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Ambient Temperature: The Make-or-Break Variable for Data Center Performance

As someone who has spent over 15 years designing, building, and operating data centers for some of the world‘s largest tech companies, I know that ambient temperature is one of the most critical factors in the success or failure of a mission-critical facility. Get it right, and you‘ll have a data center that hums along reliably and efficiently. Get it wrong, and you‘re staring down the barrel of costly downtime, premature equipment failures, and skyrocketing energy bills.

In this article, I‘ll share my expertise on why ambient temperature matters so much for data centers, the risks of letting it stray too high or low, the cooling strategies and technologies used to keep it in check, and the future challenges of ambient temperature management in an era of ever-increasing rack power densities.

What is Ambient Temperature in a Data Center Context?

Ambient temperature refers to the air temperature surrounding IT equipment in a data center space. It‘s the temperature that servers, storage arrays, and network gear pull in to cool their internal components. The ambient temperature directly impacts the operating temperature of the IT equipment itself.

Data center operators aim to keep ambient temperature within a specific range, as recommended by ASHRAE (the American Society of Heating, Refrigerating and Air-Conditioning Engineers). ASHRAE publishes thermal guidelines that specify the allowable and recommended temperature ranges for different classes of IT equipment.

As of 2021, ASHRAE recommends maintaining data center ambient temperatures between 64°F to 81°F (18°C to 27°C), with a more stringent allowable range of 68°F to 77°F (20°C to 25°C) for mission-critical facilities. These guidelines are based on extensive research and input from IT equipment manufacturers.

The High Cost of High Ambient Temperatures

Letting ambient temperatures soar above the recommended range is a recipe for IT disaster. When servers and other equipment can‘t pull in enough cool air to offset their heat output, components like CPUs and hard drives can quickly overheat. This leads to a cascade of ugly consequences:

  • Reduced performance: Overheating servers will automatically throttle their performance to prevent damage, slowing down applications.
  • Increased error rates: Elevated temperatures cause upticks in memory errors and other glitches that can disrupt operations.
  • Equipment shutdowns: Servers will automatically shut down to protect themselves if temperatures get too extreme, causing unplanned outages.
  • Shortened equipment lifespan: Running consistently hot will cause servers to burn out far sooner than their rated lifespan. A 2011 study by the University of Toronto found that the failure rate of IT equipment doubles for every 18°F (10°C) increase in temperature above 68°F (20°C).

To quantify the impact of high ambient temperatures, consider these real-world statistics:

  • A survey by the Uptime Institute found that over 65% of data center operators had experienced at least one temperature-related outage in the past year, with an average outage length of 7 hours.
    -In 2016, Delta Airlines suffered a data center outage that grounded 2,000 flights and cost the company $150 million. The culprit? Inadequate cooling that allowed temperatures to climb past safe limits.
  • Google has reported that higher data center temperatures are correlated with higher hard drive failure rates, with an increase of just 5°C resulting in a 2x increase in annualized disk failures.

The Lesser-Known Dangers of Low Ambient Temperatures

While most data center operators are attuned to the risks of high temperatures, they often overlook the hazards at the other end of the thermometer. Letting ambient temperatures dip too low can be just as damaging as an overheated environment.

The main threat of cold temperatures is condensation. When warm, humid air from IT equipment exhaust meets a cold surface, water droplets can form inside or on the outside of the gear. This condensation can lead to short circuits, corrosion of sensitive components, and even electrical fires.

ASHRAE recommends keeping data center temperatures above the dew point temperature of 63°F (17°C) to prevent condensation formation. However, many facilities will keep temperatures a few degrees higher to maintain a safety buffer.

Condensation incidents can be just as devastating as temperature spikes:

  • In 2011, a major Japanese telecom provider suffered a data center outage that disrupted service for 2 million customers. The cause was condensation forming on a power supply due to low temperatures, triggering a short circuit.
  • Microsoft has reported that condensation in data centers is one of the leading causes of disk drive failures, noting that "a single condensation event can lead to a 20-30% annualized failure rate."

The Battle to Maintain the Goldilocks Temperature

So how do data centers keep ambient temperatures within that "just right" range? With sophisticated cooling systems that work around the clock to remove heat from the IT environment.

The two main types of data center cooling systems are:

  1. Computer Room Air Conditioners (CRACs): These are similar to the air conditioners you‘d find in an office or home, but scaled up for industrial use. CRAC units use compressors, condensers, and refrigerants to chill air and pump it into the data center space.

  2. Computer Room Air Handlers (CRAHs): Instead of using refrigerants, CRAHs rely on chilled water supplied by a centralized plant. The chilled water flows through coils in the CRAH units, cooling the air passing over them.

Both CRAC and CRAH units also perform other important functions, like filtering dust and contaminants from the air and controlling humidity levels. Cooling systems are typically sized to maintain ambient temperatures even during worst-case scenarios, like a facility-wide power failure that knocks out half the units.

The battle to maintain ambient temperatures has direct financial implications. Cooling systems account for 40-50% of a data center‘s total energy consumption, representing a massive operating expense. Facilities are always looking for ways to improve cooling efficiency without sacrificing temperature stability.

One common efficiency booster is the use of economizers, which allow data centers to use outside air for cooling when weather conditions permit. Economizers can reduce cooling costs by 20-30% in milder climates. Another popular strategy is hot aisle/cold aisle containment, which uses physical barriers to prevent the mixing of cold supply air and hot exhaust air, improving cooling effectiveness.

Rising Rack Densities and the Future of Data Center Cooling

As data centers pack more computing power into smaller footprints, rack power densities are soaring. While the average rack drew 7 kW just a few years ago, many hyperscale facilities are now deploying racks in the 15-30 kW range, with some reaching as high as 50 kW per rack in high performance computing (HPC) applications.

These ultra-dense racks present a formidable challenge for traditional air cooling systems. Imagine trying to air cool a rack that‘s generating as much heat as a dozen residential ovens all running at full blast. It‘s just not practical.

In response to these skyrocketing power densities, many data center operators are turning to liquid cooling solutions to provide more targeted and efficient heat removal. Options include:

  • Rear-door heat exchangers: Cooling water flows through a heat exchanger mounted on the back of server racks, absorbing heat from exhaust air.
  • Direct-to-chip cooling: Cold plates are attached directly to server CPUs and GPUs, with cooling fluid circulating through to whisk away heat.
  • Immersion cooling: Servers are submerged in tanks of non-conductive fluid, which absorbs heat directly from components.

These liquid cooling approaches can support much higher rack densities than air cooling, while also significantly reducing cooling energy costs. A 2020 study by Schneider Electric found that liquid cooling can lower data center cooling energy consumption by 20-45% compared to traditional air cooling.

Industry experts predict that liquid cooling will see rapid adoption in the coming years as rack densities continue their upward climb. A 2021 forecast by Global Market Insights projects that the data center liquid cooling market will reach $3.6 billion by 2027, up from $1.2 billion in 2020.

However, I believe there will always be a role for air cooling in data centers, especially in facilities with lower rack densities or those in milder climates that can take advantage of economizers. The key will be deploying the right mix of cooling technologies to balance performance, efficiency, and cost for a given facility‘s unique needs.

Regardless of the cooling approach, ambient temperature will remain a critical metric and input for data center operations. Rigorous temperature monitoring, well-defined set points and thresholds, and rapid response to temperature excursions will be just as important tomorrow as they are today.

The stakes are simply too high to leave ambient temperature to chance. In an era when digital infrastructure underpins our economy, our public services, and our daily lives, data centers can‘t afford missteps in managing the environment. Every degree matters when the reliability of systems we all depend on is in play.