Study: Data center growth could worsen Phoenix heat

Researchers measured air temperatures around homes adjacent to data centers in metro Phoenix — what they found revealed that heat generated by thousands of computer servers housed in multistory warehouses around the city is drifting downwind and affecting nearby neighborhoods.

David Sailor, the lead author of the study and ASU’s Director of the School of Geographical Sciences and Urban Planning, calls it “waste heat,” like the kind emitted by cars and buildings just by virtue of consuming energy.

Waste heat contributes to the urban heat island effect, a phenomenon Arizona knows well. The way cities are built and the materials used have a direct impact on the way they trap or attract heat.

In metro Phoenix, a burgeoning data center capital, the developments are located in the middle of suburbs, the outskirts of growing exurbs and even downtown. Their proliferation has garnered significant public pushback, especially from residents who live nearby and worry about noise pollution, water consumption and increased energy costs.

Now, in the nation's hottest big city, researchers are studying their heat footprint. Sailor’s paper is the first to directly measure air temperatures around data centers, giving insight into a little-known side-effect of the data center boom — and what can be done about it.

How do data centers emit heat?

Electricity generates heat. It’s basic thermodynamics, Sailor said.

That heat radiates from whatever source is using electricity. Think of a laptop — as it runs, a fan blows out hot air. Now imagine 100,000 computer servers running in a single building 24/7, 365 days a year.

“All of that heat, all of the electricity that ultimately comes out as heat, has to go somewhere,” he said.

Data centers use a few different techniques to quell and expel heat. In other parts of the country, some use cold water or evaporative cooling. But here in the desert, where water is scarce, many opt for an air-cooling technique.

“In most cases, heat is leaving the data center through rooftop air conditioning equipment,” Sailor said. Chillers on the building’s roof eject the heat that’s generated — and a little extra that’s produced by the electricity it takes to run the air-conditioning equipment.

That warm air can move in different directions depending on atmospheric conditions. It can float upward in thermal plumes or travel downwind to neighbors.

“ It really depends very much on the wind speed, wind direction,” he said. “Ultimately a fair amount of that heat is mixed into the air and can remain near the surface affecting residential neighborhoods,” Sailor said.

Typically, waste heat is a secondary driver of the urban heat island effect, he said. Cars and buildings generate 10 to 100 watts per square meter, depending on how dense an urban area is. The sun itself generates 1,000 watts per square meter.

But based on the size and electricity consumption of hyperscale data centers, Sailor said, the heat coming off of them can reach up to 6,000 watts per square meter.

“That’s two to six times the intensity of the energy of the sun that's hitting the surface,” he said. The scale of that energy consumption is likely to be a significant driver of what he calls “urban microclimates.”

"It's a game changer in terms of local sources,” he said. Especially since many data centers are built adjacent to residential neighborhoods.

Could a data center raise nighttime temperatures?

In the peak of summer, a few degrees added on to a 115-degree day might not be so noticeable. But all that heat can create a feedback loop.

When neighborhoods warm up even by a couple of degrees, people crank their AC. Those AC units emit heat of their own, raising temperatures even higher. Previous research in Phoenix shows that waste heat from air conditioning units can increase nighttime summer temperatures by 2 degrees.

Data centers also contribute to raised overnight temperatures. High temperatures have profound consequences for human health, Melissa Guardaro, Assistant Research Professor in the School of Sustainability at ASU, told SciLine in 2024. Historically, in Phoenix, nighttime temperatures drop below scorching, providing an opportunity for our bodies to recover.

Human health is compromised at about 85 degrees or higher at night, Guardaro said. Without those overnight reprieves, it’s harder to recover from daytime heat stress, which can build and result in serious heat illnesses or death.

In recent years, climate change has raised daytime and nighttime highs across the city. Last July, Phoenix recorded nine days of lows at or above 90 degrees and 21 days of lows at or above 85 degrees, according to data from the National Weather Service.

For now, the temperature differences created by data centers are hyper-local. Sailor’s research shows that heat emitted by data centers tends to dissipate about a third of a mile away from the source. But metro Phoenix has 178 data centers built or under construction, according to Data Center Map. Last September, the Arizona Corporation Commission said that the state had 4,154 megawatts in planned data center developments. As that infrastructure expands, it could have a more cumulative, city-wide warming effect.

That difference in temperature could cost residents money, too.

“The reality is, water use and energy use are both sensitive to ambient conditions,” Sailor said.

Even a few degrees of warming can increase peak cooling demand and annual energy use in homes downwind from data centers, researchers found. That could lead to a greater energy burden for homes downwind of data centers, especially during the summer.

“If you raised the air temperature across all of the city of Phoenix by a couple of degrees Fahrenheit in the summer, that could lead to tens of millions of dollars of additional energy use for air conditioning.”

Already, Phoenicians use over 50% of their households’ electricity for cooling.

Researchers examining the effects of hyperscale data centers outside urban areas are worried about the way their heat could impact the surrounding ecosystems, too.

In Utah, a prospective 9 gigawatt data center development planned for the state's northwest corner has alarmed residents.

The data center will consume so much energy that developers shared plans to build a natural gas power plant to support it. But with heat generated by the data center and the power plant, Robert Davies, a Utah State University physics professor, told The Salt Lake Tribune he predicts daytime temperatures to rise by 5 degrees and nighttime temperatures by 28 degrees. That difference could affect dewpoint and evaporation, impacting farmers and ranchers in the Hansel Valley.

 ”To deliver 100 megawatts you're rejecting maybe another 70 to 100 megawatts in waste heat depending on the thermal efficiency of the power plant,” Sailor said. Co-locating a natural gas power plant and data center could nearly double the intensity of the heat effect very locally.

“Now, when you have a power plant, you typically have much of that heat rejected in stacks where the exit height might be relatively far removed from the surface,” he said. So, that heat mixes at a higher level in the atmosphere. “How it affects near ground environments is something we'd have to look at more carefully.”

A few Arizona data centers have plans for their own natural gas turbines, including one on the outskirts of Surprise, just over 2,500 feet from the nearest homes.

How cities could offset the heat

Ultimately, Sailor said, the new research isn’t about casting blame or adding ammunition to the already heated debates around data centers. Rather, it's about creating opportunities for solutions.

There are ways to mitigate the heat data centers put out so that they have less of an effect on downwind communities, he said. Since the heat disperses over a relatively short distance, developers could create buffer zones around data centers.

The research noted that parks downwind of data centers still had a slight cooling effect on the areas near them — though the cooling effect would probably be more significant if the data center wasn’t there.

But it suggests that there are different ways to offset the heat, just as cities are doing on a larger scale to abate urban heat islands by adding more greenery and shade.

As for data center operators, there are a few design changes they could make to their cooling equipment to assuage the heat radiating off of their developments.