APC instruments mark the rebirth of cool InfoWorld

APC instruments mark the rebirth of cool

InfraStruXure InRow and NetworkAir PA take a more efficient and flexible approach to datacenter cooling

InfoWorld | Jul 16, 2007

The tried and true methods of prepping a datacenter haven’t changed much over the years. You find a massive air conditioner or three, bring in lots of juice, and make sure there aren’t any sprinkler heads in the ceiling. But although this is the way it’s always been done, APC is betting that it’s not the way it will be done in the future — except for the sprinkler heads.

Across the globe, network and server administrators tend to keep light jackets or sweaters in their cubicles to provide some warmth when they have to spend time in the server room. This is because those massive air conditioners placed in the ceiling, the floor, or along the walls are pumping out 60-degree air and keeping the whole room frigid. It’s a solution that certainly works but is obviously wasteful. Why keep the whole room at 68 degrees when the only place you need air that cold is at the front of the racks?

Enter APC’s new in-row cooling solutions. Rather than sitting on the sidelines and blowing cold air everywhere, they’re placed between the racks, where they push the cold right where it needs to be: directly into the servers. By going right to the heat source, in-row solutions reduce waste, cut the energy bill, and eliminate the need for the «datacenter parka.»

Testing and evaluating these units is generally difficult to pull off because they’re expensive to install. However, I just recently finished building two production datacenters that make use of APC in-row cooling, and I’ve seen the deployment of these units through from start to finish.

APC’s InfraStruXure InRow cooling solutions come in two forms: the ACSC100, which is a stand-alone air conditioner built into a half-width rack form factor, and the ACRC100, which is identical in size but relies on an external water chiller unit rather than an internal compressor to provide cooling. In addition to these in-row models, I also tested APC’s NetworkAir PA4000, an R2D2-like portable cooling unit that can be placed just about anywhere for spot-cooling purposes. All three of these products are very capable, but they’re designed for different applications and budgets.

InfraStruXure InRow SC

The ACSC100 is APC’s compressor-based in-row unit, designed to be used where access to roof-mounted chillers isn’t possible or where the heat loads aren’t very high. These units incorporate an internal compressor and evaporator, drawing in hot air from the equipment racks and pumping out cold air through three front-mounted fans. The ACSC100’s exhaust and intake ducts come right out of the top of the unit, and installation typically involves routing those ducts to the plenum space above the room. Handily, APC provides the flexible ductwork and a prefit panel with mounting hardware to handle this task. In most scenarios, in which the datacenter room has a suspended acoustic-tile ceiling, the panel will fit perfectly above the unit, and the exhaust ducts can be mounted 10 inches above the intake. The finished installation certainly looks interesting, especially when the ducts are vibrating during normal operation.

Installation of the ACSC100 is simple as far as air conditioners go. The tricky part is ensuring there’s a drain within reach of the unit’s condensate hose; without that piece of the puzzle, the game’s over. Assuming you have the necessary drain, just put the unit next to a heat source, fit the ducts to the ceiling panel, run them into the top of the unit, place the temperature sensor in the front of an adjacent rack, and connect the L6-20 plug to a power source — and you’re done.

Inside the ACSC100’s lower rear panel is a number of data connections as well as the power supplies, the condensate drain, and the power input connections. I found the proximity of the condensate drain to power and data cabling a bit troubling, but that hasn’t proven to be a problem in several months of normal operation. Power inputs are located both at the top and the bottom of the unit, so you can run the power from the floor or the ceiling without extension cabling — a nice touch. The cutout in the bottom of the unit, however, is a bit on the small side, so running the power from below can require some cajoling of the cable. Other cutouts in the bottom of the unit can be used to route the temperature sensor cable and a network cable for access to the management interface.

The operation of the ACSC100 and ACRC100 is inextricably tied to the rack temperature sensor, which must be placed in front of a heat source in an adjacent rack. The unit constantly monitors the temperature of intake air into the rack, adjusting the cooling output to maintain a configurable temperature set point, so placement of the sensor is of paramount importance. You’ll want to place it in front of the hottest piece of gear in order to ensure that cooling levels are properly maintained. There is only the single sensor, though obviously nearby racks are affected by the cooling. In a typical installation with several ACSC100s, you’ll need to do some tweaking of cooling set points and thresholds not only to get the desired cooling level throughout a row of racks, but also to get each unit working at a normal level rather than one unit running at capacity while another runs at 30 percent.

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The nominal cooling output of the ACSC100 is listed at 7kW, but I’ve seen these units push upward of 8kW when taxed to their limit. The three fans can produce a maximum of 1,200 CFM (cubic feet per minute) of air movement, and the lowest output air temperatures I’ve seen were 49 degrees Fahrenheit, although 58 to 62 degrees is more typical.

I have been running three ACSC100s in a 500-square-foot datacenter for the better part of three months, and they’ve been performing admirably. The Web-based management application is easy to use, and it provides a wealth of information on the current status of the unit. The management console is SNMP-enabled, so integration with centralized monitoring platforms is possible. In fact, I wrote several SNMP-based plug-ins for popular network monitoring packages to bring these units into the fold.

