Data Center Goes Underground For Cooling
TierPoint’s Spokane, WA, facility uses a natural aquifer as part of its geothermal cooling system.
The earliest data centers were built by the U.S. government in the 1960s. At that time, a primary concern was powering the IT equipment. The task of cooling that equipment was typically relegated to HVAC architects with employee comfort top of mind. This design template existed for nearly 30 years, until servers came into the equation and companies began to empty their data closets.
As server sprawl literally heated up in data centers, finding efficient cooling methods was elevated to a priority operational objective. Traditional cooling systems could no longer accommodate the amount of heat generated by multiple server racks. Enter the era of massive water chillers and air handlers.
Typical water chillers, though, can be inefficient and expensive to maintain. A considerable amount of water is lost through evaporation. Additionally, required chemical treatments introduce contaminants during the evaporation process.
In the Pacific Northwest, a natural, eco-friendly cooling resource sits below the earth’s surface. In Spokane, WA, the Rathdrum Prairie Aquifer lies just 100 ft below one of TierPoint’s data centers. The aquifer’s sustained flow volume, accessibility, and environmental advantages are some of the factors that led to TierPoint’s decision to tap into its waters and create a unique, natural, geothermal cooling system for the data center.
Geothermal technology has been used globally as a heating method for decades. But only more recently has it been leveraged for cooling residences and businesses. Unlike traditional air cooling systems, geothermal cooling helps conserve precious natural resources and does not require the use of refrigerants, which are widely believed to contribute to decreasing ozone and ultimately, global warming.
Geothermal cooling systems typically consist of an indoor handling unit and a system of buried pipes connected to a well drilled into an underground water source. Activating it simply requires water to be pumped up and run past a heat exchanger, then returned to the same water source through injection pipes. One of the primary advantages of this system is that it does not burn fossil fuel; it simply transfers heat to and from the earth in an environmentally friendly manner.
TierPoint’s Spokane data center is thought to be the only one in the country using an aquifer for geothermal cooling.
THE AQUIFER SOLUTION
An aquifer is an underground layer of water-bearing rock with openings through which liquids and gases can easily pass. The Rathdrum Prairie Aquifer is one of the largest aquifers in the United States, stretching 370 square miles below eastern Washington and northern Idaho. It is estimated to contain ten trillion gallons of water, making it one of the most productive aquifers in the country.
Fortuitously, the Rathdrum Prairie Aquifer water running directly below the TierPoint facility consistently stays at an ideal temperature for data center cooling, in the 50° range, year-round. Another deciding factor for tapping into the aquifer was that the water sits just 100 ft below ground, a reasonable depth for drilling. Additionally, the layer of earth between the surface and water was free of large rocks and basalt — a hard volcanic rock sometimes found in the region — which made digging wells easier and less costly than if the ground had been rocky.
Because the aquifer is a pure source of drinking water across the multi-state region, environmental and regulatory considerations needed to be addressed before drilling. The design and process, therefore, were monitored by environmental agencies.
TierPoint owes a large portion of its aquifer success to Barry Baker, CEO of Baker Construction & Development in Spokane, who first suggested the idea during consultation, and to Kartchner Engineering, which designed the system.
Hydro geologists were tasked with proving that every drop of water pumped into the data center’s closed-loop chilling system would be returned and that no chemicals would be introduced, leaving the borrowed water as pristine going back into the aquifer as it was when extracted.
Additionally, because water that has run through the system returns to the aquifer slightly warmer than when it was extracted, it was necessary to ensure that temperature delta does not exceed 10°. When this requirement is met, the outgoing water quickly returns to the natural temperature of the aquifer’s untapped water.
The Rathdrum Prairie Aquifer is one of the fastest moving aquifers in the country. This allows the heated water to quickly cool after it is returned to the aquifer, reaching its original temperature within 20 to 50 ft of the re-entry point, mitigating any environmental impact.
Once approved, a 200-ft supply well was drilled to draw water from the aquifer, capable of sending 750 gallons of water per minute to the data center. Another well was dug to return the water back into the aquifer. For redundancy, backup wells were also drilled. This underground series of wells constitutes the data center system’s external loop.
