direction right beats getting the stacking order right.

◆ Air conditioning

A dedicated air-conditioned room is the right answer wherever the budget allows. The ASHRAE thermal guidelines, which the industry designs to, recommend 18 to 27 °C measured at the equipment’s air intake, with relative humidity at or below 60% and a controlled dew point. Where a whole room is not practical, self-contained air-conditioned racks are available with the cooling unit built into the cabinet.

Two air conditioners, not one.

Standard practice is to install two units, each sized to carry the full load alone, and alternate them — commonly six hours on, six hours off, on an automatic changeover controller. The reason is not energy saving; alternating them uses roughly the same power. The reasons are:

•    If one fails, the room does not cook while you wait for a technician.

•    A unit that sits idle for months develops seized compressors and dried-out seals. Alternating keeps both healthy and equalises their running hours.

•    You can service one without shutting the room down.

Size the cooling for everything in the room, not just the switches. The UPS, the PoE budget and the conversion losses all end up as heat, and network rooms are routinely under-cooled because only the obvious equipment was counted.

◆ Clean air matters as much as cool air

Cooling moves air, and moving air moves dust. Dust settles on heatsinks and stops them working, and in Mumbai’s humidity it becomes a slightly conductive film that corrodes connectors.

Filter at the source: a washable pre-filter on the air-conditioner return, a properly sealed room, and doors kept shut so you are not pulling in corridor dust every time someone walks through. A standalone HEPA air purifier in the same room is a genuinely useful supplement — especially during construction season, or where the room cannot be sealed well — but treat it as a supplement, not a replacement for filtering the air the AC is already circulating.

◆ If there is no air conditioning

Then the room needs mechanical air exchange: an exhaust fan mounted high on one wall pulling hot air out, and a filtered inlet low on the opposite wall letting cooler air in. You need both. An exhaust fan with no inlet mostly just makes noise.

Be honest about the trade-off: during the monsoon you are pulling in very humid outside air, so you are exchanging heat for moisture. If the equipment is valuable, a dehumidifier is worth more than a second fan.

◆ Noise is a design decision, not an afterthought

Every cooling fan makes noise, and the faster it spins the more it makes. In a home, a small office, or anywhere near a meeting room, this matters far more than people expect at the planning stage.

There is a useful relationship here: a cooler room lets fans run slower, or not at all. Netgear publishes acoustic figures for its AV-line switches — 0 dBA with the fan off, around 27 dBA in quiet mode, and up to 55 to 69 dBA on the larger models at full speed. Same switch, all three cases. The only difference is how hard the fan has to work, and that depends on the temperature around it. Cool the room properly and a quieter rack comes free.

For recording studios, broadcast suites and serious listening rooms there is specialised network equipment built to run with no fan at all. It uses large passive heatsinks and the chassis itself as a radiator, which is why it is bigger, heavier and considerably more expensive than the equivalent office switch. In a studio, silence is the requirement, not a luxury. But even this equipment only stays silent if the air around it is cool — most designs either fall back to a fan or simply overheat above a stated ambient limit.

◆ The short version

Check which way each device breathes and face them all the same way. Leave empty space. If you can afford air conditioning, use two units and alternate them; if you cannot, use an exhaust fan with a proper inlet and manage the humidity. Filter the air the AC is circulating, not just the air in the corner. And measure the temperature at the equipment intake, not on the wall.

Part 1 of this guide covers the small home or office rack — heat, humidity and what a single cupboard actually needs: [link to Part 1]

Sources

•    ASHRAE Technical Committee 9.9, Thermal Guidelines for Data Processing Environments — recommended envelope of 18 to 27 °C at equipment intake.

•    NETGEAR M4250 AV Line Managed Switches datasheet — published acoustic figures for fan-off, quiet and cool modes (ISO 7779 test method).

•    IEEE Std 484-2019, Recommended Practice for Installation Design and Installation of Vented Lead-Acid Batteries for Stationary Applications — 50% life reduction for every 8 °C above 25 °C.

•    Nichicon Corporation, Technical Notes CAT.8101C, "Application Guidelines for Aluminium Electrolytic Capacitors", section 2-9-3 (ambient temperature and life).

Photonics Enterprise is a bespoke technology advisory in Mumbai, working across high-end audio-video, enterprise networking and power. If you would like your rack or network room looked at properly, we are happy to come and measure it.

◆ Your Network Specialist.

Technology is only as good as the team that deploys it. Photonics Enterprise is a certified Alta Labs specialist based in Mumbai, providing professional site surveys, RF planning, and network design tailored to your premises. Their offer rapid on-site support, in-house IT team training, and ongoing post-sale monitoring — with a direct escalation channel to Alta Labs global engineering when needed.

Alta Labs products are available in ready stock through Photonics Enterprise, allowing immediate deployment without the usual procurement delays.

Part of the Photonics Enterprise culture is to share knowledge openly with interested and like-minded people, to build new relationships, and to evolve together. If anything in this guide raised a question, we would be glad to talk it through.

To arrange a demonstration or a conversation, please get in touch with Photonics Enterprise.

Vihang VASA

Founder, Photonics Enterprise — Mumbai

+91 98200 29063  ·  info@photonicsenterprise.com