Rack-based containment: Putting an end to the hot-versus-cold-aisle debate

Rack-based containment: Putting an end to the hot-versus-cold-aisle debate

Coffee and tea drinkers agree: Data center chimney containment is the way to go.

Apple or Android? Coffee or tea? Boxers or briefs? 

We can't steer you one way or the other on these divisive issues, but we will say this about the hot versus cold aisle containment debate: Rack-based containment is arguably the boxer-brief of the data center containment debate; as in, it represents an innovative alternative that's more suitable to modern, high-density facilities than either of the "classic" options.  

The problem with cold-aisle containment is that it increases mixing of cold and hot return air, which ultimately hurts PUE. Hot-aisle containment, meanwhile, creates sweltering maintenance conditions for workers, and often results in the development of hotspots toward the rear of cabinets.

But the middle ground solution, rack-based containment (or data center chimney containment), actively captures, sequesters and draws hot air directly from the cabinet to the return plenum using a combination of embedded fans and sensors. This provides several core benefits, including the following: 

1. Cooler maintenance aisles

Servers, switches, power distribution units and other mission-critical equipment is typically installed at the rear of cabinets. Likewise, any necessary maintenance is typically handled from behind a cabinet. Unfortunately for data center personnel, that results in some uncomfortably warm situations. For context, when Facebook first announced its plans to increase its cold-aisle temperatures to 85 degrees Fahrenheit, it also estimated that the new hot-aisle temperature would be as high as 120 degrees Fahrenheit. Accommodating those temperatures required a unique set of processes that would allow staff to perform maintenance from the cold aisle. Point is, it gets hot in the hot aisle. 

Active, rack-based containment utilizes chimneys that are placed directly above each rack. Rather than expelling exhaust into the maintenance aisle, that warm air is drawn directly into the return plenum so data center personnel don't have to sweat it out as badly. 

Man debating between coffee and tea thought bubbles.

Cappuccino- and matcha-lovers agree that rack-based containment is the way to go.

2. Greater efficiency

Traditionally, when maintenance was required in the hot aisle, on-demand cooling would kick in so personnel would be able to work in tolerable conditions. This would increase overall cooling capacity. However, if most of the exhaust is already being contained, then the starting temperature is already lower than it normally would be, meaning less cooling is necessary during scheduled maintenance. 

That's not the only way robust containment improves efficiency. According to the U.S. Environmental Protection Agency, effective containment can reduce fan-energy consumption by as much as 25 percent, and liquid-cooling energy by up to 20 percent. This improves PUE, and thereby saves money, without negatively impacting the reliability or resilience of your data center cooling infrastructure. 

3. Reduced bypass airflow

"Bypass airflow and recirculation air can be snuffed out with active containment."

Bypass airflow continues to be one of the top sources of cooling inefficiency in the data center. When cold and hot air are not adequately segregated, cool air may pass around the load and into the hot aisle, functionally acting as waste. Alternatively, or simultaneously, not enough cool air will actually reach the equipment inside the cabinet, inducing the intake of warm or hot air. This latter scenario is referred to as recirculation air, or what TechTarget contributor Vali Sorell calls "bypass air's partner in crime." Both result in higher cooling capacity and cause dangerous hotspots. 

That said, bypass airflow and recirculation air can be snuffed out with active containment chambers that utilize built-in fans that respond to real-time pressure sensors. Should warm air start building up inside cabinets, the sensors will tell the fans within the containment chamber to increase their RPM. If necessary, they just can just easily auto-reduce RPM. This helps maintain zero-pressure within the cabinet so that exhaust is reliably, continuously and efficiently expelled.