On the downside, when an ACSC sends out e-mail notifications, expect to get several per minute during the event. Also, although centralized authentication for the management application supports RADIUS, it does not support LDAP, which is a minor annoyance. This is true not only for APC’s air conditioning units, but also for most of its network-enabled products, since they all use the same base management platform. I’ve posted instructions on integrating APC management cards and Microsoft Active Directory authentication via Microsoft’s Internet Authentication Server on my blog.

For the price, the ACSC100s are very capable cooling units that can be easily deployed in hotspots or throughout an entire datacenter, but research into the HVAC systems used in the building are a mandatory step prior to purchase and installation. If the ACSC100s are right for the building and the room, they’re definitely a good investment.

InfraStruXure InRow RC

To the casual observer, the ACRC100 looks identical to the ACSC100, but it’s a completely different device. Where the ACSC100 is a self-contained air conditioner, the ACRC100 has no compressor, relying on an external chiller unit to deliver cold water through top- or bottom-fed piping. And whereas installing the ACSC100 is a snap, installing the ACRC100 requires skilled mechanical labor.

In addition to the chiller itself, the ACRC100 incorporates an external CDU (cooling distribution unit), essentially a large box containing pipe fittings and valves. Water from the chiller enters the CDU and flows through copper or plastic piping to each ACRC100. Water returning from the ACRC100 flows back into the CDU and on to the chiller unit, completing the circuit. APC recommends using flexible plastic piping, but the mechanical contractor doing the installation took one look at it and recommended more durable copper piping instead, at a minimal cost increase. The downside of copper piping is inflexibility; once piped, the ACRC100 cannot be moved, not even an inch.

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The installation in this case involved four ACRC100 units. The chiller that feeds them is a 21.5-ton roof-mounted unit that consistently delivers 45-degree water to each ACRC100, which then pumps out cold air via eight front-mounted fans. Hot air is pulled from the rear of the unit and dissipated into the return water, which is then passed back to the chiller to be rechilled. The ACRC100 can deliver more than three times the cooling output of the ACSC100 (up to 30kW), and the fans push more than twice the air — up to 2,900 CFM.

Operationally, the ACRC100s are managed much like the ACSC100s, using the same Web-based interface. Unlike the ACSC100s, multiple ACRC100s must be grouped into management realms, where they communicate with one another to dynamically alter cooling levels and output in a given row of racks or even throughout an entire datacenter.

Costs associated with the ACRC100s are significantly higher than with the ACSC100s, but the unit price is roughly the same. Expect chiller costs to run between $30,000 and $40,000, with installation running about the same. Plus, the complexities of an ACRC100 turn-up call for a trained technician will add to the overall cost.

Each ACRC100 is delivered with two L6-20 power whips, although only one is required. The other can be used to provide redundant power to the unit. Also, the ACRC100’s power draw is low enough to be reliably administered through a large UPS system, providing cooling even during a power outage. Although the roof-mounted chiller is still subject to power loss, the cold water in the piping and CDU should be enough to maintain a high level of cooling output and heat rejection for quite some time.

Make no mistake, the ACRC100s pump out an amazing amount of cold air. Even a single unit could take care of a small server room all by itself. In the three months I’ve been running four ACRC100s, they’ve proven reliable and very cost-effective.

Click for larger view. InfraStruXure NetworkAir PA

At the low end of APC’s air conditioning line are the NetworkAir PA units. I tested the larger of the two models, the PA4000. This unit is essentially a smaller version of the ACSC100, but in a portable package. Looking like a Shop-Vac on steroids, the PA4000 adheres to the same basic air-handling principles as the ACSC100, requiring that a single intake and exhaust duct be run to the plenum space. The management application (an older version of the software for the SC and RC units), however, is more limited; it allows for simple monitoring and basic configuration of notifications but doesn’t permit changes to the unit’s set points or other cooling parameters.

The NetworkAir PA can find a home anywhere that needs highly focused cooling or as a stopgap measure during datacenter AC maintenance. Given that the SC and RC units ride the edge of performance and that the failure of a single unit can quickly become a big problem, having the ability to rapidly deploy cooling to specific locations is a great insurance policy.

In my lab tests, it became clear that the NetworkAir PA is best suited for small rooms. With a maximum cooling output of 4kW, the PA just couldn’t keep up with the cooling needs of the lab on its own, although it certainly tried. It’s also not terribly useful in high-temperature situations. Although it can supply air roughly 20 degrees cooler than the intake air temperature, that doesn’t help if the room’s already 95 degrees Fahrenheit. For small spaces, the PA might fit the bill, but for anything beyond a single-rack server room, it’s not a solution by itself.

The APC InfraStruXure InRow SC, InRow RC, and NetworkAir PA all deliver on the promise of effectively cooling only what needs cooling, while reducing energy costs. The air-cooling SC and water-cooling RC units can be integrated into traditional datacenters or deployed as the only cooling solutions in the room. The portable PA is a viable solution for small spaces and a great unit to have around for emergency backup. In-row cooling solutions have been widely regarded as a curiosity, but as datacenters become denser and energy bills rise, it’s becoming clear that the days of traditional datacenter AC are numbered.

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