Air Flow Management (Part 1)

Air flow management in smaller environments has often been a point of contention. Mostly because it's very difficult to realise the benefits in smaller environments or it could be that no one other than you cares.

In this article, we'll discuss different forms of airflow management and various ways to take measurements both before and after. Let's get started.

Everything Starts With Measurements

No, not those kinds of measurements! We're talking temperature, humidity, airflow and the like.

Temperature/Humidity

Everyone usually has some form of temperature and/or humidity monitoring somewhere. This is either cabled to or inside of a PDU, a UPS or an OOB device and that's enough right? Not for us it isn't!

The first thing to determine is where to take measurements from and it's probably going to be different for every site. As a starting point, try to monitor the overall temperature within the room. You'll need a couple of sensors for this because you'll want to take an average across all of them. If you were to accidentally place a sensor in a hot or cold spot, hopefully the average will be levelled out thanks to the other probes and should keep you well enough informed until you are able to fix it.

Next you want to measure at the rack inlet. If your AC system supply air feeds in via the ceiling, you need to place your sensors at the bottom of the rack. If your supply air feeds in from the floor, you place your sensors at the top of the racks. What you're looking to find are the conditions of the server farthest away from the supply air which would then be our worst case scenario.

Next on the list is the supply outlets. Monitoring these with airflow and temperature sensors is a good idea because not only do you know the temperature of the air feeding the room but you also know if one or more are damaged (resulting in reduced airflow), have a restriction (resulting in reduced airflow) or the AC system has failed (resulting in no airflow). If you have redundant AC systems, it's critical you monitor the state of your AC units because you won't know when one of the units has failed. Yes, I've seen it happen and i've never seen the temperature skyrocket that fast before.

You could also measure the temperature of air outside of the room. That information could be used to help you determine how you cool the room. If it's colder outside of the room, you might consider opening a few doors or removing a few ceiling tiles etc. 

Finally, if you're using thermal containment, you may want to do the same in your hot aisle. Personally, i'd just get some cheap mercury based wall thermometers and attach them to the wall. A hot aisle is meant to be hot, so I don't see a need to continuously monitor it especially in a smaller environment.

Now that we have figured out what we want to monitor, where the sensors should be placed and how many we need, we should probably look at some products.

There are a couple of companies who specialise in this area but one that i've been quite happy with is Geist. For a small environment, you can't go wrong with the Watchdog 1200 climate monitor. The 1RU Watchdog 1200 has a couple of built in sensors for monitoring temperature, humidity, airflow, ambient light and sound but also supports up to 16 digital sensors, 3 analogue sensors and 4 IP cameras.

Geist seem to have an unending list of sensors to connect to the system. From water sensors and door sensors to isolated voltage sensors and smoke alarms, it'll make you wonder whether the 1200 is actually enough for you.

Finally, you can go online and try out the web interface for free and even navigate a 3D view of the product. Great products and accessories coupled with the ability to test drive the system made choosing Geist easy.

Thermal Imaging

Thermal imaging is a great way to perform spot checks in your datacentre. Use it to see where your hot spots are, if circuit breakers are close to overload and check seals around doors, windows and hatches. What's best is that it doesn't have to cost thousands of dollars to do it.

Take the FLIR ONE for example which is an FLIR camera attachment for your smartphone. It's portable and BLAAAACK!!! and will provide enough resolution to help you make your next move. At roughly $250 USD you can probably justify the cost of one for yourself and occasionally take it to work when you need to.

One thing an FLIR camera cannot do is predict how airflow, temperature etc will change BEFORE you make changes which essentially leads you to making changes, checking with your FLIR camera and repeating until you get it right.

How do we avoid this? With computational fluid dynamics analysis. Strap yourselves in, because take off  is going to be rough.

Computational Fluid Dynamics (CFD) Analysis

Computational Fluid Dynamics (CFD) is a technique that we utilize in datacentres to model and analyse airflow and temperature changes using tons of math! Yep, math!

As you can imagine, the people who created said math are quite expensive and let's not forget the people who have to program said math into a software package that you or I can't understand anyway. Long story short, it's an expensive piece of software. However, if you can make use of it, it's a much more powerful tool than any of the previous tools I've mentioned so far.

You can use it to determine how air will flow in and around your datacentre, discover hot and cold spots but most importantly, you can make changes like those mentioned below and measure their benefits without spending a cent!

There's a couple of options for obtaining CFD software;

• Hire someone to come in and do it all for you (expect to spend a few thousand dollars)

• Buy the software and do it yourself (expect to spend a few thousand dollars and many months studying)

• Buy some software that kinda does most of it and bodge the rest (Expect to spend a few thousand)

Ok, so the emoji keyboard has nothing to do with airflow management but it does fairly describe the art of the bodge.

Continued in Part 2...

In part 2, we'll discuss how plastic, rubber and shower curtains are going to help you achieve your goals!  Seriously...