For Datacenters, Indirect Evaporative Cooling is a Cool Idea
Cooling datacenters is one of the big issues of the times: There are more datacenters and they are getting bigger. Keeping the servers and other equipment cool is paramount – and extraordinarily expensive.
EnergyBiz this week posted a feature on indirect evaporative cooling, one of the main approaches to cooling. Bruce Baccei – the Project Manager for Energy Efficiency and Renewables at the Sacramento Municipal Utility District (SMUD) — reported on tests of this approach by his organization and UC Davis’ Western Cooling Energy Center.
The story provides outlines of the tests. The WCEC tests, he wrote, were performed three years ago. They resulted in energy efficiency ratios (EERs) of 44.3 and 45.2. The test by SMUD focused on Seeley International’s Climate Wizard equipment deployed in an old IRS office/data center that was occupied by a manufacturer Tri Tool. The maximum EER for the test was 60 and the mean EER was 29, the story said.
A terrific explanation of indirect evaporative cooling is available at Wescor. The piece begins by describing the concept, which is thousands of years old. (The piece said that the first attempt at air conditioning was an evaporative technique used by Egyptians, who hung wet mats on their doors. The wind blowing through would be cooled.) Simply, substances cool when the moisture within them evaporates. It is why, the author writes, a person feels a coolness when hit by wind: The moisture on the skin is evaporating. In that case, the energy to do so is being provided by the individual’s body.
The feature says that there are five types of evaporative cooling: direct, indirect, indirect/direct, indirect/indirect and indirect/DX. In indirect evaporative cooling, a main air stream is supplemented by a second stream, which is called a scavenger stream. The scavenger stream is cooled by water and cools the main stream in a heat exchanger. “The advantages to indirect versus direct evaporative cooling is the risk of contamination from pollutants, dust and smoke are not introduced with indirect and with indirect it can be easier to maintain relative humidity in a tighter band,” Keith Klesner, the Senior Vice President of North America for The Uptime Institute, told Energy Manager Today.
The dry bulb temperature (more commonly referred to simply as the air temperature) and the wet bulb (the temperature of air after passing over a large surface of water in an insulated channel) both are reduced without moisture being added to the main air stream, according to the Wescor piece.
Klesner make it clear in an overview at The Uptime Institute’s site that the technology has come a long way since the days of ancient Egypt. He writes that new cooling media made of plastic polymers and other materials are being used. Such systems, the piece says, are very clean and impervious to changes in outside humidity. Such systems also offer the possibility of simplification and the efficiencies that come with it:
As with many economizing technologies, greater efficiency can enable facilities to avoid upsizing the electrical plant to accommodate the cooling. A reduced mechanical footprint may mean lower engine-generator capacity, fewer transformers and switchgear, and an overall reduction in the often sizable electrical generation systems traditionally seen in a mission critical facility. For example, one data center eliminated an engine generator set and switchgear, saving approximately US$1M (although the cooling units themselves were more expensive than some other solutions on the market).
The piece points to two drawbacks: A dearth of service technicians and water requirements that can run to 1,500 cubic meters of water per megawatt annually.
The water demand issue could be significant, and the industry is aware of it. Many datacenters are purposely built near rivers, lakes and the ocean. Last June, Nortek Air Solutions introduced an indirect evaporative cooling unit, the Cool IDEC. The system, which is available in 200 watt, 300 watt and 400 watt versions, includes an “Air Economizer” for winter operation that the company claims contributes to water savings. The company says that the system can provide a partial power usage effectiveness (pPUE) of less than 1.1.
Kris Holla, Nortek’s Vice President of Data Center Products, told Energy Manager Today that savings compared to traditional approaches would be about 20 percent. Holla wrote that the segment is growing rapidly and suggests that it “optimal for both retrofit and new construction.”
Also in June, STULZ Air Technology Systems introduced the IeCE indirect evaporate cooling system and the STULZ IeCE Technical Evaluation Center. The system, according to the press release, can provide a pPUE of 1.03. The technical evaluation center, which is in Frederick, MD, is a demonstration and testing facility for perspective IeCE datacenter customers.
Klesner, who writes that indirect evaporative cooling can “significantly” reduce costs. Unlike Holla, Klesner suggests that it is optimized for new builds. “Indirect evaporative cooling requires typically an external footprint with access to air plenums/ducts to the data center,” he wrote. “Special water infrastructure for the evaporation process (often heavily filtered) is needed to each unit. From a chiller system, indirect evaporative cooling may be an add-on to improve efficiency but it would be a pretty big change.”
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