Inside the data center lays the internal loop, which contains the water warmed by the IT equipment. The internal and external loops do not come into direct contact with each other. Rather, they each connect to a heat exchanger where the water is stabilized to the required maximum of 60°F before being returned to the aquifer.
The geothermal cooling solution utilizes an estimated 45% less power than a traditional cooling system. In theory, the resources saved could power over 100 residential homes and conserve over six million gallons of water per year. How efficient and green is this method? Tables 1 and 2 provide a comparison between a traditional chiller system and TierPoint’s geothermal cooling system.
|Cooling systems water used per year||6.0 million gallons|
|Water lost to evaporation at the cooling tower||4.5 million gallons|
|Water polluted with biocides for treatment||1.5 million gallons|
Table 1. Traditional chiller systems.
|Water used per year||0 gallons|
|Water lost to evaporation at the cooling tower||0 gallons|
|Water polluted with biocides for treatment||0 gallons|
Table 2. Geothermal cooling from TierPoint Spokane data center.
INVESTMENT AND RETURN
Layers of environmental agency oversight are involved in protecting the aquifer. As it should be. Water is one of the earth’s most precious resources. But is being subject to all this EPA oversight worth it? TierPoint believes it is.
Consider a data center with a 1,000 kW IT load (excluding other power consumption from security devices, lighting, etc.). If that data center is operating at a 1.5 PUE, the facility will use a total of 1,500 kW, with 500 kW used for its cooling needs. TierPoint calculates that, due to its use of geothermal cooling, the Spokane facility achieves a 1.2 PUE. TierPoint measures that to cool 1,000 kW of data center load, it now takes less than 200 kW, a direct result from using the aquifer system. This equates to a three-to five-year ROI, based on assumptions about occupancy rate. After that threshold is met, TierPoint essentially leverages “free” cooling, aside from other operational/maintenance costs.
ANOTHER GREEN SOLUTION
In addition to the eco-friendly cooling system, the Spokane data center has installed inertia storage uninterruptable power supply (UPS) systems. These systems utilize centrifugal energy generated by a high-mass spinning flywheel to provide short-term ride-through until emergency standby generators take over. The battery-free solution eliminates the risk of acid or lead leakage associated with battery-dependent systems.
WHAT ABOUT COOLING SYSTEMS & OUTSIDE AIR ECONOMIZERS?
The expansion of social media and rapid move to a digital economy are among the factors that have led to explosive data center growth worldwide, and with it, exponential growth in power and cooling demands. To meet immediate and projected demands, data center operators continually seek innovative yet proven ways to achieve cooling that is efficient, and ideally, eco-friendly.
Many data centers utilize “free” or evaporative cooling systems to reduce ambient temperatures in the spaces where servers and computing hardware are operated. While evaporative cooling is far more operationally cost-effective than chiller units, these systems suffer from algae, fungi, bio-films, and other biological growth resulting from nutrients, chemicals, and organisms present in the water. Bacteria and organisms can also enter evaporative cooling systems through air intakes.
Algae growth increases fouling of the media and reduces overall cooling efficiency. It also creates a difficult, time-consuming maintenance problem for the facility, as it must be scrubbed from the system on a regular basis.
Still other data centers utilize outside air economizers, which are commonly considered the greenest solution available today because they require no mechanical cooling elements, but rather rely on fan banks to continually exchange the data center air with a cooler, fresh supply from outside. Air quality and cleanliness are large concerns, however, requiring large filter banks to ensure outside contamination doesn’t reach the data center floor. Further, when introducing outside air, large amounts of water are needed to ensure humidification stays within service level agreements. This solution works best in cooler climates. In areas where outside ambient temperatures climb above 70°, operators must supplement the “free” cooling with additional equipment, such as chiller plants.
In comparison, TierPoint’s geothermal system is the greenest cooling method, combining the best parts of multiple cooling solutions. It provides the constant supply of cold water that a chiller plant can provide, but without a chiller. It enjoys low overall power consumption like an outside air economizer, but without the filtering and humidification issues. The geothermal system provides reliable cooling without chemical treatment, like evaporative cooling.
For forward-thinking, eco-friendly organizations with optimal access to a natural cool water source, geothermal cooling is an elegant means to quench the thirst for never-ending data processing.